Water content as useful tool for predicting the risk of drought-induced plant mortality

This Thesis provides experimental evidences about the reliability of the relative water content to predict the drought-driven vegetation die-off and die-back. In the Introduction, I briefly discussed on the effects of global climate changes on plant fitness and survival, focusing on unresolved questions for identifying reliable indicator of plant mortality, a key issue to perform reliable plant mortality risk models and to realize vegetation monitoring programs. In a first study, I recorded a significant impact of leaf water content and membrane damages on the impairment as well as on the recovery of the leaf hydraulic conductance, the “bottleneck” of plant water transport system. Moreover, in the measured species (i.e., P. nigra), a novel negative feedback mechanism linking leaf shrinkage to the leaf hydraulic conductance has emerged. These findings suggested that water content, but also leaf shrinkage, could be used as early indicator of hydraulic failure, a key indicator of whole plant drought resistance. Therefore, in a second study, I tested this hypothesis performing measurements on two Mediterranean native Salvia species. Results recorded in this second study led me to checked the impact of leaf hydraulic failure of the two Salvia species on whole plant hydraulic conductance as well as on its ability to recover from drought recovery. Then, I performed a fourth study aimed to check if and which plant organ water content is actually a reliable proxy of plant die-off. The Conclusions chapter provides a general overview and synthesis on the key findings across these studies.