Estimation of Nitrogenase Enzyme Activities and Plant Growth of Legume and Non-legume Inoculated with Diazotrophic Bacteria

Abstract

Biological Nitrogen Fixation (BNF) process benefits the agriculture sector especially for reducing cost of nitrogen fertilizer. In the process, the diazotrophs convert N2 into ammonia (NH3) which is useable by plants. The BNF process is catalysed by nitrogenase enzyme that involved protons and electrons together with evolution of H2 therefore, the assessment of N2 fixation is also available via H2 production and electron allocation analysis. Thus, the aims of this experiment were to estimate the nitrogenase enzyme activities and observe the influence of diazothrophs on growth of legume (soybean) and non legume (rice) plants. Host plants were inoculated with respective inocula; Bradyrhizobium japonicum (strain 532C) for soybean while Azospirillum brasilense (Sp7) and locally isolated diazotroph (isolate 5) for rice. At harvest, the plants were observed for plant growth parameters, H2 evolution, N2 fixation and electron allocation coefficient (EAC) values. The experiment recorded N2 fixation activities of inoculated soybean plants at 141.2 µmol N2 h-1 g-1 dry weight nodule, and the evolution of H2 at 144.4 µmol H2 h-1 g-1 dry weight nodule. The electron allocation coefficient (EAC) of soybean was recorded at 0.982. For inoculated rice plants, none of the observations was successfully recorded. However, results for chlorophyll contents and plant dry weight of both plants inoculated with respective inocula were similar to the control treatments supplied with full nitrogen fertilization (+N). The experiment clearly showed that inoculation of diazotrophic bacteria could enhance growth of the host plants similar to plants treated with nitrogenous fertilizer due to efficient N2 fixation process