Zane Moore at UC Davis is studying why the coastal redwoods produce white waxy leaves (albinism) on parts of some trees. These chimera trees (some of the leaves are green, some are white, and some are a mix) occur at the margins of ranges. His hypothesis is that the white leaves, which cannot photosynthesize, are used to store toxic metals found in the soils. Listen to the 17 min audio at Science Solved it, here: https://motherboard.vice.com/…/these-mysterious-pure-white-… If Zane's hypothesis is correct, are there other tree species that do this? Does it only happen on heavy metal soils derived from high Ni & Mg igneous rocks, or can it be triggered by acid rain over time (as we had in the Smokies up until the 1970s when the clean air act was passed and air quality improved)
Joanne,
I'll have to look at the video, but my initial reaction would be no. The reason I say this is that the capillary action and venous system of trees is somewhat analogous to the distribution of veins in animal physiology. Note that I said venous system, since the capillary action is usually one way with nutrients travelling up the tree and exiting by transpiration. Since this is normally a one-way action, any toxins or heavy metals that enter the system end up distributed throughout the venous system, but likely accumulates in greater proportion in the ends of twigs and the leaves where transpiration is more prevalent. I do not see how a tree could target the transportation of toxins and heavy metals to specific leaves and not others. This is unlike animal physiology where these substances are filtered out by various organs. Some toxins and heavy metals pool in specific locations within the body, like the recent revelation that the cobalt in tattoo ink can travel to and concentrate in the ovaries, but transpiration makes this doubtful in plants. I could see the eventual development of some type of filtration mechanism in the root system similar to the nitrogen-fixing nodules in legumes.
This hypothesis seems easy to test by analyzing the pale leaves versus the green leaves and other part of the same tree.
JAG
Hi James. THanks for your input. They did analyze the green vs. white leaves and were surprised to find the white leaves had a much higher concentration of toxins/heavy metals. It is an audio at the link, but there are some great photos as well.
I'd be interested in how that works. I'm no botanist, but I did well enough in botany classes that my professor tried hard to get me to change my field, so I hopefully have more knowledge than the average person. I have read recent findings that some plants appear to be able to target certain areas of their physiology to fight disease or damage, so perhaps plants have more control of their venous system than we have always believed.
I have a project that came in and am currently heavily immersed in analyzing data. I'll check the audio when I feel like a break.
Joanne,
Ah. From this NPR transcript, these are small trees that have all albino leaves and are suckers that grow near the base/roots or off of limbs. So it looks like this is an evolutionary solution to filter the toxins. It would be interesting to find out if these are attached to locations that have a large flow of nutrients.
http://www.npr.org/2016/09/15/494043629/mystery-of-white-trees-among-californias-redwoods-may-be-solved
Hmmm, interesting. I wonder if mycorrhizal fungi play a role at all...
Hello James, I wrote to the researcher, and sometimes the albino leaves (needles for conifers) grow on the crowns of the trees. He says this is not an adaptation but a mutation. It can be caused by serpentine soils and/or polluted fog. The coast redwoods get about 40% of their moisture from fog.
So are the albino leaves then more susceptible to heavy metal/toxin retention than green leaves?
They are not more susceptible to it. They accumulate more of it, according to analyses of both white and green leaves.
No. What I was getting at, since you said polluted fog, was whether something in the albinism causes/allows them to absorb more of the toxins than the green leaves. There has to be some mechanism that either allows them to store more or that make them more susceptible. If the toxins are from polluted fog, then they have to be absorbing the toxins out of the moisture more rapidly or more efficiently than the green leaves.
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