Soil fungi play important roles in forest carbon and nutrient cycles, but relatively little is known about how they will respond to future climate change, especially in the context of southern hemisphere forest ecosystems. Our recent research focus has been to use controlled environment glasshouse and microcosm experiments to investigate the interactive effects of elevated atmospheric CO2, temperature and drought on Australian forest soil fungi, including those that form ectomycorrhizal associations with eucalypts.

In a glasshouse experiment, Eucalyptus saligna and E. sideroxylon seedlings were grown in field soil and maintained for 5 months under sub-ambient (280 ppm), ambient (380 ppm) and elevated (640 ppm) atmospheric CO2 conditions at both 26°C and 30°C. Multivariate analyses of molecular data showed a significant (P < 0.035) separation between fungal communities associated with the two different tree species and a clear separation between the communities from the 280, 400 and 640 ppm CO2 treatments at 34oC. This response appeared to be plant-dependent at 280 and 400 ppm CO2, however, all 640 ppm CO2 samples clustered together regardless of tree species. Interestingly, several of the key fungal species identified to respond strongly to the climate change factors were ectomycorrhizal fungi, including Pisolithus sp. so we performed a subsequent microcosm experiment and used transcriptomics to investigate the response of E. grandis (for which a genome sequence is available) to colonization by different Pisolithus isolates under ambient (400 ppm) and elevated (650 ppm) CO2. Our data showed that E. grandis varies in its susceptibility to colonization by different Pisolithus isolates in a manner that is not predictable by geographic origin or the ITS-based phylogeny of the fungal partner. Further, elevated levels of CO2 alter the receptivity of E. grandis to Pisolithus, which is correlated to a dramatic shift in the transcriptomic profile of the root. These data provide a starting point for understanding how future environmental change may alter the signalling between plants and their ectomycorrhizal partners and is a step towards determining the mechanism behind observed shifts in eucalypt-associated fungal communities exposed to elevated levels of atmospheric CO2.