Theses and Dissertations

Issuing Body

Mississippi State University

Advisor

Williams, Mark

Committee Member

Kingery, Bill

Committee Member

Baldwin, Brian

Committee Member

Peterson, Daniel

Committee Member

Schultz, Tor

Date of Degree

4-30-2011

Original embargo terms

MSU Only Indefinitely

Document Type

Dissertation - Campus Access Only

Major

Agronomy

Degree Name

Doctor of Philosophy

College

College of Agriculture and Life Sciences

Department

Department of Plant and Soil Sciences

Abstract

This study was conducted to determine dynamics of bacterial communities during decomposition and to find out whether the occurrence of bacterial communities was affected by soil and residue types. It was hypothesized that there would be a shift in bacterial community structure during decomposition. Also, distinct microbial communities in different two soils associated with two residues would result in colonization by different microbial taxa. The first hypothesis was based on expected changes in the composition of decomposing residues. The second hypothesis was based on the fact that soil microbial diversity is soil-specific and immense with numerous different functionally redundant but phylogeneticaly different microbial types. Residues with different chemical properties were also expected to affect bacterial community composition, however, its impact would be lesser compared to soil. 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 distinct separation of the communities at day 3 which coincided with high levels of cellulase enzyme activity and reduction of soluble carbon. style='mso-spacerun:yes'> Availability of labile carbon appeared to be important in driving bacterial community succession at early stage of colonization. During the later stages of decomposition (day 23-110), bacterial communities were segregated into two groups according to soil type. Although important, this segregation was relatively small compared to the community-level similarities observed between the soils and residues. For example, 16 of the 22 most abundant OTU's, dominated by a-,b- and style='fontamily:Symbol'>g- Proteobacteria, Bacilli and Shingobacteria, were shared among all soil and residue treatments indicating that residue decomposition is carried out by few key-player taxa. These results run counter to our hypothesis and suggest that decomposition process may be mediated by certain domineering bacterial taxa which occur at the later stage of decomposition. Further research is needed to determine whether key functional ecosystem processes are dominated by only a few taxa despite taxonomically hyper-diverse soils.

URI

https://hdl.handle.net/11668/16286

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