Tuesday, November 6, 2007 - 12:00 PM
188-10
Differences in Growth Form between Soil Bacteria and Filamentous Fungi Mediate Their Response to Elevated Atmospheric CO2.
An increase in the ratio of fungal:bacterial biomass in soil is frequently observed in ecosystems with experimentally-enhanced levels of atmospheric CO2. We hypothesized that saprotrophic fungi can take advantage of increased plant detrital inputs under elevated CO2 due to their predominantly hyphal growth form. This allows fungi to penetrate plant litter and integrate patchily-distributed soil resources, giving them an advantage over single-celled bacteria in degrading plant litter. This hypothesis was tested by an incubation experiment using plant detritus and soil collected from the Rhinelander FACE experiment. Soil was amended with plant detritus as either intact or ground particles; grinding was performed to remove barriers within the plant tissue (i.e. protection of cellulose by lignin). Ground detritus was also applied in a uniform or patchy distribution within the soil. Our hypothesis was supported by the finding that bacteria incorporated the most detrital C (measured using a 13C tracer) when ground detritus was applied in a uniform distribution, simulating both removal of barriers within the plant litter and a uniform distribution of resources through the soil. Surprisingly however, ground detritus applied in a uniform distribution increased fungal biomass as much as ground detritus applied in a patchy distribution. The increase in fungal:bacterial ratio due to enhanced atmospheric CO2 therefore appears to be due to both the advantage that fungi have in exploiting patchily-distributed resources and an inherent physiological advantage that fungi have over bacteria in degradation of plant detritus.
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