Defense Date

2009

Document Type

Thesis

Degree Name

Master of Science

Department

Biology

First Advisor

Rima Franklin

Second Advisor

S. Leigh McCallister

Abstract

The decomposition of plant litter is a critical biological function that aids in nutrient cycling and energy transfers within and between ecosystems. The primary decomposers of dead leaf material are bacteria and fungi, though there is no consensus as to which of these groups is dominant, nor is it known how the abundance and composition of these communities changes over time. The objectives of this study were to examine the relative contributions of bacterial and fungal populations to leaf organic matter (OM) decomposition and to consider the effect of moisture availability on the microbial community. The study was conducted across three habitats of differing moisture regimes: an upland terrestrial site, an emerging freshwater marsh, and an established freshwater swamp. Litterbags were constructed using two types of vegetation: a standardized substrate, maple leaves, and the site-specific vegetation, deployed in November 2007 following plant senescence, and retrieved after 0, 3, 6, 10, and 16 months of field incubation. The samples were then analyzed for decomposition as % OM remaining, total carbon and nitrogen content (C:N), dissolved organic carbon (DOC) release, microbial respiration via 14C heterotrophic uptake of acetate, and microbial community composition via terminal restriction fragment length polymorphism (T-RFLP) analysis. The results demonstrated that moisture regime is a significant factor in decomposition, with high decomposition at wetter sites. Vegetation type also impacted decomposition, as maple leaves were found to decay more similarly across sites, while the breakdown of site-specific vegetation varied more. These findings lack evidence to suggest one variable, moisture or vegetation time, as the driving factor of decomposition. Respiration rates varied greatly between sites and over time. Surprisingly, fungi were found to be a significant contributor to respiration at sites of high moisture, which suggests a need to better incorporated their activity in carbon budgets. Microbial communities were unique at each site and shifts were observed over time for both the bacterial and fungal populations. Changes in community structure were well correlated with changes in OM quality and quantity, though specific relationships varied by site. Future work determining functional groups and taxa of these microbial assemblages would provide a deeper knowledge of the role of these communities on decomposition processes. A better understanding of how differences in soil moisture impact decomposition rates will provide greater insight on the carbon sequestered or released from a habitat, which may be particularly important with global climate change. Although sites of high moisture exhibited accelerated decomposition, moisture alone may not be the driving factor. In turn, variables associated with high moisture, such as increased nutrients, should be further researched as they may actually be behind the increase in decomposition.

Rights

© The Author

Is Part Of

VCU University Archives

Is Part Of

VCU Theses and Dissertations

Date of Submission

August 2009

Included in

Biology Commons

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