To Grow Or Survive: Which Are The Strategies Of A Perennial Grass To Face Severe Seasonal Stress?

1. 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 perennial ryegrass.2. Three common gardens compared 385 European perennial ryegrass populations along a latitudinal environmental gradient over 3-years. Persistence, productivity and physiological traits were recorded under contrasting seasonal environments.3. Decoupling plant responses, that is, 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 perennial ryegrass populations were identified according to their contrasting strategies: (a) year-round productive but stress sensitive populations from wet areas; (b) drought-tolerant populations with low summer growth potential from drought-prone areas and (c) 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. However, such overall functional patterns were less meaningful than seasonal variations of resource acquisition potentials. The predicted potential biogeographical distribution of these groups suggests shifts of areas of suitability 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.4. The large intraspecific variability of phenological adaptations within perennial ryegrass reveals that the seasonal modulation of growth potential is crucial to plant adaptation under severe chronic abiotic stresses. 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.