Effects of Graphene on Bacterial Community Diversity and Soil Environments of Haplic Cambisols in Northeast China

Graphene is the thinnest and toughest two-dimensional nanomaterial yet discovered. However, it inevitably enters the biosphere, where it may pose potential risks to ecosystems. We investigated the impact of applied graphene concentrations on bacterial community diversity, physicochemical properties, and enzyme activities of Haplic Cambisols, the zonal soil of Northeastern China. Soils receiving 0, 10, 100, or 1000 mg kg(-1) of graphene were incubated for 7, 15, 30, 60, or 90 days. Adding graphene significantly increased the community richness and diversity index of the bacterial community in Haplic Cambisols, as well as their abundances, but this impact varied with graphene concentration and incubation time. Compared with 0 mg kg(-1) of graphene applied, soil bacteria abundance and diversity increased significantly during early stages of incubation (i.e., 7 and 15 days) under different concentrations of graphene, and was inhibited or remained unchanged by a longer incubation time, reaching a minima at 60 days but then following an upward trend. Graphene treatments influenced the bacterial community structure and metabolic function in Haplic Cambisols, and the bacterial community's metabolic regulation mechanism varied with both incubation time and graphene concentration. The rank order of bacterial similarity in soils treated with graphene was 15 > 7 > 30 > 60 > 90 days. Throughout the incubation periods, except for a few unidentified bacteria, the relative abundances of Proteobacteria and Acidobacteria in the soil samples were the highest, with the number of Pseudomonas of Proteobacteria being particularly large. The rank order of bacterial abundance at the phylum level in Haplic Cambisols was 15 > 7 > 30 > 90 > 60 days. Graphene also influenced bacterial community diversity by affecting several key soil environmental factors, such as organic matter and hydrolytic nitrogen contents, as well as urease and catalase activities.