Effects Of Change In Precipitation Amount On Soil Carbon Emissions In A Coastal Wetland In The Yellow River Delta,China

Coastal wetlands are considered as“blue carbon sinks”,which are important for mitigating global warming,due to their high primary productivity,high carbon burial rate and low rate of organic matter decomposition.Coastal wetlands are an important part of the terrestrial ecosystem carbon pool,and changes in soil carbon emissions will directly affect the concentration of greenhouse gases in the atmosphere,thereby accelerating or slowing global warming.Global warming has intensified global hydrological cycles in the future,which is predicted to enhance the inter-and intra-annual variability of precipitation.Those include change of total amount,intensity,frequency,seasonal distribution of precipitation pattern.Increasing evidences suggest that change of total amount of precipitation may be more important than seasonal distribution of precipitation in regulating ecosystem carbon cycle processes and functions.However,most of researches documented the effects of changes in precipitation pattern on ecosystem carbon cycle processes and functions in deserts,grasslands,and forest ecosystems.Few studies have investigated the effects of precipitation changes on the carbon cycle processes and functions in coastal wetland ecosystems.Precipitation changes can affect soil carbon and water emissions in coastal wetlands by changing soil water and salt transport in coastal wetlands.There are many uncertainties about the mechanism of the impact of precipitation changes on soil carbon emissions in coastal wetlands.In order to explore the impact of precipitation changes on the carbon cycle process and function of wetland ecosystems,a field manipulative experiment that simulates precipitation increase and decrease was conducted to examine the effects of precipitation changes on soil temperature,soil salinity,vegetation growth,vegetation biomass,soil respiration?Soil CO₂ emissions?,soil CH₄emissions in the coastal wetland of the Yellow River Delta.There six precipitation treatments in experiments mainly including 60%of decreased precipitation,40%of decreased precipitation,60%of control,40%of control,40%of decreased precipitation,60%of decreased precipitation,and Four repetitions for each precipitation treatment.Through continuous monitoring of wetland soil environmental factors for two consecutive years?2017-2018?,we found that increased precipitation significantly reduced soil temperature and soil salinity,while decreased precipitation significantly increased soil temperature and soil salinity.At the same time,through periodic vegetation survey of wetland vegetation,the results showed that precipitation changes significantly affected vegetation growth and vegetation biomass.The increased precipitation significantly increased the wetland vegetation species diversity index,species richness index and vegetation coverage.And the decreased precipitation significantly reduced the wetland vegetation coverage.For vegetation biomass,increased precipitation significantly increased vegetation underground biomass,but significantly reduced vegetation aboveground biomass;decreased precipitation significantly reduced vegetation aboveground biomass,and significantly increased vegetation underground biomass in 2017,but there was no significant impact on the underground biomass of vegetation in2018.Meanwhile,through the periodic measurement of soil respiration,we found that the increased precipitation significantly improved the annual average and non-flooding soil respiration.Decreased precipitation significantly reduced the non-flooding soil respiration.And with the increase of year to the precipitation treatments,the response of wetland soil respiration to precipitation treatments was gradually enhanced.During flooding period,precipitation changes had no significant effect on soil respiration,however,the surface flooding significantly suppressed soil respiration.In addition,by periodically measuring soil CH₄ emissions,we found that the decreased precipitation decreased soil CH₄ emission during the non-flooding period.While,the surface flooding increased soil CH₄emission and the soil CH₄ emission increased with the increase of the surface water depth during the flooding period.Our results indicate that increased precipitation significantly improved soil respiration by reducing the soil salinity and increasing the vegetation coverage of the wetland.And decreased precipitation significantly reduced soil respiration by aggravating soil drought and salt stress in wetland and reducing vegetation coverage.The surface flooding significantly suppressed soil respiration by causing anaerobic environment.In addition,the decreased precipitation decreased soil CH₄ emission by reducing the soil moisture,increasing the soil salinity and reducing the belowground biomass and coverage of the wetland vegetation.The surface flooding significantly promoted soil CH₄ emission by causing anaerobic environment.Meanwhile,precipitation changes affect the soil water and salt transport and changed vegetation growth and biomass allocation strategies,and thus affecting the carbon emissions of coastal wetlands.This study revealed the internal mechanism of precipitation change affecting soil carbon emissions by changing soil salinity and affecting vegetation growth and biomass allocation in wetlands,and emphasized the important role of soil salinity in soil carbon cycle processes and functions in coastal wetlands.However,the impact of precipitation changes on the carbon cycle of coastal wetland ecosystems is multi-faceted.The change of precipitation can affect soil carbon emission not only by changing soil physical and chemical properties,vegetation growth,but also by changing the distribution of photosynthetic products of vegetation photosynthesis to the underground,and influencing soil microbial community structure.Therefore,in the context of global changes,further study on the impact of microbial mechanisms on soil carbon emissions and the effects of precipitation changes on the carbon allocation strategies of wetland ecosystems are Is very much needed.The internal mechanism that explores the response of soil carbon emissions in coastal wetlands to precipitation change is of great significance.