Fig. 4 Co-occurrence network of nonrhizosphere soil fungi of A. spinulosa at different taxonomic levels
Analysis of network properties
Further analysis of the network topological properties (Figures 3, 4, and 5) revealed that the number of nodes and connections between the co-occurrence networks of rhizosphere and nonrhizosphere soil fungi ofA. spinulosa was significantly different. At different taxonomic levels, the ratio of positively correlated margins in the fungal co-occurrence network of the A. spinulosa rhizosphere soil was higher than that of the nonrhizosphere soil. The number of negatively correlated margins at the order level was higher in the rhizosphere soil than in the nonrhizosphere soil. This indicates that the rhizosphere soil fungal community of A. spinulosa tended to be more stable and that interspecific competition was more intense at the order level. According to network topology analysis, the stability of the fungal co-occurrence network of the A. spinulosa rhizosphere soil was the highest at the eye level (network stability = 0.37). The network quality and efficiency of A. spinulosa roots were higher at all taxonomic levels than those of non-roots. However, the smaller average network path length and higher network vulnerability also indicated that the co-occurrence network of these soil fungal communities in A. spinulosa roots was vulnerable to external environmental disturbances.