Shanwen Sun, Eunyoung Jung, Julian Gaviria, Bettina M. J. Engelbrecht
Grasslands cover one-fifth of the world’s surface, contain high biodiversity, and provide important ecosystem services. Many temperate grasslands are exposed to drought periods during the growing season under current climate, and the frequency and intensity of drought are projected to increase with climate change. To improve predictions of the consequences of these changes for grassland composition and productivity, we need to understand the mechanisms that underlie the differential drought resistance of grassland species. To rigorously test the role of mechanisms underlying differential drought resistance of different plant species, their traits need to be directly related to their comparatively assessed whole-plant survival under drought. Surprisingly, experimental studies of comparative whole-plant drought survival remain scarce and restricted to woody species.
Turgor loss point, i.e., the leaf water status at which leaves start wilting, has been suggested to be a key trait of drought resistance in woody species. However, little is known about the role of this parameter in temperate perennial grassland species. In this study, we measured the turgor loss point in 41 species common in Germany (20 forbs and 21 grasses) and related it to their leaf water status and survival in a drought experiment in the field.
We found that grassland species that lose leaf turgor ‘earlier’ (i.e. high turgor loss point) maintain a higher water status (i.e. effectively avoid desiccation), and survive better under drought. This strategy of drought resistance is fundamentally different from woody species, which tolerate rather than avoid desiccation.
Our results imply that mechanisms of drought resistance differ between woody and herbaceous species. They underline that it is necessary to establish the relation of traits to drought responses separately in different plant life forms, before using the traits for predicting which species will lose or win under conditions of global climate change.