**1. Introduction**

The Amazon rainforest, well known for its vast biodiversity, is a unique ecosystem and plays an irrefutable role in the maintenance of global ecosystem services. The Amazon biome is one of the main contributors to the biogeochemical functioning of the terrestrial system [1]. A contributor to this functioning is the soil, which

is considered one of the most complex and variable environmental compartments. The understanding of microbially mediated biogeochemical processes in this compartment is of particular interest in continental floodplains, where nutrient cycling is highly responsive for floating hydrology, and the gases produced in the soil may influence the global climate change [2].

Methane (CH4) is one of the most important greenhouse gases (GHG). Amazonian wetlands are considered a significant source of CH4 emissions. In addition to the positive emission of GHG such as CH4, the wetlands provide a diverse range of vegetation that enables the sequestration of organic carbon.

Arguably, the most striking variation in the nature of the forests in the Amazon floodplains system is related to seasonal flooding. Variations in the level and flow of water, along with variations in temperature and sediment load, for example, are the most important factors to guide the structure and functioning of flood systems [3, 4]. The flood pulse, responsible for the change in soil saturation, makes those areas predisposed to the activity of the anaerobic microbial community. In the absence of electron acceptors, CH4 is the final product of anaerobic decomposition of organic matter. The anaerobic oxidation of CH4 may occur in the presence of some of these electron receptors (iron, manganese, and sulfate) and nitrogenous forms (nitrite and nitrate).

Given the recent recognition of the importance of Amazonian floodplains for the global dynamics of the CH4 cycle, we emphasize the essential role of information from these systems as a key factor for the amelioration of CH4 emission models. Thus, microbiota data combined with *in situ* observations can successfully lead to new approaches of CH4 emission models for these ecosystems. This review first addresses the soil microbiota and the mechanisms related to them as part of the dynamics of the CH4 cycle. The initial topics include microbial characteristics, mainly of saturated systems (e.g., anaerobic metabolism and interactions with metals). The chapter synthesizes studies that assessed possible consequences regarding changes in hydrology caused by climate change. Subsequently, a synthesis of the different integrated approaches is reported: biogeochemistry, isotope, and soil metagenomics, revealing the importance of interfacing different methodologies to develop a more trustworthy representation of that system. The chapter ends by identifying the knowledge on the emission models in Amazonian floodplains, as well as suggests the incorporation of new variables into those models.
