The Effect Of Drought Stress And Copper Ion Stress On Soil Microorganisms And Extracellular Polymeric Substances

Soil resource is one of the most basic,extensive and important natural resources in human life and production.It is also an important part of the Earth ecosystem.Small changes in soil can have important effects on soil microorganisms,plants and humans.The problem of drought caused by global warming and the increasing heavy metal pollution will seriously affect soil quality.The extracellular polymeric substances secreted by microorganisms play an important role in the defense against environmental stress.In order to better understand the response of soil to drought stress and copper ion stress,this paper studies the effects of drought stress and copper ion stress on soil microorganisms and extracellular polymeric substances,the main research results are as follows:(1)After six soils of different utilization type were treated by air-drying and rewetting,the activity of microorganisms in the soil was inhibited,and the microbial biomass carbon(MBC)content in the six soils decreased.The decrease was between 2.20-451.81 mg kg-1(1.04%to 42.35%),The ATP content of the six soils decreased significantly,and the decrease ranged from 0.50 to 5.96 nmol g-1(39.36%to 70.30%).Both the decline of MBC and ATP showed the decrease in the total amount of microorganisms in the soil,which led to a significant decrease in the extracellular polymeric substances(EPS)content secreted by the microorganisms in the soil.(2)Impacts of soil type(different pH),substance(ryegrass,with or without),and copper ion(0,70,140,280 mg kg-1)were investigated.Results indicated that the addition of copper ion will reduce the MBC content,inhibit soil respiration,and significantly reduce EPS content in acidic soil and alkaline soil without addition of ryegrass.When the copper ion concentration was 140 mg kg-1,the MBC content in acidic soil was the lowest and the soil respiration was the weakest.The MBC content of alkaline soil decreased with the increase of copper ion concentration.When the copper ion concentration reached 140 mg kg-1,the alkaline soil EPS content decreased significantly.In acidic and alkaline soils with added ryegrass,the addition of copper ion decreased the MBC content,decreased soil respiration and decreased soil EPS content.The higher the copper ion concentration,the serious influence of the MBC content and soil respiration of acidic and alkaline soils added with ryegrass.When the copper ion concentration reached 140 mg kg-1,the EPS content in the ryegrass-added alkaline soil decreased significantly.the addition of substance significantly promoted microbial activity.The MBC content in the soil increased,the soil respiration was promoted,and the soil EPS content increased.After copper ion was added to the soil,the more addition of copper ion,the more available copper in the soil.However,as the time goes by,the available copper content will gradually decrease.The available copper content accounts for 72.40%?88.76%and 36.67%?50.12%of the total amount of added copper ion in acidic soil and alkaline soil.