Seasonal CO2 exchange in a coastal heathland in western Norway – effects of drought and bryophyte removal

Abstract

Climate models project that Western Norway will experience warmer temperatures with more frequent and extreme drought periods during the 21st century. Such climatic changes are likely to alter many vital ecosystem processes, such as plant CO2 sequestration and soil carbon storage, which ultimately may lead to a shift in ecosystem function. In Western Norway, coastal heathlands contain relatively large amounts of soil carbon due to their cold and wet climate, resulting in low microbial decomposition rates relative to plant productivity. In a warmer and drier climate, the carbon balance of coastal heathlands could be particularly vulnerable to changes, potentially shifting these ecosystems from being net sinks of atmospheric carbon to net sources. Here, we measured seasonal variation in ecosystem CO2 fluxes from above- and belowground sources in a coastal heathland site near Lygra/Bergen, Norhordland. To investigate how extreme drought events may affect future carbon dynamics in this ecosystem, we constructed an experimental drought gradient, manipulating rainfall inputs by 0, 50, and 90% using rainout shelters. Bryophytes constitute a major functional group in coastal heathlands and bryophyte water holding capacity and soil insulation properties could potentially mediate effects of drought stress on ecosystem carbon balance. To investigate the role of bryophytes in a drier climate, we also removed bryophyte cover in a factorial setup within our drought gradient. Results show limited response to treatment where an effect could only be detected statistically for net ecosystem exchange. Ecosystem respiration, gross ecosystem production and soil respiration showed no significance to either bryophyte removal or drought treatment. Ultimately the results from this study will be part of increased understanding of drought effects on the coastal heathlands but also to piecing apart how carbon storage in other similar ecosystems will react to projected changes