Phosphorus limitation on CO2, N2O, and NO emissions from a tropical humid forest soil of South Sumatra, Indonesia

We examined if there is a P limitation on microbial activities and the accompanying gas emissions in a humid tropical forest soil of South Sumatra, Indonesia. The soil was incubated for 30 d with and without adding P (Ca(H2PO4)2; 2 mg P g·soil⁻¹) after adjusting water-filled pore space (WFPS) to 75% or 100%. The cumulative CO2 emission during 30 d (mg C kg·soil⁻¹) increased by P addition from 751 ± 105 to 959 ± 66 and from 1096 ± 36 to 1294 ± 47 at 75% and 100% WFPS, respectively, suggesting that the soil microbial activity was limited by P. P addition also increased the cumulative N2O emissions (from 10.2 ± 5.08 to 19.9 ± 6.91 and from 1405 ± 161 to 1977 ± 179 at 75% and 100% WFPS, respectively) and the cumulative NO emissions (from 354 ± 25.9 to 774 ± 52.7 and from 117 ± 14.7 to 272 ± 19.4 at 75% and 100% WFPS, respectively) during 30 d. N2O/NO ratios were always smaller than 1 at 75% WFPS, ranging from 0.03 to 0.70, while always larger than 1 at 100% WFPS, ranging from 40.3 to 94.5, suggesting that the N2O and NO were emitted mainly from nitrification at 75% WFPS and denitrification at 100% WFPS. Thus nitrification and denitrification in the soil was also limited by P. We suggest soil microbial activities and the emissions of CO2, N2O, and NO in tropical forest might be limited by P availability, and P shortage in tropics might be suppressing the emissions of these unwelcomed gases.