An increasing number of studies are describing the diversity of lichen phycobionts, which is leading to a better understanding of how lichen communities are assembled at different taxonomic, evolutionary and geographical scales. The present study explores the identity and genetic diversity of the microalgal partners of Punctelia borreri and P. subrudecta, two tropical and temperate parmelioid lichen fungi that often grow in temperate and Mediterranean forest ecosystems in Europe. Based on a specimen sampling distributed in two climatically divergent regions in the Iberian Peninsula, we found that these mycobionts are associated with Trebouxia gelatinosa, whose identity was also confirmed by an ultrastructural study of the pyrenoid. The bipartite network analysis indicated that each Punctelia species was associated with a different set of low frequency T. gelatinosa infraspecific lineages, whereas the two most abundant phycobiont lineages were shared between both mycobionts. Based on the current sampling, these two algal lineages occur exclusively in one of the two studied regions, which might point towards climate-driven, fine-tuned fungal-algal interactions. Finally, we documented visible symptoms of injury on the thalli in areas likely to have been impacted by air pollution.

Species can respond to climate change by migrating to track their suitable climate space, and/or through adaptation (across generations) or acclimation (by individuals) to a changed in situ environment. Lichens provide an excellent model for studying acclimation; being poikilohydric, there is strong evidence that their phenotype presents an adaptation to different moisture regimes, and that key aspects of the phenotype, notably specific thallus mass (STM), have plasticity towards effective acclimation that maximizes water storage in drier environments. In this study we quantified acclimation of STM for Lobaria pulmonaria across a regional climatic gradient, and within sites for different microclimates, using a one-year common garden growth experiment. We found that STM tended to increase with thallus growth; however, when accounting for growth, STM shifted to be lower than average in wetter environments, higher than average in intermediate environments, and failed to respond in the driest environment where growth was compromised. The possibility of phenotypic acclimation in Lobaria pulmonaria appears to be functionally linked to the propensity for growth, and we present a scheme coupling growth with STM to define the limits of the species realized niche.

Environmental control strategies are commonly practised to limit biodeterioration issues threatening indoor cultural heritage objects, while they are still poorly exploited for the conservation of outdoor stone heritage surfaces, including rock art. In this study, we evaluated the environmental factors driving the diversity and abundance of lithobiontic communities in the Rock Engravings National Park of Naquane (UNESCO WHS n. 94, Italy). The survey considered 23 rocks that had been cleaned in the last three (3YC) or twelve (12YC) years or more than 40 years ago (NRC). A cyanobacteria-dominated biofilm and lichens (37 taxa) were the most widespread and abundant lithobiontic components, prevailing on 3YC–12YC and NRC rocks, respectively. On the latter, a turnover of xerophytic and meso-hygrophytic lichen communities was observed. On 3YC–12YC rocks lichen colonization, if present, was limited to nitrophytic species, including common epiphytes from surrounding trees and a small number of meso-hygrophytic species, with a prevalence of asexual reproductive strategies. Multivariate analyses including environmental parameters (canonical correspondence analyses) indicated that tree cover and the presence of bare or vegetated ground upstream of the rocks, probably prolonging wetness and providing nutrients by water transport, are the factors mostly related to the microbial and lichen recolonization of 3YC–12YC surfaces. On this basis, an experiment on preventive conservation was conducted, consisting of a new cleaning of a strongly recolonized 3YC surface combined with the building of a small wall to protect part of the rock from prolonged water fluxes. The fluorimetric and colorimetric monitoring of the rock surface, carried out 40 months after this new cleaning intervention, displayed recolonization on the unprotected area only, indicating the potential of preventive conservation strategies in outdoor environments.

Although epiphytic lichens are widely adopted as environmental indicators, they are not yet included among the target species listed in Annex II of the Habitats Directive, to which the system of protected areas of the Natura 2000 network refers. In this work, we aim to test the effectiveness of this system, mainly designed for the conservation of other groups of species, in protecting lichen species richness. For this purpose, we considered a case study (Central Italy) with half of the territory included in protected areas. Statistical differences in species richness and lichen communities were tested between sites located in 16 Protected Areas (PA) and 11 Non-Protected Areas (NPA) using non-parametric tests, multi-response permutation procedures (MRPP), non-metric multidimensional scaling (NMDS) and Indicator Species Analysis (ISA). Despite the broad overlap between epiphytic lichen communities of NPAs and PAs and a similar number of total and common species, PAs contain a significantly higher number of nationally rare and extremely rare species, including cyanolichens. These results are also confirmed by the indicator analysis. Although the Natura 2000 network does not explicitly address the conservation of lichens, the protected areas in our study can play a role in protecting the diversity of epiphytic lichens, especially nationally rare and endangered species. However, the future inclusion of red-listed epiphytic lichens among the target species of Annex II of the Habitats Directive would be welcome to better protect these organisms on a European level.

The species–area relationship (SAR) states that species richness increases with the increase of the sampled area, although other factors can influence the pattern. SARs have been tested on many different organisms, but only rarely on lichens. We aimed to test the SAR, across a wide range of area sizes, for three main substratum-related guilds of lichens, namely epiphytic, epilithic and epigaeic. The test was performed using data from lichen inventories carried out in 44 protected areas of various sizes across Italy. We found a positive correlation of species richness with area size for all three guilds, better fitted by the logarithmic function for epilithic lichens and by the power function for epiphytic and epigaeic lichens. Our results support the fundamental role of area size as the main driver for lichen diversity, suggesting that in an area-based conservation framework, larger protected areas are fundamental to support high lichen species richness. However, finer scale investigations are also required to better elucidate whether and how other environmental factors could interact with area size and modify SAR patterns. Exhaustive lichen inventories could be useful information sources to more robustly test such relationships, and therefore better inform conservation practices.