Relation between methanogenic archaea and methane production potential in selected natural wetland ecosystems across China

Methane (CH4) emissions from natural wetland ecosystems exhibit large spatial variability at regional, national, and global levels related to temperature, water table, plant type and methanogenic archaea etc. To understand the underlying factors that induce spatial differences in CH4 emissions, and the relationship between the population of methanogenic archaea and CH4 production potential in natural wetlands around China, we measured the CH4 production potential and the abundance of methanogenic archaea in vertical soil profiles sampled from the Poyang wetland in the subtropical zone, the Hongze wetland in the warm temperate zone, the Sanjiang marsh in the cold temperate zone, and the Ruoergai peatland in the Qinghai-Tibetan Plateau in the alpine climate zone. The top soil layer had the highest population of methanogens (1.07-8.29 x 10(9) cells g(-1) soil) in all wetlands except the Ruoergai peatland and exhibited the maximum CH4 production potential measured at the mean in situ summer temperature. There is a significant logarithmic correlation between the abundance of methanogenic archaea and the soil organic carbon (R-2 = 0.72, P < 0.001, n = 13) and between the abundance of methanogenic archaea and the total nitrogen concentrations (R-2 = 0.76, P < 0.001, n = 13) in wetland soils. This indicates that the amount of soil organic carbon may affect the population of methanogens in wetland ecosystems. While the CH4 production potential is not significantly related to methanogen population (R-2 = 0.01, P > 0.05, n = 13), it is related to the dissolved organic carbon concentration (R-2 = 0.31, P = 0.05, n = 13). This suggests that the methanogen population might be not an effective index for predicting the CH4 production in wetland ecosystems. The CH4 production rate of the top soil layer increases with increasing latitude, from 273.64 mu g CH4 kg(-1) soil d(-1) in the Poyang wetland to 664.59 mu g CH4 kg(-1) soil d(-1) in the Carex lasiocarpa marsh of the Sanjiang Plain. We conclude that CH4 production potential in the freshwater wetlands of Eastern China is mainly affected by the supply of methanogenic substrates rather than temperature; in contrast, low summer temperatures at high elevations in the Ruoergai peatland of the Qinghai-Tibetan Plateau result in the presence of dominant species of methanogens with low CH4 production potential, which in turn suppresses CH4 production.