Effects Of Plant Invasion On Soil Carbon Dynamics And CH₄ Emissions From Coastal Wetlands

Spartina alterniflora,an invasive alien species,spreads rapidly in the coastal zones of China.It has become the most important invasive plant in coastal wetlands of China and has significant impacts on ecological structure and function of the key zone to the earth.CH₄ is an important greenhouse gas and second only to CO₂.In order to investigate effects of Spartina alterniflora invasion on CH₄ emission and reveal the potential underlying mechanisms of these effects in coastal wetlands of China,each transect was set up in the high and low marshes of wetlands in the Yangtze River estuary,respectively.A pair-wise experimental design between S.alterniflora（invasive plant）and Phragmites australis（native plant）stands in the high marsh,and S.alterniflora and Scirpus mariqueter（native plant）stands in the low marsh,was used at each site of the two transects to minimize the potential effects of background heterogeneities.Compared with native plant stands,S.alterniflora invasion significantly increased plant biomass.Invasion-increase in plant biomass was significantly higher in the high marsh than that in the low marsh,which is beneficial to carbon accumulation in the early succession of coastal ecosystem.S.alterniflora invasion also significantly increased soil moisture,soil organic carbon content,soil nitrogen content,soil microbial biomass carbon and nitrogen contents of coastal wetlands of China.CH₄ emission rates were significantly higher under S.alterniflora than P.australis stands in the high marsh,with mean values of（0.68±0.08）mg/（m²·h）and（0.21±0.01）mg/（m²·h）,respectively.In the low marsh,mean CH₄ emission rate under S.alterniflora stands was（8.31±0.50）mg/（m²·h）during the study period,which was significantly higher than that under S.mariqueter stands（（8.31±0.50）mg/（m²·h））.The difference in mean CH₄ emission between S.alterniflora and P.australis stands in the high marsh（（0.47±0.08）mg/（m²·h））was significantly lower than that between S.alterniflora and S.mariqueter stands in the low marsh（（4.37±0.48）mg/（m²·h））.Our results indicated that the S.alterniflora invasion significantly enhanced CH₄ emissions from coastal wetlands of China,probably mainly through improving the quality and quantity of substrates required for CH₄ production,increasing soil microbial biomass and moisture.The invasion-related CH₄ emissions were highly spatially variable;this variability may have been driven by the soil’s anaerobic environments,induced by hydrological dynamics.The above results showed that:（1）S.alterniflora invasion significantly increased the plant biomass of the Yangtze River estuary wetland,and the increased plant biomass invading to low tidal flats was significantly higher than that of invading to high tidal flats,meaning that the invasion increased the Yangtze River estuary wetland.Carbon input is conducive to carbon accumulation in the early stages of wetland ecosystem succession.（2）Spartina alterniflora invasion significantly increased soil water content,soil organic carbon content,total nitrogen content,microbial carbon and nitrogen content in the Yangtze River estuary wetland,indicating that S.alterniflora invasion increased soil anaerobic degree and improved CH₄ produces the quality and quantity of the desired substrate.（3）S.alterniflora invasion significantly increased soil microbial carbon,total carbon pool and organic carbon pool in the Yangtze River estuary wetland,but had no significant effect on the inorganic carbon pool accounting for more than 60%of the total carbon pool of the soil,indicating the invasion of S.alterniflora.The resulting total carbon stock change in the soil is mainly achieved by increasing the soil organic carbon pool.（4）The CH₄ emission of S.alterniflora community was significantly higher than that of the indigenous plant community.The mutual flower invasion increased the quality and quantity of the substrate required by CH₄,increased the soil water content and the amount of microorganisms,and significantly increased the Yangtze River estuary wetland CH₄.Emissions.（5）The increase of CH₄ emission from S.alterniflora invasion to low tide beach is about 10 times that of S.alterniflora invasion to high tide beach,indicating that the impact of S.alterniflora invasion on the Yangtze River estuary wetland on CH₄ emission may be very high.Strong spatial heterogeneity,the invasion of S.alterniflora into a more anaerobic soil environment may have a greater impact on CH₄ emissions.（6）S.alterniflora invasion also increased soil carbon input and carbon output,but the invasion also significantly increased the soil carbon pool indicating that increased soil carbon input was significantly higher than increased soil carbon output,indicating that S.alterniflora invasion may It will enhance the soil carbon sink intensity and carbon sequestration capacity of the Yangtze River estuary wetland.However,long-term systematic monitoring studies are still needed to comprehensively and quantitatively assess the comprehensive ecological impact of S.alterniflora invading China’s coastal wetlands.These results can be applied to more reliably estimate and predict invasion-induced changes in CH₄ emissions from wetlands in the context of global climate change.These results also can provide theoretical basis and scientific support for scientific management and rational utilization of coastal zone resources as well as coping with global climate change.