Mechanism Of Methane Emission From The Mire And Cultivated Mire Soils

To estimate the magnitude of methane emission from mires in China and to understandâ‘ temporal and seasonal pattern of methane emission from the freshwater marsh,â‘¡the effect of plants on methane emission from the freshwater marsh andâ‘¢cultivation, fertilizer application and set-aside effects on atmospheric methane uptake in the drained marsh, the fluxes of methane emissions from and methane, dissolved organic carbon (DOC) and acetate concentrations in porewater in the freshwater marsh or the peatlands as well as redox potential in the vertical profile and plant biomass were measured in the field in Sanjiang plain, Heilongjiang province, northeast China, and in Hongyuan county, Sichuan province, west China.The flux rate of methane emission from the peatland in Qinghai-Tibet highland and the freshwater marsh in Sanjiang plain ranged from 0.16 to 10.0 mg CH4 m-2 h-1 with an average of 2.96 mg CH4 m-2 h-1 and 0.16-54.6 mg CH4 m-2 h-1 with an average of 19.6 mg CH4 m-2 h-1. The low flux in Qinghai-Tibet highland was due to low methane production stemmed from low temperature in summer. Based on our in situ measurement and the available data measured in previous studies around China, the estimated budget of methane emission from mires in China was 1.76 Tg a-1.The fraction of methane emission through Carex lasiocarpa, Carex meyeriana and Deyeuxia angustifolia was 72, 86 and 31%, respectively. Carex laisocarpa made a greater contribution to methane oxidation than to methane production and Carex meyeriana contributed equally to both functions, whereas Deyeuxia angustifolia stimulated methane production. As the depth of the standing water in the freshwater marsh increased and cyperaceous plants replaced the gramineous plants, the capacity of plants to transport methane from the marsh into the atmosphere increased, however the comprehensive effect of plants on methane production decreased.The flux rate of methane emission from the freshwater marsh vegetated with the different type of plants over the measuring period was in the following order: Carex lasiocarpa > Carex meyeriana > Deyeuxia angustifolia. Standing water depth determined the type of marsh plants, which governed methane transport, and the amount of plant litters inundated in water, which resulted in the difference in dissolved organic carbon for methanogenesis. The latter in turn affected methane concentration in porewater and methane emission. The aboveground plant biomass and plant density controlled spatial variation of methane emission from plots within a certain marsh.There was an apparent diel variation of methane emission from the marsh vegetated with Carex lasiocarpa with a peak at 9:00 and the lowest at 0:00. By contrast, an unclear diel pattern was observed in the Deyeuxia angusitfolia marsh. The diel variation was due likely to the variation of methane oxidation in the rhizome and rehizosphere, which was caused by the difference in the magnitude of oxygen produced through plant photosynthesis over the course of the day, and to the variation of methane production responding to diel variation of temperature.There was an apparent seasonal variation in methane concentration in porewater in the Carex lasioarpa marsh. Low metehane concentration in June was due likely to low temperature and high redox potential resulted from the more oxygen content in the rhizosphere rather than to unavailability of acetate, which inhibited methane production.The marsh is not only a source but also a sink for atmospheric methane when it was drained. Cultivation of the drained marsh enhanced bulk density of the surface soil and greatly destroyed optimal niche of methanotrophic community, which enhanced diffusion resistance of methane and oxygen and reduced methane uptake rate. Nitrogen fertilizer application increased NH4+ content in the surface soil, which possibly decreased methanotroph population and activity, leading to reduction of methane uptake. Cultivation strongly affected methane uptake rate at the initial stage of marsh cultivation and nitrogen fertilizer slowly reduced but persistently affected methane uptake.