Environmental controls on the CO sub(2) exchange in north European mires

Net CO sub(2) exchange measured under well-mixed atmospheric conditions in four different mires in Sweden and Finland were used to analyse which factors were controlling photosynthesis and respiration. The parameters of a light response function showed strong seasonal variations with similar behaviour for all mires. The half-monthly nighttime respiration rates in the central part of the growing season were about two times higher in the southernmost, warmest site, Faje, as compared to the northernmost, coldest site, Kaamanen. However, Kaamanen had high photosynthesis rates, and this in combination with the long daylight periods in the middle of the summer caused Kaamanen to have the largest net ecosystem exchange (NEE) during the summer period. Faje that showed the highest productivity had also the highest respiration and therefore, the lowest NEE during summer. Correlation between half-monthly components and different environmental variables showed the highest correlation between the components themselves. Thereafter came temperature except for Faje where water table depth (WTD) explained most of the variance both for detrended and temperature-normalized components. All sites showed dependencies between WTD and the respective components during drying up periods. Temperature sensitivity was higher for productivity than for respiration indicating that CO sub(2) uptake would increase during global warming.