Preliminary results on allometric shoot measurement for carbon sequestration assessment

Abstract

To assess carbon sequestration in perennial crops such as grapevine, both the plant’s permanent and annual structures must be measured. Shoots represent, excluding clusters, the main carbon sink produced each growing season and are removed at winter pruning, so non-destructive estimators of shoot biomass are critical to scale vineyard carbon budgets. Allometric relationships linking easily measurable shoot dimensions (length, diameters) to biomass are widely used in forestry and have proven useful in viticulture (Miranda et al., 2018; Williams & Biscay, 1991), yet their robustness across contrasting terroirs remains poorly documented for Tannat, the flagship cultivar of Uruguayan viticulture. In three phenological stages (bunch closure, veraison and pre-harvest), in 2025-2026 growing season, we measured 216 primary shoots from 12 commercial Tannat vineyards located in the two main viticultural regions of Uruguay: Canelones (C, southern region, n = 6 vineyards, 108 shoots) and Maldonado (M, eastern region with stronger Atlantic influence, n = 6 vineyards, 108 shoots). Three shoots per cane were measured on two canes (north and south) per plant. For each shoot, we recorded total length (L, cm), basal diameter D_base (mm, measured at the central part of the internode between nodes 1 and 2) and apical diameter D_apical (mm, near the terminal internode). Pearson correlations and both linear (L = a + b·D) and power (L = a·D^b) models were evaluated, and homogeneity of slopes between regions was also tested. Shoot length was strongly and positively correlated with basal diameter D_base in both regions (in C; r = 0.53, p < 0.001; in M: r = 0.66, p < 0.001), confirming D_base as a robust non-destructive proxy for shoot vigour. Power-law fits resulted in L = 12.45·D_base^0.94 (R² = 0.32) for C, and L = 3.41·D_base^1.54 (R² = 0.43) for M. The allometric exponent differed significantly between regions, where M shoots showed a steeper length–diameter scaling, consistent with their higher mean length (112.7 ± 49.8 cm vs 99.5 ± 26.7 cm in C; p = 0.017). In contrast, apical diameter D_apical was not a useful predictor of shoot length in either region (Canelones: r = −0.10, n.s.; Maldonado: r = −0.17, p = 0.08); its variability likely reflects the state of apical growth at the time of sampling rather than accumulated biomass. These preliminary results support the use of basal shoot diameter as a simple field predictor of shoot length in Tannat vineyards. However, the L–D_base relationship is region-specific and should be calibrated per terroir before being integrated into carbon sequestration assessments. Next steps include pairing these allometric fits with destructive biomass sampling to convert dimensional estimates into dry matter and carbon stocks at the plot scale.

References

Miranda, C., Santesteban, L. G., Urrestarazu, J., Loidi, M., & Royo, J. B. (2018). Allometric relationships for estimating vegetative and reproductive biomass in grapevine (Vitis vinifera L.). Australian Journal of Grape and Wine Research, 24(4), 441–448. https://doi.org/10.1111/ajgw.12349

Williams, L. E., & Biscay, P. J. (1991). Partitioning of dry weight, nitrogen, and potassium in Cabernet Sauvignon grapevines from anthesis until harvest. American Journal of Enology and Viticulture, 42(2). https://doi.org/113–117. 10.5344/ajev.1991.42.2.113

Acknowledgements

This work is supported by Agencia Nacional de Investigación e Innovación (ANII FSA 1_2024_1_180236).