Effect of Inorganic Nutrients on Relative Contributions of Fungi and Bacteria to Carbon Flow from Submerged Decomposing Leaf Litter |
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Authors: | V Gulis K Suberkropp |
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Institution: | (1) Department of Biological Sciences, University of Alabama, Tuscaloosa, AL 35487, USA, US |
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Abstract: | The relative contributions of fungi and bacteria to carbon flow from submerged decaying plant litter at different levels of
inorganic nutrients (N and P) were studied. We estimated leaf mass loss, fungal and bacterial biomass and production, and
microbial respiration and constructed partial carbon budgets for red maple leaf disks precolonized in a stream and then incubated
in laboratory microcosms at two levels of nutrients. Patterns of carbon flow for leaf disks colonized with the full microbial
assemblage were compared with those colonized by bacteria but in which fungi were greatly reduced by placing leaf disks in
colonization chambers sealed with membrane filters to exclude aquatic hyphomycete conidia but not bacterial cells. On leaves
colonized by the full microbial assemblage, elevated nutrient concentrations stimulated fungi and bacteria to a similar degree.
Peak fungal and bacterial biomass increased by factors of 3.9 and 4.0; cumulative production was 3.9 and 5.1 times higher
in the high nutrient in comparison with the low nutrient treatment, respectively. Fungi dominated the total microbial biomass
(98.4 to 99.8%) and cumulative production (97.3 and 96.5%), and the fungal yield coefficient exceeded that of bacteria by
a factor of 36 and 27 in low- and high-nutrient treatments, respectively. Consequently, the dominant role of fungi in leaf
decomposition did not change as a result of nutrient manipulation. Carbon budgets indicated that 8% of leaf carbon loss in
the low-nutrient treatment and 17% in the high-nutrient treatment were channeled to microbial (essentially fungal) production.
Nutrient enrichment had a positive effect on rate of leaf decomposition only in microcosms with full microbial assemblages.
In treatments where fungal colonization was reduced, cumulative bacterial production did not change significantly at either
nutrient level and leaf decomposition rate was negatively affected (high nutrients), suggesting that bacterial participation
in carbon flow from decaying leaf litter is low regardless of the presence of fungi and nutrient availability. Moreover, 1.5
and 2.3 times higher yield coefficients of bacteria in the reduced fungal treatments at low and high nutrients, respectively
(percentage of leaf carbon loss channeled to bacterial production), suggest that bacteria are subjected to strong competition
with fungi for resources available in leaf litter. |
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