Crop load affects assimilation rate, stomatal conductance, stem water potential and water relations of field-grown Sauvignon blanc grapevines

The effects of two shoot densities (14 and 44 shoots/vine) and two crop levels (one and two clusters/shoot) on gas exchange and water relations of field-grown Sauvignon blanc (Vitis vinifera L.) were studied in a factorial design over 3 years. the two-cluster treatments had 0.14 MPa higher stem water potential (psi(stem)), 1.4 mu mol m(-2) s(-1) higher assimilation rate (A), 0.04 mol m(-2) s(-1) higher stomatal conductance (g(s)) and 0.008 mol m(-2) s(-1) higher non-stomatal (g(m)) conductance. The two-cluster treatments had higher g(s) and transpiration rates than the one-cluster treatments, for similar psi(stem). A quantitative analysis suggests that storage capacity cannot account for the simultaneous increase in g(s) and psi(stem) in the two-cluster treatments. Similar g(s)-g(m) responses were found in the one-and two-cluster treatments, regardless of differences between the treatments in g(s)-psi(stem) response.