Last year I posted a number of resources that could help you and your students explore that age-old question–“Why do leaves turn color?” While on a “nature walk” with my 6 month old granddaughter, last week I was reminded again as we observed a number of early turning leaves.
Almost all of the bright red leaves we observed on this walk were associated with some form of tissue damage. Note the leaf tissue damage in image above. When hole leafs were affected there generally was some evidence of stem or pedicel damage.
Notice on the image above a large sumac gall may be impinging on the vascular connections to the leaf. I have a hypothesis that I think you and your students can investigate. It may be too late this year–don’t know. Could it be that partial stem damage to phloem tissues accelerates leaf color change? It would seem to be a very easy question to begin investigating. Take a plant like smooth sumac that generally have leaves that turn bright red. Systematically try out various degrees of stem, phloem damage and record the results…
Let me know if you give this a try.
p.s. Sumac galls themselves are interesting and a potential question for investigation. They are caused by aphids cut one open and take a look.