Bacillus pumilus promotes the growth and nitrogen uptake of tomato plants under nitrogen fertilization

Some plant growth-promoting bacteria (PGPB) are capable of fixing atmospheric N-2 and can be used to reduce nitrogen (N) fertilizer application in agriculture. Large amounts of N fertilizers are applied in tomato (Solarium lycopersicum L.). However, less attention has been given to the role of PGPB in the N nutrition of tomato. The present study was carried out under greenhouse conditions to investigate the principal mechanisms underlying PGPB-improved N nutrition in tomato. Tomato plants were grown in pots under -N (native soil N without N fertilization) or + N (supply 150 mg N kg(-1) dry soil in the form of urea), with or without Bacillus pumilus (PGPB) inoculation. Nitrogen supply improved the growth of tomato, soil NH4+ concentration, and plant N uptake. Nitrogen increased the rhizobacterial population, bacterial nifH gene expression, and soil nitrogenase activity only with the inoculation of B. pumilus. B. pumilus inoculation improved the tomato growth, N uptake, soil NH4+ concentrations, rhizobacterial population levels, soil bacterial gene expression, and soil nitrogenase activity only under + N condition. These results suggest that the inoculation of B. pumilus improves the growth of tomato under the condition of additional fertilizer N supply due to an increase in N uptake by roots from B. pumilus assisted fixed N in soil.