Herb and conifer roots show similar high sensitivity to water deficit

Root systems play a major role in supplying the canopy with water, enabling photosynthesis and growth. Yet, much of the dynamic response of root hydraulics and its influence on gas exchange during soil drying and recovery remains uncertain. We examined the decline and recovery of the whole root hydraulic conductance (Kr) and canopy diffusive conductance (gc) during exposure to moderate water stress in two species with contrasting root systems: Tanacetum cinerariifolium (herbaceous Asteraceae) and Callitris rhomboidea (woody conifer). Optical dendrometers were used to record stem water potential at high temporal resolution and enabled non-invasive measurements of Kr calculated from the rapid relaxation kinetics of water potential in hydrating roots. We observed parallel declines in Kr and gc to