Methanogenic pathway and fraction of CH(4) oxidized in paddy fields: seasonal variation and effect of water management in winter fallow season.

A 2-year field and incubation experiment was conducted to investigate δ(13)C during the processes of CH4 emission from the fields subjected to two water managements (flooding and drainage) in the winter fallow season, and further to estimate relative contribution of acetate to total methanogenesis (Fac ) and fraction of CH4 oxidized (Fox ) based on the isotopic data. Compared with flooding, drainage generally caused CH4, either anaerobically or aerobically produced, depleted in (13)C. There was no obvious difference between the two in transport fractionation factor (εtransport ) and δ(13)C-value of emitted CH4. CH4 emission was negatively related to its δ(13)C-value in seasonal variation (P