Methanogenesis and methane oxidation in wetlands. Implications in the global carbon cycle

Resumo

Wetlands are important ecosystems on the Earth. They are distinguished by the presence of water, saturated anoxic soils, and different kinds of vegetation adapted to this conditions. Organic matter in these environments is mineralized mainly in the sediments throughout anaerobic processes where sulfate reduction is one of the most important terminal stages of anaerobic decomposition in coastal wetlands, whereas methanogenesis is important in freshwater wetlands. In this environments, methane, a greenhouse gas, is produced as a result of the activity of a large and diverse group of methanogenic bacteria (Domain Archaea). The generated methane can be diffused to the atmosphere or can be oxidized by several microorganisms under aerobic and anaerobic conditions, such microorganisms intercept and consume this gas diminishing its emission to the atmosphere. The production and consumption of methane in wetlands involve complex physiological processes of plants and microorganisms, which are regulated by climatic and edaphic factors, mainly soil temperature and water table level. The interaction of these processes with heterogeneous environments results in large variations in the methane fluxes. Because methane is an important gas that contribute with as much as 15% to the greenhouse effect, several studies had analyzed methane production and its emission from wetlands. These studies established that natural and agricultural freshwater wetlands represent approximately 40% of the sources of atmospheric methane. However, most of the ecological studies assessing the production, consumption, and emission of methane have been performed in boreal and temperate wetlands, yet there are few studies evaluating these activities in tropical wetlands, particularly in Brazil and Panama. In Mexico there are not studies contributing to this respect.