Effects Of Precipitation Changes And Nutrient Addition On Ecosystem Carbon Exchange Of A Meadow Grassland In Hulunber

Precipitation changes and nutrient deposition are important contents of global change,and have important effects on the structure,function and process of terrestrial ecosystems.Grassland is one of the important ecosystem types.In the context of global change,studying the effects of precipitation changes and nutrient deposition on the carbon exchange of meadow grasslands is important for evaluating the future role of meadow grasslands in global carbon balance and climate change.Therefore,this thesis takes Hulunber meadow grassland as the research object and relied on the global change network experimental platform to carry out the research on the impact of precipitation changes,nutrient addition and their interaction on ecosystem carbon exchange.By measuring the process of ecosystem carbon exchange in Hulunber grassland under the treatments of increased precipitation,drought,nutrient addition and their interactions,the response of net ecosystem carbon exchange(NEE),total ecosystem respiration(ER),total primary productivity(GEP)and soil respiration(SR)to precipitation changes and nutrient addition were explored.Then by analyzing the relationship between NEE,ER,GEP and SR and plant community productivity,species diversity,soil physical and chemical properties,and soil microbial biomass,it revealed the regulation factors of ecosystem carbon exchange.The main results are as follows:(1)Plant community productivity,species diversity,soil soluble organic carbon(DOC)and inorganic nitrogen(IN)were only regulated by nutrient addition.Nutrient addition significantly increased aboveground biomass(AGB),DOC and IN,and significantly reduces species richness,Shannon-wiener index and Simpson index.Soil temperature(ST),microbial biomass carbon and microbial biomass nitrogen(MBC,MBN)were only regulated by changes in precipitation.The ST,MBC and MBN under the precipitation enhancement treatment were significantly higher than those under the drought treatment.Soil moisture(SM)is jointly regulated by precipitation changes and nutrient addition.There is no significant interaction between precipitation changes and nutrient addition on the above indicators.(2)Increased precipitation had no significant effect on NEE,ER and GEP,and drought had no significant effect on ER,but it significantly reduced GEP and the absolute values of NEE(|NEE|)by 17%and 25.9%,respectively.Nutrient addition significantly increased |NEE|,ER and GEP,with an increase of 35.55%,34.14%,and 34.83%,respectively.Changes in precipitation and nutrient addition had no significant interactions on NEE,ER and GEP.|NEE| was negatively correlated with soil temperature,and was positively correlated with above-ground biomass,soil organic carbon and inorganic carbon.ER and GEP were negatively correlated with soil temperature,and was positively correlated with soil moisture,above-ground biomass and soil organic carbon.(3)Increased precipitation had no significant effect on SR,but drought significantly reduced SR by39.6%.Nutrient addition reduced SR by 16%(not reaching a significant level).In addition,nutrient addition increased ER by increasing the proportion of above-ground plants’ respiration.There was no significant interaction between precipitation changes and nutrient addition on SR.SR was significantly positively correlated with soil moisture,microbial biomass carbon(MBC)and microbial biomass nitrogen(MBN),and was significantly negatively correlated with soil temperature.In summary,both precipitation changes and nutrient addition can significantly affect ecosystem carbon exchange,but there is almost no significant interaction between the two.Increased precipitation has no significant impact on ecosystem carbon exchange,but drought reduces SM,MBC and MBN,inhibits plant growth,thereby reducing ecosystem carbon exchange,indicating that ecosystem carbon sequestration in Hulunber grassland will reduce when affected by arid climate.Nutrient addition significantly increased the effective nutrient content of the soil and promoted plant growth,thereby promoting ecosystem carbon exchange,indicating that proper nutrient input would increase the carbon sequestration in Hulunber grassland.