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Drought is arguably the most important regulator of inter-annual variation in net ecosystem CO exchange (NEE) in peatlands. This study investigates effects of drought periods on NEE and its components, gross primary production (GPP) and ecosystem respiration (R), on the basis of eddy covariance measurements of land-atmosphere exchange of CO in 2006-2009 in a south Swedish nutrient-poor peatland. Two drought periods had dissimilar effects on the CO exchange. In 2006, there was a short but severe drought period in the middle of the growing season resulting in increased R rates, but no detectable effect on GPP rates. In contrast, in 2008 the drought period began early in the growing season and lasted for a longer period of time, resulting in reduced GPP rates, suggesting that GPP is most sensitive to drought during leaf out and canopy development compared with the full canopy stage. Both in 2006 and in 2008 the peatland acted as an annual source of atmospheric CO, while in 2007 and 2009, when there were no drought periods, the peatland constituted a CO sink. It was concluded that the timing, severity and duration of drought periods regulate the effects on peatland GPP, R and NEE.
Lund et al. (Tue,) studied this question.