Contrasting effects of exogenous phosphorus application on N(2)O emissions from two tropical forest soils with contrasting phosphorus availability

An incubation study was conducted to test the effects of phosphorus (P) addition on nitrous oxide (N(2)O) emissions from the soils taken from two tropical rain forests established on different parent materials [meta-sedimentary (MS) and ultrabasic (UB) rock] on Mt. Kinabalu, Borneo. Earlier studies suggest that the forest on UB soils is more strongly limited by P than that on MS soils is. In MS soils, P addition significantly reduced N(2)O emissions. Since neither ammonium (NH(4)(+)) nor nitrate (NO(3)(−)) contents were reduced by P addition, we assumed that the decrease in N(2)O emissions were not due to the previously-reported mechanism: P addition stimulated microbial nitrogen (N) immobilization and collateral inorganic N consumption, reducing resources for producing N(2)O. Since P addition enhanced the ratios of microbial biomass to CO(2) and N(2)O emissions (indicators of nitrifying and/or denitrifying respiratory efficiency), it was suggested that the N required for the respiration of nitrifying and/or denitrifying bacteria was reduced, leading to reduced N(2)O emissions. On the other hand, P addition had no effects on N(2)O emissions in UB soils. The respiratory efficiency did not change significantly by P addition, possibly because the microbial community in the highly-P-depleted UB soils shifted by P addition, with which the enhancement of respiration efficiency did not co-vary. We concluded that (1) P addition may control N(2)O emissions through increasing respiratory efficiency, and (2) the effects may be different depending on the differences in P availability.