小麦和玉米叶片光合-蒸腾日变化耦合机理

植物叶片光合-蒸腾耦合是陆地生态系统碳-水耦合的基础.已有研究将叶片光合-蒸腾耦合笼统归因于气孔的共同控制作用,缺乏对其耦合机理的全面分析.选择华北地区大田作物冬小麦(C3)和夏玉米(C4)为研究对象,分别在小麦开花期和玉米拔节期选择典型晴天进行叶片光合蒸腾日变化观测(8:00-18:00).结果发现:1)光合速率(An)、蒸腾速率(Tr)以及光合有效辐射(PAR)、叶片表面温度(T)和气孔导度(gs)均表现出单峰日变化特征,峰值出现在正午前后；2)An-Tr具有极显著线性正相关关系(小麦和玉米的相关系数分别为0.75**和0.92**,回归直线斜率分别为1.99和3.62)；3)PAR、T和gs与An和Tr有线性正相关关系；4)PAR-An与PAR-Tr、T-An与T-Tr、gs-An与gs-Tr的回归直线形态非常相似.分析认为:1)在光合-蒸腾耦合特征方面,C3作物小麦和C4作物玉米叶片光合-蒸腾都有明显的线性耦合关系,但两者的耦合关系特征存在明显差异,玉米的An-Tr线性回归斜率要明显大于小麦；2)在光合-蒸腾耦合机理方面,日变化中PAR、T和gs同时受太阳辐射调控与An、Tr发生趋向相同、形态相似且近似同步的变化,因此PAR-An与PAR-Tr、T-An与T-Tr、gs-An与gs-Tr具有形态相似的线性关系,这保证了在PAR、T和gs等调控因子发生较大变化的日变化过程中光合-蒸腾保持良好的线性耦合关系.

Photosynthesis-transpiration coupling mechanism of wheat and maize during daily variation

The coupling relationship between photosynthesis and transpiration of green leaf is the basis of the coupling relationship between carbon cycle and water cycle in terrestrial ecosystem. Previous studies attribute the most significant cause of the coupling relationship between photosynthesis and transpiration to the stomatal control effect. However, there are few literatures to comprehensively analyze the coupling mechanism between photosynthesis and transpiration. Photosynthesis rate (A_n), transpiration rate (T_r), photosynthetic active radiation (PAR), leaf temperature (T) and stomatal conductance (g_s) were measured in two sunny days from 8:00 to 18:00 for field grown winter wheat (C₃ plant) and summer maize (C₄ plant) in the North China Plain at the stages of anthesis and jointing, respectively. The results show that: 1) the daily variations of PAR, T, g_s, A_n and T_r are similar with each other and the peaks occur around midday; 2) A_n is significantly linearly positive correlated with T_r (the slopes are 1.99 and 3.62 and the correlation coefficients are 0.75^{* *} and 0.92^{* *} for wheat and maize, respectively); 3) both A_n and T_r show positive dependences on PAR, T and g_s; 4) the regression lines of PAR-A_n and PAR-T_r, T-A_n and T-T_r, g_s-A_n and g_s-T_r are similar to each other. In conclusion, our results show: 1) the photosynthesis and transpiration of both wheat and maize during the daily variation are linearly coupled, however their coupling patterns are different, as the slope of A_n-T_r of maize (C₄ plant) is higher than that of wheat (C₃ plant); 2) during daily variance, PAR, T and g_s are simultaneously controlled by solar radiation and show similar daily variations as those of A_n and T_r, this leads to the similar linear correlations of PAR-A_n and PAR-T_r, T-A_n and T-T_r, g_s-A_n and g_s-T_r, and ultimately results in the linear coupling of photosynthesis and transpiration.