Partitioning of CH4 and CO2 Production Originating from Rice Straw, Soil and Root Organic Carbon in Rice Microcosms

Flooded rice fields are an important source of the greenhouse gas CH(4). Possible carbon sources for CH(4) and CO(2) production in rice fields are soil organic matter (SOM), root organic carbon (ROC) and rice straw (RS), but partitioning of the flux between the different carbon sources is difficult. We conducted greenhouse experiments using soil microcosms planted with rice. The soil was amended with and without (13)C-labeled RS, using two (13)C-labeled RS treatments with equal RS (5 g kg(-1) soil) but different δ(13)C of RS. This procedure allowed to determine the carbon flux from each of the three sources (SOM, ROC, RS) by determining the δ(13)C of CH(4) and CO(2) in the different incubations and from the δ(13)C of RS. Partitioning of carbon flux indicated that the contribution of ROC to CH(4) production was 41% at tillering stage, increased with rice growth and was about 60% from the booting stage onwards. The contribution of ROC to CO(2) was 43% at tillering stage, increased to around 70% at booting stage and stayed relatively constant afterwards. The contribution of RS was determined to be in a range of 12-24% for CH(4) production and 11-31% for CO(2) production; while the contribution of SOM was calculated to be 23-35% for CH(4) production and 13-26% for CO(2) production. The results indicate that ROC was the major source of CH(4) though RS application greatly enhanced production and emission of CH(4) in rice field soil. Our results also suggest that data of CH(4) dissolved in rice field could be used as a proxy for the produced CH(4) after tillering stage.