Projected climate changes in the American Southwest forecast increased temperature and frequency of summer precipitation. The impact of these changes could be large for biological soil crust (BSC) communities that serve valuable ecosystems functions. We have observed Syntrichia caninervis, the predominant bryophyte component of BSCs, exhibiting high rates of mortality as a consequence of artificial summer rainfall.  As a first step in explaining this response, we explored the effect of temperature on carbon gain during hydration in two populations of S. caninervis originating from a cool (Great Basin) and a hot desert (Mojave).  Each population was stored desiccated at 20°C and 35°C for 2 weeks, fully hydrated for 12h under the same temperatures, and then allowed to dry. Photosynthetic responses to a range of temperatures (10°C to 40°C) were measured at 3 levels of hydration (75%, 50%, and 25%) during the dry down. Regardless of origin, samples stored and hydrated at 20°C showed higher net photosynthesis than those kept at 35°C, indicating a greater potential for C gain in lower temperatures, and the existence of phenotypic plasticity among S. caninervis from these two habitats. While photosynthesis was optimized between 15°C and 20°C at nearly all water contents, Syntrichia from both deserts showed the highest rates of C gain at 50% water content. Taken in concert, these results indicate that hydration at typical summer soil temperatures is unfavorable in terms of net C uptake, perhaps a consequence of rapid evaporation leading to a shorter time window of optimal hydration for photosynthesis.