It all comes down to the photosynthesis equation. You might not like equations but this one keeps you alive, so it’s worth a little discussion. Photosynthesis is 6CO2 + 6H2O = C6 H12 O6 + 6O2. In common parlance that means 6 molecules of carbon dioxide plus 6 molecules of water create 1 molecule of carbohydrate and some oxygen.
Oxygen Is Mainly Produced by Plants
Photosynthesis produces 98% of the oxygen in the world. During the process of photosynthesis water and carbon dioxide are split and reformed with a remaining 12 oxygen atoms. Oxygen is always found with another atom so we refer to it as O2. If you look at a healthy pond on a sunny day you will see tiny bubbles rise and burst on the surface. This is oxygen produced by plants in the water. They are taking in carbon dioxide that is dissolved in the plentiful supply of water and giving off oxygen, some of which remains in the pond and is used by other organisms. The majority of the oxygen is produced by aquatic plants. In the oceans it is mostly algae, tiny photosynthetic cells pumping out oxygen.
The Role of Sunlight and Temperature
All photosynthesis requires sunlight. A light dependent reaction takes place which involves enzyme action in a specialized plant cell. Temperature is vital for enzyme action. All enzymes have a temperature range, and the photosynthesis enzymes cause a number of things to happen. Without discussing the complex biochemistry, the plant develops a transpiration pull, which moves water from the roots up to the leaves, where excess water escapes from pores called stomata. When it gets too hot, the plant cannot pull enough water from the roots, the enzymes stop working and the plant wilts. You can see this in a garden in the heat of the day. Most plants will perk up as it cools, but if the heat is too much and water is insufficient, permanent wilt will set in and the plant will die. No amount of carbon dioxide will prevent this happening.
Too Much Carbon Dioxide
As the levels of atmospheric carbon dioxide increase there are a number of factors that affect plants. Increased heat shuts down enzyme action and transpiration pull. However, it will not be too hot all the time so photosynthesis will occur rapidly as long as there is enough water and sufficient nutrients. In some cases it has been found to proceed too rapidly, creating plants that are large but without the dense plant fibers needed for support. In forests wood density and branching have been observed to change with higher temperatures and increased CO2. Tree rings are found to be spaced further apart and wood is not so strong.
As the Climate Changes …
Other factors affecting plant growth include earlier leafing in spring, which sounds like a benefit to a plant, but spring weather is unpredictable and a frost after the buds have opened will kill the first growth and could prevent fruiting for the year. Pests and diseases are moving both in latitude and in altitude, so plants growing higher on mountains and more northerly areas are being attacked by pests that usually affect plants in different regions. Changes in rainfall patterns produce droughts, which causes drought cracks in tree heartwood. We can still rely on the marine and freshwater algae though. Or can we?
Oceanic Change with Carbon Dioxide
The algae producing all that oxygen from the sea proliferate in colder waters where nutrients are plentiful. Climate change is warming the sea surface, down to about 700 feet. Photosynthesis, remember, needs light, so the algae are always near the surface. Another aspect is that carbon dioxide dissolves in the sea, and in rain water, which is partly why rainfall is slightly acidic. Rain is weak carbonic acid. As carbon dioxide dissolves in the oceans, helped by wave action, it is creating a more acidic environment. The amount of carbon dioxide absorbed by the oceans is increasing by about 2 billion tons a year, with a corresponding rise in ocean acidity of around 30% since the start of the Industrial Revolution.
How will the acidity affect algae and oxygen production? We don’t really know the answer to this. Our children and grandchildren will certainly find out.
Sally Anne Lewis - Sally has master's degrees in science and journalism, is fascinated to a degree in most things. Always something to learn.
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