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.