Successional Development of the Phototrophic Community in Biological Soil Crusts on Coastal and Inland Dunes

SIMPLE SUMMARY: This publication focuses on a comparative biodiversity survey of cryptogamic covers along a dune chronosequence in the Baltic Sea compared to an inland dune in northern Germany. Following these gradients, the cryptogamic vegetation accumulated more and more biomass and nutrients (carbon, nitrogen, and phosphorus). Further, a habitat-specific phototrophic community composition could be revealed. The enrichment of the biotic and abiotic components suggests cryptogamic covers as key players in geochemical processes, supporting sediment moisture and stability. Moreover, it highlights these communities as ‘ecosystem engineers’ playing a valuable part in nature protection e.g., preventing sediment erosion in coastal dune areas. ABSTRACT: (1) Biological soil crusts (biocrusts) are microecosystems consisting of prokaryotic and eukaryotic microorganisms growing on the topsoil. This study aims to characterize changes in the community structure of biocrust phototrophic organisms along a dune chronosequence in the Baltic Sea compared to an inland dune in northern Germany. (2) A vegetation survey followed by species determination and sediment analyses were conducted. (3) The results highlight a varying phototrophic community composition within the biocrusts regarding the different successional stages of the dunes. At both study sites, a shift from algae-dominated to lichen- and moss-dominated biocrusts in later successional dune types was observed. The algae community of both study sites shared 50% of the identified species while the moss and lichen community shared less than 15%. This indicates a more generalized occurrence of the algal taxa along both chronosequences. The mosses and lichens showed a habitat-specific species community. Moreover, an increase in the organic matter and moisture content with advanced biocrust development was detected. The enrichment of carbon, nitrogen, and phosphorus in the different biocrust types showed a similar relationship. (4) This relation can be explained by biomass growth and potential nutrient mobilization by the microorganisms. Hence, the observed biocrust development potentially enhanced soil formation and contributed to nutrient accumulation.