Dynamic Characteristics Of Soil Moisture And Its Influencing Factors In Semi-arid Steppe Basin

Soil moisture(M_S)is an important part of the lithosphere,biosphere,atmosphere and hydrosphere,which is the main limiting factor for plant growth in semi-arid steppe.As well,water is the main environmental factor restrictings the growth and distribution of plants in semi-arid areas.Our M_S study can provide data support and theoretical support for the optimization of ecological protection measures and further research on ecohydrological processes in steppe watershed.Xilin River Basin(XRB),located in the middle east of Inner Mongolia,was chosen as the study area.Firstly,the meteorological and hydrological conditions in XRB were obtained by using principal component analysis(PCA)and drought index.Based on the result above,the M_S and related environmental factors were monitored for a long time with high frequency.Using classical statistics,redundancy analysis(RDA)and Hydrus-1D model,the spatial and temporal dynamics of M_S,environmental influencing factors and their temporal simulation were studied.In addition,geostatistics,correlation analysis and multiple linear regressions were used to explore the spatial variation of M_S in root layer and its leading factors.What's more,we deeply analyzeds the relationship between M_S and soil organic matter(SOM),vegetation community diversity and biomass.The main findings are as follows:(1)The M_S content from 0 to 180 cm profile is generally low.The variability of M_Sdecreases as the depth of the soil layer increasing.The temporal and spatial distribution of M_S was significantly different in four soil types.Elevation and vegetation height were the key driving factors for M_S variability.After optimizing soil hydraulic parameters,the Hydrus-1D model could better describe the change of M_S at a fixed point.(2)With the deepening of soil layer,the spatial correlation of M_S in the root layer of grassland was enhanced,and the random influencing factors were weakened.The dominant factors of spatial variation of M_S in different soil types were different.Kastanozems is mainly affected by underground biomass,Arenosols and Solonchaks are vegetation biomass,and Phaeozems is soil physicals and chemical properties,and underground biomass.The explanatory rate of environmental factors to M_S heterogeneity was the highest in Solonchaks and the lowest in Kastanozems.(3)The influence of environmental factors on the spatial variation of M_S was vegetation,soil,topography and meteorological factors in the order of magnitude.Among the soil factors,SOM has a higher explanatory rate for vegetation distribution.The relationship between M_S and SOM were similar in Kastanozems,Arenosols and Phaeozems,but slightly different in Solonchaks.There were significant differences in community diversity among four soil types,and the relationship between M_S and vegetation biomass was close at different growth stages.