Extreme rainfall shifts are observed across global ecosystems, and consequently, the effect of drought on vegetation is currently one of the focal points in plant ecology research. However, the sequence of water status thresholds inducing leaf functional failure and structural damage is still unclear. Moreover, little is known about the ability of vegetative tissues to recover after a drought event. We assessed the ability of leaves belonging to 10 diverse angiosperm species to rehydrate after different degrees of water loss. We also determined the effect of dehydration on the maximum quantum yield of the photosystem II (Fv/Fm) and examined its correlation with stomatal, hydraulic and mesophyll traits conferring drought tolerance. We solved a sequence of declining relative water content (RWC) and leaf water potential (Ψleaf) thresholds of functional impairment and structural damage. Finally, using anatomical imaging techniques we assessed the drought-induced damage at the mesophyll cell level.
Results/Conclusions
Species lose half of their rehydration capacity at a mean RWC of 40 ± 1 %. A much lower RWC (mean = 16 ± 3 %) induced a 50% loss of Fv/Fm. However, chlorophyll fluorescence showed no recovery after rehydration. Our study supports the hypothesis that species show a relatively narrow range of relative water content thresholds for loss of rehydration capacity and photosynthetic function, providing new perspectives to understand plant functional recovery after drought. Rehydration capacity and Fv/Fm declines occur at the end of the leaf injury sequence, and are associated with drought tolerance traits such as leaf and stomatal hydraulics and wilting point. We provide an estimation of water status thresholds of cell mortality in the mesophyll. Significant damage of the light harvesting apparatus occurs only at very low RWC, suggesting a role of mesophyll cells in buffering chloroplasts from experiencing drought-induced dysfunction.