Physiological recovery after drought increases with leaf and taproot drought tolerance among oak seedlings

Plants cope with drought stress using a range of functional adaptations involving main organs, and subsequent physiological recovery after stress release. However, there is a knowledge gap on the drought tolerance of woody plants from a whole plant perspective and the coordination of drought tolerance among plant organs, especially between shoots and coarse roots in species with strong taproots. Moreover, it remains uncertain if drought tolerance conflicts with physiological recovery from strong water stress. To address these questions, we conducted a common garden experiment with three widespread deciduous oaks in East Asia (Quercus variabilis, Quercus dentata, and Quercus mongolica) with distinct habitats linked to varying moisture conditions. Quercus variabilis, the species inhabiting the driest locations, exhibited the highest leaf drought tolerance, characterized by the lowest osmotic potential values and the most anisohydric stomatal behavior in response to water stress and the lowest vulnerability to drought-induced embolism in leaves and taproots. Stem-root hydraulic vulnerability segmentation was small in all oak species, but inexistent or negative in Q. variabilis. Recovery of water transport and gas exchange to water stress was faster in Q. variabilis, the most drought-tolerant species. Such faster recovery was linked to the ability of maintaining higher water transport capacity and stomatal conductance under severe water stress. We found limited evidence of drought tolerance coordination among plant organs. In conclusion, drought tolerance differences in oaks species are primarily linked with the foliage and the taproot, but not with the stem, and it is associated with the recovery capacity of physiological performance following severe water stress. Our study offers ecophysiological insights into the mechanisms underlying drought adaptation in oak species and contributes to understanding the regional and local distribution patterns of the studied oak species.