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The Impact of Elevated CO2 on a Widespread Ectomycorrhizal Fungi

Paper Reviewed
McCormack, M.L., Fernandez, C.W., Brooks, H. and Pritchard, S.G. 2017. Production dynamics of Cenococcum geophilum ectomycorrhizas in response to long-term elevated CO2 and N fertilization. Fungal Ecology 26: 11-19.

Ectomycorrhizal (EM) fungi play an important role in soil biogeochemical cycles and substantially influence net ecosystem primary production. Yet, despite their importance in this regard, little is known about how EM fungi might respond to both natural and anthropogenic changes in climate.

Seeking to provide some knowledge in this regard, McCormack et al. (2017) set out to study a widespread and abundant EM fungi, Cenococcum geophilum, which maintains a near-global distribution, having been observed in "essentially all forested biomes ranging from high latitude boreal forests, temperate forests, as well as wet and dry tropical forests." Specifically, they used minirhizotron camera systems to examine the spatial and temporal changes in C. geophilum in a loblolly pine stand in central North Carolina over a 12-year period (1999-2010) in response to elevated CO2 and nitrogen treatments. CO2 enrichment (+200 ppm above ambient) was provided using Free-Air-CO2-Enrichment (FACE) technology and was initially administered 24 hours per day, except when air temperatures fell below 5 °C or when wind speeds exceeded 5 ms-1. Midway through the experiment in 2003, CO2 enrichment was limited to daylight hours only. Nitrogen fertilization was applied to half of the ambient and CO2-enriched plots at a rate approximately an order of magnitude larger than background deposition rates.

Results of the analysis revealed that nitrogen fertilization strongly decreased C. geophilum production while CO2-enrichment increased it. Averaged across their entire study, McCormack et al. report there was "roughly 50% greater production of C. geophilum ectomycorrhizas with elevated CO2 compared to control plots but this difference was only significant during the second half of the study despite large initial decreases." Nitrogen fertilization, in contrast, reduced production by 83% compared to background levels. McCormack et al. also report that there was no significant interaction between elevated CO2 and nitrogen fertilization on the persistence (lifespan and disappearance) of C. geophilum ectomycorrhizas.

In light of the above findings, it would appear that, given the near-global distribution of this EM fungi and its importance in stimulating ecosystem productivity, the positive impact of elevated CO2 on C. geophilum production (~50% increase for a 200 ppm rise) represents a welcomed benefit for the future of Earth's forests.

Posted 18 September 2017