Berry carbon (δ¹³C) and nitrogen (δ¹⁵N) isotopic ratio reflects within farm terroir diffferences

ÂThe natural abundance of carbon stable isotopes has been reported to be related to water availability in grapevines quite widely. In the case of nitrogen, the natural abundance of its stable isotopes is mainly affected by the nature of the source of nitrogen (organic vs. inorganic) used by the plant, though the bibliography available for grapevine is very scarce. The aim of this work was to evaluate the effect of terroir on carbon and nitrogen stable isotope natural abundance within a single grape growing farm. Three vineyards representative of three terroirs within a grape growing farm were selected. The mesoclimatic differences between them can be considered negligible, and crop management was in general terms the same. Therefore, the differences in plant behaviour should be majorly a consequence of soil characteristics (deep gravely vs. shallower loamy soil, cover crop vs. bare soil). During five consecutive seasons, plant vegetative growth and stem water potential (Ψs) were monitored throughout the growing season and, at harvest, yield and grape composition were determined including carbon (δ13C) and nitrogen (δ15N) isotopic ratios. Consistent differences for both δ13C and δ15N were found when the three terroirs were compared. On the one hand, δ13C reflected well the differences in water availability arising from either soil characteristics (deep gravelly vs. shallower loamy soil) and from the presence of a cover crop. On the other hand, δ15N was clearly higher in the gravelly soil area, possibly indicating nitrate leakage, since soil organic matter is known to have higher δ15N than inorganic fertilizers. The competition the cover crop exerted for N was reflected in berry nitrogen content but, on the contrary, did not affect δ15N.