Carbohydrate physiology of grapevine leaves under regulated deficit irrigation and crop load strategies

Abstract

Photosynthesis and carbohydrate dynamics are highly affected by abiotic stresses, making them a target to be studied in a context of fluctuating and constraining environment. The impact of regulated deficit irrigation (RDI) and crop load on grape and wine quality have been widely studied. However, there is limited knowledge about the effects of combined RDI strategies and crop level on the leaf carbohydrate accumulation and allocation, which ultimately determines plant growth and yield. The objectives of the study were to quantify the combined effects of regulated deficit irrigation and crop load strategies on leaf carbon balance and nonstructural carbohydrates accumulation of field grown grapevines. The trial was conducted during 2009/10 growing season in Mendoza, Argentina. Two levels of water supply between fruit set and harvest (100% and 25% of reference evapotranspiration ETo), and two crop loads imposed at veraison (100% and 50% of the clusters) were applied to the vines. Daily dynamics of leaf water potential, photosynthesis (Pn) and carbohydrates concentration were determined at bloom, veraison and harvest. Deficit irrigated vines reduced their Pn at veraison and harvest and their starch concentration at veraison, while soluble sugars increased. On well watered plants, carbon accumulated during the day was locally consumed or re-allocated to other organs during the night. By contrast, RDI vines did not modify their carbon status during the night, indicating a reduced metabolic activity and carbon export. Crop load did not affect neither photosynthesis nor carbohydrate concentration. Our study showed that RDI plants allocated more carbon into soluble sugars probably as an active strategy against severe water stress. Appropriate irrigation schedule is crucial to maintain an adequate leaf photosynthetic activity to ensure yield and carbon reserves for budbreak the next growing season.