Global crop yield reductions due to surface ozone exposure: 1. Year 2000 crop production losses and economic damage

We quantitatively evaluated the effects of elevated concentration of ozone (O-3) on growth, leaf chemistry, gas exchange, grain yield, and grain quality relative to carbon-filtered air (CF) by means of meta-analysis of published data. Our database consisted of 53 peer-reviewed studies published between 1980 and 2007, taking into account wheat type, O-3 fumigation method, rooting environment, O-3 concentration ([O-3]), developmental stage, and additional treatments such as drought and elevated carbon dioxide concentration ([CO2]). The results suggested that elevated [O-3] decreased wheat grain yield by 29% (CI: 24-34%) and aboveground biomass by 18% (CI: 13-24%), where CI is the 95% confidence interval. Even in studies where the [O-3] range was between 31 and 59 ppb (average 43 ppb), there was a significant decrease in the grain yield (18%) and biomass (16%) relative to CF. Despite the increase in the grain protein content (6.8%), elevated [O-3] significantly decreased the grain protein yield (-18%). Relative to CF, elevated [O-3] significantly decreased photosynthetic rates (-20%), Rubisco activity (-19%), stomatal conductance (-22%), and chlorophyll content (-40%). For the whole plant, rising [O-3] induced a larger decrease in belowground (-27%) biomass than in aboveground (-18%) biomass. There was no significant response difference between spring wheat and winter wheat. Wheat grown in the field showed larger decreases in leaf photosynthesis parameters than wheat grown in < 5 L pots. Open-top chamber fumigation induced a larger reduction than indoor growth chambers, when plants were exposed to elevated [O-3]. The detrimental effect was progressively greater as the average daily [O-3] increased, with very few exceptions. The impact of O-3 increased with developmental stages, with the largest detrimental impact during grain filling. Both drought and elevated [CO2] significantly ameliorated the detrimental effects of elevated [O-3], which could be explained by a significant decrease in O-3 uptake resulting from decreased stomatal conductance.

Impact of elevated ozone concentration on growth, physiology, and yield of wheat (Triticum aestivum L.): a meta‐analysis

http://www.indiaenvironmentportal.org.in/files/A%20comparison%20of%20North%20American%20and%20Asian%20exposure.pdf

A comparison of North American and Asian exposure-response data for ozone effects on crop yields.

Ozone is the most important regional-scale air pollutant causing risks for vegetation and human health in many parts of the world. Ozone impacts on yield and quality of crops and pastures depend on precursor emissions, atmospheric transport and leaf uptake and on the plant’s biochemical defence capacity, all of which are influenced by changing climatic conditions, increasing atmospheric CO2 and altered emission patterns. In this article, recent findings about ozone effects under current conditions and trends in regional ozone levels and in climatic factors affecting the plant’s sensitivity to ozone are reviewed in order to assess implications of these developments for future regional ozone risks. Based on pessimistic IPCC emission scenarios for many cropland regions elevated mean ozone levels in surface air are projected for 2050 and beyond as a result of both increasing emissions and positive effects of climate change on ozone formation and higher cumulative ozone exposure during an extended growing season resulting from increasing length and frequency of ozone episodes. At the same time, crop sensitivity may decline in areas where warming is accompanied by drying, such as southern and central Europe, in contrast to areas at higher latitudes where rapid warming is projected to occur in the absence of declining air and soil moisture. In regions with rapid industrialisation and population growth and with little regulatory action, ozone risks are projected to increase most dramatically, thus causing negative impacts major staple crops such as rice and wheat and, consequently, on food security. Crop improvement may be a way to increase crop cross-tolerance to co-occurring stresses from heat, drought and ozone. However, the review reveals that besides uncertainties in climate projections, parameters in models for ozone risk assessment are also uncertain and model improvements are necessary to better define specific targets for crop improvements, to identify regions most at risk from ozone in a future climate and to set robust effect-based ozone standards.

/pdf/ozone-risk-for-crops-and-pastures-in-present-and-future-vhsx1q26pv.pdf

Moti L. Mittal

Papers

Surface ozone in the Indian region