Fig. 4. Bacterial and fungal co-occurrence network in S. ciliata rhizosheath–root system compartments.

a Significant interactions (edge, p < 0.05) between bacterial and fungal OTUs in root tissue (RT), rhizosheath (RS) and rhizosphere (RH) of S. ciliate and non-vegetated (NV) soil were visualized by co-occurrence network. Circles (nodes) represent individual OTUs (bacteria, fungi, and algae); size of circles indicates the number of connections of such node (degree); nodes were colored according to their taxonomic affiliation: black, orange and green indicate bacteria, fungi and algae, respectively. For co-occurrence networks’ properties refer to Table 2. b Proportion of bacterial, fungal and algae OTUs included in co-occurrence networks. Portion of OTUs not included in the network is also reported (white portion of bars). c Relationship between node-normalized degree (log₁₀) and betweenness centrality in networks of rhizosheath–root system and non-vegetated soil compartments. Colors indicate the taxonomic affiliation of nodes (bacterial, fungal and algal OTUs); gray-box indicate the nodes with high degrees defined as hubs; red-dashed boxes delineate the keystone species of each network (high degree and high betweenness). d Frequency of edges (connections) in the rhizosheath–root system compartments’ networks. Connections among the three components of the network are showed: bacteria–bacteria, fungi–fungi, bacteria–fungi, and algae with all the others (* = bacteria, fungi and algae). e Taxonomic affiliation of bacterial and fungal hubs detected for each network (c) expressed as normalized frequency; total number of bacterial and fungal hubs are reported on each bar, along with the number of keystone species accounted among them (numbers in square brackets). Details regarding taxonomy are reported in Supplementary Data S2.