氮添加和刈割条件下羊草光合-CO_(2)响应过程及模型比较研究

Comparison of photosynthetic-CO_(2) response process and models of Leymus chinensis under differing nitrogen addition and mowing conditions

草原植物光合作用受氮添加和刈割等草原管理措施的影响。依托内蒙古草甸草原的氮添加(0、2、5、10、20和50 g N·m^(-2)·a^(-1))和刈割(刈割和非刈割)交互处理的野外控制试验,测定其优势物种羊草的光合-CO_(2)响应过程。探究直角双曲线模型、非直角双曲线模型、直角双曲线修正模型和Michaelis-Menten模型对叶片光合-CO_(2)响应曲线的拟合效果,以及光合特性对氮添加和刈割的响应。结果表明:非直角双曲线模型拟合的初始羧化效率和光呼吸速率最接近实测值;直角双曲线修正模型对CO_(2)饱和点、CO_(2)补偿点和最大净光合速率的拟合效果最好;直角双曲线修正模型的拟合优度最高;适度氮添加能提高羊草净光合速率、水分利用效率、最大净光合速率、初始羧化效率和CO_(2)饱和点并降低CO_(2)补偿点,提升羊草对CO_(2)的利用效率;随CO_(2)浓度的升高,氮添加浓度为20 g N·m^(-2)·a^(-1)并刈割的羊草净光合速率增幅较大,具有较高的最大净光合速率、CO_(2)饱和点、水分利用效率和较低的CO_(2)补偿点。综上,非直角双曲线模型和直角双曲线修正模型较适用于氮添加和刈割条件下羊草的CO_(2)响应曲线拟合,在内蒙古草原施氮20 g N·m^(-2)·a^(-1)并刈割最有助于提高羊草光合能力,有利于增大生态系统固碳量。

Photosynthesis of plants is affected by grassland management practices such as nitrogen addition and mowing.In this research,the photosynthetic-CO_(2) response process of the dominant species,Leymus chinensis,was determined in a controlled field experiment exploring the interaction between nitrogen addition(0,2,5,10,20 and the net photosynthetic rate,water use efficiency,maximum net photosynthetic rate,initial carboxylation efficiency and CO_(2) saturation point,and decreased the CO_(2) compensation point,and thereby improved the CO_(2) use efficiency of L.chinensis.With the increase of CO_(2) concentration,the net photosynthetic rate of L.chinensis with nitrogen concentration of 20 g N·m^(-2)·yr^(-1) with mowing increased,and higher maximum net photosynthetic rate,CO_(2) saturation point and water use efficiency was observed,together with a lower CO_(2) compensation point.In conclusion,the non-rectangular hyperbolic model and the modified rectangular hyperbolic model were more suitable for fitting L.chinensis CO_(2) response curves defining responses to nitrogen addition and mowing.In this experiment conducted on an Inner Mongolian steppe,the photosynthetic capacity of L.chinensis was most efficiently increased by applying 20 g N·m^(-2)·yr^(-1) with mowing.This treatment combination is beneficial to carbon sequestration of the grassland ecosystem.