Hot and cold deserts as eco-evolutionary arenas for understanding plant resistance to multiple abiotic stressors.

During their long evolutionary history, land plants have evolved a range of adaptations to different abiotic stressors. These help explain present-day diversity and distribution patterns, as well as the potential resilience of natural and agricultural systems to a changing climate. Most previous research has focused on adaptation to individual stressors and much less is known about how plants deal with exposure to multiple abiotic stressors. Consequently, the evolutionary processes leading to abiotic stress polyresistance (i.e. resistance to multiple abiotic stressors) remain poorly understood. Here, we showcase plants in hot and cold deserts as a compelling system for studying evolution of polyresistance. We focus on three abiotic stressors with substantial physiological overlap - drought, frost and salinity - and present six plant groups that occur in both hot and cold deserts, thus being exposed to these stressors in at least parts of their ranges: Gnetales, Amaranthaceae sensu lato, Nitrariaceae, Poaceae, Tamaricaceae-Frankeniaceae and Zygophyllaceae. We examine key questions regarding the sequence and mechanisms underlying abiotic stress polyresistance evolution and summarize the diverse adaptive strategies that allow persistence under multiple environmental pressures. In doing so, we highlight how trade-offs and facilitation among abiotic stress responses may have influenced the evolutionary pathways that lead to present-day polyresistance. Despite limited evidence, broad patterns emerge for the plant groups examined here, with facilitation appearing especially important, at least during early stages of polyresistance evolution. However, fundamental knowledge gaps remain. Macroevolutionary and macroecological approaches, coupled with historical biogeography and palaeoclimatic and palaeoecological reconstructions, can be used to advance understanding of abiotic stress polyresistance evolution in plants. This will pave the way for applied trait-based research to support climate change mitigation, conservation and sustainable crop improvement in a rapidly changing world.