The complexity of the bacterial community in response to fertilization determines forage production in a semiarid grassland

The role of soil microbial diversity and interactions in controlling plant productivity after fertilization remains unknown in grassland systems. This knowledge gap hampers our understanding of how shifts in soil microbial diversity and interactions can modify soil functioning and grassland production under changing environments. In this study, we evaluated the influence of short-term field fertilization on soil microbial diversity, particularly the complexity of microbial ecological networks in controlling aboveground plant productivity under five nitrogen addition rates (0, 6, 12, 20, 32 g N m(-2) year(-1)). The N fertilization resulted in higher forage production. The bacterial and fungal alpha diversity and taxonomic composition were relatively stable across the N addition rates. Network analysis showed that the complexity of the bacterial network increased gradually with increasing N addition rates, peaking at 20 g N m(-2) year(-1), while modularity and |negative|: positive cohesion had contrasting patterns across the N addition rates. Additionally, the changes of bacterial interactions were predominantly driven by the keystone taxa richness and abundance. Compared with the bacterial co-occurrence network, the fungal co-occurrence network remained relatively stable. Strong positive linkages between plant production and the complexity of the bacterial network were also observed. Furthermore, the increment of forage production was highly related to the keystone taxa abundance. Together, our results highlighted that the complexity of the soil bacterial network plays a vital role in enhancing the connection between soil microbial diversity and plant production. Our findings exemplify a significant progress in projecting the effects of soil microbial diversity on ecosystem functions in grassland ecosystems.