| Ecosystem gas exchange, the diurnal variation and the growing season variation of soil respiration rate were studied under different grazing intensities in the Stipa breviflora desert steppe and the main impact correlation factors (soil temperature, soil moisture and soil characteristic) on ecosystem C exchange and soil respiration were analyzed.The results showed that:1. the seasonal variation curve is the same for soil respiration rate and ecosystem C exchange under different grazing intensity in the Stipa breviflora desert steppe, and grazing did not change the diurnal and seasonal curve of both soil respiration rate and ecosystem C exchange.1) The diurnal variation of soil respiration rate showed unimodel curve and the peak values appeared at14:00to16:00, whereas the lowest value in around at6:00o’clock. The diurnal variation of net carbon exchange (NEE) showed also a single peak curve, and the peak values happened at12:00to14:00, and the lowest value at18:00to20:00. However, the change of ecological respiration (ER) showed a bimodal curve, the peak values appeared at10:00to12:00and12:00to14:00, and the lowest value at18:00to20:00. The ecosystem primary productivity (GEP) diurnal variation also showed a bimodal curve, the peak value appeared at10:00to12:00and14:00～16:00. Mean diurnal and growing season soil respiration rate, NEE, ER, GEP weakened with the increase of grazing intensity under different grazing intensities, the variable orders as follows:CK> MG> LG> HG.3) Soil respiration rate, NEE, ER, of GEP reached peak value during July-September of the rain season.2. Chemical properties, with the increase of grazing intensity, total nutrient, organic matter and available nutrients showed decreasing trend. No significant differences were found between in the control plot and in heavy grazing plot. With increasing of soil depth deepen, Soil indicator gradually reduced, but no significant differences between soil layers. The physical properties of the soil surface (0cm～20cm) of water showed increased trend from June to October.20～50cm soil with soil depth in June, July and August increase and increased the lower tends to increase with soil depth in September and October. Soil under different grazing intensities0～20cm volumetric water content in June, August, October:HG> MG> CK> LG, and July, September: MG> HG> CK> LG. 3. Aboveground biomass from turning green in May began to increase and reached a peak in July, and the above-ground biomass gradually reduced from August to October. Throughout the grazing season, the above-ground biomass was higher in CK plot than in MG and HG, the trend was control> lightly grazed area> moderately grazed area> heavily grazed area. with the increase of soil depth, below-ground biomass of vertical distribution was decreased under the different treatment, the surface biomass was higher than other deep biomass, the orders was:CK> LG> MG> HG.4. With the increasing of grazing intensity, the significant correlation was showed between total nitrogen content and organic matter. The positive correlation was showed between above-ground biomass and soil nutrient (soil organic matter and total K), whereas no correlation was showed between aboveground biomass and total P, total N. Below-ground biomass and soil nutrient (total phosphorus, total nitrogen, organic matter) showed a positive significant positive correlation, and a significant positive correlation was showed between total potassium and aboveground biomass. The water above and below ground biomass, ER was significantly positively correlated, and GEP and NEE had no significant relationship. Between soil temperature and the NEE, between soil temperature and GEP were highly significant positive correlation, whereas significantly negatively correlated was found between water and ER. No correlation was showed between ER and above-, below-ground biomass. |
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