Ozone is already one of the most damaging air pollutants for the world’s crops, but almost everything we know comes from temperate staples or commodity crops such as wheat, soybean and rice. TropOz is testing how important tropical crops respond, and what rising O3 could mean for tropical farming and food security.
Why tropical crops?
Around 90% of crop species tested so far show some susceptibility to O3, and the losses can be large: a global analysis estimated ozone cuts soybean production by up to 12.4% (Mills et al. 2018). Yet these studies have focused overwhelmingly on temperate crops grown in Europe, North America and East Asia.
Across much of the tropics, O3 is rising as cities grow, fires burn and land is cleared, often in the very regions where crops are grown. Hot, sunny conditions and long growing seasons mean crops may be exposed for much of the year. Without data on tropical crops, these losses go unrecognised.
What we have found
Sugarcane (Saccharum spp.)
Sugarcane is a major commodity and bioenergy crop across the tropics and subtropics. We found that O3 reduced growth and altered how plants allocate biomass, especially to leaves, across a range of sugarcane genotypes, including two commercially relevant varieties. Combining these responses with Earth system modelling, we estimate that current O3 exposure is likely costing between 5.6% and 18.3% of sugarcane productivity in south-central Brazil, one of the world’s most important growing regions. Just as importantly, genotypes differed substantially in their susceptibility.
Cheesman et al. 2023, Science of the Total Environment
Banana (Musa spp.)
Bananas are a staple food for millions of people across the tropics, yet their response to O3 had never been tested. Growing Australia’s main commercial cultivar, Williams (Cavendish subgroup), under a range of O3 concentrations, we found that O3 significantly reduced plant biomass. Older leaves increased their antioxidant and phenolic content, showing that O3 damage builds up over a leaf’s life. By measuring defensive leaf traits across 46 diverse banana lines, we found that Williams ranks among the more tolerant, suggesting many other banana varieties may be even more susceptible to O3.
Farha et al. 2023, Functional Plant Biology
Sorghum (Sorghum bicolor)
Sorghum is the world’s fifth most important cereal and a key crop in hot, dry regions. In one of the first O3 experiments on sorghum grown under tropical conditions, we exposed a grain sorghum cultivar widely grown in Queensland to nine O3 concentrations. Unlike sugarcane and banana, this cultivar showed little effect of O3 on growth, suggesting sorghum, and other O3-tolerant C4 grasses, could be a valuable option for tropical regions facing high O3 pollution.
Oil palm and cacao
We are also examining the O3 sensitivity of oil palm (Elaeis guineensis) and cacao (Theobroma cacao), two tree crops that underpin the economies of many tropical countries.
Varieties matter. Across our crop studies, a consistent message is that susceptibility varies, not only between crops but between varieties of the same crop. That is a risk, because O3 losses may be hidden within current variation in yields, but also an opportunity: choosing and breeding more tolerant varieties could help protect tropical harvests as air quality changes.
From experiments to regional estimates
As with our work on tropical trees, the dose–response functions we measure for crops feed directly into models that estimate O3 losses across whole growing regions, today and under future scenarios. We work with collaborators in Brazil, Panama and Malaysia to link these estimates to real production landscapes.