Because of this, they played a critical role in the formation of real soils and in changing the landscape of the land.
Researchers from China have carried out excavations in the southeastern part of their country and found there traces of roots of lymphoid plants up to 15 meters in length. Scientists believe that they could only achieve such a record length if they grew up, not down. It was their unusual orientation that allowed the first terrestrial plants to radically change the structure of paleosols and prepare the appearance of real soils that dramatically changed all terrestrial landscapes of the planet. The corresponding article was published in the journal Proceedings of the National Academy of Sciences.
Even 450 million years ago, the land was free of animals and plants. For their existence, animals needed a food base in the form of plants, and they could not live on solid land, where there was little water and there was no normal soil. The hard parts of the planet were covered with debris, devoid of humus and the ability to retain water for a long time after rains. River and rain flows in such conditions affected only the surface layers and did not provide full water erosion of the surface. Because of this, they carried less dissolved minerals into the ocean, which limited the biological productivity of marine ecosystems.
The emergence of the first vascular plants on land (420-410 million years ago) dramatically changed the situation. Essentially, the entire planet has gone through terraforming. The roots and accumulation of plant debris made the protosoil richer in nitrogen and more suitable for holding water. Plants have been instrumental in efficiently breaking down rock, accelerating water erosion and washing more minerals from continents into the seas. Finally, coastal and then terrestrial species of animals began to eat them.
All this dramatically changed earthly life, but the details of this massive land colonization are still unclear. One of the most difficult questions is how the first primitive vascular plants could significantly change the structure of soils - after all, their roots were shallow. It is not easy to grow to great depths in clastic rocks, and there were no nutrients at a depth then. That is, without deep roots, the appearance of protosoils and the colonization of land were hardly real. But deep roots cannot appear in plants without normal soils. The situation at the time resembled something like a vicious vicious circle.
New finds in southeastern China have helped solve this paradox. On sedimentary rocks 410 million years old, scientists have found traces of roots of great length - up to 15 meters. They belonged to a primitive lycopoid plant of the genus Drepanophycus (long extinct). Paleobotanists know to some extent the structure of these plants. Although the exact structure of the root system is unclear for them, its length never exceeded a few centimeters, despite the fact that they themselves were up to a meter in height. Why, in this particular area, centimeters turned into meters and why deep roots in the era before the appearance of real soils?
The researchers note that, judging by the geological traces of large-scale floods, this area was systematically flooded, it was a typical river floodplain. The water brought with it a suspension from sedimentary rocks and covered the local soil with each spill. As the new soil was applied, the parts of the roots far from the surface died off. The roots of Drepanophycus were forced to grow upward, otherwise they would be deprived of the opportunity to receive nitrogen compounds and water from the near-surface layers. Flood after flood, the roots grew up. At the same time, the parts far from the soil died off when the water left, and gradually were covered with soil, in which they decomposed very slowly. And closer to the trunk of the plant, the roots grew again. The dead fragments in the ground were constantly lengthening, reaching a total length of up to 15 meters. Moreover, at any given time, the length of the living part close to the trunk isdid not exceed a few centimeters.
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All these processes have dramatically changed the soil in the area. The dead fragments of roots that went lower and lower decomposed and supplied the lower layers of the soil with organic matter, and also allowed water to penetrate deeper downward, which accelerated erosion, and added dissolved minerals to the soil water. At the same time, an extensive network of roots mechanically linked the particles of clastic rocks and made the protosoil slightly more stable before wind erosion. Together, these factors contributed to the formation of new soils, more favorable for plant growth.