Algal richness in BSCs in forests under different management intensity with some implications for P cycling

Biological soil crusts (BSCs) are highly important communities in drylands and disturbed areas worldwide, where the higher vegetation is sparse, with a diverse microalgal community as the key component. They perform important ecological functions, such as stabilization of soil and nutrient enrichment. In temperate regions BSCs are also common, but generally less studied. Changes in land use and land use intensity strongly influence biodiversity per se and ecosystem processes, as can be seen particularly in densely populated regions like Europe. However, systematic studies on the effect of land use gradients, i.e., forest management intensity, on BSCs have been missing up to now. To close this knowledge gap and enhance the understanding of management effects on BSCs from pine and beech forests under different management regimes, key primary producers of these communities (eukaryotic microalgae and cyanobacteria) were studied. Phototrophic microorganisms were identified morphologically and categorized as either coccal taxa, which typically occur in high diversity, or filamentous taxa, which have the potential to initiate BSC formation. In total, 51 algal species were recorded, most of them from the phylum Chlorophyta, followed by Streptophyta and Stramenopiles, and only 1 cyanobacterial taxon. The most abundant crust-initiating filamentous algae were three species of Klebsormidium (Streptophyta), a ubiquitous genus regularly occurring in BSCs because of its broad ecophysiological tolerance. Increasing management intensity in the forests resulted in a higher number of algal species; especially the number of coccal taxa increased. Furthermore, the proportion of inorganic phosphorus showed tendencies towards a negative correlation with the number of algal species. Thus, management of forests has an impact on the diversity of phototrophic organisms in BSCs, which might in turn affect their biogeochemical P cycling.