4.2 Elevated temperature and precipitation weaken microbial
interactions within the co-occurrence networks
The
soil microbiome
network plays a key role in helping
us understand potential biotic interactions there (Feng et al., 2021;
Sanaei et al., 2021; Zhao et al.,
2019b). Interspecific interactions among bacterial, fungal, and protist
groups were stronger at Guizhou than Guangxi. This finding was contrary
to our hypothesis. There were more bacterial nodes (OTUs) than fungal or
protist nodes. Hence, there were large, ubiquitous bacterial
populations. Readily decomposable organic C should augment bacterial
diversity to a greater extent at Guizhou than Guangxi (Poll et al.,
2008; Samal et al., 2020). High bacterial diversity fosters linkages
with fungi and protists. There were more bacterial nodes at Guizhou than
Guangxi. By contrast, fungi and protists had similar numbers of nodes at
both locations. These results suggest stronger network interactions at
Guizhou than Guangxi primarily because bacterial diversity was greater
than fungal or protist diversity at both locations. Similarly, elevated
bacterial diversity under cropland resulted in a greater number of
network interactions than those under plantation forest or shrubland.
Fungi are more tolerant of high soil C/N than bacteria (De Deyn et al.,
2008; Wang et al., 2015). Fungi might grow better in plantation forest
and shrubland soil than in cropland soil as the latter has comparatively
lower C/N (Fig. S1m). Fungi are
vital plant biomass decomposers and degrade plant litter containing
lignin and cellulose (Fontaine et al., 2011; Zeilinger et al., 2016). At
this case, correlations among fungal and protist taxa were stronger
under plantation forest and shrubland than cropland. Thus, the fungal
community plays a crucial role in vegetation restoration.
Co-occurrence
patterns can also identify keystone and indicator taxa (Fournier et al.,
2020; Wang et al., 2021). Bacterial
phyla Acidobacteria and
Proteobacteria, fungal phyla Ascomycota and Basidiomycota, and protist
phyla Cercozoa and Lobosa formed the most links with other microbial
groups and are, therefore, potentially vital to soil food webs.
Protists prey on bacteria and fungi,
thereby modifying microbial communities (Geisen et al., 2018). Cercozoa
and Lobosa are phagotrophs that consume Acidobacteria, Proteobacteria,
and Ascomycota (de Araujo et al., 2018; Seppey et al., 2020). These
predator-prey relationships were stronger at Guizhou than Guangxi.
Hence, predation of microbial decomposers by protists is more important
at low than high temperature (Geisen et al., 2021). Soil moisture
content was usually higher at Guizhou than Guangxi because low
temperature partially retards evaporation. Protist movement, feeding,
and multiplication are all affected by the water films in the soil pore
spaces (Ritz, 2011; Stefan et al., 2014). Consequently, predation of
bacteria and fungi by protists was strong in Guizhou soil.