Knowing the impact of warming on soil organic matter (SOM) is crucial for estimating future soil CO2 effluxes. Whether different soil fractions and carbon (C) complexes have different temperature sensitivities is still a matter of debate. To measure the temperature sensitivity of tropical forest soils with ongoing decomposition, we collected soil cores from three sites along an altitudinal gradient with a difference in mean annual soil temperature of about 8 °C. The intact soil cores were incubated at 5, 15, 25 and 35 °C, respiration rates quantified, and the soil cores reinstalled at the collection sites. This procedure was repeated after six months and after one year to quantify the impact of ongoing decomposition on the temperature sensitivity (Q10) of respiration. Changes in chemical composition were determined by infra-red spectroscopy, and C distribution was partitioned by fractionation into fine roots, particulate organic matter (POM) and mineral-associated organic matter (MOM) from