Plant adaptation to drought has been extensively studied at many scales from ecology to molecular biology across a large range of model species. However, the conceptual frameworks underpinning the definition of plant strategies, and the terminology used across the different disciplines and scales are not analogous. ‘Drought resistance’ for instance refers to plant responses as different as the maintenance of growth and productivity in crops, to the survival and recovery in perennial woody or grassland species. Therefore, this paper aims to propose a unified conceptual framework of plant adaptive strategies to drought based on a revised terminology in order to enhance comparative studies. Ecological strategies encapsulate plant adaptation to multidimensional variation in resource variability but cannot account for the dynamic and short‐term responses to fluctuations in water availability. Conversely, several plant physiological strategies have been identified along the mono‐dimensional gradient of water availability in a given environment. According to a revised terminology, dehydration escape, dehydration avoidance, dehydration tolerance, dormancy, and desiccation tolerance are clearly distinguishable. Their sequential expression is expressed as water deficit increases while cavitation tolerance is proposed here to be a major hydraulic strategy underpinning adaptive responses to drought of vascular plants. This continuum of physiological strategies can be interpreted in the context of the ecological trade‐off between water‐acquisition vs. water‐conservation, since growth maintenance is associated with fast water use under moderate drought while plant survival after growth cessation is associated with slow water use under severe drought. Consequently, the distinction between ‘drought resistance’ and ‘drought survival’, is emphasized as crucial to ensure a correct interpretation of plant strategies since ‘knowing when not to grow’ does not confer ‘drought resistance’ but may well enhance ‘drought survival’. This framework proposal should improve cross‐fertilization between disciplines to help tackle the increasing worldwide challenges that drought poses to plant adaptation.

Climate change associated with a greater variability of inter‐ and intra‐annual droughts and the occurrence of extreme events act in combination to challenge semi‐natural and sown productive grasslands in Europe. Successful plant strategies under drought strongly depend on stress intensity. Drought resistance to maintain leaf growth under moderate stress trades off with drought survival after growth cessation under life‐threatening drought. Substantial intra‐specific variability exists in key forage grasses originating from the Mediterranean to the cool‐temperate climates and represents a great potential for adaptation of future ecotypes and cultivars to a larger range of drought intensities. Plant species diversity offers an opportunity to stabilize forage production in two ways. First, growth reduction under stress is significantly smaller for diverse compared to simple plant communities because the former offers the opportunity to include drought‐resistant (or drought‐surviving) species. Second, positive interactions among species increase ecosystem functioning of more diverse plant communities under moderate drought, allowing them to compensate for drought‐induced yield reductions. Currently, available cultivars of perennial forage species adapted to dry climate are still rare and only a few forage species are used in productive systems. Thus, both intra‐ and inter‐specific plant diversity should be better valued to reduce vulnerability and increase resilience of productive grasslands.

Background Dormancy in higher plants is an adaptive response enabling plant survival during the harshest seasons and has been more explored in woody species than in herbaceous species. Nevertheless, winter and summer shoot meristem dormancy are adaptive strategies that could play a major role in enhancing seasonal stress tolerance and resilience of widespread herbaceous plant communities. Scope This review outlines the symmetrical aspects of winter and summer dormancy in order to better understand plant adaptation to severe stress, and highlight research priorities in a changing climate. Seasonal dormancy is a good model to explore the growth–stress survival trade-off and unravel the relationships between growth potential and stress hardiness. Although photoperiod and temperature are known to play a crucial, though reversed, role in the induction and release of both types of dormancy, the thresholds and combined effects of these environmental factors remain to be identified. The biochemical compounds involved in induction or release in winter dormancy (abscisic acid, ethylene, sugars, cytokinins and gibberellins) could be a priority research focus for summer dormancy. To address these research priorities, herbaceous species, being more tractable than woody species, are excellent model plants for which both summer and winter dormancy have been clearly identified. Conclusions Summer and winter dormancy, although responding to inverse conditions, share many characteristics. This analogous nature can facilitate research as well as lead to insight into plant adaptations to extreme conditions and the evolution of phenological patterns of species and communities under climate change. The development of phenotypes showing reduced winter and/or enhanced summer dormancy may be expected and could improve adaptation to less predictable environmental stresses correlated with future climates. To this end, it is suggested to explore the inter- and intraspecific genotypic variability of dormancy and its plasticity according to environmental conditions to contribute to predicting and mitigating global warming.

The leaf economics spectrum (LES) describes covariation in traits relevant to carbon and nutrient economics across plant species, but much less is known about the relationship between the LES and leaf water economy. We propose an approach combining the measurement of two leaf traits related to water‐use economy, leaf carbon (δ¹³C) and oxygen (δ¹⁸O) isotopic composition, and the measurement of leaf morphological and nutrient traits to investigate the link between leaf carbon and nutrient economics and water use. We tested the relationships between leaf traits linked to carbon and nutrient use within the LES and water‐use traits using leaf δ¹⁸O as a proxy of stomatal conductance (g_s) and δ¹³C as a proxy of intrinsic water‐use efficiency (WUE_i) across 15 Mediterranean rangeland species grown in an irrigated common garden and in a natural rangeland in Southern France. The target species spanned a wide range of variation in leaf morphological and nutrient trait values and a wide range of leaf δ¹⁸O and δ¹³C values. Principal component analysis revealed multiple associations among leaf morphology, nutrients and isotopic composition, with the first axis alone explaining 56.0% of the total variation across species. Leaf δ¹⁸O and δ¹³C covaried with leaf morphology and leaf nutrient concentrations along a single resource‐use axis. Species with high leaf δ¹⁸O and δ¹³C (low g_s and high WUE_i) exhibited a resource‐conservative strategy (high leaf dry matter content, low leaf N, P and K), whereas species with low leaf δ¹⁸O and δ¹³C (high g_s and low WUE_i) showed a more resource‐acquisitive strategy (high specific leaf area and leaf N, P and K). These leaf trait syndromes and resource‐use strategies were strongly conserved across sites with contrasting environmental conditions, indicating that foliar δ¹⁸O and δ¹³C can be included as an integral part of the LES for this set of rangeland species. Overall, the data suggest a tight coupling and coordination between water, carbon and nutrient‐use strategies across herbaceous plant species. A dual δ¹⁸O and δ¹³C isotope approach combined with LES trait measurements is a promising tool to more comprehensively assess the diversity of resource‐use strategies among coexisting plant species. A plain language summary is available for this article.