Effects of water stress on photosynthetic characteristics of ‘Cabernet Sauvignon’at different leaf ages

Abstract：【Objective】A study was carried out on photosynthetic and fluorescence characteristics of grape leaves under water stress. Grapes are mainly planted in the arid and semi-arid areas in China. The photosynthetic function of leaves is different in different leaf ages. Therefore, to explore the changes of photosynthesis and chlorophyll fluorescence of grape leaves at different leaf ages under water stress is of great significance to the water-saving cultivation of grape in China【Methods】The experiment was carried out in 2018 in a glass greenhouse in Yuquanying Farm of Ningxia Agricultural Reclamation Group and the experimental station of the National Grape Industry Technology System. The ranges of temperature in the glass greenhouse was 24-38 ℃, humidity 38%-58%, and air CO2 concentration 300-500 μmol·mol-1. 3-year-old‘Cabernet Sauvignon’grape (Vitis vinifera L.) vines were used as the mate-rials. The ψ b was measured with a 3005 pressure chamber (Soil Moisture Equipment Company, USA)after water stress treatment, which was carried out on June 20, 2018. The daily irrigation time was con-trolled by a time controller, and the ψ b was used to reflect the stress degree. During the shoot growth pe-riod in mid-April 2018, the first unfolded leaves on the annual branches were marked on April 20, April 30, May 10, May 20 and May 30, and named as Leaf 1, Leaf 2, Leaf 3, Leaf 4 and Leaf 5, respectively. The day (d) was used as the measurement unit of leaf age, and the unfolding date was regarded as the initial leaf age (0 d). By June 20, Leaf 1-5 (leaf age 60 d, 50 d, 40 d, 30 d and 20 d). Three water treat-ments were set including no water stress (CK), moderate water stress (T1), and severe water stress (T2),with water potential range of -0.2 MPa ≤ ψb, -0.60 MPa ≤ψb≤-0.40 MPa and ψb ≤-0.60 MPa, respec-tively. Changes in leaf area, leaf photosynthetic parameters, chlorophyll fluorescence parameters and the activities of Rubisco and fructose-1, 6-bisphosphatase in the new shoots of‘Cabernet Sauvignon’grape were measured.【Results】There were significant differences in leaf indexes among different leaf ages under water stress. The leaf area of grape increased with the increase of leaf age, and the order of leaf area was Leaf 1 > Leaf 2 > Leaf 3 > Leaf 4 > Leaf 5. There was no significant difference between T1 and CK, but T2 significantly decreased leaf area at each leaf age (p < 0.05). The results indicated that severe water stress inhibited the increase of leaf area at all leaf ages. The value of SPAD showed a similar trend. T1 increased the SPAD values in all leaf ages but there was no significant difference with CK, while T2 significantly decreased the SPAD value of leaves of all leaf ages (p < 0.05). With the in-crease in leaf age, Pn, Gs and Tr all increased at first and then decreased, and decreased with the severity of water stress. T2 significantly reduced Pn and the activities of Rubisco and fructose-1,6-bisphospha-tase in leaves of each leaf age, but there was no significant difference between T1 and CK. Water stress decreased Fv/Fm, Yield, ETR, qP, and significantly increased F0 of all leaf ages. T2 increased NPQ in leaves of all ages, but with the increase in leaf age, NPQ of T2 leaves was significantly lower than that of the other two treatments. Among the measured indexes, Leaf 1, Leaf 2 and Leaf 5 were greatly affect-ed, indicating that both the old and young leaves were greatly affected by water stress, while the mature leaves were less affected and became the main contributors to photosynthesis. Grape leaves at the ages of 60-110 days were less susceptible to water stress as reflected by relatively high photosynthetic capaci-ty under water stress.【Conclusion】With the increase in leaf age of‘Cabernet Sauvignon’grape, the photosynthetic capacity increased at first and then decreased, and was highest in leaves at the age of 60-90 days. Water stress reduced photosynthetic efficiency of leaves of all ages, while severe water stress hindered the normal development of the young leaves and accelerated the senescence of old leaves. This study provides a theoretical basis for grape defoliation practice and water- saving cultivation in grape production.