The Impact of the Mycorrhizal Association of Understory Plants on Soil Dynamics in Temperate Forests

The dominant plant-fungal framework for understanding nutrient cycling in forests typically focuses on the dominance of ectomycorrhizal (ECM) and arbuscular mycorrhizal (AM) overstory trees. However, ericoid mycorrhizal (ERM) fungi and their associated understory shrubs are also common in temperate forests, yet often overlooked in larger scale nutrient cycling assessments. These fungi have different nutrient mining capabilities, and therefore likely vary in their environmental characteristics and interactions. We approached understanding mycorrhizal functional type ecology in the context of northeastern North American temperate forests by analyzing a suite of soil and microbial characteristics in plots of both ECM and ERM plant- association within a single forest stand. To analyze differences in nutrient cycling, we assessed microbial biomass, carbon mineralization, and soil nitrogen mineralization. We also explored if these different mycorrhizal associations store nutrients differently by analyzing the carbon and nitrogen content of six different ecosystem pools: leaf, stem, fine root, coarse root, soil minerally associated matter (MAOM) and soil particulate organic matter (POM). We then investigated the effects of a large pulse of nitrogen consistent with ungulate birth on these two different mycorrhizal-plant systems to explore if they respond differently to nutrient inputs. We found significant differences in underlying nutrient cycling and storage within the soil-plant system depending on mycorrhizal type. In addition, the two communities had different extent of C mineralization and N mineralization increase in response to the experimental nitrogen pulse. Demonstrating these differences underlines the importance of understanding mycorrhizal-plant associations in soil nutrient dynamics and storage capacities, which can vary significantly even on the local within-stand scale and gives support to calls for further consideration of ericoid mycorrhizal fungi and shrubs in this framework. Further effort in this vein could be important for the effective management of forests and forest soils for hardwood production, carbon sequestration, and other desirable services.