Ideas and perspectives: patterns of soil CO2, CH4, and N2O fluxes along an altitudinal gradient – a pilot study from an Ecuadorian neotropical montane forest

Abstract

Abstract. Tropical forest soils are an important source and sink of greenhouse gases\n(GHGs), with tropical montane forests, in particular, having been poorly studied. The\nunderstanding of this ecosystem function is of vital importance for future\nclimate change research. In this study, we explored soil fluxes\nof carbon dioxide (CO 2 ), methane (CH 4 ), and nitrous oxide\n(N 2 O) in four tropical forest sites located on the western flanks of\nthe Andes in northern Ecuador. The measurements were carried out during the\ndry season from August to September 2018 and along an altitudinal gradient\nfrom 400 to 3010\u2009m\u2009a.s.l. (above sea level). During this short-term campaign, our measurements\nshowed (1)\xa0an unusual but marked increase in CO 2 emissions at high\naltitude, possibly linked to changes in soil pH and/or root biomass, (2)\xa0a\nconsistent atmospheric CH 4 sink over all altitudes with high temporal\nand spatial variability, and (3)\xa0a transition from a net N 2 O source to\nsink along the altitudinal gradient. Our results provide arguments and\ninsights for future and more detailed studies on tropical montane forests.\nFurthermore, they stress the relevance of using altitudinal transects as a\nbiogeochemical open-air laboratory with a steep in situ environmental gradient\nover a limited spatial distance. Although short-term studies of temporal\nvariations can improve our understanding of the mechanisms behind the\nproduction and consumption of soil GHGs, the inclusion of more rigorous\nsampling for forest management events, forest rotation cycles, soil type,\nhydrological conditions and drainage status, ground vegetation composition\nand cover, soil microclimate, and temporal (seasonality) and spatial\n(topographic positions) variability is needed in order to obtain more\nreliable estimates of the CO 2 , CH 4 , and N 2 O source/sink\nstrength of tropical montane forests.