Productivity and community structure of ectomycorrhizal fungal sporocarps under increased atmospheric CO2 and O3.

Sporocarp production is essential for ectomycorrhizal fungal recombination and dispersal, which influences fungal community dynamics. Increasing atmospheric carbon dioxide (CO2) and ozone (O3) affect host plant carbon gain and allocation, which may in turn influence ectomycorrhizal sporocarp production if the carbon available to the ectomycorrhizal fungus is dependant upon the quantity of carbon assimilated by the host. We measured sporocarp production of ectomycorrhizal fungi over 4 years at the Aspen FACE (free air CO2 enrichment) site, which corresponded to stand ages seven to 10 years. Total mean sporocarp biomass was greatest under elevated CO2, regardless of O3 concentration, while it was generally lowest under elevated O3 with ambient CO2. Community composition differed significantly among the treatments, with less difference in the final year of the study. Whether this convergence was due to succession or environmental factors is uncertain. CO2 and O3 affect ectomycorrhizal sporocarp productivity and community composition, with likely effects on dispersal, colonization and sporocarp-dependent food webs.