Simulated climate change affects how biocrusts modulate water gains and desiccation dynamics after rainfall events

Soil surface communities dominated by mosses, lichens and cyanobacteria (biocrusts) are common between vegetation patches in drylands worldwide, and are known to affect soil wetting and drying after rainfall events. While ongoing climate change is already warming and changing rainfall patterns of drylands in many regions, little is known on how these changes may affect the hydrological behaviour of biocrust-covered soils. We used eight years of continuous soil moisture and rainfall data from a climate change experiment in central Spain to explore how biocrusts modify soil water gains and losses after rainfall events under simulated changes in temperature (2.5°C warming) and rainfall (33% reduction). Both rainfall amount and biocrust cover increased soil water gains after rainfall events, whereas experimental warming, rainfall intensity and initial soil moisture decreased them. Initial moisture, maximum temperature and biocrust cover, by means of enhancing potential evapotranspiration or by soil darkening, increased the drying rates and enhanced the exponential behaviour of the drying events. Meanwhile, warming reduced their exponential behaviour. The effects of climate change treatments on soil water gains and losses changed through time, with important differences between the first two years of the experiment and five years after its setup. These effects were mainly driven by the important reductions in biocrust cover and diversity observed under warming. Our results highlight the importance of long-term studies to understand soil moisture responses to ongoing climate change in drylands.