Flowering is essential for fruit production. The effects of nitrogen (N) on flower bud differentiation and early harvest in strawberry are not clear. Experiments were conducted to investigate the most effective concentration of N treatment during the seedling stage and further elucidate the mechanism of flower bud differentiation in cultivated strawberry (Fragaria ananassa Duch.'Benihoppe'). The results demonstrated that T2 (treatment 2) of 0.1 g/plant was the suitable concentration for flower bud differentiation in strawberry seedlings and then fruit early ripening. Further studies showed that the period of flower bud differentiation happened between August 19 and August 24. The total carbon (C) contents of all treatments except T3 displayed an increasing trend in seedlings before August 14. The C/N ratio (21.45-53.44) increased at the stage of flower bud differentiation in each treatment, which was promoted by an appropriate C/N ratio. Relatively higher ABA and CTKs levels but relatively lower GAs and IAA levels required during flower bud differentiation were detected. Further analysis of ABA/IAA ratio (0.53-0.76) suggested that it was also close to the flower bud differentiation in strawberry. N levels increased at phenological phases of each treatment. Different N levels during the seedling stage had little effect on fruit quality. It also exhibited the highest early harvest (183.0 g/plant) as well as the highest yield (380.3 g/plant) with T2. We found that a relatively high C/N ratio and an appropriate ABA/IAA positively initiate the flower bud differentiation, which suggested that ABA may play an important role in promoting flower bud differentiation in strawberry.

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