Mangrove ecosystems are an important component of "blue carbon". However, it is not clear whether the stems play roles in the CH4 budget of mangrove ecosystems. This study investigated the CH4 emission from mangrove stems and its potential driving factors. We set up six sample plots in the Zhangjiang Estuary National Mangrove Nature Reserve, where Kandelia obovata, Avicennia marina and Aegiceras corniculata are the main mangrove tree species. Soil properties such as total carbon content, redox potential and salinity were determined in each plot. The dynamic chamber method was used to measure mangrove stems and soil CH4 fluxes. Combined field survey results with Principal Component Analysis (PCA) of soil properties, we divided the six plots into two sites (S1 and S2) to perform statistical analyses of stem CH4 fluxes. Then the CH4 fluxes from mangrove tree stems and soil were further scaled up to the ecosystem level through the mapping model. Under different backgrounds of soil properties, salinity and microbial biomass carbon were the main factors modified soil CH4 fluxes in the two sites, and further affected the stem CH4 fluxes of mangroves. The soil of both sites are sources of CH4, and the soil CH4 emission of S2 was about twice higher than that of S1. Results of upscaling model showed that mangrove stems in S1 were CH4 sinks with -105.65 g d-1. But stems in S2 were CH4 sources around 1448.24 g d-1. Taken together, our results suggested that CH4 emission from mangrove soils closely depends on soils properties. And mangrove stems were found to act as both CH4 sources and CH4 sinks depend on soil CH4 production. Therefore, when calculating the CH4 budget of the mangrove ecosystem, the contribution of mangrove plant stems cannot be ignored.
Keywords: Emission and consumption; Mangrove stem; Mangrove tree species; Methane; Soil; Subtropical mangrove wetland.
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