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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.
