Effect Of Grazing On Soil Respiration In Typicalleymus Chinensis Grassland Of Xilin River Basin In Inner Mongolia

Typical Leymus chinensis grassland ecosystem in temperate and semi-arid area in Inner Mongolia, China, was targeted in this experiment based on the grassland ecosystem-oriented research station in Inner Mongolia of Chinese academy of sciences. The effects of different environmental factor and different land use(grazing pot,fenced plot) on soil respiration in typical Leymus chinensis grassland in temperate and semi-arid area were statistically investigated in this experiment with field experiment combined with laboratory chemical analysis. During which course, the numerical one to one correspondence mode between environmental factor and soil respiration flux was set up; the yearly soil respiration flux amount was evaluated with a whole year series of intact observation data; the contribution of root respiration to soil respiration in grassland was also estimated, and the role of root metabolizability in soil discharge of N2O and CH4 was preliminarily discussed. After two year's field observation and laboratory chemical analysis, following results were concluded:(1) The effects of grazing on soil respiration rate in Leymus chinensis grasslandThe seasonal dynamics of soil respiration in Leymus chinensis grassland was not affected by grazing, while the magnitude of seasonal changes in soil respiration in grazing plot tends to be lower than that in fenced plot. The soil respiration rate in grazing plot was significantly lower than that in fenced plot in growing season, and the soil respiration in two lands kept almost the same in winter, both remained in low-level and even to a point at which the soil respiration flux reached a value lower than zero, it is calculated that annual soil respiration in Leymus chinensis grassland was decreased by 33.95% due to grazing.In a year round, the soil respiration rate in Leymus chinensis grassland was mainly affected by temperature, and temperature dependence of soil respiration was increased by grazing, the soil respiration in both fenced plot and grazing plot were significantly correlated with temperature( p<0.01,n=15), which fitted best with the temperature at 10 cm soil depth. By using step by step regression analysis method, we concluded that: the role of soil moisture was greater than that of temperature in determine the soil respiration, became the main factor limiting soil respiration in growing season. Changes of soil moisture in range of 0～10 cm soil depth accounted for 87.4% in soil respiration variation in fenced plot, while the changes of soil moisture in range of 10～20 cm soil depth together with that in range of 20～30 cm soil depth accounted for 74.9% in soil respiration variation in grazing plot.(2) Employing root biomass extrapolate method to differentiate root respiration and soil respiration in grassland ecosystemBy using root biomass extrapolate method, following results were determined: root respiration accounted for 55.1%～72.9% of soil total respiration in free-grazing plot in Leymus chinensis grassland of Xilin River basin in growing season, the mean value was 59.5%. The soil moisture in deep soil was closely correlated with soil total respiration amount, soil water content in range of 20～30 cm soil depth accounted for 88.6%～96.5% of soil total respiration. Soil surface temperature,temperature in 10 cm soil depth and soil water content in range of 20～30 cm soil depth were closely correlated with root respiration amount. Root biomass was the main biological factor that determine soil total respiration amount and root respiration amount.There was obvious linear correlation existed between Root biomass and soil discharge rate of CH4, while no correlation was observed between soil microorganism and soil discharge of CH4, microorganism absorb as well as discharge CH4 under an unknown mechanism.There was no significant correlation between root biomass and soil discharge rate of N2O.