Effects of light quality on photosynthetic characteristics and fruit quality of‘Chunmei’peach

Abstract:【Objective】Photosynthesis is the most important chemical reaction on the earth, providing foodfor all living organisms. Light is the driving force of photosynthesis. Light quality regulates plant growth,photosynthesis, morphogenesis, metabolism and gene expression. The effects of light quality on photosynthetic characteristics, fluorescence characteristics and fruit quality of peach (Prunus persica L.) were studied in plants grown under films of different colors in order to select films that promote fruit growth andfruit quality.【Methods】Five-year-old‘Chunmei’peach trees grown in an open field in Baoding were se⁃lected as the experimental materials. Red, blue, green and white films with a thickness of 0.15 mm weretested. The colored films were laid on the stent, covering the entire trees with room for growth. Filters wereset in the films 40 cm from the ground to promote air circulation and to prevent vapor condensation insidethe films. The treatments started from one week after fruit set and continued until fruit ripened, when thecovering films were removed. Light transmittance of the films was measured. Leaf chlorophyll content, photosynthetic characteristics and chlorophyll fluorescence were measured after 30 days of treatment. The appearance and intrinsic quality of ripe fruit were determined. The experimental data were processed and analyzed statistically using Microsoft Excel and DPS7.05.【Results】The light through the white film had thehighest light gray values at various wavelengths. The peak light gray value of light through the red film appeared between 580-620 nm corresponding to the orange light. The light through the blue film had a peakgray value at 450-490 nm, corresponding to the blue light. Green film generated a light with a peak lightgray value at 520-580 nm, which is the green light. Chlorophyll a, chlorophyll b and chlorophyll a+b con⁃tents changed consistently and were in a descending order of green film> blue film> red film> white film. Chlorophyll contents under the green film were significantly higher than under the white film and red film.Those under the blue film were significantly higher than under the white film. The chlorophyll a, chlorophyll b and total chlorophyll contents in the blue film treatment were 9.65%, 16.83% and 9.75% higherthan in the white film treatment, respectively. The ratio of chlorophyll a/b in red film treatment was signifi⁃cantly lower than in the other treatments. The ratio was in the order of white film> green film> blue film>red film. Net photosynthetic rate in the red film and the white film treatments was significantly higher thanthat in the blue film treatment. In the red film treatment, net photosynthetic rate was 72.51% higher thanthat in the blue film treatment. The stomatal conductance in the red film treatment was significantly higher than that in the other film treatments, and it was the lowest in the blue film treatment. The stomatal con⁃ductance in the red film treatment was 53.53% higher than that in the blue film treatment. Intercellularcarbon dioxide was not significantly different between treatments, but was highest in the blue film treat⁃ment. The transpiration rate under white film was significantly higher than that in other treatments, andthe red film treatment was the lowest. The white film treatment had a transpiration rate which was 42.57% higher than that in the red film treatment. The change trends of Fo, Fm and F_v/F_m were the same among different color film covering. The values under the blue film were the highest, followed by the green film andred film, and the white film treatment had the lowest values. Fo, Fm and F_v/F_m in the blue film treatmentwas 8.39%, 10.87% and 1.6% higher than those in the white film treatment, respectively. The qP in thewhite film and the red film treatments was significantly higher than that in the blue film treatment. Y(NPQ) and Y (NO) were highest under the treatment of blue film. Y (NPQ) was lowest in the white filmtreatment, and Y (NO) was lowest in the red film treatment. Y (Ⅱ) was significantly higher in the red filmtreatment than in the blue film treatment, which had the lowest value. There were significant differencesin excursion coefficient β/α-1 between PSⅡ and PSⅠ, and the open degree of PSⅡ reaction center washigher in the blue film and the green film treatments than in the other treatments. β/α-1 was smaller under the red and white films, and more of the excitation energy was transferred to PSⅠ. Fruit weight in different treatments was between 187.6-194.3 g, and there was no significant difference among the treat⁃ments. There were significant differences in fruit coloration among different treatments. The color area offruit treated by the white film was 93.75%. It was 84.38%, 75% and 50% in fruit under the red, the greenand the blue films, respectively. The content of total soluble sugars in the fruit was in the order of greenfilm> white film> red film> blue film. It was significantly higher in the green film treatment than in theother treatments. The blue film treatment was significantly lower than the other treatments. The green filmtreatment had a soluble sugar content which was 8.8% higher than the blue film treatment. The content oftitratable acids in mature fruit was in a descending order of red film> blue film> green film> white film. Itwas significantly higher in the red film treatment than in the other treatments, and in the red film treatment, it was 35% higher than that in the white film treatment. There was no significant difference betweenthe treatments in sugar/acid ratio.【Conclusion】Comprehensively, in the white film treatment, fruit color⁃ation was the best, and the green film covering can improve the soluble sugar content of the fruit.