The resilience of perennial grasses under two climate scenarios is correlated with carbohydrate metabolism in meristems.

Extreme climatic events (ECEs) such as droughts and heat waves impact ecosystem functioning and species turnover. This study investigated the effect of elevated CO2 on species resilience to ECEs. Monoliths from an upland grassland were exposed to 2050 climate scenarios with or without an ECE under ambient (aCO2: 390 ppm) or elevated (eCO2: 520 ppm) CO2. Eco-physiological traits of two perennial grasses (Dactylis glomerata, Holcus lanatus) were measured before, during and after ECE. At similar soil water content, leaf elongation was greater under eCO2 for both species. The resilience of D. glomerata was enhanced under eCO2 (+ 60%) whereas H. lanatus mostly died during ECE. D. glomerata accumulated 30% more fructans, which were more highly polymerised, and four fold less sucrose than H. lanatus. Fructan concentration in leaf meristems was significantly increased under eCO2. Their relative abundance changed during the ECE resulting in a more polymerised or depolymerised assemblage in H. lanatus and D. glomerata, respectively. The ratio between low-DP fructans to sucrose in leaf meristems was the best predictor of resilience across species. This study underlines the role of carbohydrate metabolism and the species-dependent effect of eCO2 on resilience of grasses to ECE.