Mechanism Of Soil Greenhouse Gas Emission In Soil Profile Under Precipitation Changes In Artificial Grassland

Increased atmospheric greenhouse gas concentrations resulting from human activities lead to precipitation change patterns worldwide,which in turn would have profound effects on soil greenhouse gas emissions.Soil greenhouse gas emissions are the result of greenhouse gas production and emissions at different depths of the soil,and grassland ecosystems,as an important part of terrestrial ecosystems,play a vital role in the regulation of global climate change feedback.Therefore,understanding the spatio-temporal changes of soil greenhouse gases in grassland ecosystems under precipitation changes and their impact mechanisms can more accurately assess soil greenhouse gas budgets under future precipitation models.In this paper,taking artificial grassland（mainly Poa annua communities）in Changwu County,Shaanxi Province was studied,and the method of rain shelter and artesian drip irrigation system was used to intervene in precipitation.The use of natural precipitation water resources to form different precipitation conditions（normal precipitation,40%increased precipitation,40%decreased precipitation）.In situ observations of CO2 and N2O emissions and CH4 uptakes of soil surface and profiles under precipitation changes were observed by static dark box method and soil profile gas collection method.Combines non-biological factors such as soil temperature and moisture,nitrate nitrogen,ammonium nitrogen and soluble carbon and nitrogen,as well as biological factor parameters such as root biomass,microbial carbon nitrogen and enzyme activity.To discuss the temporal and spatial dynamic changes of greenhouse gas emissions in soil profiles of artificial grasslands under precipitation change and their driving mechanisms.The main research results are as follows:（1）Soil greenhouse gas total fluxes components showed seasonal dynamic changes,and overall,the soil greenhouse gas fluxes in the growing season were higher than that in the non-growing season.The decreased precipitation treatment significantly reduced soil respiration,mainly due to the significant reduction of microbial respiration by the decreased precipitation treatment,but the total respiration,microbial respiration,and root respiration of the soil under the increased precipitation treatment did not show significant differences between normal precipitation treatment.The decreased precipitation treatment also significantly reduced the N2O discharge rate of plant-free soil,and different precipitation treatments had no significant effect on soil CH4 uptakes.（2）With the increase of soil depths,the seasonal dynamic changes of soil CO2 and CH4fluxes tended to stabilize,but the N2O fluxes of deep soils still showed large seasonal dynamic changes.The soil profile CO2 and N2O diffusion fluxes were higher than those in the non-growing season,and the CH4 diffusion fluxes did not show significant differences between the growing season and the non-growing season.Precipitation changes had a significant effect on the greenhouse gas fluxes of the soil profile,increased precipitation significantly promoted the 10-20 cm soil greenhouse gas fluxes,and the precipitation reduced the N2O and CH4 fluxes of the soil profile.The soil CO2 emissions rate was relatively close to that of 0-20 cm soil CO2 fluxes in static chamber,the soil N2O emission rate was much lower than that of 0-20 cm in static chamber,and the CH4 absorption rate was higher than 0-10 cm and 0-20 cm soil CH4 fluxes in static chamber.（3）Precipitation changes had no effect on soil temperature,and the seasonal change trend of soil temperature in all soil layers was consistent.Precipitation changes significantly affect soil moisture,and the soil moisture of each soil layer under decreased precipitation treatment is significantly lower than that of increased and normal precipitation.The relationship between soil temperature and soil CO2 fluxes in each soil layer is an exponential function,and the relationship between soil moisture and soil CO2 fluxes is mainly quadratic curve.The soil CO2 fluxes of soil under increased and normal precipitation showed a trend of increasing first and then decreasing with the increase of soil moisture.This indicates that there may be a moisture threshold for soil CO2 fluxes in soil layers of 0-10 cm.Soil N2O fluxes was positively correlated with soil temperature and negatively correlated with soil moisture,and soil CH4 fluxes and soil temperature and moisture were negatively correlated,and soil CH4 fluxes was mainly affected by soil moisture.There are seasonal differences in soil nitrate,ammonium and soluble carbon and nitrogen.There were significant correlations between soil nitrate nitrogen,ammonium nitrogen and soluble carbon and nitrogen content and soil CO2 fluxes under precipitation changes,and there was a significant correlation between soil ammonium nitrogen content and soil N2O fluxes.（4）The grassland roots in the study area were mainly distributed in 0-10 cm soil,and the root biomass of the 0-10 cm soil layer under precipitation changes was increased precipitation(1159.40 g m^-2)>normal precipitation(850.96 g m^-2)>decreased precipitation(647.61 g m^-2).There was a significant positive correlation between root biomass and soil N2O fluxes under precipitation changes.The soil microbial carbon and nitrogen content fluctuated greatly,and the soil microbial carbon content in august was slightly higher than that in May.Under decreased precipitation treatment,the soil microbial carbon and nitrogen content of different soil layers in the grassland in August was lower than that of the increased precipitation treatment and normal precipitation.There was no significant correlation between soil microbial carbon and nitrogen content and soil greenhouse gas fluxes under precipitation changes.Phosphatase and cellulose disaccharidase activities in soil show seasonal differences.The activities of the five enzymes in grassland soils were significantly higher than those in bare land soils,and the phosphatase activity was the highest in both grassland and bare soils,while N-acetamidomin-β-glucosidase activities were the lowest.There was a significant correlation between cellulosic disaccharidase and soil CO2 fluxes under precipitation changes,and betweenβ-glucosidase,cellulose disaccharidase and leucinase and soil N2O fluxes.