Maria Májeková, Jana Martínková and Tomáš Hájek
Grasslands are an important ecosystem that sustains much biodiversity. They are predicted to be strongly affected by increasing changes in the magnitude and variability of precipitation. However, we still understand very little about how grassland plants cope with drought. Do they rely mainly on leaf drought tolerance, as is the case in woody plants, or do they employ other strategies? Leaf drought tolerance, assessed as the ‘turgor loss point’, is understood as an ability of leaf to maintain turgor, hence photosynthesis and growth, under water deficit.
In the past, measuring leaf drought tolerance took hours of laborious work and therefore was not used in field studies or for more than a few species at a time. This changed recently when a so called ‘osmometry’ method, which is easier and 30-times faster, was developed and tested for the assessment of leaf drought tolerance. Here we successfully validated this method for herbaceous, i.e., non-woody, plants.
We then applied this method to test whether plants from dry grasslands are better adapted to drier soils by having higher leaf drought tolerance than plants from wet grasslands. We also tested whether plants from dry grasslands can better acclimate to an actual drought event by adjusting their leaf drought tolerance.
We demonstrated that species from dry and wet grasslands did not differ in their leaf drought tolerance. Moreover, they also did not differ in their ability to adjust to acute drought stress. All species enhanced their leaf drought tolerance after being exposed to seven weeks of drought. Interestingly, they then rapidly lost this potentially costly adjustment after only one week of recovery.
Our study extends the applicability of the novel ‘osmometry’ method to herbaceous species, and thus has uncovered a yet unexploited direct method for assessing leaf drought tolerance in a wide range of species. This is especially important in light of our findings that, unlike in woody species, leaf drought tolerance in grassland plants does not fully translate into whole-plant drought resistance. The question of what other mechanisms grassland species employ to cope with drought still remains open for further investigation.