The Spatial Pattern And Environmental Interpretation Of The Community Ecology Of Hulunber Grassland Under Different Degradation Degree

Analyzing daily air temperature and precipitation observed during48years from1958, we quantified changes in temperature and precipitation with year in Kherlon River Basin of semiarid northern China. In addition, the relationship between the dry biomass measured23years from1983at grassland and the corresponding temperature accumulated for higher temperature than5℃(AET) and precipitation accumulated after1April (CP) was determined. Moreover, we compared the spatial distribution of the underground biomass and characteristics of the root types and discuss the deterioration pattern of the environment to reveal the vegetation-soil interaction function law in the three communities under different grazing intensities of Stipa krylovii steppe. The main results were as following:1.It was estimated that the annual mean air temperatures during non-growing season (October to April) and growing season (May to September) had significantly risen during50years from1958by2.38℃and1.83℃, respectively. The year-to-year variation in the annual mean air temperature had a tendency to increase with year during the48years. Changes in annual precipitation and precipitation days for any of the entire year (January to December), growing and non-growing seasons with year were not significantly observed. Both the AET and CP (especially CP) during the growing season affected the biomass growth in the semiarid grassland.2. The partitioning ratios of the root functional groups of the three communities had clear differentiation under different grazing intensities. Both the compositions of three communities and the types of the root functional groups tended to simplify with the increase of grazing intensity. There were ten plant species and six types of the root functional groups in the light grazing site, nine plant species and five types of the root functional groups in the moderate grazing site, and six plant species and four types of the root functional groups in the heavy grazing site. Spatial distribution of the belowground biomass of the three communities appeared to be T-shaped under different grazing intensities and the biomass showed a sharp decline in the heavy grazing site. In the0～10cm soil layer the heavy grazing site had higher belowground biomass than the other sites; however, in the10～20cm,20～30cm and30-40cm soil layers the light grazing site had the highest belowground biomass. The constructive species were Stipa krylovii, Cleistogenes squarrosa, and Allium polyrhizum in the light, moderate, and heavy grazing communities, respectively. The root/shoot ratios of the constructive species decreased with increased grazing intensity, with the values of0.47,1.0, and4.1in the light, moderate, and heavy grazing communities, respectively. The root number, root volume, root biomass, specific root length and root length density also varied with different grazing intensities. Moreover, the root/shoot ratio and specific root length showed a significant correlation with contents of the soil available nitrogen (P<0.05).3. The aboveground biomass content a decreased with increased grazing intensity; the soil organic matter content within10cm depth was light grazing>moderate grazing>heavy grazing and total nitrogen and alkali-hydrolyzable nitrogen were ranked as light grazing>heavy grazing>moderate grazing. Results of geostatistical analyses was that the spatial heterogeneity of aboveground biomass increased with increased grazing intensity, and the spatial heterogeneity of soil organic matter within10cm depth was ranked as moderate grazing>light grazing>heavy grazing, total nitrogen was heavy grazing>light grazing>moderate grazing and alkali-hydrolyzable nitrogen was moderate grazing>heavy grazing>light grazing. The relationships of aboveground biomass, soil organic matter, total nitrogen, alkali-hydrolyzable nitrogen were different under different grazing intensities.