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An Overview of the Problems and Prospects for Circular Agriculture in Sustainable Food Systems in the Anthropocene

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  • In this overview paper, we outline and explore problems and prospects for circular agriculture’s contributions to transformative change toward sustainable food systems in the Anthropocene. We define circular agriculture (CA) and provide historical context on its development. We then discuss how CA can contribute to food system transformations in four key areas: multi-functional landscapes; sustainable intensification (focusing on nitrogen/crop-livestock management and digital agriculture); smallholder farmers; and dietary change. We find that food systems transitions will be challenging due to the depth, scale, and speed of changes necessary for humans to remain within safe planetary boundaries out to 2050.
  • Huangqin tea (HQT, Fig. 1), also called Huangjin tea in Chinese, has a long history of consumption in China[1]. It is a healthy herbal tea crafted from the aerial parts of Scutellaria baicalensis Georgi, S. scordifolia Fisch, S. amoena C. H. Wrigh, and S. viscidula Bung[24]. Unlike traditional tea made from Camellia sinensis (L.) O. Kuntze, HQT lacks stimulating components and is renowned for clearing heat and dry dampness, eliminating toxins, promoting digestion, and soothing fire[1,5]. It can be enjoyed both as a hot beverage and as a cold drink, and modern research suggests that HQT exhibits several pharmacological properties, such as anti-inflammatory, chemopreventive effects of colorectal cancer[6], anti-aging[7], cardiovascular protection, hypoglycemic effect, hypolipidemic effect, anti-tumor, anti-bacterial, anti-influenza virus, and enhance human resistance[812]. The predominant compounds found in HQT are flavonoids and essential oils and its potential health benefits are likely attributed to the presence of distinctive flavonoids, including isocarthamidin-7-O-β-D-glucuronide, carthamidin-7-O-β-D-glucuronide, apigenin-7-O-β-D-glucopyranside, chrysin-7-O-β-D-glucuronide, scutellarin, baicalin, wogonoside, and chrysin[1318].

    Figure 1.  The aerial parts of S. baicalensis Georgi, dried and brewed Huangqin tea.

    HQT is made using simple ingredients and has a straightforward preparation method. Traditionally, the above-ground portions of Scutellaria species have been utilized for crafting HQT, with the differentiation between stems and leaves remaining unessential. During the hot summer season (July to August), the aerial parts (stem, leaves, flowers) of these species of Scutellaria from a single source are collected and cut into small sections, which are then directly dried for later use. Alternatively, freshly harvested branch and leaf sections may undergo a transformative process through multiple rounds of steaming and subsequent drying within a steamer. Once suitably conditioned, they find their place within sealed containers, poised for extended storage periods. The brewing ritual commences by incorporating 7−8 g of this tea into 2 L of water, with subsequent replenishments of water at intervals 2−3 times. As the brewing ritual concludes, HQT graces the senses with a resplendent golden infusion—earning it another name, 'Huangjin tea'.

    HQT boasts a range of health advantages and is frequently gathered from the upper sections of Scutellaria species plants cultivated in the vicinity, intended for tea consumption. In recent years, large planting bases have been established in several regions, such as Beijing, Inner Mongolia Wuchuan, Yakeshi, Hebei Chengde, Shanxi Province, and Shandong Province, to comprehensively develop S. baicalensis resources. HQT has gained more attention and is now produced by specialized operating companies in various grades, such as bulk tea, bagged tea, and unique tea culture[12].

    To provide up-to-date information on the chemical composition, bioactivity, and safety aspects of the Scutellaria genus from HQT, this review paper has collected related literature from various databases, such as PubMed, Web of Science, Sci Finder, Scopus, Baidu Scholar, China National Knowledge Internet (CNKI), Wanfang and Weipu Data. This paper aims to draw attention to the need for further research and application of HQT in preventing and managing certain chronic diseases.

    HQT can be derived from several Scutellaria species. S. baicalensis is the most extensively cultivated, with a significant biomass in its aerial parts. Consequently, the primary source of HQT is the aerial part of S. baicalensis, and research focused on these aerial parts is also the most extensive.

    The aerial part and the root of S. baicalensis share similarities in their primary constituents, notably the significant presence of flavonoids, which are regarded as the main active components. However, there are specific chemical differences between the above-ground and underground parts of S. baicalensis. Our preliminary experiments have revealed the disparities in chemical composition between these two parts[18]. Notably, the root of S. baicalensis finds its primary use in medicinal applications, characterized by notably higher expression levels of specific 4′-deoxyflavones compared to the aerial organs. In contrast, the above-ground parts of the plant are employed to prepare tea. This differentiation in utilizing these plant components reflects the accumulated wisdom of generations cultivated through extensive periods of tasting and experience.

    This section provided an in-depth review of the chemical composition of the plant from which HQT is derived. Additionally, a specific emphasis on reviewing the aerial parts of S. baicalensis, which serve as the primary source of HQT has been placed.

    In the 1970s, researchers began to study the chemical composition of the aerial parts of S. baicalensis. The flavonoids are the most abundant chemical components in the aerial parts (flowers, stems, and leaves), and about 54 flavonoid compounds were identified (Table 1, Fig. 2). Most of them are flavonoids, dihydro flavonoids, and glycosides. The main glycoside-forming sugars are arabinose, glucose, and glucuronide, with the most abundant glucuronide glycosides. The optimization of extraction processes can yield a remarkable total flavonoid content of up to 5% in the stems and leaves of S. baicalensis[19].

    Table 1.  Flavonoids of HQT.
    NumberNameFormulaSpeciesRef.
    12',5-Dihydroxy-3',6,7,8-tetramethoxyflavoneC19H18O8S. baicalensis[17]
    22',6-DihydroxyflavoneC15H10O4S. baicalensis[16]
    33',4',5,5',7-PentamethoxyflavoneC20H20O7S. baicalensis[16]
    44',5-Dihydroxy-3',5',6,7-tetramethoxyflavoneC19H18O8S. baicalensis[22,27]
    54',5-Dihydroxy-7-methoxyflavanoneC16H14O5S. baicalensis[16]
    65,4′-Dihydroxy-6,7,8,3′-tetramethoxyflavoneC19H18O8S. baicalensis[17]
    75,2′-Dihydroxy-6,7,8-trimethoxyflavoneC18H16O7S. baicalensis[17]
    85,2′-Dihydroxy-6,7,8,3′-tetramethoxyflavoneC19H18O8S. baicalensis[17]
    95,2′-Dihydroxy-7,8-dimethoxyflavoneC17H14O6S. baicalensis[17]
    105,2′-Dihydroxy-7,8,6′-trimethoxyflavoneC18H16O7S. baicalensis[17]
    115,6,7,3',4'-Pentahydroxyflavone-7-O-glucuronideC21H20O13S. baicalensis[13]
    125,6,7,4'-TetrahydroxydihydroflavoneC15H12O6S. baicalensis[17]
    135,6,7-Trihydroxy-4'-methoxyflavoneC16H12O6S. baicalensis[15]
    145,7-Dihydroxy-6-methoxyflavanonC16H14O5S. baicalensis[17]
    155,7,4′-Trihydroxy-6-methoxyflavanoneC16H14O6S. baicalensis[22]
    165,7,4'-TrihydroxyflavanoneC15H12O6S. baicalensis[13]
    17(2S)-5,7,8,4'-Tetrahydroxyflavanone 7-O-β-D-glucuronopyranosideC21H20O12S. baicalensis[21]
    18(2S)-5,6,7,4'-Tetrahydroxyflavanone 7-O-β-D-glucuronopyranosideC21H20O12S. baicalensis[21]
    196-Hydroxyluteolin-7-O-glucuronideC21H18O13S. baicalensis[13]
    207-MethoxychrysinC16H14O4S. baicalensis[16]
    21ApigeninC15H10O5S. baicalensis, S. amoena,
    S. scordifolia, S. viscidula
    [17,2125]
    22Apigenin-4'-glucopyransideC21H20O10S. baicalensis[17]
    23Apigenin-6-C-glucoside-8-C-arabinosideC26H28O14S. baicalensis[13]
    24Apigenin-7-O-β-D-glucopyransideC21H20O10S. baicalensis[17]
    25Apigenin-7-O-β-D-glucuronideC21H18O11S. baicalensis, S. amoena,
    S. scordifolia
    [13,23,24]
    26Apigenin-7-O-methylglucuronideC22H20O11S. baicalensis[28]
    27BaicaleinC15H10O5S. baicalensis, S. amoena,
    S. scordifolia, S. viscidula
    [2225]
    28Baicalein-7-O-D-glucopyransideC21H20O10S. baicalensis[22]
    29BaicalinC21H18O11S. baicalensis, S. amoena,
    S. scordifolia, S. viscidula
    [16,2325]
    30CarthamidinC15H12O6S. baicalensis[13,20]
    31Carthamidin-7-O-β-D-glucuronideC21H20O12S. baicalensis[22]
    32ChrysinC15H10O4S. baicalensis, S. amoena,
    S. scordifolia
    [13,2124]
    33Chrysin-7-O-β-D-glucuronideC21H20O9S. baicalensis, S. amoena[23,29]
    34DihydrobaicalinC21H20O11S. baicalensis[22,28]
    35Dihydrooroxylin AC21H20O11S. baicalensis[13]
    36GenkwaninC16H12O5S. baicalensis[16]
    37IsocarthamidinC15H10O6S. baicalensis[20,28]
    38Isocarthamidin-7-O-β-D-glucuronideC21H20O12S. baicalensis[28]
    39IsoschaftsideC26H28O14S. baicalensis[13,16]
    40IsoscutellareinC15H10O6S. baicalensis[21,30]
    41Isoscutellarein 8-O-β-D-glucuronideC21H18O12S. baicalensis[21]
    42Kaempferol 3-O-β-D-glucopyranosideC21H20O11S. baicalensis[13,28]
    43LuteolinC15H10O6S. baicalensis[22,30]
    44Norwogonin-7-O-glucuronideC21H18O12S. baicalensis, S. amoena[13,17,23]
    45Oroxylin AC16H12O5S. baicalensis, S. amoena[17,23]
    46Oroxylin A-7-O-D-glucopyransideC22H22O10S. baicalensis[22,28]
    47Oroxylin A-7-O-β-D-glucuronideC22H20O11S. baicalensis, S. amoena[13,23]
    48PinocembrinC16H12O5S. baicalensis[13]
    49Pinocembrin-7-O-glucuronideC21H20O11S. baicalensis[13,16,22]
    50SalvigeninC18H16O6S. baicalensis[21]
    51ScutellareinC15H10O6S. baicalensis[28]
    52ScutellarinC21H18O12S. baicalensis, S. amoena,
    S. scordifolia, S. viscidula
    [2325,29]
    53WogoninC16H12O5S. baicalensis, S. amoena,
    S. scordifolia, S. viscidula
    [2125]
    54WogonosideC22H20O11S. baicalensis, S. viscidula[13,25]
     | Show Table
    DownLoad: CSV
    Figure 2.  Chemical structure of flavonoids in HQT.

