Oxygen

Plants use lots of oxygen. 45% of a dried plant consists of oxygen atoms. I Plants are not that much different from humans in that they need the same I fresh air as people do. Cell for cell, plant cells use similar amounts of oxygen as human cells do. In conditions where the air is poor or contains i less than 20% oxygen, plants will not do well.

The leaves have easy access to oxygen because they are making it and breathing it out as a by-product of photosynthesis. However, the roots struggle to find enough oxygen (in advanced gardens, most of the air for the roots is supplied aeroponically or with multiple aerators). lack of oxygen at the roots reduces root respiration, and this is one of the factors that shut down photosynthesis.

The health and vigour of a plant are dependent upon its roots getting I
enough oxygen. The plant can only grow as well as its roots allow and its
yield is totally proportional to root growth. I

Very cold fresh water can hold up to 0.0014% (14 PPM or 14 mglL) dissolved oxygen. Fresh water at room temperature can only hold about 0.0008% (8 PPM or 8 mglL) dissolved oxygen. Fresh water at 86°F (30oe) holds about 0.0005% (5 PPM or 5 mglL) dissolved oxygen. DO meters (dissolved oxygen meters) are available for measuring the amount of dissolved oxygen in nutrient solutions.

The oxygen directly from the nutrient solution is only 1 % of the plants needs, and nutrient oxygenation is not sufficient for any water culture. If the roots in water culture are not given most of their time for breathing air, they will soon brown and become sick.

Nutrient water is only a minor source of root oxygen. The main reason we oxygenate the nutrient mix with air pumps and stones is to kill off all the pathogens that can not live in air, called anaerobes. This method keeps the nutrient fresh for a long time. It is also the reason why we add hydrogen peroxide (H202) to the nutrient water.

Oxygen at the roots has another very important function. The oxygen changes the electrical charges in the water and nutrients, and allows the roots to extract water and nutrients with much less energy. For this reason, the roots need as much oxygen as they can get.

Aerated water will accept 0.0005 - 0.0008% oxygen and hold it for about 24 hours, which is a lot less than that available in air. This is why direct aeration of the roots (aeroponics) is better because it provides so much oxygen to the roots, the plant will actually grow a lot better.

Respiration Burning Sugar for Life

To oversimplify plant growth, imagine the plant using light and carbon dioxide all day to make and store sugar, then using the excess stored energy to continue building itself at night. Gardeners are always surprised when plants look bigger the following morning.

Plants respire 24 hours a day to stay alive both in the light and in the dark. Respiration to a plant is not quite like a human's, but it combines sugar with oxygen for energy just as human respiration does.

Plant respiration involves the splitting of a sugar molecule and combining it with an oxygen atom. Every glucose molecule delivers 36 energy molecules of A TP (read page 8S where photosynthesis makes ATP prior to turning it into sugar and starches). This is like a small fire in each cell that creates energy for the plant to use. Like most heat engines, the conversion to usable energy is only about 40% efficient; the remainder is given off by the plant as heat.

In the light period, plants will use oxygen slightly faster if there is a lot of oxygen available. Oxygen is usually not a problem to plants in the light periods because the leaves are constantly producing it (roots do not produce their own oxygen). The plants' internal oxygen comes from the leaves splitting hydrogen from the water (H20) molecule to make sugar (H6C606), and this in fact releases excess oxygen. The latest biosphere experiments show that a person can easily get enough oxygen to breathe from a few thousand plants, but only when the lights are on. When the lights go off, the plants have to use the air around them for oxygen.

In the dark period, plant respiration drops to a steady maintenance level. The plant does not want to use its stored sugars at night any faster than it has to. In this period, surrounding oxygen is vital because the leaves are not processing any. Plants must have fresh air at night. In the dark period,
respiration speed is not affected by oxygen levels, but rather by temperature.

Respiration rate is also growth rate and is temperature dependent. Each 18°F (1 QOC) temperature rise dou bles the plants' respiration rate. Faster respiration of warm roots releases more energy to build bigger and better roots and plants. Shortage of available root air at night slows root growth.