Increased atmospheric CO2 is changing the energy balance of the Earth and altering global precipitation. Drylands cover >40% of the terrestrial surface and may be among the most responsive ecosystems to these changes. My dissertation addresses the influences of global change on biocrust mosses, a group of plants instrumental to biogeochemistry in drylands. First, I provide an overview of the physiological ecology of biocrust mosses. These plants are adapted to pulse-dynamic water and resource availability in drylands because they are desiccation tolerant, which (1) enables carbon fixation during precipitation events, and dormancy (including protection from light and temperature extremes) between them, but (2) places constraints on performance owing to the costs of responding to precipitation, resulting in vulnerability to changes in precipitation regime. Second, I examine the physiological effects of 10 years elevated CO2 and high temperature events on biocrust mosses. I show that, unlike vascular plants, mosses do not acclimate photosynthetically to elevated CO2. High temperatures reduce photosynthetic performance, but elevated CO2 exposure partially alleviates this stress, potentially reflecting reallocation of nitrogen to cellular components that offer photosynthetic thermotolerance. Third, I study the influence of changes in precipitation event size, frequency, and seasonality on moss carbon balances from precipitation events. Precipitation event size was ! positively correlated with (and was the strongest driver of) carbon balance because mosses remain photosynthetically active longer during large events. Rainfall frequency was negatively correlated with carbon balance because the cost to regain functional capacity during a precipitation event is higher after longer dry periods. Finally, carbon balance varied over the course of the year, even for events of identical magnitude, indicating that intrinsic physiological differences are present across seasons than influence response to precipitation. Lastly, I combine physiology with meteorological records from Western North America to create a predictive model for biocrust moss functioning in the next 100 years. Using simulations, I show that subtle shifts in intra-annual precipitation can drive long-term performance, rare large precipitation events can change the trajectory of survival, and most projected dryland scenarios will result in reduced performance in biocrust mosses. !