Effects of water-nitrogen coupling on photosynthetic characteristics, yield, water and nitrogen use efficiency for mountain apple trees under surge-root irrigation in Northern Shaanxi area of China.

Taking 7-year-old apple trees (Hanfu) as the test material, an experiment with three irrigation levels including high water (W, 85%-100%, was the field water holding capacity), medium water (W, 70%-85%) and low water (W, 55%-70%), and three nitrogen application levels, high (N, 600 kg·hm), medium (N, 400 kg·hm) and low (N, 200 kg·hm), was conducted to investigate the effects of water and nitrogen coupling on photosynthetic characteristics, yield and water and nitrogen utilization of apple trees in mountainous areas under surge-root irrigation (SRI). The results showed that the net photosynthetic rate (), transpiration rate (), stomatal conductance (), intercellular CO concentration (), leaf instantaneous water use efficiency (WUE) of apple trees leaves decreased with decreasing nitrogen application rates under the same irrigation amount, but increased. Under the same nitrogen application rate, foliar , , and WUE decreased with decreasing irrigation amount, but increased.