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.

With the leaves changing color and the cooler temperatures, fall has most certainly arrived. The advent of fall is also noticeable in our ozone gardens. The coneflowers have stopped flowering, and the leaves of all the plants are showing signs of aging and will soon drop.

Ozone garden in the fall at the Mesa Lab

The ozone garden at NCAR’s Mesa Lab entrance is starting to show signs of aging, and the plants will soon die for the season.
Credit: Danica Lombardozzi/NCAR

The ozone gardens throughout Boulder had a good season, and the plants served their function: to show us when ozone concentrations were high. The earliest signs of ozone damage started in June, and since ozone damage accumulates, the signs of damage became more intense as the season progressed. For example, the damage observed on the coneflower leaves started as a few black pinpoint spots, or stipples, and increased in number through the summer. In the last several weeks, the damage grew larger in size and turned bronze, which are signs of extensive ozone damage. The onset of severe damage in August, particularly for the potato and bean plants, were harbingers of the high ozone concentrations that accompanied the haze from forest fires on the West Coast.

Black stipples on cutleaf coneflower leaf

Ozone damage on cutleaf coneflower leaves on August 3, 2015 were black, pinpoint spots called "stipples".
Credit: Danica Lombardozzi/NCAR

Damaged areas on leaf due to ozone accumulation

As the damage from ozone accumulated, the signs worsened, turning from stipples to larger areas of bronze by September 15.
Credit: Danica Lombardozzi/NCAR

In addition to showing us that ozone reached damaging levels this summer, we collected data from a few of the gardens during the summer to quantify the visible damage. On July 24, students ages 6-8 estimated that 35% of plants in NCAR’s cafeteria patio garden showed visible signs of ozone damage, increasing to 80% on September 9, as calculated by Front Range Community College students. On August 5, high school students calculated that 52% of plants showed visible signs of damage at CU’s Mountain Research Station garden. On a scale of 0 to 4, ozone injury averaged around 1 for coneflowers, 2 for snap beans, and 2.5 for potatoes.

The Environmental Protection Agency is considering tightening the ground-level ozone regulations, and a decision is expected within the next week. The ozone gardens in Boulder helped to show us that ozone reached damaging levels in Colorado’s Front Range this summer. A reduction in the allowable levels of ozone can help to reduce the damage to plants. Therefore, we will continue planting the ozone garden and collecting data in future summers to see how ozone concentrations and plant damage change in the Front Range.