Nitrous oxide emissions from three ecosystems in tropical peatland of Sarawak, Malaysia

Nitrous oxide (N2O) emissions were measured monthly over 1 year in three ecosystems on tropical peatland of Sarawak, Malaysia, using a closed-chamber technique. The three ecosystems investigated were mixed peat swamp forest, sago (Metroxylon sagu) and oil palm (Elaeis guineensis) plantations. The highest annual N2O emissions were observed in the sago ecosystem with a production rate of 3.3 kg N ha(-1) year(-1), followed by the oil palm ecosystem at 1.2 kg N ha(-1) year(-1) and the forest ecosystem at 0.7 kg N ha(-1) year(-1). The N2O emissions ranged from -3.4 to 19.7 mu g N m(-2) h(-1) for the forest ecosystem, from 1.0 to 176.3 mu g N m(-2) h(-1) for the sago ecosystem and from 0.9 to 58.4 mu g N m(-2) h(-1) for the oil palm ecosystem. Multiple regression analysis showed that N2O production in each ecosystem was regulated by different variables. The key factors influencing N2O emissions in the forest ecosystem were the water table and the NH4+ concentration at 25-50 cm, soil temperature at 5 cm and nitrate concentration at 0-25 cm in the sago ecosystem, and water-filled pore space, soil temperature at 5 cm and NH4+ concentrations at 0-25 cm in the oil palm ecosystem. R-2 values for the above regression equations were 0.57, 0.63 and 0.48 for forest, sago and oil palm, respectively. The results suggest that the conversion of tropical peat swamp forest to agricultural crops, which causes substantial changes to the environment and soil properties, will significantly affect the exchange of N2O between the tropical peatland and the atmosphere. Thus, the estimation of net N2O production from tropical peatland for the global N2O budget should take into consideration ecosystem type.