Carbon (δ¹³C) and nitrogen (δ¹⁵N) variability across vineyards and grapevine components

Abstract

Stable isotopes of carbon (δ¹³C) and nitrogen (δ¹⁵N) provide valuable integrative indicators of grapevine water status (Gaudillère et al., 2002; van Leeuwen et al., 2023) and nitrogen metabolism (Santesteban et al., 2015, Santesteban et al., 2024). Here, we quantified δ¹³C and δ¹⁵N in three vineyards on Waiheke Island (New Zealand), with different topography, rootstocks, and management, to determine which grapevine component(s) most reliably reflect grapevine variation in δ¹³C and δ¹⁵N. For this, we analysed 54 samples, including leaves, seeds, skin, pulp, bulk juice, and whole berry, and tested:

• δ¹³C and δ¹⁵N isotopic differences among grapevine components: we found modest but significant differences for both δ¹³C (Pr(>F)=04) and δ¹⁵N (Pr(>F)=0.01). For δ¹³C, values showed low variability, with means ranging from –29.2 ‰ in seeds to –28.1 ‰ in bulk juice, likely reflecting the uniformly non-stressed water status of the sampled grapevines (δ¹³C < –26 ‰; van Leeuwen et al., 2023). δ¹⁵N differed significantly among components, with seeds enriched (2.88 ‰) relative to all other components (0.61–1.40 ‰).
• δ¹³C–δ¹⁵N correlations among components: we found a significant correlation for bulk juice (r=0.71, p=0.03), showing that higher δ¹⁵N was associated with higher δ¹³C.
• δ¹³C and δ¹⁵N isotopic variability by vineyard: vineyard site had a highly significant effect on both δ¹³C and δ¹⁵N (Pr(>F)<0.01). While δ¹³C likely reflected topographic differences among vineyards, δ¹⁵N did not distinguish the vineyard managed under organic practices.
• δ¹³C and δ¹⁵N isotopic variability among grapevine components by vineyard: both site and component showed significant differences for δ¹³C and δ¹⁵N (Pr(>F)<0.01). Within vineyards, δ¹³C did not differ among components, indicating that it was mainly driven by whole-vine physiology. We found no site × component interaction for δ¹³C, while δ¹⁵N resulted in a marginal interaction (Pr(>F)=0.05), suggesting that the component differences in δ¹⁵N depend on vineyard-specific nitrogen dynamics.

Overall, our results show that under no water stress, vineyard characteristics, rather than sampled grapevine component, drive most of the δ¹³C and δ¹⁵N isotopic variability. Among the sampled components, bulk juice appears as the best integrator of both isotopic signals.

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Acknowledgments

We would like to thank Matt Sloan for granting us access to the vineyards and sharing his valuable knowledge, Heinrich Storm and Clement Brevet for their assistance. TG was supported by the School of Environment Internal DRDF Fund 2025, University of Auckland. IR acknowledges the support of the Marie Skłodowska-Curie Actions (Grant No. 101152621) HORIZON-MSCA-2023-PF-01.