Effects of light regimes on photosynthetic characteristics and antioxidant system in seedlings of two alder species

doi:10.3724/SP.J.1258.2012.01062

Abstract

Abstract:

Aims Our objective was to investigate the effects of different light intensities on leaf morphology, photosynthetic capacity, heat dissipation and antioxidant enzyme activities in seedlings of Alnus formosana and A. cremastogyne from a hilly region near Lingyan Mountain in northwestern Sichuan Province in China. We also discuss photosynthetic acclimation and photoprotection strategies in seedlings of the two species --Methods-- Three light regimes of 100%, 56.2% and 12.5% of natural light were simulated to match forest openings, forest gaps and forest canopies, respectively. After more than three months, we measured the parameters of gas exchange, including maximum net photosynthetic rate (Pmax), light saturation point (LSP), light compensation point (LCP), net photosynthetic rate (P_n), stomatal conductance (G_s), transpiration rate (T_r), intercellular CO₂concentration (C_i), fluorescent non-photochemical quenching (NPQ), maximum efficiency of PSII photochemistry (F_v/F_m) and light use efficiency (LUE), using a LI-6400 in seedling leaves. We also determined pigment contents per unit leaf area, lamina mass per unit area (LMA) and activity of antioxidant enzymes (superoxide dismutase, catalase and ascorbate peroxidase). --Important findings-- LMA, carotenoid content (Cars), ratio of carotenoid to total chlorophyll (Car/Chl) and activities of superoxide dismutase, catalase and ascorbate peroxidase in leaves increased with the increase of light intensities. P_max, LSP, LCP and NPQ tended to increase, while the chlorophyll content (Chl) and LUE decreased. However, the C_i decreased with the increase of P_n, G_s and stomatal limitation value (L_s). We speculated that non-stomatal limitation was the main factor that inhibited P_n. Seedlings of the two alder species could acclimate to different light regimes in this study through changing of physiological and morphological traits. Under all light regimes, diurnal photoinhibition of photosynthesis, as judged by F_v/F_m, was significantly more severe in A. cremastogyne than in A. formosana. The acclimation capacity to high light regime was stronger in A. formosana than in A. cremastogyne. With the increase of light intensities, P_maxand antioxidant enzyme activities increased significantly, but not NPQ in A. formosana. The opposite trends occurred in A. cremastogyne. At the same light intensity, thermal dissipation was much lower, but P_max was much higher in A. formosana than in A. cremastogyne. These results indicated that A. formosana seedlings might adapt resistance to photoinhibition through improving the use of solar energy by higher P_max and antioxidant enzyme system, while A. cremastogyne seedling avoided photoinhibition mainly through converting excess light energy to heat energy in the form of non-radiative dissipation through the antenna system.

Key words: Alnus cremastogyne, A. formosana, antioxidant enzyme, heat dissipation, photoinhibition, photosynthetic acclimation

LIU Shi-Liang, MA Ming-Dong, PAN Yuan-Zhi, WEI Liu-Li, HE Cheng-Xiang, YANG Kai-Mao. Effects of light regimes on photosynthetic characteristics and antioxidant system in seedlings of two alder species[J]. Chin J Plant Ecol, 2012, 36(10): 1062-1074.

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URL: https://www.plant-ecology.com/EN/10.3724/SP.J.1258.2012.01062

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Figures/Tables 10

Fig. 1 Effect of light regimes on the lamina mass per unit area (LMA) and pigment content in seedling leaves of two Alnus species (mean ± SE). LT1, full light; LT2, (56.2 ± 1.03)% full light; LT3, (12.5 ± 0.21)% full light. L, light; S, tree species; S × L, interaction of tree species and light. **, p < 0.01; *, p < 0.05. Different capital letters indicate significant differences among two tree species under the same light regimes (p < 0.05); Different small letters indicate significant differences among three light regimes of the same species (p < 0.05).

Fig. 2 Light-photosynthetic response curves of two Alnus seedlings under different light regimes. LT1, full light; LT2, (56.2 ± 1.03)% full light; LT3, (12.5 ± 0.21)% full light.

Table 1 Maximum net photosynthetic rate (Pmax), light saturation point (LSP) and light compensation point (LCP) for the seedlings of two Alnus species under different light regimes (mean ± SE)

物种 Species	处理 Treatment	P_max (μmol CO₂ ?m^-2?s^-1)	LSP (μmol CO₂?m^-2?s^-1)	LCP (μmol CO₂ ?m^-2?s^-1)
台湾桤木 A. formosana	LT1	8.52 ± 0.45^{A, a}	1205.7 ± 104.0^{A, a}	98.05 ± 1.49^{B, a}
	LT2	7.48 ± 0.43^{A, a}	995.8 ± 55.4^{A, ab}	83.22 ± 1.76^{A, b}
	LT3	5.46 ± 0.27^{A, b}	755.9 ± 79.5^{A, b}	38.42 ± 3.12^{B, c}
桤木 A. cremastogyne	LT1	7.13 ± 0.05^{B, a}	877.3 ± 60.9^{A, a}	104.57 ± 3.02^{A, a}
	LT2	6.62 ± 0.30^{B, a}	749.4 ± 56.1^{B, a}	86.93 ± 5.04^{A, b}
	LT3	4.75 ± 0.18^{A, b}	489.6 ±16.0^{B, b}	84.69 ± 1.06^{A, b}

