Fungal Microbiome Within Lichen as a Potential Bioindicator of Climate Change: Insights from Transplant Field Study

Global warming is a major driver of ecological change, yet its impacts on bioindicators such as lichens remain unclear. Lichens, formed by symbiotic associations between fungi and photosynthetic partners, are widely used to assess environmental conditions. However, studies relying on traditional physiological measures, including chlorophyll content and photosynthetic activity, have reported inconsistent responses to climate change. We hypothesized that short-term exposure of lichens to elevated temperatures would not alter these conventional physiological traits but might instead lead to changes in their associated microbiomes. Using a field transplant experiment, we exposed lichens to higher temperature environments and assessed both physiological and microbiome responses. Chlorophyll content and tissue damage showed no significant differences between control and warmed conditions. In contrast, high-throughput sequencing of 16S and ITS regions revealed pronounced shifts in microbial communities. Fungal assemblages exhibited marked declines in alpha diversity, co-occurrence network complexity, and stability of the core microbiome. By comparison, bacterial communities demonstrated greater resilience. Notably, the black yeast Cutaneotrichosporon debeurmannianum became dominant in high-temperature environments. Our findings show that while traditional physiological traits of lichens remain stable under short-term warming, their fungal microbiomes are highly sensitive to thermal stress. We identify fungal community structure-particularly the presence of C. debeurmannianum-as a promising indicator of climate change. These results highlight the importance of considering microbial symbionts when evaluating the ecological responses of lichens to global warming.