Abstract: 【Objective】The purpose of this study is to explore the effects of zinc deficiency on the chlorophyll content, photosynthetic rate and chlorophyll fluorescence characteristics of apple tree leaves, and to reveal the damage mechanism of Zn deficiency to the photosynthetic system of apple leaves.【Method】Normal trees without Zn deficiency symptoms and rosette trees with typical Zn deficiency symptoms (called “little leaf”) in field of ‘Red Fuji’ apple (rootstock Malus hupehensis Rehd) were used as materials, and the zinc content, chlorophyll content, net photosynthesis rate and fluorescence parameters of apple leaves under different Zn stress levels were measured.【Result】Under Zn deficiency, the chlorophyll content, single leaf area and specific leaf weight of apple leaves decreased significantly; the stomatal conductance decreased, intercellular CO2 concentration increased, net photosynthetic rate and water use efficiency also decreased. As the aggravation of Zn deficiency, the original fluorescence Fo rose while Fv/Fo, ΦPSⅡ, qP and Fv’/Fm’ decreased under Zn deficiency. The relative variable flurescence at J-step(VJ) and the ratio of variable fluorescence Fv to the amplitude Fj-Fo at the K-step(Wk) increased, the quantum yield for electron transport further than QA¬ (ETo/ABS), the density of active PSⅡ reaction centers per cross section(RC/CSo) and the performance index on absorption (PI) basis decreased.【Conclusion】Non-stomatal limitation was one of the reasons for the reduction of photosynthesis rate under zinc deficiency. Zn deficiency first caused the damage of oxygen evolving complex (OEC) and then the reactive center of PSⅡ, followed by the inhibited electron transfer of donor side and receptor side of the reaction center at the same time, which finally affected the absorption, transmission and utilization of light energy in apple leaves.

Key words: apple , zinc , leaves , photosynthesis rate , chlorophyll fluorescence