Here we use a top-down and bottom-up approach in landscape ecology to analyze the active microbes processing methane fluxes (FCH4) in seasonally flooded-forest (FOR) andtraditional farming systems (TFS) in Amazonian floodplains flooded with black, white, and clear water. Our results revealed higher CH4 emissions from water-atmosphere interface in clear water floodplain, followed by black and white water floodplain, respectively. Active methanogenic and methanotrophic taxa were ubiquitous at 0-15 and 15-30 cm soil layer in FOR and TFS, with differences among the water types with respect to the richness, evenness and diversity of the methanogenic communities. These ecological results were not generalizable regarding to FOR and TFS sites, soil layers, and non-flooded and flooded periods. Despite the predominant oxidation of CH4 in the non-flooded period, higher richness and diversity of methanotrophs were revealed for FOR and TFS in the flooded period. In turn, the structure of the methanogenic and methanotrophic communities and their variation were influenced mainly by soil physicochemical factors, water type, soil depth and the presence of nitrifiers, as Nitrososphaera and Nitrospira. Our study reveals a signature across methanotrophic communities in soils from Amazon floodplain with different water types, with a putative disproportionate role of NC10 phylum in CH4 mitigation in natural and agricultural Amazonian floodplains. These findings open the possibilities to explore the role of NC10 phylum in the carbon cycling in Amazon.
Amazon floodplain ecosystems include open water and intermittent flood forest and agricultural systems with different water types. They are a significant natural source of methane (CH 4) in the tropics. When soils are flooded and become anoxic, CH 4 is produced by methanogenesis, while microbially mediated aerobic and anaerobic oxidation of CH 4 serves as the primary biological sink of this greenhouse gas. Measurements of rates and controls on CH 4 production and emission in the Amazon basin mainly come from studies on individual wetlands and floodplain lakes. Similarly, microbial communities in those Amazon floodplain habitats have been studied on individual lakes based on sequence-specific DNA analysis. Existing biogeochemical ecosystem models of CH 4 from the Amazon floodplains focus on soil properties or involve factors such as pH, redox potentials, or substrates. None of these models incorporate appropriate seasonal inundation; neither the microbiota does it as a component. In this sense, our chapter will highlight how the important efforts already contributed to understand the CH 4 emission and its connections with abiotic and biotic factors in Amazon floodplains, as well as emphasize the need of encouraging cooperation and exchange of experience between research teams by using different approaches and scientific methods.
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