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High temperature, as one of the major abiotic stresses restricting the growth of cool-season turfgrass, is an important and difficult problem for turfgrass management, especially during summer[3]. Heat stress induced the limitation of physiological and metabolism in various turfgrass species[30−32]. The heat-induced damage also occurred in the morphology and growth of plants, especially when turfgrass species suffered continuous severe heat stress[33]. It was previously found that heat-tolerant species usually had better growth performance and physiological characteristics than heat-sensitive plants in creeping bentgrass[9, 34]. In the present study, exogenous chitosan with 100 mg·L−1 significantly enhanced thermotolerance in association with superior plant growth indexes (Figs 1, 3 & 4), photosynthesis (Fig. 5) and cell membrane stability (Fig. 6) compared with the untreated plants under heat stress in creeping bentgrass as discussed below.
Shoot growth and development were directly associated with turf quality in turfgrass. Studies have shown that high temperature stress would reduce turf quality and increase the ratio of yellow leaves in creeping bentgrass[35]. Turf quality and canopy height also significantly decreased due to heat stress in perennial ryegrass (Lolium perenne) [36]. Chitosan serves as not only a plant growth regulator to promote growth and development of various plants, but also an abiotic stress tolerance inducer[37−39]. In our study, foliar application of chitosan improved turf quality and shoot biomass in response to heat stress during the experimental period (Figs 1 & 4a). Similar result was also found by Younas et al.[40] that growth and yield characteristics of maize including shoot dry weight, cob weight and grain yield were improved by applying chitosan under water deficit conditions. Furthermore, chitosan treatment improved growth and quality in soybean sprouts (Glycine max)[41], increased shoot height and number of nodes in potato (Solanum tuberosum)[42]. Chitosan-induced increase in turf quality and biomass in this study indicated that chitosan could enhance heat tolerance and promote plant growth in creeping bentgrass under high temperature conditions.
Heat stress also leads to injury of belowground root as well as the aboveground shoot. Roots are the main organs for acquiring water and mineral nutrients from the soil in plants[43]. However, root system are more sensitive to heat stress in comparison to shoots[31]. In general, root growth was positively correlated with heat tolerance as reported in various cool-season turfgrass species, such as in tall fescue (L. arundinaceum), perennial ryegrass and creeping bentgrass[10,44,45]. Hence, root growth played a crucial role in enhancing thermotolerance in turfgrass species in response to heat stress. In our study, foliar application of chitosan led to the significant promotion of root length, root-shoot ratio and root biomass compared with the untreated control (Figs 3 & 4). The positive effects of chitosan in thermotolerance through facilitating plant roots have been widely documented in several previous studies. For example, chitosan alleviated adverse effects of salt stress through inhibiting the decline in root length in maize seedlings[24]. Chitosan also mitigated the suppression of root growth in maize under cadmium stress as reflected by higher root length, root surface and root volume[46]. Those results suggested that chitosan played a positive role during root growth under high temperature stress.
Various physiological activities in plants were limited by high temperature of which photosynthesis as one of physiological processes is sensitive to external temperature. Heat-induced negative effects were observed when creeping bentgrass was subjected to heat stress, as reflected by reduction in chlorophyll content, Fv/Fm and Pn as well as inhibition in rubisco activity and rubisco activation state involving in photosynthesis[1, 47]. In this study, a significant decrease in both Fv/Fm and Pn was detected in plants due to imposition of heat stress, but exogenous chitosan effectively alleviated the decline in Fv/Fm and Pn (Fig. 5). It has also been found that chitosan pretreatment significantly mitigated the adverse effect on Fv/Fm in creeping bentgrass under salt stress[25]. Application of irradiated chitosan significantly increased chlorophyll content and Pn as well as enhanced drought tolerance of sugarcane (Saccharum spp.)[48]. Similarly, the result in this present study demonstrated that chitosan alleviated severe damage in photosynthetic system caused by high temperature. Furthermore, high temperature also led to electrolyte leakage and membrane lipid peroxidation resulting from cell membrane damage[49]. In our study, both EL and MDA content in plants without chitosan treatment significantly increased, but chitosan application significantly inhibited the increase in EL and MDA content under high temperature stress (Fig. 6). This result was also reported by other studies in several plant species, such as in potato[42], thyme (Thymus daenensis)[17] and edible rape (Brassica rapa)[50] indicating that exogenous chitosan contributed to the promotive effects on cell membrane stability and integrity and improved heat tolerance in creeping bentgrass.
In summary, foliar application of chitosan significantly enhanced heat tolerance as reflected through promoting both shoot and root growth in creeping bentgrass as shown by higher turf quality, root length, root-shoot ratio and biomass. Furthermore, chitosan application also could inhibit the decline in photosynthesis and maintain cell membrane stability. The mechanisms involved in chitosan-induced thermotolerance at the molecular level under heat conditions need to be further investigated in our next studies. This study will provide new insight for turf managers to enhance heat tolerance of perennial turfgrass species, especially during the summer season in cool-season grasses.
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Cite this article
Li Q, Li R, He F, Yang Z, Yu J. 2022. Growth and physiological effects of chitosan on heat tolerance in creeping bentgrass (Agrostis stolonifera). Grass Research 2:6 doi: 10.48130/GR-2022-0006
Growth and physiological effects of chitosan on heat tolerance in creeping bentgrass (Agrostis stolonifera)
- Received: 14 August 2022
- Accepted: 17 October 2022
- Published online: 27 October 2022
Abstract: High temperature is one of the major abiotic stresses limiting growth and development of cool-season grass species, but chitosan could effectively enhance heat tolerance and improve plant growth. The objective of this study was to determine the optimal concentration of chitosan that could alleviate heat stress in creeping bentgrass (Agrostis stolonifera) and investigate the effects of exogenous chitosan on photosynthesis and cell membrane stability under heat stress. Under heat stress (38/28 °C, day/night), different chitosan concentrations of 0, 50, 100 and 500 mg·L−1 were applied on the leaves of creeping bentgrass (cv. 'Penn-A4'). Foliar application of chitosan exhibited the positive effects on plant growth and the optimal concentration was 100 mg·L−1 which significantly improved turf quality, root length, root-shoot ratio as well as shoot and root biomass. Chitosan-treated plants subjected to high temperature stress had a lower decline in photosynthetic rate and photochemical efficiency as well as less increase in electrolyte leakage and malondialdehyde content. The results demonstrate that chitosan-improved heat tolerance as reflected by the superior growth performance of both shoot and root, photosynthesis and cell membrane stability in creeping bentgrass under heat stress.
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Key words:
- Creeping bentgrass /
- Exogenous substances /
- Heat stress /
- Growth