I have wondered for a long time what exactly causes leaves to change colors. I remember reading several years ago about the color change being associated with the reuptake of cholorplasts by the trees in preparation for winter. If this is true, then there must be some reason, energetically, why trees reabsorb their cholorplasts. The answer must be that in doing so, some of the energy that was spent producing the cellular bodies in such vast quantities can then be stored for the photosynthesis-less winter. During this time, trees must respire to survive, so they need stores of sugar, and chloroplasts provide that.
Okay, simple enough, but why is this process beautiful? Shouldn’t the trees, stripped of their verdant trillions of chloroplasts turn brown, just as a dead leaf is? Today, I read what seems a pretty convincing answer to this question. The process by which chloroplasts are broken down into sugars to be stored proceeds very quickly unless compounds called red anthocyanins are present to slow it down. Their release is triggered by cold nights, but the quantity of red anthocyanin release is governed by how much sunlight falls on a given leaf.
Maple leaves are a particularly good illustration of this phenomenon (see the picture). In direct sunlight (and with plenty of water present, thus drought stricken trees will not color so brilliantly), the leaves erupt into a violent crimson, while partially shaded trees such as those in forests will carpet the ground with nearly-flourescent yellow leaves. So, now with a few simple facts, we can all forecast how beautiful the colors will be, and where they shine most brightly, this fall by asking these questions: 1) Were the last few months wet enough? 2) Have the nights been cold, but above freezing? 3) For yellow leaves: is there plenty of shade, or for red: have the last few weeks been relatively cloud-free?
This view of fall colors is what philosophers of the 19th century called Materialistic. Materialism at its core seeks to explain the world around us, thus it is often called scientific materialism (though one could be a spiritual materialist by explaining everything in terms of spiritual arguments such as energy vortices and chakras). Poets decried this most horrific act of dissection, but scientific-minded naturalists found more beauty in a forest than all the world’s poets had swooned over. Viewing something materialistically only enhances its beauty, for to understand is truly to appreciate. Now, when I look at the trees I see not only color, but light, shadow, drought, and plenty. We can all admire the workings of some intricate clock, but only those who understand its movements can be awed by the delicacy of its Creation.
[…] Grape wines undergo what is called a biphasic maturation. First, the flesh and skin expand in volume very quickly. During that time, organic acids such as malate and tartrate are produced and stored in the mesocarp. These acids taste tart to the human tongue and are believed to have evolved in order to dissuade foraging creatures from eating the immature seed within the fruit. Once the expansion slows, the second phase of berry development begins. This is the ripening phase, in which (for reds at least) anthocyanins are produced, reddening the exocarp. (Remember those? They are what turn our leaves red in the fall). During this phase, the malates and tartrates are largely broken down and converted to other, less tart VOCs. The primary components of wine flavor are organic acids, proanthocyanidins (tannins), terpenoids, and various aromatic aldehydes, esters, and thiols (don’t know what those are? Neither do I, but that may mean something to the organic chemists among us). […]