关键词: 水稻, CO2浓度升高, 根系形态, 细胞分裂素, 光合作用, 干物质生产

Abstract: 【Objective】To explore the comprehensive response difference and physiological mechanism of different rice cultivars in response to elevated atmospheric CO₂ concentration and nitrogen nutrition. 【Method】In this study, a rice cultivar Liangyoupeijiu (LY) showed high response to CO₂ (high-response rice cultivar) and a rice cultivar Nanjing 9108 (NJ) showed low response to CO₂ (low-response rice cultivar) were selected as materials. Hydroponic experiments were carried out in the climate chamber. Two CO₂ treatments and two nitrogen treatments were set up with ambient CO₂ concentration (A-CO₂, 400 μmol mol^-1) and elevated CO₂ concentration (E-CO₂, 600 μmol mol^-1), and high nitrogen (HN, 1.25 mM NH₄NO₃) and low nitrogen (LN, 0.25 mM NH₄NO₃), respectively. The effects of elevated CO₂ concentration on root morphology and physiological activity, cytokinin (CTKs) content in leaves and roots, nitrogen assimilation enzyme activity, physiological characteristics of leaves, photosynthetic parameters, and dry matter accumulation of different rice cultivars were analyzed.【Result】(1) E-CO₂ significantly increased the total crown root number, total root length (except LN level), total root surface area and average diameter of LY, improved root respiration rate and maintained high root oxidation power, but had no significant or opposite effects on NJ. (2) Regardless of nitrogen level, E-CO₂ significantly increased CTKs content in LY leaves and roots, but significantly decreased zeatin nucleoside (ZR) content in NJ roots at HN level. (3) At LN level, E-CO₂ significantly increased GOGAT and GDH activities in LY leaves, but significantly decreased NR activities in NJ leaves. At HN level, the activity of LY nitrogen assimilation enzyme increased under E-CO₂ condition, but only NR activity increased in NJ. (4) At the LN level, E-CO₂ increased the net photosynthetic rate (Pn) of LY and NJ by 28.0% and 29.4%, respectively. At the HN level, that of the two varieties increased by 41.0% and 28.1%, respectively. The significant increase in photosynthetic response of LY was attributed to the significant increase in leaf maximum carboxylation efficiency (V_c,max), maximum photosynthetic electron transport efficiency (J_max), ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) content, chlorophyll content, and leaf nitrogen content. (5) E-CO₂ significantly increased the leaf area per plant of LY under different nitrogen levels, but had no significant effect on NJ. (6) E-CO₂ significantly increased the organs and total biomass of LY, and the increased level under HN was significantly higher than that under LN level. E-CO₂ did not significantly affect the total biomass of NJ under different nitrogen treatments, but significantly reduced the underground biomass of NJ under HN (-16.7%). 【Conclusion】No matter at the HN or LN treatment, the response of dry matter production and physiological characteristics of LY to E-CO₂ was higher than that of NJ. In the early growth stage, LY had better root morphological characters and root activity, higher CTKs content, stronger nitrogen assimilation ability, larger green leaf area and photosynthetic response capacity, which were important reasons accounting for the higher response of dry matter production under E-CO₂ conditions.

Key words: rice, elevated CO₂ concentration, root morphology, cytokinin, photosynthesis, dry matter production