| Free grazing in long term bring about less litter reserving and the drying climate is disadvantages to decompose for litter in desert steppe meadow, however, sheep dung can rapidly return nutrients in short time which has impront effects to grazing grassland ecosystem. Meanwhile, grazing and shrub invasion leading to spatial distribution of soil resources influences species composition and community distribution and effect the stability of meadow. In smaller spatial scales, the spatial distribution of plant leading for ecological factors such as geography, grazing and interspecific competition may be a key factor for maintaining community diversity and productivity and plant stability in larger spatial scale. The effect of sheep dung return presenting a certain pattern of gradient distribution in spatial was a very important factor which effected the spatial distribution of soil and vegetation and dynamics of succession in meadow with free grazing conditions. In order to develop a deeper understanding on the effect of grazing to the pattern of influenceing and the mechanism of action of meadow in desert steppe, we conducted a research that the heterogeneity of soil nutrients and plant and the relationship between variability and environmental factors were studied based on the filed investigation and lab analysis in three different microrelief scales in Ningxia desert steppe ecosystem. The main conclusions indicated that:1) In term of spatial structure of soil nutrients, total phosphorous (TP) showed high spatial autocorrelation, soil organic carbon (SOC) and total nitrogen (TN) indicated moderate spatial autocorrelation on the first tiny terrain. All soil nutrients showed moderate spatial autocorrelation on the third tiny terrain. The similar spatial structure of soil nutrients was indicated between the first and second tiny terrain. In term of spatial range of influence calculated for total nitrogen (TN) is maximum and for total phosphorous (TP) is minimum on the first and second tiny terrain, however, spatial range of influence calculated for soil organic carbon (SOC) is maximum on the third tiny terrain.2) According to the influening factors of soil nutrients variability at0-5cm layer. On the first tiny terrain, relative elevation, sheep dung content and vegetation coverage were the dominant influencing factor of SOC, TN and TP variations respectively on the first tiny terrain, the location and size of Caragana intermedia also had significant effect on SOC distribution, sheep dung content was the dominant effecting factor of N/P variations. On the second tiny terrain, relative elevation and the content of0.25-2mm soil particle were the significant affecting factor of SOC variation, species number and litter content were the significant influencing factor of TN variation, relative elevation, the content of0.0385-0.25mm soil particle and the location of Caragana korshinskii Kom had the significant effects on TP variation. Species number had significant contribution on N/P variation. On the third tiny terrain, litter content and plant density were the dominant influencing factor of SOC and TN variations respectively. Relative elevation, total salt and plant cover had significant contribution on TP variation. The influencing factors of C/N and N/P were a little complex.According to the influening factors of soil nutrients variability at5～10cm layer. On the first tiny terrain, relative elevation and litter content were the dominant affecting factor of SOC variations, plant cover was the dominant influencing factor of TN and TP variations, the content of0～0.0385mm soil particle was the dominant affecting factor of N/P. On the second tiny terrain, relative elevation, the content of0.0385～0.25mm soil particle and litter content had remarkable contribution on SOC variation, species number and the content of0.25-2mm soil particle had striking effect on TN variation, total salt had significant contribution on TP variation, species number and total salt had remarkable effect on N/P. On the third tiny terrain, relative elevation, total salt and the content of0.0385-0.25mm soil particle had remarkable contribution on SOC variation, total salt was the significant influencing factor of TN variation, relative elevation and total salt were the remarkable influencing factor of TN variation, the location of Caragana korshinskii Kom had the significant effects on C/N variation.3) Parameters of theoretical variogram models for plant showed that:On the first tiny terrain, plant cover had strong spatial dependence, density secondly in plant features. In the features of community diversity, Margalef indicated the strongest spatial variability, Pielou secondly. On the second tiny terrain, the rank of plant features of spatial variability was species number firstly, density secondly and cover thirdly. And the order of spatial variability for the index of community diversity was Shannon-Wiener firstly, Margalef secondly and Pielou thirdly. On the third tiny terrain, plant density had strongest spatial dependence, cover secondly in plant features. However, the spatial dependence of features of community diversity had disappeared.4) In term of the influcing factors of plant variability, On the first tiny terrain, relative elevation was the dominant influencing factor of plant distribution in environment factors. In soil nutrients factors, TP at0-5cm layer and SOC at5-1Ocm were the dominant influencing factor of plant density and cover respectively, The affecting factors of species number were a little complex, plant diversity was mostly controlled by TN at0-5cm and SOC at5-10cm. On the second tiny terrain, species number and community diversity were mostly determined by relative elevation in environment factors, In soil nutrients factors, TP at0-5cm layer was the dominant influencing effect of plant, soil nutrients at5～10cm had a complicated influence to plant, community diversity was mostly controlled by TP and TN. On the third tiny terrain, litter content, the content of0.25-2mm soil particle and TP were the dominant affecting effects of plant cover, plant density and Margalef were controlled by relative elevation and TP. Shannon-Wiener was mostly controlled by litter content and TN. According to the variance contribution (exponential models with the nugget effect), the contribution of relative elevation was decrease.5) Spatial distribution of soil resources was relevant to sheep dung content which was the dominant influencing factor of TN at0～5cm and which was mostly controll the distribution of plant on the second tiny terrain. Relative elevation was the dominant influencing factor of SOC and TN variability, and this effect was decreaseing from the first to the third tiny terrain, TN variability was mostly determined by plant factors, The influencing factors of C/N and N/P were a little complex. The relationship between relative elevation and the spatial distribution of plant was decreaseing from the first tiny terrain to the third tiny terrain. In the plant factors, the location and size of Caragana korshinskii Kom had the significant effects on the spatial distribution of plant but were not the dominant influencing factor, litter content had a increaseing affecting on plant variabilit. Soil nutrients factors had a complicated effect on plant.6) Firstly, The redistribution of soil nutrients and spatial pattern of vegetation caused by topography in the small scale.Secondly, the sheep dung controled spatial pattern of soil total nitrogen and then affected the distribution and heterogeneity of vegetation under heavy grazing disturbance.In the smaller scale, the sheep dung, for example one square meter scale, might be have a influence on soil and vegetation spatial pattern which also mainly caused by soil-plant interaction. Meanwhile ecological status of litter have enhanced tremendously under moderate and light grazing disturbanc e.In small scale, the ecological process such as the redistribution of soil nutrients caused by topography, the choice of sheep feeding, the adaptability of plant populations and soil-plant interaction maintained landscape heterogeneity in the large scale. |
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