How Does Ozone Damage Plants?

How Does Ozone Damage Plants?

This blog post was contributed by Danica Lombardozzi, a scientist at the National Center for Atmospheric Research (NCAR). Danica works in the Terrestrial Sciences group of the Climate and Global Dynamics Laboratory, and one of her research interests is the impact of ozone on plants.

Over the past couple weeks we have noticed moderate to severe ozone injury on several plants in our gardens. This increase in damage coincides with the high ozone concentrations that have come with the smoky haze from the forest fires on the west coast. The onset of such a notable increase in plant ozone damage raises the question: How does ozone actually damage plants?

Plants have microscopic pores on the bottoms of their leaves called stomata (singular: stoma). You can think of stomata as the mouths of the plant: plants open and close them to ‘breathe’. Thus, when they are open, gases in the air surrounding the plant can get inside the leaves through the stomata. Keeping stomata open is necessary so that the plants can get carbon dioxide from the air, which they turn into sugars for food during a process called photosynthesis. At the same time, however, ozone also gets inside the leaf and damages parts of the leaf cells that make the sugars. This can ultimately reduce the growth of the plant, reduce the production of wood and fruits and vegetables in timber and crop plants, and decrease the amount of carbon stored in plant tissues.

Plants are able to protect themselves from ozone damage in several ways. For example, antioxidants, like vitamin C, can protect against ozone damage, so plants with more antioxidants are less susceptible to ozone damage. Also, plants protect themselves by closing their stomata to reduce the amount of ozone getting inside their leaves. Plants close their stomata for other reasons, like when they are stressed by drought, and this also helps to protect the plant against ozone damage. Plants that have smaller and fewer stomata are typically less susceptible to ozone damage because less ozone enters the leaf.

While closing the stomata is a good short-term solution that plants use to protect against ozone damage and drought stress, closing the stomata for long periods of time also means that the plants can’t get the carbon dioxide they need to make their food.

Ozone damage on plants at NCAR’s Mesa Lab Cafeteria Patio garden has rapidly progressed over the past several weeks. There was little ozone damage on the potato (far left) and bean (center) plants on August 3, 2015 (top photo), but extensive damage by September 1, 2015 (bottom photo).
Credit: Danica Lombardozzi/National Center for Atmospheric Research

Brown patches on these potato leaves are evidence of moderate ozone damage, observed on September 1, 2015.
Credit: Danica Lombardozzi/National Center for Atmospheric Research

Ozone damage starts as stipple, which are dark pinpoint spots, visible on the left side of this snap bean leaf. The more extensive yellow-ringed brown patches on the top and right side of this leaf are evidence of severe ozone damage, observed on September 1, 2015.
Credit: Danica Lombardozzi/National Center for Atmospheric Research