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

Sugarcane a vitally important crop across many tropical and subtropical regions. São 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 ‘green’ 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 O₃ yield 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.

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 São Paulo alone due to the direct impacts of O₃ exposure – 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.