    In 1976, Takido et al.[20] isolated two flavanone derivatives, carthamidin and isocarthamidin, for the first time as natural products from the leaves of S. baicalensis. Later, Yukinori et al.[21] identified two new flavanones, (2S)-5,7,8,4'-tetrahydroxyflavanone 7-O-β-D-glucuronopyranoside and (2S)-5,6,7,4'-tetrahydroxyflavanone 7-O-β-D-glucuronopyranoside), in the leaves of S. baicalensis. Eight compounds of chrysin, wogonin, apigenin, salvigenin, scutellarein, isoscutellarein, apigenin 7-O-glucuronide, and isoscutellarein 8-O-glucuronide were also isolated. Wang et al.[15] used column chromatography to isolate seven flavonoids (wogonin, chrysin, 5,6,7-trihydroxy-4'-methoxyflavone, carthamindin, isocarthamidin, scutellarein, and chrysin 7-O-β-D-glucuronide) from a water extract of the leaves of S. baicalensis. Liu et al.[13] identified 21 flavonoids in the stems and leaves of S. baicalensis by HPLC-UV/MS and NMR, and found one flavonone (5,6,7,3',4'-Pentahydroxyflavone-7-O-glucuronide) was a new compound. Zhao[17] firstly isolated 5,6,7,4′-tetrahydroxyflavanone 7,5,7-dihydroxy-6-methoxyflavanone, oroxylin A, 5,4′-dihydroxy-6,7,8,3′-tetramethoxyflavone, 5,2′-dihydroxy-6,7,8,3′-tetramethoxyflavone, 5,2′-dihydroxy-7,8,6′-trimethoxyflavone, 5,2′-dihydroxy-7,8-dimethoxyflavone, 5,2′-dihydroxy-6,7,8-trimethoxyflavone, apigenin 4'-β-D-glucopyranoside, and apigenin-7-β-D-glucopyranoside from the aerial parts of S. baicalensis. Ma[22] firstly isolated 5,7,4'-trihydroxy-6-methoxyflavone, 5,4'-dihydroxy-6,7,3',5'-tetramethoxyflavone, from stems and leaves of S. baicalensis. Wang et al.[16] isolated 5,4'-dihydroxy-7-methoxyflavanone, genkwanin, 7-methoxychrysin, 3',4',5,5',7-pentamethoxyflavone from 60% ethanol extracts for stems and leaves of S. baicalensis for the first time. Also, the compounds of carthamidin-7-O-β-D-glucuronide, oroxylin A-7-O-β-D--glucuronide, and chrysin were isolated from this plant for the first time.

    The concentration of these chemical components in HQT varies depending on the plant part utilized. Employing the HPLC-DAD method, Shen et al.[18] established that the aerial parts (stems, leaves, and flowers) of S. baicalensis are rich in flavonoids, resembling the roots in composition but exhibiting significant disparities in content. The contents of isocarthamidin-7-O-β-D-glucuronide (106.66 ± 22.68 mg/g), carthamidin-7-O-β-D-glucuronide (19.82 ± 11.17 mg/g), and isoscutellarein-8-O-β-D-glucuronide (3.10 ±1.73 mg/g) were the highest in leaves. The content of apigenin-7-O-β-D-glucopyranoside (18.1 ± 4.85 mg/g) and chrysin-7-O-β-D-glucuronide (9.82 ± 5.51 mg/g) were the highest in flowers. HQT has a high content proportion of flavone glycosides, which is closely related to the activity of HQT. The concentrations of the nine main flavonoids in HQT infusions were measured using HPLC. The content of isocarthamidin-7-O-β-D-glucuronide (52.19 ± 29.81 mg/g) was the highest; carthamidin-7-O-β-D-glucuronide (31.48 ± 6.82 mg/g), chrysin-7-O-β-D-glucuronide (10.65 ± 0.40 mg/g) and apigenin-7-O-β-D-glucopyranside (5.39 ± 0.92 mg/g) were found at moderate levels in HQT samples. As for flavone aglycones, scutellarin (12.77 ± 1.14 mg/g), baicalin (1.88 ± 0.48 mg/g), isoscutellarein-8-O-β-D-glucuronide (2.84 ± 0.60 mg/g), wogonoside (0.23 ± 0.02 mg/g) and chrysin (0.03 ± 0.01 mg/g) has lower content in HQT[6].

    Although there are few studies on the chemical constituents of the aerial parts of S. amoena, S. scordifolia, and S. viscidula it has been shown that the compounds of the aerial parts are similar to S. baicalensis. The aerial parts of S. amoena contain the compounds of baicalein, baicalin, oroxylin A, oroxylin A-7-O-β-D-glucuronide, wogonin, chrysin, chrysin-7-O-β-D-glucuronide, norwogonin, 5,7-dihydroxy-6,8-dimethoxyflavone, scutellarin[23]. Zhang et al.[24] identified compounds of chrysin, wogonin, baicalein, apigenin, apigenin-7-O-β-D-glucoside, baicalin, and scutellarin in whole plants of S. scordifolia. The stems and leaves of S. viscidula all contain compounds of wogonoside, apigenin, baicalein, wogonin, baicalin, and scutellarin. The contents of baicalein, wogonoside, wogonin, and apigenin in the stem of S. viscidula were higher than those in the stem of S. baicalensis. In the leaves of the two species, the content of scutellarin was higher, while the content of other compounds was lower[25]. The content of scutellarin in S. viscidula was stem (2.30%) > leaf (1.78%) > flowers (0.38%)[26].

    The aerial parts of S. baicalensis are rich in essential oils, and the taste of HQT is closely related to this. The flowers of S. baicalensis are thought to have a Concord grape aroma, while HQT has a bitter flavor with distinctive herbal notes. Extensive analysis has identified 145 components in the essential oil obtained from the aerial parts of S. baicalensis. These components span various chemical classes, such as alkanes, carboxylic acids, fatty acids, monoterpenes/oxygenated monoterpenes, sesquiterpenes triterpenoids and Vitamins (Supplemental Table S1), which have demonstrated their efficacy in combatting bacteria, reducing inflammation and inhibiting tumor growth[2731]. Among these, major constituents include germacrene D (5.4%−39.3%), β-caryophyllene (29.0%), caryophyllene (18.9%), eugenol (18.4%), caryophyllene (15.2%), caryophyllene oxide (13.9%), (E)-β-caryophyllene (11.6%), 5-en-3-stigmasterol (11.3%), carvacrol (9.3%), thymol (7.5%), vitamin E (7.4%), neophytadiene (7.3%), γ-elemene (6.2%), 1-octen-3-ol (6.1%), allyl alcohol (5.5%), bicyclogermacrene (4.8%), myristicin (4.7%), acetophenone (4.6%), α-amyrin (4.6%), β-amyrin (4.4%), germacrene d-4-ol (4.3%), spathulenol (4.2%), β-pinene (4.1%), α-humulen (4.0%), 1-vinyl-1-methyl-2-(1-methylvinyl)-4-(1-methylethylidene)-cyclohexane (4.0%) are found in the aerial parts of S. baicalensis from different places[2731].

    Takeoka et al.[27] identified 64 components in volatile components of S. baicalensis flowers by solid-phase microextraction and analyzed them by GC and GC-MS. These flowers were collected at San Francisco State University (USA). Among the flower volatiles, the content of β-caryophyllene, germacrene D, δ-cadinene, γ-muurolene, and γ-cadinene were more than 3%. The essential oil obtained from the stem of S. baicalensis is mainly composed of diphenylamine, 2,2-methylenebis (6-tert-butyl-4-methylphenol), bornyl acetate, β-caryophyllene, germacrene D and 1-octen-3-ol.[32]. Gong et al.[28] analyzed and identified the specific chemical constituents of the aerial parts of S. baicalensis by using GC-MS technology and identified 37 compounds in total, such as allyl alcohol, acetophenone, caryophyllene, α-humulene, germacrene D, and γ-elemene. The plant material was collected in the Qinling Mountains in China. Lu et al.[29] found a big difference in essential oil components between the aerial and root of S. baicalensis from Kunming Botanical Garden, Yunnan Province (China). The aerial part of S. baicalensis mainly contained enols and sterols such as neophytadiene and vitamin E. However, it has the same compounds as the roots, such as nerolidol, hexadecanoic acid, 1,2-benzenedicarboxylic acid, squalene, stigmast-4-en-3-one, and partial alkanes. Recently, Wang et al.[31] found the essential oil level of the aerial parts of S. baicalensis was 0.09% (v/w, based on fresh weight) while its density was 0.93 g/mL, and obtained 31 components accounting for 97.64% of the crude essential oil, including sesquiterpenoid, monoterpenoids, phenylpropanoids, and others. It is also reported that the major components of the essential oil from the aerial parts of S. baicalensis were myristicin, eugenol, caryophyllene, caryophyllene oxide, germacrene D, spathulenol, and β-pinene, with eugenol as the most abundant. The sample of the aerial parts were harvested from Tangshan City (China). The composition of S. baicalensis essential oils varies according to the plant part used, geographical location, and growing conditions.

