Intraspecific variation in plant response to drought: assessing the current state of knowledge

Because plant growth, fitness, and survival strongly depend on water availability, it is imperative that plants are able to cope with water stress when drought occurs. Therefore, understanding plant adaptation to drought has major implications in basic and applied science, from informing fundamental ecological theory explaining plant distributions and interactions, to predicting and modeling local to global responses to climate change, to implementing effective ecological restoration. Research shows that plants vary greatly in their response to drought, with significant differences in sensitivity to drought and drought coping strategies. However, current work primarily focuses on differences between species or distantly related functional groups (interspecific variation), while little is known about variation in drought response between populations within the same species (intraspecific variation). How this variation is structured between and within species remains a fundamental question in plant ecophysiology. A formal assessment of literature considering intraspecific variation in plant drought adaptation across ecosystems, plant taxa, functional groups, life history strategies, or drought response traits has not yet been made. Therefore, the extent of variation between versus within species is unknown, and the current state of this field may poorly inform applications in ecology, crop science, climate science, ecological restoration, and more. To characterize what is currently known about within-species variation in drought adaptation, I conducted a literature review assessing intraspecific variation in natural (non-crop) plant populations. Analyzing all publications hosted on Web of Science pertaining to this topic, I asked how intraspecific variation is structured within the literature across ecosystem types, geographical regions, plant taxa, functional groups, life history strategies, and drought response traits. I assessed if and when there are differences between populations of the same species in adaptation to drought, and, in the case of some studies, whether or not this variation is genetic, plastic, or both. I also considered which ecosystem types, geographical regions, plant taxa, functional groups, drought response traits, and experiment types are most represented in the literature. The results of this review characterize the current state of knowledge of intraspecific variation in plant drought adaptation and identify areas most in need of further research, specifically the need for multi-trait, multi-species, rangewide studies assessing drought adaptation traits. Ultimately, this review will aid in assessing current ecological theory pertaining to plant adaptation to drought and inform applied applications, from predicting forest mortality under climate change, to improving the efficacy of restoration projects in drought-prone areas, to informing future research