Effects Of Changes In Spring Rainfall Distribution On Soil Respiration In Coastal Wetlands Of Yellow River Delta

Coastal wetland is an important"blue carbon sink"due to the strong capacity of sequestering soil carbon,high primary productivity and low decomposition rate of organic carbon.As a key process of soil carbon cycle,soil respiration profoundly affects the soil carbon sink in coastal wetlands.Global warming leads to changes in the global hydrological cycle.Drought or flooding caused by the changes in seasonal precipitation distribution could impact the soil water and salt environment,regulate the physiological metabolism processes of vegetation,and then affect the soil carbon sink in the coastal wetlands.Although the effects of seasonal precipitation distribution on soil respiration in dryland ecosystems such as farmland,grassland and forest have been systematically and comprehensively studied,the mechanisms in coastal wetland are still unclear due to the complex hydrological processes.Furthermore,the current studies on soil respiration in coastal wetlands mostly focus on the change of total precipitation at the annual scale,and less on the change in seasonal precipitation.Therefore,under the background of changes in global precipitation pattern,it is urgent to understand the responses and mechanisms of soil respiration to seasonal precipitation distribution,which is of great significance for understanding and accurately evaluating the function of carbon sink in coastal wetland and building models.In 2019 and 2020,we conducted a 2-year's manipulative experiment to explore the influences and mechanisms of seasonal precipitation distribution on soil respiration in a coastal wetland of the Yellow River Delta.The responses of soil environment and biological factors to the changes in spring precipitation distribution were also determined to explore the mechanism of spring precipitation distribution on soil respiration.The experiment consisted of 5 treatments as control,increased(+73,+56)and decreased(-56,-73)precipitation in spring,while each treatment had four replicates.When the proportion of precipitation in spring was increased or decreased,this proportion in other seasons was correspondingly reduced or increased to maintain the same amount of annual precipitation among five treatments.The results showed that:(1)increasing spring precipitation distribution significantly decreased annual average content of soil moisture and soil salinity,in which the two factors was increased in spring,and was decreased in another three seasons.Increasing spring precipitation distribution had no significant effect on soil temperature at 10 cm depth.(2)Increasing spring precipitation distribution increased plant height,plant number and coverage of Phragmites australis and Phyllostachys sinensis,but decreased plant height of Suaeda salsa in 2019 and 2020.At the same time,the underground biomass and root-shoot ratio of vegetation significantly increased following the increase in spring precipitation distribution,and then changed the relative abundance of soil bacteria at different depths in2019.(3)Increasing spring precipitation distribution significantly increased the annual and spring soil respiration rate,which was in the order of+73>+56>control>-56>-73.The annual soil respiration rate was positively correlated with soil temperature at 10 cm depth,and the increase of spring precipitation distribution significantly increased Q₁₀of soil respiration.And(4)there was a significant negative correlation between soil salinity and annual soil respiration rate under the treatment of-73,whereas a positive linear correlation between soil moisture content and annual soil respiration rate was found under the treatment of+73 in 2019.Soil salinity at the depth of 10 cm was negatively correlated with soil respiration rate in autumn.The soil respiration rate significantly decreased in autumn and increased in winter following the increased soil water content.Plant height,plants number and vegetation community coverage had a significant and positive correlation with soil respiration rate,respectively.In 2019,soil respiration rate had significant and positive relationships with total underground biomass,the proportion of deep underground biomass to total biomass and root-shoot ratio,respectively.However,soil respiration rate was negatively correlated with proportion of shallow underground biomass to total biomass.In2020,there was a significant and positive correlation between soil respiration and aboveground biomass,whereas soil respiration had no relationship with root-shoot ratio,belowground biomass and the proportion of shallow or deep underground biomass to total biomass.