TropOz is tackling one question from several directions: how much is O3 harming tropical plants, and what does that mean for the planet? Our experiments measure how individual species respond to O3. We turn those measurements into parameters that models can use, and we test those models against real O3 levels and damage measured inside tropical forests and cropping systems around the world. By improving our understanding of how O3 impacts tropical plants we can help better predict global climate change and develop strategies to mitigate its impact on important ecosystems.
Why ozone matters
High in the stratosphere, O3 shields life from ultraviolet radiation. Near the ground, it is a pollutant. It forms when sunlight drives reactions between nitrogen oxides (from vehicles, industry and biomass fires) and volatile organic compounds (VOCs), many of which are emitted by plants themselves. Surface O3 has roughly doubled since pre-industrial times and is now thought to reduce plant productivity around the world.
Why the tropics?
Three factors make the tropics a particular concern. First, emissions of O3-forming pollutants are rising fastest here, driven by population growth, urbanisation, land clearing and fire. Second, hot, sunny conditions and abundant plant VOCs favour O3 formation. Third, tropical forests are highly productive and keep their stomata wide open, so they may take up more ozone than almost any other ecosystem. Modelling by Sitch et al. Nature (2007) flagged tropical forests as potentially the most vulnerable to future ozone. Yet when TropOz began, almost no experiments had tested tropical species.
How O3 harms plants
Ozone enters leaves through the stomata and generates reactive oxygen species, triggering oxidative stress. Plants divert energy into repair and defence, photosynthesis falls and leaves age early. The result is slower growth and less carbon drawn down from the atmosphere.