TOTAL AND HETEROTROPHIC RESPIRATION IN A TROPICAL LOWLAND FOREST, PAHANG, PENINSULAR MALAYSIA

Abstract

Soil respiration is the second largest flux in the carbon (C) cycle, contributing close to 40% of annual atmospheric input. It was hypothesised that partitioning total soil respiration (Rs) and heterotrophic respiration (Rh) during wet and dry seasons will improve understanding on the effects of environmental variables, organic detritus input and decomposition on soil respiration trends in the tropics. A trenching experiment was conducted to quantify Rs and Rh over a period of 30 months, and climatic variables, soil bulk density, water and air filled pore space, fine root biomass, decomposition ratio and litterfall coinciding with soil respiration measurements were recorded using chamber methods. The Rs was significantly different across time where elevated levels (518.60–784.08 mg CO2 m^-2 h^-1) were observed during wet season but Rh did not differ. The Rh contributed a larger portion (73–90%) to Rs compared to autotrophic respiration (Ra). Soil temperatures and relative humidity were significantly different in Rs and Rh plots. Wet season also significantly elevated fine root biomass (222.93–237.96 g m^-2), fine root decomposition ratio (0.49) and litterfall (304.64 g m^-2) that contributed to Rs. It was concluded that climatic and primary productivity variables affect Rs and Rh in a tropical forest ecosystem. However, long term temporal and spatial observations are necessary to improve the understanding of forecast soil CO₂ sequestration dynamics in a changing environment.