Shifts in the rhizosphere bacterial community and improved essential oil yield and quality in Chamomilla recutita L. through Nostoc sp. inoculation

The rhizosphere bacterial community plays a crucial role in improving nutrient availability, disease and stress resistance, and overall plant development. Biofertilizers can enhance plant growth but less is known about their mode of interaction. Here, we studied the impact of two nitrogen-fixing cyanobacterial strains (Nostoc sp. NoHu, Anabaenopsis circularis AnHu) on the growth, essential oil yield and quality, and apigenin-7-O-glucoside content of chamomile plants (Chamomilla recutita L.) as well as their associated microbiota in field experiments in Egypt. During the experiments, flowers were collected every 7-10 days and kept at -20C. At the end of the experiment, each plant was harvested, and the fresh and dry weights of shoots, roots, and flowers were recorded, and analysis of essential oil yield and chemical composition and the flower's apigenin-7-O-glucoside content were performed. The bacterial community of the rhizospheres was analyzed based on 16S rRNA amplicon libraries and cultivation and was composed in general of 31 phyla and 164 different genera. Compared to untreated plants, the application of both strains showed contrasting results. While Nostoc application significantly enhanced all tested plant growth parameters, no effect was found for A. circularis. Nostoc sp. treatment also increased the yield and content of vital constituents of the essential oil, as well as the apigenin-7-O-glucoside content, indicating its potential as an efficient bioinoculant for boosting chamomile essential oil productivity. Furthermore, Nostoc sp. application increased the abundance and diversity of the rhizosphere bacterial community, suggesting an indirect effect of treatment through altering the rhizosphere microbial structure. The study emphasized strain-specific effects with the Nostoc sp. NoHu as a promising candidate for chamomile medicinal plant.