Trees as net sinks for nitrous oxide (N2O) and methane (CH4) in tropical rain forest on La Reunion island

0518577 - ÚVGZ 2020 eng A - Abstract
Macháčová, Kateřina - Borák, Libor - Agyei, Thomas
Trees as net sinks for nitrous oxide (N2O) and methane (CH4) in tropical rain forest on La Reunion island.
Geophysical Research Abstracts. Vol. 21. European geoscience union, 2019.
[EGU General Assembly Conference 2019. 07.04.2019-12.04.2019, Vídeň]
R&D Projects: GA ČR(CZ) GJ17-18112Y
Research Infrastructure: CzeCOS III - 90123
Institutional support: RVO:86652079
Keywords : n2o * ch4 * greenhouse gas * tropical rain forest * lava flow * volcanic * tree stem * soil * ftir * exchange * flux * uptake * sink
OECD category: Forestry

Tropical forests are considered a natural sink for methane (CH4) and a natural source of nitrous oxide (N2O), both important greenhouse gases (GHGs). Forest ecosystem exchange of CH4 and N2O has been mostly estimated based on GHGs exchange at the soil–atmosphere interface only. However, trees of various climatic zones are known to emit CH4 and N2O into the atmosphere. Recent research revealed tropical wetland trees as considerable sources of CH4. Nevertheless, there is little known about CH4 and N2O exchange capacity of tropical trees growing under „non-flooded“ conditions. We determined CH4 and N2O exchange of soil and stems of mostly endemic tree species in a tropical lowland rain forest on lava flow of La Reunion Island in the South Western Indian Ocean. We investigated (1) whether the tree stems exchange CH4 and N2O with the atmosphere, (2) how the tree fluxes contribute to the forest GHGs exchange, and (3) whether the tropical rain forest is a source or sink for CH4 and N2O at the beginning of the rain season. The experiment was performed in Mare-Longue Nature Reserve in October-November 2018. The studied forest is situated on 400 years old basaltic lava flow covered with irregular and thin soil layer. Fluxes of CH4 and N2O in mature tree stems and soil were measured using non-steady-state chamber systems and a portable FTIR gas analyser. The stems of studied tree species were net sinks for both CH4 (-15.1 ± 2.2 µg CH4 m-2 stem area h-1) and N2O (-3.1 ± 0.8 µg N2O m-2 h-1). Such uptake potential for CH4 and N2O by tropical tree species represents a novel and unique finding which is in contrast to current limited studies presenting tropical trees as CH4 emitters. The soil was a significant net CH4 sink (-79.5 ± 11.5 µg CH4 m-2 soil area h-1). The soil N2O fluxes showed a high spatial heterogeneity including both N2O emissions and uptake (net flux -0.18 ± 1.61 µg N2O m-2 h-1). Concluded, the studied tropical tree species were net sinks for CH4 and N2O.
Permanent Link: http://hdl.handle.net/11104/0303695