Meteorological and functional response partitioning to explain interannual variability of CO2 exchange at an Irish Atlantic blanket bog

This study aims to develop models to describe CO2fluxes in terms of environmental and meteorolog-ical variables and their variation over an Atlantic blanket bog in Glencar, southwest Ireland. Ten fullyears (September 2002–August 2012) of data were included in the assessment of CO2flux and micro-meteorological data. Models were based on non-gapfilled growing season data, using complete calendaryears for annual models, and the entire time-series for weekly models, whilst taking interaction betweenvariables into account for increased model accuracy. This was to determine which environmental vari-ables were most influential in directly controlling CO2exchange on a long- and short-term basis. Ahomogeneity of slopes (HOS) model was used to determine if there was any ecosystem response to indi-rect effects (functional response) of environmental or meteorological interannual variation. This modeluses multiple regression analysis to determine if the ecosystem response can be better predicted as alinear function of the variables using a single slope model for all years, or a separate slopes model foreach year. The separate slopes model gave a different (and improved) outcome for both daytime andnight-time CO2fluxes, and so functional responses were deemed to have occurred. The contribution tovariation of day and night-time net ecosystem exchange (NEEdayand NEEnightrespectively) was then sep-arated into four components: indirect functional responses, direct interannual meteorological variability,direct week to week meteorological variability, and random error, which identified 13.8%, 36.6%, 28.2%and 21.4% respectively of the variation in NEEday, as well as 23.4%, 24.4%, 22.2% and 30% respectively ofthe variation in NEEnight. Water table level (WTL) had the greatest influence upon functional variationof NEE at the Glencar blanket peatland, and comparisons of modelled NEEdaywith leaf area index (LAI)measurements verified the estimate of functional contribution using the separate slopes model. The sig-nificance of interannual variation (IAV) and functional responses on NEE at Glencar suggests that it is aresilient ecosystem which might be able to adapt to environmental or climatic changes, although givencurrent climate change predictions, it is likely to have a reduced carbon dioxide sink status in the future