Hierarchical traits of rhizosphere soil microbial community and carbon metabolites of different diameter roots of Pinus tabuliformis under nitrogen addition

Abstract

Abstract Structures and functions were varied among roots with different diameters, and responded differently to nitrogen (N) addition, a phenomenon called hierarchical trait. However, the presence of this trait in carbon (C) metabolite of root exudate and rhizosphere microbial community remains unclear. We studied the patterns of C metabolites and microbial communities of rhizosphere soil among different diameter roots of Pinus tabulaeformis and their responses to N addition using metabolomics and high-throughput sequencing methods. Root C metabolites and rhizosphere soil microbial communities had hierarchical traits, in which exudates of R1 roots (0–0.5 mm) were rich in fatty acids and organic acids, while exudates of R3 roots (1–2 mm) were rich in carbohydrates and alcohols. With the increasing root diameters, numbers of bacteria and fungi of rhizosphere soil decreased and increased, respectively, while diversities of bacteria and fungi increased. N addition had a promotion effect on abundance of root C metabolites. Numbers of bacteria and fungi of rhizosphere soil were enhanced and inhibited, respectively, while diversities of bacteria and fungi were facilitated by N addition. N addition promoted microbial populations of rhizosphere soil by reducing exudates of R1 roots, and increasing exudates of R2 (0.5–1 mm) and R3 roots. Hippuric acid and cytidine-5´-monophosphate of R1 roots, lactic acid of R2 roots, glucose 1 and spermidine 2 of R3 roots were the functional C metabolites that affected microbial populations of rhizosphere soil, such as Actinobacteria, Acidobacteria, Proteobacteria, Basidiomycota, and Ascomycota. Hierarchical traits were extended from root to rhizosphere soil in this study. Graphical Abstract

Keywords

• Root exudate
• Metabolomics
• High-throughput sequencing
• Bacteria
• Fungi