Straw application in paddy soil enhances methane production also from other carbon sources

Abstract. Flooded rice fields are an important source of the greenhouse gas methane. Methane is produced from rice straw (RS), soil organic matter (SOM), and rice root organic carbon (ROC). Addition of RS is widely used for ameliorating soil fertility. However, this practice provides additional substrate for CH4 production and results in increased CH4 emission. Here, we found that decomposing RS is not only a substrate of CH4 production, but in addition stimulates CH4 production from SOM and ROC. Apart from accelerating the creation of reduced conditions in the soil environment, RS decomposition resulted in enhancement of SOM-derived CH4 production. In particular, hydrogenotrophic methanogenesis from SOM-derived CO2 was stimulated, presumably by H2 released from RS decomposition. On the other hand, the enhancement of ROC-derived CH4 production after RS application was probably caused by the significant increase of the abundance of methanogenic Archaea in the RS treatment compared with the untreated control. Our results show that traditional management of rice residues exerts a positive feedback on CH4 production from rice fields, thus exacerbating its effect on the global CH4 budget.