Biocrust tissue traits as potential indicators of global change in the Mediterranean

Background and aims: Functional traits are promising indicators of global changes and ecosystem processes. Trait responses to environmental conditions have been examined widely in vascular plants. In contrast, few studies have focused on soil lichens and mosses composing biocrusts. We aimed to evaluate the potential of biocrust tissue traits as indicators of changes in climate and soil properties. Methods: Isotope ratios and nutrient content in biocrust tissue were analyzed in 13 Mediterranean shrublands along an aridity gradient. Differences in tissue traits between biocrust groups (lichens and mosses), and relationships between tissue traits and climatic and soil variables were examined. Results: Lichens and mosses differed in δ13C, δ15N and N content, indicating distinct physical and physiological attributes. Tissue traits correlated strongly with numerous climatic variables, likely due to a modulator effect on biocrust water relations and metabolism. We found contrasting responses of lichen and moss traits to climate, although they responded similarly to soil properties. Overall, the most responsive trait was δ15N, suggesting this trait is the best to reflect integrated processes occurring in the atmosphere and soil. Conclusions: Biocrust tissue traits arise as cost-effective, integrative ecological indicators of global change drivers in Mediterranean ecosystems, with potential applications in response-effect trait frameworks.