plants Article Modeling Carbon Balance and Sugar Content of Vitis vinifera under Two Different Trellis Systems Linda Salvi 1 , Eleonora Cataldo 1 , Sofia Sbraci 1 , Francesca Paoli 1 , Maddalena Fucile 1 , Eleonora Nistor 2 and Giovan Battista Mattii 1, *   Citation: Salvi, L.; Cataldo, E.; Sbraci, S.; Paoli, F.; Fucile, M.; Nistor, E.; Mattii, G.B. Modeling Carbon Balance and Sugar Content of Vitis vinifera under Two Different Trellis Systems. Plants 2021, 10, 1675. https:// doi.org/10.3390/plants10081675 Academic Editor: Fermin Morales Received: 19 July 2021 Accepted: 13 August 2021 Published: 15 August 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Department of Agriculture, Food, Environment and Forestry (DAGRI), University of Florence, 50144 Florence, Italy; linda.salvi@unifi.it (L.S.); eleonora.cataldo@unifi.it (E.C.); sofia.sbraci@unifi.it (S.S.); francesca.paoli@unifi.it (F.P.); maddalena.fucile@unifi.it (M.F.) 2 Department of Horticulture, Banat University of Agricultural Sciences and Veterinary Medicine, 300645 Timis , oara, Romania; nisnoranisnora@gmail.com * Correspondence: giovanbattista.mattii@unifi.it; Tel.: +39-(0)5-5457-4043 Abstract: Environmental factors might influence the carbon balance and sugar content in grapevine. In this two-year research, the STELLA software was employed to predict dry matter accumulation in Sangiovese vines, comparing the traditional vertical shoot positioning (VSP) and the single high wire (SHW) trellis systems. Every week, vegetative, eco-physiological and grape quality parameters were collected for 15 tagged vines per trellis system to set up the software. Significant differences in photosynthesis were recorded in 2014, with higher values in VSP (23–25% more). Shoot growth was significantly higher in VSP (20–25% more), whereas higher dry matter (30%) and yield (9–11% more) were detected for SHW. At harvest, berry composition suggested a slower ripening in SHW compared to VSP, which was linked to the shading of clusters in SHW. Finally, for the first time, linear regressions were found between measured berry sugar content and STELLA-estimated dry matter (R 2 = 0.96 in VSP; R 2 = 0.95 in SHW). This latter evidence allowed the estimation of berry sugar content, showing this software to be a practical tool to support winegrowers in decision making. Other studies are already underway to calibrate and validate the model for other varieties, training systems and environments. Keywords: grapevine management; climate change; photosynthesis; yield; quality; STELLA software; vertical shoot positioning trellis; single high wire trellis 1. Introduction In the next decades, the climate will be characterized by increasing temperatures and concentrations of greenhouse gases in the atmosphere, as well as by changes in precipitation patterns [1]. Grapevine, one of the most widespread perennial crops in Europe [2], provides an example of an agricultural system that is highly sensitive and adaptive to changes in climate conditions [3,4]. High temperatures, in combination with water deficit, influence vine physiology and accelerate berry ripening processes, resulting in unbalanced wines with a high alcoholic content and low polyphenolic complexity [5–8]. Moreover, the rise of the atmospheric CO 2 concentration, through its influence as the source of carbon for photosynthesis, will have a significant stimulatory effect on grapevine vigor and yield, affecting sugar content and secondary metabolites [9–11]. Hence, the evaluation of the carbon balance in grapevine is of great importance, espe- cially in premium-wine producing areas, where the proper management of the vineyard represents a sustainable method to reach optimal grape quality [6,12–14]. The quantification of carbon dioxide depletion through photosynthesis can be achieved at the “whole-plant level” by enclosing whole plants in large air flux chambers coupled Plants 2021, 10, 1675. https://doi.org/10.3390/plants10081675 https://www.mdpi.com/journal/plants