To evaluate the potential of tannins derived from
Acacia mangium bark to mitigate soil N
2O 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 KNO
3 was added and the water-filled pore space was adjusted to 100%.
Acacia mangium bark tannins significantly decreased N
2O emissions compared with the control. However, they did not significantly affect CO
2 emissions or inorganic N concentrations except for soils with LMTs, where cumulative CO
2 emissions were significantly decreased, and for the fact that NH
4+ 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 N
2O emissions by inhibiting denitrification regardless of the degree of polymerization. The crude tannin extract, which probably contained other non-tannic C sources, also reduced N
2O emissions, suggesting that the toxic effects of HMT and LMT in it would overcome the effects of other C compounds on soil N
2O emissions. Tannic acid, which is different in structure from condensed tannins, suppressed the N
2O 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 N
2O emissions from
A. mangium plantation soils.
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