Hi there - I've posted this in "Maples" as well. It was suggested that I link it or post as well in Soils and Fertilizers, but I don't know how to link the posts. ---------- Greetings all, I have a question about red maple leaves and their herbicidal behaviour. A Toronto Star article says that the red leaves contain anthocyanin, which is produced in the fall. When the chlorophyll breaks down, the yellow colours emerge. But the reds are caused by the production of anthocyanin - which also turns out to be a natural herbicide. (Pg F4 of Oct. 23rd issue for folks who read it, sorry I couldn't find it online for every one else.) Tests were performed using 4 different types of leaves green beech, yellow beech, green maple and red maple leaves. Lettuce seedlings came into contact with green and yellow leaves sprouted fine, however the seedlings that came in contact with the red maple leaves were inhibited. The theory is that Maple leaves stop growth of other plant seedlings and saplings, so it's own will have an advantage. My questions: 1) When the red leaves dry up and turn brown - do they lose the anthocyanin? 2) If not - at what point is red maple leaf content in a backyard leaf mulch going to cause risk to flower bed seedlings and saplings? (HOw much is too much?) Thanks for your thoughts.
Hello just some thoughts ... There is a great deal of interest again in anthocyanins and their related compounds flavonoids. both are bioactive and have been used recently as a health food fad!! reluctantly without much thought as to why the plant needs them or uses them. They were thought to be secondary compounds that the plant did not need and so were good deposits of wastes and other unwanted things in the vacuole of the plant cell. there is a great deal of information out there by Jeffery Harborne at Reading University in England and Bruce Bohm and the late Neil Towers at UBC in Vancouver. Both Professors were looking not only at the activity of these anthocyanins but their building blocks and their related compounds and their relationships to the plant as a species. it is unlikely the anthocyanins alone are responsible for the suppression of the seelings. The common flavonoid "Rutin" is known to have anti-fungal characteristics. But ... both are water soluable and unstable in an acid or a basic solution for any length of time as they are never found in their pure state. to answer the question 1) When the red leaves dry up and turn brown - do they lose the anthocyanin? yes it is most likely degraded into the basic building blocks of a cinnamic acid and a coumarin both of which can be bioactive in anti bacterial and anti fungal senses. these are also water soluable, colourless and so do not hang around for any great length of time. therefore the plant looses the red colouring!! you should also know the anthocyanins fluoresce in Ultra violet light and suppress UVA & UVB damage to the internal organs of the plant. the compounds that are left in a brown leaf are the terpenoids and the things that make Tea and coffee that wonderful taste and colour ... the tannins. an overdose of all of these compounds in a concentrated area will suppress growth due to their combined actions. to answer the second point 2) If not - at what point is red maple leaf content in a backyard leaf mulch going to cause risk to flower bed seedlings and saplings? (HOw much is too much?) you should be putting the leaves in to your compost and letting the good fungus and good bacteria break down the tannins and organic materials left over a long period of time. the heat generated will also degrade any compounds in the leaves. Obviously do not make your compost out of only one plant as this will result in an nutrient imbalance. mix it in with the normal green matter and vegetablke waste in order to produce a balanced compost. I hope this helps Pierrot
Hey Vcallinan, Here is a link to the Toronto Star article: There's a reason those maple leaves are red (free registration required) Here is the story from a source that does not require registration: Mother Nature's Weapon of Mass Destruction? Red Leaves, from CollegeNews.org The article seems to indicate that the anthocyanin may remain in the soil surface long enough to inhibit spring germination. It is compared to catechin in the article. I think more research is needed, but this sounds like something plants would do, eh?
from the article this is the important part (IMHO) "The molecular structure of anthocyanin is nearly identical to catechin, a well-described toxin that causes root cells to self-destruct," he says. catechin and epi catechin (the isomer) are waht cause bloat in cattle. if a ruminant eats too much alfalfa then the catechin acts as a frothing agen causing gass problems. catechin also has an anti bacterial effect. Pierrot
Hi Pierrot and Eric - I was going to respond to each of you individually, but you're too fast for me. Pierrot, Thanks for that very informed response. Too much of anything is not good - and luckily there are a large variety of shrubs and trees in our backyard so there is always a good mix of leaves in our leafpile. We have 3 composters, which are doing a great job. You mentioned that the brown leaves contain terpenoids and tannins. That's interesting because one practice is to put coffee grinds and tea bags around certain trees like maples, and in the compost. Is there any scientific truth to that? Can it also become "too much of anything is not good". A common practice, around here anyway, is to pile dried leaves on beds and around roses over winter, as a mulch (not the green ones, just dried brown ones). I was concerned that too many red maple leaves in the mixture could suppress seedlings or young plants. But, from what you wrote, the flavinoid chemical compounds don't last long and shouldn't pose a problem provided there is a good mixture of leaf varieties. Eric for the " how to link" info and the link to the article. The College News article sounds very much like the background used in the Toronto Star piece. The findings there seem somewhat different to what Pierrot was saying, however, the test was probably using "pure" extracts rather than what happens in nature - which is the blending of everything that gathers on the ground. It's interesting that a new focus of the anthocyanins isn't just it's affect on plants but it's potential to retard the growth of cancer cells. ***** Here in the Toronto Ontario area, the trees in general had a very tough summer with heat, smog and hummidity. The result is that there aren't as many reds as usual. Apparently, all the energy was put into staying alive rather than saving some for fall to produce the anthocyanin. It's all so fascinating!
Anthocyanin (red, blue, purple, magenta) is, pretty much, always present in leaves throughout their life span, so to the carotene (yellow, orange, red), xanthophyll (yellow) etc... The only reason why a leaf is generally green is its ratio of chlorophyll of green pigments being the dominant pigment... this is one of the reason why new leaves are usually a yellowy-green, as the chlorophyll has not maintained its dominance amongst the other pigments. When days become shorter and colder, the tree retracts all chlorophyll from the leaves for storage to help the following spring. Once the tree has stored a sufficient amount of chlorophyll, it then begins extracting the other compound types individually at a time, which is when you get the subtle changes of autumn colour as each pigment is removed to give the others dominance. The tree will attempt to extract all of these compound types and leave only the tannins behind etc... However, FOR the subtle changes in autumn colour to happen, the end of summer/autumn needs to be generally dry, reletively clear and cold (but not freeze), if those conditions are not met and there is an autumn freeze, or very wet and dark, the tree will switch to 'overdrive' and 'suck' all pigment compound types out of the leaves A.S.A.P before the leaves fall off "prematurely" (which it would rather not do as this requires more energy, but needs to if its going to store enough to flourish next spring) So yes, if the colour of the leaf makes it look 'DEAD' (pigment characteristics of tannin), then the leaf contains very little anthocyanin as the tree has already extracted the vast majority of it. Hope you found this interesting.
Unregistered, I'll present this: Acer circinatum and this: Autumn Colours (PDF) as evidence against your assertions that the non-chlorophyllic pigments are always present and that it is the ratio of pigments that cause autumn colour.
