New research shows that elevated tropospheric ozone (O₃) is a biologically active gas that affects plants, insects, and soil microorganisms. Operating across multiple levels of the ecosystem, it has the potential to alter biodiversity in ways that are subtle and multi-layered.
Since the mid-1900s, the levels of ground-level ozone have been rapidly growing due to pollution from vehicles, industry, and other human activities. In many rural regions of the Northern Hemisphere, ozone levels today are 30–70% higher than historical baselines. Although emission controls have improved air quality in some areas, ozone levels are still high — and projections for the rest of this century don’t look good, either.
Ozone has a strong effect on plants: it can cause leaf damage such as discoloration and premature aging. But the deeper impact lies in physiological changes: the gas disrupts photosynthesis, alters plant chemistry, and shifts how plants allocate resources between shoots and roots. Not all species respond equally: flowering plants are typically more sensitive than non-flowering ones, and legumes often suffer more than grasses. Over time, these differences can shift species composition, reduce diversity, and alter ecosystem structure – even if the number of specimens doesn’t change.
Research also highlights less obvious consequences – for example, the difference in chemical signals that plants release into the air. These signals guide pollinators and herbivores to their host plants, but when ozone reacts with these molecules, scent signals degrade more quickly, shortening the distance over which insects can detect flowers.
Below ground, ozone exposure often reduces carbon allocation to roots, limiting the flow of energy into soil systems. This affects microbial communities and nutrient cycling, potentially weakening long-term soil fertility and resilience.
One of the most worrying findings is that many of the world’s biodiversity hotspots are also projected to face high ozone exposure. If emissions remain high, ozone levels considered harmful to plants could be exceeded across large parts of the Northern Hemisphere by 2100. Estimates suggest that between one quarter and one half of plant-rich regions may be affected.
These findings position ozone as an underrecognized driver of biodiversity change. For policymakers and environmental planners, it means that air-quality management must be viewed not only as a public health issue but as a biodiversity strategy. For researchers, it underscores the need for long-term, multi-trophic studies that link atmospheric chemistry to ecosystem dynamics. And for agriculture and forestry sectors, it highlights potential risks to crop productivity, forage quality, and ecosystem services.
Reference
Agathokleous, E., Feng, Z., Oksanen, E., Sicard, P., Wang, Q., Saitanis, C. J., Araminiene, V., Blande, J. D., Hayes, F., Calatayud, V., Domingos, M., Veresoglou, S. D., Peñuelas, J., Wardle, D. A., Marco, A.
D., Li, Z., Harmens, H., Yuan, X., Vitale, M., . . . Paoletti, E. (2020). Ozone affects plant, insect, and soil microbial communities: A threat to terrestrial ecosystems and biodiversity. Science Advances. https://doi.org/abc1176
