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Review Article

Biological soil crusts of the Succulent Karoo: a review

Published in: African Journal of Range & Forage Science
Volume 35, issue 3-4, 2018 , pages: 335–350
DOI: 10.2989/10220119.2018.1527782
Author(s): Bettina WeberMax Planck Institute for Chemistry, Germany, Alexandra TammMax Planck Institute for Chemistry, Germany, Stefanie MaierMax Planck Institute for Chemistry, Germany, Emilio Rodríguez-CaballeroDepartment of Desertification and Geo-Ecology, Experimental Station of Arid Zones (EEZA-CSIC), Spain


The Succulent Karoo is characterised by a dense coverage of biological soil crusts (biocrusts) belonging to different types and successional stages. Whereas the Soebatsfontein region hosts cyanobacteria-dominated and minor amounts of lichen- and bryophyte-dominated biocrusts, the Knersvlakte comprises a rich cover of hypolithic crusts growing on the sides and undersides of quartz pebbles. Apart from dominating photosynthesizers used to classify biocrusts, each crust type hosts a rich and specific fungal and bacterial community and also diverse protists. In a remote-sensing mapping approach, soil-inhabiting biocrusts of the Soebatsfontein region covered ∼27% of the surface area, whereas in the Knersvlakte soil-inhabiting biocrusts covered ∼16% and hypolithic biocrusts ∼42% of the region. Combining these data with biomass contents, results suggested that the Knersvlakte, despite somewhat harsher environmental conditions, harboured about 65% more biocrust biomass per surface area. In physiological measurements we observed that biocrusts emit the reactive nitrogen compounds nitric oxide and nitrous acid, showing water pulse-dependent emission patterns. In addition, CO2 gas fixation showed characteristic type-specific patterns depending on climatic conditions. Long-term microclimate measurements along a gradient revealed that forecasted climate and land-use change may be detrimental for biocrusts with potentially adverse effects on soil stability and overall fertility of the Succulent Karoo.

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