Roots go through rapid hydraulic recovery following moderate water stress

Plant dehydration and rehydration cycles are universal phenomena in natural environments, especially in arid environments. Once a moderate water stress is relieved, the plant hydraulic system can recover, but the recovery process across roots, stems and leaves remains unknown. We examined the recovery dynamics of plant hydraulics and photosynthetic activity following moderate water stress in one herbaceous plant (Glycine max) and one woody shrub (Caragana korshinskii).

The research was conducted on pot-grown plants in a glasshouse and the recovery dynamics of the predawn leaf water potential (ψleaf), hydraulic conductance of the leaf (Kleaf), stem (Kstem) and root (Kroot), stomatal conductance (gs), leaf photosynthetic rate (An) and non-structural carbohydrates (NSCs) were monitored after the plants were released from a moderate water stress.

Under moderate water stress with decreasing predawn ψleaf, Kleaf and Kroot in both species were more sensitive to water deficit than was Kstem, and the decrease in gs was faster than that in An, resulting in an increase in intrinsic water use efficiency (WUEi); NSCs decreased in leaves and stems but accumulated in roots. After rehydration, both species showed a faster recovery in Kroot and Kstem than in Kleaf, and a slower recovery in gs than in An, resulting in an increase in WUEi.

The rapid recovery in Kroot contributes to plant recovery from water stress, and slow recovery in Kleaf limits stomatal reopening, thus reducing transpiration and maintaining high WUEi. These traits enable species to tolerate drought.