Comparison of COsub2/sub and Osub2/sub fluxes demonstrate retention of respired COsub2/sub in tree stems from a range of tree species

摘要

The ratio of COsub2/sub efflux to Osub2/sub 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/sub uptake provides a measure of in situ stem respiration (due to the low solubility of Osub2/sub ), the overall mean indicates that on average 41?% of COsub2/sub 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 COsub2/sub in the xylem sap and transport away from the site of respiration cannot explain the low ARQ values. We suggest refixation of respired COsub2/sub in biosynthesis reactions as possible mechanism for low ARQ values.