| Soil moisture is a key medium connecting the atmosphere-vegetation-soil continuum,which greatly affects many hydrological and ecological processes by influencing water infiltration,runoff generation,soil erosion and solute transport.As an important ecological function area in the Yangtze River Basin,the Three Gorges Reservoir Area has obvious changes in vegetation cover in small mountainous watersheds,as well as the transformation of slope cultivated land and vegetation restoration projects represented by returning farmland to forest,so it has important theoretical and practical significance for the study of ecological-hydrological processes under different land uses.In humid and semi-humid subtropical regions,soil moisture change is an important part of the study of the production and convergence mechanism of the watershed,and rainfall is the direct driving force affecting soil moisture change,and the response characteristics of soil moisture to rainfall are very important for understanding the rainfall runoff process mechanism in the humid and semi-humid mountains of southern subtropical subtropical and subhumid mountains.In this paper,Zhangjiachong Small Watershed,a typical mountainous watershed in the Three Gorges Reservoir Area,was selected as the main research area,and four typical land use types(forest land,tea garden,grassland and cultivated land)in the basin were selected to experiment and analyze the soil hydrological properties of vegetation,and the soil moisture monitoring was carried out for long-term series and high-frequency location.The ecohydrological functional characteristics of vegetation soil,the temporal and spatial distribution of soil moisture,the response characteristics of soil moisture to rainfall and its influencing factors were analyzed.Therefore,it is expected to provide a useful reference for the ecohydrological process of vegetation in the watershed and the related research on the distribution and change characteristics of soil moisture under mountain vegetation cover.The main conclusions are as follows:(1)There are obvious differences in vegetation and soil properties under different land uses.The litter thickness and litter accumulation of woodland were 66.67%and 13.72%higher than those of tea gardens,respectively,and the water holding performance of litter in woodland was better than that of tea gardens,and the effective retention capacity,effective retention rate and effective storage depth were 49.60%,28.62%and 49.60%higher than those of tea gardens,respectively.The root biomass distribution was between0.21～1.29 kg/m~3,and the root density,root surface area,root volume proportion and average root diameter were all shown that the forest land was higher than the tea garden than the grassland,and the vertical distribution characteristics of straight root plants and whiskered root plants were significantly different.The differences between soil properties under different land uses were obvious,and with the increase of soil depth,there were laws such as increase of sand particles,decrease of clay particles,increase of bulk density and capillary porosity,and decrease of saturated water conductivity,total porosity and non-capillary porosity.(2)The distribution range of soil water content under different land uses was between0.10～0.30 m~3/m~3,which showed that forest land and tea gardens were larger than grassland and cultivated land.The soil water content of each land use plot showed a trend of increasing with the increase of soil depth,and the difference of soil moisture between different soil layers was related to soil properties and root distribution characteristics.The monthly coefficient of variation of soil moisture was distributed between 0.01～0.34,and the vertical coefficient of variation was distributed between 0.04～0.23,and the different months of the year were divided into three periods according to the law of soil moisture and its coefficient of variation:January～May was the stable period,there was no obvious change in soil moisture during the stable period,and the time coefficient of variation and vertical coefficient of variation increased month by month;June～September is the growth period of soil water content,which is significantly higher than that of other periods,and the temporal coefficient of soil moisture and vertical coefficient of variation are the highest in the year.October～December is the period of soil water content reduction,during this period,soil water content decreases month by month,and the time coefficient of variation and vertical coefficient of variation gradually decrease.(3)The distribution range of soil moisture change under different land uses was0.023～0.044 m~3/m~3,which was manifested as tea garden>cultivated land>woodland>grassland,and the average distribution range of peak time difference was 3.935～6.187 h,which was manifested as woodland>tea garden>cultivated land>grassland,and the distribution range of wet front rate was 10.323～17.981 cm/h,which showed that cultivated land>tea garden>grassland>Woodland.The results show that vegetation cover has a positive effect on slowing down the peak of soil moisture,maintaining soil moisture,and promoting precipitation infiltration.With the increase of soil depth,the soil moisture change decreased,the peak time difference increased,and the wetting front rate increased.The explanations of vegetation factors,rainfall factors and soil property factors for soil moisture changes were 8.14%,30.23%and 61.64%,respectively.The explanatory degrees of peak time difference were 7.37%,60.65%and 31.98%,respectively.The explanatory degrees of wetting front rates were 1.38%,78.68%and 19.95%,respectively.Rainfall factors control the rainfall-soil moisture response process by controlling the amount and frequency of water input into the soil,soil factors control the process by controlling the infiltration and retention of water in the soil,vegetation factors control the rainfall-soil moisture response process by controlling the redistribution of rainfall before it reaches the surface,and the impact on soil properties. |
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