Disentangling functional trait variation and covariation in epiphytic lichens along a continent-wide latitudinal gradient

Characterizing functional trait variation and covariation, and its drivers, is critical to understand the response of species to changing environmental conditions. Evolutionary and environmental factors determine how traits vary among and within species at multiple scales. However, disentangling their relative contribution is challenging and a comprehensive trait-environment framework addressing such questions is missing in lichens. We investigated the variation in nine traits related to photosynthetic performance, water use and nutrient acquisition applying phylogenetic comparative analyses in lichen epiphytic communities on beech across Europe. These poikilohydric organisms offer a valuable model owing to their inherent limitations to buffer contrasting environmental conditions. Photobiont type and growth form captured differences in certain physiological traits whose variation was largely determined by evolutionary processes (i.e. phylogenetic history), although the intraspecific component was non-negligible. Seasonal temperature fluctuations also had an impact on trait variation, while nitrogen content depended on photobiont type rather than nitrogen deposition. The inconsistency of trait covariation among and within species prevented establishing major resource use strategies in lichens. However, we did identify a general pattern related to the water-use strategy. Thus, to robustly unveil lichen responses under different climatic scenarios, it is necessary to incorporate both among and within-species trait variation and covariation.

Effectiveness of aerobiological dispersal and microenvironmental requirements together influence spatial colonization patterns of lichen species on the stone cultural heritage

Dispersal patterns of lichen species in monumental and archaeological sites and their relationships with spatial population structure are almost unknown, hampering predictions on colonization dynamics that are fundamental for planning conservation strategies. In this work, we tested if the local abundance and distribution pattern of some common lichen species on carbonate stones of heritage sites may be related to their patterns of propagule dispersal. We combined analyses of the spatial population structure of eight species on the calcareous balustrade of a heritage site in Torino (NW Italy) with aerobiological analyses. In situ and laboratory analyses were mainly focused on the ejection of ascospores and their air take-off and potential dispersal at short and long distance. Results indicate that the spatial distribution of lichens on the stone surfaces is influenced by both species-specific patterns of propagule dispersal and microenvironmental requirements. In particular, apotheciate species that have a higher ejection of ascospores with higher potential for long range dispersal are candidate for a much aggressive spreading on the monumental surfaces. Moreover, their occurrence on natural or artificial stone surfaces in the surroundings of the stone monumental surface may easily support recolonization dynamics after cleaning interventions, as an effective supply of propagules is expected. On the other hand, species with a lower dispersal rate have a more clustered distribution and are less effective in rapid recolonization, thus representing a minor threat for cultural heritage conservation. These results support the idea that information on the reproductive strategy and dispersal patterns of lichens should be coupled with traditional analyses on stone bioreceptivity and microclimatic conditions to plan effective restoration interventions of stone surfaces.