PS 7-61
Decomposition by ectomycorrhizal fungi alters soil carbon storage and efflux

Monday, August 5, 2013
Exhibit Hall B, Minneapolis Convention Center
Jessica A.M. Moore, Ecology and Evolutionary Biology, The University of Tennessee, Knoxville, TN
Wilfred M. Post, Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN
Aimee T. Classen, Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville

Interactions between plants and their symbiotic mycorrhizal fungi are at the interface of above and belowground systems and their interactions can influence soil carbon (C) dynamics. Plants allocate a portion of their C to mycorrhizae, where it becomes hyphal biomass. In return, mycorrhizal fungi increase plant water and nutrient uptake. However, when plants become stressed the symbiosis can breakdown as they reduce C allocation to mycorrhizae. Mycorrhizae then shift to gain C via soil organic matter (SOM) decomposition. The plant-mycorrhizal interaction could become a source of C to the atmosphere instead of a sink. The shift from sink to source is two-fold: with plant stress hyphal biomass no longer stores plant C, and mycorrhizal fungi begin to acquire C from soil. The effect magnitude of ectomycorrhizal C acquisition, whether from plants or SOM, is crucial to predicting soil C efflux to the atmosphere and storage in soils. In this study we asked (1) if soil C is reduced and efflux is increased when plants are defoliated, and (2) if there is a threshold of plant defoliation that causes a change in the magnitude of soil C storage and efflux. We addressed this question using mathematical theory and a greenhouse experiment.


Decomposition by ectomycorrhizal fungi reduces soil C storage and increases efflux compared to ectomycorrhizal fungi that do not decompose SOM. Our results demonstrate that when plants are defoliated soil C storage decreases by 10-40% due to ectomycorrhizal decomposition compared to when ectomycorrhizae do not decompose SOM. There is a threshold, according to our mathematical model, between 30 and 60% defoliation where the effect of mycorrhizae on soil C storage is minute. This is likely due to reduced total enzyme production associated with low mycorrhizal abundance when plants are defoliated. We manipulated plant defoliation in a regression design from 0 – 50% in a greenhouse experiment to validate our theoretical findings. In all, our study suggests that belowground interactions play a key role in C storage and release from soil.