Irrigated Shiraz vines (Vitis vinifera) upregulate gas exchange and maintain berry growth in response to short spells of high maximum temperature in the field

Abstract

We tested the hypotheses that (i) a short period of high maximum temperature disrupts gas exchange and arrests berry growth and sugar accumulation in irrigated Shiraz vines (Vitis vinifera L.), and (ii) the magnitude of these effects depend on the phenological window when stress occur. Using a system combining passive heating (greenhouse effect) and active cooling (fans) to control daytime temperature, we compared vines heated to a nominal maximum of 40°C for three consecutive days and untreated controls. Maximum air temperature in heated treatments was 7.3°C (2006–07) and 6.5°C (2007–08) above ambient. Heat episodes were aligned with the beginning of a weekly irrigation cycle and applied in one of four phenological windows, namely post-fruit set, pre-veraison, veraison and pre-harvest. Heating systems did not affect relative humidity, hence vapour pressure deficit (VPD) was increased in the heated treatments and tracked the daily cycle of temperature. Heat did not affect the dynamics of berry growth and sugar accumulation, except for a 16% reduction in berry size and sugar content in vines heated shortly after fruit set in 2006–07. Vines upregulated stomatal conductance and gas exchange in response to heat. Stomatal conductance, photosynthesis and transpiration at a common VPD were consistently higher in heated vines than in controls. We suggest that stomatal behaviour previously described as part of Shiraz anisohydric syndrome may be adaptive in terms of heat tolerance at the expense of short-term transpiration efficiency.

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“…Subsequent studies have shown, that these differences in g were also triggered in response to VPD (Soar et al 2006a), and correlated with differential expression of key genes in the ABA biosynthetic pathway in leaves but not roots (Soar et al 2006a). However, recent findings in an outdoor 'heating experiment' (40°C for three consecutive days) showed that anisohydric Syrah vines up-regulated g, E, and A in response to temperature (Soar et al 2009) at a common VPD. However, recent findings in an outdoor 'heating experiment' (40°C for three consecutive days) showed that anisohydric Syrah vines up-regulated g, E, and A in response to temperature (Soar et al 2009) at a common VPD.…”