Effects Of Vegetation On Soil Moisture Among Different Restoration Methods In Semi-arid Loess Plateau,China

Soil moisture is the core constraint factor for vegetation restoration in arid and semi-arid regions.Taking the Longtan watershed in Dingxi City,Gansu Province,as an example,the effects of vegetation on soil moisture under different restoration methods in semi-arid loess watershed are studied.In the 2016-2017 growing season,measured the vegetation,topography,soil properties,and dynamic monitoring of moisture content of 0-1.8 m soil under two typical vegetation restoration methods(natural restoration and human induced restoration)and original state(natural grassland).The temporal dynamic and profile distribution of soil moisture content in this area are clarified,which provides feasible suggestions for soil water conservation and ecosystem protection in this area.Understand the impact of vegetation on soil moisture,and based on the vegetation functional traits studied the relationship between vegetation functional structure and soil moisture,and established a relationship model between vegetation functional traits and soil moisture.It can provide a new way to study the vegetation restoration methods in the area.(1)Dynamic monitoring of soil moisture in natural restoration,artificial restoration and natural grassland during the 2016-2017 growing season.The results showed that the profile of soil moisture in the semi-arid area showed a increasing first and then decreasing,and then the soil moisture content below 1 m was gradually stable.The temporal dynamics of soil moisture are significantly consistent with local rainfall.Moreover,there are some differences in the vertical distribution of soil moisture content under different recovery conditions.The results showed that there was no significant difference in soil moisture content under different vegetation restoration methods within 0-1 m.But there were significant differences in the soil moisture content in 1-1.8 m under different vegetation restoration methods.The deep soil moisture content in the natural restoration process was significantly higher than that in the natural grassland,and the deep soil moisture content of the natural grassland was significantly higher than the artificial restoration process.Based on the results of the effects ofvegetation on soil moisture under different restoration methods in this area,it is believed that natural restoration is more conducive to the conservation of soil water resources and the stability of ecosystems in this area.(2)Through the monitoring of topography,soil and vegetation factors in the study area,the impact factors of soil moisture in the small watershed scale were studied,and the intensity of each factor's soil moisture in the area was quantitatively decomposed.The results show that the interpretation of the variance of soil moisture in the environment and vegetation is 22.36% and 26.53%,respectively.A total of 46.92% of the difference in soil moisture distribution in arid and semi-arid loess hilly areas was explained.Among the topographic factors,altitude and slope have significant effects on soil moisture.The main manifestation is that the soil moisture content gradually increases with the elevation.As the slope increases,the soil moisture content gradually decreases.Among soil elements,soil organic matter and soil available phosphorus were significantly positively correlated with soil moisture content of 0-1 m and 0-0.4 m,respectively.The soil bulk density was significantly negatively correlated with soil moisture in the area.Among the vegetation factors,larger vegetation gross biomass and underground root distribution will cause further deficit of soil moisture.(3)Soil moisture content plays an important role in terrestrial ecosystem.Understanding the effects of re-vegetation on soil moisture content is very important for sustainable vegetation restoration in water-limited area.The vegetation's role on soil moisture content can be effectively identified and quantified by in-situ vegetation removal experiment.However,there are limited studies concerning on the effects of two typical vegetation restoration methods on soil moisture content.The effects of the two re-vegetation methods on soil moisture content in near surface(0-0.4m),subsurface(0.4-1m)and deep layer(1-1.8m)were studied in a typical semi-arid hilly watershed based on in-situ vegetation removal experiment and soil moisture monitoring.The research results proved that:(1)Both two vegetation restoration methods can induce soil moisture deficit,but the negative impacts of vegetation on soil moisture content in human-induced revegetation was higher than that in lands with natural restoration in growing seasons.(2)The natural re-vegetation process had relatively higher soil moisture content than human-induced revegetation.(3)The natural re-vegetation was beneficial to the soil moisture conservation.This study suggests that the natural re-vegetation is a better restoration method than humaninduced revegetation when considering soil moisture availability in the semi-arid regions.(4)Based on the mass-ratio hypothesis and the niche complementation hypothesis,the effects of community functional traits on soil water content were studied.The results of the study showed that there was a significant autocorrelation between the functional traits.Among them,there was a significant correlation between FD-H(FD : Functional diversity,H: Height),belowground biomass(BGB),CWM-LW(CWM: Community weighted mean,LW: leaf width)and FD-LDMC(LDMC: Dry matter content of leaves)and soil moisture.FD-LDMC was significantly positively correlated with surface Log response ratio(LNRR)within 0.4 m,FD-H and subsurface LNRR(0.4-1)showed a significant negative correlation,CWM-LW showed a significant positive correlation with subsurface LNRR(0.4-1 m),and BGB and deep LNRR(1-1.8 m)showed significant negative correlation,CWM-LW and deep LNRR(1-1.8 m)showed a significant positive correlation.