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

CH4 emission and the concentration of dissolved CH4 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 CH4 emission and CH4 concentration in the soil solution and floodwater. A positive seasonal correlation was also observed in the variation between CH4 flux and CH4 concentration in soil solution. The seasonal total CH4 emission (51.6 g CH4 m(-2)) in Treatment WS (straw applied) was about 168% higher than that in Treatment CK (without straw). The emitted CH4 and CH4 in soil solution were initially relatively enriched, then depleted and finally enriched again in C-13 in both treatments, while CH4 in floodwater became isotopically heavier. The carbon isotopic signature of emitted CH4 and CH4 in floodwater averaged around -62 parts per thousand and -45 parts per thousand for both treatments, respectively, and was not significantly influenced by the application of straw. However, straw application caused the CH4 in soil solution to be significantly depleted in C-13 during the middle of the rice season, and the mean delta C-13 value was lower in WS (-57.5 parts per thousand than in CK (-49.9 parts per thousand). Calculation from the isotopic data showed that straw application increased the fraction of CH4 oxidized, causing no significant difference in the delta C-13 value of the emitted CH4 between the two treatments.