Characterization of four highly efficient ammonifying bacteria from Camellia Oleifera and their effects on soil chemical properties

BACKGROUND: Camellia oleifera is an ammonium-preferring woody oil crop. However, cultivable ammonifying bacteria from its rhizosphere remain insufficiently characterized, and their potential to improve soil chemical properties and enhance nitrogen availability has not yet been evaluated. Four high-efficiency strains were selected and identified as Arthrobacter sp., Chryseobacterium sp., Stenotrophomonas sp., and Bacillus sp. based on phenotypic characteristics and 16S rRNA gene sequencing. Culture optimization showed that pH 7-8, 20-30 °C, 200 rpm, and a 2% inoculum size supported optimal bacterial proliferation. No antagonistic interactions were detected among the four strains, indicating compatibility for consortium construction. In a pot experiment, inoculation with individual strains or their consortium significantly increased rhizosphere ammonium nitrogen, nitrate nitrogen, and available nitrogen compared with the control. Soil enzyme activities related to nitrogen transformation were also enhanced, with most reaching peak levels 60 days after inoculation. CONCLUSIONS: Four efficient ammonifying bacteria isolated from the C. oleifera rhizosphere exhibited strong ammonium-producing capacity, compatibility for consortium formulation, and improved soil nitrogen supply and chemical properties.