Soil is one of the most fascinating aspects of our garden and landscape ecosystems with some outright amazing qualities that are often unnoticed.
It’s the medium that provides plants space for roots to expand in search of water and nutrients, two of their most vital requirements for life. In the natural world, it is one of the best recyclers, capturing terrestrial resources such as dead plant parts and returning them to the plant-available nutrients they originated from through a complex system of microorganisms and chemical processes.
So many of these amazing qualities are unseen by human eyes and become overlooked for the more tangible things we can experience, such as texture or organic-matter content.
Soil microbiology is something that has fascinated me for many years, sparking interest as I learned of the intricate relationship between plant roots and soil fungi, called mycorrhizae. In this symbiotic, or mutually beneficial relationship, mycorrhizae infect plant roots in search of the energy that plants produce from the sun, since fungi are unable to photosynthesize. In return, the root’s ability to take in water and nutrients is enhanced greatly by the fungus. This relationship has been identified in soil ecosystems around the globe and serves as an incredibly important co-evolved partnership that in some cases becomes essential to plant life.
However, mycorrhizae are just the beginning of an incredibly complex and interesting soil ecosystem filled with equally fascinating fauna that do many things for both plants and humans. In recent years, research has uncovered more and more of these complexities, making them more and more comprehensible to us in our daily lives above ground.
Almost 30 years ago, the “Hygiene Hypothesis” was developed from research that identified an increasing incidence of autoimmune and allergic diseases presumed to be the result of decreased exposure to microorganisms in the environment.
As human populations have become more urbanized, removing us from the environment of many microorganisms, and as we have become better at disinfecting everything around us, we have removed many of these organisms from our lives, some of which are actually beneficial.
The lack of exposure from these microorganisms, especially in childhood, can lead to changes in the way our immune system develops, resulting in a higher occurrence of certain diseases. This relationship has been explored, with fascinating results, by comparing human populations in developing countries, which have contact with a greater diversity of microorganisms, to populations in the developed world, which lack exposure.
The “Old Friend Hypothesis” was developed in the early 2000s to address unanswered questions from the “Hygiene Hypothesis.” This newer line of thinking explores a co-evolutionary dependency between the human immune system and microbes around us. These “Old Friends” are beneficial microorganisms that have been present since our days as hunter-gather societies, influencing development of our immune systems. Since many are present in soils, close contact with the soil around us lead to regular human exposure in ancient times.
In return, we have also influenced their development over the past 10,000 years or longer, creating a mutually beneficial relationship that we have begun to unintentionally dismantle as we become more separated from so many aspects of nature.
Soil mycobacteria are one example of an “Old Friend” that many humans may have lost contact with. Recent studies have focused on the beneficial effect from exposure to a naturally occurring soil bacterium called Mycobacterium vaccae. It has been shown to reduce stress for both humans and mice. Since it occurs in a wide range of soil conditions, it’s easy to get a dose of the beneficial microorganism from your average garden soil.
Although it is certainly still important to follow the basic recommendations for personal hygiene, such as regular hand washing, low doses of the beneficial microorganisms have the potential to boost our health in ways we are only beginning to understand.
So the next time you get your hands dirty in the soil ecosystem of your garden, add exposure to M. vaccae to the long list of ways that gardening keeps us healthy.