PS 30-116 - CANCELLED - Mycorrhizal fungi-plant associations and intra-stand variation of nutrient cycling and storage

Background/Question/Methods

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 microbial 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 (MOAM) and soil particulate organic matter (POM).

Results/Conclusions

We found significant differences in nutrient cycling and storage within the soil-plant system depending on mycorrhizal type. ECM plants demonstrated significantly higher nitrogen mineralization rates while both carbon mineralization rates and microbial biomass were not significantly different between fungal types. Analysis of nitrogen concentrations across the pools (leaf, stem, fine roots, coarse roots, POM, and MAOM) showed significant differences, with ECM having significantly higher nitrogen concentrations in almost all pools. The percentage of total carbon was significantly related to mycorrhizal functional type for the leaf and MAOM pools, where ERM associations had higher carbon storage in leaves, and ECM higher storage in MAOM. 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.