Shoot thinning effects on seasonal whole-canopy photosynthesis and vine performance in Vitis vinifera L. cv. Barbera

Background and Aims: While shoot thinning is one of the most widely applied practices in the vineyard as a tool to regulate canopy density and/or crop level, its physiological bases are still fairly obscure and have been poorly investigated. Our aim was to assess seasonal modification of whole-canopy net CO(2) exchange rate (NCER) in thinned and non-thinned grapevines, as well as establishing correlations with grape composition. Methods and Results: Potted, mature cv. Barbera vines were thinned (ST) to 10-15 shoots/m over the two trial years and compared with a non-thinned control (C). The data logged each season included whole-vine NCER monitored pre-and post-veraison for periods of variable lengths, vine growth, yield components and grape composition. While final leaf area per vine did not differ between treatments, ST showed reduced yield and improved berry colour and must sugar accumulation. In 2009, NCER/vine recovery in ST was 85% of C at verasion, whereas in 2010 full recovery was already reached around bloom. Conclusions: A load of 15 shoots/m maximised canopy efficiency by inducing the fastest recovery of whole-vine photosynthesis and markedly improved sugar, colour and phenolics. Retaining 10 shoots/m delayed NCER recovery while improving overall grape composition as compared to C. Significance of the Study: Direct assessment of the complex seasonal canopy NCER dynamics triggered by shoot thinning indicates that the source-sink balance evolves in ST towards a higher supply of assimilates per unit of crop than that available in non-thinned canopies during the veraison-to-harvest period.