Effects of elevated ozone concentration and nitrogen addition on the photosynthetic characteristics of poplar at different leaf positions and growth stages

doi:10.17521/cjpe.2024.0352

Abstract

Abstract:

Aims The combined effects of ozone (O₃) pollution and nitrogen (N) addition on plant photosynthesis are still controversial, which may be related to factors such as measurement period, time, and leaf position. This study mainly explored the differences in the response of photosynthetic parameters of poplar to O₃ and N addition at different growth stages, diurnal variation, and leaf positions, in order to comprehensively understand the combined effects of O₃ pollution and N addition on plant carbon sequestration.

Methods The cuttings of hybrid poplar clone 107 (Populus euramericana cv. ‘74/76’) were exposed to six open top chambers. Two O₃ concentration treatments were set up (NF, non-filtered ambient air; NF45, NF + 45 nmol·mol^-1 O₃), with four N addition treatments nested under each O₃ treatment (N0, no N added; N50, N0 + 50 kg N·hm^-2·a^-1; N100, N0 + 100 kg N·hm^-2·a^-1; N200, N0 + 200 kg N·hm^-2·a^-1). The photosynthetic parameters of poplar at different growth stages, daily times, and leaf positions were measured.

Important findings When averaged across four N treatments, NF45 treatment significantly reduced the entire growth season photosynthetic rate (P_n), stomatal conductance (g_s), and chlorophyll content (SPAD) by 44.2%, 18.2%, and 24.7% compared with NF treatment, respectively. However, O₃ increased the intercellular CO₂ concentration (C_i) by 9.0%, indicating that the reduction of P_n by O₃ was mainly limited by non-stomatal factors. The results showed that NF45 treatment had a greater reduction in leaf P_n and SPAD at the middle and late stages of growth than at the early stages. The response of P_n and SPAD to O₃ varied among different leaf positions. O₃ significantly reduced P_n and SPAD at the lower leaf position, while O₃ increased P_n and SPAD at the topmost leaf position, indicating a compensatory effect of plants in response to O₃ stress. O₃ caused varying degrees of decrease in P_n of poplar at different times within a day, but there was no statistically significant interaction between O₃ and time on the photosynthetic parameters. The N addition significantly increased the leaf P_n and SPAD of poplar throughout the entire growing season, with no significant effect on g_s, but significantly reduced C_i. There was no significant difference in the promotion of photosynthesis by N addition at different growth stages and leaf positions. In addition, no significant interaction effect was observed between O₃ and N addition on all photosynthetic parameters, indicating that N addition did not alleviate the negative impact of O₃ on poplar photosynthesis.

Key words: ozone, nitrogen addition, growth period, diurnal dynamics, leaf position, poplar

TIAN Tong-Tong, SHANG Bo, XU Yan-Sen, YUAN Xiang-Yang, LIU Shuo, FENG Zhao-Zhong. Effects of elevated ozone concentration and nitrogen addition on the photosynthetic characteristics of poplar at different leaf positions and growth stages[J]. Chin J Plant Ecol, 2025, 49(11): 1919-1933.

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URL: https://www.plant-ecology.com/EN/10.17521/cjpe.2024.0352

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Figures/Tables 9

Table 1 RM-ANOVA results (p values) of the interaction between O3 treatment, nitrogen addition, different growth stages and their interaction on photosynthetic parameters of poplar

变量 Parameter	净光合速率 Net photosynthetic rate	气孔导度 Stomatal conductance	胞间CO₂浓度 Intercellular CO₂concentration	叶绿素相对值 Relative chlorophyll content
臭氧 O₃	<0.01	<0.01	<0.01	<0.01
氮处理 Nitrogen (N)	<0.01	0.33	<0.01	<0.01
时期 Date	<0.01	<0.01	<0.01	<0.01
臭氧×氮处理 O₃ × N	0.49	0.72	0.37	0.65
臭氧×时期 O₃ × Date	<0.01	0.32	<0.01	<0.01
氮处理×时期 N × Date	0.40	0.10	0.18	0.02
臭氧×氮处理×时期 O₃ × N × Date	0.70	0.63	0.90	0.02

Fig. 1 Effects of different ozone and nitrogen (N) addition treatments on the leaf photosynthetic rate (Pn) of poplar at different growth stages (mean ± SD). NF, non-filtered ambient air; NF45, NF + 45 nmol·mol-1 O3. N0, no N added; N50, N0 + 50 kg N·hm-2·a-1; N100, N0 + 100 kg N·hm-2·a-1; N200, N0 + 200 kg N·hm-2·a-1. *, p < 0.05; **, p < 0.01.

