Study On Soil Respiration At Grazing And Fenced Typical Leymus Chinensis Steppe, Inner Mongolia

Soil respiration was measured with a closed static chamber method for continuous two years (2001²002) in fenced and grazing typical Leymus chinensis steppe, Inner Mongolia, China. The diurnal and seasonal dynamics of soil respiration were similar between fenced and grazing plots. The diurnal patterns of soil respiration could be expressed as a one-humped curve and the lowest and highest values appearing at 1:00³:00 and 11:00¹4:00, which were similar with air temperature. The rates of soil respiration rose to a seasonal maximum from the middle of June to the end of July and then gradually decreased. Soil respiration rate was significant larger at the fenced plots than that at the grazing plots, and their values were 219.18 mg·m^-2·h^-1 and 111.27 mg·m^-2·h^-1, respectively, which might be the increases in soil water content and biomass. Among the influencing factors on soil respiration, grazing decreased the effects of soil water content and relative humidity and increased the effect of photosynthetic rate, and had no significant effects on other factors. At the fenced plots, the correlation of soil respiration rate with soil water content was largest, followed by photosynthetic rate, air temperature, relative humidity, air CO₂ concentration, intercellular CO₂ concentration, stomatal conductance and the lowest being photosynthetically active radiation. Soil water content and air temperature were the main environmental factors, and photosynthetic rate was the critical biotic factor. The affecting factors on soil respiration were the same at the fenced and grazing plots, however the importance of those influencing factors was changed quantitatively. Based on the widely used models at present, temperature and moisture were analyzed as principal predictors of soil respiration, and the validation of those models at the fenced and grazing plots was evaluated. Soil respiration rate was controlled mainly by...