Grapevine row orientation mediated temporal and cumulative microclimatic effects on grape berry temperature and composition

Ambient radiation and temperature are global drivers of grapevine growth, grape yield and composition, and wine quality. Knowledge of the implications of vineyard row orientation/microclimate is required for decision-making in current and future macro- and mesoclimates. Temporal and cumulative microclimatic changes, induced by vine row orientation (NS; EW; NE-SW; NW-SE) of vertically trellised Shiraz grapevines, on berry pulp temperature and composition at different ripeness levels were investigated. Berries dynamically gained heat energy relative to: ambient climate/weather; direct canopy wall/bunch irradiance; and berry skin colour development. Berries exposed to direct solar radiation during the morning, leading to higher pulp temperatures than ambient, but having a cooling profile after that, resulted in slightly advanced sugar ripening and generally higher skin total anthocyanins and phenols, without significant effects on pH and titratable acidity, at the respective ripeness levels. In contrast, excessive exposure of bunches and those that built up heat, reaching highest temperatures during late afternoon, seemed not conducive to grape composition associated with higher quality. The S, SE, E and NE canopy sides showed consistently higher skin total anthocyanin and phenol contents than their counter sides. Except for acylated forms of peonidin-glucoside, anthocyanin (mono-, acetyl- and coumaroyl-glucosides) accumulation was mostly favoured in berries exposed to exterior canopy sides, but differences in acylated anthocyanins between exterior-facing and interior-facing berries were less than for mono-glucoside anthocyanins. Over-exposure and heat peaking during late afternoon seemed detrimental. Novel information on berry pulp temperature variation in a developing composite grape bunch, exposed to weather and microclimate fluctuation, is provided. An ostensibly homogeneous bunch in reality represents a dynamic berry pulp thermal range at any point in time. Cumulative thermal and radiation impact was evident. This is the first comprehensive attestation on the role of grapevine row orientation (or any viticulture practice) in the management of seasonal nocturnal- and diurnal berry temperature and concomitant composition.