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.

• Klíčová slova
• basaltic lava flows, cryptogams, methane flux, nitrous oxide flux, soil, tree stem, tropical lowland rain forest, uptake,
• MeSH
• deštný prales MeSH
• lesy MeSH
• methan MeSH
• oxid dusný * MeSH
• oxid uhličitý MeSH
• půda MeSH
• stromy * MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Geografické názvy
• Réunion MeSH
• Názvy látek
• methan MeSH
• oxid dusný * MeSH
• oxid uhličitý MeSH
• půda MeSH

The role of trees in the nitrous oxide (N2O) balance of boreal forests has been neglected despite evidence suggesting their substantial contribution. We measured seasonal changes in N2O fluxes from soil and stems of boreal trees in Finland, showing clear seasonality in stem N2O flux following tree physiological activity, particularly processes of CO2 uptake and release. Stem N2O emissions peak during the vegetation season, decrease rapidly in October, and remain low but significant to the annual totals during winter dormancy. Trees growing on dry soils even turn to consumption of N2O from the atmosphere during dormancy, thereby reducing their overall N2O emissions. At an annual scale, pine, spruce and birch are net N2O sources, with spruce being the strongest emitter. Boreal trees thus markedly contribute to the seasonal dynamics of ecosystem N2O exchange, and their species-specific contribution should be included into forest emission inventories.

• MeSH
• atmosféra chemie   MeSH
• ekosystém * MeSH
• methan metabolismus   MeSH
• oxid dusný metabolismus   MeSH
• oxid uhličitý metabolismus   MeSH
• půda chemie   MeSH
• roční období * MeSH
• stonky rostlin metabolismus   MeSH
• stromy fyziologie   MeSH
• tajga * MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Geografické názvy
• Finsko MeSH
• Názvy látek
• methan MeSH
• oxid dusný MeSH
• oxid uhličitý MeSH
• půda MeSH

Naturally produced by microbial processes in soil, nitrous oxide (N2O) is an important greenhouse gas contributing to climate change. Accordingly, there is a need to accurately quantify the capability of forest ecosystems to exchange N2O with the atmosphere. While N2O emissions from soils have been well studied, trees have so far been overlooked in N2O inventories. Here, we show that stems of mature beech trees (Fagus sylvatica) may act as a substantial sink of N2O from the atmosphere under conditions of soils consuming N2O. Consistent consumption of N2O by all stems investigated (ranging between -2.4 and -3.8 µg m-2 h-1) is a novel finding in contrast to current studies presenting trees as N2O emitters. To understand these fluxes, N2O exchange of photoautotrophic organisms associated with beech bark (lichens, mosses and algae) was quantified under laboratory conditions. All these organisms were net N2O sinks at full rehydration and temperature of 25 °C. The consumption rates were comparable to stem consumption rates measured under field conditions. Cryptogamic stem covers could be a relevant sink of N2O in European beech forests.

• MeSH
• autotrofní procesy MeSH
• buk (rod) metabolismus   MeSH
• oxid dusný metabolismus   MeSH
• oxid uhličitý metabolismus   MeSH
• půda MeSH
• půdní mikrobiologie * MeSH
• skleníkové plyny metabolismus   MeSH
• stromy metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Geografické názvy
• Evropa MeSH
• Názvy látek
• oxid dusný MeSH
• oxid uhličitý MeSH
• půda MeSH
• skleníkové plyny MeSH