Effects of rising CO2 and O3 on agricultural ecosystems

Rising population size, changes in land-use, introduction of novel and invasive pests and diseases, and global changes in climate and atmospheric composition pose significant challenges to maintaining and improving future agricultural production and global food supply.  Two global changes that directly affect crop productivity are rising carbon dioxide concentration ([CO₂]) and rising tropospheric ozone concentration ([O₃]).  While elevated [CO₂] directly stimulates photosynthesis in C₃ crops, rising tropospheric [O₃] negatively impacts photosynthesis and subsequent growth and production.  Literally thousands of individual studies of crop responses to elevated [CO₂] or elevated [O₃], either singly or in combination, provide a rich database from which to extract estimates of the mean responses of major food crops to these important global changes.  Over the past 4 decades, the methods for fumigating plants with [CO₂] and [O₃] have changed, the cultivars of major crops have changed, and the background (ambient) concentrations of [CO₂] and [O₃] have changed.  These factors pose challenges to calculating a mean response.  However, meta-analysis provides a tool for drawing quantitative conclusions from diverse data sources and experiments.  This research will summarize the response of the major grain and oilseed crops, namely maize (Zea mays), rice (Oryza sativa), wheat (Triticum aestivum) and soybean (Glycine max), to rising atmospheric [CO₂] and [O₃] concentrations using meta-analysis.  The advantages and disadvantages of this type of analysis will be discussed, along with a comparison of fumigation methods.  Understanding the mean response of crops to rising [CO₂] and [O₃] is a first step towards developing adaptation strategies for the future.