Abstract
An incubation study was conducted to test the effects of phosphorus (P) addition on nitrous oxide (N2O) 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 N2O emissions. Since neither ammonium (NH4+) nor nitrate (NO3−) contents were reduced by P addition, we assumed that the decrease in N2O 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 N2O. Since P addition enhanced the ratios of microbial biomass to CO2 and N2O 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 N2O emissions. On the other hand, P addition had no effects on N2O 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 N2O emissions through increasing respiratory efficiency, and (2) the effects may be different depending on the differences in P availability.
Highlights
Nitrous oxide (N2O) is the third most important global warming gas (IPCC 2007) and the most important ozone-depleting gas (Ravishankara et al 2009)
The inconsistence was due to the differences in the relationship between microbial biomass C (MBC)/CO2 with and without P addition (Fig. 2a)
They reported that P addition stimulated N2O emissions both from nitrification and denitrification, possibly because of the following two mechanisms: (1) P addition directly activated nitrifying and/or denitrifying bacteria; (2) P addition stimulated O2 consumption by heterotrophic activities and created a more reduced condition, which is suitable for denitrifying bacteria and stimulates denitrification
Summary
Nitrous oxide (N2O) is the third most important global warming gas (IPCC 2007) and the most important ozone-depleting gas (Ravishankara et al 2009). In tropical forest ecosystems, which account for 14–23 % of the current N2O budget (IPCC 2007), phosphorus (P) availability may be another important factor controlling N2O emissions. Microbial activity including nitrification or denitrification is suggested to be limited by P availability (Minami and Fukushi 1983; Kitayama et al 1997, 1998; Cleveland et al 2002; Ilstedt et al 2003; Kitayama et al 2004; Ilstedt and Singh 2005; Cleveland and Townsend 2006; Mori et al 2010b, 2013a; He and Dijkstra 2015). Several studies reported that P application reduced N2O emissions They suggested that added-P stimulated plant N uptake and reduced N resources for N2O production (Mori et al 2013b; Baral et al 2014; Zhang et al 2014; Chen et al 2015). This idea was experimentally confirmed by Mori et al, demonstrating that P addition reduced N2O emissions from Acacia mangium plantation sites with roots, while stimulated the emissions from root-excluded sites (Mori et al 2014)
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