Mechanisms of xylem hydraulic recovery after drought in Eucalyptus saligna

Abstract

The mechanisms by which woody plants recover xylem hydraulic capacity after drought stress are not well understood, particularly with regard to the role of embolism refilling. We evaluated the recovery of xylem hydraulic capacity in young Eucalyptus saligna plants exposed to cycles of drought stress and rewatering. Plants were exposed to moderate and severe drought stress treatments, with recovery monitored at time intervals from 24 hrs to 6 months after rewatering. The percentage loss of xylem vessels due to embolism (PLV) was quantified at each time point using micro-computed tomography with stem water potential (Ψx) and whole plant transpiration (Eplant) measured prior to scans. Plants exposed to severe drought stress suffered high levels of embolism (47.38 ± 10.97 % PLV) and almost complete canopy loss. No evidence of embolism refilling was observed at 24 hrs, one week, or three weeks after rewatering despite rapid recovery in Ψx. Recovery of hydraulic capacity was achieved over a 6-month period by growth of new xylem tissue, with canopy leaf area and Eplant recovering over the same period. These findings indicate that E. saligna recovers slowly from severe drought stress, with potential for embolism to persist in the xylem for many months after rainfall.

Functional xylem characteristics associated with drought‐induced embolism in angiosperms

“…Therefore, natural selection appears to have shaped the hydraulic systems of plants, including the nonxylem pathways in roots and leaves, in such a way that the impact of drought‐induced embolism is minimised. This can be done in three ways: (1) by building resistant xylem (Davis et al ., 1999a), (2) by preventing xylem sap pressures from exceeding critical thresholds (Martin‐StPaul et al ., 2017), and/or (3) by developing new wood tissue that leads to hydraulic recovery (Gauthey et al ., 2022).…”

Testing the limits of plant drought stress and subsequent recovery in four provenances of a widely distributed subtropical tree species

“…Another unresolved aspect of plant drought stress is how tree species restore hydraulic function following drought events (Choat et al, 2018;Klein et al, 2018;Ruehr et al, 2019). It has been reported that some tree species can repair embolized xylem through xylem refilling in a relatively short time (hours) (Ogasa et al, 2013;Secchi et al, 2021), while other species may take much longer (months to years) to restore xylem function via xylem regrowth (Brodribb et al, 2010;Gauthey et al, 2021;Hammond et al, 2019).…”

“…Another unresolved aspect of plant drought stress is how tree species restore hydraulic function following drought events (Choat et al, 2018; Klein et al, 2018; Ruehr et al, 2019). It has been reported that some tree species can repair embolized xylem through xylem refilling in a relatively short time (hours) (Ogasa et al, 2013; Secchi et al, 2021), while other species may take much longer (months to years) to restore xylem function via xylem regrowth (Brodribb et al, 2010; Gauthey et al, 2021; Hammond et al, 2019). Furthermore, interspecific variation in hydraulic recovery has been correlated with the concentrations of nonstructural carbohydrate (NSC) reserves in stems of several tree species (Savi et al, 2016; Tomasella et al, 2019; Trifilò et al, 2019; Zeppel et al, 2019).…”

Predicting resilience through the lens of competing adjustments to vegetation function

“…A drawback of our approach to modelling legacy is that it is sensitive to the parameterization of $${r}_{k}$$. However, xylem recovery capacity itself may be sensitive to drought severity (Gauthey et al, 2022), and so may the value of $${r}_{k}$$. Therefore, even though we derived $${r}_{k}$$ from site measurements over a period that comprised notable dry spells (October 2012–November 2013), we cannot exclude the possibility that $${r}_{k}$$ may be different during a longer, more severe drought, for example, if it were derived using data from the 2017–2020 drought period.…”