When you think of microbes such as bacteria and fungi, what is your first reaction? What do you think when you see that moldy cheese or bread? What do you think when you consider them on your hands? Me too! I am a certified germaphobe. I am the person who washes his hands in a public restroom, hangs on to the towel, and opens the door with the towel. Those are some clean hands!
Though I support the clean hands principle, it is important to note that not all — but perhaps most — microbes are actually beneficial. If you are familiar with helper (“good”) microbes, you might think about those in your intestinal tract. Yes, we absolutely need those working properly. No question. But what about those types of microbes in soil? They are dirty little beasts, right? Well, not always, and perhaps not typically. In fact, what would you think if scientists explained that soil microbes are critical to our planet and its survival, providing you with free services such as clean and fresh water, nutrients in our food, and food for our forests and grasslands? What if they told you certain types are mandatory for plant growth and success? They control our atmosphere and even weather!
To get to the point, one special type of fungi infects most plant roots, and collectively, this organism interaction is known as a mycorrhizae (fungus-root). Though some may find it difficult to believe, most land plants rely upon these fungi and their hyphae (tiny root-like appendages) to access soil nutrients. Without the help of these mutualistic fungi, nutrients would be unavailable to plants and thus usurp plant growth and health.
In the scientific world of soil and ecology, it has been well shown that these fungi are critical to plant health. They can deliver phosphorus, and in some cases N and water to plants. It is thought that they do considerably more, however. Other micronutrients, for example, have also been studied, but it still remains uncertain whether these fungi aid in iron (Fe) nutrition.
Iron (Fe) is an interesting nutrient because its total concentration in soil is very high, often reaching several percent. It is, however, highly insoluble in water and not easy for plants to access. Borrowing from a famous quote from Samuel Taylor Colridge, “Fe, Fe is everywhere, but none for the plant to drink!”
Fe can greatly limit plant growth, and in the case of crops, greatly reduce Fe content. As we move to more sustainable food ecosystems, with less reliance on meat and more reliance on crops, Fe content in food becomes an important replacement. The problem is ever-more important in countries where land resources cannot support large quantities of cattle or other animals. Indeed, billions of people face the threat of low Fe in their diet, which leads to many health issues, especially among growing children, such as susceptibility to diseases, stunted growth, and permanent damage during brain development, which effectively lowers a person’s IQ. It is a particularly large problem during pregnancy.
Our study utilized a different approach to help show the potential importance plant Fe and mycorrhizal fungi. It is difficult to prove an idea in science, and so using different methods to support a similar idea is an important way to move closer to the concept of proof. In our experiment, we added available forms of iron to potato leaves and expected that plant Fe content would send a strong signal to the belowground roots to affect root microbes such as mycorrhizae. What was found, indeed, showed that very small quantities of a nutrient such as Fe inoculated on leaves resonated to root microbes, and this supported the idea that mycorrhizal fungi are an important mediator of plant Fe.
Follow-up studies by ourselves and other scientists are needed, of course. However, we are so confident about the importance of these fungi for plants and planets, that we are working on experiments to grow plants with and without mycorrhizal fungi in Martian soil. Why? Earth has an exploding population and a great need for food. Scientists widely acknowledge that earth has a carrying capacity. That is, give or take a few billion people and the right technology, at some point more people will not be supported without risking a worldwide population crash. Theoretically, birth rates could slow, but there is no evidence this will happen to the extent needed. Reproduction and development of a family is a foundation of our DNA. It is a bedrock of our past survival as a species.
To Mars, we must think. It is not science fiction, or at least it won’t be in the future, we hope. Though we do not plan nor wish to abandon our beautiful blue marble, making new planets habitable through terraforming will require plants and soil microbes like mycorrhizae. Not only do these two organisms have a major influence on earth’s ecosystems and atmosphere, but they will also be a critical foundation for terraforming and stabilizing the ecosystems and cycles of gases and water that will allow human survival on a new planet. First stop, Mars!
So how did we get from public restrooms, clean hands, and gut microbes to soil, mycorrhizae, plants, Fe and eventually human survival? That’s elementary: microbes and plants are the keys to human survival wherever we live. Be especially thankful for the helper (good) microbes. The next time you see one, likely wearing a white cowboy hat, give ’em a wink, and say, “I am rooting for you, little buddy!”