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.
Reproductive success largely defines the fitness of plant species. Understanding how heat and drought affect plant reproduction will thus be key to predicting future plant fitness under rising global temperatures. Recent work suggests reproductive tissues are highly vulnerable to water stress in perennial plants where reproductive sacrifice could preserve plant survival. However, most crop species are annuals where such a strategy would theoretically reduce fitness. We examined the reproductive strategy in tomato (Solanum lycopersium) to determine whether water supply to fruits was prioritized above vegetative tissues during drought. Using optical methods, we map xylem cavitation and tissue shrinkage in vegetative and reproductive organs during dehydration to determine the priority of water flow under acute imposed water stress. Stems and peduncles of tomato showed significantly greater resistance to xylem cavitation than vegetative tissues. This prioritization of reproductive water supply enabled tomato fruit to continue expanding during acute water stress, utilising xylem water made available by capacitance and cavitation of vegetative tissues. Here, tomato plants prioritize water supply to reproductive tissues, maintaining fruit development in drought conditions. These results emphasize the critical role of water transport in shaping tomato life history and suggest a broad relevance of hydraulic prioritization in plant ecology.
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