Effects of nitrogen and phosphorus on the regulation of nonstructural carbohydrate accumulation, translocation and the yield formation of oilseed flax

Nutrients can significantly affect nonstructural carbohydrates (NSC) of crops. This field experiment was conducted to reveal how nitrogen (N) and phosphorus (P) regulated NSC accumulation, translocation as well as the seed yield formation of oilseed flax. The treatments were as follows: (1) application of 0 kg N ha−1 and 0 kg P ha−1 (N(0)P(0)), (2) application of 75 kg N ha−1 and 0 kg P ha−1 (N(75)P(0)), (3) application of 150 kg N ha−1 and 0 kg P ha−1 (N(150)P(0)), (4) application of 0 kg N ha−1 and 75 kg P ha−1 (N(0)P(75)), (5) application of 75 kg N ha−1 and 75 kg P ha−1 (N(75)P(75)), and (6) application of 150 kg N ha−1 and 75 kg P ha−1 (N(150)P(75)). Results showed that application of N decreased the concentration and content of leaves soluble sugar (SS), and increased stems SS and starch (ST) concentration and content at pre-anthesis of oilseed flax, compared to no application of N. Application of P increased the SS concentration in leaves, stems, and seeds at all growth stages, and decreased ST concentration in leaves, seeds and stems at post-anthesis, compared to no P application. Mixed application of N and P significantly improved leaves and stems SS concentration at post-anthesis, promoted more leaves and stems NSC translocation to seeds, thus seed numbers (SN) of per capsule and effective capsules (EC) significantly increased and no-effective capsules (NEC) obviously decreased, compared to only application of N or P. Meanwhile, the average seed yields were improved 14.3%-42.6% than that of only application of N or P. We also found that the SN of per capsule had significantly positive correlation with the leaves SS concentration at post-anthesis, and it had highly positive correlation with the buds and flowers SS concentration at budding and anthesis stages, respectively. The NEC had largely positive correlation with the stems ST concentration at post-anthesis. Our results suggested that N with P mixed application is an effective way for oilseed flax production in semiarid areas by increasing the SN, EC and decreasing the NEC by regulating the leaves and stems NSC at budding, anthesis and post-anthesis, and improving oilseed flax production.