Plant Residue Retention Releases Dissolve Organic Carbon from Paddy Soils Priming CH4 Production.

Management of rice residue in paddies often results in higher methane (CH₄) emissions, but the carbon (C) sources contributing to higher emissions are not well characterized.  We examined the relative contribution of soil and residue C sources for CH₄ production in three different soils using ¹³C-labeled rice residues.  Residue addition induced substantial releases of dissolve organic carbon (DOC) from soil organic matter (SOM), resulting in up to 3-fold increases in this source of C when compared to the non-residue treatment.  This straw-induced production accounted for from 30% to 90% of the total DOC in various soils, but most of the values decreased over time as a result of decomposition.  As anticipated, CH₄ production was also increased by residue addition, with the timing and magnitude of emission varying across soils, likely due to differences in soil C and availability of electron acceptors (EAs).  Further partitioning the sources of CH₄ production demonstrated that 30 to 50% of CH₄ was derived from SOM.  The straw-induced production of CH₄ from SOM was positively correlated to the degree of residue decomposition (R² = 0.97, p < 0.05).  Our results suggested that plant residue retention can cause significant DOC production from paddy soils, which requires careful field management to minimize its potential export, and its stimulatory effect on CH₄ production may vary across soils having diverse EA concentrations.