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Axial diffusion of respired CO2 confounds stem respiration estimates during the dormant season

De Roo, Linus, Bloemen, Jasper, Dupon, Yentl, Salomón, Roberto Luis, Steppe, Kathy
Annals of forest science 2019 v.76 no.2 pp. 52
Quercus, carbon dioxide, forest stands, growth chambers, photosynthesis, respiratory rate, temperature, tissues, transpiration, trees
KEY MESSAGE : Efflux-based estimates of stem respiration in oak trees during the dormant season were biased by axial diffusion of locally respired CO ₂ . Light-induced axial CO ₂ diffusion along the stem due to woody tissue photosynthesis may lead to equivocal estimates of stem respiratory coefficients during the dormant season, which are generally used to estimate maintenance respiration throughout the year. CONTEXT: Stem CO₂ efflux (EA) does not reflect respiratory rates of underlying tissues. Recent research has focused on the significance of CO₂ transport via the transpiration stream. However, no studies have yet addressed the potential role of light-induced axial CO₂ diffusion on EA during the dormant season when there is no transpiration. AIMS: This study investigated to which extent woody tissue photosynthesis and axial diffusion of respired CO₂ affect EA during the dormant season. METHODS: EA was measured in a stem cuvette on dormant oak trees in a growth chamber at constant temperature. Different rates of axial CO₂ diffusion were induced by woody tissue photosynthesis by means of illuminating stem sections at varying distances from the stem cuvette, while light was excluded from the remainder of the tree. RESULTS: Axial diffusion of respired CO₂ led to reductions in EA of up to 22% when the stem section closest to the cuvette was exposed to light. CONCLUSION: Dormant-season efflux-based estimates of stem respiration might be biased by axial diffusion of respired CO₂, particularly in open forest stands with sufficient light penetration. Consequently, this may lead to ambiguous estimates of dormant season EA coefficients (Q₁₀ and EA_₀) generally used to estimate maintenance respiration throughout the year.