How do ectomycorrhizal fungal communities on temperate-boreal tree roots respond to a gradient of experimental warming and drought?

Background/Question/Methods

Climate change poses challenges to many high latitude trees in terms of reduced photosynthesis and growth in response to warming and altered precipitation. How these changes will affect ectomycorrhizal (ECM) fungal communities, which may be influenced both directly in terms of altered environmental conditions and indirectly through changes to host tree physiology, remains poorly understood. To address this topic, we sampled the ECM fungal communities present on fine roots of three co-occurring hosts, two (Picea glauca, Pinus banksiana) of which are boreal and the other (Pinus strobus) temperate in geographic range. Sampling was conducted in the B4Warmed experiment in northern Minnesota, USA, which has a factorial combination of experimental warming (ambient, +1.7ºC, +3.3ºC) and drought (ambient, 30% reduced rainfall). Fungal communities were assessed with Illumina MiSeq High Throughput Sequencing. We hypothesized that ECM fungal community operational taxonomic unit (OTU) richness would be highest in intermediate “stress” treatments, consistent with the intermediate disturbance hypothesis. Further, we expected significant shifts in ECM fungal community composition with warming and reduced precipitation towards ascomycetes, which are generally more tolerant of high temperatures and drought than other major fungal phyla.

Results/Conclusions

Contrary to our first hypothesis, ECM fungal OTU richness did not differ significantly across hosts or among the warming and drought treatments. There was, however, a significant difference in ECM fungal OTU evenness across hosts as well as treatments. Specifically, Pinus banksiana had higher community evenness than Pinus strobus, although the particular effect of tree host on ECM fungal OTU evenness also varied among climate treatments. Additionally, the relative abundance of ECM ascomycete fungi was highest in the +3.3º C warming treatment on Pinus banksiana and Pinus strobus roots and other aspects of fungal community composition also varied with treatments and hosts. We will also explore how plant performance influences ECM fungal community composition under warming and drought conditions. Collectively, the observed changes in ECM fungal community composition in response to altered environmental conditions could have significant implications for tree physiology under climate change, especially given the detrimental impacts of warming and drought on tree growth and survival. Further, illuminating the impacts of climate change on the ectomycorrhizal symbiosis will inform our understanding of how ecotonal forest composition and function will respond to future climate.