Archaea

Today we are going to delve deep into the soil under our feet and talk about something you will probably never see.

Discovered in 1977, archaea [are-KI-ah] used to be classified as bacteria and were called archaebacteria. Scientists now know they are their own group. Their name means “ancient things” and they are believed to be one of earth’s oldest life forms, first occurring some 3.8 billion years ago.

The many forms of archaea (Maulucioni) CC BY-SA 4.0

Archaea are completely new to me. But it ends up they are very important to soil and plant health, so let’s see what we can find out.

Classifying life

In the world of living things, there are three basic groups: eukaryotes, bacteria, and archaea. Eukaryotes have nuclei and organelles. Bacteria and archaea do not. Archaea and bacteria are prokaryotic. Prokaryotes are primitive, single-celled organisms with no organelles or nucleus. Archaea are slightly more complex than bacteria, but not by much. Simple as they may be, there are more bacteria and archaea in the soil than any other microorganism and they are critical to nutrient cycling.

Archaea are found pretty much everywhere on Earth, including some pretty extreme environments. These microscopic beings can tolerate hot springs, salt marshes, and even deep, frigid ocean environments. Some species live inside of plankton and termites, as well as in our guts and on our skin. In fact, archaea make up 10% of the microbes in our digestive systems, but I digress.

Archaea found in volcanic hot springs (Jim Peaco) Public Domain

Types of archaea

Archaea come in several shapes and sizes. There are flat archaea, square archaea, and cylindrical archaea. Archaea can range in size from 0.1 micrometers (μm) to 15 μm. For perspective, an American dime has a diameter of almost 18,000 μm.

In some cases, archaea will form chains that can be 200 μm long. These chains form biofilms. Scientists are unsure about why these chains form, but many believe that they facilitate communication and nutrient exchanges, much the way other soil microorganisms work to share nutrients with nearby plants.

Archaea feeding

Archaea are classified by what they eat. These nutritional groups choose from an extensive menu. There are phototrophic archaea that use sunlight for food. Other archaea break down inorganic minerals such as carbon and sulfur for food. Yet other archaea eat sugar, ammonia, and even hydrogen gas. [I guess when you’re as small as they are, a molecule of hydrogen probably looks like a potato chip.]

As they feed, archaea become major players in nutrient cycling. They fix atmospheric nitrogen in the nitrogen cycle, make sulfur available to plants in the sulfur cycle, and are essential to decomposition and the carbon cycle. Put simply, without archaea, many plants would starve.

Nitrogen fixation

Plant growth is most often limited by insufficient nitrogen. There’s plenty of nitrogen floating around in the atmosphere, but plants can’t use it in that form. Instead, atmospheric nitrogen needs to be “fixed” into compounds, such as ammonia, that can be used by plants. Archaea help fix that nitrogen.

While bacteria and fungi can cause several garden variety diseases, archaea are not known to be pathogens or parasites. On the contrary, they tend to be very helpful wherever they are.

So what can we, as gardeners, do to protect and provide for these microscopic helpers?
 

• Avoid using chemicals that can disrupt natural processes.
• Avoid using unnecessary herbicides, insecticides, and pesticides.
• Add organic material to your soil through top dressing and mulching.
• Only apply soil amendments as indicated by a lab-based soil test.

Now you know,