vendredi 25 décembre 2015

63- The soil -2- Roots


A few weeks ago, National Geographic published a nice article "Digging deep Reveals the intricate world of roots", written by Becky Harlan.
The studies she speaks about concern herbaceous perennials, and have both a scientific objective, studying roots development and their exploration of the soil by Dr. Jerry Glover of the Land Institute in Salina, Kansas, and an artistic and didactic purpose demonstration by photographer Jim Richardson.

Dr. Jerry Glover washing roots with a soft water jet, no to break any root (photo Jim Richardson)

I recommend the reading of this article, if only to admire all the amazing photos of whole root systems. The hidden part of plants is really spectacular.

Note, however, that these photos are not really representative of the natural architecture of the roots. In fact, both for the purposes of the study and for the purposes of the photographer, plants were grown in large PVC tubes as a vase, without particular difficulty or competition. Obtained root systems are a kind of ideal potential, quite usable by both the scientist and the artist. In nature, the difficulties (heterogeneity of soil, pests, climate problems, various attacks, competition with other plants) would have given root systems probably very different. What doesn't remove absolutely nothing from their beauty and usefulness.

It is very interesting to observe that finally, the plant looks like an iceberg, the largest part is not seen.
Roots are prospecting the soil for feeding the plant, and are able to descend to unsuspected depths, if the soil permits.
Photo from the article of National Geographic

The deepest known roots are those of a wild fig in the Transvaal, South Africa, down to 120 meters deep, and those of an English elm 110 meters. One winter rye plant can produce 623 km of tiny roots. The most extensive root system known to date is that of a trembling aspen of Canada, which covers 43 hectares, and weighs 6000 tons. In other words, this tree is at the center of an area occupied by its own roots of about 750 meters in diameter!!! (Source of this information: )

The roots world is unsuspected and fundamentally important.

Because roots have diverse, numerous and fundamental roles in soil life and ecosystems in general.
Some of these roles are well known, others less so.
- Anchoring plants. This allows them to withstand wind, rain, erosion.
- Feeding plants. This is from the roots the plants collect most of the water and nutrients they need.
- Body of survival. Many plants (not all though), are able to recreate their aerial part from their root system, following a fire, frost or certain external attacks.
- Soil Stabilizer. The presence of very dense root lattices can stabilize the soil and reduce or prevent erosion. Deforestation often results in desertification by disappearance of the most fertile and stable part of the soil.
- Structuring soil. Root prospecting products galleries which, when the root dies and disappears serves to aerate the soil, for movement of water, for movement of soil microorganisms. This role allows, for example, improve biodiversity and carbon storage.

The life of a root in the soil is far from a cakewalk. It will undergo all kinds of aggressions, due to climate (frost, floods and asphyxia, drought and breaks by soil cracking) due to rodents, disease, insects, and nematodes. Whenever a root will be amputated, the plant will fight by producing another. Its survival involves the permanent regeneration.

Roots do not all have the same role in the soil. One can distinguish in particular
- Superficial roots often extremely fine and numerous, closely connected to the aerial part of the plant, responsible for absorbing nutrients released by the mineralization of organic matter, which is generally produced in the first 40 centimeters of the soil,
- Deep roots, connected to large roots that descend to great depths of the soil, loaded particularly with water supply they will look as deeply as necessary.

Agronomy has traditionally widely studied the mode of penetration of nutrients from the soil solution within the absorbent hairs, these billions of tiny roots which play a major role in the life of the plant. So we know relatively well the root relationship with its mineral environment.

What we know by cons very wrong is the relationship of the root with its biological environment. I spoke recently about the relationship between nitrogen-fixing plants and rhizobia in mutual benefit. I will tell you one day about mycorrhizae, these microscopic soil fungi that live in symbiosis with plants, using the benefits of photosynthesis, in exchange for a transformation of soil phosphorus that the plant is struggling to absorb alone.
There are very many other microorganisms in the soil, whose interactions with plants are not known. They nevertheless play an unknown but probably very important role, both in the life of soils and plant life.

This is very good news, to learn that several American scientific teams will receive significant funds for research on these relationships, working on switchgrass (Panicum virgatum).

This perennial grass, native to North America, long considered weed, largely eliminated to make way for maize and wheat, and with a very strong root system, represents an interesting potential crop for the future. It is a large consumer of carbon, and a plant whose potential is biomass and animal feed, with the ability to grow on marginal land. Its very great development provides significant volumes of crop with few resources.
It falls into the category of perennial grains that could find a new place in the agriculture of the future, consuming less water resources, nutrition and fertile land.

In short, in years, we'll know a little more about these interactions. These findings certainly deeply influence agriculture in its management of soils, water resources and plant nutrition.

Picture from  Michael Halbert

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