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

Abstract

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 μg C g soil^-1 in the primary and secondary forests respectively) and N (109–143 and 106–117 μg 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 μg 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.