Surface soil organic carbon pools, mineralization and CO₂ efflux rates under different land-use types in Central Panama

The global carbon cycle is being perturbed by changes in land-use, especially in the tropics. This chapter compares surface soil organic carbon stocks, carbon mineralization rates and soil CO₂ efflux between an undisturbed forest and a clearing at Barro Colorado Island and between a pasture and plantation at Sardinilla, Central Panama. Our results on C cycling at two study sites with contrasting parent material and soil type were compared with other studies throughout the moist tropics. Differences in soil carbon stocks in the topsoil (0–5 cm) of the clearing (15 Mg C ha⁻¹) and the undisturbed forest site (22 Mg C ha⁻¹) were statistically not significant. Our inventory revealed that the highest carbon stock (29 Mg C ha⁻¹) was found under the native tree plantation, although at least part of this high value is site-related. Thus, no carbon change could be detected two years after the conversion of the site from a pasture into a native tree plantation. Soil CO₂ efflux rates at the pasture site (8 µmol CO₂ m⁻² s⁻¹) were significantly higher than in forest, clearing and plantation (5–6 µmol CO₂ m⁻² s⁻¹). Large CO₂ flux rates in the pasture might be explained by high belowground biomass production which leads to high root respiration rates. Our incubation experiment showed that pasture and clearing soil had a higher proportion of active pool carbon than plantation and forest. Higher amounts of active pool C indicate the existence of carbon readily mineralizable by microbes. Our results demonstrate that the active pool C is a good predictor of soil respiration. Thus, active soil organic carbon is a sensitive indicator for changes in soil organic carbon following land use change.