Is soil enzyme activity related to the identity of ectomycorrhizal fungi colonizing tree roots in a northern hardwood forest?

Background/Question/Methods

Ectomycorrhizal (ECM) fungi are able to produce extracellular and cell-bound enzymes that catalyze the hydrolysis of nitrogen (N) and phosphorus (P) containing compounds in soil organic matter as well as other enzymes involved in the degradation of lignin and cellulose.  Enzyme activities seem to vary among ECM fungal species. Since ECM fungal communities are usually highly diverse we explored whether the activities of α-glucosidase (AG-a type of cellulase), β-glucosidase (BG-a type of cellulase), N-acetyl-glucosaminidase (NAG-a type of chitinase) and acid phosphatase (PHOS) were related to identity of ECM fungi colonizing plant roots.  We collected 60 soil cores to a depth of 5 cm in a beech-maple forest in Northeastern Ohio.  Roots were separated from soil and DNA was extracted from root tips.  Terminal restriction fragment length polymorphism (TRFLP) profiles were obtained after PCR amplification of the internal transcribed spacer (ITS) region of the rRNA gene to determine the presence of mycorrhizas and their proportional abundance within each soil core.  Enzyme activities were determined on fresh soil samples using a standard fluorometric analysis.  A portion of the soil was used to determine soil moisture, pH, C, N and NaHCO₃ extractable organic and inorganic P.
Results/Conclusions

Enzyme activities were significantly correlated with certain ECM genera. NAG activity was positively correlated with species of the genus Russula and negatively correlated with members of the Boletus genus while PHOS activity was positively correlated with the Hymenoscyphus genus. Except for NAG all enzyme activities were positively correlated with soil C and N content, but not soil C/N ratio.  Only the genus Tomentella was positively correlated with soil C and N content while the other ECM genera were not related to those parameters.  However, the genus Tomentella was not significantly correlated with soil enzyme activity.  Although soil environment may control ECM distribution, specific ECM genera also appear to affect soil enzyme activity and soil function in different ways.  Experiments that can address the individual abilities of ECM genera and species to access soil nutrient pools not otherwise directly available to host plants will further advance our understanding of the functional consequences of ECM fungi and ECM diversity.