Co-occurrence patterns in the N-loading system
A co-occurrence network was built
for the identified nematodes at the genus level. Compared with N0, there
was a slight rising of positively correlated edges at N1 treatment, then
decreased at N2 and N3 treatments (Fig. 4a). N1 treatment had the most
positive correlations (74.2%) and network connections (31 edges), while
N2 and N3 levels had more negative correlations. The structure values in
the N-loading networks were greater than or equal to those in N0 (Fig.
4b).
Pathways
determining the abundances of soil nematode trophic groups
SEM analysis was performed to reveal the relationships between the
abundance of nematode trophic groups and environmental attributes under
a good model fit using χ2 test
(χ2=7.55, Fig. 5). As for the four nematode trophic
groups, the SEM explained 0.8-42.5% of total variance with N loading.
The
abundance of the PF group (r2 =0.42) was
directly affected by N loading (P <0.001), and was
indirectly affected by soil pH under N-loading regulation
(P <0.001, Fig. 5a). By altering soil available
nutrients and soil water content, N loading significantly changed the
abundance of FF
(P <0.001,r2 =0.31) and BF groups
(P <0.01, r2 =0.43). Moreover, N
loading was as a whole beneficial to the fungal- (Fig. 5b; Table S2) and
bacterial-feeding (Fig. 5c; Table S2) nematodes, while was detrimental
for the plant-feeding nematodes (Fig. 5d; Table S2).