Print PageBiological soil crusts (BSC) vary considerably between different biomes according to species composition, structure and photosynthetic behavior. Biological soil crusts of savannahs, semi-deserts, and deserts are often dominated by filamentous cyanobacteria, forming either flat mats in the top soil layer or pinnacled mats with numerous erect bunches of upright cyanobacterial filaments. These crusts may develop into BSCs with cyano- and chlorolichens as well as bryophytes. Undisturbed BSC may finally be dominated by one of the three later groups. Biological soil crusts in temperate regions are normally dominated by filamentous green algae in early developmental stages and if undisturbed develop into BSC composed of green algae, cyano- and chlorolichens and bryophytes. In high Polar Regions BSCs are dominated by either chlorolichens with few unicellular green algae or moss dominated types. Since both, BSC-structure and species composition strongly influence photosynthetic carbon gain especially at different water content, we investigated BSCs from different biomes with regard to their photosynthetic performance.
Results/Conclusions
Six different types of crusts were investigated for species composition, structure and photosynthetic behavior. The tropical savannah-BSC (Queensland, Australia) was dominated by the filamentous cyanobacterium Symplocastrum sp., with a surface paralleling layer of cyanobacteria and numerous erect pinnacles. The crust performed positive net photosynthesis at temperatures as high as 47 °C and was active only during the rainy season. BSCs from the Sonoran Desert, Baja California were dominated by the cyanobacterial lichens Peltula patellata, Peltula richardsii and the chlorolichens Psora decipiens and Placidium squamulosum, all accompanied by cyanobacteria. Although to a quite different extend, both chlorolichen BSCs gained positive net photosynthesis when reactivated with high air humidity alone, while the cyanolichen-dominated BSCs needed liquid water for reactivation. The two cyanobacterial types exposed a wide range of water content and the two chlorolichen BSCs exposed a rather narrow range of water content for optimal net phototsynthesis. At water supra-saturation, the Psora decipiens-type drastically decreased net photosynthesis to almost zero. The Diamond Hill, 80° S, Antarctica harbored the most hostile environment for BSC. Dominated by the chlorolichen Acarospora gwynii and accompanied by three different unicellular green alga species, this crust showed optimal net photosynthetic rates at 5° C and even reached almost 90% of the maximum at 2°C. These results underpin the importance of detailed knowledge of the specific BSC type and its photosynthetic behavior for understanding their ecosystems contribution in terms of the carbon cycle and a changing climate.
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