Monday, November 13, 2006

Microbial Community Succession on Plant Litter, from the Phyllosphere to the Rhizosphere.

Jude Maul, Cornell University, 147 Plant Science, Ithaca, NY 14850, United States of America and Laurie Drinkwater, 124 Plant Science, Cornell University, Ithaca, NY 14853, United States of America.

In this study we use molecular genetic techniques to quantify succession of the microbial community across a sequence of decompositional stages in two contrasting plant litters. Prediction of the rate and mechanisms of plant litter decomposition is important to understand long-term soil fertility as well as fluxes of carbon within the soil environment. Throughout the process of decomposition the quality and location (microhabitat) of the litter changes, creating or destroying niches for decomposer organisms.  We hypothesize that as litter is decomposed the changes in quality and microclimate will result in successional changes in the microbial community. Succession will reflect the transition from fast growing copiotrophic taxa on fresh litter to slow growing oligotrophic taxa occupying the partially decomposed buried litter. We have used taxon specific PCR primers coupled with terminal restriction fragment length polymorphism (TRFLP) techniques to determine the change in distribution of a-Proteobacteria, b-Proteobacteria, Actinobacteria, Firmicutes, Bacteroidetes, Acidobacteria, and Basidiomycota (fungi) on decomposing litter of either White clover (Trifolium repens) or Reeds canary grass (Phalaris arundinacea).  The microbial communities on both plant materials were assess in three locations (Phyllosphere, on soil surface, and buried in bulk soil) and in either the litter source plot or exchanged into the contrasting litter source plot for a total of 10 treatments per replicate.  We found microbial communities on the litter tended to shift from being dominated by b-Proteobacteria on the fresh litter (phyllosphere) to Acidobacteria and a-Proteobacteria on the soil surface. Acidobacteria dominated the microbial community on the litter buried in the soil.  Reeds canary grass, with a high lignin content, tended to support more Basidiomycota in the soil surface and burred litter treatments than White clover.