Phosphorus gradient fertilization and rhizosphere effect co-determine phoD-harboring bacterial network complexity and stability

Abstract:

[Objective] This study explored the characteristics, network complexity and stability of the bacterial community harboring the alkaline phosphatase gene (phoD) and the phosphatase activity in rhizosphere and bulk soils under long-term gradient phosphorus (P) fertilization, aiming to reveal the microbial mechanism of P fertilization and rhizosphere effect in regulating soil organic P mineralization. [Methods] The calcareous soil of wheat-maize rotation system with long-term gradient P application in North China Plain was selected for the rhizobox experiments. We designed three P fertilization levels: 0, 50, and 200 kg P/hm² (P0, P50, and P200, respectively). The rhizosphere and bulk soils were collected 30 days after the sowing of maize seeds. High-throughput sequencing was carried out to analyze the phoD-harboring bacterial community, which helped reveal the effects of P gradient fertilization and rhizosphere effect on the community and network characteristics of phoD-harboring bacteria and their relationship with phosphatase activity. [Results] With the increase in P application, available P (AP) and alkaline phosphatase (ALP) activity increased significantly, which were significantly positively correlated with each other. Under P0 and P200 treatments, the abundance of phoD in the rhizosphere soil was significantly higher than that in the bulk soil. Under P50 treatment, the alpha diversity of the phoD-harboring bacterial community in the rhizosphere soil was significantly higher than that in the bulk soil. The redundancy analysis (RDA) showed that AP, organic P (Po), and total P (Pt) were the main factors affecting the phoD-harboring bacterial community. Compared with P0 treatment, P50 and P200 reduced the total nodes and edges and increased the robustness of the bacterial network in rhizosphere soil, while they increased the total nodes and edges and decreased the robustness of the bacterial network in the bulk soil. The Mantel test showed that the dominant taxa of phoD-harboring bacteria were significantly correlated with AP, acid phosphatase (ACP), cohesion, and network robustness in rhizosphere soil, while the correlations were not significant in the bulk soil. [Conclusion] P gradient fertilization and rhizosphere effect co-affected the abundance of phoD, alpha diversity, community structure, dominant taxa, network complexity, and stability of phoD-harboring bacteria, which further affected phosphatase activity and consequently regulated the mineralization of organic P.

Key words:phosphorus fertilizer;rhizosphere;phoD;network characteristics;community stability