RainForest-GHG aims to quantify ecosystem sinks and emissions of three major greenhouse gases (GHGs),
i.e. carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O), in a tropical rainforest, and examine the
contributions of the soil and the woody tissues to the ecosystem-scale GHG fluxes. RainForest-GHG further
aims to determine the main environmental drivers responsible for the temporal and spatial variations of
these GHG fluxes.

H2020-MSCA-IF-2017, RainForest-GHG Project. Grant Agreement 796438

https://cordis.europa.eu/project/rcn/215445

CO₂, CH₄ and N₂O are major GHGs whose increasing concentrations are responsible for global warming. CO₂ is the principal GHG by virtue of its high atmospheric concentration, but CH₄ and N₂O, respectively, have a 23 and 296 times higher greenhouse warming potential than CO₂, per molecule on a 100-year basis. Despite significant advances in quantifying these GHGs, simultaneously measuring fluxes and budgets of CO₂, CH₄ and N₂O over ecosystems has rarely been done, and this holds especially for tropical rainforests.
Tropical forest ecosystems cover 7 - 10% of global land area, contain 40 - 50% of all carbon (C) in terrestrial vegetation and annually cycle approximately six times as much C via photosynthesis and respiration as humans emit through the use of fossil fuels. Therefore, tropical forests are a critical component of the global C cycle. Soils are main contributors to the ecosystem GHG fluxes in the tropics. In fact, tropical forest soils are the largest natural source of soil CO₂ and N₂O and can be significant sinks of CH₄. In the soil, CO₂ is mainly produced by roots, mycorrhiza and decomposers. CH₄ originates from anaerobic methanogenesis in water-saturated soils, but is oxidized by methanotrophic bacteria in aerobic soils. N₂O originates from denitrification, anaerobic dissimilatory nitrate reduction to ammonium, and aerobic nitrification. In the tree’s woody tissues, CO₂ is produced by growth and maintenance respiration in living woody tissues, but is also transported from roots and rhizosphere via the xylem stream, whereas CH₄ and N₂O can either diffuse from the soil to the atmosphere in the aerenchyma and / or the xylem stream or be formed by microorganisms living within the trees or by physiological and photochemical processes. Through passive transport from the soil, via the xylem stream to the atmosphere, N₂O and CH₄ can bypass the soil-atmosphere exchange. In recent decades, studies on rainforest GHG fluxes have predominantly been performed on CO₂ fluxes, whereas those on CH₄ and N₂O fluxes were mostly based solely on soil fluxes. Studies on woody tissue gas exchange in tropical trees are also rare, even more so for CH₄ and N₂O. In summary, this project would be the first detailed study of the full GHG balance of a tropical rainforest, including an assessment of its soil and woody tissue component fluxes.

The available flux estimates of GHG from forest ecosystems are mostly from the layer above the canopy (eddy covariance) and locally from the forest soil. Partitioning between soil, foliage, and woody tissue fluxes, which can be achieved with chamber setups, is scarce. Still, such data are necessary to determine the contribution of each component flux to the overall ecosystem respiration - to partition the overall fluxes - and achieve a new level of understanding of GHG dynamics.

Therefore, the RainForest-GHG project will 1) simultaneously quantify CO₂, CH₄ and N₂O gas exchange from the soil, woody tissues, leaves and above-canopy of a tropical forest, 2) estimate the respective contribution of the three compartments (soil, trees and atmosphere) to the measured fluxes, and 3) identify the spatiotemporal variation in fluxes of CO₂, CH₄ and N₂O from different compartments and investigate the main environmental drivers thereof.