Recovery from extreme desiccation enhanced by humid air and elevated CO2 in a widespread desert plant.

Global climate change, driven by anthropogenically elevated atmospheric carbon dioxide (CO2), is causing fluctuations in resource availability across ecosystems. Drylands are especially vulnerable to such shifts because water limitations strongly constrain species performance and survival, with water arriving as liquid precipitation and non-rainfall water (NRW) such as fog, dew, and atmospheric water vapor (humidity). To cope with water limitation, some plants exhibit desiccation-tolerant traits that allow them to survive extended dry periods. This study examined the ecophysiological effects of long-term elevated CO2 exposure, prolonged desiccation, and NRW on Syntrichia caninervis, a moss that dominates many dryland biocrust communities. Plants grown under elevated CO2 exhibited 20-50% greater biomass, longer shoots, and more ramets than those grown under ambient CO2. After 17 years of desiccation, shoots were able to recover photosynthetic function and were able to do so even when only exposed to high humidity (NRW). Chlorophyll fluorescence (Fv/Fm 0.3-0.5) indicated that photosynthetic capacity under high humidity was similar to levels achieved after liquid water hydration. Regeneration and recovery rates were also faster under combined elevated CO2 and NRW treatments over both short (24-hour) and long-term (21-day) timescales. These findings demonstrate that elevated CO2 and atmospheric humidity enhance recovery and productivity in S. caninervis following prolonged desiccation. This work provides new insight into the physiological resilience of an ecologically important dryland moss under future climate scenarios.