Spatial and seasonal variations in stem CO2 efflux of Pinus canariensis at their upper distribution limit

We calculated stem CO2 efflux (E (S)) of Pinus canariensis at a timberline site in Tenerife, Canary Islands, from March 7, 2008 and February 9, 2009. E (S) varied markedly throughout the year. Although E (S) generally followed the seasonal trends in temperature, we observed seasonal adjustment of E (S) in both E (S) normalized to temperature (E (S10)) and the temperature sensitivity (Q (10)) resulting in lower E (S10) values during the warm and dry season as compared during the cold and wet season; the latter corresponding with the period of stem growth. The Q (10) by contrast, was higher during the warm and dry summer than during the cold and wet season, an observation suggesting that climate extremes such as summer drought in the Mediterranean may override the observation that Q (10) declines with increasing temperature. As concurrent measurements estimating the potential impact of sap flow on E (S) revealed no interaction in P. canariensis, the Q (10) values were used along with E (S10) and stem temperature records to predict annual total E (S) and for partitioning total E (S) into its maintenance (E (m)) and a growth (E (g)) component.