Response Of Soil Moisture To Rainfall In Arid And Semi-arid Grassland And Relationship Between Plant Community And Meteorological Factors

The stability of grassland ecosystem has been threatened by human factors and climate change.Grassland desertification has become more and more serious.The characteristics of grassland hydrological changes and plant community response under human influence have become the key and research hotspots for maintaining grassland ecological stability.Arid and semi-arid grassland is the main component of grassland ecosystem in China.Soil water is the link between atmospheric water,surface water and groundwater,and it also significantly affects the growth and development of grassland vegetation.This paper takes the typical arid and semi-arid grassland in Inner Mongolia as the research object,combined with continuous monitoring,periodic sampling and laboratory experiments,based on meteorological data,soil moisture data,vegetation data and soil characteristics data to describe the impact of grazing on grassland soil moisture and soil water content response to rainfall;using correlation analysis,aggregation classification,analysis of variance and other methods to explore the distribution of plant communities(composition,comprehensive status)and its relationship with meteorological factors;analysis of rainfall,relative humidity,temperature,solar radiation the direct or indirect effects of aboveground biomass,underground biomass,root-shoot ratio change;in order to summarize the conversion law of rainfall and soil moisture and the characteristics of meteorological conditions on grassland vegetation community change,to understand the local grassland hydrological process,predict or improve grassland productivity provides basic data and theoretical basis for developing reasonable grazing policies,protecting grassland species diversity,and combating grassland desertification.The main findings are as follows:(1)Grazing will lead to a decrease in biomass on the grassland,an increase in soil evaporation,and a decrease in rainfall conversion rate;grazing will affect the roots of 0?15 cm vegetation,resulting in weaker water absorption capacity of the roots,and faster migration of upper soil moisture,so the water content of the 0?15cm layer is smaller than the forbidden pastoral area,but the 30cm layer is larger than the forbidden pastoral area;the soil moisture of the 5cm,10cm and 15cm layers response to the rainfall is similar in the forbidden pastoral area and the grazing area.When the single or cumulative rainfall greater than 10mm,there is a significant increase on soil water content,but it will change due to the interval of drought interval(the number of days without rain between two rainfall events).The water content in the forbidden pastoral area is more sensitive to rainfall,and the increase is larger;there is obvious hysteresis in the response of soil moisture to rainfall at 30cm layer.When the single rainfall in the grazing area is greater than 30mm or the cumulative rainfall is greater than 20mm and the drought interval is<3d,the soil moisture increases significantly.The 30cm layer in the grazing area is only continuous in the short interval(?2d)big rainfall(>35mm),there is obvious fluctuation;the increase of soil moisture in the 0?30cm layer of the grazing area is extremely significant with rainfall and rainfall intensity.Grazing 0?15cm layer associated with significant rainfall,0?10cm layer and the rainfall intensity significantly correlated.(2)After 5 years of grazing prohibition,the soil vertical heterogeneity is enhanced.During the rainfall process,the soil moisture content of each soil layer is significantly different,while the grazing area is opposite.The lag time of soil moisture response to rainfall in the two regions increases with the depth of the soil layer.Compared with the grazing-free area,the shallow soil(5cm,10cm)in the grazing area has weaker water holding capacity and shorter infiltration time;the rainfall below 5mm has no obvious replenishment effect on the soil moisture in the grazing grazing and grazing areas;And the strength is not more than 5 mm/h is most favorable for infiltration,the infiltration depth of the grazing area reaches 15cm and 30cm layer respectively requires 7.9mm and more than 25mm of rainfall,while the grazing area greater than 5mm of rainfall can infiltrate into the 30cm soil layer;The independent rainfall with intensity of 5?6mm/h can only infiltrate into the topsoil(5cm).The rainfall with intensity greater than 15mm/h can penetrate into the 30cm and deeper soil through the macropores in the forbidden pastoral area,and the surface layer in the grazing area.The shallow infiltration is slower(0-5cm),which will result in surface runoff and even flood disasters.(3)According to the changing trend of the comprehensive status of plants in the growing season,the plants in the forbidden pastoral area are mainly divided into type ?Leymus,type ? yellow sylvestris+rough sage,type ? Mi's grass+Stipa krylovii,Class IV double-toothed onion+fine-leaved onion,grazing area:Class I,Stipa krylovii,Class ?Leymus chinensis+C.sylvestris,Class ? M.sylvestris+N.sylvestris,Class IV double-toothed onion+fine Onion.Rainfall and temperature in the pastoral area were the main factors affecting the comprehensive status of the species in the community.Rainfall had significant effects on the important values of the four types of plants(p<0.05),and the interpretation deviations of GAM fitting were 46.2%,30.8%,and 42%,respectively.24.7,the response of Leymus chinensis to temperature is not significant,and the explanatory power of temperature for the important values of plants of Class ?,? and IV is 32.6%,56.8%and 34.6%,respectively.The temperature and radiation in the grazing area are the main factors affecting the important values of plants.Except for the meteorological factors,the important values of plants of Class II,III and IV have obvious responses to temperature and radiation.<0.05),the explanatory power of temperature for the important values of various plants is 76.2%,65.7%,39.4%,and the explanatory power of radiation is 72.8%,68.7%,67%.Rainfall is the main decision-making variable affecting above-ground biomass.In addition to its direct promotion of biomass,it also indirectly affects above-ground biomass by changing relative humidity.The rainfall threshold that triggers plant leaf growth is not fixed,the threshold The lower limit increases with the increase of biomass,and the lower limit is the lowest at the beginning of May;rainfall,rainfall event size and rainfall intensity are the main rainfall parameters affecting the aboveground biomass of grassland.When the total rainfall or the rainfall per field increases by 1mm,the productivity of the pastoral area changes.The amount increased by 3.1g and 5.85g,respectively,while the productivity change in grazing area is more dependent on grazing intensity,and the correlation with rainfall pattern is not significant;grazing area temperature and solar radiation are the main decision variables for changing underground biomass,and underground biomass Direct inhibition,the underground biomass in the grazing area is only affected by temperature;the distribution of underground and aboveground biomass in the grazing area is affected by rainfall,humidity,radiation and temperature,and the direct effect of temperature and radiation is greater.The indirect effect of meteorological factors is small,and rainfall can be further affected by affecting relative humidity.Affecting the root-shoot ratio,the root-shoot ratio of the grazing area is only significantly correlated with rainfall and temperature.