The World of the Infinitely Small: Life on Plants

Did you know that everywhere in the world, on practically every surface, there is life? Even if you can’t see anything, even if you’ve applied disinfectant, there’s life! And that’s just as well, because these tiny organisms have a huge influence on their environment, especially in plants!

Microbiota: a very, very small world

What are these “intruders” that we can’t see? They are microbes, fungi, bacteria, viruses, protists and prokaryotes.

Forget the button mushroom! We’re talking yeast, and some of these tiny things are even unicellular. That’s right, some living organisms are made up of a single cell. That’s how small they are!

Oh, sure, there are some single-celled organisms big enough to see, but the majority are microscopic. Have you ever seen a virus? Probably not with the naked eye!

All these organisms have very important roles to play: breaking down matter, cleaning up impurities, transforming molecules and so on. Obviously, the microorganisms that live in the earth are not the same as those that live on your face: they all have their own role and specific habitat.

When we speak of the microbiota, we mean all the little organisms that live in a given place. We hear this word more often in an organ context: “intestinal microbiota” is the word par excellence for selling probiotics. It sounds just scientific enough to be impressive.

But today, I’m talking about plant microbiota. Life on leaves, in leaves. Life on trunks, in the soil… In short, nature’s microbiota.

Every Environment Has Its Microbes

There are undoubtedly billions of species of microorganisms. But with the increasingly efficient methods available to us, particularly in DNA analysis, we’re gaining a better understanding of this mysterious world. Not only can we detect it, but we can also understand the role of these microbes.

Research shows that from one plant to another, the microbiota changes enormously. A maple tree and a birch tree will not have the same microbes. And from one city to another, from one continent to another, it’s just as changeable. There could, for example, be a very high concentration of one species of yeast on one plant, a wide variety of yeasts on another, or a great diversity of yeasts, bacteria, etc., on another plant!

In addition to plant species and their origins, there are many other factors that influence microbiota: temperature, exposure to the vagaries of the weather, air quality, human presence, and so on.

Imagine the soil microbiota in a field: lots of microbes living on and in the roots. If the soil is ploughed, there will be less life: the disturbance caused by ploughing makes survival and reproduction difficult. If the soil has been sprayed with fungicides, protists and bacteria may proliferate more than if they had been in competition with fungi. If it’s a soil where a monoculture of the same plant has been growing for twenty years, diversity will be very low.

In short, many factors influence this tiny, fragile world. An organism may be beneficial in small quantities, but harmful if it proliferates too much.

Sometimes, when we notice that something is wrong with our plants, it’s actually the microbiota that’s wrong. We give fertilizer, apply pesticides or repot, and everything falls into place: the little world that lives on, in and around your plant has been restored, without you even knowing it.

The Role of These Microbes

Some plants have co-evolved with microbes and share the benefits of their association with them. For example, members of the large Fabaceae family (which includes, among many others, legumes) form an association at root level with bacteria of the Rhizobium genus. This association enables beans, clovers, alfalfa, etc., to develop nodules on their roots and gain access to a form of nitrogen in the soil that is not normally available to plants.

Some orchid seeds, including vanilla, germinate only in association with a fungus of the Sebacina genus. Mycorrhizal fungi are also useful microorganisms.

These are well-known examples, but there are many other less studied or more passive interactions. Microbes, particularly at root level, have different roles and effects. Some make certain molecules available, while others stimulate growth by producing nutrients. Some protect plants from infection or disease, while others enable them to survive drought.

Not only do mycorrhizae help plants develop a larger root system, but did you know that they also store carbon? Yes, a useful double role! And that’s not all: in the leaves, there are microbes that have a positive effect on photosynthesis!

The role of microbes is very diverse, but all together they contribute to the growth and survival of plants… And to the general well-being of the environment, when you think about it! These little friends are like bonuses added to plants. (Of course, there are some less “friendly” microbes, but it takes all kinds to make a world!)

Plants: A Collection of Organisms?

Some researchers see plants not as individuals, but as groups of organisms. It’s both an interesting and strange point of view… But it’s probably not totally wrong!

Many plants, whether it’s your landscaping, wheat in a field, a tree in the forest or your tomatoes, won’t survive in an aseptic environment. Remove everything that lives on the plant and… it will die! Maybe slowly, but certainly. It will lack water, nutrients, it will get sick, its leaves will abort, in short, it will miss a lot! It can’t live without all these associations.

So it’s logical to say that a plant is a whole, a community, isn’t it?

Well, if we stick to that logic, we can say the same thing about ourselves! Because humans have a whole host of microbes on and in their bodies that keep them alive.

You know, in the vast world of living things, everything is interconnected: each living thing depends on the others. I often repeat that life wants to live: the various associations with plants are a good example. Short of phosphorus? Why not team up with a fungus capable of fetching it?

I hope I’ve tickled your curiosity and made you realize what’s going on in the unseen under our eyes. Take care of your microbiota: washing every leaf of your plants with vinegar can be a real nuisance when you think about it!