Straw Application Altered CH4 Emission,Concentration and 13C-Isotopic Signature of Dissolved CH4 in a Rice Field

CH 4 emission and the concentration of dissolved CH 4 in soil solution and floodwater in a rice field and their stable carbon isotopic signatures as affected by straw application were investigated in 2009 in a field experiment at Jurong,Jiangsu Province,China.Straw application increased CH 4 emission and CH 4 concentration in the soil solution and floodwater.A positive seasonal correlation was also observed in the variation between CH 4 flux and CH 4 concentration in soil solution.The seasonal total CH 4 emission(51.6 g CH 4 m 2) in Treatment WS(straw applied) was about 168% higher than that in Treatment CK(without straw).The emitted CH 4 and CH 4 in soil solution were initially relatively enriched,then depleted and finally enriched again in 13 C in both treatments,while CH 4 in floodwater became isotopically heavier.The carbon isotopic signature of emitted CH 4 and CH 4 in floodwater averaged around 62‰ and 45‰ for both treatments,respectively,and was not significantly influenced by the application of straw.However,straw application caused the CH 4 in soil solution to be significantly depleted in 13 C during the middle of the rice season,and the mean δ 13 C value was lower in WS(57.5‰) than in CK(49.9‰).Calculation from the isotopic data showed that straw application increased the fraction of CH 4 oxidized,causing no significant difference in the δ 13 C value of the emitted CH 4 between the two treatments.