Abstract:

We measured N2O fluxes and CH4 uptake rates following NH4Cl and KNO3 (100kg N ha-1) application with and without FH layer during a relatively dry season in an Acacia mangium plantation stand in Sumatra, Indonesia. High N2O fluxes at control (no treatment) with FH (0.46 – 0.53 mg N m-2 d-1) suggested that A. mangium soils function as a larger source of N2O than natural forest soils. In the relatively dry season, FH layers in the A. mangium plantation were not a direct source of N2O, but appear to contribute to nitrogen cycling and the following N2O production in mineral soils as a supplier of available carbon and nitrogen. Application of NO3- fertilizers significantly increased N2O fluxes irrespective of the FH removal treatment, suggesting that increased NO3- availability enhanced N2O emissions through the denitrification process and that anaerobic microsites can exist even in the relatively dry soils in the A. mangium plantation. CH4 uptake rates at control with FH layer ranged between 0.70 – 0.84 mg C m-2 d-1, which is consistent with other natural tropical forest soils. A. mangium soils supplied with N rich litter do not appear to decrease the function as a sink for atmospheric CH4 at least in a relatively dry season, though NH4+ addition significantly reduced CH4 uptake rates.

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