Supporting information

Summary <br>•More severe seasonal stresses resulting from climate change affect the survival of perennial plant species. The growth survival trade-off exemplified in dormant species, is a key issue to understand adaptation. As the validity of this trade-off has yet to be tested in non-dormant species, it was assessed by exploring the intraspecific variability of strategies to face drought and frost within the Lolium perenne grass.<br>•Three common gardens compared 385 European ryegrass populations along a latitudinal environmental gradient over three years. Persistence, productivity, and physiological traits were recorded under contrasting seasonal environments.<br>•Decoupling plant responses, i.e. growth under favourable summers/winters and plant survival under harsh summers/winters, showed a general trade-off between growth potential and dehydration survival. Three groups of ryegrass populations were identified according to their contrasting strategies: (1) year-round productive but stress sensitive populations from wet areas; (2) drought tolerant populations with low summer growth potential from drought-prone areas and, (3) frost tolerant populations with low winter growth potential from frost-prone areas. Overall, the populations surviving drought best were more resource conservative whereas populations of the other groups were more resource acquisitive, although global patterns were less meaningful than seasonal variations. The predicted potential biogeographic distribution of these groups suggests areas of suitability shift under climate change over the next decades in Europe. Dehydration escape and dehydration tolerance through reduction of growth potential in summer may become the strategies best adapted to an increasingly large area of Europe. <br>•The large intraspecific variability of phenological adaptations within ryegrass reveals that the seasonal modulation of growth potential is crucial to plant adaptation under severe chronic abiotic stress. The global plant economics spectrum cannot account for contrasting seasonal trade-offs which points out the importance of integrating phenological traits as key components of plant strategies. The identification of the trade-off between growth potential and frost or drought stress survival in this non-dormant species provides key knowledge to understand the future regional distribution of this major species for grassland ecosystem services.<br><br>Supplementary materialsMeth. S1 - List of the perennial ryegrass natural populations in study including information on collection sites and genebanks maintaining seed samples of these populations.<br>Meth. S2 - Technical management of the three common gardens.<br>Meth. S3 - Climatic conditions at the three common gardens over the duration of the experiments.<br>Meth. S4 – Description and justification of the traits used in this study, computation methods for mean population values and trait summary statistics.<br>Table S1 - Table of values of phenotypic traits recorded on studied populations from the natural diversity of <i>Lolium perenne</i><br>Meth. S5 - Bioclimatic variables characterizing sites of origin of perennial ryegrass natural populations<br>Table S2 - Values of environmental variables at sites of origin of studied populations from the natural diversity of <i>Lolium perenne</i><br>Table S3 - Mean values of the phenotypic traits for each of the three phenotypic groups identified within the studied natural diversity of <i>Lolium perenne</i><br>Table S4 - Correlations between bioclimatic variables and the first two canonical components of the LDA (Linear Discriminant Analysis) performed on the three ryegrass groups with bioclimatic variables<br>Figure S1 - Illustration of summer persistence in 2016 at Lusignan (LU) for three plots sown with different perennial ryegrass natural populations. Severe drought occurred during summer 2016 at Lusignan. The left-hand picture was taken in May 2016 before occurrence of drought, the central one in September 2016 during the drought period and the right-hand one in November 2016 during growth recovery. Soil coverage by living plants was scored in June 2016 before start of drought and in November 2016 after rainfalls and start of regrowth. The left-hand plot on pictures was scored as the less persistent one after summer 2016.<br><br>