Effects Of Rainfall Events On Soil Carbon Mineralization And Its Mechanism In Typical Coastal Salt Marsh Wetlands Of The Yellow River Delta

With the intensification of global climate change,global and regional rainfall regimes are changing,which will affect the carbon sink function of coastal salt marshes.Therefore,studying the effect of rainfall regimes(include rainfall amount and timing)on soil carbon mineralization(soil CO₂and CH₄fluxes)is of great important for assessing the carbon cycling processes and accumulation mechanism of salt marshes.This study selected a typical salt marsh in the Yellow River delta that is not affected by tidal processes as the research object.By combining with field rainfall simulation experiment and indoor incubation experiment in 2019-2020,I studied the responses of soil CO₂and CH₄fluxes,soil physical and chemical properties as well as microbial community biomass and structure to rainfall events and soil water and salt interactions.The main conclusions are as follows:(1)There was a significant interaction between rainfall amount and timing on soil CO₂fluxes.During the dry season,heavy rainfall events(5 mm and 10 mm)significantly reduced soil CO₂fluxes.However,rainfall events in wet season had no significant effect on soil CO₂fluxes.Rainfall amount and timing had no significant effect on soil CH₄fluxes and CH₄/CO₂ratio.There was a positive relationship between CH₄/CO₂ratio and soil water content as well as salinity.(2)Rainfall events significantly reduced soil microbial biomass carbon and nitrogen contents,and there was a significant positive relationship between soil microbial biomass carbon content and soil CO₂fluxes,but no relationship for soil CH₄fluxes.Rainfall events in wet season had no significant effect on soil microbial biomass carbon and nitrogen contents.There was no significant relationship between soil CO₂and CH₄fluxes and soil microbial biomass carbon and nitrogen contents.(3)The incubation experiment showed that there was no interaction between soil water content and salt on soil CO₂,CH₄fluxes and soil CH₄/CO₂ratio.Soil CO₂fluxes increased first and then decreased with the increase of soil water content,while soil CH₄fluxes increased with the increase of soil water content.The increase of soil salinity significantly inhibited soil CO₂and CH₄fluxes.(4)The changes of soil water and salt can significantly change the component of soil microbial community.The increase of soil water content significantly increased the abundance and diversity index of soil bacteria,while the increase of soil salt significantly inhibited the abundance and diversity index of soil bacteria,and the soil CO₂and CH₄fluxes were significantly positively correlated with them.Rainfall time and rainfall amount significantly changed soil physical and chemical properties and microbial community composition by regulating soil water and salt migration,and then affected salt marsh soil carbon mineralization processes and carbon sink function.Therefore,the changes of rainfall regimes in the future may have a profound impact on the"blue carbon"sequestration capacity and carbon cycling processes of coastal salt marshes.