PLANT GROWTH & PHYSIOLOGY. (Part 5)

There are three classes of plants. Each of these classes metabolize in a different way. The first class are succulent plants called CAM. These plants like low light and high humidity levels and so thrive indoors, in bathrooms and kitchen areas.

The second class of plants is called C4. These plants grow in hot arid regions and are very efficient at using both Carbon Dioxide (CO2) and Sunlight. Most C4 plants are grasses.

The third and last class of plants are called C3. These plants join two 3-Carbon atoms together to produce sugar. The chemical formula for sugar is C6H12O6 which is 6 Carbon, 12 Hydrogen and 6 Oxygen atoms stuck together. Most of our favourite plants are to be found in this class.

HOW DOES A PLANT WORK?

Like all living things, plants breathe 24 hours a day. In order to make energy each plant cell respires (converts plant sugar to energy). The plant uses Oxygen (O2) and expires, or breathes out, Carbon Dioxide (CO2).

In the same way that energy moves around the human body, so water, nutrients and plant sugars are continually being transported around the plant body. The leaves create a circular flow with the roots. This circulation occurs when the leaves draw up, water from the roots, through their Xylem.

These are straw like cells found in the plant stem. The water continually evaporating from the leaves sucks up more water from the roots and creates the internal water pressure that keeps the plant rigid. Thus if the plant is deprived of water, as in a drought, it loses its rigidity and begins to wilt when the internal pressure drops.

The leaves return energy to the roots in the form of sugar solutions. These are transported from the leaves via the plants Phloem. These are also straw like cells found in the plant stem. In this way the leaves exchange sugars for water and nutrients, while the roots exchange water and nutrients for sugar solutions. This liquid circulation is constant and continuous throughout the life of the plant.

THE MAIN PLANT PARTS.

The 3 main parts of a plant are the Roots, the Stems and the Leaves. Each of these parts is of great importance and any problem that arises in any of them will be a major one. The most sensitive part is the roots, as well as being the most difficult to see should a problem occur.

The Roots:

The miracle of growth starts at the roots. As already mentioned, roots transport nutrients up to their leaves and plant sugars are returned by the leaves. The roots also act as storerooms for the excess sugars that are produced by the leaves. These sugars are stored in the form of starch. The size of the root ball and therefore the amount of starch that can be stored, determines the success of the plant in terms of growth and productivity.

The size of the root system is directly affected by the amount of moisture, the temperature, the available Oxygen and the supply of plant sugars being transported down from the leaves. According to Graham Reinders, in his book How to Supercharge Your Garden, a research Rye plant in a 12 inch pot was said to have had 14 billion root hairs. These hairs would have stretched 6200 miles (nearly 10,000 km) if placed end to end and covered an area of 180ft by 180ft (about 55m by 55m). The greater the root system is the more energy (starch) it will be able to store and so, the more nutrients it will be able to send up to nourish the leaves. The plant will then have the capability to grow stronger. The end result of this is that the leaves will be able to pass more plant sugars back down to the roots and so the cycle continues.

Another factor to be taken into account is the root medium. Plants take their nourishment from the medium surrounding their roots. It stands to reason that the less energy the plant has to expend in order to get that nourishment the more energy it will have available to use for growth and nutrient exchange with its leaves. Because a plant takes most of its water in via its roots, (the root hairs trapping the water molecules surrounding it) and transpires about 99% of that water out via its leaves, it will wilt and fall over if its roots cannot extract enough water out of its surrounding medium.

A plant growing in the ground will take its moisture from the surrounding soil. This moisture normally gets into the soil as rain and the plant absorbs that rain and the nutrients that have dissolved in it, via its root hairs. After the rain has stopped the topsoil quickly dries out as the water filters into the ground. Because of this drying out the plant has developed a means of absorbing Oxygen via its upper roots. The top third of the roots become specialized as Air Roots while the bottom third becomes specialized as Water Roots.

It is vital to ensure that the Air Roots are not kept constantly wet as this will result in the plant drowning. The Water Roots however, may be kept wet all the time, providing that the water has sufficient Oxygen dissolved in it. Insufficient Oxygen will result in roots with brown, discoloured root tips and subsequent infections. Healthy roots are a crisp, white looking structure.

The plant is quite capable of healthy living with the roots exposed to light as long as they remain moist. However, light will encourage the growth of Algae which will cause odours. The Algae will also compete with the plant for Oxygen during the dark periods and nutrients in the light ones. This, of course will mean the plant has to work harder in order to produce sufficient sugars for its needs. The Oxygen produced during the dark periods is used to help the roots convert these sugars, from the leaves, into energy (Starch).

Copyright (C) 2004, 2005.
J R Haughton. ITEC MIPTI
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