Coordinated decline of leaf hydraulic and stomatal conductances under drought is not linked to leaf xylem embolism for different grapevine cultivars

Authors: ALBUQUERQUE, CAETANO - University Of California, Davis; SCOFFONI, CHRISTINE - University Of California (UCLA); BRODERSEN, CRAIG - Yale University; BUCKLEY, THOMAS - University Of California, Davis; SACK, LAWREN - University Of California (UCLA); McElrone, Andrew

Submitted to: Journal of Experimental Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/18/2020
Publication Date: 12/11/2020
Citation: Albuquerque, C., Scoffoni, C., Brodersen, C., Buckley, T., Sack, L., McElrone, A.J. 2020. Coordinated decline of leaf hydraulic and stomatal conductances under drought is not linked to leaf xylem embolism for different grapevine cultivars. Journal of Experimental Botany. 71(22):7286-7300. https://doi.org/10.1093/jxb/eraa392.
DOI: https://doi.org/10.1093/jxb/eraa392

Interpretive Summary:

Technical Abstract: Drought decreases the water transport capacity of plants and limits gas exchange in part by reducing leaf hydraulic permeability. Changes in leaf hydraulic conductance (Kleaf) are known to involve reduced transport capacity in the xylem and outside-xylem (i.e. where water moves in cell walls and across living cells) pathways. Some literature suggests that grapevines are hyper-susceptible to drought-induced xylem embolism, and grapevine cultivars exhibit differential responses to drought. We evaluated whether leaf vein embolism and Kleaf play a significant role in the responses of two different grapevine cultivars (Vitis vinifera L. cvs. Cabernet Sauvignon and Chardonnay) subjected to mild-moderate water stress. We combined Kleaf and gas exchange measurements with synchrotron-based microCT images of intact leaves on plants subjected to dehydration. We then used a spatially explicit model of the outside-xylem to simulate the possible anatomical drivers of leaf responses during drought. Cabernet Sauvignon and Chardonnay exhibited similar vulnerabilities of Kleaf and gs to dehydration, decreasing substantially before embolism was present in the leaves. Leaf xylem cavitation initiated around 'leaf = -1.25 MPa in the midribs and little to no embolism was detected in minor veins even at severe dehydration for both varieties. Cabernet Sauvignon exhibited twice the gs of Chardonnay throughout dehydration range. We conclude that during moderate water stress, changes in the water pathways outside-xylem, rather than xylem embolism, are responsible for reduced Kleaf and gs during mild dehydration. Modelling results indicated that reduced membrane permeability associated with a Casparian-like band in the bundle sheaths of leaf veins would explain declines in Kleaf of both cultivars. For crop species such as grapevines understanding this mechanism is of great importance the maintenance of hydraulic capacity ensures adequate carbon capture for photosynthesis and thus crop performance under water stress.