Effects Of Increasing Or Decreasing Rainfall On Soil Properties And Plant Communities In Degraded Grasslands Of Inner Mongolia

Rainfall is the main source of water in arid and semi-arid areas.Rainfall,rainfall duration,rainfall intensity,and surface vegetation conditions together affect the rainfall infiltration process,which in turn affects soil water replenishment,and ultimately affects the growth of surface vegetation.Degraded grassland ecosystem stability and its desertification mechanism have been hot and difficult issues in grassland ecological hydrology research in recent years.This article is based on meteorological data,soil moisture data(5,15,30,60,and 100 cm soil layers),soil physical and chemical properties data(volume moisture content,bulk density,saturated moisture content,conductivity,pH,and organic matter content)and vegetation data(species,Height,coverage and aboveground and underground net primary productivity),through classical statistics,geostatistical methods,and BIOME-BGC model simulations,the natural rainfall,increased rainfall(plus 50%),and reduced rainfall(decreased by 50%)and other characteristics of soil and plant characteristics under different rainfall treatment conditions.It is of great significance to reveal the key elements of soil and water in typical degraded grasslands in Inner Mongolia,the prevention of grassland desertification,and the impact of climate change.The main research results are as follows:(1)The analysis of the soil background in 2018 found that the soil moisture dynamics and the rainfall distribution pattern remained basically the same.The soil moisture increment of each soil layer in the same rainfall process showed a downward trend.High rainfall intensity and higher soil moisture content before the rainfall had Conducive to rainwater infiltration,the soil water increase in 5 and 15 cm soil layers has a significant and extremely significant linear relationship with rainfall intensity,initial soil moisture content,and the interaction between the two;30 and 60 cm soil layers only interact with rainfall intensity and the two There is a very significant linear relationship,there is no significant linear relationship between the 100cm soil layer and the three.The soil is weakly alkaline.As the soil layer deepens,pH,electrical conductivity,and bulk density increase,and organic matter content and saturated moisture content decrease.The bulk density and pH showed weak variation,and the other soil characteristic indexes showed moderate variation.The coefficient of variation of soil water content in the 5?60cm layer decreased with the increase of soil water content.(2)There was a significant difference in soil volumetric water content between 5 to 60 cm of soil layer in natural rainfall(CK),increased rainfall(PA),and reduced rainfall(PR)subregions,and the average values of soil volumetric water content in each soil layer were in the PA subregion.When the maximum value is reached,the change trend of the volumetric water content of the shallow soil layer and the rainfall is basically the same,and the change range decreases with the deepening of the soil layer.There is no significant fluctuation in the volumetric water content of the soil layer at 60 and 100 cm.There is a significant correlation between soil volumetric water content in each soil layer and soil temperature,and the soil temperature in each soil layer first increases and then decreases.There is a linear positive correlation between soil electrical conductivity and soil volumetric water content.There is a significant difference in electrical conductivity between June and October in a 5cm soil layer;there is a significant difference between the PA and CK and PR zones in a 15cm soil layer in June,and 3 in the remaining months.There were significant differences in the electrical conductivity of the zonings;there were significant differences in the electrical conductivity of the three zonings in the 30,60,and 100 cm soil layers during the growing season.The soil moisture in each zone in descending order is:PA>CK>PR;the soil temperature in descending order is:PR>CK>PA;the change in electrical conductivity with soil volumetric water content is PR>PA>CK.(3)Decreasing rainfall will reduce species richness,which can increase the important value of Artemisia frigida,reaching the maximum of 3 subregions;increasing rainfall increases species richness,and the important value of Artemisia frigida,Leymus chinensis and woody ground in the growing season is generally greater than the CK subregion.The Shannon-wiener diversity index of the CK and PA subregions was significantly different from that of the PR subregion,with the richness index PA>CK>PR.After one year of increased rainfall experimental treatment,although the species diversity has been improved to a certain extent,the contribution to the comprehensive vegetation index has been small.Appropriate rainfall increase can increase the above-ground biomass of the vegetation.The above-ground biomass in each subdivision of the whole growing season generally increases first and then decreases.Proper rain increase can help the root system of 5 and 15 cm soil layers.(4)The optimized BIOME-BGC model has a good effect on the simulation of soil moisture and NPP in the study area.It has certain credibility and can be used for simulation.The maximum NPPs were all in mid-August.There was no significant change in the NPP when rainfall increased by 80%,and the maximum NPP increased by 120%and 160%increased by 1.93%and 3.03%,respectively.The maximum values were reduced by 0.28%,6.34%,and 11.29%,respectively.5.The minimum value of soil moisture in 15cm soil layer increases with the increase of rainfall,and the increase range is 15cm<5cm soil layer;the maximum value decreases with the decrease of rainfall,and the decrease range of 15cm>5cm soil layer;the frequency of soil water fluctuation is 15cm 5cm soil layer.For a 30 cm layer of soil,there is no significant difference in the amount of soil moisture increased by 120%and 160%rainfall,but both are greater than the amount of soil moisture increased by 80%rainfall.The greater the reduced rainfall,the smaller the maximum and minimum soil moisture.The smaller it is.For 60 and 100 cm deep soils,the amplitude and frequency of soil moisture fluctuations are significantly smaller than that of 5,15 and 30 cm soil layers and the changes are not significant.(5)The NPP in the two emission scenarios RCP4.5 and RCP8.5 have an increasing trend in the next 30 years.The overall trend of NPP in the RCP4.5 scenario is higher than that of the RCP8.5 scenario,and the NPP fluctuation in the RCP4.5 scenario is small.Under the RCP4.5 scenario,the maximum value of NPP appears in 2033 and can reach 198.24g/m2,and the minimum value appears in 2021,which is 169.25g/m2.Under the RCP8.5 scenario,the maximum value of NPP appears in 2027.It reached 196.35 g/m2,and the minimum value appeared in 2030,which was 165.43g/·m2.The maximum and minimum values in the RCP8.5 scenario are smaller than the maximum and minimum values in the RCP4.5 scenario.