The Effects of the Tree Structure of Zaosu Pear on the Transport and Distribution of Photosynthetic Assimilates and Fruit Quality under Desert-Area Conditions

Abstract

Pear is an important fruit tree in China, and the Hexi area is the main pear-planting area in Gansu Province. Tree shapes have different effects on photosynthesis that influence fruit quality and development. Thus, in the current study, five tree shapes of Zaosu pear, including the Y-shaped, trunk, single-arm, double-arm, and spindle tree shapes, were selected, and their effects on photosynthesis and fruit quality were investigated. The thickness and length of shoot branches were highest in the single-, double-arm, and spindle tree shapes. The level of photosynthetically active radiation (PAR) varied by tree shape; from highest to lowest, the order was double-arm > single-arm > spindle > Y-shaped > trunk tree shapes. Leaf area and chlorophyll content were highest in the single- and double-arm tree shapes, with higher increases in the net photosynthetic rate to light intensity (Pn-PAR), the net photosynthetic rate to CO2 (Pn-CO2), the relative variable fluorescence (Vj), PSII maximum photochemical efficiency (Fv/Fm), and the light energy absorbed per unit reaction centre (ABS/RC). For fruit quality, the fruit shape index, fruit colour parameters, and content of soluble solids increased significantly in the single- and double-arm tree shapes, while the content of total acids, malic acid, and citric acid in the single- and double-arm tree shapes was lower than in the other tree shapes. All these results demonstrated that the single- and double-arm tree shapes are well ventilated and light-transmitting, which can promote fruit growth and quality.