Rapid hydraulic recovery in Eucalyptus pauciflora after drought: Linkages between stem hydraulics and leaf gas exchange

Abstract

In woody plants, photosynthetic capacity is closely linked to rates at which the plant hydraulic system can supply water to the leaf surface. Drought-induced embolism can cause sharp declines in xylem hydraulic conductivity that coincide with stomatal closure and reduced photosynthesis. Recovery of photosynthetic capacity after drought is dependent on restored xylem function, although few data exist to elucidate this coordination. We examined the dynamics of leaf gas exchange and xylem function in Eucalyptus pauciflora seedlings exposed to a cycle of severe water stress and recovery after re-watering. Stomatal closure and leaf turgor loss occurred at water potentials that delayed the extensive spread of embolism through the stem xylem. Stem hydraulic conductance recovered to control levels within 6h after re-watering despite a severe drought treatment, suggesting an active mechanism embolism repair. However, stomatal conductance did not recover after 10d of re-watering, effecting tighter control of transpiration post drought. The dynamics of recovery suggest that a combination of hydraulic and non-hydraulic factors influenced stomatal behaviour post drought. Xylem embolism has been identified as one of the principal factors involved in drought associated declines of forest health and primary productivity. We investigated links between leaf gas exchange and hydraulic conductivity in Eucalyptus pauciflora during drought and recovery. Close coordination was observed among leaf gas exchange, leaf tissue water relations and the hydraulic capacity of the stem during the dry down phase. Although almost complete hydraulic failure occurred at a Ψx of -3.0MPa, stem hydraulic capacity was rapidly restored by a xylem refilling mechanism upon re-watering. These results provide crucial information for understanding how linkages between stem and leaf traits influence the recovery of woody plants from drought.