不同高度层冬小麦叶片水分利用效率对CO2浓度变化的响应

大气CO2浓度升高会给地球生态系统带来一系列环境问题,植物能够通过气孔调节光合作用和蒸腾作用,对环境变化做出响应。本研究以评价植物光合作用和蒸腾作用相互关系的指标水分利用效率为切入点,以冬小麦为研究对象,在灌浆期将冠层按距离地面高度分上、中、下三层,采用LI-6400便携式光合作用测量系统测定数据对各层叶片光合、蒸腾特性随CO2浓度变化的响应进行了对比分析。结果表明：随着CO2浓度的增加,（1）各层叶片净光合速率呈直角双曲线形式增加,不同层叶片之间净光合速率对CO2浓度响应的差异不显著（P〉0.05）,但各层羧化速率、光合能力、光呼吸表现不一致,均为上层〉中层〉下层;（2）各层叶片蒸腾速率总体下降,不同层叶片之间蒸腾速率对CO2浓度响应的差异显著（P〈0.01）,蒸腾速率的变化是气孔导度随CO2浓度变化的结果,两者呈显著正相关（P〈0.01）;（3）净光合速率提高与蒸腾速率降低,共同使叶片水平水分利用效率提高。研究工作有利于加深气候变化对农业影响的认识,也为农田生态系统碳、水耦合循环的多层模型研究奠定基础。

Responses of Leaf-level Water Use Efficiency of Winter Wheat to CO2 Enrichment in Different Canopy Layers

Elevated atmospheric CO_2 concentration will bring about a series of environmental problems to earth ecosystem. Plant photosynthesis and transpiration can response to the environmental change through stomatal regulation. The water use efficiency ( WUE) was taken as the breakthrough point to evaluate the correlation of plant photosynthesis and transpiration with study object of winter wheat. The responses of leaf - level photosynthesis and transpiration to CO_2 concentration enrichment were measured by using a LI - 6400 portable photosynthesis system after dividing the canopy height into three layers of top, middle and bottom, during the grain filling stage in 2008. The results showed that with the CO_2 concentration enrichment, the leaf net photosynthesis rate of every layer had a rectangular hyperbolic increase with no standard difference ( P > 0. 05), while the parameters of photosynthetic characteristics, including carboxylation efficiency, maximum net photosynthesis rate and respiration rate decreased with canopy depth. The both leaf transpiration rate and stomatal conductance of each layer decreased with standard difference ( P <0. 01) , which had a significant relationship ( P <0. 01). The net photosynthetic rate increased and transpiration rate decreased which led to an increase in leaf - level WUE due to CO_2 enrichment.