Effects of nano zero-valent iron on the growth and photosynthetic characteristics of the new shoots and leaves of Pinot Noir in Wuwei production area

Abstract:【Objective】This study focused on the grape variety Pinot Noir, predominantly cultivated in the Wuwei area of Gansu Province. The primary objective was to analyze the potential of nano zero-valent iron (NZFI) in enhancing grape growth through foliar spraying on the top traditional fertilization practices. The research specifically examined the impact of foliar spraying with varying concentrations of nano zero-valent Fe fertilizer on the photosynthetic characteristics, as well as the growth and development of new shoots and leaves of Pinot Noir in the arid region of Gansu Hexi Corridor. The study aimed to identify the optimal concentration of nano zero-valent Fe for grapevine growth. The ultimategoal was to enhance the physiological attributes of wine grapes, increase yields, and improve quality. Additionally, by establishing a reliable scientific foundation for the judicious application of nano zerovalent iron fertilizer, this research endeavors to facilitate the sustainable growth of the wine grape industry.【Methods】This experiment was conducted in 2021 at Enuo Winery, Wuwei city, Gansu province (102°82′26″ E, 37°18′06″ N). The vineyard utilized the east-west-oriented single-armed hedgerow cultivation method, adopting a model characterized by“deep ditching, shallow planting, and mechanization”. The soil in the vineyard was neutral to weakly alkaline sandy loam, with an average annual rainfall of 150-247 mm, an average annual sunshine hours of 2 876.9 h, an average annual temperature of 7.1 ℃, an average annual precipitation of 123 mm, and a substantial temperature difference between day and night, reaching approximately 15 ℃ in the summer, with a hydrothermal coefficient of ＜1.5. Throughout the trial period, irrigation adhered to the guidelines of the“Drip Irrigation Quota for Brewing Grapes in Wuwei”. Routine management operations, including bud wiping, tying, tendril removal, weeding, etc., followed the production management calendar. The experiment employed a randomized block design, using 4-year-old field grown Pinot Noir plants as the test material. Six treatments were applied: five different concentrations of nano iron fertilizer spray treatments (T1: 5 mg·L^-1 , T2: 10 mg·L^-1 , T3: 15 mg·L^{- 1} , T4: 20 mg·L^{- 1} , T5: 25 mg·L^{- 1} ), utilizing ultrasonic vibration (100 W, 40 kHz) to disperse nano zero-valent iron particles into de-ionized water, uniformly sprayed on the fruit and foliage, with vines sprayed clear water serving as the control (CK). Each treatment consisted of fifty-four vine plants with robust growth and neat appearance, and the experiment was organized into three replications. The spraying commenced on June 18, and the fertilizer was applied every 15 days for a total of five times. Various indicators, including leaf SPAD value, leaf area, length and thickness of the new shoots, and leaf fluorescence parameters, were determined.【Results】Upon analyzing the experimental outcomes, diverse promoting effects on the basal roughness, internode length, relative chlorophyll content, and leaf area of the new shoots were observed with the foliar application of different concentrations of nano zero- valent iron fertilizer. The highest basal roughness and internode length of the new shoots were achieved by T5 treatment. Additionally, in comparison to the control group (CK), this treatment not only significantly enhanced leaf photosynthesis, light energy absorption, and transmission but also increased the SPAD value of the leaves to varying extents, reaching its peak at 60 days after flowering. Further examination of the impact of nano zero-valent iron on the dynamic changes in grape leaf SPAD value revealed that within seven days of continuous application, the leaf SPAD values exhibited a gradual increasing trend. The results demonstrated that spraying nano zero-valent iron was conducive to a rapid increase in the relative chlorophyll content of grape leaves. Spraying nano zero- valent iron fertilizer was effective in increasing the leaf area of grapes and enhancing the basal roughness of grape branches, with a concentration of 25 mg·L^-1 (T5) being the most effective. The initial fluorescence (F0) of the leaves from each treatment exhibited a pattern of initial decrease followed by an increase with the increase in concentrations of nano zero-valent iron fertilizer applied, reaching the lowest point 60 days after flowering. Nano zero-valent iron treatment reduced the initial fluorescence in grape leaves to varying degrees. Spraying nano zero-valent iron fertilizer increased the Fv/Fm of grape leaves to varying extents, showing an initial increase and subsequent decrease with the growth and development of grape. At 30 days after flowering, the Fv/Fm in T3, T4 and T5 were 1.78%, 35.71% and 32.14% higher than in CK (0.60), respectively, while the Fv/Fm of the other treatments was lower than CK. At 45 days after flowering, the Fv/Fm of T3, T4, and T5 were all higher than that of CK. At 60 days after flowering, the Fv/Fm in all treatments was higher than that in CK. After 90 days of flowering, the T4 treatment resulted in the highest Fv/Fm. Moreover, foliar spraying of nano zero-valent iron fertilizer improved the electron transfer rate of grape leaves to varying degrees. After 75 days of flowering, the electron transfer efficiency in the treated plants reached its maximum value, with T5 being the highest at 52.73, which was 89.2% higher than CK (27.87). After 45 days of flowering, spraying nano zero-valent iron enhanced the photochemical quenching coefficient to varying extents, with T5 treatment showing the best effect. The non-photochemical quenching coefficient exhibited an initial increase and subsequent decrease with the growth and development of grape berries. After 30 days of flowering, the non-photochemical quenching coefficient in T1 was the highest (0.66). Spraying nano zero-valent iron increased the net photosynthetic rate of leaves to varying extents. At 30 days after flowering, T2, T3, T4, and T5 treatments were all higher than CK. Spraying nano zero-valent iron on the leaves enhanced the stomatal conductance and transpiration of grape leaves, promoting the efficiency of photosynthesis.【Conclusion】Spraying appropriate concentrations of nano zero-valent iron fertilizer significantly enhanced plant leaf photosynthetic performance, increased relative chlorophyll content, basal thickness of the new shoots, and internode length, with the best effect of the treatment at the concentration of 25 mg·L^-1 (T5).