土壤水分条件对内蒙古典型草原水汽和二氧化碳通量的影响研究

本文基于2007年和2008年生长季内蒙古羊草和大针茅草原湍流观测资料，分析了两种典型草原下垫面生长季的不同土壤水分条件下水汽和二氧化碳通量交换特征及其控制因子。主要结果如下:（1）在植被生长峰值期，日尺度上，干旱条件下土壤湿度是潜热通量的主要控制因子，而土壤水分条件较好时潜热通量主要受净辐射控制。（2）与大针茅草原相比，羊草草原叶面积指数较大，水分条件较好时，其潜热通量平均值更大，CO₂吸收能力更强，吸收CO₂更多；但在土壤水分胁迫出现时，羊草草原叶面的气孔闭合度急剧增加，大针茅草原的潜热通量、和CO₂吸收反而更大，表现出更为耐旱的植被特性。（3）地表导度可以用来解释土壤水分条件对羊草和大针茅草原碳水通量的影响。

A Study of the Impact of Soil Water Conditions on Water and Carbon Dioxide Fluxes over Typical Grasslands in Inner Mongolia of China

Based on turbulence observations during the growing seasons of 2007 and 2008 in the semi-arid grasslands of Inner Mongolia, where Leymus Chinensis and Stipa Grandis are two dominant species, the characteristics of water and CO₂ fluxes under different soil water conditions and the controlling factors of these fluxes are analyzed. Results indicate that:(1) during the peak growing season on a daily time scale, the surface latent heat flux is largely dependent on soil water content under dry conditions, while it is more determined by net surface radiation under wet conditions when soil moisture content is sufficient; (2) compared with the grassland where Stipa Grandis is the dominant species, the grassland with dominant species of Leymus Chinensis has higher leaf area index, larger latent heat flux, higher CO₂ assimilation capacity and larger net CO₂ uptake under conditions with ample water in the soil. In contrast, the stomata of the grass leaf close at the Leymus Chinensis site in response to soil water stress, and the latent heat flux and the CO₂ uptake are larger at the Stipa Grandis site. This indicates that the Stipa Grandis grassland is more drought-resistant than the Leymus Chinensis grassland; (3) the surface conductance is a key factor that can explain impacts of soil water condition on the water and CO₂ fluxes over Leymus Chinensis and Stipa Grandis grasslands.