Summer Drought Survival Strategies and Sustainability of Perennial Temperate Forage Grasses in Mediterranean Areas

Perennial grasslands provide numerous agroenvironmental benefits due to continuous soil cover. In Mediterranean areas, chronic summer drought is expected to increase as a result of climate changes. Plant adaptations that protect meristematic tissues include dehydration delay, dehydration tolerance, and summer dormancy. Summer dormancy can only be reliably tested in plants not subjected to water deficit. Under summer irrigation, complete dormancy is manifested by cessation of growth in association with full senescence of foliage and induced dehydration of leaf bases. Incomplete dormancy occurs when leaf growth is partially constrained and associated with moderate levels of foliage senescence. Summer dormancy is under hormonal control and is induced under increasing photoperiod and temperature. Recent results show that drought cannot induce summer dormancy under early-spring short days, although a water deficit under late-spring long days reinforces it and could enhance drought survival. Dehydration tolerance and dormancy are independent phenomena. Summer dormancy has been correlated with superior survival after severe summer droughts in many perennial grass species. This trait has potential for improving cultivars able to meet agronomic and environmental goals.