Vascular

As the vascular plants evolved in the soil they were able to grow much taller. Flowering plants, angiosperms, came later and are now the most numerous of the modern plants. Insects probably came after the first terrestrial plants, The new environment was being colonised by trees.

The more you look, the more we have to find conditions where the minerals for growth are together, as without any of them plants cannot grow as they do. They need all at the same time to make roots, stems and leaves to capture energy for their growth. And most plants throughout the world use similar structures and processes. So what could supply all those materials? There is one substance that contains all those elements. Volcanic ash. A lot of it will be needed all over the place, if soil is to be created all over the planet. There were vast amounts of volcanic ash at this time with all the long lived orogonies. 

The plants evolved in the sandy beeches with the clastic covering, on the mudflats and in the swamps would all need volcanic elements to evolve new soil structures. We are seeing soil animals co-evolving with first vascular plants, in particular conifer-like plants. Some of the plant remains, and small soil animals could have got washed or blown away, and we saw the Geological Society said the oceans were being eutrophied by plant remains and volcanic dust. However, elsewhere soil could be starting to settle, as the currents declined and more water was held by the aggregates. Only then can plants take over the world. They needed a structure to grow in, water to pump up the plant and nutrients to feed them. The plants now also lived a longer time - years instead of months. Yet they have to acquire all their nutrients during this extended time from the same place - unless they are by some aquatic environment brnging them nutrients. So the fungi extending their reach and and the small animals mixing the nutrients would play a vital role in extending their lives - and the areas where they could survive away from open water.

Do you remember those questions Mike Benton was asking about the period around 400mya:“how on earth do you develop roots, and how is water stored and how do you obtain it” will emerge in this Period.  The only answer must be the co-evolution of soils that enable the vascular plants to function by providing support and nutrition throughout the roots. But how did they grow down? Presumably the substrates were hard to crack in many places, but the crashing and banging do on would open up such cracks and crevices.

“Plant growth and development largely depend on the combination and concentration of mineral nutrients available in the soil. Plants often face significant challenges in obtaining an adequate supply of these nutrients to meet the demands of basic cellular processes due to their relative immobility. A deficiency of any one of them may result in decreased plant productivity and/or fertility." (Morgan & Connelly 2013)

Two classes of nutrients are essential for plants: macronutrients and micronutrients. Macronutrients are the building blocks of proteins and nucleic acids and required in large quantities. Nitrogen, phosphorus, magnesium, and potassium are some of the most important macronutrients. Carbon, hydrogen, and oxygen are also considered macronutrients as they are required in large quantities to build the larger organic molecules of the cell, but are non-mineral. Micronutrients include iron, zinc, manganese, and copper, and are required in very small amounts, often in enzymes. These nutrients may be in the soil, but not always available to the plants. Plants may respond with changes in root growth or various methods of regulating uptake.

For instance, plants induce the activity of H+-ATPase, using ATP energy to pump protons out of the root cells and into the rhizosphere. This acidifies the rhizosphere and this drop in pH solubilizes ferric iron (Fe3+), making it more available for plant uptake.

When roots go down, they can employ a system call ‘Hydraulic redistribution’ or Uplift. This is the process by which plants can passively transfer water from deep, moist soil layers to shallow, dry soil layers. This water provides the plant with access to limiting resources (nutrients).

In order to support this sort of height, they needed a firm footing. We want concentrate on what was going on under the surface. While there have been signs of roots going back to 400mya, this was a period of rapid growth. Roots require phosphates and nitrogen for growth. This is widely recognised as these are two of the famous elements in most fertilisers – the N& P of NPK

A detailed study of sedimentary rocks in earliest Carboniferous seasonal wetlands of SE Scotland found “Roots are abundant through all the palaeosols, from shallow mats and thin hair-like traces to sporadic thicker root traces typical of arborescent lycopods." (Kearsey et al 2016) Just as we expected. But were there springtails too? Because of the possible significance of this period for rapid soil evolution, I asked one of the authors only to be told ‘Terrestrialisation went on for 100my’. I replied by asking if anybody had seen signs of springtails on the roots. I never got a reply. While some are pre-occupied with those animals that came on to the earth, I’m still curious as to those which created in the earth – and a lot happened at that time.

It seems that Archaeopterids which we saw in the Devonian period, spreading across the surface in this period was the main driver going deeper.

The increase in fallen leaves leading to a deeper litter would have led to an increase in Saprophytic fungi. These are free living fungi digesting dead debris, aerobically, are the largest group of fungi. Saprophytic fungi release enzymes to break down and digest the lignin, cellulose or chitin in dead matter into simple soluble compounds that can be absorbed by them, then by plants as nutrients. In so doing, they play a vital role in reducing the accumulation of dead organic. We see the fruit-bodies see on dead trees, leaf litter, animal bones, even faeces.

It seems that the weather conditions went from wet to dry and created cracks in soils. These would have opened up opportunity of roots to grow down, when creatures could follow them down, opening up new environments to create living soils as we know them. The trees did not just grow roots, they needed all sorts of factors to encourage growth downwards, as they cannot grow into rock, bacteria fungi, soil animals all evolve to fit the new conditions, and in so doing create new conditions too. The soil animals spread the bacteria and fungi.

Retallack starts his Chapter 10 ‘ Roots’ also pointing to soil growth and biogeochemical cycles: “As trees evolved from small early land plants some 370mya, they invigorated soil formation to produce novel kinds of soils, fertile clayey Alfisols, infertile clayey Ultisols, infertile sandy Spodosols and thick peaty Histosols. Enhanced and deeper weathering depleted atmospheric carbon dioxide to produce widespread glaciation.”