<p>Tropical forest soils are an important contributor to the global greenhouse (GHG) budget and understanding this ecosystem function is of vital importance for future global change and climate research. In this study, we quantified soil fluxes of carbon dioxide (CO<sub>2</sub>), methane (CH<sub>4</sub>) and nitrous oxide (N<sub>2</sub>O) of four tropical forest sites located along an altitudinal gradient from 400 to 3010 m a.s.l. on the western flanks of the Andes in northern Ecuador. We assessed the physicochemical soil properties influencing these fluxes during the dry season, as well as the bulk isotopic signature of N<sub>2</sub>O. The CO<sub>2</sub> fluxes ranged between 55.3±12.1 and 137.6 ± 32.8 mg C m<sup>−2</sup> h<sup>−1</sup>, with the highest and lowest emissions at the highest strata, at 3010 and 2200 m a.s.l., respectively. CH<sub>4</sub> fluxes at all sites exhibited a net consumption of atmospheric CH<sub>4</sub> and ranged between −74.4 ± 25.0 µg C m<sup>−2</sup> h<sup>−1</sup> at 2200 m a.s.l. to −46.7 ± 14.7 µg C m<sup>−2</sup> h<sup>−1</sup> at 3010 m a.s.l. Net fluxes of N<sub>2</sub>O ranged between −5.1 ± 1.9 and 13.2 ± 31.3 µg N m<sup>−2</sup> h<sup>−1</sup>, with a marked net sink at 2200 and 3010 m a.s.l., whereas a net source at 400 m. pH<sub>water</sub> and nitrate (NO<sub>3</sub><sup>−</sup>) content at 5 cm depth were able to explain 83 % of the observed temporal (daily measurements) and spatial (four forest sites) variability of the CO<sub>2</sub> fluxes; indicating that an increase in pH<sub>water</sub> and NO<sub>3</sub><sup>−</sup> contents lead to an increase in CO<sub>2</sub> emissions. For CH<sub>4</sub> fluxes, it was not possible to obtain a statistically significant model to identify the physicochemical soil drivers responsible for the CH<sub>4</sub> consumption. For N<sub>2</sub>O, bulk density and pH<sub>water</sub> at 5 cm depth were negatively correlated to the N<sub>2</sub>O fluxes, but able to explain only 36 % of the temporal and spatial variability. In addition, the bulk isotope N<sub>2</sub>O data confirmed that N<sub>2</sub>O reduction was at the basis of the observed net soil sink at higher altitudes. Finally, the soil GHG budget showed that all studied soils were net sources of GHG's. CO<sub>2</sub> emissions represented the largest component of the total soil GHG budget, CH<sub>4</sub> consumption was quite consistent along the elevation gradient, whereas N<sub>2</sub>O was highly variable, and the transition from sources to net sinks at higher altitudes represented the biggest change in the net GHG balance. Overall, for non-CO<sub>2</sub> GHGs, we noticed a transition from a net source to a net GHG sink along altitude.</p>