供磷水平和根际效应协同影响含碱性磷酸酶基因细菌群落的网络复杂性和稳定性

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

摘要:

【目的】通过研究长期不同供磷水平下根际、土体土壤中编码碱性磷酸酶基因(alkaline phosphatase gene, phoD)细菌群落特征、网络复杂性、群落的稳定性及其与磷酸酶活性之间的关系，揭示供磷水平和根际效应在调控土壤有机磷矿化中的微生物学机制。【方法】选取华北平原长期施磷的小麦-玉米轮作体系石灰性土壤为基质土壤，开展根箱试验。选取的试验处理包括3个供磷水平，分别是0、50.0、200.0 kg P/hm² (分别表示为P0、P50、P200)。玉米种子播种30 d后，采集玉米的根际土和土体土。采用高通量测序技术分析根际和土体土壤中编码碱性磷酸酶基因(phoD)细菌群落，探究施肥及根际效应对含phoD基因细菌的群落特征、网络特征的影响及其与磷酸酶活性的关系。【结果】随着施磷量的增加，速效磷(available P, AP)和碱性磷酸酶(alkaline phosphatase, ALP)活性在根际、土体土壤中均显著提高，且两者呈显著正相关。phoD基因丰度在P0、P200处理的根际土壤中显著高于土体土壤。含phoD基因细菌群落的α多样性在P50处理下的根际土壤显著高于土体土壤。冗余分析(redundancy analysis, RDA)表明，土壤中AP、有机磷(organic P, Po)和全磷(total P, Pt)是影响微生物群落的主要因素。与不施磷处理(P0)相比，施磷处理(P50、P200)下根际土壤中网络节点数和连接数降低，而土体土壤中网络节点数和连接数增加；同时，施磷处理含phoD基因细菌群落的鲁棒性(robustness)在根际土壤中显著提高，而在土体土壤中显著降低。Mantel检验表明，含phoD基因微生物群落中的优势物种在根际土壤与AP、酸性磷酸酶(acid phosphatase, ACP)、内聚力(cohesion)和网络的鲁棒性显著相关，在土体土壤中无显著性。【结论】供磷水平及根际效应协同影响phoD基因丰度、含phoD基因细菌群落的α多样性、群落结构、优势物种、网络的复杂性及群落的稳定性，进而影响磷酸酶活性，调控了土壤中有机磷的矿化。

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.