Discrimination in Tree Stems O2 Uptake and the Dole Effect

Boaz Hilman, Alon Angert

Research output: Contribution to journalArticlepeer-review


The difference in δ18O between the atmospheric O2 and seawater is named the Dole effect (DE). Interpretation of past DE variations, a proxy for monsoonal intensity, is based on current understanding of global O2 fluxes. One such O2 flux that was poorly studied is the discrimination in O2 uptake by tree stems (Dstem). Stems differ from leaves in their lower gas permeability, which reduces the internal [O2] and poses diffusion limitations to local respiration. Diffusion limitations are expected to lower the effective discrimination below enzymatic values (17–30‰). Given fixed permeability, the lowest internal [O2] and thus the greatest diffusional effect are expected in high O2 influx. Dstem and O2 influx values were obtained by measurements of stem-chamber air and a numerical model that resolves the gas exchange in the chamber. According to 101 results of temperate, Mediterranean, and tropical trees, the global Dstem is 19.2‰. Assuming basal O2 diffusion limitation in the stems, the results indicate involvement of the alternative oxidase respiration, with enzymatic discrimination factor of above 20‰. Small seasonal variations in Dstem were uncoupled from the O2 influx rates that tracked the temperature changes. This indicates a possible adjustment between the aeration capability of the stems and O2 uptake rate, which helps to maintain sufficient O2 supply. The mean Dstem value agrees with the assumed discrimination for leaf respiration, thus supporting current DE understanding. The small Dstem seasonal variations give an indication that climate variations on millennial and interglacial scales did not have a strong effect on Dstem values.

Original languageAmerican English
Pages (from-to)1208-1225
Number of pages18
JournalGlobal Biogeochemical Cycles
Issue number8
StatePublished - Aug 2018


  • Dole effect
  • alternative respiration
  • diffusion
  • oxygen isotopes
  • oxygen uptake
  • stem respiration

All Science Journal Classification (ASJC) codes

  • General Environmental Science
  • Global and Planetary Change
  • Environmental Chemistry
  • Atmospheric Science


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