Abstract
Stem CO2 efflux (E s) has been estimated from a temperature-related equation, but sap flux often affects measurements of E s, which leads to misunderstanding real stem respiration. In order to observe the relationship between E s and stem temperature and to analyze the effect of sap velocity on E s, stem temperature, E s and sap flux were measured from a subtropical Schima superba plantation in South China on three trees for consecutive 3 days in July and October 2009. Stem temperature, E s and sap velocity were significantly higher in July than in October. Stem temperature could explain 17–41 and 54–75% variations of E s in July and October, respectively. A negative relationship between E s and stem temperature was found during 1800–2300 hours in July. The daytime E s was 9.2, 4.3 and 2.4% higher than the predicted for three trees in July, and this occurred only on Tree 1 in October. Sap velocity was positively correlated with E s for three trees in July, and the increase of E s with the increase of sap velocity was only observed on Tree 1 in October. These results demonstrated that the occurrence of sap flux could account for the increase of daytime E s, and the effect of sap velocity on E s varied with the seasons from the S. superba stem.
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