Unraveling the complex relationship between lichen fungal and algal partners has been crucial in understanding lichen dispersal capacity, evolutionary processes, and responses in the face of environmental change. However, lichen symbiosis remains enigmatic, including the ability of a single fungal partner to associate with various algal partners. Psora decipiens is a characteristic lichen of biological soil crusts (BSCs), across semi-arid, temperate, and alpine biomes, which are particularly susceptible to habitat loss and climate change. The high levels of morphological variation found across the range of Psora decipiens may contribute to its ability to withstand environmental change. To investigate Psora decipiens acclimation potential, individuals were transplanted between four climatically distinct sites across a European latitudinal gradient for 2 years. The effect of treatment was investigated through a morphological examination using light and SEM microscopy; 26S rDNA and rbcL gene analysis assessed site-specific relationships and lichen acclimation through photobiont switching. Initial analysis revealed that many samples had lost their algal layers. Although new growth was often determined, the algae were frequently found to have died without evidence of a new photobiont being incorporated into the thallus. Mycobiont analysis investigated diversity and determined that new growth was a part of the transplant, thus, revealing that four distinct fungal clades, closely linked to site, exist. Additionally, P. decipiens was found to associate with the green algal genus Myrmecia, with only two genetically distinct clades between the four sites. Our investigation has suggested that P. decipiens cannot acclimate to the substantial climatic variability across its environmental range. Additionally, the different geographical areas are home to genetically distinct and unique populations. The variation found within the genotypic and morpho-physiological traits of P. decipiens appears to have a climatic determinant, but this is not always reflected by the algal partner. Although photobiont switching occurs on an evolutionary scale, there is little evidence to suggest an active environmentally induced response. These results suggest that this species, and therefore, other lichen species, and BSC ecosystems themselves may be significantly vulnerable to climate change and habitat loss.
Keywords: Europe; Myrmecia; biological soil crusts; environmental change; genetic diversity; green algae; latitudinal gradient; morphological variability; plant–climate interactions; plasticity.