EFFECTS OF SELECTIVE LOGGING AND APPLICATION OF PHOSPHORUS AND NITROGEN ON FLUXES OF CO2, CH4 AND N2O IN LOWLAND TROPICAL RAINFORESTS OF BORNEO

We compared fluxes of carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4) in a primary forest and a secondary forest that has experienced selective logging more than 14 years ago. Effects of phosphorus (P) and nitrogen (N) application were also reported. We observed lower CO2 fluxes in the logged forest (2.0-2.4 g carbon (C) m(-2) day(-1)) than the primary forest (2.4-3.5 g C m(-2) day(-1)). The lower fluxes were probably because root respiration and heterotrophic respiration were lower in the logged forest. Smaller amounts of microbial biomass C (840-985 and 589-641 mu g C g soil(-1) in the primary and secondary forests respectively) and N (109-143 and 106-117 mu g N g soil(-1)) in the secondary forest than the primary forest suggested that there were less substrate inputs such as leaf and root litters, soil organic matters and root exudates in the former which produced less microbial population with lower heterotrophic respiration. Application of P increased CO2 emission (from 2.0-2.7 to 2.2-3.5 g C m(-2) day(-1)) and microbial biomass N (from 106-115 to 110-143 mu g N g soil(-1)), suggesting that the belowground ecosystems of both forests were limited by availability of P as reported in other tropical forests. Fluxes of CH4 showed no differences between forests or manipulation of nutrient because of the high variability of fluxes. Logging operation and nutrient application did not influence N2O fluxes. The invariable N2O fluxes occurred because water content was low during sampling and emission of N2O was restricted by water availability, which might have masked the effects of logging or nutrient application on N2O emission.