Dynamics and Phylogenetic Composition of Soil Bacterial Communities During Colonization and Decomposition of Straw Residues.

The dynamics of bacteria during the colonization and decomposition of plant residues has received some attention, but their roles are much less known than that of fungi. This study was conducted to determine whether soil and straw type would impact the colonization and occurrence of bacterial communities on decomposing residues. It was hypothesized that the distinct microbial communities found in two different soils would result in colonization by different microbial taxa. Residues with different chemical properties were also expected to display different bacterial communities. A 2 x 2 x 4 factorial experiment was conducted consisting of Switchgrass (Panicum virgatum) and Rice (Oryza sativa) straw; 2 soil types (Sharkey and Marietta series); and 4 incubation periods ( 3, 23, 48 and 110 days). Clone libraries of the bacterial communities were constructed from the detritusphere (residues and adhering soil).  Non-metric multidimensional scaling of the detritusphere communities showed a distinct separation of the communities at Day 3 which coincided with high levels of cellulase enzyme activity and the disappearance of soluble C.  The availability of labile C may be important in driving bacterial community succession during this early stage of colonization. During the later stages of decomposition (Day 23-110), bacterial communities were segregated into two groups according to soil type. This segregation was important but relatively small compared to the community-level similarities showed between the soils and residues. For example, 16 of the 22 most abundant OTU's, which were dominated by a-,b- and g- Proteobacteria, Bacilli and Shingobacteria, were shared among all soil and residue combinations. These results run counter to our hypothesis and suggest that the decomposition process may be mediated by certain domineering bacterial taxa. Further research is needed to determine whether key functional ecosystem processes are dominated by only a few taxa despite taxonomically hyper-diverse soils.