Xilin River Basin, A Grazing Grassland Soil Respiration And Its Impact Factor

A number of studies on the soil respiration in grassland communities of the world were reviewed. Periodical measurements of soil respiration by gas chromatography method and relevant environmental factors in a grazed steppe community in the Xilin River Basin of Inner Mongolia were conducted from June 5 to Oct. 15 in 2001. The relationships were analyzed between the soil respiration rate and temperature,soil moisture and biomass components. Root respiration was extrapolated by the relation of soil respiration and root biomass. Soil respiration rate was measured by alkali absorption method in both the steppe community and a meadow community concurrently in order to compare their differences in different habitats,and then tried to figure out the causes. At the same time,a comparative study of the two commonly used methods for soil respiration measurement was conducted in the steppe community. The major results were summarized as follows: The seasonal patterns of biomass (including both aboveground and belowground),temperature (including air and soil temperature),soil moisture,and soil respiration in the steppe community during the measurement period showed fluctuant curves. There existed a distinct relation between soil respiration and soil moisture,and some weak positive relations between soil respiration and temperature,especially soil temperature,and belowground biomass;while there were nearly no relations between soil respiration and both the total aboveground biomass and the live biomass.The seasonal changes of soil respiration in the two communities had quite similar dynamic patterns,the soil respiration rate of the steppe community and the meadow community ranging from 312.8 to 1738.9 mg C m-2 d-1 and from 354.6 to 2235.6 mg C - m2 . d-1,with an average of 785.9 mg C . m-2 . d-1 and 1349.6 mg C.m-2.d-1 during the measuring period respectively. Both of them had two peaks,which occurred in late June with the highest temperature and late July with the highest soil moisture. Soil respiration rate in the meadow community was higher than that in the steppe community markedly.Soil moisture was the major controlling factor for soil respiration in the steppe community,while it had almost no influence in the meadow community. A very significant power function relation was detected between the soil respiration rate and the green biomass in the meadow community. However,there was no evident relation between the CO2 evolution rate and either the total aboveground biomass or green biomass.The proportion of root respiration to the total soil respiration ranged from 60.7% to 93.3%,with an average of 82%.The results by the alkali absorption method and the gas chromatography method were highly correlated (R2=0.7563). The soil respiration shared similar seasonal dynamic patterns,with the soil respiration rate by alkali absorption method ranging from 249.2-1795.1 mg C m-2 d-1 and by gas chromatography method from 312.8-1738.9 mg C . m-2 - d-1,with an average of 634.2 mg C - m-2 - d-1 and 802.7 mg C m-2 d-1 during the measuring period respectively in the steppe community. The average value of the soil respiration rate measured by alkali absorption method was about 1.4 times that by gas chromatography method.