Simulation And Prediction Of Grassland Soil Moisture And NPP Response To Rainfall And Grazing

The typical grassland in Inner Mongolia is an important green security barrier in China,and under the dual influence of climate change and human activities,there is increasingly serious degradation,which threatens the national ecological security,so the response of grassland soil moisture and vegetation productivity to different climate scenarios and management patterns becomes a key and research hotspot to maintain the ecological stability of grassland.In this thesis,we take the grassland of Zhengxiangbaiqi under the condition of grazing ban as the research object,and use In this thesis,we use Biome-BGC and Daycent hydrological model to simulate soil moisture content and vegetation net primary productivity at different depths with good simulation results,and compare the changes of soil moisture and vegetation productivity under different rainfall conditions,grazing intensity and the latest CMIP6 climate model.The effects of meteorological and soil factors on soil volume water content,vegetation net primary productivity and the relationship between soil moisture and vegetation productivity at different depths were analyzed.This study provides basic data and theoretical basis for the subsequent study of grassland hydrology-soil-vegetation processes,the implementation of the integration of "landscape,water,forest,field,lake,grass and sand",and the strengthening of ecological protection and restoration.The study results are as follows:1.Both the Biome-BGC and Daycent models can simulate soil volumetric water content and net primary productivity of vegetation at different depths,and the net primary productivity simulation is most sensitive to the time of the beginning and end of the growing season with surface active organic matter C: N and soil litter C: N parameters,respectively,and the Biome-BGC model has relatively better simulation results.2.The effect of reducing rainfall on soil volume water content and net primary productivity of vegetation was stronger than that of increasing rainfall,and the effects of reducing and increasing rainfall on net primary productivity were concentrated in JulySeptember and June-October of each year,respectively.With the linear increase of grazing intensity,soil moisture in 15 cm and 30 cm soil layer increased,and the peak time of net primary productivity was delayed.Among them,under moderate grazing,the soil moisture of 15 cm soil layer increased the most,the time delay of the peak value of vegetation net primary productivity was the longest,and the total value decreased very little.3.The annual mean soil water content in each soil layer under the SSP585(high)emission scenario is higher than that under the SSP245(medium-low)emission scenario from 2021 to 2065,but the frequency of fluctuation is more consistent.Each soil moisture in the soil under the SSP245 mean emission scenario than average at SSP585 emissions scenarios;and under SSP245 SSP585 emission scenarios respectively NPP was smooth,and the trend to reduce the growth of emissions scenarios under SSP245 mean NPP the same is greater than the mean at SSP585 emission scenarios.4.Temperature had a greater effect on soil moisture in the 5 cm soil layer,while relative humidity and wind speed mainly affected soil moisture changes in the 15 cm and 30 cm soil layers,and soil volumetric water content in each soil layer was basically significantly correlated with soil temperature and soil conductivity in each soil layer.The effects of air temperature,relative humidity and wind speed were excluded respectively,which had a weakening effect on the correlation between soil moisture and vegetation net primary productivity.Meanwhile,excluding the effects of soil temperature and soil conductivity and excluding the effects of soil conductivity had a strong weakening effect on the correlation between soil moisture and vegetation productivity.5.For the same depth soil layer,environmental factors on soil moisture changes are higher than grazing conditions.Comparing soil moisture changes of soil layer to environmental factors,net primary productivity and soil conductivity under the ban on grazing have a great influence on 15 cm soil soil moisture changes;meteorological factors and soil temperatures under the conditions of dispensing conditions;Soil electrical conductivity and soil temperature interaction affect the moisture change of 5cm and 15 cm soil,the soil temperature and NPP interaction of each soil layer and soil electrical conductivity and NPP interaction affect the change of soil moisture of 30 cm and 60 cm soil;under grazing conditions NPP,soil temperature of each soil layer and soil conductivity interaction in each soil layer affect the change of soil moisture of 15 cm soil.