Enzyme production as a key mycorrhizal trait
Results/Conclusions: Exclusion of mycorrhizas in ectomycorrhizal-dominated systems increased CO2 respiration, nitrogen mineralization rates, and production of hydrolytic enzymes per unit microbial biomass. This is indicative of competition between ectomycorrhizal fungi and free-living decomposers for soil nutrients. The magnitude of the exclusion effect also scaled with ectomycorrhizal abundance: sites with higher levels of ectomycorrhizal fungi exhibited greater increases in carbon and inorganic nitrogen cycling upon mycorrhizal exclusion. Excluding arbuscular mycorrhizal fungi in the arbuscular mycorrhizal system had no detectable effect on carbon or nitrogen cycling. Reciprocal transplants showed that net nitrogen mineralization rates significantly declined when arbuscular mycorrhizal soils were moved to the ectomycorrhizal stand. In contrast, more nitrogen was mineralized when ectomycorrhizal soils were moved to the arbuscular mycorrhizal stand. While these results are limited to a single set of experimental conditions in a particular temperate forest, evidence is mounting from many systems that this distinction between mycorrhizal classes is useful for predicting mycorrhizal effects on ecosystem level carbon and nitrogen cycling rates. Further distinctions in fungal enzyme production, such as different types of oxidative and cellulolytic enzymes, may be useful for understanding soil and ecosystem level processes.