Vitis vinifera L. varieties (cv. Cabernet Sauvignon and Chardonnay) vary in leaf water flux in response to elevated CO2 growing conditions and a gradual water deficit.

Abstract

Grapevine (Vitis vinifera L.) stomata are highly sensitive to atmospheric changes and influence the tradeoff between water and carbon, as estimated by intrinsic water use efficiency (iWUE). The aim of this study was to examine how elevated CO₂ concentrations and water deficit affect the iWUE and whole plant evapotranspiration of two grapevine varieties (cv. Cabernet Sauvignon and cv. Chardonnay). Dormant cuttings were collected from a vineyard in Temecula Valley, CA, and were grown in a growth chamber under one of two CO₂ treatments: near ambient (410 ppm) or elevated (700 ppm). After 8 weeks of vegetative growth, grapevines were subjected to a well-watered (25% soil water content [SWC]) or gradual water-deficit treatment implemented over 12 days. We measured leaf gas exchange, including photosynthesis (A _net), stomatal conductance (g _s), intercellular carbon (C _i ), and calculated iWUE (A _net/g _s), as well as daily cumulative evapotranspiration per unit leaf area (g cm^-2 day^-1). Vines were harvested to determine total dry weight, root mass fraction, and nitrogen content. We found that elevated CO₂ and water deficit interactively increased the iWUE for both varieties, with Cabernet Sauvignon having 20% greater iWUE than Chardonnay at ~5% SWC. Chardonnay exhibited greater maximum conductance, and 43% more water transpired than Cabernet Sauvignon under a well-watered treatment. Chardonnay plants were also more impacted by elevated CO₂ and water-deficit treatment than Cabernet Sauvignon, exhibiting greater stomatal sensitivity under these treatments. At ambient CO₂, water deficit negatively impacted Chardonnay's photosynthesis than Cabernet Sauvignon. However, this effect was not observed at elevated CO₂. This study elucidates the intraspecific differences in stomatal behaviour, productivity, and water use of two V. vinifera L. genotypes (Cabernet Sauvignon and Chardonnay), under elevated CO₂ concentrations and short-term water deficit.