Inoculation with nitrogen-fixing bacteria on nitrogen forms in rhizosphere soil and medicinal components in bulbs of Fritillaria taipaiensis P. Y. Li

Background: A study was conducted to investigate the effects of different nitrogen-fixing bacteria (NFB) on nitrogen forms in rhizosphere soil, bulb biomass, and medicinal component contents of Fritillaria taipaiensis, aiming to provide references for quality improvement of this medicinal plant. Results: Compared to the CK group, ammonium nitrogen, nitrate nitrogen, and amide nitrogen in the seven treatment groups inoculated with NFB were significantly increased. The bulb biomass of F. taipaiensis was increased to varying degrees by all NFB inoculations, with the most pronounced effects observed in the R. aquatilis and P. stellifer inoculated group. Similarly, the total alkaloid content in the bulbs was significantly enhanced by NFB inoculation. Among the seven NFB-inoculated groups, the total alkaloid content increased by 22.92%, 40.45%, 43.42%, 58.51%, 61.36%, 46.47%, and 54.42%, respectively, relative to the non-inoculated group. Principal component analysis indicated that the combination of R. aquatilis and P. stellifer exhibited the strongest enhancement effect on alkaloid content. Correlation analysis revealed that ammonium nitrogen was negatively correlated with nitrate nitrogen but positively correlated with amide nitrogen (r=0.756), fresh weight, dry weight, and total alkaloid content. Nitrate nitrogen showed negative correlations with total alkaloids, sipeimine, and sipeimine glycosides, while demonstrating positive correlations with amide nitrogen, peimine, peiminine, and peimisine. Amide nitrogen was negatively correlated with sipeimine. Fresh weight was positively correlated with total alkaloid content (r=0.815). Peiminine exhibited a negative correlation with sipeimine (r=−0.721) but positive correlations with peimisine and sipeimine glycosides. Conclusion: Inoculation with NFB was found to effectively enhance nitrogen form contents in the rhizosphere soil of F. taipaiensis, as well as its bulb biomass and medicinal components. The most pronounced effects were observed in the treatment group inoculated with R. aquatilis and P. stellifer.