Leaf color vs sugar level

[BreezyHill]

I was out raking hay and noticing all the spectacular foliage color. Suddenly I found myself think...How is it that certain maple trees always turn to red while others turn to yellow. Then I noticed on tree was mostly orange with some red up high and yellow down low.

Does the sugar level of a tree have anything to do with its coloration of leafs in fall?

[Buffalo Creek Sugar Camp]

Our trees in southern PA seem to mostly have a fungal disease on the leaves such as anthracnose. Most of the leaves are just turning brown and falling. It has been a wet summer for the most part. It will be interesting to see what the sugar content is this spring.

[unc23win]

Seems like we had a lot of leaves fall off early this year hardly changed color at all.

[lyford]

Jeremy, I'm in Erie county ny and we have the same spots all over the maples, but they aren't turning brown, mostly shades of red, also a wet summer here

[DrTimPerkins]

Does the sugar level of a tree have anything to do with its coloration of leafs in fall?

In general yes. For those leaves that turn brown and fall off....it is typically some foliage disease (anthracnose), so we're not talking about that.

Very simply and briefly (OK....brief for me anyhow)....leaves have green (chlorophyll) and yellow colors (carotenoids....ancillary pigments) that serve to "harvest" energy in the light reactions of photosynthesis (it causes the electrons to be boosted to a higher energy state....kind of like vibrations in a wine class when you ping it with your finger). This energy then pass through an electron transfer chain (ETC=a group of different compounds close together that successively "funnel" that energy down to a specialized photocenter pigment) to "fix" or convert physical energy (electron excitation stages) into chemical energy (carbohydrates). Very simply, the vibration energy is passed through the ETC to the photocenter where enzymes hold "carbon" compounds close to each other. This vibration energy provides enough of a "push" to force the carbon compounds to fuse....eventually into sugar (that is a huge simplication....the process itself if quite involved). These fused carbon compounds provide (at least part of) the building blocks for sugar. The whole process of photosynthesis is just that of a very small electro-chemical plant that uses light to fuse carbon (from carbon dioxide in the air). Put a few million of these in a leaf....and you're really making sugar.

In the fall, an abscission layer starts to form to cut off the leaf from the twig. Some trees (like maple) do this very effectively -- others aren't so good at it (oaks, beech). As this happens, photosynthesis doesn't shut down.....it just keeps cranking awy, so the leaves keep making sugar. However because one of the first layers to be affected by the abscission process is the phloem (just inside the twig bark, which serves in sugar transport from the leaves to the rest of the plant), which impairs the ability of sugars to be exported to the stem (so you haven't shut down the leaf "machinery" forming the sugar....just slowed down or stopped the trucks taking the sugar away. Since these sugars are trapped in the leaf (more or less depending upon the abscission layer development), the leaves utilize some of this excess sugar to actively form new pigments, anthocyanin, which is a red-colored (usually) pigment (so kind of like the factory that can't shut down the machines...so sugars stack up....and to get rid of some of that sugar, you turn it into candy). At least in maple, it doesn't appear that these anthocyanins are playing any major functional role in terms of protecting the leaves from excess light and/or cold temperature oxidative damage (the current theory in most textbooks....at least for maple it is incorrect). In other plants, red color "may" have some addition function. So the red colors in maple form "just because......"

Other stresses can cause temporary or permanent red color to form. Look at leaves early in the spring when the buds are breaking. The leaves are red....the phloem transport system is just getting ramped up at that time so the sugars that accumulate can't be transported out.

So, the leaves that are less able to export sugars are those that tend to develop more red color. Some years you have little export due to prevailing weather conditions, you get lots of anthocyanin production and red leaves. If they do it less (some years), they form orange (mixture of anthocyanin and carotenoids). With more export, you get yellow (carotenoids) as the chlorophylls die off and degrade. You can see this on individual portions of trees.....often the outer edges, those that get the color trigger cue (and the leaf abscission cue) early, will turn red.

Some trees naturally are better at quick leaf abscission.....others not so much. It also depends upon the individual year, but like the sap sugar content, trees tend to have consistent rankings of color development. What does this mean for sugarmakers? Probably not a great deal, although we've never really looked to see if trees that are very red also tend to have higher (or lower) sap sugar contents. Might be an interesting study.

You want to know more about this subject.....ask Dr. Abby van den Berg (at UVM PMRC). Her Ph.D. (with me as her advisor) is in anthocyanin (red pigments) in maple leaves. She still does a little work in that area.

[lpakiz]

Thanks, Dr. I knew it was somethng simple, I just couldn't put my finger on it......

[BreezyHill]

Thanks for the info.
Ben

[tuckermtn]

not to hijack the thread, but are other regions of the maple world seeing Anthracnose on the leaves? We are seeing it on some, but not all, sugar maples here in central NH.

last time we had a bad anthracnose outbreak was the fall of 2011. 2012 was a pretty bad maple season. I hope we do not have a repeat of this pattern.

[BreezyHill]

I would say in my area it is slight. Only on a few of the leaves, mostly those that are low an shaded heavily. Trees in hedge rows and in open areas look fine. We are wetter now than in June when we started cutting hay and finally finished in mid July. Our field tiles are running full bore and water is laying in wet areas on top of the ground. One field had 3" of water laying on top. It is directly over a tile and the far end of the tile got cleated by the tractor but no water laying...so the tile...6"...is pumping out millions of gallons since the last rain.

A few leaves I say yesterday have these funny horns sticking out of them. Never seen that before. I will get a pic later and post it.

Ben

[GeneralStark]

Definitely have some anthracnose happening in areas here. Many of the sugar maples' leaves where I currently live are browning, shriveling and falling, but 10 miles away at my new property they are still green. Could be a difference in aspect, west vs. east, but it does not seem too widespread.

[happy thoughts]

A few leaves I say yesterday have these funny horns sticking out of them. Never seen that before. I will get a pic later and post it.

Ben

Ben, that sounds like some sort of leaf gall. Should be harmless. Here's an article with some pics

http://ohioline.osu.edu/hyg-fact/2000/2004.html

anthracnose seems a little less prevalent here than usual. I have one big sugar in a wet area that's usually affected. This year I may actually see the leaves on it turn color before they fall. Should be a really nice year for fall color :)