Table 2 Gas exchange parameters and instantaneous light utilization efficiency in seedling leaves of two Alnus species under different light regimes (mean ± SE)

物种 Species	处理 Treatment	P_n (μmol CO₂·m^-2·s^-1)	T_{r (}mmol H₂O·m^-2·s^-1₎	G_s(mmol H₂O·m^-2 ·s^-1)	C_i (μmol CO₂?m^-2?s^-1)	LUE (mmol?mol^-1)	L_s
台湾桤木 A. formosana	LT1	7.32 ± 0.42^{A, a}	5.61 ± 0.21^{A, a}	236.91 ± 13.48^{A, a}	249.15 ± 15.91^{A, b}	8.81 ± 0.77^{A, b}	0.24 ± 0.01^{B, a}
台湾桤木 A. formosana	LT2	7.45 ± 0.32^{A, a}	4.12 ± 0.14^{A, b}	192.41 ± 4.20^{A, b}	281.85 ± 12.71^{A, ab}	13.11 ± 2.12^{B, b}	0.27 ± 0.01^{A, a}
	LT3	2.96 ± 0.36^{A, b}	2.93 ± 0.09^{A, c}	161.09 ± 13.27^{A, b}	337.01 ± 21.78^{B, a}	35.98 ± 1.11^{B, a}	0.14 ± 0.01^{A, b}
桤木 A.cremastogyne	LT1	6.66 ± 084^{B, a}	3.73 ± 0.49^{B, a}	196.32 ± 15.35^{A, a}	262.24 ± 10.86^{A, b}	9.63 ± 0.33^{A, b}	0.29 ± 0.01^{A, a}
桤木 A.cremastogyne	LT2	5.47 ± 0.78^{B, a}	2.89 ± 0.09^{B, a}	151.46 ± 11.87^{B, ab}	291.87 ± 7.97^{A, b}	15.25 ± 3.09^{A, b}	0.26 ± 0.02^{A, a}
	LT3	2.30 ± 0.45^{A, b}	1.71 ± 0.22^{B, b}	108.16 ± 25.93^{A, b}	340.35 ± 8.39^{A, a}	30.81 ± 3.70^{A, a}	0.15 ± 0.01^{A, b}

Table 3 Correlation coefficients among gas exchange parameters and LUE in seedling leaves of two Alnus species (n = 18)

	P_n	T_r	G_s	C_i	L_s	LUE
P_n	1.00
T_r	0.77^**	1.00
G_s	0.72^**	0.87^**	1.00
C_i	-0.73^**	-0.80^**	-0.65^**	1.00
L_s	0.81^**	0.50^*	0.49^*	-0.73^**	1.00
LUE	-0.89^**	-0.66	-0.68^**	0.79^**	-0.89^**	1.00

Fig. 3 Diurnal changes of maximum efficiency of PSII photochemistry (Fv/Fm) for the seedling leaves of two Alnus species under different light regimes (mean ± SE). LT1, full light; LT2, (56.2 ± 1.03)% full light; LT3, (12.5 ± 0.21)% full light.

Fig. 4 Diurnal changes of non-photochemical quenching (NPQ) for the seedling leaves of two Alnus species grown under different light regimes (mean ± SE). LT1, full light; LT2, (56.2 ± 1.03)% full light; LT3, (12.5 ± 0.21)% full light.

Fig. 5 Malondialdehyde (MDA) and H2O2 contents in seedling leaves of two Alnus species under different light regimes (mean ± SE). LT1, full light; LT2, (56.2 ± 1.03)% full light; LT3, (12.5 ± 0.21)% full light. L, light; S, tree species; S × L, interaction of tree species and light. **, p < 0.01; *, p < 0.05; ns, p > 0.05. Different capital letters indicate significant differences among two tree species under the same light regimes (p < 0.05); Different small letters indicate significant differences among three light regimes of the same species (p < 0.05).

Table 4 Correlation coefficients among malondialdehyde (MDA) content, H2O2 content, superoxide dismutase (SOD) activity, catalase (CAT) activity and ascorbate peroxidase (APX) activity in seedling leaves of two Alnus species (n = 18)

	MDA含量 MDA content	H₂O₂含量 H₂O₂ content	CAT活性 CAT activity	SOD活性 SOD activity	APX活性 APX activity
MDA含量 MDA content	1.00
H₂O₂含量 H₂O₂ content	0.20	1.00
CAT活性 CAT activity	0.15	0.82^**	1.00
SOD活性 SOD activity	-0.21	0.81^**	0.84^**	1.00
APX活性 APX activity	-0.04	0.80^**	0.91^**	0.89^**	1.00

Fig. 6 Activities of antioxidant enzyme in seedling leaves of two Alnus species under different light regimes (mean ± SE). APX, ascorbate peroxidase; CAT, catalase; SOD, superoxide dismutase. LT1, full light; LT2, (56.2 ± 1.03)% full light; LT3, (12.5 ± 0.21)% full light. L, light; S, tree species; S × L, interaction of tree species and light. **, p < 0.01; *, p < 0.05; ns, p > 0.05. Different capital letters indicate significant differences among two tree species under the same light regimes (p < 0.05); Different small letters indicate significant differences among three light regimes of the same species (p < 0.05).

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