PS 43-179 - Capturing photobiont turnover in lichens transplanted into stressful environments

Abstract: Lichenologists hypothesize that lichen-forming fungi are capable of swapping algal partners (photobionts) and forming new associations with more locally-adapted strains of algae. This process, known as “photobiont turnover,” is documented across established environmental gradients but has not been studied in the context of rapid changes in environment such as those associated with anthropogenic activities.

We looked for evidence of photobiont turnover in two lichen transplant studies using algal genotyping by amplicon sequencing. In our first study, Evernia mesomorpha thalli were transplanted in 2013 into experimental warming plots of the SPRUCE (Spruce and Peatland Responses Under Changing Environments) experiment. After being subjected to warmer temperatures for 6 years, we sampled the transplanted Evernia and captured shifts in the Trebouxia photobiont composition. For our second ongoing study, we are working with another Parmeliaceae lichen that also associates with Trebouxia. We are examining photobiont turnover in Flavoparmelia caperata in response to transplantation into an urban environment. These lichens were exposed to urban stressors such as air pollution, lead deposition, lower humidity, and hotter temperatures for 5 months. We hypothesize that the transplanted F. caperata will experience a shift in its photobiont composition to a greater proportion of Trebouxia that are able to survive in an urban environment.



In our first investigation, we found that E. mesomorpha experienced a shift in its photobiont composition. As warming increased, the lichens shifted to a greater proportion of the clade I Trebouxia genotypes. This clade may be more adapted to hotter and drier conditions, which could enhance this boreal lichen’s survival in a changing climate. We expect a similar photobiont composition shift to more locally-adapted Trebouxia genotypes in transplanted F. caperata. Genetic composition of photobiont communities will be combined with physiological data including chlorophyll fluorescence and CO2 uptake to assess if different photobiont composition profiles are enhancing the survival of the transplants in low air quality conditions and other urban stressors. It is unknown how fast photobiont turnover can occur in lichens and our project aims to narrow this gap in knowledge.

This research shows that photobiont turnover is a possible mechanism for slow-growing lichens to adapt to a rapidly changing climate and anthropogenic habitat disturbances like urbanization.