Semi-arid grasses combine contrasting strategies of dehydration tolerance associated with carbohydrate storage and embolism resistance under drought

Dehydration tolerance and embolism resistance contribute to plant drought survival, but their limits and combinations in perennial grasses remain unexplored. We investigated four grasses (Stipa species and Dactylis subspecies) from Mediterranean sites prone to intense summer drought. Plant tolerance to soil water deficit and tissue dehydration, embolism resistance (P50), and water-soluble carbohydrates (WSCs) were measured under severe drought. Dactylis were more dehydration tolerant, reaching 50% survival at a lower soil water potential (-6.07 MPa) than Stipa (-2.64 MPa), and at a lower leaf base water content (32.8%) than Stipa (50.0%). Dactylis accumulated higher WSCs in leaf bases [479 mg g-1 dry mass (DM), high fructan concentration] than Stipa (17 mg g-1 DM, high sucrose concentration). WSCs contributed 47% (Dactylis) and 29% (Stipa) to osmotic adjustment. However, Stipa had higher embolism resistance (P50= -8.7 MPa) than Dactylis (-2.9 MPa). Plants from the most arid sites had the highest dehydration tolerance, while embolism resistance was uncorrelated with aridity of the sites of origin. We found the highest embolism resistance and dehydration tolerance reported for herbaceous species. We showed that semi-arid grasses combine contrasting strategies to survive drought. Assessing these strategy combinations is crucial to predicting plant resilience under climate change.