Abstract: A field experiment was conducted to study the effects of water-nitrogen interaction on the flag leaf photosynthetic rate, penult stem fructan content, fertilizer N use efficiency, and soil water use efficiency of strong gluten wheat variety ‘Jimai 20’. Three N application levels (N0, 0 kg·hm-2; N1, 180 kg·hm-2; and N2, 240 kg·hm-2) and four irrigation schedules (W0, no irrigation; W1, irrigation before sowing and at jointing and flowering stages; W2, irrigation before sowing, before wintering, and at jointing and flowering stages; W3, irrigation before sowing, before wintering, and at jointing, flowering, and grain-filling stages) were designed. The irrigation amount was 60 mm each time. Among the N treatments, treatment N1 had a higher flag leaf net photosynthetic rate and penult stem fructan content, and the highest grain yield, apparent N use efficiency, agronomic N use efficiency, and water use efficiency. Treatment N2 had a higher penult stem fructan content than treatments N0 and N1. No N application and applying excessive N did not benefit the increase of grain yield, fertilizer N use efficiency, and water use efficiency. Treatment W1 promoted the fructan accumulation in penult stem and accelerated the translocation of the accumulated fructan to grain, being beneficial to the increase of grain yield. Treatment N1W1 had the highest grain yield, and higher fertilizer N use efficiency and water use efficiency. Excessive irrigation and N application increased the flag leaf net photosynthetic rate and penult stem fructan content, but decreased the fertilizer N use efficiency and water use efficiency, with no significant effects on grain yield.

Key words: water-nitrogen interaction, soil water, fructan content in stem, fertilizer N and water use efficiency, Dendrobium officinale,  D. nobile,  D. chrysotoxum, partial least square regression,  quality.