Particle size rather than concentration of silver nanoparticles mainly affects soil N2-fixing bacterial communities

Soil N2-fixing bacterial communities are essential for nitrogen cycling. Large amounts of silver nanoparticles released into the environment (especially farmlands) can dramatically affect soil N2-fixing bacterial communities. Thus, high-throughput sequencing technology was implemented to address the ecotoxicological effects of silver nanoparticles with different particle sizes and concentrations on soil N2-fixing bacterial communities in the wheat rhizosphere. Soil pH value is inversely related to the diversity of soil N2-fixing bacterial communities likely mediated by the changes in nutrient availability in the soil subsystems. AgNPs. Silver nanoparticles with 30 nm significantly decrease the diversity of soil N2-fixing bacterial communities compared with the control. The decreased diversity of soil N2-fixing bacterial communities can reduce the soil nitrogen availability for wheat via the decreased nifH gene abundance. Treatments with silver nanoparticles and silver ions significantly increase soil silver ion concentration compared with the control. Thus, the inhibition of silver nanoparticles on soil N2-fixing bacterial communities is presumably due to the released silver ions. Silver ions pose a stronger inhibition on the diversity and richness of soil N2-fixing bacterial communities compared with silver nanoparticles. The inhibition of silver nanoparticles on the diversity and richness of soil N2-fixing bacterial communities increases as the particle size decreases. The concentration of silver nanoparticles does not exert notable effects on the alpha and beta diversity of soil N2-fixing bacterial communities. Accordingly, particle size, rather than concentration, is the most important determinant of the inhibition of silver nanoparticles on soil N2-fixing bacterial communities.