Influence of vegetation cover and soil features on CO2, CH4 and N2O fluxes in northern Finnish Lapland

Abstract

Understanding the drivers affecting SOM decomposition, GHG emissions and feedback to climate change in subarctic fragile and highly patterned landforms is crucial nowadays. A field campaign was conducted at catchment scale in Finnish Lapland, aiming at detecting differences in GHG fluxes in a mosaic of subarctic landforms: pine, mixed, birch and open birch forest, alpine tundra, alpine palsa, non-mire wetland, palsa mires and wetland mires. Soil profiles were described and analyzed for chemical and physical properties. CO2, CH4 and N2O fluxes from vegetated soil surface were measured by static chamber method.The largest amount of CO2 was emitted by birch forests>palsa mires>tundra and pine forest>wetlands and was driven by organic layer thickness in palsas and by priming effect mechanisms when environmental conditions favored the mineralization of organic matter stored in birch forest. Depth and organic matter content of humified organic layer, vegetation development and permanent flooding conditions triggered CH4 emissions, with 6-fold higher emissions from wetland than palsa mires and net uptake in the other landform types. N2O emissions in tundra and birch forests derived mainly from nitrification, sustained by oxygen and N availability. Differently, the higher C/N ratio and lower pH in pine and mixed forests caused N2O uptake in the soil.Possible feedbacks to climate change in the next few years or decades were identified: i) huge CH4 emissions in case of seasonally frozen soil or permafrost disappearance and ii) an increase of CO2 and N2O emissions in response to birch forest expansion.