Conclusion
The eukaryotic phytoplankton and bacterial networks constructed in our
research conformed to the properties of non-randomly connections,
modular structure, and ”small world”. The complexity of the network was
susceptible to temperature, high and low temperatures were not conducive
to the stability of communities. For example, eukaryotic phytoplankton
networks in spring and autumn were more complex than in summer and
winter. In co-occurrence patterns, the positive interactions between
bacteria and eukaryotic phytoplankton OTUs may be evidence of mutual
influence (cooperation), while the negative correlations may indicate
predation or competition. Through its within-module connectivity
(Zi ) and among-module connectivity (Pi ), we identified the
keystone species that can maintain the stability of microbial networks.
The keystone species in bacterial networks were mainly OTUs of
Proteobacteria, Planctomycetes, Bacteroidetes, Verrucomicrobia,
Acidobacteria, Chloroflexi, and Firmicutes, which were defined as rare
taxa; and in eukaryotic phytoplankton networks, most OTUs of
Chlorophyta, Bacillariophyta, and Ochrophyta belonging to rare taxa, and
only 2 OTUs of Chlorophyta were abundant taxa. With the disappearance of
the ”keystone species” in the network center, the aggregation structure
will suffer major damage, which may bring huge biogeochemical
consequences. The abundance of these keystone species was significantly
related to many ecosystem functions and environmental changes,
highlighting the key ecological role of rare species, and providing a
new ecological significance for the seasonal succession patterns of
bacteria and eukaryotic phytoplankton in urban aquatic ecosystems.