Drought affects biocrust more than increased rainfall in the Tabernas Desert (SE Spain)

Abstract Composed of poikilohydric organisms, biocrusts have the ability to survive during periods of drought, making them particularly important in arid and semi-arid areas. However, despite recent research into climate change, the limits of this tolerance to desiccation and the effects of increased water availability, are not very well known. Our objectives were to analyze the effect of prolonged droughts on the cover and metabolism of various crust types, as well as the effect of increased precipitation. Five types of crusts representative of hypothetic successional stages were studied (Physical, Incipient, Cyanobacteria, Squamarina and Lepraria). Two representative areas were selected for each crust type. Nine plots were established in each area, delimited by a 10-cm-diameter ring, and distributed in sets of three plots. In each set, three treatments were applied (control, watering and rain exclusion), and changes in cover, CO 2 fluxes and chlorophyll a fluorescence were analyzed. Rain exclusion led to cover losses due to respiration, although this effect differed among successional stages. However, increased precipitation did not increase biocrust cover, because both photosynthesis and respiration rates increased. Chlorophyll a fluorescence was higher in lichens; under watering, it was not different from the control but decreased under rain exclusion.