The variation of methane emission from freshwater marshes and response to the exogenous N in Sanjiang Plain Northeast China

摘要

The methane emitted from freshwater marsh is the difference between the production and oxidation of CH_4 which reaches the atmosphere via diffusion, ebullition, or by passage through aerenchymous tissues of higher plants. To evaluate the variation of CH_4 emission and the effects of increased exogenous N on CH_4 emission, we have raised in situ the exogenous N with the rates of OgNm~(-2) (control), 6 g N m~(-2) (low nitrogen level), 12 g N m~(-2) (medial nitrogen level) and 24 g N m~(-2) (high nitrogen level), respectively, in Sanjiang Plain marsh ecosystem Northeast China. CH_4 emissions were measured using the static chamber and gas chromatogram techniques. The daily average CH_4 emission during the different growing stages from the marsh varies from -0.06 to 13.54 mg CH_4 m~(-2) h~(-1) with the daily observation. The exogenous N significantly increased the mean seasonal CH_4 emission rate by 181% (low nitrogen level, P < 0.01), 254% (medial nitrogen level, P < 0.01) and 155% (high nitrogen level, P < 0.01), respectively. The effects of exogenous N strongly interacted with the plant aboveground biomass, which was a variable explaining most variation in CH_4 emission. We also find the net effect of exogenous N on CH_4 emission from freshwater marshes most likely depends on the counterbalance between the N-induced increases in CH_4 production and oxidation, as a N excess may result in the inhibition of CH_4 emission, and in the stimulation of CH_4 emission.