Collaborative Research: Defining the Scope and Consequences of Ectomycorrhizal Fungal Control on Forest Organic Matter Decomposition

Fungi play an essential role in forest ecosystems, breaking down leaf litter and woody debris that has fallen to the forest floor. As this organic matter is decomposed by fungi, much of it is incorporated into soils, adding to the significant carbon and nitrogen pools they harbor. There is growing recognition that ectomycorrhizal fungi, which form nutritional symbioses with many forest trees, can slow the breakdown of organic matter and stabilize soil carbon. This research seeks to critically assess how ectomycorrhizal fungal suppress organic matter decomposition, and to characterize the impacts of this suppression on soil carbon and nitrogen dynamics. Determining how ectomycorrhizal fungi mediate carbon and nutrient fluxes during the decomposition of organic matter will be useful for forest management focused on carbon retention in soils and on tree health. In addition, defining the scope of ectomycorrhizal fungal suppression of organic matter decomposition across diverse temperature and moisture conditions will be important for accurately formulating carbon and nitrogen dynamics in Earth system models. This project provides support for science, technology, engineering and math (STEM) graduate and undergraduate mentoring, K-12 experiential learning, and public engagement through collaborations with the Cedar Creek Ecosystem Science Reserve, Minute Earth, California Academy of Sciences, and the Florida Museum of Natural History.

The capacity of ectomycorrhizal fungi to modify organic matter decomposition is hypothesized to depend on three factors: organic matter chemistry, ectomycorrhizal fungal community composition, and environmental conditions. This hypothesis will be tested with a series of field-based experiments at research sites in Minnesota, Florida, and California. By utilizing a single research site in Minnesota in which a wide range of organic matter types are concurrently deployed across forest stands differing in ectomycorrhizal fungal community composition, the independent and interactive roles of organic matter chemistry and ectomycorrhizal fungal community composition can be determined while holding multiple environmental variables constant. At the same time, by deploying a common organic matter type across multiple sites varying in temperature and precipitation (in Minnesota, Florida, and California), the extent to which variation in edaphic conditions influence ectomycorrhizal fungal suppression of organic decomposition can also be assessed. Additionally, detailed analyses of the carbon held in various soil fractions will provide a critical missing link between ectomycorrhizal fungal-induced changes in organic matter decomposition rates and retention of carbon in soil.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.