Abstract
Estimating food production under future air pollution and climate conditions in scenario analysis depends on accurately modelling ozone (O3) effects on yield. This study tests several assumptions that form part of published approaches for modelling O3 effects on photosynthesis and leaf duration against experimental data. In 2015 and 2016, two wheat cultivars were exposed in eight hemispherical glasshouses to O3 ranging from 22 to 57 ppb (24 h mean), with profiles ranging from raised background to high peak treatments. The stomatal O3 flux (Phytotoxic Ozone Dose, POD) to leaves was simulated using a multiplicative stomatal conductance model. Leaf senescence occurred earlier as average POD increased according to a linear relationship, and the two cultivars showed very different senescence responses. Negative effects of O3 on photosynthesis were only observed alongside O3-induced leaf senescence, suggesting that O3 does not impair photosynthesis in un-senesced flag leaves at the realistic O3 concentrations applied here. Accelerated senescence is therefore likely to be the dominant O3 effect influencing yield in most agricultural environments. POD was better than 24 h mean concentration and AOT40 (accumulated O3 exceeding 40 ppb, daylight hours) at predicting physiological response to O3, and flux also accounted for the difference in exposure resulting from peak and high background treatments.
Highlights
The air pollutant ozone (O3 ) reduces yield in many crops including wheat, rice, and soybean [1,2].Ozone at the ground level forms from precursor gases— NOx and volatile organic compounds (VOCs)—in chemical reactions catalysed by sunlight and heat [3]
The main differences in these experiments were in the ozone concentration profiles to which plants were exposed
The first aim of the analysis presented here was to assess whether published approaches for modelling O3 -induced senescence can account for inter-cultivar variation in response
Summary
The air pollutant ozone (O3 ) reduces yield in many crops including wheat, rice, and soybean [1,2].Ozone at the ground level forms from precursor gases— NOx and volatile organic compounds (VOCs)—in chemical reactions catalysed by sunlight and heat [3]. Short peak ‘episodes’ of very high concentrations are predicted to become more frequent in India and China [10,11], while in Europe and North America a decline in peak episode frequency, alongside steadily increasing annual mean O3 concentrations, was observed between 1990 and 2010 [12]. Modelling suggests this decline in peak episode frequency in Europe and North America is likely to continue to 2050 [10]
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