Impacts of ground-level ozone on sugarcane production.

Sugarcane is a vital commodity crop often grown in (sub)tropical regions which have been experiencing a recent deterioration in air quality. Unlike for other commodity crops, the risk of air pollution, specifically ozone (O), to this C crop has not yet been quantified. Yet, recent work has highlighted both the potential risks of O to C bioenergy crops, and the emergence of O exposure across the tropics as a vital factor determining global food security. Given the large extent, and planned expansion of sugarcane production in places like Brazil to meet global demand for biofuels, there is a pressing need to characterize the risk of O to the industry. In this study, we sought to a) derive sugarcane O dose-response functions across a range of realistic O exposure and b) model the implications of this across a globally important production area. We found a significant impact of O on biomass allocation (especially to leaves) and production across a range of sugarcane genotypes, including two commercially relevant varieties (e.g. CTC4, Q240). Using these data, we calculated dose-response functions for sugarcane and combined them with hourly O exposure across south-central Brazil derived from the UK Earth System Model (UKESM1) to simulate the current regional impact of O on sugarcane production using a dynamic global vegetation model (JULES vn 5.6). We found that between 5.6 % and 18.3 % of total crop productivity is likely lost across the region due to the direct impacts of current O exposure. However, impacts depended critically on the substantial differences in O susceptibility observed among sugarcane genotypes and how these were implemented in the model. Our work highlights not only the urgent need to fully elucidate the impacts of O in this important bioenergetic crop, but the potential implications air quality may have upon tropical food production more generally.