    Zgórka & Hajnos[33] identified the phenolic acid compounds of aerial parts of S. baicalensis by solid-phase extraction and high-speed countercurrent chromatography: p-coumaric acid, ferulic acid, p-hydroxybenzoic acid, and caffeic acid. Chirikova & Olennikov[34] found that the aerial part of S. baicalensis contains 11 kinds of saturated fatty acids and nine kinds of unsaturated fatty acids, among which the palmitic acid content is the highest. Chlorogenic acid, fernlic acid, protocatechuic acid, vanillic acid, rosmarinic acid, caffeic acid, p-hydroxybenzoic acid, and p-coumaric acid were also detected.

    Zhao [17] isolated four sterol compounds: β-sitosterol-3-O-β-D-glucoside, α-apinasterol, β-sitosterol, and four ester compounds: methoxyphaeophorbide, p-hydroxybenethyl ethanol hexadecanoic methyl ester, ethoxyphaeophorbide, and n-octadecanol, lutein from the aerial parts of S. baicalensis.

    It is reported that flavonoids and diterpenes are the two main groups of active constituents in the genus Scutellaria. However, only one diterpene (scutebaicalin) was identified in the stems and leaves of S. baicalensis[35].

    By atomic absorption spectrophotometry, Yuan et al.[36] determined the contents of 11 metal elements in different parts of S. baicalensis. It was found that the leaves and stems of S. baicalensis were rich in Mg, K, Cr, Ni, Co, Fe, Mn, and Pb. Meanwhile, Yan et al.[37] developed an inductively coupled plasma mass spectrometry method and determined 23 kinds of inorganic elements in the stems and leaves of S. baicalensis from eight regions. Although there were no differences in the types of inorganic elements in the stems and leaves of S. baicalensis from the different areas, the content of these elements varied significantly. Among these elements, Fe, Zn, Cu, Mn, Cr, Co, Ni, Sr, B, and Ni were essential human body elements. The content of Al (516.83 μg/g) and Fe (700.62 μg/g) was the highest, while the content of B (31.54 μg/g), Ti (23.10 μg/g), Mn (65.64 μg/g), Sr (62.27 μg/g), and Ba (89.68 μg/g) was relatively high.

    Olennikov et al.[38] studied the water-soluble polysaccharides from the aerial parts of S. baicalensis from Russia and found that the polysaccharides from S. baicalensis gradually accumulated before flowering and progressively decreased after flowering.

    Yan et al.[39] found that the stems and leaves of S. baicalensis were rich in amino acids, and there was no difference in the kinds of amino acids among different producing areas, but there was a significant difference in the contents of amino acids. The content of proline, threonine, glutamic acid, lysine, glutamine, and arginine was higher, and the content of methionine, hydroxyproline, and citrulline was low.

    Several studies have focused on the functional properties of HQT, with increasing attention given to the aerial parts of S. baicalensis as the main raw material for HQT production. S. baicalensis stems and leaves flavonoids (SSF) are considered the functional components of HQT. Modern pharmacology has shown that the flavonoids extracted from the stem and leaf of S. baicalensis have been found to possess anti-inflammatory, anti-bacterial, antiviral, antipyretic and analgesic, anti-tumor, hepatoprotective, antioxidant, hypoglycemic, hypolipidemic, detoxification, myocardial ischemia protection, brain injury protection, and immunomodulatory effects. However, few studies have been conducted on the individual flavonoid compounds in the total flavonoid extract from S. baicalensis. Therefore, this paper aims to summarize and supplement the current research on the functional properties of HQT and its primary raw material (S. baicalensis) extract.

    Injury and infection could lead to inflammation, which plays a key role in the accelerated pathogenesis of immune-mediated disease[40]. Tong et al.[41], Zhou et al.[42], and Zhao et al.[43] found that S. baicalensis stem-leaf total flavonoid (SSTF) could inhibit acute exudative inflammation caused by xylene, glacial acetic acid, and egg white and also have a significant inhibitory effect on chronic inflammatory of granulation tissue hyperplasia. Wang et al.[44] observed the effect of SSTF on the aerocyst synovitis of the rat model and found that it could reduce capillary permeability, reduce the aggregation of neutrophils and basophils in tissues, reduce histamine, bradykinin, and other substances that increase vascular permeability, which is conducive to the recovery of vascular permeability in inflammation. Studies have shown that the SSTF significantly inhibits specific and non-specific inflammatory responses and can regulate the body's cellular and humoral immune functions. The mechanism of action is closely related to the effective reduction of capillary permeability, inhibition of PGE2 and NO synthesis in vivo, reduction of TNF-α expression, and reduction of inflammatory exudation[45,46]. SSTF (200 mg/kg) could balance the CD+4 Tlymphocyte subsets Th1/Th2 cells and the related cytokines IL-10 and IFN-γ in the rheumatoid arthritis model[47]. SSTF (17.5, 35 and 70 mg/kg for 38 d) could significantly improve the impairment of relearning ability and retention ability on memory impairment and nerve inflammation in chronic cerebral ischemia rats, which might be due to the inhibition of the proliferation of astrocyte and balanced the expression of the inflammatory factors in the brain[48]. Besides, the extract of S. baicalensis stem-leaf shows anti-inflammation effects both in vitro and in vivo. In cultured macrophage cells (RAW 264.7), the extract of S. baicalensis stem-leaf showed a strong anti-inflammation effect, which inhibited the expression of IL-1β. Similarly, it suppressed the LPS-induced transcriptional activity mediated by NF-κB in fish aquaculture[49]. S. baicalensis stems and leaves (3, 6, and 12g /kg, gavage for 7 d, once per day) have anti-inflammatory effects on 2% carrageenan-induced acute pleurisy in rats, and the mechanism of action may be related to the reduction of the production of inflammatory factors and the down-regulation of TRPV1 signaling protein[50]. The combination of S. baicalensis stems- Polygonum cuspidatum (3.5, 7, and 14 g/kg, gavage for 7 d) has a protective effect on lipopolysaccharide-induced acute lung injury rats, and its mechanism may be related to down-regulating the expression of TRPV1 and inhibiting the levels of TNF-α and IL-1β in inflammatory cells[50]. It is also reported that S. baicalensis stem-leaf combined with Morus alba (4, 8, and 16 g/kg/d, gavage, 10 d) has a protective effect on rats with acute pneumonia induced by lipopolysaccharide, and the mechanism might be related to the reduction of inflammatory factors and the down-regulation of TRPV1 signaling pathway[51]. Besides, the network pharmacology showed that S. baicalensis stem-leaf could prevent and control COVID-19 by intervening in 30 targets and 127 pathways, potentially preventing and treating inflammation caused by COVID-19[52].

    Based on the studies, S. baicalensis stem-leaf extract shows promising anti-inflammatory properties. These effects are likely mediated through a combination of factors, including the modulation of immune responses, reduction of inflammatory mediators, and potential interactions with signaling pathways like TRPV1. However, it's important to note that while these studies provide valuable insights, further research, including clinical trials, is needed to establish the full extent of its benefits and its potential for therapeutic applications in humans.

    Scutellaria baicalensis stem and leaf aqueous extract exhibit different degrees of inhibition of 36 strains from 13 kinds of bacteria, such as Staphylococcus aureus, Staphylococcus, Streptococcus pneumoniae, alpha-hemolytic streptococcus, beta-hemolytic streptococcus and Escherichia coli. This shows that anti-bacterial activity against Staphylococcus aureus is strong (MIC50 0.94 g/L, MBC 0.94 g/L). In vivo (217 mg/kg), it protects against the death of mice infected by Staphylococcus aureus and shows a certain dose-dependence[53]. Zhang et al.[54] found that the stem and leaves of S. baicalensis against Staphylococcus aureus and Shigella dysenteriae with MIC values of 1 and 4 mg/mL, respectively. Besides, it is reported that the water extract of the aerial part of S. baicalensis could inhibit the growth of several common pathogenic bacteria in aquacultures, such as Aeromonas hydrophila, Edwardsiella tarda, Vibrio alginolyticus and V. harveyi[49].

    Zhao et al.[55] found that the active part of the stem and leaf of S. baicalensis could inhibit the cytopathic effect caused by 10 kinds of viruses such as Coxsackie B virus, influenza virus, parainfluenza virus, adenovirus, respiratory syncytial virus, and herpes simplex virus. It is suggested that the active parts of the stem and leaf of S. baicalensis can be used for the prevention and treatment of influenza virus, parainfluenza virus, coxsackievirus, and other related infectious diseases.

    These findings indicate that S. baicalensis stem and leaf extract possess anti-bacterial and antiviral properties, making it a potentially valuable natural resource for combating infections caused by various pathogens. However, while these results are promising, further research, including clinical trials, would be necessary to fully establish the effectiveness and safety of using S. baicalensis extract for preventing or treating bacterial and viral infections, including COVID-19.

    In a series of studies, Tong et al.[41] demonstrated that SSTF at a dosage of 20 mg/kg significantly reduced body temperature in rats with fever induced by subcutaneous injection of a 10% dry yeast suspension. Zhang et al.[56] conducted research on the antipyretic effect of scutellarin, an extract from S. baicalensis stems and leaves, in febrile rabbits and observed an antipyretic substantial impact induced by pyrogen. Yang et al.[57] conducted several animal experiments, where they discovered that intraperitoneal injection of effective doses of SSTF (42.2 and 84.4 mg/kg) exhibited a specific inhibitory effect on infectious fever in experimental animals. Moreover, intraperitoneal injection of appropriate SSTF doses (30.1, 60.3, and 120.6 mg/kg), as found in Yang et al.'s experiments[58], effectively inhibited the pain response in experimental animals. Furthermore, Zhao et al.[59] noted that SSTF exhibited a certain inhibitory effect on the pain response in experimental animals subjected to chemical and thermal stimulation.

