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《Acta Ecologica Sinica》 2002-08
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On the Small Scale Spatial Heterogeneity of Soil Moisture, Carbon and Nitrogen in Stipa Communities of the Inner Mongolia Plateau

BAI Yong Fei 1,XU Zhi Xin 2, LI De Xin 2 (1.Laboratory of Quantitative Vegetation Ecology, Institute of Botany, CAS, Beijing 100093,China; 2.Inner Mongolia Agriculture University, Huhhot 010018,China).  
Grassland Vegetation in Inner Mongolia Plateau is the main part of the central Eurasian Steppe region. The gradient distribution of precipitation and temperature is the main factor that affects the zonal distribution of grassland vegetation in the Plateau. Grassland vegetation in the plateau can be divided into three sub vegetation zones: meadow steppe, typical steppe, and desert steppe. They are distributed successively from the east to the west with the increase in temperature and decrease in precipitation. Among them, Form. Stipa baicalensis in the meadow steppe, Form. Stipa grandis and Form. Stipa krylovii in the typical steppe, and Form. Stipa klemenzii in the desert steppe are representative communities of Stipa steppe in the plateau. In this paper, we designed the present study to address the general need for basic information about soil resource heterogeneity and to address the specific need for information about heterogeneity in grassland ecosystems in the Inner Mongolia plateau. Our study sites were located at Ewenke Qi, Xiwu Qi, Abaga Qi and Damao Qi respectively, the typical areas of Stipa steppe in the Inner Mongolia Plateau. They are dominated by four Stipa species, i.e. S. baicalensis, S. grandis, S. krylovii, and S. klemenzii respectively. We established an 8m×12 m plot in each of the 4 sites. In each case, we attempted to sample a level and apparently topographically uniform field site to avoid anisotropic effects. In each plot, a sampling grid of 40 points was established at two spatial scales. First, the plot was divided into 24 cells, each 2m×2m in size, and a sampling point was located randomly in each cell. One additional point was cast randomly to locate a 2m×2m subplot in the 8×12 plot. It was divided into 16 0 5m×0 5m cells. Each sample was a 4 5cm diameter soil core taken from 0 to 20 cm depth. Soils were sampled over a 20d period in the mid August. This corresponds with the approximate time of peak aboveground standing crop in each site. We use geostaticics to describe the spatial variation in soil moisture, carbon and nitrogen in different Stipa communities by calculation of semi variogram, which shows the average variance found in comparisons of samples taken at increasing distance interval. Spherical model was used to fit the form of semi variogram. The results showed that within site variability of three soil properties (soil water, organic carbon and total nitrogen) were highly spatially dependent for all experiment sites. The distance of spatial autocorrelation in soils properties increased across four Stipa communities from S. baicalensis, S. grandis, S. krylovii, to S. klemenzii. This suggests a trend that the distance of spatial autocorrelation in soils becomes longer, while the grain becomes coarser across the Stipa communities from S. baicalensis, S. grandis, S. krylovii, to S. klemenzii. Geostatistics indicate that 35 31%~99 71% of the variation in soil water in the four Stipa communities is found within distances from 2 96~10 81m; 63 33%~98 73% of variation in soil organic carbon is found within distances from 1 91~4 12m; and 76 67%~99 74% of variation in soil total nitrogen is found within distances from 2 91~6 20m in the four communities. The small scale spatial variation in soil properties may affect patterns and processes of grassland ecosystems, i.e. soil moisture pattern → vegetation patch →soil carbon pattern →soil nitrogen pattern. As a result of feedback from ecological processes soil nitrogen pattern may affect the dynamics of vegetation patch and soil moisture pattern. Changes in spatial pattern of soil properties can be a major force for community succession and a useful index for grasslands degradation under the effects of human activities, especially overgrazing.
【Fund】: 国家重大基础研究资助项目 (G2 0 0 0 0 1 860 7) ;; 中国科学院知识创新工程重大项目资助项目 (KSCX1 -0 8)
【CateGory Index】: S812
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