Chemotaxis Mediates Nitrogen Acquisition of Maize Under Long-Term Nitrogen Input

Chemotaxis is a process that enables motile bacteria to move along nutrient gradients, thereby exploring nutrient hotspots, and potentially playing important biogeochemical roles in agricultural ecosystems. In this study, a 36-year field experiment of nitrogen (N) input was conducted, along with the use of a synthetic community (SynCom) inoculation, to confirm the role of chemotaxis in the cycling of N. The chemotaxis genes abundances of N+ treatments were 97.2% and 95.3% higher than that of N- treatments in bulk soil and rhizosphere, respectively, indicating a significant increase in chemotaxis genes under long-term N input. Positive correlations between chemotaxis genes and N metabolism genes in N+ treatments suggested an important role of chemotaxis in N cycling. The chemotaxis genes abundance was 3.6 times higher in rhizosphere than in bulk soil, and chemotaxis genes showed the most complex correlations with N metabolism genes in rhizosphere under N input, suggesting a key role of chemotaxis in plant N uptake. To assess the potential function of chemotactic bacteria, a SynCom consisting of 10 bacterial strains isolated from in situ N-input soils and capable of chemotaxis, was applied to the maize rhizosphere. The promotion of N acquisition in maize plants through inoculation was confirmed by about 30% greater N content in the shoots of SynCom inoculated soil than in the control. Long-term N input enhanced the functions related to metabolite transport and energy metabolism in the bacterial community, particularly in the rhizosphere. Thus, plants may provide bacteria that migrate to the rhizosphere via chemotaxis with more root metabolites as nutrients. In summary, this study provides novel ecological and molecular insights into chemotaxis-mediated biogeochemical cycling in agricultural ecosystems.