A new stable isotope approach identifies the fate of ozone in plant–soil systems

Abstract

Summary• We show that the stable isotope 18 O can be used to trace ozone into different components of the plant-soil system at environmentally relevant concentrations.• We exposed plants and soils to 18 O-labelled ozone and used isotopic enrichment in plant dry matter, leaf water and leaf apoplast, as well as in soil dry matter and soil water, to identify sites of ozone-derived 18 O accumulation.• It was shown that isotopic accumulation rates in plants can be used to infer the location of primary ozone-reaction sites, and that those in bare soils are dependent on water content. However, the isotopic accumulation rates measured in leaf tissue were much lower than the modelled stomatal flux of ozone.• Our new approach has considerable potential to elucidate the fate and reactions of ozone within both plants and soils, at scales ranging from plant communities to cellular defence mechanisms.

Dry Deposition of Ozone Over Land: Processes, Measurement, and Modeling

“…Based on mechanistic modeling, we suggest the contribution of thermal decomposition may be important (see Appendix ). The results of Toet et al () also imply aqueous ozone reaction in soil at low soil moisture may dominate.…”

“…Isotopic experiments in the laboratory and field may be able to pinpoint the primary sites of ozone surface reactions and thus improve understanding of ozone deposition pathways (Subke et al, ; Toet et al, ). Subke et al () present a method for adding 18 O into an electric discharge ozone generator and using a silica gel to separate 18 O ozone from 18 O O 2 .…”

“…Subke et al () present a method for adding 18 O into an electric discharge ozone generator and using a silica gel to separate 18 O ozone from 18 O O 2 . However, 18 O from the generated ozone leads to 18 O enriched water vapor as well as other gases (e.g., O 2 ) that do not necessarily remain on a surface, complicating estimates of deposited ozone (Toet et al, ). The authors conclude that better understanding of the reactions determining loss of 18 O ozone into other gases is needed for this technique to be useful for constraining ozone deposition pathways.…”

A new method for using 18O to trace ozone deposition

“…We have shown elsewhere that a shift in the 18 O 2 level of air at this magnitude results in no measurable change in the δ 18 O value of either plant or soil matter (see Fig. 1 in Toet et al 23…”

“…The data presented here are used to demonstrate the proof of concept for 18 O 3 fumigation and tracing of the isotopic label. They form part of a wider investigation of O 3 interactions within plant‐soil systems, with explicit treatment of the influence of soil moisture conditions on 18 O accumulation, and its implications for O 3 deposition modelling 23, 30. Further work into the nature of ozone deposition targets in soils is needed to give new insights into the likely sink strengths of different soil types for atmospheric O 3 , and this 18 O 3 ‐labelling approach is well placed to lead the way in this research.…”