Fig. 2 Effects of different ozone and nitrogen (N) addition treatments on the stomatal conductance (gs) of poplar at different growth stages (mean ± SD). NF, non-filtered ambient air; NF45, NF + 45 nmol·mol-1 O3. N0, no N added; N50, N0 + 50 kg N·hm-2·a-1; N100, N0 + 100 kg N·hm-2·a-1; N200, N0 + 200 kg N·hm-2·a-1. *, p < 0.05; **, p < 0.01.

Fig. 3 Effects of different ozone and nitrogen (N) addition treatments on the intercellular CO2 concentration (Ci) of poplar at different growth stages (mean ± SD). NF, non-filtered ambient air; NF45, NF + 45 nmol·mol-1 O3. N0, no N added; N50, N0 + 50 kg N·hm-2·a-1; N100, N0 + 100 kg N·hm-2·a-1; N200, N0 + 200 kg N·hm-2·a-1. *, p < 0.05; **, p < 0.01.

Fig. 4 Effects of different ozone and nitrogen (N) addition treatments on the relative chlorophyll content (SPAD) of poplar at different growth stages (mean ± SD). NF, non-filtered ambient air; NF45, NF + 45 nmol·mol-1 O3. N0, no N added; N50, N0 + 50 kg N·hm-2·a-1; N100, N0 + 100 kg N·hm-2·a-1; N200, N0 + 200 kg N·hm-2·a-1. *, p < 0.05; **, p < 0.01.

Fig. 5 Linear relationship between relative chlorophyll content (SPAD) and photosynthetic rate (Pn), stomatal conductance (gs), and intercellular CO2 concentration (Ci) of poplar leaves under different ozone treatments throughout the growth season. NF, non-filtered ambient air; NF45, NF + 45 nmol·mol-1 O3. ANCOVA, analysis of covariance.

Fig. 6 Effects of different ozone (O3) and nitrogen (N) addition treatments on the diurnal variation (T) of photosynthetic rate (Pn), stomatal conductance (gs), and intercellular CO2 concentration (Ci) in poplar leaves (mean ± SD). NF, non-filtered ambient air; NF45, NF + 45 nmol mol-1·O3. N0, no N added; N200, N0 + 200 kg N·hm-2·a-1. The blue asterisk indicated significant differences between the two O3 treatments under N0 treatment; The red asterisk indicated a significant difference between the two O3 treatments under N200 treatment. *, p < 0.05; **, p < 0.01. Only statistically significant p-values are shown.

Fig. 7 Effects of different ozone (O3) and nitrogen (N) addition treatments on the photosynthetic rate (Pn) at different leaf positions (P) of poplar (mean ± SD). NF, non-filtered ambient air; NF45, NF + 45 nmol·mol-1 O3. N0, no N added; N50, N0 + 50 kg N·hm-2·a-1; N100, N0 + 100 kg N·hm-2·a-1; N200, N0 + 200 kg N·hm-2·a-1. *, p < 0.05; **, p < 0.01. I-V is 1-5, 6-10, 11-15, 16-20, 21 to botton leaves form top to bottom, respectively.

Fig. 8 Effects of different ozone (O3) and nitrogen (N) addition treatments on the relative chlorophyll content (SPAD) at different leaf positions (P) of poplar (mean ± SD). NF, non-filtered ambient air; NF45, NF + 45 nmol·mol-1 O3. N0, no N added; N50, N0 + 50 kg N·hm-2·a-1; N100, N0 + 100 kg N·hm-2·a-1; N200, N0 + 200 kg N·hm-2·a-1. *, p < 0.05; **, p < 0.01. I-V is 1-5, 6-10, 11-15, 16-20, 21 to botton leaves form top to bottom, respectively.

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