Comparison of CO 2 and O 2 fluxes demonstrate retention of respired CO 2 in tree stems from a range of tree species

Hilman, Boaz; Muhr, Jan; Trumbore, Susan E.; Kunert, Norbert; Carbone, Mariah S.; Yuval, Päivi; Wright, S. Joseph; Moreno, Gerardo; Pérez-Priego, Oscar; Migliavacca, Mirco; Carrara, Arnaud; Grünzweig, José M.; Osem, Yagil; Weiner, Tal; Angert, Alon

The ratio of inline-formulaCO2 efflux to inline-formulaO2 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 inline-formula< 1.0 values are common across 85 tropical, temperate, and Mediterranean forest trees from nine different species. Mean ARQ values per species per site ranged from 0.39 to 0.78, with an overall mean of 0.59. Assuming that inline-formulaO2 uptake provides a measure of in situ stem respiration (due to the low solubility of inline-formulaO2), the overall mean indicates that on average 41 % of inline-formulaCO2 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 inline-formulaCO2 in the xylem sap and transport away from the site of respiration cannot explain the low ARQ values. We suggest refixation of respired inline-formulaCO2 in biosynthesis reactions as possible mechanism for low ARQ values.

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Hilman, Boaz / Muhr, Jan / Trumbore, Susan E. / et al: Comparison of CO2 and O2 fluxes demonstrate retention of respired CO2 in tree stems from a range of tree species. 2019. Copernicus Publications.

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