Algal diversity of temperate biological soil crusts depends on land use intensity and affects phosphorus biogeochemical cycling

Abstract. Biological soil crusts (BSCs) form the most productive microbial biomass in many drylands and disturbed areas with a diverse microalgal community as key component. In temperate regions, BSCs are also common, but generally less studied, and they conduct important ecological functions, like stabilization of soil and enrichment of nutrients. Changes in land use and its intensity strongly influence biodiversity per se and it's role for ecosystem processes, particularly in regions which are densely populated like Europe. But systematic studies on land use (i.e. management intensity) gradients in temperate forests on BSCs are missing up to now. To close this gap of knowledge and enhance the understanding of management effects on BSCs, Cyanobacteria and eukaryotic microalgae as key primary producers of these communities were identified from pine and beech forests under different management regimes. Algae were identified morphologically based on enrichment cultivation and categorized in either coccal taxa, which occur typically in high diversity, or filamentous taxa, which have the potential to initiate BSC formation. In total, 52 algal species were recorded, most from the phylum Chlorophyta, followed by Streptophyta and Heterokontophyta; Cyanobacteria were much less abundant in temperate forest BSCs. The most abundant crust-initiating filamentous algae were three species of Klebsormidium (Streptophyta) a ubiquitous genus often associated with BSCs worldwide and a high tolerance to low pH. Increasing management intensity resulted in a higher richness of algae, especially the proportion of coccal algae rose. Furthermore, the proportion of inorganic phosphorus was positively correlated with the algal richness, indicating that higher diversity of algae results in a more closed P cycle. Thus, management of forests has an impact on the diversity of phototrophic organisms in BSCs, which in turn affects P cycling in the BSC.