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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.

Although water deficit and iron deficiency chlorosis are common environmental stresses in the Mediterranean area, few data are reported in the literature on their effects on vineyards, when acting simultaneously. The main objective of this research was to study the combined effects of iron deficiency and water status on vigor, yield and fruit composition in rainfed vineyards. Moreover, the investigation aimed to evaluate the feasibility of using foliar chlorophyll content (Chl) and predawn leaf water potential (LWP), measured at veraison, to assess potential quality of grapes in the framework of precision viticulture. For this, 24 non-irrigated 'Tempranillo' vineyard subzones were monitored in Ribera del Duero (North-Central Spain) during three consecutive seasons (2011)(2012)(2013). The analysis of variance and principal component analysis showed that malic acid concentrations of the must were impacted only by Chl, whereas total soluble solids and total acidity were mainly modified by LWP. Both water and iron status reduced yield and berry weight and had additive effects on extractable anthocyanin content in grapes, total polyphenol index and color density of the must. In all seasons, the ratio Chl/LWP had a better predicting value for quality parameters of these grapes than leaf area index, Chl or LWP individually. The present work demonstrates the potential interest of physiological indexes combining water status and foliar chlorosis as indicators of grape phenolic potential in rainfed vineyards affected by iron deficiency.