Soil nutrient legacies surpass the effects of CO2 and O3 concentration on mycorrhizal fungal communities

Background/Question/Methods

The role of atmospheric chemistry in structuring ecosystems, and the biological communities within them, has increasingly been recognized as a strong determinant of ecological structure and dynamics. Two important gases, carbon dioxide (CO₂) and ozone (O₃), have been afforded special attention based on their elevated levels following industrialization, and their effects on ecosystem health and vigor. Indirect effects on mycorrhizal fungi occur through changes in C fixation cascading through to the fungal symbionts. Previous studies have also demonstrated the importance of changing nutrient availability in structuring mycorrhizal fungi and their community dynamics. At the AspenFACE site, we studied the response of ectomycorrhizal fungal communities to elevated CO₂ and O₃ over a pre-existing soil nutrient gradient within a deciduous forest ecosystem, expressing this response in terms of above- and below-ground productivity and abundance.

Results/Conclusions

We have found that reproductive responses to CO₂ and O₃ levels are relatively straightforward: CO₂ increases sporocarp production while O₃ can inhibit production, ultimately leading to convergence of sporocarp communities over time. Belowground, however, mycorrhizal response is contingent on soil nutrient legacies. These nutrient levels have changed over time, but remain consistent in their relative ranks among plots. Individual fungal species’ responses to elevated CO₂ and O₃ become elucidated once nutrient levels are taken into account. Thus, response of ectomycorrhizal fungal communities to CO₂ and O₃ appears to be contingent on soil nutrient availability. These results have strong implications for understanding mycorrhizal fungal community dynamics within the context of global environmental change.