Ectomycorrhizal enzyme production is largely resilient to N-deposition in a Mediterranean forest system

Background/Question/Methods:

                Ectomycorrhizal fungi are critical mutualists for many woody plants. Trees of the genus Pinus are particularly reliant on ectomycorrhizal fungi to aid nutrient uptake in forest systems where much of the soil nutrient pool is contained in organic matter and unavailable to trees. One common forest disturbance that has been shown to alter the community composition of ectomycorrhizal fungi is increasing ecosystem nitrogen concentration from anthropogenic sources (N-deposition).  Though N-deposition has been shown in many systems to alter ectomycorrhizal community composition, there is little known about whether ectomycorrhizal function is affected.

                We used a well-established N-deposition gradient in southern California to ask whether the extracellular enzyme production of ectomycorrhizae is affected by N-deposition. Root tips colonized by ectomycorrhizal fungi were removed from soil cores collected beneath the canopy of ponderosa pine at 8 sites along the N-deposition gradient and assayed for the production of 10 enzymes typically produced by soil fungi. 

Results/Conclusions:

                 Enzyme assay results indicated that production was not strongly affected by N-deposition for most enzymes and that the enzyme production function of ectomycorrhizal fungi is largely resilient to this disturbance. However, the activity of peroxidase, an enzyme that targets recalcitrant soil components decreased with N-deposition. Contrary to expectations, leucine amino peptidase activity, an enzyme that targets organic N sources, had a positive relationship with N-deposition. These results suggest that N-deposition does not strongly influence the enzyme production function of ectomycorrhizal communities for most enzymes.