Ozone Impacts on Maize Overview

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Ozone Impacts on Maize Overview

• Maize crop production in South Africa
• Ozone exposure effects on crops
• Impact assessment - way forward

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Maize Crop Production

• Available information for Zea mays
• Crop Estimates Committee and South African Grain
  Information Service
• (httpwww.sagis.safrica.co.za)
• Commercial and subsistence/ developing agriculture

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Maize Production in CAPIA Countries(thousands of
tons)
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Ozone exposure effects (1)

• AOT40 concept
• Accumulated ozone exposure above a threshold of
  40ppb
• Daylight hours when stomata open
• No distinction between frequency and intensity of
  exposure

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Ozone exposure effects (2)

• Flux concept
• Replaces concept of exposure to ambient
• Considers uptake of ozone by plant
• phenology (growth stage), climate (T, relative
  humidity), soil moisture, photosynthetic pathway
  (C3vs C4 plants),vapour pressure deficit

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Ozone stress physiology Ozone triggers the
pathogen defense pathway
O3
Reactive oxygen species accumulate

• Oxidative burst
• Local cell death
• Activation of plant
• defense genes

Hyper sensitive response
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Photosynthetic pathway

• C3 plants
• Wheat, oats, rice
• Photosynthesis

• C4 plants
• Maize, sugar cane, sorghum
• Photosynthesis 3x more efficient
• Less water needed, smaller stomatal openings
• Less ozone uptake

CO22H2O CH42O2
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Sensitivity to ozone

• Plant growth phase is important
• High sensitivity from flowering until seed
  maturity (grain filling period)
• Current photosynthesis provides 60-70 of
  assimilates to developing grain (wheat)

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RSA maize flowering periodStart and end
dates(maps provided by Enviro Vision)
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RSA maize flowering period
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Impact assessment Way forward

• Most sensitive period for SA maize
• 4 December to 18 March - flowering
• Check harvest dates for regions?
• Use risk assessment approach to identify areas
  where high ozone levels gt40ppb occur during
  maize-flowering and grain-filling

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Impact assessment Assumptions (1)

• Adopting exposure risk assessment rather than an
  ozone flux or uptake approach
• Wheat (C3 plant)used as a surrogate for maize
  (C4 plant)
• Photosynthate allocation ratios similar for wheat
  and maize

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Impact assessment Assumptions (2)

• Accommodate differences in maize phenology across
  South Africa and region
• Consider different maize varieties
• Consider other factors drought, infrastructure,
  pests and disease, HIV/AIDS

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