• Keywords
• FTIR, gas chromatograph, greenhouse gas, interference, methane (CH4) flux, nitrous oxide flux, tree stem gas exchange, volatile organic compound (VOCs),
• MeSH
• Rainforest MeSH
• Methane MeSH
• Nitrous Oxide * MeSH
• Carbon Dioxide MeSH
• Spectroscopy, Fourier Transform Infrared MeSH
• Trees MeSH
• Volatile Organic Compounds * MeSH
• Publication type
• Letter MeSH
• Comment MeSH
• Research Support, Non-U.S. Gov't MeSH
• Geographicals
• Reunion MeSH
• Names of Substances
• Methane MeSH
• Nitrous Oxide * MeSH
• Carbon Dioxide MeSH
• Volatile Organic Compounds * MeSH

Trees are known to emit methane (CH4 ) and nitrous oxide (N2 O), with tropical wetland trees being considerable CH4 sources. Little is known about CH4 and especially N2 O exchange of trees growing in tropical rain forests under nonflooded conditions. We determined CH4 and N2 O exchange of stems of six dominant tree species, cryptogamic stem covers, soils and volcanic surfaces at the start of the rainy season in a 400-yr-old tropical lowland rain forest situated on a basaltic lava flow (Réunion Island). We aimed to understand the unknown role in greenhouse gas fluxes of these atypical tropical rain forests on basaltic lava flows. The stems studied were net sinks for atmospheric CH4 and N2 O, as were cryptogams, which seemed to be co-responsible for the stem uptake. In contrast with more commonly studied rain forests, the soil and previously unexplored volcanic surfaces consumed CH4 . Their N2 O fluxes were negligible. Greenhouse gas uptake potential by trees and cryptogams constitutes a novel and unique finding, thus showing that plants can serve not only as emitters, but also as consumers of CH4 and N2 O. The volcanic tropical lowland rain forest appears to be an important CH4 sink, as well as a possible N2 O sink.

• Keywords
• basaltic lava flows, cryptogams, methane flux, nitrous oxide flux, soil, tree stem, tropical lowland rain forest, uptake,
• MeSH
• Rainforest MeSH
• Forests MeSH
• Methane MeSH
• Nitrous Oxide * MeSH
• Carbon Dioxide MeSH
• Soil MeSH
• Trees * MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Geographicals
• Reunion MeSH
• Names of Substances
• Methane MeSH
• Nitrous Oxide * MeSH
• Carbon Dioxide MeSH
• Soil MeSH

One of the characteristics of global climate change is the increase in extreme climate events, e.g., droughts and floods. Forest adaptation strategies to extreme climate events are the key to predict ecosystem responses to global change. Severe floods alter the hydrological regime of an ecosystem which influences biochemical processes that control greenhouse gas fluxes. We conducted a flooding experiment in a mature grey alder (Alnus incana (L.) Moench) forest to understand flux dynamics in the soil-tree-atmosphere continuum related to ecosystem N2O and CH4 turn-over. The gas exchange was determined at adjacent soil-tree-pairs: stem fluxes were measured in vertical profiles using manual static chambers and gas chromatography; soil fluxes were measured with automated chambers connected to a gas analyser. The tree stems and soil surface were net sources of N2O and CH4 during the flooding. Contrary to N2O, the increase in CH4 fluxes delayed in response to flooding. Stem N2O fluxes were lower although stem CH4 emissions were significantly higher than from soil after the flooding. Stem fluxes decreased with stem height. Our flooding experiment indicated soil water and nitrogen content as the main controlling factors of stem and soil N2O fluxes. The stems contributed up to 88% of CH4 emissions to the stem-soil continuum during the investigated period but soil N2O fluxes dominated (up to 16 times the stem fluxes) during all periods. Conclusively, stem fluxes of CH4 and N2O are essential elements in forest carbon and nitrogen cycles and must be included in relevant models.

• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH