Research progress in sweet cherry photosynthesis

Abstract: Sweet cherry has the highest intensity of photosynthesis among all stone fruit crops. Physiological fruit drop contributes to low fruit yields, which is closely related to leaf photosynthetic rate, carbon fixation and biomass accumulation. Studies on photosynthetic physiology to use limited lighting resources and to improve the photosynthetic utilization provide a theoretical basis for increasing and stabilizing yield in sweet cherry. (1) Internal factors: The diurnal variation of photosynthetic rate of most sweet cherry varieties shows a“bimodal”pattern, and there is an obvious“noon break”phenomenon. Some cherry varieties are affected by stomatal restriction, which leads to changes in Pn, while others are not. When the photosynthesis is approaching“noon break”, Ci does not decrease but increases, and the supply of CO2 in leaves does not decrease, indicating that the formation of“noon break”is not caused by the decrease of Gs. Rootstock genotype affects all physiological parameters. The contents of total chlorophyll and total carotenoid, and chlorophyll a / chl b (Chla / Chlb) values in the leaves of scion varieties on dwarf rootstocks are always higher than those on vigorous rootstocks. Dwarf rootstocks have a strong regulatory effect on the photosynthesis of scion varieties. When the content of chlorophyll in leaves is high, the energy conversion efficiency is high and the photosynthetic capacity is strong. Carotenoids in leaves can absorb residual light energy, which prevents membrane lipid peroxidation and protects photosynthetic function. Rubisco protein level shows an increasing trend after the release of dormancy in sweet cherry, during ecological dormancy and until green shoot stage, indicating that the carbon assimilation capacity increases in these development stages, resulting in the gradual increase of fresh and dry weight of sweet cherry buds. The ratio of ¹³C fixed and transported to vegetative branches in leaves of fruiting branches and non-fruiting branches is low. The ¹³C (60%-80%) contribution in leavesof fruiting branches to fruit is higher than that of non- fruiting branches (30%-70% ) and vegetative branches (17%-60%), which provides useful physiological information for pruning and fruit load regulation. The radiation conditions in the canopy are changed by summer pruning to affect the sugar distribution in the cherry tree. It should be noted that the crown should not be too large during pruning, and the branches are not easy to be too dense, otherwise it is not conducive to photosynthetic accumulation, resulting in reduced fruit quality. (2) External factors: The photosynthetic characteristics and yield of super slender spindle system are higher than those of V-shaped tree shape, at 4.0 × Under the planting density of 4.5 m, the photosynthetic capacity, yield and fruit quality of sweet cherry Rabins are the best, followed by 4.0 m × 5.0 m, and 3.5 m × 4.0 m is the worst. Mulching culture can significantly promote the bud break and branching of sweet cherry, and make the cuttent shoots grow rapidly. The length, thickness, palisade tissue quality and leaf area of new shoots under mulching culture are significantly higher than those of the control, which can significantly increase the chlorophyll content in cherry leaves with the increased photosynthetic efficiency. The ability of cherry tree to use weak light under rain sheltered cultivation has been significantly improved, which could increase the accumulation of photosynthetic products in the tree, and improve the yield and quality of fruit. Finally, photosynthesis, protein synthesis, enzyme activity, lipid and hormone metabolism will be affected when salt stress occurs. Severe salt stress leads to damage of photosynthetic system and inhibition of photosynthesis in sweet cherry. (3) Environmental factors: Fruit trees normally carry out photosynthesis at 10-35 ℃, and the optimum temperature is 25-30 ℃. Under suitable light conditions, the chlorophyll content and photosynthetic rate of plants increase, while the respiratory rate decreases. Increased light causes increased temperature, increased transpirationexcessive water loss in leaf cells and increased cell osmotic pressure, resulting in stomatal closure, reduced cell absorption of CO2, and reduced dark reaction of photosynthesis. Low light intensity can reduce transpiration and cell osmotic pressure, open stomata, absorb more CO2, and enhance the dark reaction of photosynthesis. Proper shading could protect cell membrane, leaf water status and photosynthetic pigments. Flooding conditions inhibit root growth, absorption, transportation and other activities, resulting in the inhibited growth aboveground. Under severe drought stress, the total chlorophyll, chlorophyll a and chlorophyll b contents in leaves show a downward trend. Elevated CO2 concentration in the atmosphere has both positive and negative effects. Additionally, elevated CO2 will increase the photosynthetic rate of light saturated net leaves of plants, thus increasing the biomass. (4) Research prospects aim to clarify the basic photosynthetic attributes of sweet cherry, explore the physiological and ecological factors of photosynthesis of sweet cherry + gene and protein engineering, study the photosynthesis mechanism of sweet cherry, clarify the structure of photosynthetic organs of sweet cherry leaves and the molecular structure of photosynthetic membrane proteins and their relationship with function + the method of combining the new generation of transgenic technology with molecular mechanism design, and cultivate new sweet cherry varieties with high light efficiency as well as provide a basis for high and stable yield.