Pulse labelling of deep soil layers in forest with 13CH4: testing a new method for tracing methane in the upper horizons, understorey vegetation and tree stems using laserbased spectrometry

Methane is one the main greenhouse gases and upland forests are one of its main biological sinks. However, vegetation could reduce this sink by allowing a direct path for the methane produced in deep soils to escape into the atmosphere. By tracing emissions with 13CH4, we show for the first time that methane emitted by trees in upland forest could have a deep soil origin even though the soil is an overall methane sink. However, we found that the trees and understorey vegetation at our site had only a small impact on the methane budget.