Characterizing the O3 yield gap in the sugarcane production of SE Brazil

<p>Sugarcane a vitally important crop across many tropical and subtropical regions. S&#227;o Paulo (SP) state, Brazil the largest single regional producer of both raw sugar and the production of bioethanol has experienced large-scale conversion of pasture to sugarcane production in recent decades. This predominantly rain-fed agricultural area is exposed to seasonal drought and periodic high tropospheric ozone (O₃) pollution at levels known elsewhere to be detrimental to plant productivity. Given the large current extent, and planned expansion of sugarcane production to meet global demand for &#8216;green&#8217; biofuels there is a pressing need to characterize the risk of current tropospheric O₃ to the sugarcane industry. This is a key step towards limiting the O₃yield gap under future climate and land use change scenarios. In this study, we therefore sought to a) derive realistic sugarcane O₃ dose response functions across a full range of O₃ exposure and b) model the implications of this observed O₃ response across the globally important production area of SE Brazil.</p> <p>We found a significant and substantial impact of O₃ on a range of sugarcane cultivars, including a number of commercially relevant varieties. When combined with biologically relevant predictions of O₃ exposure across Brazil this allows us to predict the current regional impact of O₃ on sugarcane production. We find that up to 25 million tonnes of total crop productivity a year may be lost across S&#227;o Paulo alone due to the direct impacts of O₃ exposure &#8211; but that substantial differences in O₃ sensitivity of different cultivars highlights the need for future work to elucidate the true impacts of O₃ in this important tropical cropping system.</p>