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

摘要

Vertical profile measurements of stem CO2 efflux (E-stem) 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 E-stem at 0.75, 1.3, 3.5, 7 and 14 m tree trunk height. The highest mean E-stem 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 E-stem was higher at night and started to decrease with the ascending xylem sap and elevating air temperature in the early morning. E-stem 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.