Emission of CO₂ from tropical riparian forest soil is controlled by soil temperature, soil water content and depth to water table

Tropical forests play a key role in the global carbon cycle. However, little is known about carbon cycling in the substantial portion of tropical forests that are low-lying, with shallow and fluctuating water tables. This study aimed to determine what factors control emissions of CO₂ from soil in a riparian rainforest in Queensland, Australia. Emissions were measured over the course of 1 year, using static chambers. Emission rates were significantly related to soil temperature (0–0.1 m depth), soil water content (0–0.12 m depth) and depth to water table. The most efficient linear model of emissions as a function of measured parameters, which also included soil pH (0–0.1 m depth), had r² = 0.355. CO₂ emissions were highest (5.2–7.5 μmol m⁻² s⁻¹) at moderate soil temperature (24-28°C), water table depth (0.2–1.5 m) and soil water-filled porosity (0.25–0.79). They were lowest (<0.5 μmol m⁻² s⁻¹) at low soil temperature (