The aims of this work were (i) to study the relationships between leaf water potential, foliar chlorophyll content and photosynthetic performance of grapevines under field conditions, and (ii) to evaluate the feasibility of chlorophyll fluorescence parameters to assess water status in commercial vineyards. During three consecutive seasons (2011 to 2013), 20 non-irrigated “Tempranillo” vineyard subzones were monitored in Ribera del Duero, Spain. Data on foliar chlorophyll content, midday and predawn leaf water potential, net assimilation and chlorophyll fluorescence parameters were measured at fruit set, pre-véraison and véraison. The results show that the water potential indicated weak to moderate stress in the study years and decreased along the vegetative cycle, while foliar chlorophyll contents showed an increasing trend. The correlation between both variables was not consistent. Linear regression of the chlorophyll fluorescence parameters in dark-adapted leaves, Fo, Fv and Fv/Fm, over chlorophyll content was strong in all the study years (higher determination coefficients for Fv/Fm at fruit set in 2012 and 2013). In general, the water potential with low coefficients of variation showed a low effect on photosynthesis activity, although values in variables such as Fm, Fv, Fv/Fm, Fs/Fo and ΦPSII registered an increasing trend when midday leaf water potential decreased in the pre-véraison and véraison stages. These variables could be useful to estimate water status in commercial vineyards for application in precision viticulture.

ISHS I International Symposium on Grapevine Growing, Commerce and Research COLOUR OF 'TEMPRANILLO' GRAPES AS AFFECTED BY DIFFERENT NITROGEN AND POTASSIUM FERTILIZATION RATES