PARENT SESSION
Oral Session #22: Mycorrhizae and ecosystem function.
Presiding: A. Tuininga
Monday, August 5. 1:00 PM to 3:45 PM. Grand Ballroom East, Radisson.

Mycorrhizal influences on soil carbon processing: the fate of root and hyphal inputs.

Langley, Jonathan^*,1, Johnson, Nancy¹, Koch, George¹, Hungate, Bruce¹, ¹ Northern Arizona University, Flagstaff, AZ, USA

ABSTRACT- It is well known that mycorrhizal type and abundance affect ecosystem nutrient cycling by increasing mineral uptake, and by active breakdown of recalcitrant organic matter. Direct contributions of mycorrhizae to the soil system have been overlooked. By strongly altering root architecture and chemistry, mycorrhizal colonization status could influence root decomposition rates. Hyphal production represents a tremendous sink for plant photosynthate in many systems, yet the fate of hyphae in soil is largely unexplored. We surveyed chemical parameters for mycorrhizal and nonmycorrhizal roots for arbuscular (AM) and ecto-mycorrhizal (EM) plant species. Mineral nutrients (N, P, Ca) that tend positively affect decomposition rates occur in higher concentrations in mycorrhizal than nonmycorrhizal roots, as do more recalcitrant compounds (chitin, lignin, phenolics). We grew Helianthus annuus with a suite of AM inocula and under sterile conditions. Pinus edulis roots from the field were visually sorted according to the presence of EM structures. To each species a fertilizing treatment was applied in order to generate root litter that varied in mineral nutrient concentration independently of mycorrhizal status. We monitored carbon dioxide evolution from microcosms of native soil, mycorrhizal and uncolonized root systems from each species. AM and EM fungal presence stunted CO₂ evolution in early stages of decomposition. Increased mycorrhizal colonization, often found under elevated CO₂, could represent a mechanism by which soil carbon content may increase.

KEY WORDS: arbuscular mycorrhizae, belowground litter, decomposition, ectomycorrhizae