Berry composition and climate: responses and empirical models

Abstract

Climate is a strong modulator of berry composition. Accordingly, the projected change in climate is expected to impact on the composition of berries and of the resultant wines. However, the direction and extent of climate change impact on fruit composition of winegrape cultivars are not fully known. This study utilised a climate gradient along a 700 km transect, covering all wine regions of Western Australia, to explore and empirically describe influences of climate on anthocyanins, pH and titratable acidity (TA) levels in two or three cultivars of Vitis vinifera (Cabernet Sauvignon, Chardonnay and Shiraz). The results showed that, at a common maturity of 22° Brix total soluble solids, berries from the warmer regions had low levels of anthocyanins and TA as well as high pH compared to berries from the cooler regions. Most of these regional variations in berry composition reflected the prevailing climatic conditions of the regions. Thus, depending on cultivar, 82-87 % of TA, 83 % of anthocyanins and about half of the pH variations across the gradient were explained by climate-variable-based empirical models. Some of the variables that were relevant in describing the variations in berry attributes included: diurnal ranges and ripening period temperature (TA), vapour pressure deficit in October and growing degree days (pH), and ripening period temperatures (anthocyanins). Further, the rates of change in these berry attributes in response to climate variables were cultivar dependent. Based on the observed patterns along the climate gradient, it is concluded that: (1) in a warming climate, all other things being equal, berry anthocyanins and TA levels will decline whereas pH levels will rise; and (2) despite variations in non-climatic factors (e.g. soil type and management) along the sampling transect, variations in TA and anthocyanins were satisfactorily described using climate-variable-based empirical models, indicating the overriding impact of climate on berry composition. The models presented here are useful tools for assessing likely changes in berry TA and anthocyanins in response to changing climate for the wine regions and cultivars covered in this study.

Fig. 1

Map of study areas in Western Australia. Numbered dots in enlarged picture represent study site locations. October–April average temperature, average annual rainfall, and dominant soil types for each site are indicated in parentheses. Climate data (average for the 1976–2005 period) was obtained from SILO DataDrill database (Jeffrey et al. 2001)

Fig. 2

Levels of grape quality attributes [anthocyanins, titratable acidity (TA), and pH] at total soluble solids (TSS) of 22 °Brix. Sites are listed (from left to right) according to their long-term growing season temperature in decreasing order

Fig. 3

Correlations between grape quality attributes (TA, pH and anthocyanin concentrations) at common maturity (22 °Brix TSS) and climate variables for Cabernet Sauvignon, Shiraz and Chardonnay. Months are denoted by their initial three letters. Tmn Minimum temperature; Tav average temperature; Tmx maximum temperatures; RP ripening period; DR diurnal range; D25, D30 number of days with maximum temperature over 25 °C or 30 °C; H25, H30 number of hours over 25 °C or 30 °C; Evp Class A pan evaporation; VPD vapour pressure deficit; Rad net radiation; AWC available soil water holding capacity; Rn_SN, Rn_GS rainfall during September to November or during growing season, respectively

Fig. 4

Relationships between berry anthocyanin concentrations at 22 °Brix TSS and the veraison period average temperature for Cabernet Sauvignon (filled circles) and Shiraz (open circles). Data points represent different sites. b Slope of the regression line, P probability of the trend line being different from zero

Fig. 5

Relationships between berry a TA, b pH and the growing season maximum temperature for Cabernet Sauvignon (filled circles), Shiraz (open circles) and Chardonnay (triangles). Data points represent sites. b Slope of the regression, P probability of the trend line being different from zero

Fig. 6

Relationships between the veraison period average temperature and rates of change in a TA, b anthocyanin concentration per unit of TSS increase for Cabernet Sauvignon (circles), Shiraz (squares) and Chardonnay (triangles). Two extreme values of (filled circles) Cabernet Sauvignon TA were not included in the regression. Inset Estimation of the rates of change of quality attributes over the veraison to harvest period using the sequential sampling data for the Kudardup site in Season 2