Daily UV-B treatments and elevated CO2 increases pigment concentrations and net photosynthesis of basil (Ocimum basilicum L.)

T. Casey Barickman; Skyler R. Brazel; Akanksha Sehgal; Charles Hunt Walne; K. Raja Reddy; T. Casey Barickman; Skyler R. Brazel; Akanksha Sehgal; Charles Hunt Walne; K. Raja Reddy

doi:10.48130/TIH-2022-0002

Treatment	P_NET¹	g_sw	C_i	ETR	E	T_leaf	C_i/C_a²
Ambient [CO₂]
No UV-B	24.477^b	0.375^a	295.09^b	187.33^a	6.786^a	30.484^c	0.704^a
UV-B	18.949^c	0.315^a	303.50^b	150.69^b	6.504^a	31.761^ab	0.723^a
Elevated [CO₂]
No UV-B	31.514^a	0.312^a	530.71^a	184.97^ab	6.671^a	31.263^bc	0.737^a
UV-B	30.715^a	0.302^a	529.59^a	178.02^ab	6.449^a	32.344^a	0.736^a
P-Value^3,4
UV-B	**	NS	NS	NS	NS	**	NS
CO₂	***	NS	***	NS	NS	*	NS
UV-B x CO₂	*	NS	NS	NS	NS	NS	NS
¹Units: P_NET – μmol CO₂ m⁻² s⁻¹; gsw – mol m⁻² s⁻¹; Ci – CO₂ μmol⁻¹; ETR – μmol photons m⁻²s⁻¹; E – mmol H₂O m⁻²s⁻¹; T_leaf – °C. ² The measured intercellular CO₂/ambient CO₂ of LI-6400XT leaf cuvette. ³ The standard error of the mean was P_NET – 1.318; g_sw – 0.302; C_i – 9.601; ETR – 11.247; E – 0.480; T_leaf – 0.278; C_i/Ca – 0.0206. ⁴ NS, , , ** indicate non-significant, significant at P ≤ 0.05, P ≤ 0.01, and P ≤ 0.001, respectively. Values followed by the same superscript letter are not significantly different within each column.

Table 1.

Effects of UV-B radiation and CO₂ concentration on net photosynthesis (P_NET), stomatal conductance (g_sw), internal CO₂ (C_i), electron transport rate (ETR), transpiration rate (E), leaf temperature (T_leaf), and intercellular/ambient CO₂ ratio (C_i/C_a). Measurements were taken on the fourth/fifth fully expanded leaf of plants grown without UV-B radiation (No UV-B) and with UV-B radiation (UV-B) at 437 (ambient [CO₂]) and 725 ppm (elevated [CO₂]) CO₂ concentration between 33 and 35 days of treatment.

Treatment	F_o'	F_m'	F_s	F_v'/F_m'	Φ_PSII	${\Phi_{\rm{CO_2}}} $	q_P	q_N
Ambient [CO₂]
No UV-B	448.31^a	840.48^ab	622.16^a	0.466^b	0.261^ab	0.0195^b	0.559^ab	1.875^b
UV-B	430.78^a	809.76^b	617.25^a	0.467^b	0.238^b	0.0155^c	0.509^b	1.878^b
Elevated [CO₂]
No UV-B	440.77^a	907.91^a	674.12^a	0.513^a	0.259^ab	0.0248^a	0.507^b	2.058^a
UV-B	440.13^a	836.64^ab	603.64^a	0.474^b	0.279^a	0.0245^a	0.587^a	1.902^b
P-Value^1,2
UV-B	NS	NS	NS	*	NS	*	NS	*
CO₂	NS	NS	NS	**	NS	***	NS	**
UV-B x CO₂	NS	NS	NS	*	NS	*	*	*
¹ The standard error of the mean was F_o' – 9.503; F_m' – 28.161; Fs – 26.365; F_v'/F_m' – 0.00983; Φ_PSII – 0.0111; ${\Phi_{\rm{CO_2}} }$ – 0.000976; q_P – 0.0232; q_N – 0.0383. ² NS, , , ** indicate non-significant, significant at P ≤ 0.05, P ≤ 0.01, and P ≤ 0.001, respectively. Values followed by the same superscript letter are not significantly different within each column.

Table 2.

Effects of UV-B radiation and CO₂ concentration on light-adapted, minimal fluorescence (F_o'), light-adapted, maximal fluorescence (F_m'), steady-state fluorescence (F_s), light-adapted maximal quantum yield of photosystem II photochemistry (F_v'/F_m'), effective quantum yield of photosystem II photochemistry (Φ_PSII), effective quantum yield of gas exchange measurements ($\Phi_{\rm{CO_2}} $), photochemical quenching (q_P), and non-photochemical quenching (q_N). Measurements were taken on the fourth/fifth fully expanded leaf plants grown without UV-B radiation (No UV-B) and with UV-B radiation (UV-B) at 437 (ambient [CO₂]) and 725 ppm (elevated [CO₂]) CO₂ concentration between 33 and 35 days of treatment.

