3.5 Bacterial general co-occurrence network in different land uses
We constructed four co-occurrence networks based on OTU-OTU correlations for different land uses and seasons, and found striking differences in the network size between land uses (Figure 8). There were three main clusters in maize field for both seasons, while only one main cluster in woodland. The networks of maize field in the spring and autumn (376 and 371 nodes) were more complex than that of woodland (278 and 334 nodes). Positive correlation (co-occurrences) displayed as edges was significantly higher than negative ones (mutual exclusions) in all the networks (Table 2). As shown in Table 2, network topological parameters varied in two land uses. The woodland network exhibited considerably higher average degrees, higher clustering coefficient and higher network density compared with the maize field network. The highest positive and negative correlation were recorded in maize field in the spring and woodland in the autumn, respectively, while the lowest positive and negative correlation were both recorded in the maize field in the autumn. More than 70% of all nodes were assigned to five dominant phyla includingProteobacteria , Acidobacteria, Actinobacteria andChloroflexi . Interestingly, Bacteroidetes was found as the dominant group in the maize field co-occurrence network, while not shown in woodland network (Figure 8).