Differential bacterial ammonia oxidation patterns in soil particles from two contrasting forests: The importance of interfacial interactions

•Upon adsorption on soil, bacterial metabolic activity was lower than free bacteria.•Interfacial interactions affected bacterial ammonia oxidation patterns.•Soil particle sizes determined the strength of interfacial interactions.•Natural forest soils had lower NH4+-N oxidation rate than plantation soils.•Bacteria-clay interfacial interactions induced a stronger protection of NH4+-N.