How nitrogen and drought stress affect growth and nitrogen use efficiency for Fuji and Qinguan apple seedlings

【Objectives】The effects of nitrogen stress and drought on the growth, photosynthetic parameters, nitrogen(N), phosphorus(P), potassium(K) absorption in different parts of apple seedlings and the nitrogen use efficiency were analyzed. 【Methods】Two cultivars of one\|year\|old apple seedlings(Fuji and Qinguan grafted Malus hupehensis Rehd.) were used in sandy pot culture experiment.Four treatments with two levels of nitrogen and water were designed. Normal nitrogen and normal water(ZZ), low nitrogen and normal water(DZ), normal nitrogen and droughts(ZG), low nitrogen and droughts(DG). Normal nitrogen(6 mmol/L NO-3\|N) and low nitrogen(0.3 mmol/L NO-3-N); normal water(keep the relative water content as 80%-85%) and drought(keep the relative water content as 60%-65%). For both Fuji and Qinguan the biomass of stems and leaves, plant height and stem diameter, photosynthetic rate, stomatal conductance and transpiration rate showed the highest results under normal water and N supply supply(ZZ), then descanted in order of low N and normal water(DZ), normal N and drought(ZG) and N and drought stress(DG) treatments. All the indices determined in Qinguan were higher than in Fuji under the same treatments. In normal water supply, the root/shoot ratios of Fuji and Qinguan with N stress treatment were 2.05% and 22.40% higher than normal N supply in Fuji and Qinguan respectively. The N, P, K contents in Fuji and Qinguan seedlings decreased with treatment of ZZ, DZ, ZG and DG. N and K contents in leaves were higher than in roots and stems, P content were increasing in order of root， leaf and stem. The net photosynthetic efficiency of unit leaf area(PNUE) and N efficiency were significantly different between treatments in Qinguan，not significant in Fuji. Under N stress and normal water supply, the PNUE and N efficiency in Qinguan were higher than in Fuji, the N efficiency in Qinguan was 42.07% higher than Fuji under N stress and normal water supply, and 64.14% higher under N stress and drought treatment. The N efficiencies were increased significantly in the two cultivars with the higher increase in Qinguan than in Fuji under N stress treatment. 【Conclusion】 Water stress will reduce the absorption of nitrogen by leaf, increase of nitrogen application could improve drought tolerance of fruit trees. The growth index, photosynthetic index and N efficiency of Qinguan were superior to Fuji, and Qinguan showed more tolerant than the low nitrogen supply.