Drought can cause major damage to plant communities, but species damage thresholds and post-drought recovery of forest productivity are not yet predictable. We used an El Niño drought event as a natural experiment to test whether post-drought recovery of gas exchange could be predicted by properties of the water transport system, or if metabolism, primarily high abscisic acid level, might delay recovery. We aimed to test the hypotheses that recovery of gas exchange would be limited by xylem embolism, carbon limitation or high foliar abscisic acid levels. To do this we monitored sapflow of a single cohort of leaves, as well as leaf level gas exchange, water status and foliar abscisic acid for evergreen coniferous and mixed evergreen and deciduous broadleaf species through a severe drought event and following subsequent rehydration.
Results/Conclusions
Severe drought caused major declines in leaf water potential, elevated foliar abscisic acid levels and reduced stomatal conductance and assimilation rates in our sample canopy and understory species. Leaf water potential surpassed levels associated with incipient damage to the vascular system in two species. Following heavy rainfall gas exchange in all species, except those trees predicted to have suffered xylem damage, recovered to pre-stressed rates within one day. Thus, recovery of plant gas exchange was predicted by xylem safety margin providing strong support for cavitation vulnerability as an index of damage under natural drought conditions.