Effect of nitrogen fertilizer on hydrolytic enzyme production, root colonisation, N metabolism, leaf physiology and growth of rice inoculated with Bacillus sp. (Sb42)

A study was conducted at Universiti Putra Malaysia, Malaysia, glasshouse to determine the inoculation effect of Sb42 (locally isolated diazotroph) with different doses of nitrogen fertiliser (0, 30 and 60kg N ha) on hydrolytic enzyme production and the growth of rice variety MR219. Using 16S rRNA partial gene sequencing, Sb42 was identified as Bacillus sp. Plants were harvested at 45 days after transplanting, and specific enzyme activities of endoglucanase (EG) and endopolymethylgalacturonase (EPMG) were determined. Results showed that the growth of rice and hydrolytic enzymes production were significantly (P<0.05) affected by bacterial inoculation and N application. The application of N at concentrations of 30 and 60kg ha to inoculated plants reduced plant growth and specific enzyme activities. Inoculated plants without N application showed significantly higher (P<0.05) specific hydrolytic enzyme activity (88.9% EG and 20.1% EPMG), plant biomass (72.46%), rate of photosynthesis (9.38μmolCO2m s), leaf N content (3.16%) and N uptake (74.59mg plant) compared to non-inoculated treatments. Root colonisation was observed by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM), which proved that Sb42 is able to colonise at the surface and interior of roots. The ability of Sb42 to produce hydrolytic enzymes and biological nitrogen fixation was affected by the application of N fertiliser.