    These findings suggest that S. baicalensis stem and leaf extract may have antipyretic and analgesic effects, particularly its total flavonoid component. These effects could be beneficial for managing fever and providing pain relief. However, as with any natural remedy, further research, including controlled clinical trials in humans, is necessary to fully understand the effectiveness, safety, and optimal dosing of S. baicalensis extract for these purposes.

    Amyloid protein (Aβ) has been widely recognized as the initiator of Alzheimer's disease (AD)[60]. The SSTF can improve cognitive function and delay the process of dementia. SSTF has been found to exert neuroprotective effects in AD animal models through various mechanisms. Ye et al.[61] demonstrated that oral administration of SSTF (50 mg/kg) could effectively improve cognitive function and reduce neuronal injury in Aβ25-35-3s -induced memory deficit rats. The underlying mechanisms may involve inhibiting oxidative stress and decreasing gliosis[62,63]. Furthermore, SSTF was shown to reduce Aβ-induced neuronal apoptosis by regulating apoptosis-related proteins Bax and Bcl-2[64]. Subsequent studies further validated the neuroprotective effects of SSTF. Cheng et al.[65] found that SSTF treatment inhibited neuronal apoptosis and modulated mitochondrial apoptosis pathway in composited Aβ rats. Ding & Shang[66] found that the SSF improves neuroprotection and memory impairment in rats due to its inhibition of hyperphosphorylation of multilocus Tau protein in rat brains. SSTF has also been found to exert neurogenesis-promoting effects by regulating BDNF-ERK-CREB signaling[12] and activating the PI3K-AKT-CREB pathway[67].

    In further studies, Ding et al.[11] proposed that the effect of SSF on promoting neurogenesis and improving memory impairment may be related to the regulation of abnormal expression of Grb2, SOS1, Ras, ERK, and BDNF molecules in the BDNF-ERK-CREB signaling pathway. Zhang et al.[68] found that SSF (25, 50, and 100 mg/kg) could significantly modulate okadaic-induced neuronal damage in rats, which provides a basis for evaluating SSF as a means to reduce tau hyperphosphorylation and Aβ expression in Alzheimer's disease. Cao et al.[69] found that SSTF (100 mg/kg, 60 d) may alleviate tau hyperphosphorylation-induced neurotoxicity by coordinating the activity of kinases and phosphatase after a stroke in a vascular dementia rat model. Gao et al.[70] demonstrated that the stems and leaves of S. baicalensis (SSF, 25, 50, and 100 mg/kg/d, 43 d) could inhibit the hyperphosphorylation of tau in rats' cerebral cortex and hippocampus induced by microinjection of okadaic acid, which may be related to the activities of protein kinase CDK5, PKA and GSK3β. Furthermore, Liu et al.[67] demonstrated that SSF (35, 70, and 140 mg/kg/d, 43 d) improved composited Aβ-induced memory impairment and neurogenesis disorder in rats through activated the PI3K-AKT-CREB signaling pathway and up-regulated the mRNA and protein expression of TRKB, PI3K, AKT, CREB and IGF2. More recently, a new study demonstrated that SSF (35, 70, and 140 mg/kg) alleviated myelin sheath degeneration in composited Aβ rats, potentially modulating sphingomyelin metabolism[71]. Collectively, these findings suggest that SSTF holds therapeutic potential for AD by targeting multiple Alzheimer's pathogenesis-related processes.

    Li et al.[72] confirmed that SSTF (5 mg/kg) could improve the behaviors and the numbers of dopaminergic neurons in the substantia nigra in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced Parkinson's disease in mice, and these beneficial activities appear to be associated with the reduction of the level of serum malondialdehyde.

    These studies suggest that S. baicalensis stem and leaf extract have the potential to exert neuroprotective effects in various neurodegenerative conditions, including Alzheimer's disease and Parkinson's disease. These effects could be attributed to its ability to modulate oxidative stress, apoptosis, signaling pathways, and protein hyperphosphorylation. However, as with any potential therapeutic agent, further research is needed to establish the full extent of its benefits, optimal dosages, and mechanisms of action, as well as its potential applications in human patients.

    In recent years, ischemic cerebrovascular disease has seriously threatened human health. Cerebral ischemia is one of the leading causes of death. It can occur in focal or global ischemia, with most cases associated with ischemic stroke[73]. Neuronal protection against oxidative damage has been proposed as a potential therapeutic strategy to avoid damage during ischemic stroke[74]. It is reported that SSTF can reduce neuronal apoptosis and free radical damage caused by heart and brain ischemia. Zhao et al.[75] have found that the pretreatment of SSTF (100 mg/kg/d) can protect the ischemia-reperfusion myocardium by enhancing the activity of the anti-oxidative enzyme, inhibiting lipid peroxidation and attenuating the oxygen-free radicals-mediated damage to the myocardium in rats. In further studies, Zhao et al.[76] proposed that SSTF (50, 100, or 200 mg/kg/d, 7 d) pretreatment could alleviate the neuronal damage incurred by ischemia-reperfusion, demonstrating a neuroprotective effect in focal ischemia-reperfusion rat model, which may involve the prohibition of the apoptosis of the neurons. Yu et al.[77] confirmed that SSTF (17.5, 35, and 70 mg/kg/d, 7 d) could attenuate cardiomyocyte apoptosis during ischemia reperfusion injury by down-regulating the protein expression of the JAK2 gene. Qin et al.[78] found that SSF (17.5, 35, and 70 mg/kg/d, 38 d) can decrease the expression of the NMDAR in hippocampus, and increase the expression of VEGF in the cerebral cortex of chronic cerebral ischemia rats.

    Focal cerebral ischemia-reperfusion can result in neuronal loss but strongly promotes activation and proliferation of hippocampal glial cells. Losing hippocampal neurons is considered one of the basic pathological mechanisms of cognitive impairment[79]. Zhao et al.[79] found that the pretreatment with SSTF (100 and 200 mg/kg) could improve neurological function after focal cerebral ischemia-reperfusion injury, with preventive and protective effects. Shang et al. found flavonoids from S. baicalensis (35−140 mg/kg) could attenuate neuron injury and improve learning and memory behavior in rats with cerebral ischemia/reperfusion[80]. In further studies, Kong et al.[81] found that the mechanisms of the protective effects on the brain against cerebral ischemia/reperfusion injury of SSTF may involve decreasing the content of brain water, increasing microvascular recanalization, reducing the apoptosis of hippocampal neurons, and attenuating free radical damage. Bai et al.[82] proposed that SSTF (100 mg/kg/d, 7 d) could protect the neurological function in rats following I/R injury by alleviating the damage to the ultrastructure of cerebral cortex neurons and synapse. Yan et al.[83] found that SSTF (100 mg/kg/d, 7 d) pretreatment can exert preventive, protective effects on cerebral tissue by relieving brain edema, decreasing neural damage, promoting microvascular repatency, and increasing enzyme activity. It has been reported that the SSTF may protect neurons and their synaptic structures in multiple ways, but whether this mechanism enhances the resistance of neurons to damage or increases the repair function remains to be further explored.

    Essential hypertension is a common chronic cardiovascular disease, which can lead to multiple target organ damage, such as heart, brain, and blood vessels. It is a risk factor for coronary heart disease, heart failure, and other cardiovascular diseases. It is reported that SSTF (17.5, 35.0, and 70 0 mg/kg, 8 weeks) can inhibit myocardial remodeling in primary hypertensive rats, and the medium dose exerts the best inhibitory effect, and the mechanism may be related to inflammatory response induced by inhibiting the NF-κB signaling pathway[84].

    S. baicalensis stem and leaf extract have the potential to provide neuroprotective effects in conditions related to ischemic cerebrovascular disease and hypertension. Its ability to modulate oxidative stress, inflammation, and apoptotic pathways appears to contribute to its beneficial effects. However, further research is needed to fully understand the mechanisms and optimal usage of SSTF for these therapeutic purposes.

    Aging is associated with the deterioration of physiological function and the decline of cognitive ability[85]. It is reported that the alcohol extracts from roots, stems, leaves, and flowers of S. baicalensis (400 mg/kg, 7 weeks) could regulate the content of differential metabolites in urine samples of D-gal-induced aging-model rats to different degrees and play a certain role in improving the metabolic disorders of aging rats[7]. A further study investigated the anti-aging effects and potential mechanisms of S. baicalensis leaves and flower extract. S. baicalensis leaves (400 and 800 mg/kg, 7 weeks) have an anti-aging effect, which can improve the acquired alopecia, slow response, and other characteristics of aging rats, increase the spontaneous activity of aging rats, and reduce the damage of lipid peroxidation and glycosylation induced by D-galactose[86]. The S. baicalensis flowers extract (400 and 800 mg/kg, 7 weeks) could effectively reverse the cognitive decline and oxidative stress injury and alleviate liver pathological abnormalities in the D -galactose-induced aging rats, which are involved in the glutamine-glutamate metabolic pathway[85].

    S. baicalensis extracts, particularly those from leaves and flowers, may have anti-aging properties by regulating metabolic disorders, improving cognitive function, reducing oxidative stress, and alleviating aging-related physiological abnormalities. However, further research is necessary to fully understand the mechanisms underlying these effects and to determine the potential of these extracts for human applications in addressing age-related issues.

    The SSTF (200 mg/kg d, 35 d) can reduce the joint damage of collagen-induced arthritis mice and balance the CD+4 T lymphocyte subsets Th17 and Treg cells[87]. Besides, on the multiple sclerosis model, the SSTF (100, 200 mg/kg d, 16 d) displayed a protective effect on experimental autoimmune encephalomyelitis rats through a balance of the CD+4 Tlymphocyte subsets Th17 and Treg cells[88]. Zhang et al.[89] have found that SSTF attenuated EAE disease severity, accompanied by enhanced Treg frequency and level of Treg-associated cytokines (IL-10 and TGF-β), as well as downregulated Th17 frequency and expression of Th17-related cytokines (IL-17 and IL-23).

