Impact of excessive nitrogen application on growth and rhizosphere microbial community of Tartary buckwheat

Nitrogen fertilizer was excessively applied in modern intensive agriculture production.Excessive N application (ENA) reduced crop production and caused severe environmental pollution.It is urgent to improve N use efficiency and crop yield under ENA.However, the regulatory mechanism of ENA affecting root-soil interactions remains unclear, which limit crop yield improvement.This study aims to investigate the mechanism on the rootrhizosphere microbe interactions in Tartary buckwheat (TB) (Fagopyrum tataricum (L.) Gaertn.), a traditional pseudocereal crop.The agronomic traits of four TB cultivars under 90, 180 and 270 kg ha -1 N fertilizer were investigated by field experiments.The ENA reduced growth, grain yield and root development of TB.Compared with normal N fertilizer application (90 kg ha -1 ), 270 kg ha -1 N treatment decreased the yield, total root length and root volume of the four TB cultivars by 30.2% ~ 45.8%, 17.2% ~ 29.4% and 8.8% ~ 16.6%, respectively.The rhizosphere soil microbial community was investigated by 16S rDNA/internal transcribed spacer (ITS) sequencing analysis.The bacteria such as Nitrosospira, Lechevalieria and Nocardioides and fungi such as Verticillium, Mycosphaerella and Monilinia showed significant correlation with agronomic traits.The ENA inhibited the abundance of beneficial bacteria including Nocardioides and Amycolatopsis, while increased the abundance of pathogenic fungi such as Fusarium.Furthermore, correlation and co-occurrence network suggested the bacteria and fungi involved in ENA response, such as Nitrospira, Lechevalieria, Gemmatimonas, Rhizobiales, Verticillium and Monilinia.This study improved our knowledge on the links between plant and root microbiota under ENA condition.