降水和氮沉降对内蒙古半干旱草地羊草和大针茅叶片碳交换的影响

本研究对我国北方半干旱草地进行春季增雪、夏季增雨和施氮处理，通过监测羊草（Leymus chinensis）和大针茅（Stipa grandis）的光响应曲线，以期探讨降水和氮沉降对半干旱草地叶片碳交换的影响。结果表明：夏季增雨（100 mm）分别提高了羊草和大针茅最大光合速率，提高了气孔导度和土壤含水量，降低了土壤温度；但春季增雪（25 mm雪水当量）对以上各指标的影响不显著；施氮（10 g· m^-2）显著提高了羊草叶绿素含量，但对以上各指标影响均不显著。本研究表明增水和施氮对关键物种叶片碳交换的作用主要通过影响叶片光合生理特性以及土壤微环境实现。

Effects of Precipitation and Nitrogen Deposition on Leaf Carbon Exchange of Leymus chinensis and Stipa grandis in Semi-arid Grassland of Inner Mongolia

To explore the effects of precipitation and nitrogen deposition on leaf level carbon exchange,we investigated the light response curves of two dominant species including Leymus chinensis and Stipa grandis to changes in spring snowfall or summer rainfall with or without N addition in the semiarid temperate steppe in northern China. The results showed that summer rainfall (100 mm) increased the maximum photosynthetic rate of L. chinensis and S. grandis by 22.8% and 8.3%,which was mainly attributed to the significantly increases in their stomatal conductance by 32.8% and 24.9%. It also increased soil moisture by 35.3%,but decreased soil temperature by 3.5%. However,effects of spring snow (25 mm snow water equivalent) on the maximum photosynthetic rate of L. chinensis and S. grandis was not significant. N application (10 g m^-2) significantly increased leaf chlorophyll content of L. chinensis,but it had no effects on that of S. grandis and other indicators mentioned above. There was no interaction between spring snow addition or summer water addition and nitrogen application on the maximum photosynthetic rate of L. chinensis and S. grandis. The results suggest that the effects of water and N application on leaf carbon exchange in key species are mainly archieved by affecting the photosynthetic physiological characteristics of the leaves and the soil microenvironment.