Nitrogen fertilizer regulates purple rice seed endophytes and grain amino acid accumulation

Abstract

The effects of different nitrogen (N) application levels on seed endophytes and grain nutritional quality are not yet clear. The impact of four N application levels on endophytes and amino acid accumulation in purple rice seeds was examined using 16S rRNA and ITS amplicon sequencing technology. This study integrates 16S rRNA, ITS amplicon sequencing technology and amino acid-targeted detection to explore the effects of four different nitrogen application levels (0 kg hm⁻², Y1N0; 180 kg hm⁻², Y1N1; 270 kg hm⁻², Y1N2; 360 kg hm⁻², Y1N3) on the accumulation of endophytic bacteria, fungi and amino acid content in purple rice seeds and their interaction mechanisms. The findings indicated an increase in the contents of most amino acids with increasing N application. The dominant bacterial species in the community were mainly from the phyla Proteobacteria and Actinobacteriota, while the dominant fungal species were from the phyla Ascomycota and Basidiomycota. There was a significant difference in the richness of endophytic fungal communities between Y1N0 and Y1N2. Y1N1 showed significant differences in Mucoromycota compared to Y1N3. The quantity of operational taxonomic units (OTUs) in the bacterial and fungal community co-occurrence network increased with increasing N fertilizer, showing strong correlations with Sporidiobolus, Chaetomium, Humicola, Botryotrichum, Ophiosphaeria and Dioszegia for most amino acids. These findings indicate that a high amount of N fertilizer greatly increases amino acid contents in purple rice seeds and improves the diversity and stability of endophytic fungal populations.