Scambi gassosi e risposte fisiologiche di viti di Sauvignon blanc durante deficit idrici in pre- e post-invaiatura

As global climate change intensifies, adapting viticulture to shifting conditions will be crucial. In regions experiencing higher temperatures and increased water scarcity, effective management of water stress will emerge as a vital component of vineyard management. Understanding the physiological responses of grapevines to water limitations can inform targeted interventions, ensuring that vine health and grape quality are maintained. The study aimed to evaluate the effects of two consecutive drought stress cycles, one before and one after veraison, on Sauvignon Blanc grapevines through physiological approaches. The trial was conducted in a semi-controlled tunnel at the "L. Toniolo" Experimental Farm of the University of Padua, in Legnaro, northeast Italy, from mid-June to mid-July 2024. Fifty vines of Sauvignon Blanc clone 108, grafted onto Kober 5 BB rootstock, were grown in 30-liter pots and divided into two groups: well-watered control plants and water-stressed plants. The control group was maintained at 85-90% of field capacity throughout the experiment, which started just before veraison (June 18th) and lasted until ripening (July 22nd). In the water-stressed group, irrigation was halted until a stem water potential (SWP) of -1.3 MPa was reached (First stress), followed by a six-day recovery period with well-watered conditions. After recovery, a second drought stress cycle was imposed: half of the stressed plants experienced similar conditions to the First stress (Second short-stress), while the other half underwent a more prolonged stress, with an SWP of -2.3 MPa (Second long-stress). Both groups then went through another six-day recovery period at well-watered conditions. Throughout the experiment, daily measurements of stomatal conductance were taken using a porometer (LI-COR 600), while chlorophyll fluorescence and leaf gas exchange were assessed during peak stress and recovery phases using a LI-COR 6800 system. A/Ci measurements were conducted at 30°C and 400 ppm CO2, followed by 300, 200, 100, 50, 400, 400, 600, 800, 1000, 12000 and 1400 ppm CO2 under 1500 µmol m2 s-1 of photosynthetic photon flux density (PPFD). The Farquhar, von Caemmerer, and Berry photosynthesis model ('FvCB model') was fitted to the experimental data to estimate the maximum carboxylation (Vcmax) and maximum electron transport (Jmax) rates. Plant water status was assessed by stem and leaf water potential (Ψleaf, MPa) using a PMS-600 pressure chamber. Malic acid levels were monitored starting just before the onset of veraison. The results confirmed the detrimental effects of water deficit on photosynthesis and stomatal conductance. Significant differences emerged between the second long-stress and both the first and second short-stress cycles, highlighting the grapevines' ability to recover from water stress. However, following the extended second-stress cycle, this recovery capacity weakened. This decline was reflected in the photosynthesis and fluorescence data, indicating a reduction in photosynthetic efficiency. This research contribute to a deeper understanding of the effects of climate change on viticultural practices, adding knowledge for the study of water management strategies in the viticulture sector.