Influence of Canopy Vineyard Management on Physiological Behaviour and Radiation Interception Efficiency in Syrah

Historically, certain physiological behaviours were typically attributed to genetic factors. However, some grape varieties exhibit different responses depending on crop management and environmental conditions. The present study examines whether the physiological responses of grapevines traditionally attributed to genotypic traits (near-isohydric or near-anisohydric behaviour) can instead be substantially modified by canopy architecture. The objective was to determine how canopy management influences water relations (leaf water potential—ΨL), physiological plant responses (water use efficiency (WUE), stomatal conductance (gs), transpiration (E) and photosynthetic (A) rates), and radiation interception efficiency (εi), particularly under warm Mediterranean conditions. To test this, two training systems were evaluated in a Syrah vineyard: a vertical shoot position (VSP1) and a sprawl (S1) system with 12 shoots·m−1, under the same irrigation regime. The results showed that under stressed conditions (high vapor pressure deficit [VPD] and relatively lower ΨL, from −1.4 to −0.6 MPa), the S1 system—despite a similar leaf area index, LAI—exhibited lower gs values than those of the VSP1 system (10–30%), with plants closing their stomata to reduce water consumption and prevent their dehydration caused by steep E rates. Meanwhile, the VSP vines exhibited higher gs values (isohydric-like response), indicating higher E rates, which reduced their WUE and intrinsic water-use efficiency (IE). This strategy (similar to the anisohydric one) allowed the S1 treatment to obtain higher WUE and interception radiation efficiency (εi) ratios, even at low ΨL (more efficient), produced by the higher canopy demand (more exposed surface area [SA]). These contrasting behaviours indicate that sprawl systems can enhance radiation interception and WUE compared with vertical systems under semiarid Mediterranean conditions.