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

Abstract

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 (ψ_stem), 1.4 μmol 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 ψ_stem. A quantitative analysis suggests that storage capacity cannot account for the simultaneous increase in g_s and ψ_stem in the two-cluster treatments. Similar g_s-g_m responses were found In the one- and two-cluster treatments, regard less of differences between the treatments in g_s-ψ_stem response.

Grapevine, stomatal conductance, assimilation rate, water relations