Long-term phosphorus deficiency decreased bacterial-fungal network complexity and efficiency across three soil types in China as revealed by network analysis

Abstract Soil bacteria and fungi are essential constituents of arable ecosystems. Long-term phosphorus (P) deficiency has been proven to significantly affect microbial community diversity and composition. However, how P deficiency impacts the interplay between bacteria and fungi remains unclear. The objective was to explore the bacterial-fungal co-occurrence patterns in soil as influenced by long-term P deficiency, using network analysis. Bacterial and fungal community datasets were obtained from soils which have consistently and continuously been fertilized with P (+P) or without P (−P) for >20 years in three long-term field experiments in China. Our results showed that the −P network was less complex and less efficient as indicated by fewer edges, lower average degree and higher average path length. Chronic P deficiency simultaneously decreased positive and negative bacterial-fungal edges, implying that both synergistic and antagonistic interactions were enhanced by P application. The keystone species differed between +P and −P network, and those from the +P network showed significant correlations with less soil properties, indicating the −P network was more sensitive to environmental disturbances. Four major modules were observed in both +P and −P networks, and they related with different soil properties, suggesting distinct habitat heterogeneity or niche partitioning. All the modules had similar ecological roles, while the module composition was altered by long-term P deficiency, indicating a possible ecological redundancy. Most of the fungi from the −P treatment were distributed in a special module negatively correlated with available P, indicating that fungi may prefer niches with low P concentration. Taken together, our results illustrated the crucial roles of P availability in microbial community assembly and investigated the responses of co-occurrence patterns to long-term P deficiency by regulating the topological properties, keystone species and module composition of the bacterial-fungal network.