Fluxes of CH4, N2O, and kinetics of denitrification in disturbed and undisturbed forest soil in India

Abstract

Raut, N., Sitaula, B. K., Bakken, L. R. and Dörsch, P. 2014. Fluxes of CH4, N2O, and kinetics of denitrification in disturbed and undisturbed forest soil in India. Can. J. Soil Sci. 94: 237–249. Soil disturbance due to grazing has been severe in Indian forests. This may alter ecosystem functions such as the cycling of nitrogen, and may hence affect the emission of greenhouse gases. We measured fluxes of CH4 and N2O with a closed chamber technique throughout one year in a forest of Western Ghats, Karnataka state, southwest India and determined the product stoichiometry of denitrification under standard anoxic incubations in soil samples from disturbed and undisturbed forest. In both areas, there was a net flux of CH4 from the atmosphere to the soil, and the undisturbed forest soil was a stronger sink for CH4 than the disturbed (P<0.05). The accumulated CH4 uptake averaged for all four seasons was 1.5 times higher in undisturbed than disturbed forest. Contrary to our expectation, the N2O emission was significantly higher for undisturbed than for disturbed forest (P<0.05). The accumulated N2O emission averaged for all four seasons was 1.6 times higher in undisturbed than disturbed forest. Together our data suggest that increase of N2O release and decrease in CH4 sink in soil induced by grazing disturbance can affect the global warming potential (GWP) of forest in this region. The incubation study showed a strong correlation between oxic respiration rate (R) and subsequent denitrification rate (D) and the ratio D/R was 1:3 and 1:6 for soil from undisturbed and disturbed soils, respectively. The N2O/(N2+N2O) product ratio of denitrification tended to be higher in undisturbed than disturbed site, despite lower soil pH.