Effect And Mechanism Of Stimulated Precipitation Change On Soil Respiration In Yellow River Delta Wetland

Due to their high primary productivity,low organic matter decomposition rate,and high carbon deposition rate,coastal wetlands are known to be an important "blue carbon" resource for mitigating global warming.At the same time,coastal wetlands,located in ecologically fragile areas at the interface between land and sea,are sensitive to global changes,especially to changes in precipitation caused by the intensification of the global hydrological cycle under a warming climate.The response of soil respiration,as the largest flux of carbon released from the soil carbon pool of coastal wetlands to the atmosphere,to changes in precipitation is important to properly assess the carbon sequestration potential of coastal wetlands.However,the response patterns and mechanisms of soil respiration rate and its components to precipitation changes in coastal wetlands remain poorly understood,and whether soil respiration sensitivity to precipitation changes is influenced by ambient climate as experimental duration increases contain extensive uncertainties.Therefore,in this study,a multi-year field precipitation manipulation experiment and laboratory analysis experiments were conducted in the coastal wetland ecosystem of the Yellow River Delta in combination with soil respiration component separation techniques.We mainly investigated the response of soil properties,vegetation community,and soil respiration rates and its components(soil autotrophic respiration and heterotrophic respiration)to precipitation changes.And we also explored the effect of ambient climate change on the sensitivity of soil respiration to precipitation changes.The main results were as follows:(1)Simulated precipitation changes significantly affected soil physicochemical properties and vegetation community characteristics in coastal wetlands.Specifically,soil moisture,soil ammonium nitrogen,soil dissolved organic carbon,and soil microbial carbon significantly increased with the increase in gradient precipitation under different precipitation treatments.And soil temperature and electrical conductivity significantly decreased with increased precipitation under different precipitation treatments.On the other hand,simulated precipitation changes significantly affected vegetation community characteristics,and vegetation species diversity index,vegetation leaf area index,and vegetation aboveground and belowground biomass increased significantly with the increase in gradient precipitation under different precipitation treatments.(2)Soil respiration rate showed a positive asymmetric response trend along the experimental precipitation gradient in coastal wetlands.The annual average soil respiration rate under different precipitation treatments was exponentially positively correlated with annual precipitation,and the enhancement of soil respiration rate under increased precipitation treatments was significantly greater than the reduction under decreased precipitation treatments.Meanwhile,both vegetation belowground biomass and leaf area index also showed positive asymmetric responses along the experimental precipitation gradient.Moreover,the magnitude of the linear regression slope between vegetation belowground biomass and leaf area index and soil electrical conductivity were greater under increased precipitation than that under decreased precipitation.Thus,the acclimation of vegetation to salinization was a major determining factor in the asymmetric response of soil respiration rates along an experimental precipitation gradient in coastal wetlands.(3)Precipitation treatments significantly altered the proportion of soil respiration components to total respiration in coastal wetlands,while soil autotrophic respiration was more sensitive to precipitation treatments compared to soil heterotrophic respiration.Increased precipitation significantly increased the proportion of soil autotrophic respiration to total respiration,but significantly decreased the proportion of soil heterotrophic respiration to total respiration.Meanwhile,both soil autotrophic respiration and heterotrophic respiration were exponentially positively correlated with precipitation under different precipitation treatments,and the regression parameter between soil autotrophic respiration and precipitation was larger than those of soil heterotrophic respiration and precipitation.Moreover,the response of soil autotrophic respiration to precipitation treatments was related to soil electrical conductivity,aboveground biomass,and leaf area index,while the response of soil heterotrophic respiration to precipitation treatments was mainly derived from soil moisture,aboveground biomass,and soil microbial carbon.(4)The interannual variability in ambient climate determined the sensitivity of soil respiration to the experimental gradient precipitation treatments in coastal wetlands.The sensitivity of soil respiration to the experimental precipitation treatments was quantified by an exponential model,and a significant negative correlation was found between ambient precipitation in the ambient climate and the sensitivity of soil respiration to the precipitation treatments.Meanwhile,the sensitivity of soil respiration to precipitation treatments was positively correlated with the sensitivity of vegetation belowground biomass to precipitation treatments.Furthermore,both soil respiration components(soil autotrophic and soil heterotrophic respiration)were also positively correlated with vegetation belowground biomass.Thus,ambient climate affects the sensitivity of soil respiration to precipitation treatments mainly by affecting the sensitivity of vegetation belowground biomass to precipitation treatments.In summary,the acclimation of vegetation growth to salinization is the main determinant of the positive asymmetric response of soil respiration rate along experimental precipitation gradients in coastal wetlands.Meanwhile,soil autotrophic respiration was more sensitive to the experimental precipitation treatments compared to soil heterotrophic respiration.Moreover,ambient climate determines the sensitivity of soil respiration to precipitation treatments in coastal wetlands.Our results emphasize that soil salinity and ambient climate play an important role in regulating the response of the soil carbon cycle to precipitation changes in coastal wetlands.Meanwhile,the differences in the sensitivity of soil respiration components to precipitation treatments suggest that future increases in precipitation variability may negatively affect the stability of soil carbon pools in coastal wetlands.