5 Conclusion
In this study, we characterized soil chemical properties, microbial communities of rhizosphere and non-rhizosphere soils, and root tissue metabolites of quinoa planted at different densities. With increased planting density, soil salt content and microbial diversity increased. However, intense inter-plant competition in high-density planting resulted in taller and thinner plants with small panicles, but higher grain yield in gih-density than low-density planting. A high abundance of up-regulated metabolite S-adenosylmethionine was found in roots in low-density planting, which might have had a positive effect on plant growth and development. The mechanism by which S-adenosylmethionine promotes quinoa growth should be studied further.

Acknowledgements

This work was financially supported by the Jiangsu Agricultural Science and Technology Independent Innovation Fund Project [CX(19)3116], Forestry Science and Technology Innovation and Extension Project in Jiangsu Province (LYKJ[2019]07), and the National Key Project of Scientific and Technical Supporting Programs funded by the Ministry of Science & Technology of Jiangsu Province (BE2018387 and BE2017310-2).