Tropical trees on La Réunion island qualify for substantial net sinks of nitrous oxide (N2O) and methane (CH4)

0518452 - ÚVGZ 2020 US eng A - Abstract
Macháčová, Kateřina - Agyei, Thomas - Borák, Libor - Schindler, T.
Tropical trees on La Réunion island qualify for substantial net sinks of nitrous oxide (N2O) and methane (CH4).
AGU Fall Meeting. Washington: American Geophysical Union, 2019.
[AGU Fall Meeting 2019. 09.12.2019-13.12.2019, San Francisco]
R&D Projects: GA ČR(CZ) GJ17-18112Y
Institutional support: RVO:86652079
Keywords : methane * nitrous oxide * ch4 * n2o * greenhouse gas * tropical trees * lava flow * tropical rain forest * sink * deposition * cryptogams * soil
OECD category: Forestry

Trees are known to emit important greenhouse gases (GHGs) - methane (CH4) and nitrous oxide (N2O). 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. In October-November 2018 we determined CH4 and N2O exchange of soil and stems of six dominant tree species in a tropical lowland rain forest (La Réunion island, 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. Further, we measured the GHGs exchange of widespread cryptogamic covers growing on tree bark to perceive the deposition mechanisms. The studied forest is set on a 400 years old lava flow covered with irregular and thin soil layer. Fluxes of CH4 and N2O in mature tree stems (n=24), soil (n=24), and cryptogams (n=4) were measured using non-steady-state chamber/incubation systems and a portable FTIR gas analyser. The stems of all studied tree species were net sinks for CH4 and N2O (-15.6 ± 2.0 and -3.0 ± 0.8 µg CH4/N2O m-2 stem area h-1, mean ± s.e.). Likewise, cryptogams were also net sinks of CH4 and N2O (-8.3 ± 3.0 and -1.9 ± 0.7 µg CH4/N2O m-2 stem area h-1) thus potentially contributing to CH4 and N2O consumption by tree stems. Such unique uptake aptitude by trees and cryptogams is contrary to current limited studies presenting tropical trees as CH4 emitters. Despite rain season start, the soil deposited CH4 (-83.3 ± 9.8 µg CH4 m-2 soil area h-1). The N2O fluxes were low (1.8 ± 2.5 µg N2O m-2 h-1). Concluded, the studied tree species and cryptogams consumed CH4 and N2O from the atmosphere. This tropical lowland rain forest appears to be a net sink for CH4 and to play a minor role in the global N2O exchange.
Permanent Link: http://hdl.handle.net/11104/0303588