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What Is Apical Dominance?

Auxins are hormones found in plants that cause shoots to grow toward light and roots to grow away from light.
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  • Last Modified Date: 15 July 2014
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Apical dominance is a phenomenon seen in plants in which a central stem becomes dominant, growing faster than other stems and secreting hormones which inhibit stem growth below the terminal bud at the end of the apical stem. A number of plants and trees exhibit apical dominance, with fir trees being a classic example. The distinctive triangular shape of the fir tree is the result of apical dominance, with the trunk of the tree being the apical stem.

There are a number of reasons why plants adopt apical dominance. By pouring energy into a central stem, plants can achieve height quickly, which increases their access to nutrients and also helps the plant block competition. This phenomenon is also exhibited in rooting systems, where apical dominance results in a long, very strong taproot which keeps the plant firmly anchored in place, unlike a fibrous root system, which can make the plant unstable in some soils.

The terminal bud on the apical stem secretes the hormone auxin, which blocks growth in lower stems. If it is removed or the circulation is inhibited, other stems below will start to shoot up, and one may in turn become apical. Apical dominance can also be seen in branches; branches which grow from the main stem will in turn inhibit the growth of smaller branches from stems along their length.

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Gardeners can manipulate plant shape by removing terminal buds. Doing this promotes a bushy, shrublike growth habit with a number of spreading branches, none of which becomes dominant. This look may be desired for some trees and plants, and gardeners can use pruning and other manipulative techniques to force plants to grow in a particular way. It is important to identify the terminal bud for removal if the goal is to create a shrubby growth.

In trees and plants which lack apical dominance, growth tends to take on a more chaotic and less controlled appearance. The branches will sprawl, and many will be the same length or very similar in length because no stem is dominant. Tomatoes are an example of a plant which does not exhibit apical dominance, with all of the stems growing at more or less the same rate. These plants tend to grow out rather than up, sometimes requiring support for their spreading branches, as they are designed to eliminate competition by spreading out to create a cleared area all their own.

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Emilski
Post 5

The woman who lives beside me has some beautiful rose bushes that are the envy of the neighborhood. They at least have me envious.

After seeing her pruning them several times, I asked her what the purpose was, and she explained that by clipping certain buds, she could control their shape and size. Whether she knew the science behind it, now I know that she was talking about clipping the apical buds and controlling the auxin levels.

Anyone who has gardened will know that vegetables like cucumbers and squash tend to take a vine-like form. Is there a term for the form plants like cucumbers and ivy take that sprawl across the ground?

cardsfan27
Post 4

I live in Kentucky where ice storms are a regular occurrence in the winter. Several years ago, we had a major ice storm that broke out the tops of most of the trees in our forest.

If anyone has ever seen something like this happen, it is easy to see how a tree responds afterward. Instead of having their normal shape, most of the trees are now starting to grow in all directions to make up for the lost limbs.

jcraig
Post 3

@matthew23 - I have a pine tree in my yard that I would call more bushy than triangular. I'm not sure where the cutoff point is, since all trees would have a certain amount of apical dominance since they don't necessarily spread out along the ground like the tomato plant mentioned.

Does anyone know if there are any other hormones besides auxin that go into what shape a tree has?

matthewc23
Post 2

I guess I have always taken for granted how much effort went into a tree having the shape it has. The example of a tree with apical dominance was a fir. Do all evergreens have apical dominance, and are there any deciduous trees with the same characteristics?

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