Abstract: The trunk fruit-shaped walnut(Juglans regia L.) of Wen185 walnut was selected as the research material, and the coupled mode of nitrogen fertilizer with uniconazole with different concentration gradient was set to study the effect of nitrogen fertilizer on the photosynthetic characteristics of walnut fruits during the expansion stage. The results showed that the net photosynthetic rate(Pn) of walnut treated with nitrogenous fertilizer coupled with uniconazole was higher than that of the control group,among them,N 665.5 g/plant, uniconazole(S) 250 mg/L treatment reached the maximum, which was 21.17 μmol/(m²·s), an increase of 37.99%. Compared with the control group, intercellular carbon dioxide(Ci) change was relatively stable. The high nitrogen fertilizer treatment had a large Ci, and the high nitrogen treatment had great Ci value; Transpiration rate(Tr) and stomatal conductance had a large range of variation and the variation trend was consistent, both reached the maximum value in treatment N 665.5 g/plant, S 150 mg/L, and high concentration enizolium treatment had a certain inhibitory effect on transpiration rate(Tr) and stomatal conductance. The instantaneous water use rate(WUE) changed little with the treatment, which was promoted by low-concentration and inhibited by high-concentration on the whole. The main influencing factors of stomatal limiting value(Ls) was nitrogen fertilizer, and low nitrogen fertilizer promoted the improvement of Ls value to a certain extent, while high nitrogen fertilizer inhibited it. In addition, the coupling treatment of high nitrogen fertilizer and high uniconazole can increase the leaf saturated vapor pressure deficit(V_pdl). The combination treatment of 665.5 g/plant nitrogen fertilizer and 250 mg/L uniconazole improved the photosynthetic performance of trunk fruit-shaped walnut the best, which achieved the high yield and high quality cultivation of walnut.

Key words: nitrogen fertilizer, uniconazole, photosynthetic characteristics, walnut(Juglans regia L.)