PARENT SESSION
Contributed Oral Session 146: Biogeochemistry: Nutrient Dynamics; Carbon Sequestration
Thursday, August 11, 1:30 PM - 5:00 PM, Meeting Room 524 C, Level 5, Palais des congrès de Montréal

Microbial community composition suggests spatially explicit patterns of C, N, P biogeochemistry in two southeastern U.S. floodplain forests.

Navaratnam, John^*,1, Walbridge, Mark¹, ¹ West Virginia University, Morgantown, WV, USA

ABSTRACT- Microbial communities are an important and yet comparatively unexplored component of phosphorus (P) retention and transformation in freshwater wetlands. Floodplain forests (FFs) play a key role in the retention and transformation of P received from upland hydrological inputs and overbank flooding, thereby improving water quality in aquatic ecosystems downstream. Phosphates can be transformed to organic P prior to export, or retained within FFs through sediment deposition, soil adsorption, plant uptake, and/or microbial immobilization. Although microorganisms are important short-term sinks for phosphate in freshwater wetlands, little is known about how microbial diversity affects P retention and transformation. We investigated microbial diversity in surface soils collected from one alluvial (Wateree R., SC) and one blackwater (Black R., NC) FF. At each site, soils were collected from higher elevation (less frequently flooded) ridges and lower elevation (more frequently flooded) swales. We established a library of 520 archaeal, eubacterial, and fungal isolates using soil DNA extraction, PCR amplification, plasmid cloning, and sequence analysis. A majority of the archaea were the CH4-producers, Methanosarcina and Methanobacteria spp. Among the eubacteria, obligate anaerobic N-fixers were limited to frequently flooded swales, while facultative anaerobic denitrifiers were distributed independently of microsite elevation. Acidobacterium spp., known to function in enhanced biological phosphorus removal, were common to both sites but more prevalent in ridges. Denaturing gradient gel electrophoresis (DGGE) analysis on soils from the alluvial site revealed a dominant fungal species, Verticillium coccosporum (representing 59% of ridge and 43% of swale isolates in the clone library), which primarily degrades particulate organic carbon. A DGGE profile of soil samples from the blackwater site, revealed the dominant fungal isolate Cryptococcus podzolicus (representing 40% of ridge and 57% of swale isolates in the clone library), known to metabolize phospholipids. Overall, data suggest diverse microbial metabolic activities related to C, N, and P cycling, with differences in biogeochemical processing in both ridges vs. swales, and alluvial vs. blackwater FFs.

Key words: Floodpalin forests, Phosphorus, Microbiology, DGGE