| Estuarine intertidal wetland is an important component of the global carbon cycle with high carbon density.It receives large soil organic carbon?SOC?from the terrestrial ecosystem and then emits small carbon molecules such as carbon dioxide?CO2?and methane?CH4?into the atmosphere after carbon decomposition and mineralization,which increased atmospheric greenhouse gases concentrations and held responsible for global climate warming.Plant litter is an exogenous source of SOC,and it connects the material and energy between wetland and terrestrial ecosystems.The changes of its quantity or quality not only affect the carbon cycle of wetland,but also intensify the climate warming.Therefore,the study of SOC decomposition characteristics and mechanism in wetland with plant litter addition is conductive to scientifically evaluate the carbon function and quality of wetland soil,and thus improve the understanding of global carbon cycle mechanism.Based on the National Science Foundation?NO.41473094?,named‘Effects of Estuary Wetland Vegetation on the Generation and Emission of CH4 and N2O and Its Control Mechanism',this study performed two stages of incubation experiments of the soil from the Yangtze estuarine wetlands over a period of 120 days,to investigate the effects of plant litter addition on SOC components as well as the emissions of CO2and CH4,and to explore the contributions and effects of new carbon input on wetland SOC decomposition.The main research results and conclusions are:?1?The culture-online analysis system of gas concentration and carbon isotope characteristics was established by using the self-designed incubation apparatus and online gas isotope analyzer.The online system can analyze trace gas fluxes of CO2and CH4 as well as carbon isotope changes generated in the wetland soil.?2?With the addition of plant litter,the rates of CO2 and CH4 generated by the SOC decomposition presented two stages,with a rapidly increasing rate in the early stage,and then a small and stable rate in the later stage.The litter addition significantly promoted the SOC decomposition and the production of CO2?P<0.01?and CH4?P<0.05?.Different plants showed different effects on soil gas emissions due to their varied nature components and decomposition characteristics.The effect of Scirpus mariqueter on SOC decomposition was greater than those of Spartina alterniflora and Phragmites australis.Soil CO2 and CH4 emissions increased significantly with the litter addition from the stem and leaf of P.australis?P<0.05?.?3?With the addition of plant litter,the cumulative emission of CO2-C and CH4-C were 4-11 times and 51-1391 times higher than the soil without litter addition,respectively.Under the treatment of leaf and stem addition,the cumulative CO2-C emissions were 3-13 times and 2-10 times higher than that of no addition,respectively.Besides,the cumulative emissions of CH4-C were 13-87 times and 5-76 times higher than that of control soil,respectively.All groups with plant litter additions showed the higher incremental proportions of CO2-C and CH4-C in the total emissions than the proportion of plant litter in the total carbon input.The decomposition rate of fresh organic carbon input from plants was higher than that of the original SOC,which turned out plant litter was the main source of wetland CO2 and CH4 emissions.?4?Without the addition of plant litter,TOC,MBC and EOC decreased during the period of SOC decomposition,except of the increased DOC.Besides,the litter decomposition significantly increased the contents of SOC and LOC?P<0.05?.Different plants had different effects on SOC.For instance,among the three typical plants in Dongtan,S.mariqueter>S.alterniflora>P.australis.The effects also varied in different plant organs,P.australis leaf>P.australis stem.?5?There was a significant positive correlation between TOC and EOC?P<0.01?.LOC was significantly negatively correlated with DOC?P<0.05?,but positively correlated with EOC?P<0.01?.The correlation coefficient of LOC and EOC was the largest,which suggested that the changes of EOC and LOC were consistent during the period of soil decomposition.Soil physical and chemical properties affected the changes of organic carbon components.TOC and EOC were negatively correlated with granularity?P<0.05?.The contents of TOC,EOC and MBC were positively correlated with moisture content?P<0.05?,and the contents of TOC and EOC were negatively correlated with pH?P<0.05?.?6?According to the changes of soil and plant litter?13C,it showed that soil?13C had a slight decrease during the process of organic carbon decomposition.Besides,plant litter?13C changed and affect the soil?13C.?13C values of different plant organs also varied slightly,but the differences were much smaller than those caused by different photosynthetic pathways.According to the?13C value characteristics of the CO2 produced by SOC and plant,the?13CO2 produced by soil increased,while the?13CO2 produced by plant dwindled.It may be related to the fractionation in the process of SOC decomposition and the selective decomposition of organic matter.?7?The addition of glucose alone increased the cumulative emission of soil CO2-C by 20.80%38.19%,and the cumulative emission of CH4-C by 3.50%.When P.australis litter?stem/leaf?and glucose were added together,the cumulative emissions of soil CO2-C were 1.19%and 61.17%higher than that of soil with only P.australis stem litter or P.australis leaf litter.Meanwhile,glucose increased the decomposition of P.australis leaf by 67.23%,and P.australis stem by 1.29%.?8?In this study,with the addition of plant litter and glucose,the proportion of soil CO2-C emission increment in the total CO2-C emission?Litter:57.18%92.12%,glucose:17.22%27.64%?and the proportion of soil CH4-C emission increment in the total CH4-C emission?Litter:79.92%98.85%,glucose:about 3.39%?were both higher than the proportion of carbon addition in the total carbon?Litter:32.55%48.17%,glucose:1.72%?.Therefore,most of the CO2 and CH4 emissions in wetland soil are derived from the fresh organic carbon due to the exogenous labile carbon input promoted soil microorganisms to take advantage of the easily available carbon source. |
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