From Symbionts to Decomposers: Climate-Induced Lifestyle Shifts in Ericoid Mycorrhizal Fungi

Ericoid mycorrhizal (ERM) fungi are essential mediators of nutrient cycling in heathland ecosystems, helping host plants access organic nutrients in nutrient-poor conditions. Traditionally, these fungi are regarded as mutualists; they also possess saprotrophic capabilities that may become increasingly important under changing environmental conditions. Such climate-driven lifestyle flexibility could reshape soil carbon cycling and feedbacks to the atmosphere. Yet, how these lifestyle shifts reshape ERM and broader fungal community composition, and their consequences for soil carbon dynamics, remain poorly understood.

This study examines the impact of climate change on the decomposer activity and carbon allocation dynamics of ERM fungi using DNA-Stable Isotope Probing (DNA-SIP). Experiments were conducted within climate manipulation mesocosms representing past (2009-2013) and future (2080-2089) climate scenarios. Two complementary DNA-SIP experiments were employed. In the first experiment, mesh bags containing ¹³C-labeled cellulose or hemicellulose were used to trace the capacity of ERM fungi to decompose plant polymers. Samples were collected at 2 and 7 days post-labeling to capture the early and later stages of substrate utilization. In the second, entire mesocosms were fumigated with ¹³CO₂ for 5 days, and samples were collected 2, 7, and 15 days post-fumigation to quantify carbon transfer from plants to ERM fungi and evaluate shifts in belowground carbon allocation under future climate conditions.

By linking isotopic enrichment in fungal DNA with molecular community profiling, this project aims to identify which ERM taxa actively assimilate carbon from distinct sources under varying climates. We expect that future climate conditions will promote ERM taxa with greater saprotrophic potential and modify the temporal dynamics of carbon flow from plants to mycorrhizal fungi. Such shifts are likely to influence fungal community composition, intensify interactions with saprotrophic decomposers, and accelerate the turnover of soil organic matter.

Understanding these potential lifestyle shifts is crucial for predicting how ERM fungi mediate soil carbon balance and ecosystem resilience in response to ongoing climate change.