The most important part of the organism of each plant is not immediately visible and for this reason it is very often ignored. It’s about the roots.
The lack of knowledge of how the root system is constituted and the functions it performs, is the basis of most of the mistakes that are made in the management of plants and especially of trees.
If you ask someone to draw a tree, everyone will go to depict the trunk, branches and crown. Few will instead go to depict the root system and, if this is done, it will be represented in the most disparate forms and ways, as proof of a substantial ignorance of how a plant is actually constituted.
Types of root system
Let’s start by saying that the root system is composed of two main types of roots: anchor roots and absorption roots.
The anchoring roots depart from the base of the trunk in a specular manner to the branches from which the crown of the tree originates.
They are lignified exactly like the branches and are therefore made up for the most part of dead wood, since they mainly perform the function of physically anchoring the plant to the ground. It is therefore obvious how essential it is not to damage them by carrying out excavations close to the plant in order not to compromise the stability of the tree.
Even more important is to ensure that the root system has enough soil to ensure that the anchor roots can deepen and enlarge sufficiently.
At the base of many of the tree falls in the city there is just an insufficient space for the deepening of the anchor roots: too superficial roots due to layers of impermeable soil determined by the cementation and asphalting of the ground cause the plant to tip over because of extreme weather events.
The absorbent roots instead perform the function of providing the plant with the water and mineral elements necessary for its metabolism, taking them from the soil. In fact, the tree can be compared to a large pump that, due to the evaporation that takes place in the leaves, draws water from the roots attracting it upwards.
Water penetrates the younger roots (absorbent roots) as a result of a process called osmosis.
They are very thin and constitute a dense network that occupies a large part of the soil close to the plant, and at the end they are each covered with billions of tiny root hairs.
Absorbent roots have the ability to record a lot of soil data, such as the degree of humidity, the concentration of chemical elements, the acidity of the soil and others. They are then able to direct themselves where the soil can offer water and nutrients, until they extend far beyond the projection of the foliage.
The search for the best areas of the soil by the roots does not happen by chance or by default, but is based on the specific characteristics of the place where they live.
Interestingly, recent studies have clarified that the root system of a plant behaves in unison, acting like a widespread intelligence system. Each absorbent root, similarly to what happens in animal groups such as ant or bee colonies, is able to communicate with others through chemical signals and to coordinate a complex action such as the exploration of space in the subsoil.
Where are the roots located?
Having made the necessary distinctions among the species of plant in question, that allow us to distinguish between plants with taproots and plants with fasciculated root system, it can be said that the anchoring roots go deeper while the absorbent roots extend for a very large area, even greater than two or three times the projection of the foliage on the ground.
Contrary to what you may think, the latter are distributed mainly in the first centimeters of soil below the surface.
In fact, they are alive and like every living part of the plant they need air to breathe. Breathing is here understood for what it technically is, a chemical exchange between organism and environment that involves oxygen.
The absorbent roots and all the green parts of the plants need oxygen, so, beyond the natural shape of the different species, they will be located in a layer of about 50 centimeters deep, at most up to 80 cm below the surface.
Above all, here comes into play the type of soil in which the plant has to grow. In soils very permeable to air and water such as sandy ones, the absorbent roots will tend to deepen more, because they will go in search of water at greater depths without sacrificing the necessary presence of oxygen.
In less permeable soils such as clay, the root system will tend to remain more superficial.
In any case, even for large trees, most of the absorbent roots will be concentrated just below the surface. So it is clear that going to waterproof the soil will hardly make available the water and air that the root system needs, as well as rough interventions carried out on the ground will damage the absorbent roots present immediately below the surface.
What happens in the rhizosphere
A fertile soil is the prerequisite for healthy plants, and this obviously depends on the interaction between soil and root system.
The fertility of the soil is given by a sufficient supply of organic substance in the subsoil, and by the presence of microflora and microfauna that activate the transformation cycle.
The whole area of soil explored by the absorbent roots of a plant, called the rhizosphere, is rich of life and complex interactions between plants and animals.
Fungi, bacteria, annelids and other beneficial organisms, break down the organic substance by eating it. In this way they improve the physical and chemical properties of the soil and make the mineral elements available to plants. The soil will be well ventilated, with an optimal micro and macro porosity for the development of the root system of plants, and will have a balanced supply of nutrients.
Beneficial microorganisms play a strong antagonistic action against pathogens, of which they are natural enemies, and create symbiotic relationships with plants, such as mycorrhizae.
Mycorrhizae is the symbiosis between a fungus and the roots. The fungus penetrates inside the root in order to draw nourishment from it, or the complex sugars produced by the plant thanks to chlorophyll photosynthesis. At the same time, however, the fungus acts as an extension of the root, allowing the plant to reach unexplored soil spaces and absorb nutrients that it alone would not be able to assimilate.
Suffice it to say that thanks to the mycorrhizal symbiosis, the root system of a plant can extend over an area several times larger than the projection of the foliage on the ground.
Our task is therefore to bring organic matter to nourish life in the subsoil, and if necessary inoculate the microorganisms that inhabit the soil.
Finally, it should be remembered that the root system constitutes the largest reserve of nutrients of the plant. It is here that the plant goes to store in the form of starch all the surplus of complex sugars that it has produced in the spring and autumn, and then make use of it during the winter.
Therefore the roots constitute the primary source of supply of mineral elements and storage of nutrients of the whole organism of the plant.
The root system of plants is a complex system yet to be fully understood.
When we are faced with a large tree, let us not forget that a large part of its organism expands and lives underground. Only in this way can we respect it and take care of it.