| We selected Leymus secalinus communities of fenced and grazed plots of grassland ecosystem research station in2012and2013in Yanmenguan, Shanxi. During the growing season, we investigated dynamic variation of aboveground and belowground biomass in fenced and grazed plots. Soil respiration rate, net ecosystem carbon exchange (NEE), ecosystem respiration (ER) and gross ecosystem primary productivity (GEP) were measured by using a LI-840a analyzer with static chamber in Leymus secalinus communities. In addition, we also analyzed relationships of these characteristics with temperature and moisture content which could provide scientific foundation for grassland use and carbon budget mechanism. Our results showed as follow:The aboveground biomass variation of Leymus secalinus communities showed unimodal curve in two growing seasons and the peak values appeared in August in fenced and grazed plots. Aboveground biomass of fenced and grazed plots in2012and2013were364.03g·m-2,414.62g·m-2,140.11g·m-2,153.27g·m-2, respectively. The variation of belowground biomass in2012showed also a single peak curve and the peak values of grazed plots happened in July for2327.54g·m-2, whereas the peak values of fenced plots in August for4237.51g·m-2. In2013, the single peak values of belowground biomass in grazed plots appeared in August for2559.28g·m-2, but the change of fenced plots showed a bimodal curve, the peak values happened in July and September, for4148.4g·m-2and4359.27g·m-2, respectively. With increasing of soil depth deepen, belowground biomass gradually reduced, and belowground biomass were mainly located at10cm depth in fenced and grazed plots which accounted total belowground biomass for77.21%and79.25%, respectively. In addition, belowground biomass of grazed plots at10cm depth was significantly higher than fenced plots, and the average root-shoot ratio in fenced plots (11.48) was significantly lower than grazed plots (19.93).Soil respiration rate of Leymus secalinus communities had significant change with diurnal and seasonal variations, and the peak values happened in around at12:00o’clock, whereas the lowest value in around at4:00o’clock, and the lowest values appeared in May, June and September, whereas the highest values appeared in July and August. Grazing reduced soil respiration rate, but the trend did not significantly change. On the diurnal variation scale, relationships of soil respiration rate with atmospheric temperature was significantly higher than with soil temperature at10cm depth. On the seasonal variation scale, soil respiration rate was mainly regulated by soil temperature in0-10cm, and coefficient of temperature sensitivity (Q10) in fenced plots (2.36) was significantly higher than grazed plots (2.12). In addition, we also founded that exponential model could better simulate relationship of soil respiration and skin temperature, and that hydrothermal complex model could better explain the seasonal variation of soil respiration rate compared with single factor model.During the growing season, the diurnal and seasonal variations of NEE, ER and GEP in Leymus secalinus communities showed unimodal curve, the peak values of diurnal variations appeared in around at12:00o’clock, and the highest values of seasonal variations happened in July or August. On the diurnal variation scale, relationship of NEE, ER and GEP with atmospheric temperature was higher than with soil temperature in0-10cm, but the correlation showed opposite trend on seasonal variation scale. Moreover, relationships of NEE, ER, GEP with temperature were parabolic, exponential and linear, respectively, and correlations with soil volumetric moisture content at10cm depth.In addition, we also measured that total net carbon sequestration in fenced and grazed plots were744.3gCO2·m-2,327.62gCO2·m-2in2012and775.51gCO2·m-2,575.93gCO2·m-2in2013. |
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