Carbon isotope discrimination (δ13C) as an indicator of vine water status and water use efficiency (WUE): Looking for the most representative sample and sampling time

• The correspondence between δ13C and plant water status and WUE is highly variable.
• A more specific sampling procedure for δ13C determination is needed.
• Pot and field experiments in grapevines were carried out for this propose.
• δ13C measured in grapes at veraison-ripening shows the better correspondence with WUE and plant water status.

Dry mass Carbon isotope composition (δ13C) is a representative parameter of water use efficiency (WUE) in plants, as previously demonstrated by different authors for different species under different environmental conditions. Nevertheless, the relationship between δ13C and WUE in grapevines shows important variations among different experiments thus limiting its interest as indicator of water status or WUE. Our hypothesis was that such representativeness could be improved choosing an adequate sample and sampling time. Thus, the main objective of the present work was to identify the most representative sample and sampling time for a better assessment of grapevine water status and WUE by measuring: (i) the variability of WUE and δ13C in leaves and berries along growing season; (ii) the effect of water availability on WUE parameters and on δ13C; (iii) the relationships between leaf and plant WUE and the δ13C. Experiments were performed in the field at the Univertsity of Balearic Islands (Mallorca, Spain). The first experiment was carried out during the 2012 and 2013 seasons using cv. Tempranillo plants growing in 30-l pots under three levels of soil water content: (i) Control (100% of Field Capacity); (ii) Moderate water deficit (50% of Field Capacity) and (iii) Severe water deficit (25% of Field Capacity). The second experiment was performed under field-grown grapevines in the 2013 season, in cvs. Tempranillo and Grenache under two treatments: (i) Control (irrigation, 50% ETo) and (ii) No irrigation. In both experiments the correlation between the measured δ13C, in both young leaves (located in the middle zone of stem) and mature leaves (located in the basal zone of the stem) and berries in different growth stages and water use efficiency measured at the leaf level defined as intrinsic WUE (AN/gs) were studied, as well as at the whole plant level, defined as WUEplant (biomass increment/water consumed) and at the crop level, WUEc (yield/water applied). The best correlations were attained between δ13C and soil water status or intrinsic WUE (AN/gs). Berries at ripening showed to be the most appropriate organ to estimate both, the plant water status and the leaf and plant water use efficiency in grapevines.