In the ozone garden, we are studying how ozone damages plants. Currently, we are tracking damage on coneflowers, milkweed, and snap beans. Last week, we talked about how the plants are tagged. This post will explain how we record the data.
What Ozone Damage Looks Like
Ozone causes three types of damage in plants which can be tracked visually; stippling, chlorosis, and necropsy. Stippling is when small black dots appear only on the top side of leaves and do not cluster. Chlorosis is when the top of the leaf turns yellow. Neither stippling or chlorosis will cover or cross the veins of a leaf. Necropsy is when part of the leaf becomes dead, and looks dark brown. There is often damage on leaves besides the types caused by ozone, so we must look carefully. Bugs, lack of water, and other things can mimic ozone damage.
To record the amount of damage, we look at each leaf, and estimate the percentage of the leaf’s surface that contains each type of damage. The rating system and collection method is based on techniques developed by the National Parks Service and St. Louis Ozone Gardens. There are six different ratings we use, which correspond with percent ranges. For example, a rating of 3 for chlorosis means 7%-25% of the leaf is covered in chlorosis.
1 = 0%
2 = 1%-6%
3 = 7%-25%
4 = 26%-50%
5 = 51%-75%
6 = 76%-100%
We rate each type of damage (stippling, chlorosis, and necropsy) separately for each leaf we are tracking.
What if a Leaf is Missing?
Along with the rating system, we also have classes for different types of leaf loss. Occasionally, we look for a leaf and only find a stem. Sometimes, a storm can cause leaves to break off, we may accidentally break one, or something besides ozone kills a leaf. This would be class 7. A missing leaf that previously only had a high chlorosis rating is class 8. A lost leaf that had stippling only is class 9. Class 10 is when a leaf is lost after showing more than one type of ozone damage. If a leaf is still there, we write n/a for not applicable, in the section on the charts we use.
In Order to See Damage…
Make sure the sun is out and bright when collecting data. If you carefully turn a leaf so it is vertically, more sunlight can shine through. The sunlight causes the natural green color of the leaf to become brighter and a little translucent while the ozone damage remains dark and becomes easier to see. If any damage is too small to see clearly, looking through a magnifying glass can help.