Treatment	Neo¹	Viol	Anth	Zea	Lut	β-car	Total Xan²	ZA/ZAV³	ChlB	ChlA	Total Chl⁴
Ambient [CO₂]
No UV-B	276.43^c	204.25^c	68.76^a	163.94^a	793.09^b	509.66^c	436.95^b	0.531^a	871.50^c	7005.67^c	7877.17^c
UV-B	307.30^b	249.89^b	68.70^a	168.79^a	914.27^a	606.80^a	487.38^a	0.487^b	1010.37^b	9234.86^b	10245^b
Elevated [CO₂]
No UV-B	222.36^d	208.03^c	74.30^a	157.75^a	561.09^c	384.95^d	440.08^b	0.526^ab	767.96^c	7132.75^c	7900.70^c
UV-B	348.88^a	303.08^a	44.26^b	78.49^b	916.49^a	566.26^b	425.83^b	0.288^c	1329.67^a	12523^a	13853^a
P-Value^5,6
UV-B	***	***	**	***	***	***	NS	***	***	***	***
CO₂	NS	**	*	***	***	***	*	***	***	***	***
UV-B x CO₂	***	**	**	***	***	**	*	***	***	***	***
¹ Neo – Neoxanthin; Viol – Violaxanthin; Anth – Antheraxanthin; Zea – Zeaxanthin; Lut – Lutein; β-car – Beta carotene; Xan – Xanthophylls; ChlB – Chlorophyll B; ChlA – Chlorophyll A; Chl - Chlorophylls. All values expressed as μg g⁻¹ dry mass, except for ZA/ZAV. ² Total Xan – Sum of Viol, Anth, and Zea. ³ Xanthophyll Cycle Ratio = (Zea and Anth)/(Zea, Anth, and Viol). ⁴ Total Chl – Sum of ChlB and ChlA. ⁵ The standard error of mean was Neo – 10.99; Vio – 8.83; Anth – 3.77; Zea – 7.90; Lut – 27.19; β-car – 17.13; Total Xan – 12.72; ZA/ZAV – 0.015; ChlB – 50.99; ChlA – 349.82; Total Chl – 395.77. ⁶ NS, , , ** indicate non-significant, significant at P ≤ 0.05, P ≤ 0.01, and P ≤ 0.001, respectively. Values followed by the same superscript letter are not significantly different within each column.

Table 3.

Effects of UV-B radiation and CO₂ concentration on carotenoids and chlorophyll concentrations in basil leaves grown in the Soil-Plant-Atmosphere-Research (SPAR) units at Mississippi State University. Leaf samples were taken from basil plants grown without UV-B radiation (No UV-B) and with UV-B radiation (UV-B) at 437 (ambient [CO₂]) and 725 ppm (elevated [CO₂]) CO₂ concentrations between 33 and 35 days of treatment.

Treatment	Concentration
Treatment	MDA^1,2	Perox	SOD	Asc	Tre	Glth
Ambient [CO₂]
No UV-B	0.008^b	0.1912^a	0.0304^b	0.101^b	0.089^b	0.192^a
UV-B	0.053^a	0.2132^a	0.0308^b	0.110^b	0.110^ab	0.205^a
Elevated [CO₂]
No UV-B	0.008^b	0.1832^a	0.0392^a	0.191^a	0.126^a	0.177^a
UV-B	0.007^b	0.1914^a	0.0402^a	0.119^b	0.105^ab	0.159^a
P-Value^3,4
UV-B	***	NS	NS	NS	NS	NS
CO₂	***	NS	**	*	NS	NS
UV-B x CO₂	***	NS	NS	NS	NS	NS
¹ MDA – Malondialdehyde; Perox – Hydrogen Peroxide; SOD – Superoxide Dismutase; Asc – Ascorbate; Tre – Trehalose; Glth – Glutathione. ² Units: MDA – nmol g⁻¹∙dw⁻¹; Perox – μmol g⁻¹∙dw⁻¹; SOD – units mg⁻¹∙protein⁻¹; Asc – nmol g⁻¹∙dw⁻¹; Tre – μmol g⁻¹∙dw⁻¹; Glth – nmol g⁻¹∙dw⁻¹. ³ The standard error of mean was MDA – 0.00287; Perox – 0.02763; SOD – 0.00212; Asc – 0.02417; Tre – 0.01284; Glth – 0.02096. ⁴ NS, , , ** indicate non-significant, significant at P ≤ 0.05, P ≤ 0.01, and P ≤ 0.001, respectively. Values followed by the same superscript letter are not significantly different within each column.

Table 4.

Effects of UV-B radiation and CO₂ concentration on the concentrations of malondialdehyde, hydrogen peroxide, superoxide dismutase activity, ascorbate acid, trehalose, and glutathione in the concentration of basil leaves. Samples were taken 33 days of treatment from plants grown without UV-B radiation (No UV-B) and with UV-B radiation (UV-B) at 437 (ambient [CO₂]) and 725 ppm (elevated [CO₂]) CO₂ concentration.