    It is reported that the essential oils from the aerial parts of S. baicalensis showed toxicity against booklice (Liposcelis bostrychophila) with an LC50 of 141.37 μg/cm2. The components of myristate, caryophyllene, eugenol, and caryophyllene oxide displayed dramatic toxicity against the L. bostrychophila, with LC50 values of 290.34, 104.32, 85.75, and 21.13 μg/cm2, respectively[31].

    Guo & Xu[90] have found that SSTF could inhibit the proliferation of Hela cells obviously (p< 0.01). Tang et al.[10] have found that SSTF could play an anti-colon cancer role by up-regulated the expressions of Cleaved Caspase-3 and the ratio of Bax/Bcl-2 (p < 0.05 and 0.01) and significantly down-regulated the expressions of MMP-2 and MMP-9 in HCT116 cells (p < 0.05 and 0.01). Recently, Shen et al.[6] studied the chemopreventive effects of HQT against AOM-induced preneoplastic colonic aberrant crypt foci in rats and found HQT inhibits AOM-induced aberrant crypt foci formation by modulating the gut microbiota composition, inhibiting inflammation and improving metabolomic disorders.

    Cardiovascular disease is one of the most important threats to human health. Hyperlipidemia is a major risk factor for atherosclerosis, which can cause various cardiovascular and cerebrovascular diseases. Different doses of SSTF (50, 100, and 200 mg/kg) can effectively reduce the body weight increase of rats with hypertriglyceridemia, reduce the serum levels of triglyceride(TG), total cholesterol(TC), low-density lipoprotein cholesterol (LDL-C) and high-density lipoprotein cholesterol (HDL-C), which indicate that SSTF has the effect of regulating blood lipid[91].

    Oxidative stress is important in developing tissue damage in several human diseases[92]. The antioxidant capacities of separated organs (flower, leaf, stem, and root) of S. baicalensis were conducted by DPPH, ABTS+, and RP methods, respectively. The results showed that the antioxidant activity of the root (66.9 ± 0.3, 121.6 ± 0.5, and 80.2 ± 0.4 μg/mL) was the highest, followed by the leaf (68.4 ± 1.3, 128.2 ± 2.1, and 135.8 ± 2.0 μg/mL), stem (127.8 ± 3.1, 199.2 ± 1.7, and 208.2 ± 8.3 μg/mL) and flower (129.8 ± 6.3, 285.7 ± 4.7, and 380.3 ± 14.2 μg/mL)[93]. The antioxidant activities of the extracts of the aerial part of S. baicalensis and separated organs were conducted by DPPH assay and reducing power method with the antioxidant ability 7.73–8.83 mg TE/g DW and 51.48–306.09 mg TE/g DW, respectively. The content of total polyphenols and total flavonoids were significantly positively correlated with the reducing power[94]. Liu et al.[95] found that the flavonoids extracted from the stems and leaves of S. baicalensis (SSF, 18.98, 37.36, and 75.92 μg/mL) could protect rat cortical neurons against H2O2-induced oxidative injury in a dose-dependent manner. Cao et al. found that SSTF could alleviate the damage of human umbilical vascular endothelial cells injured by H2O2 and reduce their apoptosis, which may be related to the increasing level of Bcl-2[96].

    Preventive treatment with SSTF (50, 100, and 200 mg/kg) could significantly inhibit the blood glucose increase induced by alloxan in mice, and SSTF treatment could reduce the blood glucose level in diabetic mice. Both the prevention group and the treatment group could increase the activity of serum superoxide dismutase and decrease the content of malondialdehyde[97]. Liu et al.[98] found that SSTF (75 and 150 mg/kg) could significantly reduce blood glucose and blood lipid and improve insulin resistance in type 2 diabetic rats with hyperlipidemia.

    Yang et al.[99] found that SSTF (35 mg/kg/d, 8 weeks) could resist hepatic fibrosis by inhibiting the expression of α-smooth muscle actin in Hepatic Stellate Cells. In vivo, it is reported that SSTF (50, 100, and 200 mg/kg) could significantly reduce alanine transaminase activities in serum, increase the expression of superoxide dismutase and reduce the content of malondialdehyde in acute hepatic injury mice induced by carbon tetrachloride and ethanol[100].

    These findings suggest that S. baicalensis stem and leaf extract hold promise in promoting various aspects of health, including immune modulation, antioxidant activity, anti-tumor effects, cardiovascular health, oxidative stress protection, and more. However, further research, including clinical studies, is necessary to better understand the full therapeutic potential and safety of these effects in human applications.

    Flavonoids are considered the main active components in HQT. As the active substance basis of HQT, the safety of SSTF has also been investigated. After 90 d of oral administration of SSTF (0.5, 1, and 2 g/kg) to rats, no abnormal changes were observed in all indexes, and no delayed toxic reactions or obvious toxic reactions were observed, indicating that the toxicity of SSTF is low[101]. The LD50 value of SSTF was 14.87 g/kg is equivalent to 68.5 times the maximum dose in the pharmacodynamic test of mice, and the experiment confirms the safety of oral administration of the SSTF. Intraperitoneal injection of SST showed certain toxicity in mice, with an LD50 value of 732.11 mg/kg[102]. Liu et al.[103] conducted a systematic safety assessment experiment on the aqueous extract of S. baicalensis stem and leaves based on the China National Standard 'Guidelines for the Safety Evaluation of Food Toxicology (GB15193-2014)'. The results indicated that S. baicalensis stem and leaves are non-toxic, non-teratogenic, and non-mutagenic. Acute toxicity tests in mice revealed a Maximum Tolerated Dose of 15.0 g/kg. A 90-d feeding trial showed no changes in toxicological damage in animals, even at a high dosage of 8.333 g/kg (equivalent to 100 times the recommended human daily intake), suggesting the safety and non-toxicity of consuming S. baicalensis stem and leaves. In addition, HQT has long been used in folklore, and no toxicity has been reported.

    These findings collectively indicate that HQT is generally safe for consumption. However, as with any herbal product, it's important to follow recommended dosages and consult healthcare professionals, especially for individuals with pre-existing health conditions or medications.

    In recent years, HQT, a non-Camellia tea with a long history in China, has attracted attention due to its diverse pharmacological activities. Among various Scutellaria species, S. baicalensis is the most extensively studied and cultivated source for HQT. The aerial parts, including flowers, stems, and leaves, serve as the principal source of HQT preparation. HQT are rich in flavonoids and volatile components with various beneficial effects. To date, about 295 compounds have been identified from HQT, including approximately 54 flavonoid compounds and 145 volatile components identified online. The current research on the activity of HQT primarily focuses on flavonoid compounds, with limited studies on the larger quantity of volatile oil compounds.

    Additionally, the processing and brewing techniques used to prepare HQT may influence the bioactivity of its flavonoid content, although few studies have investigated this. More research is necessary to optimize the processing and brewing techniques to maximize the health benefits of HQT. Comparative studies reveal that the aerial parts of S. baicalensis, while sharing similarities with the roots, contain varying flavonoid compositions. Limited research on S. scordifolia, S. amoena, and S. viscidula, indicates the presence of comparable flavonoid compounds in their aerial parts. Although individual flavonoids like baicalin, wogonin, and scutellarin have demonstrated various therapeutic properties, it is essential to consider the synergistic effects of these compounds when consumed together in the form of tea. These findings contribute to laying the groundwork for quality assessment of HQT and offer insights into potential health benefits.

    HQT is mainly derived from the aerial parts of S. baicalensis. Recent studies have increasingly recognized the pharmacological value of the aerial parts of S. baicalensis. Preliminary pharmacological studies have shown that the aerial parts of S. baicalensis may possess beneficial activities in antioxidant, anti-tumor, antiviral, anti-bacterial, protection of ischemia-reperfusion injured neural function, neuroprotective effects against brain injury, and blood lipid regulation. These findings suggest that the value of using HQT may be attributed to these pharmacological activities. Although HQT is generally safe for consumption, further investigation is required to understand its safety profile, particularly in special populations such as pregnant or lactating women, children, and individuals with pre-existing medical conditions. Additionally, potential interactions between the flavonoids in HQT and conventional medications must be examined to ensure their safe and effective use with pharmaceutical treatments. In addition, although the safe dose of HQT on rodents has been studied, the safe dose for humans has yet to be determined.

    In conclusion, these initial research results support the potential health benefits of HQT and encourage more in-depth studies on its raw materials. Further studies are necessary to elucidate the synergistic effects of the flavonoids in HQT, optimize the processing and brewing techniques for maximum bioactivity, and investigate the safety profile and potential interactions with conventional medications. A comprehensive understanding of HQT will contribute to developing evidence-based recommendations for promoting health and well-being.

    The authors confirm contribution to the paper as follows: Conceptualization and writing: Quan Y, Li Z, Meng X, Li P, Shen J; Figure and table modification: Quan Y, Li Z, Meng X, Li P; review and editing: Wang Y, He C, Shen J. All authors reviewed the results and approved the final version of the manuscript.

    The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.

    This research was funded by the Shandong Provincial Natural Science Foundation, China (ZR2022QH147, ZR2022QH165) and the Innovation Team and Talents Cultivation Program of National Administration of Traditional Chinese Medicine (No. ZYYCXTD-D-202005).

  • The authors declare that they have no conflict of interest.

