Influence of rice straw on priming of soil C for dissolved organic C and CH4 production

Aims We investigated the priming effect (PE) of plant residue on soil organic carbon (SOC) to release substrates for methane (CH 4 ) production. Methods Carbon-13-labeled rice straws were anaerobically incubated with paddy soils with a range of SOC contents (2%, 6% and 15%) for 32 days. Stable isotope techniques were used to partition the production of dissolved organic carbon (DOC) and CH 4 into their sources, and the PE was quantified. Results Straw addition resulted in up to a 3-fold increase in the release of DOC from SOC with the largest magnitudes found in the 15% SOC soils, where the priming of DOC production was associated with the reduction of Fe 3+ to Fe 2+ . In straw-amended soils, SOC was always the dominant source of DOC. Nonetheless, the primed DOC production did not result in a proportional increase of CH 4 production. The contribution of SOC to CH 4 production increased 30 to 50% with residue addition, depending on SOC content. However, more than 52% of the total CH 4 production was straw-derived. The straw-induced priming of CH 4 from SOC sources was positively correlated to the degree of residue decomposition, while the priming efficiency of straw on CH 4 production was seemingly negated by the existence of various electron acceptors. Conclusions Our results suggest that field residue incorporation will exacerbate the role of rice paddies as significant sources of atmospheric CH 4 , and likely DOC as well.