LAUSR

Eco-physiological characterization of photoautotrophic communities is not only necessary to identify the response of carbon fixation related to different climatic factors, but also to evaluate risks connected to changing environments. In biological soil crusts (BSCs), the description of eco-physiological features is difficult, due to the high variability in taxonomic composition and variable methodologies applied. Especially for BSCs in early successional stages, the available datasets are rare or focused on individual constituents, although these crusts may represent the only photoautotrophic component in many heavily disturbed ruderal areas, like parking lots or building areas with increasing surface area worldwide. We analyzed the response of photosynthesis and respiration to changing BSC water contents, temperature and light in two early successional BSCs. One BSC was dominated by the cyanobacterium Nostoc commune , the other by the green alga Zygogonium ericetorum . Independent of species composition, both crust types had convergent features like high light acclimatization and low or no depression in carbon uptake at water suprasaturation. This particular setup of eco-physiological features may enable these communities to cope with a high variety of climatic stresses, and may therefore be a reason for their success in heavily disturbed areas with ongoing human impact. Nevertheless, a major divergence between the two BSCs was their absolute carbon fixation rate on a chlorophyll basis, which was significantly higher for the cyanobacterial crust. This study emphasizes the importance of measuring intact BSCs under natural conditions for collecting reliable data.