Carbon isotope discrimination in primary products of photosynthesis varies with plant water uptake conditions. This property was used to show that the 13C/12C ratio (called ΔC13) in grape sugars and tartrate measured at ripeness can be a valuable indicator of vine water deficit. Correlation between ΔC13 in grape sugar and minimum pre-dawn leaf water potential is excellent (R2 = 0,81; n = 36). A statistically significant effect of soil and vintage is pointed out. When measured on a great number of plots of an estate, ΔC13 varies with the soil type. This proves ΔC13 can be a valuable tool in « terroir » studies. ΔC13 measured on phenolic compounds in wine is also significantly correlated to minimum pre-dawn leaf water potential as well as to ΔC13 in grape sugar. ΔC13 is actually the only tool capable to assess global vine water uptake conditions between veraison and harvest at a low cost, without the installation of heavy equipment in the vineyard.
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