HR: 11:20h
AN: B12A-05    [Abstracts]
TI: Nitrogen Additions Increase the Diversity of Carbon Compounds Degraded by Fungi in Boreal Forests
AU: * Gartner, T B
EM: tgartner@uci.edu
AF: University of California-Irvine, Department of Ecology and Evolutionary Biology, 361 Steinhaus Hall, Irvine, CA 92697
AU: Turner, K M
EM: kmturner@uci.edu
AF: University of California-Irvine, Department of Ecology and Evolutionary Biology, 361 Steinhaus Hall, Irvine, CA 92697
AU: Treseder, K K
EM: treseder@uci.edu
AF: University of California-Irvine, Department of Ecology and Evolutionary Biology, 361 Steinhaus Hall, Irvine, CA 92697
AB: Boreal forest soils in North America harbor a large reservoir of organic C, and this region is increasingly exposed to long-range atmospheric N transport from Eurasia. By examining the responses of decomposers to N deposition in these forests, we hope to improve predictions of the fate of boreal carbon pools under global change. We tested the hypothesis that the functional diversity of decomposer fungi would increase under N fertilization in boreal forests where fungal growth was otherwise N-limited, owing to a reduction in competitive exclusion of fungal groups. We collected soil and leaf litter from three Alaskan sites that represent different successional stages at 5, 17, or 80 years following severe forest fire. Each site had been exposed for two years to nitrogen and phosphorus fertilization in a factorial design, with four plots per treatment. Nutrient limitation of fungal growth varied depending on successional stage. The standing hyphal length of decomposer fungi in soil (i.e. Ascomycota and Basidiomycota) responded to neither N nor P in the 5-year old site, increased under N fertilization in the 17-year old site, and increased where N and P was added simultaneously in the 80-year old site (site x N x P interaction: P = 0.001). We used BIOLOG microplates for filamentous fungi to obtain an index of the diversity of carbon use by decomposer fungi; each of 95 wells of these plates contains a different carbon-based compound, as well as a dye that changes color upon metabolism of the compound. Saline leaf litter extracts were mixed with fungal growth medium and then added to the microplates. The number of wells displaying metabolic activity was counted following incubation for five days. We found that N fertilization raised the average number of positive wells per plate from 14 to 27 (P = 0.012), with no significant differences in responses among sites. Phosphorus additions did not alter functional diversity of fungi in any site. Since increases in functional diversity occurred even in forests where fungal growth was not limited by N, alleviation of competitive exclusion does not appear to be the mechanism underlying this response. Our findings indicate that N fertilization could potentially result in the decomposition of a wider variety of organic carbon compounds in boreal forest soil, with possible consequences for CO2 release to the atmosphere.
DE: 4805 Biogeochemical cycles (1615)
DE: 1615 Biogeochemical processes (4805)
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting