Biological soil crusts are composed of cyanobacteria, often associated with green algae, lichens, mosses and microfungi. Subproject S05 aims at studying the diversity, structure and function of BSCs (see maps for present results, Map 1: Diversity of BSC taxa , Map 2: Diversity of BSC-biomass along the transect). The effects of large- and small-scale abiotic and biotic factors on the development and composition of BSCs will be examined. Another main focus of this project will be to analyse the effects of biological soil crusts on the carbon cycle. Since the sink of about 25% of the annual CO2 production is unknown up to now, it is expected, that biological crusts on soil and rock, which cover wide areas in arid and semiarid ecosystems, will fill a major part of this knowledge gap.

During the first phase of the BIOTA project, S05 aimed at obtaining data on the a-diversity of cyanobacteria, green algae, and cyanobacterial lichens as components of BSCs as well as data on biomass, N-content, C/N-ratio and C-/N- isotope fractionation along the BIOTA-transect. As a result, the known a-diversity of BSCs in that area almost doubled. The highest diversity of cyanobacteria was registered for the observatory number 22

(Quaggafontein/Soebatsfontein) with 17 identified genera and 43 species. This partly could be explained by the high sampling number at this site. The biomass found in BSCs (expressed as chlorophyll a) varied between 1 and 193 mg/m². It frequently reached or even exceeded that of plankton density in the nearby Atlantic Ocean. An obvious dependency of the species diversity on the precipitation regime, as it was found for phanerogamous plants, could not be detected up to now. Two main types of BSCs could be distinguished: pioneer crusts (found in the dry forest, thornbush savanna and fynbos vegetation) and climax crusts (found in the more arid zones and winter rainfall regions of the Namib Desert and the succulent Karoo). Further subdivision of BSCs was done according to major taxonomic groups and growth type (e.g. cyanobacterial crusts, hypolithic crusts, lichen crusts and moss crusts).

A second work package aimed at the diversity and pattern formation of the lichen vegetation in the Namib Desert in relation to species distribution and abiotic (climate, substrate, relief) as well as biotic factors. As a result, six different zones of lichen communities in the Namib Desert, determined by microclimate, relief and special wind events could be defined. A description of the new cyanobacterial lichen species Peltula inversa was published in 2003.

In order to understand the role of BSCs in their ecosystem context, we outlined a research plan for the second phase of the BIOTA-project, consisting of the following seven work packages: Further assessment of biodiversity and implementation of a molecular identification technique (WP 1), Development of remote sensing techniques for upscaling and long term monitoring (WP 2), Climatic parameters as ecological regulators of BSCs and their response (WP 3), Functional ecology and the importance of BSCs on nutrient cycling (WP 4), Effects of human impact on the dynamics and diversity of BSCs (WP 5), Data management, GIS-analysis and Web-Map presentation (WP 6), Functional types of lichen vegetation forming the basis of biodiversity and productivity in the fog zone of the Central Namib (WP 7).
http://www.uni-kl.de/FB-Biologie/Botanik/biota_south.htm