Mycorrhizal community dynamics and drivers after glacier retreat across the globe

Background/Question/Methods

Mountain and high-latitude glaciers have been retreating around the world since the Little Ice Age. However, the rate has increased dramatically in recent decades and is predicted to accelerate further. Large areas of newly deglaciated substrates are exposed to biotic colonization and soil development, but changes in habitat and climatic conditions could influence the formation of these young ecosystems. Thus, there is an urgent need to predict the evolution of these deglaciated areas, which requires fine-scale analyses of current patterns and common factors that call for global studies in glacier forelands around the world. Ecosystem development in these nutrient-poor and harsh environments is limited, with primary production heavily dependent on symbiotic associations such as mycorrhiza.To evaluate the effects of time and local microhabitats on mycorrhizal fungal community, we conducted a comprehensive inventory of 1862 plots in 266 forelands of 48 mountain and high-latitude glaciers around the globe, with sites spanning from 1 to 520 years since the retreat of ice sheets. For each plot, we assessed the richness and composition of fungal communities using metabarcoding of soil environmental DNA. For a subset of 32 glaciers, the microhabitat conditions were determined by measuring soil chemistry, temperature and humidity.

Results/Conclusions

We showed that the overall fungal richness increases rapidly after glacier retreat, although a delay is observed for mycorrhizal fungi. Ectomycorrhizal fungi were virtually absent in the early stages of soil development but increase rapidly after ~ 50 years. Arbuscular mycorrhizal fungi were present soon after glacier retreat and appeared to reach their greatest richness after 200 years. Even after accounting for microhabitat variation, time since glacier retreat remained the strongest predictor of mycorrhizal diversity, but the rate of colonization differed strongly by glacier location. Furthermore, local temperature also had an impact, with ectomycorrhizal fungi achieving greater diversity in cold environments and the opposite for arbuscular mycorrhizal fungi. Community composition was also largely influenced by time since glacier retreat and soil pH for arbuscular mycorrhizal fungi, while moisture was the strongest parameter influencing community composition for ectomycorrhizal fungi.Although mycorrhizal fungi rapidly colonize areas after glacier retreat, their expansion is strongly influenced by microhabitat parameters that locally interact. Therefore, changes in climatic conditions could disrupt biotic colonization, potentially by causing a mismatch between symbiotic partners. This could slow ecosystem development, but further analyses using multi-trophic surveys is needed to predict ecosystem-level impacts.