Oxygen

We breathe oxygen in and exhale carbon dioxide.

Plants are just the opposite.

​Well, mostly.

​Of course, there’s a lot more to it than that.​

The origin of oxygen

Most of the Earth’s oxygen was first produced by bacteria during the Great Oxygenation Event some 2.3 billion years ago. This was before plants existed. The bacteria responsible for originally oxygenating our world are called cyanobacteria. More commonly known as blue-green algae, cyanobacteria can perform photosynthesis. I suppose we could say that the oxygen we breathe started out as algae farts.

Photosynthesis splits water to release oxygen and fix carbon dioxide into sugar (Daniel Meyer) CC BY-SA 4.0

Abundant oxygen

Oxygen is the third most abundant element in the universe. We now have a lot of it here on Earth, though the numbers can vary. Oxygen currently makes up more than 20% of our atmosphere. You may be surprised to learn, as I was, that oxygen, in the form of oxides, makes up nearly half of the Earth’s crust and nearly 90% of our oceans. Oxides are molecules made up of at least one oxygen atom which is bound to some other element.

Oxides, such as iron oxide or rust, form when oxygen combines with other elements (Paulnasca) CC BY 2.0

Binding is common in the world of oxygen (O). Two oxygen atoms tied together form the dioxygen (O2) found in our atmosphere. Add two hydrogen atoms to an oxygen atom and we get water (H20). Add two oxygen atoms to a carbon atom and you get carbon dioxide (CO2). But I digress.

Plant respiration

We’ve all heard how trees provide us with oxygen, but that’s not as true as we once believed. We now know that 50-80% of the oxygen we breathe comes from marine plants and plant-like organisms. So the majority of our oxygen comes from plankton. Also, plants only produce oxygen when they are performing photosynthesis. At night, plants are using rather than producing, oxygen.

Plant respiration takes place through leaves, tree roots, outer stem cells, and root hairs. And respiration is more than just breathing. Respiration refers to any process within a living thing that uses a gas exchange to generate or release energy. When a plant is actively producing energy from light, carbon dioxide is inhaled and converted into sugar, and oxygen is exhaled. This is called the Krebs Cycle. Oxygen molecules are also used to break the sugars into usable bits. This is called oxidization.

Some plants reduce the amount of oxygen available to neighboring plants using tannins in a type of chemical warfare known as allelopathy.

Oxygen and decomposition

If your compost pile doesn’t have enough oxygen present, it will turn into a stinky, rotten mess, or nothing will happen at all. The microorganisms responsible for decomposition breathe air and drink water just as we do. This is why it is important to flip and moisten your compost pile regularly for it to break down into usable bits for your plants.

Oxygen in the soil

Dissolved oxygen in the soil is critical for healthy plants. Soil that contains a lot of dissolved oxygen tends to produce plants with significantly larger root systems. Larger root systems mean healthier, more productive plants. Pumping oxygen into your garden soil probably isn’t on your to-do list. But there are two things you can do to increase the amount of oxygen and other helpful gases in your soil: improve drainage and reduce soil compaction.

Compacted soil has less room for air and water (Kate Russell)

I hope that you will breathe deeply and enjoy the changing scents of your garden as we move through the seasons. And remember to give that compost pile a turn.