Biocrusts Are Highly Vulnerable to Multidimensional Global Change

Biocrusts are a critical component of terrestrial environments, playing vital roles in soil stability, carbon and nitrogen cycling, and ecosystem functioning, particularly in drylands. Yet their responses to global change stressors remain poorly understood, with most evidence derived from local-scale experiments. Here, we conducted a meta-analysis synthesizing 657 observations from 48 publications conducted at 38 sites to assess how structural traits (cover, species richness, and moss biomass) and a key functional trait (chlorophyll content) of biocrusts respond to warming, altered precipitation, nitrogen addition, and their interactions. We found that nitrogen addition produced the strongest overall decline in biocrust cover (-52%). Warming (-21%) also significantly reduced biocrust cover, and its combined effect with decreased precipitation caused greater losses (-44%). Species richness declined under combined warming and decreased precipitation (-8%). Chlorophyll content responded negatively to decreased precipitation (-26%), combined warming and decreased precipitation (-35%), and nitrogen addition (-21%), but increased under elevated precipitation (+55%). Moss biomass exhibited weak and inconsistent responses to nitrogen addition. The response of biocrusts varied among dominant biocrust types, ecosystems, and climate zones. Late-successional crusts (moss- and lichen-dominated) exhibited the strongest declines, whereas cyanobacterial crusts often persisted or even expanded under stress. Biocrusts in semi-arid grasslands were most negatively affected by warming and reduced precipitation, whereas those in humid tundra and forests were most sensitive to nitrogen addition. In addition, biocrust responses were shaped by the characteristics of global change manipulations, with warming and precipitation reduction being more sensitive to duration than magnitude, whereas nitrogen addition rate exerted stronger effects than duration. Together, these findings demonstrate that biocrusts are highly vulnerable to global change, potentially undermining their capacity to control erosion and regulate carbon and nutrient cycling. We emphasize the urgent need to safeguard biocrusts in a rapidly changing world.