Response Of Organic Carbon In Decomposing Shichito Matgrass Litter To Nitrogen Addition In A Marsh Of The Min River Estuary

Nitrogen(N)pollution has become a global environmental problem,and the impact of N load enhancement on estuarine marsh ecosystem has caught the attention of scholars Estuarine wetland,as an important global carbon(C)sink,is part of the most sensitive ecosystems to global climate change.And the accumulation and release of litter organic C involved the C sources and sinks of the ecosystem.Elucidating the dynamic of litter C in the soil,water,and atmosphere system has crucial ecological significance for soil C storage,greenhouse gas emissions,and plant nutrient supply in N-rich estuary marsh Therefore,it is necessary to consider the decomposition of litter C in estuarine marsh under the background of N load enhancement.This study aimed to investigate the effects of N addition on the litter C decomposition dynamic,drive mechanism,and pathway in the soil,water,and atmosphere system.An N addition experiment in Cyperus malaccensis Lam.subsp.monophyllus(Vahl)T.Koyama(shichito matgrass)litter decomposition was conducted in the Tajiaozhou marsh of the Min River Estuary Microbial community composition and enzymatic activity,as well as spectroscopy techniques(fluorescence and ultraviolet spectrum),was used to analyze litter microbial community composition and enzymatic activity.Three N treatments,including low N(N6,6 g N m-2 yr-1),intermediate N(N16,16 g N m-2 yr-1)and high N(N24,24 g N m-2 yr-1),were set in the in-situ experiments.And two N treatments were set in a short-term leaching experiment,including low N(5.76 mg N L-1)and high N(11.52 mg N L-1)They all set control treatments without any N addition.The research results can fill in research gaps in the distribution and storage of litter C in the N-rich estuary marsh,and it can provide theoretical basis for the government to make relevant decisions on dealing with N deposition.The main results showed as following:(1)The stage-specific response of litter organic C to N addition was investigated.In the early and middle stages of decomposition,the litter water-soluble organic C(DOC),labile pool ? carbon(LP?-C)and labile pool ? carbon(LP?-C)decreased(p<0.05).And total organic carbon(TOC)significantly changed after partial N addition in the middle stages(p<0.05).Humus carbon(HC)significantly increased after N addition in the middle and late stages(p<0.05).However,there was no significant difference in litter TOC,LP-C,LPI-C,LPII-C and DOC contents in the late stage.During the whole decomposition period,N addition increased the recalcitrance index(PRC),although recalcitrant carbon(RP-C)did not change under N addition.Generally,N addition did not affect the accumulation of all studied C components in the early decomposition stage.However,N addition increased the accumulation of TOC,DOC,HC and RP-C in the middle and late stages,as well as the accumulation of LPI-C.In addition,the accumulation of LPII-C was similar during the entire decomposition period.(2)N addition changed the composition of litter C to some extent.As far as litter-derived DOM was concerned,on the one hand,N24 treatment increased humic-like materials and fulvic-like acid at day 10,but N16 and N24 treatments decreased them at day 20.In the middle stage,most of the N treatment reduced humic-like materials and fulvic-like acid litter-derived DOM,whereas protein-like,tryptophan-like and tyrosine-like,soluble microbial products containing amino acids and carbohydrates were observed in advance at N24 treatment.In the late stage,N addition can promote humic-like materials and fulvic-like acid,protein-like,tryptophan-like and tyrosine-like and soluble microbial products to different degrees.On the other hand,the aromaticity index(SUVA254)at N24 treatment decreased in the early and middle stage,and increased in the late stage,although SUVA254 was similar at N6 and N16 treatments.During the whole decomposition period,both humification index of emission and synchronous mode did not change after N addition.In terms of litter-derived labile pool ?(LP?),N16 and N24 treatments decreased fulvic-like acid in the early stage.In the middle stage,N6 treatment decreased fulvic-like acid,whereas N24 treatment increased fulvic-like acid in LPI.However,there was no significant difference among the N treatments in the late stage.In the case of litter-derived labile pool ?(LP?),humic-like materials and fulvic-like acid,protein-like,and soluble microbial products decreased at all N treatment in the early stage,but these materials increased conversely in the later stage.In addition,both ?logK and E4/E6 of the extract liquid of HC were decreased in the middle stage.(3)The CO2 evolution rates of litter were peaked in the early stage,and weaken in the middle stage,finally kept at a relatively low level in the late stage.Most of litter CO2 evolution rates were similar except for an increase of CO2 evolution rates after N24 addition at day 20(p<0.05).Overall,N addition increased the accumulative CO2 release in the middle and late stages of decomposition.At the end of the experiment,compared with the control treatment,the accumulative CO2 release under N6,N16 and N24 treatments increased by 69.75%,76.62%,and 39.93%,respectively(4)In the short-term litter leaching experiment,microorganisms promoted the leaching of litter C.After inhibiting microorganisms,the stage-specific response of litter C leaching to N addition was struck.Specifically,partial N addition increased the leaching rates of total C(TC)and TOC,however,inhibited the leaching rate of total inorganic C(TIC).And N addition slightly promoted the accumulation of TC and TOC leaching at 168 h with microbial mediation.With microbial mediation,N addition decreased leaching rates of TC and TOC from 0 to 4 h,but increased the leaching rate of TIC from 96 to 168 h,as well as leaching rates of TC and TOC at 168 h.Furthermore,most of N addition increased the accumulation of TC,TOC and TIC leaching after 48 h,and their maximum promotion were 71.91%,81.05%and 483.42%,respectivelyThe above results indicated that N addition had little effect on litter TOC contents,however,the response of different litter C fraction to N addition differed.All N treatments promoted the storage of TOC,LPI-C,LPII-C,RP-C,and HC due to the increase of shichito matgrass litter production after N addition,as well as the increases of litter CO2 release and litter C leaching and,thus accelerating the cycle of litter TOC in the soil,water,and atmosphere system.In general,the increase of N load will promote the C storage of coastal shichito matgrass in the soil,also increase CO2 emission in the marsh of River Estuary.In future studies,the response of litter C to N addition from different ecosystem types and vegetation can be carried out in long-term with frequent sampling in the early stage.