Shiraz vines maintain yield in response to a 2–4 °C increase in maximum temperature using an open-top heating system at key phenostages

We measured the effects of increased daytime temperature during 2- (2007/08) or 3-week periods (2008/09) on the yield and yield components of irrigated Shiraz vines in the Barossa Valley of Australia. A simple and inexpensive open system was used to elevate temperature during a single phenological window, either bracketing budburst (E-L stage 4), shortly after flowering (E-L stage 23), bracketing pea size (E-L stage 31), around veraison (E-L stage 35) or shortly before harvest (E-L stage 38). Two important features of the heating systems were tracking of diurnal temperature dynamics, and maintaining relative humidity, hence avoiding the interaction between temperature and vapour pressure deficit. Minimum temperature was unchanged.Compared to controls, maximum ambient temperature was increased between 1.8 and 4.1 °C in treated plots but canopy temperature of treated vines only increased by 0.9–1.1 °C. Elevation of bunch temperature was 2.3–3.2 °C. Increasing temperature around budburst transiently accelerated development in comparison to controls; no phenological changes were detected for other timings of treatment. Yield averaged 4.3 kg vine−1 in 2007–08 and 6.1 kg vine−1 in 2008–09. In both seasons and for all timings of treatment, increasing temperature did not affect yield or its components; lack of yield response did not result, therefore, from compensatory mechanisms, e.g. heavier berries compensating for fewer fruit. The dynamics of berry growth and total soluble solids were largely unaffected by temperature. Under our experimental conditions, the capacity of irrigated Shiraz canopies to partially buffer a 2–4 °C increase in maximum ambient temperature may have been important for the maintenance of yield, and berry growth and sugar accumulation.