Diazotrophic Community Structure and  Functioning in the Soil of Crop Plants (Legumes  Versus Non–Legumes) at Two Depths

Sandhya Rai; Dileep Kumar Singh; Kannepalli Annapurna

Volume : II, Issue : XI, November - 2013

Diazotrophic Community Structure and Functioning in the Soil of Crop Plants (Legumes Versus Non–Legumes) at Two Depths

Sandhya Rai, Dileep Kumar Singh, Kannepalli Annapurna

Abstract :

This study was undertaken to compare the diazotrophic community structure and functioning (nitrogenase activity) in the crop soil of gram, pea, mustard and wheat sampled at two depths, 0–15 cm and 15–30 cm. The nitrogenase activity was higher in the soil of leguminous crop plants (1236.93 ? 23.4 ηmole C2H4 g–1 soil h–1 and 199.97 ? 33.7 ηmole C2H4 g–1 soil h–1 in 0–15 cm depth soil of gram and Pea respectively) compared to that of the non–legumes and significantly decreased along the depth in all the crops. The diazotrophic community structure of different soils was compared using Terminal Restriction Fragment Length Polymorphism (T–RFLP) analysis. Each crop soil provided distinct T–RFLP profile of its own which showed comparatively lesser deviation with increase in depth. Abundance of certain nifH genotypes is more pronounced in legumes while in non–leguminous crops, the T–RFLP profile showed more number of TRFs but could not be correlated to the nitrogenase activity. Considerable functional redundancy of nifH gene pool was found at the experimental site due to lack of correlation between the diazotrophic community structure and functioning. Summary. The present study aimed to compare nifH (one of the structural genes encoding Component II of nitrogenase enzyme complex involved in biological Nitrogen fixation) as well as nitrogenase activity of plant soil of four crop plants (legumes vs non–legumes) sampled at two depths (0–15 cm and 15–30 cm). Spatial analysis of diazotrophic community functioning of the rhizospheric soil of various crop plants revealed higher activity in legumes than non–legumes which decreased significantly along the depth. Each crop provided a specific HaeIII–TRFLP profile of its own and depth–wise profiles showed lesser deviations from each other. Profound effect of crop type was observed on nifH community structure as the dominant T–RFs of legumes rhizospheric soil indicated functional nitrogen fixers. Considerable functional redundancy of nifH gene pool was found at the experimental site due to lack of correlation between the diazotrophic community structure and functioning.