UC Irvine

We assessed the degree to which ectomycorrhizal fungi exploit organic nitrogen in situ. In an Alaskan boreal forest, we identified pairs of sporocarps from five taxa of ectomycorrhizal fungi. We added 13C-labeled alanine to the soil surrounding one sporocarp within each pair; the second served as an unlabeled control. Peak rates of 13C-respiration from alanine were higher in the labeled sporocarp plots than the controls, indicating that the 13C-alanine was detectably respired from the soil. “Reference” plots adjacent to the sporocarps served as an indication of background 13C-respiration rates released by the soil community as a whole. Ectomycorrhizal sporocarps displayed higher 13C-respiration rates than their reference plots. Thus, the sporocarps and associated mycorrhizal mycelium appeared to contribute significantly to the release of alanine-derived 13CO2, confirming the hypothesis that ectomycorrhizal fungi may access soil amino acid pools under natural conditions.