Shading affects the nitrogen cycling process and plant nitrogen uptake by altering the rhizosphere microbial...

Plants adapt to environmental changes by affecting the rhizosphere environment and microbial pathways. Shading affects nitrogen absorption and accumulation in plants by directly or indirectly altering the light intensity. However, the effects this has on the rhizosphere micro-environment and especially the microbial community are not fully understood. Utilizing non-targeted metabolomics and metagenomics, we investigated the changes in the microbial community structure in the cigar tobacco rhizosphere and the nitrogen cycling process and its relationship with nitrogen absorption by the plants under artificial shading conditions. Shading significantly increased the rhizosphere soil organic carbon, hydrolyzable nitrogen, ammonium nitrogen, nitrate nitrogen, and nitrogen contents in tobacco plants. Metabolomics revealed that shading significantly affected the arginine biosynthesis pathway in the rhizosphere soil, with the expression levels of L-oxornithine, citrulline and L-arginine significantly increasing. Metagenomics analysis indicated that shading significantly altered the rhizosphere microbial community structure and the nitrogen cycling process. The abundances of organic nitrogen-decomposition (gdh A, ansB) and nitrification genes (amoA_B, amoB_B, amoC_B, hao) significantly increased. Flavobacterium and Stenotrophomonas may play important roles in the nitrogen cycle in the rhizosphere. Correlation analysis indicated that Flavobacterium and Stenotrophomonas were significantly positively correlated with L-glutamic acid, L-ornithine and L-arginine (p < 0.05). These results reveal the biological mechanism by which shading affects nitrogen absorption in crops via changes in the rhizosphere microbial community and the nitrogen cycling process, providing a scientific foundation for guiding nutrient management strategies in shaded cultivation.