| Salt marsh acts as dual function of carbont sources and sinks of greenhouse gases (GHG),which plays an important role in the fixation and release of greenhouse gases such as CO2, CH4 and N2O, and poses important impacts on global climate change. The study of CO2, CH4 and N2O in different types of salt marsh soils in Yancheng coastal wetland is valuable for the further study of carbon and nitrogen cycling in wetland.The rate of soil greenhouse gas emission from Phragmites australias saltmarsh (PAS), Spatina alternifora saltmarsh (SAS),Suaeda salsa saltmarsh (SSS)was measured in the field, field experiment and indoor temperature-controll culturing experimenst were conducted to analyze the GHG flux characteristics and influencing factors of greenhouse gas emissions in three salt marsh soils. The results show:Three salt marsh soil were CO2 emission sources,the total flux of soil carbon dioxide was SAS>PAS> SSS, the average annual flux was 499.51 mg·m-2·h-1,323.67 mg·m-2·h-1,150.41 mg·m-2·h-1.The seasonal variation of soil temperature was the main reason for the seasonal variation of soil CO2, soil moisture and soil CO2 flux were positively correlated. The root respiration of PAS, SAS and SSS accounted for 52.6%, 64.8% and 5.0% of total soil CO2 emissions respectively. The difference of root respiration was one of the important reasons for the spatial heterogeneity of CO2 emission in saltmarsh soil.Three salt marsh soil were CH4 emission sources, the total CH4 flux of soil was SAS> PAS>SSS,the average annual flux was 2.08 mg·m-2·h-1,0.57 ·m-2·h-1,0.15 mg·m-2 h-1. There was a positive correlation between soil CH4 flux and atmospheric temperature, and the CH4 flux of SAS was significantly correlated with atmospheric temperature. Soil water and soil CH4 flux were positively correlated. The presence of roots provides sufficient nutrition for soil microbes, which contribute to the rate at which bacteria produce CH4. In SPS and SAS, the CH4 flux of root soil was 25 times and 1.7 times higher than that of root-free soil. The root has the least effect on the CH4 flux of SSS.The N2O fluxes of the three salt marsh soils were characterized by alternate source and sink,but the overall performance was emission. The total N2O flux was SAS > SSS > PAS,the average annual flux is 5.63 μg·m-2·h-1,3.27 μg·m-2·h-1,1.76 μg·m-2·h-1.The relationship between soil moisture and soil N2O was more complex, and there was a weak positive correlation between water and N2O in PAS.With the double effect of tide and rainfall, there was a phenomenon that water and N2O emission are inhibited in SAS and SSS. The effect of lower temperature on soil N2O flux was not obvious.The results of the indoor simulation experiment showed that: PAS, SAS, SSS have the lowest CO2 emission rates at 5 ℃,the highest at 40 0C.The highest values were 481.96 mg·m-2· h-1, 394.00 mg·m-2·h-1,218.29 mg·m-2·h-1. In PAS,SAS and SSS, the rate of soil respiration was 11.22%, 9.83%and 6.13%, respectively, at 1℃ for each temperature increase. The temperature sensitivity of soil CO2 was PAS (2.19)> SSS (2.15)> SAS (1.58). The temperature increase of the N2O emission of the PAS was 10℃ to 30 ℃. SAS’s N2O emissions increase the temperature range of 5℃～20℃.SSS’s N2O emission temperature increase interval of 5℃～25 ℃. The temperature sensitivity of soil N2O was SAS (1.24)> PAS (1.18)> SSS (1.03). The GWP of PAS, SAS and SSS were 6.3 7x 104 kg·hm2·a-1, 8.67×x104 kg·hm-2·a-1, 4.16 x104 kg·hm-2·a-1. The contribution of the three salts to global warming was SAS> PAS> SSS. |
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