Partitioning of biomass and carbohydrates in field‐grown radish under ambient concentrations of ozone, and treated with the anti‐ozonant ethylene‐diurea (EDU)

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Abstract
Summary: The use of an anti‐ozonant provides a potential way for assessing yield losses caused by oxidant air pollution, predominantly ozone (O3), in field‐grown crops without the need of enclosures like open‐top chambers. One major prerequisite for the soundness of this method is the absence of direct effects of the anti‐ozonant EDU (ethylenediurea) itself on plant growth at low concentrations of O3 pollution. This condition was tested for field‐grown cultivars of radish (Raphanus sativus L.) parallel with investigations on the influence of soil drench treatments with EDU on the partitioning of biomass and carbohydrates between shoot and sink organs, i.e. hypocotyl and fibrous root, under ambient amounts of atmospheric O3, pollution. During 9 staggered plantings in two years, radish cultivars of differential sensitivity to O3 were harvested at two‐day intervals from emergence until vegetative maturity. Mean relative growth rates (RGR) for both sink and shoot organs were compared between EDU‐treated and non‐treated plants.When the relative deviation in RGR between EDU‐treatments was regressed vs. the O3 exposure of corresponding time intervals, linear relationships were highly significant for the sink organs of all three cultivars tested. Significant decreases in RGR attributable to O3 occurred above thresholds of O3 exposure equivalent to 52‐58 nl l−1O3 (daily 7‐h mean). No significant alterations of RGR of shoots were observed due to O3. Shoot growth rate of one variety was slightly increased by EDU as was RGR of sink organs in two of the cultivars at low‐levels of O3.Amounts of soluble carbohydrates (TSC) increased with biomass accumulation of both shoot and sink organs, and starch content decreased. These patterns were more apparent in sink tissues than in shoots. No significant differences in carbohydrate partitioning between treatments or between cultivars were detected. The linear relationship between the sink‐to‐shoot ratios of biomass and total non‐structural carbohydrates (TNC) was highly significant. From the results it is suggested that sink‐to‐shoot patterns of TNC occur synchronously with or slightly precede the partitioning of biomass rather than lag behind it.

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