Low soil temperature inhibits the effect of high nutrient supply on photosynthetic response to elevated carbon dioxide concentration in white birch seedlings

摘要

To investigate the interactive effects of soil temperature (T_soil) and nutrient availability on the response of photosynthesis to elevated atmospheric carbon dioxide concentration ([CO₂]), white birch (Betula papyrifera Marsh.) seedlings were exposed to ambient (360 μmol mol−1) or elevated (720 μmol mol−1) [CO₂], three T_soil (5, 15 and 25 °C initially, increased to 7, 17 and 27 °C, respectively, 1 month later) and three nutrient regimes (4/1.8/3.3, 80/35/66 and 160/70/132 mg l−1 N/P/K) for 3 months in environment-controlled greenhouses. Elevated [CO₂] increased net photosynthetic rate (A_n), instantaneous water-use efficiency (IWUE), internal to ambient carbon dioxide concentration ratio (C_i/C_a), triose phosphate utilization (TPU) and photosynthetic linear electron transport to carboxylation (J_c), and it decreased actual photochemical efficiency of photosystem II (ΔF/F_m′), the fraction of total linear electron transport partitioned to oxygenation (J_o/J_T) and leaf N concentration. The low T_soil suppressed A_n, transpiration rate (E), TPU, ΔF/F_m′ and J_c, but it increased J_o/J_T. The low nutrient treatment reduced A_n, IWUE, maximum carboxylation rate of Rubisco, light-saturated electron transport rate, TPU, ΔF/F_m′, J_c and leaf N concentration, but increased C_i/C_a. There were two-factor interactions for C_i/C_a, TPU and leaf N concentration, and a significant effect of CO₂ × T_soil × nutrient regime on A_n, IWUE and J_c. The stimulations of A_n and IWUE by elevated [CO₂] were limited to seedlings grown under the intermediate and high nutrient regimes at the intermediate and high T_soil. For J_c, the [CO₂] effect was significant only at intermediate T_soil + high nutrient availability. No significant [CO₂] effects were observed under the low T_soil at any nutrient level. Our results support this study’s hypothesis that low T_soil would reduce the positive effect of high nutrient supply on the response of A_n to elevated [CO₂].