Ozone before emergence: how air pollution could affect tree seed germination

Ground-level ozone is a widespread air pollutant known to damage plants, but we know much less about how it affects trees at the earliest stage of their lives: germination. In our study, published in Environmental and Experimental Botany, we investigated whether ozone exposure influences the germination of five widespread temperate tree species.

We exposed seeds of Scots pine, silver birch, alder, sycamore and Sitka spruce to ambient or elevated ozone over 27-day germination periods. Scots pine was the most sensitive species, with elevated ozone delaying germination and reducing germination success by 17%. Silver birch and Sitka spruce showed similar but weaker trends, whilst alder and sycamore weren't affected.

By analysing the hormones within the seeds, we identified a possible mechanism behind these effects. In ungerminated Scots pine seeds, ozone altered several hormones involved in regulating germination and stress responses, including abscisic acid, auxin, jasmonic acid and salicylic acid. These hormonal changes appear to shift the physiological balance towards maintaining the non-germinating state.

Our findings show that ozone pollution could affect trees before they even emerge as seedlings, with different species responding in different ways. By delaying or preventing germination in sensitive species, ozone could influence forest regeneration, restoration outcomes and, over time, the composition of future forests.

Read the full article here: Ozone-induced hormonal effects underpin germination dynamics in temperate tree species

DOI: 10.1016/j.envexpbot.2026.106434