Comparison of leaf photosynthetic characteristics of pendulous canopy and horizontal canopy in Chambourcin grape

Abstract: 【Objective】This study compared the ozone damage and photosynthetic performance of grape leaves in pendulous canopy and horizontal canopy.【Methods】Five-year-old Chambourcin grapevines were selected as the experimental materials. Ozone concentration in the air was monitored from July to September using an ozone monitor, and ozone damage in pendulous canopy and horizontal canopy was recorded according to the degree of damage on the leaves. Determinations of leaf area and total chlorophyll content in leaves of primary and lateral shoots from both canopy types were conducted at berry maturity stage. The net photosynthetic rate and fluorescence characteristics of leaves from the two canopy types were measured using a CIRAS-3 portable photosynthesis meter and a Handy PEA.【Results】During the experiment, the air ozone concentration at the Taian Zhongqing winery site(117.21°E, 36.17°N) was monitored in real time, and the daily maximum ozone concentration ranged from 14 nL·L^-1 to 56 nL·L^-1 from June to September, with the highest ozone concentration occurring on July 4th and the lowest on June 28th. The average daily maximum ozone concentration from June to September was 30.6 nL·L^-1, and the ozone concentration decreased after the commence of rainy season in late July. The ozone damage was mitigated by adopting pendulous canopy, and the ozone injury inci-dence in leaves of primary shoots of the pendulous canopy was lower than that of the horizontal canopy in June and July. The degree of ozone injury to leaves of the primary and lateral shoots of the pendulous canopy was significantly lower than that of the horizontal canopy in June, and the number of leaves in the primary and lateral shoots without injury was 169.34% and 4.66% higher than that of the horizontal canopy, respectively. The difference in leaf area in the primary shoots between the two canopy types was not significant, while leaf area in the lateral shoots in the pendulous canopy was significantly (53.25%) higher than that of the horizontal canopy. The total chlorophyll content in leaves of the primary and lateral shoots of the pendulous canopy was 131.18% and 59.52% significantly higher than those of horizontal canopy, respectively. The net photosynthetic rate of the leaves at the middle node of the primary shoots of pendulous canopy was 13%-56% and 28%-99% higher than that of horizontal canopy at the veraison and berry maturity stages, respectively. The O-J-I-P curve pattern of Chambourcin grapevine leaves in the pendulous canopy differed significantly from those in the horizontal canopy, and the relative variable fluorescence (F_m) at the P point in the pendulous canopy was higher than that of the horizontal canopy at veraison and maturity stages, indicating that the pendulous canopy leaves have a higher capacity to absorb light energy. Both canopy types showed a clear J point (2 ms) on July 31st and September 6th. The injury degree at the PSII receptor side in the horizontal canopy was significant-ly higher than in pendulous canopy, indicating that electrons from Q-A to Q-B was restricted. The maxi-mum photochemical quantum yield of PSII (F_v/F_m) of the horizontal canopy was 3.08% lower than that of pendulous canopy at veraison stage. The number of active reaction centers per unit area (RC/CSm) was 12.79% and 23.58% lower than that of the pendulous canopy at veraison and maturity stages, re-pectively. The quantum yield of light energy absorbed by reaction centers for electron transfer (φEo) in the horizontal canopy leaves was 19.02% and 26.08% lower than that in the pendulous canopy at the two stages. The relative variable fluorescence of J points (Vj) in the horizontal canopy was 12.25% and 24.98% higher than that in the pendulous canopy on July 31st and September 6th, respectively. The Wk in the horizontal canopy was 5.92% higher than in the pendulous canopy on July 31st. The initial slope of relative fluorescence (Mo) had no significant difference between the two canopy types at both veraison and maturity stages.【Conclusion】Pendulous canopy alleviated the ozone damage on grape leaves,increased chlorophyll content in leaves, and improved net photosynthetic rate in leaves at the middle node of the primary shoots compared with the horizontal canopy.