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Abstract

Biological soil crusts (biocrusts) cover about 12% of the Earth ’ s land masses, thereby providing ecosystem services and affecting biogeochemical fl uxes on a global scale. They comprise photoautotrophic cyanobacteria, algae, lichens and mosses, which grow together with heterotrophic microorganisms, forming a model system to study facilitative interactions and assembly principles in natural communities. Biocrusts can be classi fi ed into cyanobacteria-, lichen-, and bryophyte- dominated types, which re fl ect stages of ecological succession. In this study, we examined whether these categories include a shift in heterotrophic communities and whether this may be linked to altered physiological properties. We analyzed the microbial community composition by means of qPCR and high-throughput amplicon sequencing and utilized fl ux measurements to investigate their physiological properties. Our results revealed that once 16S and 18S rRNA gene copy numbers increase, fungi become more predominant and alpha diversity increases with progressing succession. Bacterial communities differed signi fi cantly between biocrust types with a shift from more generalized to specialized organisms along succession. CO 2 gas exchange measurements revealed large respiration rates of late successional crusts being signi fi cantly higher than those of initial biocrusts, and different successional stages showed distinct NO and HONO emission patterns. Thus, our study suggests that the photoautotrophic organisms facilitate speci fi c microbial communities, which themselves strongly in fl uence the overall physiological properties of biocrusts and hence local to global nutrient cycles.