The effect of rice straw on the priming of soil organic matter and methane production in peat soils

• Straw addition releases large amounts of DOC from SOM.
• Straw addition induces SOM mineralization.
• Straw addition causes unidirectional succession of microbial community.
• Straw addition induces strong and positive priming effect on CH4 production.
• The priming effect on CH4 production is non-linear and last for long period of time.

Rice residue management often leads to increased methane (CH4) emissions but the outcomes of edaphic and management factors are not always predictable. Rice residue can act as a substrate for CH4 production; however the role it plays in priming (mineralization) of soil organic matter (SOM) to release additional substrates for CH4 production are not well established. We anaerobically incubated a highly organic soil with 13C-enriched rice straw for 3 months to investigate its priming effect (PE) on SOM and source of C for CH4 production. Anaerobic decomposition of SOM was accompanied by iron (Fe) reduction with minimal CH4 production when straw was absent. Straw addition enhanced Fe reduction and increased CH4 production concurrently with a clear succession of microbial community structure and function assessed with phospholipid fatty acid (PLFA) profiling. The PE on CH4 production from SOM was strong and positive during the entire experiment. Overall, PE on SOM (CO2 plus CH4 production) was slightly positive at the end of the experiment, associated with only a 32% mineralization of the added straw-C (as CO2 plus CH4). Straw addition also released large amounts of dissolved organic carbon (DOC) from SOM. Our results suggest that straw addition effects on PE of SOM and CH4 production can last for a long period of time showing that straw will cause non-linear response in CH4 production and potentially result in significant losses of soil C as DOC by leaching or direct exports in histosols.