Incorporation of 13C-labeled rice-straw-derived carbon into microbial communities in submerged rice field soil and percolating water

Rice straw is a major organic material applied to rice fields. The microorganisms growing on rice-straw-derived carbon have not been well studied. Here, we applied 13C-labeled rice straw to submerged rice soil microcosms and analyzed phospholipid fatty acids (PLFAs) in the soil and percolating water to trace the assimilation of rice-straw-derived carbon into microorganisms. PLFAs in the soil and water were markedly enriched with 13C during the first 3 days of incubation, which indicated immediate incorporation of rice-straw-derived carbon into microbial biomass. The enrichment of PLFAs in the percolating water with 13C suggested that microorganisms other than the population colonizing rice straw also assimilated rice-straw-derived carbon or that some bacterial groups were selectively released from the straw. The microbial populations could be categorized into two communities based on the carbon isotope data of the PLFAs: those derived from rice straw and those derived from soil organic matter (SOM). The composition of the PLFAs from the two communities differed, which indicated the assimilation of rice-straw-derived carbon by a subset of microbial populations. The composition of rice-straw-derived PLFAs in the percolating water was also distinct from that in the soil.