Increased connections among soil microbes and microfauna enhances soil multifunctionality along a long‐term restoration chronosequence

Abstract The functional role of soil microbes in the restoration of degraded lands is greatly influenced by interactions within and between microbial communities, as well as by soil organisms at higher trophic levels (microfauna). However, little is known about how changes in connection patterns among soil microbes and their co‐existing microfauna contribute to associated changes in soil function over the ecosystem restoration process. In this study, the effects of afforestation and natural regeneration approaches on connection patterns among soil microbes and their co‐existing microfauna were assessed in ex‐arable lands on the Loess Plateau in China along a 50‐year restoration chronosequence. The relationships between soil network connections, microbial functional associations, and multiple soil functions (e.g. multifunctionality) were assessed quantitatively. Although both afforestation and natural regeneration approaches enhance connections among soil microbes and their co‐existing microfauna compared to recently abandoned sites, connection trends were opposed between these two approaches across the restoration chronosequence. Afforestation resulted in a higher number of soil microbial and microfauna species with a unimodal connection pattern, while natural regeneration resulted in a continuous increase in soil network connections over the progress of succession. These increases in soil network connections, particularly those of soil microfauna‐microbe and microbial inter‐kingdom connections, corresponded to enhanced microbial functional associations. This result is corroborated by significant correlations between microbial functional genes encoding different central functional pathways, which, in turn, were positively correlated with soil multifunctionality. Synthesis and applications . Changes in the connections among soil microbes and their co‐existing microfauna were positively associated with changes in soil multifunctionality, mediated by microbial functional associations. While in the early restoration stages, soil networks following afforestation contained more connections than those following natural regeneration, in later restoration stages, the number of connections of the afforestation network declined and was eventually surpassed by those following natural regeneration. These findings raise concerns about the ecological sustainability of afforestation measures in historic grasslands on the Loess Plateau, suggesting that natural regeneration is the preferred approach to achieve long‐term ecological restoration success.