Root pressure-volume curve traits capture rootstock drought tolerance

Authors: BARTLETT, MEGAN - University Of California, Davis; SINCLAIR, GABRIELA - University Of California, Davis; FONTANESI, GABRIELA - University Of California, Davis; KNIPFER, THORSTEN - University Of British Columbia; WALKER, M - University Of California, Davis; McElrone, Andrew

Submitted to: Annals of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/18/2021
Publication Date: 10/20/2021
Citation: Bartlett, M.K., Sinclair, G., Fontanesi, G., Knipfer, T.M., Walker, M.A., McElrone, A.J. 2021. Root pressure-volume curve traits capture rootstock drought tolerance. Annals Of Botany. 129(4):389-402. https://doi.org/10.1093/aob/mcab132.
DOI: https://doi.org/10.1093/aob/mcab132

Interpretive Summary:

Technical Abstract: Roots are an important bottleneck for whole-plant drought tolerance. Water stress causes the roots to lose volume and turgor, which are crucial to root structure, hydraulics, and growth. Thus, we hypothesized that root pressure-volume (p-v) curve traits, which quantify the effects of water potential on bulk tissue turgor and volume, would strongly impact plant drought tolerance. We used a greenhouse experiment to conduct a novel test of the relationships between p-v curve traits and gas exchange, whole-plant hydraulic conductance, and growth under drought across 8 grape rootstocks grafted to the same scion variety. These traits varied significantly across rootstocks, and droughted plants significantly reduced turgor loss point, osmotic potential at full hydration, and capacitance (C) values, suggesting these roots retain greater turgor and volume under water stress. The rootstocks with a lower C, which indicates a smaller decline in root volume with water potential, maintained greater stomatal conductance and photosynthesis under water stress. All traits were correlated with root system size, but rootstock variety was a stronger predictor than any individual trait. These traits were not related to whole-plant hydraulic conductance or canopy size. The turgor loss point, osmotic potential at full hydration, and C in well-watered plants were significantly lower in the rootstocks classified as drought tolerant by previous field trials, but turgor loss point and osmotic potential at full hydration in water-stressed plants were significantly higher in these varieties, indicating greater vulnerability to turgor loss. Altogether, these findings suggest that trait plasticity, to reduce declines in root volume, improves gas exchange and water uptake in consistently dry soil, potentially through impacts on root hydraulics or root-to-shoot chemical signaling. However, retaining turgor and volume as previously unstressed roots deplete wet soil to moderately negative water potentials could be more important to drought performance in the deep, highly heterogeneous rooting zones in the field.