Relationships between xylem embolism and tree functioning during drought, recovery, and recurring drought in Aleppo pine

Recent findings suggest that trees can survive high levels of drought-induced xylem embolism. In many cases, the embolism is irreversible and, therefore, can potentially affect post-drought recovery and tree function under recurring droughts. We examined the development of embolism in potted Aleppo pines, a common species in hot, dry Mediterranean habitats. We asked (1) how post-drought recovery is affected by different levels of embolism and (2) what consequences this drought-induced damage has under a recurring drought scenario. Young trees were dehydrated to target water potential (Psi(x) ) values of -3.5, -5.2 and -9.5 MPa (which corresponded to similar to 6%, similar to 41% and similar to 76% embolism), and recovery of the surviving trees was measured over an 8-months period (i.e., embolism, leaf gas-exchange, Psi(x) ). An additional group of trees was exposed to Psi(x) of -6.0 MPa, either with or without preceding drought (Psi(x) of -5.2 MPa) to test the effect of hydraulic damage during repeated drought. Trees that reached -9.5 MPa died, but none from the other groups. Embolism levels in dying trees were on average 76% of conductive xylem and no tree was dying below 62% embolism. Stomatal recovery was negatively proportional to the level of hydraulic damage sustained during drought, for at least a month after drought relief. Trees that experienced drought for the second time took longer to reach fatal Psi(x) levels than first-time dehydrating trees. Decreased stomatal conductance following drought can be seen as drought legacy, impeding recovery of tree functioning, but also as a safety mechanism during a consecutive drought.

Automated summary

Recent findings indicate that trees can survive high levels of drought-induced xylem embolism, but this irreversible damage can affect post-drought recovery and tree function under recurring droughts. The study examined the development of embolism in potted Aleppo pines and investigated the impact of different levels of embolism on post-drought recovery and the consequences of drought-induced damage under a recurring drought scenario. The results showed that trees with higher levels of embolism took longer to recover and stomatal conductance decreased following drought, impeding tree functioning.