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  • Cite this article

    Grumbine RE, Xu J, Ma L. 2021. An Overview of the Problems and Prospects for Circular Agriculture in Sustainable Food Systems in the Anthropocene. Circular Agricultural Systems 1: 3 doi: 10.48130/CAS-2021-0003
    Grumbine RE, Xu J, Ma L. 2021. An Overview of the Problems and Prospects for Circular Agriculture in Sustainable Food Systems in the Anthropocene. Circular Agricultural Systems 1: 3 doi: 10.48130/CAS-2021-0003

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An Overview of the Problems and Prospects for Circular Agriculture in Sustainable Food Systems in the Anthropocene

Circular Agricultural Systems  1 Article number: 3  (2021)  |  Cite this article

Abstract: In this overview paper, we outline and explore problems and prospects for circular agriculture’s contributions to transformative change toward sustainable food systems in the Anthropocene. We define circular agriculture (CA) and provide historical context on its development. We then discuss how CA can contribute to food system transformations in four key areas: multi-functional landscapes; sustainable intensification (focusing on nitrogen/crop-livestock management and digital agriculture); smallholder farmers; and dietary change. We find that food systems transitions will be challenging due to the depth, scale, and speed of changes necessary for humans to remain within safe planetary boundaries out to 2050.

    • In the modern era, humans have not often attempted to intentionally design a food system at any scale much beyond a local farm or limited region. In 2021, however, it is increasingly clear that profound transformation across multiple levels is required in how we produce and consume food if we are to stay within safe planetary boundaries on Earth[1, 2, 3]. This is evident from the scientific literature as well as recent reports on achieving sustainable food systems from major international organizations[4, 5, 6].

      The common catch phrase in this literature is that fundamental, or transformative change is needed within our food systems, where ‘transformative’ means 'system-wide reorganization across technological, economic, and social factors, making sustainability the norm rather than the altruistic exception'[7]. In this sense, food systems include all elements (nature, people, institutions, governance) and actions (from production through consumption) along with their environmental, economic, and social outcomes[8, 9]. This expansive definition is rooted in a social-ecological systems perspective on nature and people in which both environmental and human factors are considered in relation as they are mutually shaped by key drivers, interact across many scales, exhibit complex dynamics, respond to multiple feedbacks, and are subject to uncertainty and change over time[10].

      If the goal of a sustainable food system is the delivery of food and nutritional security for all people over the long-term with limited environmental degradation, then the biophysical basis for transformative change is obvious. Croplands cover about one third of terrestrial land on Earth[11] and agricultural activities contribute about 26% of total global greenhouse gas emissions[12]. Food systems are the primary driver of biodiversity loss and ecological degradation[11], the largest contributor to freshwater consumption[1], and are major sources of multiple pollutants including nitrogen[13], phosphorus[14], heavy metals[15], antibiotics[16], and microplastics[17]. If all non-food greenhouse gas emissions ended immediately, food systems emissions alone would likely carry us beyond a 1.5C rise in global temperature soon after 2050[18].

      Staying within safe planetary boundaries, however, is not just about the biophysical elements of food systems; the social aspects are equally important within a social-ecological framework. And, since 2014, in spite of six years of implementation of the food-oriented targets of the United Nations (UN) Sustainable Development Goals (SDGs), global food insecurity has been growing, with the number of hungry people reaching 690 million, about 9% of the human population[19].

      The above data portray elements of food security before COVID-19. The number of additional undernourished people resulting from impacts from COVID-19 is modelled to increase 83-150 million by the end of 2021[20], and projections show that there may be up to 840 million hungry people by 2030[19]. Therefore, the virus is seen by many as a wake-up call that has brought social vulnerabilities into focus across multiple elements of food systems, including farmer and laborer vulnerability, global supply chains, import/export trade policy, and more[21, 22]. Yet, as of the beginning of 2021, individual country responses to strengthen food systems have been minimal, despite multiple calls from international agencies and researchers to link food security measures with expanded support for public health.

      As COVID-19 spotlights weaknesses in food systems, other trends continue to put inexorable pressure on conventional agricultural activities. Total greenhouse gas emissions are projected to increase at an annual average rate of 2−6% out to 2030 with major contributions from rising carbon-intensive livestock production, growing beef and dairy consumption, and continuing cropland expansion into natural ecosystems[23, 24]. Longer-term trends appear to offer little relief. Out to 2050, the medium range projection for human population growth is 9.7 billion people, an increase of about 2 billion over 2020[25]. Over this period, some two billion people are expected to enter the global middle class with projections that they will use their increased wealth for more resource-intensive consumption, including eating many more animal products[26]. These two trends underlie projections for a 25−70% rise in global food production to meet demand to 2050[27].

      Transformative change in food systems is uniquely challenging given the links between food as a source of physical and cultural sustenance and its commodification through heterogeneous systems of private and public economics, institutions, and governance. Fostering change in food systems requires more than technical innovation; it is about how culture and identity shape individual attitudes about food. And food systems transformation is also about political decisions that influence policy, institutions, and governance[28].

      In response to these challenges, current food systems research is expanding to address links within and beyond how crops are grown in fields to the full range of agriculture practices within tele-coupled food systems in the 21st century[29]. However, even as concomitant understanding of the ecological and social sides of food systems is growing, coordinated research and international policy remains missing.

      In this broad overview paper, we briefly outline and explore critical problems and promising prospects for circular agriculture’s contributions to transitions to sustainable food systems in the Anthropocene. We define circular agriculture (CA) and provide historical context on its development. We then consider how CA may contribute to food system transformations in four key areas: multi-functional landscapes; sustainable intensification (focusing on nitrogen/crop-livestock management and digital agriculture); small holder farmers; and dietary change. We selected multi-functional landscapes, sustainable intensification, and dietary change following recent research that has identified specific sectors of food systems that, if prioritized, can deliver large co-benefits for climate change mitigation and adaptation, biodiversity protection, and degraded lands restoration[30, 31, 32]. We focus on smallholder farmers since their productivity and livelihoods are a major target of SDG2. For each of these areas, we offer suggestions for CA research that can stimulate new advances toward sustainability.

    • The idea of minimizing harmful inputs and outputs in any production system through creating closed loops that recycle valuable end products back into a circular economy has been discussed for decades[33]. Several countries have pioneered versions of a circular economy as state policy (Germany in 1996, Japan in 2000), yet circularity in agriculture is a much older idea following the principles of ‘grow, make, use, restore’[34]. Circular agricultural systems involve 1) system thinking to design closed cycles of nitrogen, phosphorus, carbon, energy and water along ecological cycles and waste treatment re-use along social value chains; 2) consideration of multiple organisms including microbes (bacteria and fungi), plants, animals, and insects as they form food webs from producers to decomposers; 3) innovations using smart design, digital technology, artificial intelligence, and big data; 4) and efficient and effective design and decision making across multiple scales throughout the entire value chain, often using life cycle assessment (LCA) on a farm, within a company or a country, or at the global scale[35, 36]. CA is but one of several sets of practices that are aimed at implementing food system transitions; others include agroecology[37] and climate-smart regenerative agriculture[38]. There is considerable overlap among these collections of practices, even as they seek somewhat divergent goals.

      Today, CA in various forms is being implemented around the world from small farm fields to large countries. There is a tremendous diversity of projects, for example, in Europe[39], Africa[40], Asia[41], North America[42], Australia[43], and South America[44]. China and the European Union (EU) are leading CA proponents. China has had a national strategy for a circular economy since 2013, making much progress in increasing resource use efficiencies, and the country has been implementing a national sustainable agriculture plan since 2015[45]. In 2018, the EU issued a farm-to-fork agricultural policy including a comprehensive set of CA practices, though it has yet to be approved by member nations[46].

      One of the challenges of designing CA at any scale in any place is capturing the elements of complex food systems. These challenges are related to debates about whether to narrowly frame food systems as only about technological, supply-side issues (increase crop yields, close nutrient loops, re-couple crop-livestock links, etc.) to produce more food efficiently, or whether to include social and demand-side issues (improve smallholder livelihoods, create sustainable supply chains, promote dietary shifts, etc.) to produce more food security[47]. CA has a history of being technically framed; on these grounds, it has been critiqued for placing agricultural efficiency above social outcomes[48, 49]. But including all elements of food systems in CA is not a win/lose proposition; using a social-ecological framework in a world where food systems are often inefficient and inequitable requires that the social aspects of food systems be accounted for. Certainly, the international discussion about food system goals is no longer confined to maximizing productivity, recapturing wastes, and lowering environmental costs; it now includes optimizing outcomes across the full range of environmental and social concerns in complex systems of production and consumption[50, 51].

    • Given the impacts of agriculture on natural ecosystems, it is clear that food systems transitions must include eliminating new cropland expansion into natural ecosystems while increasing on-farm protection of biodiversity, ecological functions and ecosystem services[11]. The latter can be accomplished through creating multifunctional landscapes on lands where crops are grown, thereby increasing biodiversity and ecosystem services values[52]. A host of practices are already being employed on farms to do this including: diversifying vegetation on field edges; incorporating agroforestry into fields; protecting semi-natural patches of vegetation in and around farms; creating ravine and riparian buffers; managing to increase pollinators; enhancing soil biodiversity; and more[53, 54, 55]. Understanding how much of the area of agricultural lands should be managed for biodiversity and ecosystem services is evolving. Currently, few countries have any minimum area requirements for conservation of natural habitats within working lands, though there is some research that shows protecting as little as 5% of within-field natural habitat yields benefits[56]. New work suggests a minimum goal of 20%, though the authors recognize that some places may need more or less land area protected[57].

      In addition to these practices, innovative CA projects are moving to increase connectivity across watersheds and regional landscapes to support plant and animal dispersal[58, 59]. Restoration of both on-farm and surrounding degraded lands is another practice that can link working lands with protected areas[60]. Connecting farms with larger landscapes requires a commitment from CA workers to gather science-based evidence about landscape links from field locations where they work and then sharing it with other actors at multiple scales. This is beginning to occur in China, where agricultural lands are being incorporated into spatial planning for the national system of Ecological Conservation Red Line areas[61]. At the global scale, linking food system and biodiversity goals will be especially important in 2021 since the UN Convention on Biological Diversity is convening, and the draft Global Biodiversity Framework that will set policy out to 2030 as yet contains no specific strategy for agricultural lands[62].

