Combining soil and tree‐stem flux measurements and soil gas profiles to understand CH4 pathways in Fagus sylvatica forests. Issue 1 (14th February 2017) - Maier, Martin
Abstract: Quantifying and understanding fluxes of methane (CH4 ) and carbon dioxide (CO2 ) in natural soil–plant–atmosphere systems are crucial to predict global climate change. Wetland herbaceous species or tree species at waterlogged sites are known to emit large amounts of CH4 . Upland forest soils are regarded as CH4 sinks and tree species like upland beech are not known to significantly emit CH4 . Yet, data are scarce and this assumption needs to be tested. We combined measurements of soil–atmosphere and stem–atmosphere fluxes of CO2 and CH4, and soil gas profiles to assess the contribution of the different ecosystem compartments at two upland beech forest sites in Central Europe in a case study. Soil was a net CH4 sink at both sites, though emissions were detected consistently from beech stems at one site. Although stem emissions from beech stems were high compared to known fluxes from other upland tree species, they were substantially lower compared to the strong CH4 sink of the soil. Yet, we observed extraordinarily large CH4 emissions from one beech tree that was 140% of the CH4 sink of the soil. The soil gas profile at this tree indicated CH4 production at a soil depth > 0.3 m, despite the net uptake of CH4 consistently observed at the soil surface. Field soil assessment showed strong redoximorphic color patterns in the adjacent soil and supports this evaluation. We hypothesize that there is a transport link between the soil and stem via the root system representing a preferential transport mechanism for CH4 despite the fact that beech roots usually do not bear aerenchyma. The high mobility of gases requires a holistic view on the soil–plant–atmosphere system. Therefore, we recommend including field soil assessment and soil gas profiles measurements when investigating soil–atmosphere and stem–atmosphere fluxes to better understand the sources of gases and their transport mechanisms.