The effects of tannins derived from <i>Acacia mangium</i> bark on N₂O emissions from water saturated acacia plantation soil

Abstract

To evaluate the potential of tannins derived from Acacia mangium bark to mitigate soil N 2 O 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 2 O 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 2 O 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 2 O emissions, suggesting that the toxic effects of HMT and LMT in it would overcome the effects of other C compounds on soil N 2 O emissions. Tannic acid, which is different in structure from condensed tannins, suppressed the N 2 O 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 2 O emissions from A. mangium plantation soils.

Acacia mangium Willd: benefits and threats associated with its increasing use around the world

“…This may be attributed to both the lower turnover of old C and a higher accretion of new C (Resh et al 2002). Another beneficial impact of A. mangium is its ability to contribute to climate-change mitigation goals, since emissions of N 2 O, one of the main greenhouse gases, may be reduced by the application of its bark tannins in water-saturated soil (Matsubara and Ohta 2015).…”