Effects of vascular plants on methane emissions from natural wetlands

The presence of vascular plants was recently recognized as one of the key factors controlling methane emissions from natural wetlands because it affects all the processes coupled to production,oxidation,and transport of methane. This paper is a literature summary and study on the progression of research concerning the effects of vascular plants on methane emissions from natural wetlands.Carbon fixed by photosynthesis can be allocated below ground and supplied as decomposable carbon to the soil/sediment through root exudation and plant litter for CH_4-producing bacteria(methanogen).So,the intensity of photosynthesis rate and root density,especially in the presence of the finest roots and root hairs,have important effects on methane production. Rhizosphere,roots,and rhizomes of emergent aquatic macrephytes are habitats for CH_4-oxidizing bacteria(methanotrophs).Vascular plants transport atmosphetric O_2 to the rhizophere for methanotrophs,where rhizospheric oxidation accounts for about 80% of the total methane oxidation,which,during the growing stage, is a much more important process for the consumption of CH_4 than soil surface oxidation.The oxidation of methane may be influenced by environmental factors such as light intensity,nitrogen available,etc. Methane transport through vascular plants is frequently mentioned as one of the major pathways for soil-atmosphere CH_4 fluxes in wetlands.Transport through plants typically accounts for 50～90% of the total methane flux from sediment to the atmosphere,and the magnitude of the contribution is controlled by speciesspecific differences.Different transport mechanisms,such as diffusion and convective transport,are deployed in different species,which lead to variations of transport efficiency.The role of stomatal control of ventilation on methane transport is a controversy issue discussed in this paper. Methane emissions from wetlands are highly variable,both temporally and spatially.Vascular plants,are an important factor,mediating seasonal methane variations from natural wetlands.Different transport mechanisms of vascular plants lead to various diurnal trends of methane.Spatial variations in methane emission can also be connected with characteristics of vascular plants,such as NEE(Net Ecosystem Exchange).Thus some researchers regard vegetation as an important indicator of spatial variations,and that it has predictive value for CH_4 emissions at a large scale.However,to get more accurate evaluation,abiotic factors should be considered.