Objectives The suitable combination of nitrogen (N), phosphorus (P) and potassium (K) fertilizers was studied from the yield, atrctylodin content and the activity and gene expression of acetyl coenzyme A carboxylase (ACC) of A. chinensis, so to propose a scientific fertilizer combination for improving the productivity and quality of A. chinensis.

Methods A field experiment including 10 combined applications of N, P and K fertilizers was set up following a L₉(3⁴) design, with one-year-old Atractylodes chinensis as experimental material. The fresh weight of aboveground part, rhizome, and fibrous root of A. chinensis were weighed at vegetative growth, flowering, early fruiting, full fruiting and withering stages. The plant samples were collected at the same time for determination of atrctylodin content by HPLC method, the ACC activity in rhizome by double antibody ELISA method, the relative expression level of ACC gene using real-time PCR. Spearman correlation analysis was used to determine the molecular regulation mechanism of atrctylodin synthesis.

Results All the NPK combined applications promoted the growth of aboveground part, rhizome and fibrous root of the crop. The most significant effects were observed in T3 (N₁P₃K₃) and T6 (N₂P₃K₁), the fresh weight of aboveground part were respectively 1.52 and 1.47 times that from N₀P₀K₀ at full fruiting period, the fresh weight of underground rhizome were 2.08 and 2.09 times of that from N₀P₀K₀ at withering period, and the fresh weight of fibrous roots were 1.30 and 1.41 times of that from N₀P₀K₀ at withering period. Compared with N₀P₀K₀, T3 and T6 increased atrctylodin by 33% and 61% at withering period. Moreover, according to the dynamic accumulation characteristics of atrctylodin in different growth stages, it was speculated that the most important period for atrctylodin accumulation was the withering period to the next year before emergence. According to the results of correlation analysis, the correlation coefficients between atrctylodin content and ACC enzyme activity, ACC gene expression were 0.66 and 0.583, respectively. The correlation coefficient between ACC enzyme activity and ACC gene expression was 0.839, which reached extremely significant positive correlation (P<0.01). Treatment of high P with low and medium N rates improved the gene expression of ACC and enhanced the ACC activity thereby increased the accumulation of atrctylodin. While high level of N and K inhibited the gene expression of ACC, thereby decreased the accumulation of atrctylodin.

Conclusions High level of P fertilizer (225 kg/hm²), combined with appropriate level of N (90 kg/hm²) and K fertilizer (315 kg/hm²) or P (225 kg/hm²), N (180 kg/hm²) and K fertilizer (105 kg/hm²) are beneficial to the yield of A. chinensis, which will stimulate the gene expression, enhance ACC activity, and promote the synthesis and accumulation of atrctylodin.