Comparison of CO2 and O2 fluxes demonstrate retention of respired CO2 in tree stems from a range of tree species

[摘要] The ratio of CO₂ efflux to O₂ influx (ARQ, apparent respiratory quotient) in tree stems is expected to be 1.0 for carbohydrates, the main substrate supporting stem respiration. In previous studies of stem fluxes, ARQ values below 1.0 were observed and hypothesized to indicate retention of respired carbon within the stem. Here, we demonstrate that stem ARQ 2 uptake provides a measure of in situ stem respiration (due to the low solubility of O₂ ), the overall mean indicates that on average 41 % of CO₂ respired in stems is not emitted from the local stem surface. The instantaneous ARQ did not vary with sap flow. ARQ values of incubated stem cores were similar to those measured in stem chambers on intact trees. We therefore conclude that dissolution of CO₂ in the xylem sap and transport away from the site of respiration cannot explain the low ARQ values. We suggest refixation of respired CO₂ in biosynthesis reactions as possible mechanism for low ARQ values.

[学科分类] 地球化学与岩石