Changes in climate, including the combined effects of increased drought and heat stress, are affecting many of the world’s forested ecosystems. The mycorrhizal fungi that form associations with the roots of most plant species increase access to soil resources and can thereby improve plant survival and growth in hot, dry conditions. However, it has been challenging to understand the importance of these fungi to the responses of long-lived trees in the field. We used long-term field studies before and during drought, a moisture manipulation experiment in a common garden, greenhouse experiments and laboratory studies to examine the importance of ectomycorrhizal fungal community composition and host genetics to drought tolerance in Pinus edulis, a conifer that has experienced widespread mortality due to a warming, drying climate. We also describe the consequences of widespread P. edulis mortality for these fungi, which depend on plants for fixed carbon.
Results/Conclusions
We found that: 1) Pinus edulis seedlings had similar patterns of growth and mortality during drought as their maternal trees and their siblings suggesting that drought tolerance is inherited, 2) drought tolerance was strongly associated with ectomycorrhizal fungal species composition, with drought tolerant trees consistently associating with ascomycete fungi in the genus Geopora, 3) neutron radiography showed that root colonization by Geopora increased water flow velocity in the roots of drought tolerant seedlings but had the opposite effect in drought intolerant seedlings, and 4) some of the ectomycorrhizal fungal species that promote drought tolerance survive in the soil for many years following P. edulis mortality, but other species do not, likely reducing the probability of successful regeneration. These results show that intraspecific differences among plants in their interactions with ectomycorrhizal fungi contribute significantly to variation in drought tolerance and explain patterns of growth and mortality of mature trees with climate change.