Study On The Spatio-Temporal Variation Of Soil Respiration And The Controlling Factors In The Xilin Rive Basin Of Inner Mongolia

Soil CO2 efflux in terrestrial ecosystems is an important consideration in the studies of the global carbon cycle,its contribution to the global carbon budget has been the focus of wide concern. Soil respiration is also crucial for figuring out the "missing sink" of carbon. It has been widely accepted that temperature,moisture and vegetation are the most important factors regulating soil CO2 respiration rate. The relationship between the variation of soil CO2 efflux and environmental factors can be used to scale up the chamber measurements of CO2 efflux to the ecosystem and larger scales. All these factors will change with the global climate change,which may cause positive feedbacks to CO2 flux from soil. Temperate grassland is one of the major terrestrial ecosystem types. However,only a few studies about soil respiration were conducted so far. Thus,we measured the soil respiration rate periodically using the alkali absorption technique in 11 communities along a belt transect which was about 160 km long and 30 km wide in the southern part of the Xilin River Basin,Inner Mongolia during the growing season in 2001. The spatio-temporal patterns of soil respiration and the controlling factors such as temperature,soil moisture and vegetation were analyzed.Spatial and temporal variations in soil respiration were detected in the area. Significant relationships had been found between CO2 evolution rate and temperature for the 11 communities,which could be best described by exponential equations. The influence of temperature was more conspicuous at lower temperature than at higher temperature. Accordingly,the seasonal variations of soil respiration were not in complete accordance with temperature,especially in the mid-growing season with high temperature. Differences in the temperature sensitivity of soil respiration existed among the 11 communities. The spring wheat community had higher Q10 value than other communities,which implied that land use could affect the sensitivity of soil respiration to temperature. We also analyzed the relationship between Q10 values and the soil moisture content by the Spearman's Rank-Order correlation method,and found that the Q10 values were positively related to average surface soil moisture,indicating that soil moisture has great bearings on soil respiration. Furthermore,Q\Q values calculated from air temperature and the temperature at shallower soil layers were lower than those based on deeper soil temperature,because the fluctuation of temperature was more in air and shallower soil layers than deeper soil layers.Soil moisture had great influence on soil respiration,but the degree varied with the time of the season. The influence of soil moisture on soil respiration was greater in the mid-season than other months. Water condition in each community limited the effect of soil moisture on soil respiration. There were no notable functional relations between soil respiration and soil moisture in communities in which soil water content was higher or fluctuated less,whereas notable linear relationship existed in communities where soil water content was lower. After removing the confounded effect of temperature,the linear relationships were more significant than above in all11 communities. Though soil moisture was very low in the Achnatherum splendens community,the linear relation was not obvious between soil respiration and soil moisture. This might be due to the fact that the root of Achnatherum splendens could reach deeper soil layers and absorb water there.Relationships between seasonal changes in soil respiration and vegetation were related to water conditions or the mechanism of utilizing water by the vegetation in each community. Soil respiration rate increased with the green biomass,and exponential functions could be used to describe relationships between soil respiration and green living biomass in communities with higher soil moisture or communities with vegetation being drought-tolerant or being able to use deeper subsoil water. However,there was weak relationship b...