2015 Volume 24 Issue 2 Pages 65-74
To evaluate the potential of tannins derived from Acacia mangium bark to mitigate soil N2O emissions, a laboratory incubation study was conducted. We prepared a crude tannin extract by water extraction from A. mangium bark, and fractionated the crude extract into high- and low-molecular-weight tannins (HMTs and LMTs, respectively). Soils were incubated with and without the addition of A. mangium bark tannins and commercial tannic acid after KNO3 was added and the water-filled pore space was adjusted to 100%. Acacia mangium bark tannins significantly decreased N2O emissions compared with the control. However, they did not significantly affect CO2 emissions or inorganic N concentrations except for soils with LMTs, where cumulative CO2 emissions were significantly decreased, and for the fact that NH4+ contents in tannin-treated soils were significantly lower than in the control soil at 7 days. These results suggest that the antimicrobial activities of purified tannins of A. mangium bark reduced N2O emissions by inhibiting denitrification regardless of the degree of polymerization. The crude tannin extract, which probably contained other non-tannic C sources, also reduced N2O emissions, suggesting that the toxic effects of HMT and LMT in it would overcome the effects of other C compounds on soil N2O emissions. Tannic acid, which is different in structure from condensed tannins, suppressed the N2O emission but it was not significant and less effective than HMT and LMT. Our results suggest that the application of A. mangium bark tannins has the potential to mitigate N2O emissions from A. mangium plantation soils.