Bacterial Composition and Diversity During Early Decomposition of Rice Straw.

Research has been conducted on residue decomposition and the associated dynamics of microbial communities in soil. Information on the dynamics bacterial colonization during the early stages of residue decomposition, however, are limited. Bacterial community composition during early stages rice straw decomposition in soil were thus investigated. Following one and two week incubations (20^oC),16S rRNA clone libraries were constructed from bulk soil and detritusphere (residues and adhering soil) samples. A total of 429 clones produced 197 operational taxonomic units (OTU; D=0.03). At both sampling times, DOTUR analysis showed that bacterial communities developing in straw detrituspheres had no common taxonomic units with those in the soil. The communities in the detritusphere overlapped considerably between week one and two, however, there was no overlap between the communities sampled from the bulk soil at either time. The communities in the detritusphere and the bulk soil during week 1 were dominated by relatively few members (34 and 31 OTU’s respectively). In contrast, the community in the bulk soil during week 2 was described showed no dominance and was described by an even distribution (78 singletons). These results suggest that the detritusphere habitat favors a few community members. Most likely these members were derived from the bulk soil and were not detected there because of low population numbers. We suspect that during the first week of decomposition, water soluble organics in the residues would have triggered the growth and fostered the dominance of the detected bacterial heterotrophs. During this time a portion of the water soluble substances would have diffused into the bulk soil and promoted the growth and dominance of other bacterial groups. During the second week the production and diffusion of these water soluble compounds probably slowed, which resulted in substantial turnover of the dominant members.