Abstract: Water is a key factor limiting the improvement of both quality and yield of walnut industry in arid areas. The effects of different water supply amounts on physiology, growth, and fruit quality of walnut trees remain unclear. We conducted an irrigation experiment with three treatments, i.e., deficit (DI), conventional (CI), and excess irrigation (EI). We measured leaf hydraulic traits, photosynthetic physiological characteristics, soluble sugar content, leaf area, branch growth, fruit morphology and no kernel or deflated kernel rate at different canopy heights of ‘Wen 185’ walnut trees. The results showed that: (1) Midday leaf water potential decreased significantly  with decreasing irrigation and increasing canopy height. Midday leaf water potential at the upper canopy was significantly lower than that at the lower canopy. (2) Different irrigation amounts did not affect light compensation point, light saturation point, maximum net photosynthetic rate, maximum photochemical efficiency, and chlorophyll SPAD. (3) Irrigation treatments did not significantly affect soluble sugar content of leaves and fine roots, but the soluble sugar content of walnut kernels was significantly increased with decreasing irrigation and accumulated with increasing canopy height. (4) Leaf area was significantly decreased and Huber value was significantly increased with the reduction of irrigation. The reduction of irrigation did not affect fruit morphology, but increased the no kernel or deflated kernel rate, with a rate being 87.9% higher in the DI group than in the EI group. The no kernel or deflated kernel rate at the upper canopy was 41.8% higher than that at the lower canopy. Our results indicated that walnut trees resist drought by increasing Huber value and decreasing leaf area to maintain stable photosynthesis, but the hydraulic restriction caused by increasing canopy height will aggravate the drought stress of plants, resulting in an increase in the no kernel or deflated kernel rate.

Key words: ‘Wen 185’ walnut, drought stress, no kernel or deflated kernel rate, soluble sugar, gas exchange, canopy.