      Given the tremendous diversity of food systems from smallholder to large corporate farms, there is much room for CA to make contributions to learning about best practices to integrate agricultural lands into multifunctional landscapes. A general strategy of testing mixes of the practices mentioned here depends on the establishment of multiple pilot projects, monitoring research results to help define what works and what does not work at scale, and identifying costs and trade-offs to optimize implementation. Three critical actions can help support successful implementation. The first is working with local farmers to discover and implement place-specific, field-level practices that have co-benefits for crop production and biodiversity[63]. The second is developing regional landscape-scale spatial planning that can explore connecting food systems with biodiversity, ecosystem services, climate, and other outcomes[64]. The third action lies with looking for opportunities to convey research outcomes to local and regional/national decision makers. These links can serve to build support for project outcomes with institutions and decision makers, and may spark initiatives that support new multifunctional landscape policies.

    • Sustainable intensification, where agricultural outputs are increased while environmental impacts are reduced, is an essential component of transforming food systems[47]. There is much overlap here with CA. Sustainable intensification has focused on reducing external inputs (fertilizers, pesticides,) and decreasing environmental impacts in service of growing more food on less land. CA has emphasized closing nutrient loops and creative recycling of wastes. Both approaches begin at the field level and share a broad mix of technical practices; we focus here on two: nitrogen/crop-livestock management, and digital agriculture.

      Nitrogen cycles on most agricultural lands are open, highly inefficient, and unsustainable due to the overuse of synthetic fertilizers, poor animal waste management, and the de-coupling of animal/crop production loops[65]. Together, these inefficient practices have resulted in dramatic increases of various forms of nitrogen pollution in air, water, and soils[13,66, 67]. Growing global livestock production resulting from increasing demand for consumption of animal products, especially meat and dairy, accounts for the vast majority of these pollutants, and there are large global disparities in all forms of nitrogen pollution between regions, countries, and subnational areas[68]. For example, fertilizer application rates in China are four times greater than in the EU, while application rates in Africa are minimal[69].

      Yet the economic and social value of livestock production add complexity to finding solutions for better nitrogen management. Globally, 34% of all farm market value comes from animal products[70]. Some one billion people, mostly local smallholders often living on lands less suitable for growing crops, depend on stock for their nutrition, livelihoods, and many cultural values[71].

      Ongoing research is helping to identify what places and practices must be prioritized so that CA and sustainable intensification solutions for livestock production can be better targeted and implemented. The general use of LCA is widely advocated[72, 73]. Many studies also recommend particular focus on three areas: local fertilizer use efficiencies, changes in animal feed production, and manure management[66, 74, 75].

      Numerous changes in fertilizer use efficiency are being pursued within CA. These include reducing urea-based fertilizer application rates, deep placement of fertilizers, and changes in crop straw use[76]. Much innovative work is being done with improving animal feeds including using a variety of new supplements in animal foods (food wastes, tannin-rich plants, fungi, algae, insect proteins)[77, 78, 79]. For improved manure management, there is active experimentation using anaerobic digesters, biogas production, membrane filtration systems, worm composting, algal cultivation, and fungal digestion[77, 80, 81, 82].

      Efforts to reconnect crop-livestock loops are focused on getting animal wastes back onto fields to replace synthetic fertilizers[83, 84]. In addition, researchers are pursuing innovations using algal and fungal-based waste treatments[77]. Zhang and colleagues[85] in China have gone farther than many researchers by looking at county-level nitrogen management practices to discover and showcase where the most efficient management is being done. This kind of fine-scale research provides a model that other countries can pursue to optimize livestock management.

      Nitrogen inefficiencies are not limited to agricultural practices; they occur across food systems from fertilizer production and processing to retail and trade[86]. Further, global trade in animal feedstocks (soy and corn) and meat allows importing countries to avoid the embodied LCA costs of nitrogen pollution. Embodied costs also extend to ground water depletion[87], ecosystems services[88], and carbon emissions[89]. We know of no country accounting for embodied flows in their agricultural policy or national food systems planning; this is an area where CA research using LCA and other modelling at the global scale can make important contributions.

      At all scales, for nitrogen management to meet the sustainability standards of safe planetary boundaries, major transformation of conventional practices will be needed. These include more mainstream use of cost/benefit and trade-off analyses across national agricultural sectors and international trade, redesign of research programs, local extension services, agricultural credit and insurance systems, and food safety regulations[90, 91]. It is also clear that increasing supply-side efficiencies without also addressing demand-side dietary change (and food loss and waste) will not solve nitrogen cycle problems[92]. The expectation is that the positive co-benefits from reduced water and air pollution and greenhouse gas emissions along with increases in benefits to public health and food security will drive increasing nitrogen cycle efficiencies throughout food systems.

    • Innovative use of digital technologies is expanding across food systems at all scales, providing producers with more targeted information and tools to assist with growing crops efficiently and linking them into supply chains[93, 94]. Digital agriculture refers to the integrated use of digital and geospatial information technologies to assess, manage, and monitor conditions in the field so that optimal agricultural outcomes may occur. Mehrabi[95] outlines three key areas: data generation (for example, mobile devices, drones, field sensors, satellites), data processing and predictive analytics (big data, machine learning), and human–computer interactions (ways to blend voice, text and images to improve understanding and communication of results). These technologies are assisting farmers to optimize amounts, timing, and placement of fertilizers, nutrients, and water, while also enabling better monitoring and communication of environmental conditions in fields and across landscapes. Digital technologies can also help to create supply-side links to financial services for farmers and foster demand-side environmental traceability along supply chains.

      Digital agriculture is evolving, but it is not a panacea to solve food system problems. While digital methodologies have been hailed as a breakthrough to provide smallholders with useful data and market links primarily through mobile phones, such use remains limited. Only 24−37% of global smallholders are connected to the Internet, and there are wide country and regional disparities in access and use[95]. In less wealthy countries, there are technological barriers due to poor internet infrastructure, data access costs, and private sector control of software and security[96]. Social barriers include disparities in adoption readiness, concerns about data ownership, and unequal gender access; these issues highlight the fact that adoption of digital agriculture has political as well as technological sides. Even where digital agriculture methods are in relative wide use, research has yet to determine their many tradeoffs[97], and economic and environmental costs/benefits[98]. CA researchers can make contributions here by using LCA studies that analyze trade-offs that extend beyond individual farms/farmers throughout supply chains to determine the comparative costs and benefits of using smart farming tools.

      Overall, the future is bright for the continued expansion of multiple sustainable intensification practices. Farmers working on 9% of global agricultural lands are already implementing at least one sustainable intensification measure[47]. CA researchers can focus on how to speed up adoption of the broad range of sustainable intensification practices, especially in regions where farmer needs are great and progress has been slow.

    • Smallholder farmers are important actors in the transition toward sustainable food systems; they are the focus of SDG2 with its goal of doubling smallholder productivity and income by 2030. Of all farms in the world, about 83% are less than 2 h in size[99]. These farms provide 50% of global food calories and over 70% of food calories to people living in Latin America, sub-Sahara Africa, and South and East Asia[100]. At the same time, smallholders are often poor and subject to food insecurity.

      Despite relatively limited research, we do know something about what smallholder farmers need to be better served in sustainable food systems. These include enhancing extension services while respecting local agricultural knowledge, building farmer cooperatives, offering education and training, securing market access, and increasing targeted forms of private sector and government support[28]. With a focus on meeting SDG2, CA researchers and practitioners can play important roles by working with smallholders to experiment with, understand, and implement these actions.

      Extension services need to scale up provision of: forward-looking information about crop varieties suitable to regional changing climates[101]; methods for smallholders to re-couple crop/livestock links, including managing crop biomass[69]; and assistance with producing crops (legumes, nuts, etc.) that can replace animal products as dietary shifts occur[32]. Respect for farmers’ local knowledge must be part of enhanced extension services given that smallholders have not often been consulted about their needs[102].

      Farmer cooperatives and other forms of self-organized groups have been shown to support collective action around growing new crops, and gaining access to markets[103]. Co-ops often build mutual trust among farmers which is often necessary to support innovative behavior during times of change in food systems. Creating more co-ops, however, does not automatically lead to better outcomes for smallholders; group efforts often show a positive effect on farmer income and a mixed influence on crop yields and crop quality[104]. Working with farmer co-ops can help CA researchers to better evaluate costs and benefits of this form of social organization and how it may contribute to greater on-farm efficiencies and off-farm market links.

      Two large studies of smallholder needs found that education and training provide important ingredients for making progress in food system transitions[101, 28]. These actions can be integrated into extension services and cooperatives with particular attention paid to women, who make up about 50% of the rural agriculture labor force[105]. Women are commonly overlooked by local officials and academic researchers, but recent work is beginning to change this[106]. Chanana and colleagues[105] use a multi-factor model that maps locations where female farmers are most vulnerable to climate change and food insecurity so that decisions about where to provide services can be prioritized. This model can be adopted by CA researchers and other investigators to provide details that are specific to local research sites.

      CA researchers are beginning to work to establish better links between smallholders and new markets for their products. This work often begins on a farm assisting a smallholder to connect with nearby markets (often urban consumers) to purchase her new, sustainably-grown product[107]. But it does not end there. Supply chains with their multi-faceted environmental and social footprints often extend beyond local and regional levels since one-third of all food is globally traded and crosses two or more international boundaries[70]. For globally important products like soy and beef, the embedded impacts of production and consumption have serious environmental consequences; for example, the greenhouse gas emissions footprint of beef exported to the EU from Brazil comes close to cancelling out all EU carbon mitigation goals[108]. Food systems policy research suggests building transparent and traceable supply chains from smallholder farms to global networks using digital means to close loops in tracking environmental and social costs and benefits[109, 110]. This work faces complex challenges across multiple sectors of tele-coupled food systems[29]. For CA researchers working with smallholders, a critical decision is deciding how far up supply chains and away from small farm study sites one should go to account for these impacts[111, 112]. Eco-certifications, improved product labelling, and LCA are tools to help do this, but transformative change in global food systems will eventually require reevaluation of national and international supply chains.

