Soil-atmosphere exchange of nitrous oxide, methane and carbon dioxide in a gradient of elevation in the coastal Brazilian Atlantic forest

Abstract

Soils of tropical forests are important to the global budgets of greenhouse gases. The Brazilian Atlantic Forest is the second largest tropical moist forest area of South America, after the vast Amazonian domain. This study aimed to investigate the emissions of nitrous oxide (N₂O), carbon dioxide (CO₂) and methane (CH₄) fluxes along an altitudinal transect and the relation between these fluxes and other climatic, edaphic and biological variables (temperature, fine roots, litterfall, and soil moisture). Annual means of N₂O flux were 3.9 (± 0.4), 1.0 (± 0.1), and 0.9 (± 0.2) ng N cm⁻² h⁻¹ at altitudes 100, 400, and 1000 m, respectively. On an annual basis, soils consumed CH₄ at all altitudes with annual means of −1.0 (± 0.2), −1.8 (± 0.3), and −1.6 (± 0.1) mg m⁻² d⁻¹ at 100 m, 400 m and 1000 m, respectively. Estimated mean annual fluxes of CO₂ were 3.5, 3.6, and 3.4 μmol m⁻² s⁻¹ at altitudes 100, 400 and 1000 m, respectively. N₂O fluxes were significantly influenced by soil moisture and temperature. Soil-atmosphere exchange of CH₄ responded to changes in soil moisture. Carbon dioxide emissions were strongly influenced by soil temperature. While the temperature gradient observed at our sites is only an imperfect proxy for climatic warming, our results suggest that an increase in air and soil temperatures may result in increases in decomposition rates and gross inorganic nitrogen fluxes that could support consequent increases in soil N₂O and CO₂ emissions and soil CH₄ consumption.