| The carbon cycle is a vital part in the cycle of mass and energy fluxes of ecosystem. Wetland soil is the source and sink of various green gas and important pool of organic carbon with high carbon density and long-term of storage, and which is very sensitive to the global climate change. At present, researching on the mechanism of wetland carbon cycle mainly focus on the wetland in high latitude temperate zone, but lack in the subtropical wetland. In this study, three typical wetland ecosystems in subtropical monsoon climate zone were picked as the research objects. We simulated the decomposition process of wetland soil organic matter in the aerobic and anaerobic conditions. The CO2, CH4emission flux and other indicators like soil organic carbon (SOC), dissolved organic carbon (DOC), total nitrogen (TN), carbon-nitrogen ratio (C/N) and pH value.etc. were measured in the process of laboratory culture frequently. From this study, we wanted to know more about the greenhouse-gas emission in subtropical different kinds of wetland soil and some affective factors on the organic matter decomposition. The main research harvests are as follows:(1) The content of soil organic matter in three types of wetland was significant different, ranging from16to32mg/g. There existed a huge diversity of SOC in each sample point of the lake-wetland, but, in the city secondary wetland and artificial wetland, the difference was little, comparatively.(2) During the period of70d incubation, the CO2took the most part of the gas released, about1-3mg/g. In anaerobic condition, the CO2emission was slightly higher than that of it in aerobic condition. The accumulated CO2emission was positively related to the content of SOC and TN. The amount of CH4released was much lower than that CO2. In aerobic group, the cumulative CH4emission was about0.2-1ug/g, and, in anaerobic group, the amount was about0.3-28ug/g. Emission of CH4from paddy soil under anaerobic condition was far more than the other two species of wetland types. The higher CH4flux in the ecosystem made more CH4oxidizing bacteria in the soil. In both aerobic and anaerobic condition, the CO2release could be divided into three stages in each sampling point. The rate of release at first14days was rather high but dropped very quickly. And then, at the day from14to45the emission curve became stable. In the last25days, the emission rate gradually attenuated. This phenomenon was caused by the soil samples were pretreated by air-drying, grinding and sifting, after the start of culture soil rewetting. The soil CH4releasing was mainly concentrated in for fifteen days after the start of culture. In each sampling, there was no consistent and regular pattern on the CH4emission. The majority of SOC was relatively stable and not easy to be decomposed, so the change of it with the culture was not significant. As the culture time lengthened, the ability of releasing CO2, CH4by unit SOC decreased significantly, the SOC tended to be stable. The organic nitrogen accounted for the most part of the TN in the wetland sediment and the NH4+-N occupied approximately0.6-2.6%of total nitrogen pool. The content of NO3--N in soil kept little (about1-10%of NH4+-N) throughout the whole culture period. Hence, the inhibition effect of NO3--N on methane production was feeble. The soil pH value increased significantly in7days of the experiment, and the value packed at20-27days. Then it decreased slowly. The process of ammonium nitrogen produced by the decomposition of organic compounds containing nitrogen was the main driving force leading to sustained pH value rising, in anaerobic culture. The DOC was mainly composed by carbohydrate, polysaccharide, carboxylic acids, aromatic etc.. With the culture time lengthened, the percentage of polysaccharides and aliphatic compounds decreased but the proportion of carboxylic acids increased. In aerobic, the unit quality of DOC could release more CO2, and more DOC would be generated in anaerobic culture conditions. The CO2and CH4emission rate was tightly concerned with DOC concentration. Moreover, in aerobic culture group, when the DOC aromatic degree increased, the CO2, CH4emission rate would decrease, and the DOC became more difficult to decompose. In anaerobic culture group, no correlation was concluded between the release rate of CO? and the DOC aromatic degree.(3) According to the wetland hydrology type classification can be found that the cumulative release amount of seasonal waterlogged wetland CO2emission was significantly higher than that of perennial water soil and the soil without water. Emission of CH4from paddy soil under anaerobic condition was far more than the other two species of wetland types, and the oxide rate was correspondingly higher. The CO2emission rate of the waterlogged wetland soil would be comparatively reduced in aerobic short-term culture. |
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