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A case study on the vertical and diurnal variation of stem CO2 effluxes in an Amazonian forest tree

Kunert, Norbert
Trees 2018 v.32 no.3 pp. 913-917
Scleronema, air temperature, carbon, carbon dioxide, case studies, diurnal variation, ecosystems, forest trees, forests, global carbon budget, prediction, sap, stems, tree crown, tree trunk, tropical plants, xylem, Amazonia
KEY MESSAGE: Dial and vertical patterns of stem CO₂ efflux are highly variable in tropical trees. Thus, tree level respiratory carbon fluxes remain a defective measure within the forest carbon budget. Vertical profile measurements of stem CO₂ efflux (Eₛₜₑₘ) were conducted on a Scleronema micranthum tree growing in an old growth terra firme forest in the Central Amazon. A commonly applied portable closed dynamic chamber system was used to assess vertical and diurnal variations of Eₛₜₑₘ at 0.75, 1.3, 3.5, 7 and 14 m tree trunk height. The highest mean Eₛₜₑₘ was measured at the tree base at 0.75 m. Averaging all measurements over the entire study period, mean effluxes constantly decreased to a height of 3.5 m and increased again the further the measurements reached to the tree top. On average Eₛₜₑₘ was higher at night and started to decrease with the ascending xylem sap and elevating air temperature in the early morning. Eₛₜₑₘ did not follow any predictable pattern during the rest of the day, especially at the higher parts of the tree stem. Predicting autotrophic respiratory processes in tropical tree stems remains a challenge and is one of the unsecure estimates in the forest carbon budget in terrestrial tropical ecosystems.