Background
The authors note that sporocarps (the reproductive structures of fungi) can be significant carbon sinks for the ectomycorrhizal fungi that develop symbiotic relationships with plants by forming sheaths around their root tips, where they are the last sinks for carbon in the long and winding pathway that begins at the source of carbon assimilation in plant leaves. They also note that "it is critical to understand how ectomycorrhizal fungal sporocarps are affected by elevated CO2 and O3 [ozone]" because, as they continue, "sporocarps facilitate genetic recombination, permit long-distance dispersal and contribute to food webs," and we need to know how these important processes will be affected by continued increases in the concentrations of these two trace constituents of the atmosphere.

What was done
The authors sampled aboveground sporocarps for four years at the Aspen FACE (free-air CO2 enrichment) site near Rhinelander, Wisconsin, USA, which provided, in their words, a "unique opportunity to examine the effects of both elevated CO2 and O3 on a forested ecosystem," which examination was conducted during years 4 through 7 of the aspen and aspen-birch forests' exposures to ambient and enriched concentrations of the two gases: CO2 (350 and 550 ppm) and O3 (33-67 and 50-100 ppb).

What was learned
The two researchers found that total mean sporocarp biomass "was generally lowest under elevated O3 with ambient CO2," and that it "was greatest under elevated CO2, regardless of O3 concentration." In another place in their paper, they state there was "a complete elimination of O3 effects on sporocarp production when [extra] CO2 was added." And they say they "expect that the responses seen in the present study were conservative compared to those expected under regional to global changes in CO2 and O3."

What it means
By itself, or in combination with rising ozone concentrations, the ongoing rise in the air's CO2 content appears destined to enhance the genetic recombination and long-distance dispersal of the ectomycorrhizal fungi that form symbiotic relationships with the roots of aspen and birch trees, thereby positively contributing to various food webs that will be found within aspen and aspen-birch forests of the future.