      To better address the needs of smallholders far removed from global trade, local and national governments have roles to play in three main areas—infrastructure, incentives, and financial support. For infrastructure, governments should prioritize provision of irrigation for the 37% of smallholders in water-stressed regions around the globe who likely lack any means to irrigate their fields[113]. Digital network connections for smallholders and facilities for food storage and transport to reduce post-harvest food losses (and bolster farmer profits) are two additional areas where more government attention is needed. Creating positive incentives that influence smallholder behavior is another area where governments can act. These range from relatively straightforward actions like providing greater access to credit and crop insurance[107] to revising regulations for digital access and data privacy[114]. More challenging changes are the need to address long-standing land tenure problems that confer high levels of risk to farmers and reduce agricultural innovation[115].

    • Dietary shifts toward more nutritious, plant-based foods will also be challenging as we learn how to construct a more sustainable food system. In fact, of all strategies out to 2050, plant-based diets (56% reduction) and diets following improved nutrition guidelines (29% reduction) yield the largest modelled decreases in greenhouse gas emissions from global food systems[18,116 ]. This means that animal products, especially meats, must play a reduced role in many human diets going forward. This is a demand-side area of food systems analysis that has been so far been little addressed by CA researchers.

      Dietary shifts away from animal foods at the speed and scale that appear to be required will be difficult to encourage. Though animal products are the single largest source of greenhouse gas emissions from food systems, global production and consumption of these products are rising[5]. And there are pronounced dietary differences between countries that must be accounted for in crafting strategies to encourage shifts away from animal foods. For example, beef consumption in the US has declined almost 36% since the 1970s, but overall consumption of all meats remains very high[23]. In China, per capita meat consumption is much less than in many countries, but it is steadily rising[117].

      There are multiple strategies that are essential to promoting global dietary transformative change. The question is, if dietary change is a priority, then what do we know that would facilitate the rapid adoption of new ways of eating? Given the diversity of global diets, there is no single answer to this question; dietary shifts must be attuned to every country and cultural context. However, scientific information does not much influence peoples’ decision making when it comes to what they choose to eat; taste, tradition, and values about foods are more important. The main drivers of dietary change are social norms among peer groups and individuals’ beliefs that what they choose to eat can contribute to group dietary shifts[118]. Lack of knowledge about the environmental impacts of food choices is widespread. Even in a relatively well-educated country such as the US, only 43% of people know about the climate impacts of eating meat[119]. This suggests that government-led programs that employ relatively strong dietary incentives will likely be needed[120]. Past government efforts to spur national dietary shifts have occurred in several countries over spans of 2−4 decades, however, most of these programs only focused on supply-side growth in crop yield and income from products with scant attention to overall food systems sustainability[121].

      The Lancet Commissions’ work[3] has established a global model to encourage transitions toward healthy eating. Yet, less than half of all countries have established national dietary guidelines[122], and costs of dietary change for poor people in less wealthy nations may be prohibitive without some form of subsidy[123]. An important knowledge gap that CA researchers could address here is evaluation of what cost-effective, protein-rich crops might help to replace animal products as the transition toward consuming less meat and dairy proceeds. Other steps would be for countries to solidify national dietary standards followed by efforts to reach international consensus on global guidelines and monitoring to track progress. These actions will certainly demand some form of international cooperative mechanism; it is here that trade-offs between food systems and climate, biodiversity, public health, and sustainable development goals may lead to co-benefits that compel action.

    • At the beginning of this paper, we observed that humans have little historical experience with intentionally designing food systems much beyond local levels. The task humanity faces today is considerably greater; from tiny subsistence farms in sub-Sahara Africa to the more than US100 billion dollars of international trade in beef, corn, and soy, food systems require a 'major shift in mindsets'[2]; engagement with 'a massive scientific challenge'[124]; and 'radical and coordinated action'[125].

      How may we accomplish these things? There is some general work that describes how social transformations unfold over 10−30 years[126, 127], and reviewing the history of progress on meeting international goals for climate mitigation and biodiversity protection confirms that 2−3 decades (or more) are likely required. Studies at national[75] and global scales[32] suggest that significant progress can be made in food system transitions by 2030 and out to 2050, but none of this research comes close to projecting net zero greenhouse gas emissions from food systems. Given these timelines and projections, it is imperative that CA and all food system researchers be more cognizant of how their work addresses implementation of transformative actions as described in this paper. To encourage such efforts, we offer four observations.

      First, food system researchers can benefit from what has already been discovered about how societal transformations are shaped and stimulated[128, 129]. Are there actions that may accelerate change in food systems in a preferred direction? Research suggests that societal transitions may be encouraged by: supporting transdisciplinary knowledge co-production so that the science, social issues, and the politics of change are equally addressed[130, 131]; identifying and then working with actors, institutions, and decision makers who are willing to support innovative projects[132]; setting strategic priorities for action since resources (funding, workers) will likely be insufficient to accomplish every task[133]; and experimenting with multiple pilot projects to learn what works best before scaling up initiatives[134]. These actions, by themselves, may not yield much momentum for change; however, used in combination, they may spark shifts that lead to deeper transformations. Researchers investigating climate change and energy transitions are already using these lessons to design projects and recommend implementation measures; CA researchers may also benefit from experimenting with these methods.

      Second, it is important to emphasize how the employment of innovative tools can stimulate food systems transitions. These tools include: More frequent use of LCA to help define cost/benefits of CA projects; incorporating the full range of food system actors and institutions into CA analyses so that trade-offs throughout the system are routinely revealed; and greater use of multi-actor, multi-sector spatial assessments that build links between land, water, food, and social systems[97]. If sufficient use of these tools can be sustained across multiple sectors of a countries’ food system, then the scientific basis for national planning may be strengthened. Science-based national planning may, in turn, contribute key ingredients to the negotiation of a platform for international food systems cooperation.

      Third, on the matter of governance, general lessons from transformative change research along with specific observations from food systems analysts show that transitions are often slowed down by established institutions and decision-makers[135, 136, 137, 138]. This makes sense since, by definition, CA and other movements toward food systems sustainability offer alternatives to the existing norms, policies, and power relationships of conventional, linear agriculture. Conventional agriculture actors often believe that the price of food systems transformation is prohibitive due to redistribution of cost and benefits throughout social-ecological systems[4,139]. Despite these challenges, there are methods that CA scientists and practitioners can wield to more directly address the governance aspects of food systems. One way is for CA workers to strategically use the tools and techniques outlined in this paper while continuing to ask fundamental questions: ‘what does full cost accounting reveal about barriers and bridges to the true price of affecting change in food systems here?’; ‘how can we work collectively with local people, government, and other actors in this place to design and implement sustainable foods solutions?’; ‘who are the specific decision makers that could use my research to promote change and how do I best communicate with them?’ These practical questions demand active solutions to sort out the inevitable tradeoffs that are found throughout all food systems.

      Finally, it is important to remember that food systems evolve through peoples’ everyday behavior where seeds of change are planted that accumulate and are amplified over time. These incremental, 'small wins'[140], 'small stories of closing loops'[141], and 'bright seeds'[142] range from a farmer adopting a climate-smart crop, to a county-level decision maker funding more extension services, to a food systems researcher incorporating ecosystem services, food systems, and urban land-use into an improved, spatially-explicit model that can better serve government planners. CA researchers do not have to foment a revolution; however, they do have to think more strategically about which steps have a better chance than others to initiate and sustain food systems transformations.

      The Anthropocene will continue to offer many challenges and opportunities to effect transformative change in food, climate, and biodiversity protection so that human endeavors stay within safe planetary boundaries. In 2021, there will be additional opportunities to support secure food systems including the UN Food Systems Summit (https://www.un.org/en/food-systems-summit); the Nutrition for Growth Summit (https://nutritionforgrowth.org/events/); the Convention on Biodiversity Conference of the Parties 15 (https://www.cbd.int/convention/); and the United Nations Framework Convention on Climate Change Conference of the Parties 26 (https://www.ukcop26.org/). The time for planting transformative seeds of change is now.

    • The field of sustainable agriculture is vast; there are 685,000 hits to the subject on Google Scholar since 2016, and over 12,000 papers referenced in Scopus (as of 12/21/20). For this review paper, we did not attempt to thoroughly summarize this literature; instead, we selectively searched for papers within this extensive field that focused on circular agriculture; multifunctional landscapes; sustainable intensification (including nitrogen management in agriculture, crop/ livestock management, and digital agriculture); smallholder farmers; and global and national-level dietary change. We emphasized work published since 2015 (reflecting the timeline of implementation of the SDGs), and scoping reviews and other syntheses of the above portions of the sustainable agricultural literature that offered results extending beyond a specific farm field setting. We filtered our search to highlight transdisciplinary processes and cross-links to multiple areas of food systems that suggested innovative areas of research. In all, we reviewed abstracts from 409 papers which led to the reading of 210 papers of which 142 are cited in this review.

      • This work was generously supported by the Key Project from the Ministry of Sciences and Technology of China (No: 2017YFC0505101), and CGIAR Research Program on Forests, Trees and Agroforestry (FTA). REG was supported by the Chinese Academy of Sciences President's International Fellowship Initiative (PIFI) for visiting scientists. We thank three reviewers for comments that improved the manuscript.

      • The authors declare that they have no conflict of interest.

      • Copyright: © 2021 by the author(s). Published by Maximum Academic Press, Fayetteville, GA. This article is an open access article distributed under Creative Commons Attribution License (CC BY 4.0), visit https://creativecommons.org/licenses/by/4.0/.
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    Grumbine RE, Xu J, Ma L. 2021. An Overview of the Problems and Prospects for Circular Agriculture in Sustainable Food Systems in the Anthropocene. Circular Agricultural Systems 1: 3 doi: 10.48130/CAS-2021-0003
    Grumbine RE, Xu J, Ma L. 2021. An Overview of the Problems and Prospects for Circular Agriculture in Sustainable Food Systems in the Anthropocene. Circular Agricultural Systems 1: 3 doi: 10.48130/CAS-2021-0003

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