| Apple production is one of the most importantly agricultural leading industries in Shaanxi province and the major income source for growers in main apple producing area. In Shaanxi province, the major apple producing areas are Weibei and the south of Northern Shaanxi, which belong to arid or semi-arid regions. Of these areas, the attitude is high, and the light and heat resources are enriched. The annual solar radiation is about 7000MJ/m2 and the sunshine duration is 2500-3500 h, 15% higher than those in the south of Shaanxi. The day and night temperature difference of these areas is pronounced very much, about 11.8-16.6 oC. However, the per capita water capacity in these areas is only 1/6 of that in the country-wide. The annual rainfall is around 300-550 mm, but 65% of it occurs in July, August, and September, which is inharmonious with the development of apples. During the key water demanding period of apples, from April to June, the rainfall in Weibei and the south of Northern Shaanxi is deficient, less than the ground evaporation due to the abounding light and heat resources. As a result, the apple trees in these areas often suffer drought and water shortage for a long time, affecting the production and quality of apples.Partial rootzone irrigation is a new irrigation technique. It means that only part of the rootzone is wetted as in full irrigation, while the rest is un-watered during certain periods of the growing season of a crop. In this way, the root system in drying soil can respond to the drying by sending a root-sourced signal to the shoots where stomata may be inhibited so that the plant water consumption is reduced.In this study, eight-year-old'Fuji'apple trees grown in the mountain area of Ansai city were used. Four levels of water supply, 1/4, 2/4, 3/4, and 4/4, were processed for the partial rootzone irrigation treatment. Photosynthesis, drought resistance, growing characteristics, and fruit quality were analyzed. The results are as follows:1) The diurnal variation of photosynthesis, evaporation, and stomatal conductance of the tree leaves showed a typically unimodal curve under 3/4 and 4/4 water supply treatments but exhibited a bimodal curve under 1/4 and 2/4 water supply treatments. In addition, with the increase in water supply, photosynthesis, evaporation, and stomatal conductance increased, reaching the maximum under the treatment of 3/4 water supply, whereas leaf evaporating efficiency decreased and became minimal under the treatment of 3/4 water supply.2) With the decrease in water supply, the concentration of MDA and free proline, relative electric conductivity, and leaf water-holding capacity were all enhanced, which indicate that regulating water supply could improve the drought resistance and then increase the accumulation of photosynthetic carbohydrates in the leaves of'Fuji'growing in the mountain area.3) Before budding, a suitable supply of water could postpone the budding and flowering date for 1-2 days, enhance the budding efficiency, and shorten the flowering period. With the increase in water supply, the branch budding efficiency was increased, reaching the maximum under 3/4 water supply. Nevertheless, the blooming capacity and fruit-setting rate were reduced while the water supply was increased.4) As the water supply was increased, the length of spring shoot tips, autumn shoot tips and new shoot tips was increased too. The ratio of autumn shoot tips length to new shoot tips length was increased while the ratio of spring shoot tips length to new shoot tips length was decreased with the increasing water supply. In addition, the length of most branches was less than 60 cm under 1/4 water supply treatment, 5-60 cm under 2/4 water supply treatment, beyond 5 cm under 3/4 water supply treatment, and beyond 30 cm under 4/4 water supply treatment.5) With the increase of water supply, fresh weight, surface color, firmness, and the concentration of anthocyanins, total soluble solid, total sugars, Vc and calcium of fruits were all enhanced. All of them reached the maximum under 3/4 water supply treatment but then decreased when the water supply was increased further. The acid concentration decreased with the increasing water supply, being the minimal under 3/4 water supply treatment.
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