Mycorrhizal fungi differ in form and function with well defined differences in their ability to degrade soil organic matter. As such, mycorrhizas affect soil carbon storage and the response of ecosystems to global change via direct [e.g., decomposition] and indirect [e.g., nutrient retention with hyphae] pathways. Over the last decade our research group has examined plant-mycorrhizal interactions in the hope of better understanding patterns of belowground plant-C allocation, how this C affects the costs of nutrient acquisition and the role of mycorrhizal vs. saprotrophic microbial activity in regulating decomposition and the provisioning of nutrients to host plants. The objective of this talk is to present this research beginning with local-scale observations in a mid-latitude forest in central Massachusetts, USA where we use in-growth cores to study soil organic matter decomposition. I then discuss our research from other sites and the results of a meta-analysis of belowground C allocation.
We have found a clear imprint of ectomycorrhizal fungi on the ecology and biogeochemistry of soils and the soil-C cycle. At the stand scale, the presence of ectomycorrhizal roots and/or hyphae stimulates the decomposition of soil organic matter to a greater extent than arbuscular mycorrhizal tree roots or hyphae. At the global scale we find that the costs of nutrient acquisition varies inversely with climate [e.g., high latitude = high cost, low latitude = low cost] because of changes in the composition of mycorrhizal communities and plant-mycorrhizal competition for those nutrients. An emergent property of this interaction is vast storages of C at high latitudes despite exceptionally low rates of primary production. These results suggest a scalable connection between climatic and biotic drivers of the soil C cycle.