Inundation strongly stimulates nitrous oxide emissions from stems of the upland tree Fagus sylvatica and the riparian tree Alnus glutinosa

摘要

Nitrous oxide (N2O) and methane (CH4) can be emitted from surfaces of riparian plants. Data on the emission of these greenhouse gases by upland trees are scarce. We quantified CH4 and N2O emissions from stems of Fagus sylvatica, an upland tree, and Alnus glutinosa, a riparian tree. The gas fluxes were investigated in mesocosms under non-flooded control conditions and during a flooding period using static chamber systems and gas chromatographic analyses. Despite differences in the presence of an aerenchyma system, both tree species emitted N2O and CH4 from the stems. Flooding caused a dramatic transient increase of N2O stem emissions by factors of 740 (A. glutinosa) and even 14,230 (F. sylvatica). Stem emissions of CH4 were low and even deposition was determined (F. sylvatica controls). The results suggest that CH4 was transported mainly through the aerenchyma, whereas N2O transport occurred in the xylem sap. For the first time it has been demonstrated that upland trees such as F. sylvatica clearly significantly emit N2O from their stems despite lacking an aerenchyma. If this result is confirmed in adult trees, upland forests may constitute a new and significant source of atmospheric N2O.