Tuesday, June 21, 2011

Camellia Not Sinensis, And Some Ecology

Does this look just a little bit like a tea plant?

That's because it's from the same genus, Camellia, as the tea plant, Camellia sinensis. I found this plant growing in a garden in west Philadelphia. Since I do not live in an area where the tea plant grows (and certainly not where it is native), I cannot say much firsthand about the ecological relationships involving the tea plant. However, much about ecology is fairly universal: the same relationships play out on different continents and different regions with different species playing more or less similar roles.

There are some interesting lessons about ecology in this seemingly simple photograph, and they are surprisingly relevant to tea cultivation.

Why are the young leaves red, but the older leaves green?

Just as the young of humans and other animals are vulnerable and in need of protection, the young leaves of plants are most vulnerable. Soft and tender, and growing rapidly, the newest leaves are those most vulnerable to being eaten by insects and other herbivores. They also have not yet fully developed their photosynthetic apparatus, to capture energy from sunlight and convert it to food or usable energy for the plant, so they risk being damaged by this high-energy radiation.

The red color in these leaves is due to pigments that is designed to absorb harmful high-frequency radiation (like ultraviolet light and blue visible light). The pigment is red in color because it reflects red light, a lower-frequency type of radiation, less likely to cause cellular damage. This cultivar may have been selected to enhance or bring out the red color, much like a copper beech has been selected for the same reasons, but the same phenomenon is frequently observable in wild plants. Go out in nature and look at plants, and you will see a number of plants that have a reddish tinge to the newly sprouted leaves, that is not evident on the older, tougher leaves. Interestingly, many of these red pigments, such as anthocynanins, function as antioxidants, just like the antioxidants in tea.

In the tea plant, Camellia sinensis, caffeine is manufactured as a method to protect the plant against being eaten by insects. Large animals like humans can metabolize the caffeine, which is essentially a poison, but smaller animals like insects cannot, as it is too cumbersome to manufacture and carry all the enzymes necessary to metabolize caffeine and all the other chemicals the insect may be exposed to. This explains why tippy teas tend to be more caffeinated. This phenomenon also explains why many insects are specialized, eating only specific plants, whereas large herbivores like deer or elephants, eat a larger variety of plants.

Why are there ants on the leaves?

Let's take a closer look at the ants on these Camellia leaves:

These ants are tending aphids, small insects that feed off plant juices. The aphids exude a honey-like substance which the ants eat. In exchange, the ants protect the aphids from predators, and carry them for larger distances than they could easily walk. This is an example of symbiosis, a relationship that benefits both species.

Are they conspiring to exploit the plant? Not at all. Notice that the plant in this picture looks very healthy, and shows no evidence of any damage to its leaves. I have gardened for years, and observed this ant-aphid pairing on numerous plants, and I noticed that the ants not only tend the aphids, but they protect the plant from other herbivores. When ants and aphids take over a new plant, the ants clear out caterpillars and other critters feeding on the plant. The aphids only feed near the tip of the plant, on the tender, new leaves, and the strong ant presence here deters other herbivores from the part of the plant that is most vulnerable. The relationship benefits all three species, and is an example of a form of mutualism that involves more than just two species.

I have also noticed that aphid infestations are more likely to kill indoor plants, where there are no ants, whereas I have never seen them kill an outdoor plant; I can't help but wonder if the ants help to keep the aphid population at the optimum level for the plant's health.

What does this say about tea cultivation, and agriculture in general?

People often see insects on a plant, and think "it's an infestation, there's a problem", but this is not necessarily true. In some cases, having insects on a plant can be beneficial. Our modern agriculture has relied on brute-force "pest control" methods which destroy not only all the insects and other small animals around a plant, but often have other negative ecological impacts as well.

Tea was successfully cultivated without the use of any synthetic chemicals, for hundreds of years. Tea was discovered as a beverage, and tea cultivation was developed into a complex art, long before modern organic chemistry. Synthetic chemicals are not necessary to grow tea, and in fact, not necessary to eat any of the food crops that are part of the rich, older traditions of plant cultivation.

I would like to invite people to think more about ecological relationships in all aspects of your life. Look for them, and you will see them all around you. Even if you live in a city, you can see ecology all around you, in the relationships between the plants growing up in cracks in the sidewalk, the insects that eat them, and the birds that eat those insects. Ultimately, the more aware we are of ecology and how ecosystems work, the more likely we will be to make responsible choices and decisions that will lead to a sustainable future for all of us.

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