Plant Functional Traits Predict the Drought Response of Native California Plant Species

Premise of research. As extreme climate events, such as California's 2012-2016 drought, become more frequent with climate change, it is imperative to understand how different native plant communities respond to drought-induced dehydration stress. Chaparral and California sage scrub (CSS), two widespread plant communities in California, face threats from droughts of increased frequency and severity. Despite chaparral and CSS plants being adapted to seasonal drought conditions, it is not known how the strategies of recovery from extreme multiyear droughts associated with changing climate differ between them. Methodology. We measured chlorophyll fluorescence and water potentials for two evergreen chaparral shrubs (Heteromeles arbutifolia and Quercus berberidifolia) and two drought deciduous CSS shrubs (Salvia leucophylla and Salvia mellifera) in the Santa Monica Mountains both during and after the extreme drought in California (between 2015 and 2017). Pivotal results. We found that the maximum electron transport rate (J(max)) varied seasonally for all species, decreasing in the dry season and recovering in the wet season. However, J(max) and the seasonal change in J(max) (Delta J(max)) were larger for the CSS species than for the chaparral species, and recovery of J(max) began earlier in the year for CSS species than for chaparral species. Dark-adapted maximum photochemical efficiency of photosystem II (Fv/Fm) and both midday (psi(MD)) and predawn (psi(PD)) water potential for all species also followed similar seasonal patterns-higher in the wet season than in the dry season, with CSS species exhibiting the largest seasonal changes in psi. A strong linear relationship was found between J(max) and psi(MD) for all species except Q. berberidifolia. Conclusions. Our results show that recovery from drought-induced dehydration differs between representatives of two major plant communities in California and is linked to life-history strategy: the higher sensitivity to and quicker recovery from seasonal drought for the CSS species compared with the chaparral species could be attributed to the shallower rooting depths and dehydration tolerance of the CSS species. In addition, water relations and chlorophyll fluorescence can serve as useful metrics to compare species-specific dehydration stress tolerance or avoidance strategies in the field.