Relief from summer drought in Mediterranean ecosystems often comes as short rainfall events. These short pulses of water after long dry periods may be intercepted entirely by the canopy or only wet the soil surface i.e. may not be sufficient to replenish soil water availability. Given that water availability is one the most influential factors dictating plant community composition and functional adaptations, Mediterranean species may be adapted to physiologically exploit this rainfall to maintain viability. Specifically, canopy interception of rainfall and direct water uptake via leaf surfaces may contribute to plant survival and aid in post-stress recovery. We aimed to investigate whether canopy rainfall interception alone was enough to recover Prunus dulcis trees from drought imposed stem water potentials of -3 MPa. Stressed trees were supplied water to the canopy alone, soil alone, or both canopy and soil. Two sets of trees provided control conditions; trees were either never stressed or never re-watered. Recovery was evaluated by measuring midday stem water potential, stomatal conductance, leaf ABA concentration, and non-structural carbohydrate content in twigs. In addition, rehydration kinetics of water absorbed through the leaf surface was compared to rehydration via petioles.
Results/Conclusions
Watering of soil and canopy as well as of soil alone resulted in the recovery of midday water potentials to those of non-stressed plants within a few hours. Trees from canopy only treatments recovered water potentials within two days. Trees from both soil treatments recovered the physiological status of non-stressed plants within two days following re-watering. Interestingly, trees in the canopy only treatment were able to partially recover high stomatal conductance and low ABA content by the end of the experiment (six days of nighttime canopy irrigation) despite their lack of access to soil water. P. dulcis leaf surfaces were found to be permeable to liquid water at all levels of stress, allowing for significant uptake especially during prolonged exposure to leaf wetness (fog or light rain). These results suggest that trees in ecosystems exposed to light rainfall events following drought may capitalize on canopy interception by adapting their capacity for foliar water uptake to mitigate drought-induced physiological impacts and facilitate recovery from stress.