Effects Of Nitrogen And Litter Addition On Soil Organic Carbon Pool Components In Minjiang River Estuary Wetland

The estuary wetland is an important carbon?C?sink and storageon the Earth,and its changes reflect the balance between the input and output of the C and N of terrestrial ecosystems.The storage of soil C in wetland is not only an important part of the global C cycle but also a critical part of terrestrial soil C pool.In the estuary area,nitrogen?N?is a key element in controlling the primary productivity of plants,and affects the return of the plant litter C pool in the soil,which in turn affects the soil C pool and C components.In recent years,the N-load of coastal wetlands,especially the estuary,has increased due to the enhancement of human activity intensity,which affects the C and N cycles in the estuarine wetland ecosystem.In this paper,the soil under the community of Cyperus malaccensis var.brevifolius was taken as the research object,and the experiment was conducted by adding N and litter in situ in the Tajiaozhou in the Minjiang River estuary to study the effect of litter and N addition on soil organic carbon?SOC?components,mineralization,and their driving factors Four treatments were set,including litter(K,15 g litter,0 g N·m^-2·a^-1),low N(LN,15 g litter,6 g N·m^-2·a^-1),medium N(15 g litter,16 g N·m^-2·a^-1)and high N(15 g litter,24 g N·m^-2·a^-1),and a control treatments without any litter and N addition.The main findings and conclusions are as follows:?1?The addition of N and litter did not fundamentally change the seasonal variation of soil water content and bulk density,but change the seasonal variation of soil total N?TN?concent and ratio of soil carbon and nitrogen?C/N?.Under the N and litter addition treatments,soil TN and C/N were significantly higher in summer and autumn,but significantly lower in winter.The addition of N and litter increases the soil total C?TC?content and TN,indicated that N and litter addition can enhance the fixation of soil carbon and nitrogen in estuary wetlands.N and litter addition,to some extent,increased soil C/N and reduced soil N supply potential.?2?In general,N and litter addition promoted SOC,and the combined effect of nitrogen and litter addition was higher than K treatment.There was a significant positive correlation between TN and SOC under the CT and LN treatment?P<0.01?,but a negative correlation between TN and SOC under HN treatment?P<0.01?.SOC was mainly affected by soil moisture content under K,LN,and MN treatments,and by soil redox potential and soil TN under HN treatment?P<0.05?.Soil soluble organic carbon?DOC?showed an increasing trend with time under the N and litter addition treatments.Soil DOC was inhibited by the addition of N and litter except for an increase in winter.DOC was positively correlated with soil moisture content but negatively correlated with soil temperature?P<0.01?,indicated that soil DOC was sensitive to soil moisture content and soil temperature.K treatment promoted soil oxidized carbon?EOC?,while the addition of nitrogen and litter inhibited soil EOC.There was a significant positive correlation between soil EOC and soil TC under K treatment?P<0.01?.K treatment promotes soil microbial biomass carbon?MBC?,while nitrogen and litter treatments have different effects on soil MBC.Specifically,MN and HN decreased MBC,while LN inhibits MBC in spring and winterbut promoting MBC in summer and autumn.Soil temperaturewas significantly positively correlated with MBC under the LN treatment?P<0.05?,indicating that soil temperature and nitrogen addition gradient would affect soil MBC.Compared with the CT treatment,soil activated carbon?AOC?was promoted under K and LN treatments,while AOC was inhibited under MN treatment except for summer.However,under MN treatment,AOC was inhibited in spring and autumn,promoted in summer and winter.The relationship between soil AOC and soil TC was positive under each treatment?P<0.05?,suggeated that soil AOC was more sensitive to the variations of soil TC.?3?Compared with the CT treatment,the activities of acid phosphatase?AP?,?-glucosidase??G?,?-N-acetylaminoglycosidase?NAG?and cellulose hydrolase?CBH?were increased under LN and MN treatments,while the activities of AP,?G,NAG and CBH were decreased under K and HN treatments.The content of microbial biomass N?MBN?was increased under K and LN treatments than CT treatment.Soil?G activity was different in different seasons,when a relatively high values was found in summer.The addition of N and litter did not fundamentally change soil AP activity and seasonal variation,but changed soil CBH and NAG activity and seasonal variation.The levels of N addition had a significant effect on soil enzyme activity and MBN contents.?4?The accumulation of SOC mineralization depended on cultivation time.The rapid increase of SOC mineralization rates and its accumulation were observed before 12days cultivation.The SOC mineralization rates significantly increased in summer and winter?P<0.05?,but they did not reach a significant level in other seasons.Under the combined addition of nitrogen and litter,the accumulation of SOC mineralization decreased than CT treatment in spring and summer,while it was on the contrary in winter.The mineralization rates of SOC was positively correlated with soil DOC under all treatments?P<0.01?,as well as positively correlated with SOC under LN and MN treatments?P<0.01?.The mineralization rates of SOC was negatively correlated with soil AOC under LN treatment?P<0.01?.Soil DOC has a significant effect on SOC mineralization.The effect of SOC and AOC on the rates of SOC mineralization depended on the levels of N addition.