tongues of red, the greens and stems
of wondrous beasts–their
twisted necks and leprous bumps
a chic warning, do not eat!
A continuation that I actually began before my previous leaf article… (A timey-wimey moment.)
Today as I was driving I kept getting caught in these swirling storms of falling leaves.
(It’s interesting how much better colors look in nature. Yellow of road signs isn’t what I would consider a pretty color, but I saw a lot of leaves so close to it today that the signs were blending in. With the sun at just the right angle that color on trees is luminous.)
Several weekends ago a friend mentioned something about how leaves don’t just fall, but are forced off by trees. I can’t remember if the word she used was expelled or excreted, but either way it wasn’t the right word and left us all with some entertaining images.
It was one of those ‘sounds vaguely familiar’ things. So I had to check it out. (I never did figure out quite what word she’d been intending to use.)
Apparently trees shed their leaves here in the northern latitudes (and on the southern half of the globe in the southern latitudes) because if left to their own devices leaves would try to photosynthesize during any warm spell. Then the leaves would die when the water in them from photosynthesis froze as soon as the weather turned cold again.
Rather than risk the likelihood of permanent leaves dying in the execution of their duty, deciduous trees have evolved to cast off their leaves in the fall and live on the food produced during the warm months.
Shorter and cooler days cause deciduous trees to release a hormone that in turn causes new cells to grow where the leaf stem and branch meet.
These are called abscission cells. Their job is to create a thin line of cells that grows and pushes the leaf stem away from the branches. That way they are only tenuously connected and ready to fall at the next autumn gust.
Since on of those friends is an NPR fan I’m guessing this was probably her original source.
For ice tea I like to blend English breakfast, green tea, rooibos, peppermint and spearmint. With hot tea I tend more toward plain black teas. I was in the mood, so collected a tea treasury on etsy while nursing the last of my orange spice with Assam. (They changed the blend, I don’t like the new one as much. Grr.)
What’s interesting is that all tea proper-be it white, green, black or oolong comes from the same species of tropical/subtropical evergreen-Camellia sinensis. There are different varieties and subspecies, but for the most part the difference comes from how the plant is treated after it is picked. (And of course, what flavors and scents it is blended with.)
The rooibos and mints that I like to add to my ice tea are technically not teas at all. That’s why sometimes herbal teas are called tisanes or infusions to avoid confusion.
But still, such variety due to what seems like a minor thing compared to the whole *same plant* aspect kind of amazes me. (Especially given how much I adore some teas and loathe others.)
Though I suppose it’s like a grapes and wine thing. I don’t think we normally eat the same breeds of grapes that most wines come from…I’m not much of a drinker (or any sort of gourmand) foodies want to weigh in on this one?
The wondering led to: We’re always told that leaves change because the trees stop making chlorophyll and they stop making chlorophyll because winter is coming.
But how does the one connect to the other, and what are those other colors doing hiding in there in the first place?
It seems to be another of those more interesting and more complex than it sounds subjects!
Leaf cells contain organelles (diminutive for the word organ-a cell organ-it’s so much fun to say and I probably haven’t been able to use it in writing since college, so sorry for the gratuitous vocabulary) called chloroplasts.
Chloroplasts are the part of the cell that uses photosynthesis to make food for the tree. Photosynthesis is a process that uses the energy from light to turn carbon dioxide and water into oxygen and sugar. These sugars are what gives the tree the energy to go about living. (And incidentally us oxygen so we can do the same…)
Chlorophyll is the pigment that absorbs the sunlight, so it is critical for photosynthesis. In good weather this green pigment masks any other pigments.
Chlorophyll is not chemically stable, it requires warmth and sunlight. As the days get shorter and trees start blocking water to their leaves as they prepare to shed them, the pigment breaks down. This exposes the orange and yellow pigments-carotenoids and xanthophylls. (The pigments found in corn, carrots, bananas, buttercups and daffodils amongst others…noticing the color scheme?) Their spring and summer jobs are to protect the chlorophyll from breaking down and are only seen in the fall as the days grow shorter.
The reds and purple hues come from pigments called anthocyanins. (They’re what make the reds in cranberries and apples, the purple in plums and the blues in blueberries.) These pigments are manufactured by the trees in the fall. What’s interesting is that scientists aren’t sure why trees go through the effort of creating a new pigment so late in the season. It has something to do with the trees trying to save as much sugar as possible. They’ve observed that there seems to be a correlation between soil quality and color intensity. The less nutrients in the soil the richer the crimson and purple leaf color as the trees try to salvage as much from the leaves as they can before they fall.
Temperature is a huge influence on the crop of reds and purples. Let’s hope for warm sunny days and cool but not freezing nights!
(Sounds good to me anyway…)
On sunny days leaves are still producing sugars but the cool nights and closing veins as the leaves shut down prevent the glucose from leaving as easily and combine to produce the strongest anthocyanin concentrations.
Moisture is also has a large role to play in the colors of the season. Drought can delay the color change and dampen the colors when they do emerge. Every fall is a bit different, since you’re not going to have the same moisture and temperature variations from year to year. (Or pretty much ever.)
The browns are from wastes left in the leaves after food production has stopped.
Studies done in Europe and Japan have shown that trees are flowering earlier and holding onto their leaves longer. This seems to be linked to long term climate changes. While it sounds like a nice growth period for trees, there is a danger that some species could be killed off in their native habitats is the summer temperatures get too warm.
Sources and Further reading:
This science project just looks like fun, studying the pigments in leaves.
PBS article from last fall.
Nature article on the question of why leaves turn red.
A nice USDA Forest Service article.
Today I Found Out article.
(The title quote is from the 1995 movie of Sense and Sensibility, I just always liked it and this seemed like an excuse.)