Plants

Carboniferous 360-300mya

Vascular Micro-aggregation Early Soils
Animals - Early & Late Oribatids Insect Origins

By the later Carboniferous, the full modern complement of overall vascular plant architectures was present. These range from small perennial herbs and shrubs to climbers to large trees including both woody and nonwoody forms. Forest canopies may have routinely been more than 20 m tall, and the tallest trees were at least 50 m tall.

"The Carboniferous represents a high watermark for vegetative disparity: Lycopsids, sphenopsids, ferns, and seed plants each produced trees of wildly different construction that were all important elements of forest canopies, and each dominated at least some environments." (Boyce & Leslie 2012) Modern trees are almost exclusively seed plants.

The color-codes show vascular plant lineages.

“Ferns” as used here is an aggregate of several lineages. (Boyce & Leslie 2012)

Digging Deeper

Can we work out which plants, and their rhizosphere, contribute in their various habitats to the evolution of early soils?

Sigillaria

This group rarely grew in the swamps, instead seemed to favour mainly drier, clastic soils which were alongside river channels. The leaf base pattern is distinctive, each being hexagonal in shape, and spiralling around the stem, but lining up longitudinally along the stem to form vertical rows.

Sigillaria have deeper and stronger stigmarian roots than other scale trees, to reach the deeper water table and anchor the plant. The tall trunks had almost no branches, except when cone bearing. It was straight, branching dichotomously at the top only at maturity. Here, the plant bore many leaves.

The cones broke up during water borne dispersal to other channel-side locations. This group is the only one where a cyclical reproductive pattern has been detected. The cycles were probably linked to wet/dry environmental changes to maximise successful colonisation. They are found fossilised with seed ferns. The latter are lower growing plants that would have formed an understorey in the plant structure.

Lepidophloios

This group, above all the others, provides the swamp lycopod that ended up as coal in the geological record. They were abundant in the peat forming environment, tolerant of long periods of standing water and low nutrient soils.

They are found fossilised in low diversity plant assemblages as the dominant genus, surviving in environments that precluded many other plants. They grew as a tall straight trunk, only forming cone-bearing branches at the top at maturity.

The cones broke up during dispersal and fell from the crown in sections called aquacarps. They had a leaf laminae as a "wing" to help wind dispersal, and then keep them afloat on the water until they were fertilized and able to develop and grow in new areas.

Sketch Section across Coal Measure peat swamp redrawn from Taylor et al 2009. See how the different zones produced different Early Soils

Paralycopodites

This group grew most abundantly in the transition from peat to clastic substrates - that could be MISS Dimichele & Bateman 2020

It is often found fossilised with seed ferns in Later Carboniferous.

It appears to colonise open, disturbed, nutrient rich areas that were probably not affected by long term flooding. It has been reconstructed as a small tree that produced opposing rows of lateral branches that were deciduous (they dropped off) and had numerous cones at the end.

Crown branching only occurred at maturity. Spores were released continuously over an extended life span, with re-colonisation assisted by water dispersal.

Lepidodendron

These plants grew on the edges of swamps, many that gave rise to coal. At maturity they developed cones (strobili) up to 40 cm in length on the ends of the crown branches which then shed male microspores and female macrospores into the waters below.
Recent work has led to the renaming of several species that were originally included in Lepidodendron into new groups called Synchysidendron and Diaphorodendron. Some on clastic substrate on mud, and others on margins of peat swamp

Synchysidendron

There are two species in this genus, S. dicentricum (formerly Lepidodendron dicentricum) and S. resinosum. Members of this group grew in swamps with clastic soils, only infrequently establishing themselves on the edge of a hostile peat swamp area. They had a thick cortex and could probably withstand long periods of flooding. They grew rapidly as an unbranched, leafy pole to exceed 35 metres in height, with some species then branching to form a crown with strobili, just once, before it died. The spores were released from a great height to be dispersed by wind and water.

Diaphorodendron

Members of this group all look very similar, but fall into two reproductive groups: polycarps, that produce cones many times in a lifetime, and monocarps, that produce cones only once, at maturity, just before death. Both are found in peat and clastic swamps. The polycarps seem to favour areas of infrequent and irregular disturbance, whilst monocarps attained large sizes, able to survive in disturbed areas for long periods. Monocarp forms grew to 30 metres tall as an unbranched pole-like trunk till the crown, and cones, formed at maturity. The polycarp forms developed limited side branches that later fell away. These bore a more limited number of cones, but cone production recurred several times over a lifetime.

Roots are abundant through all the palaeosols (from early Carboniferous,) from shallow mats and thin hair-like traces to sporadic thicker root traces typical of arborescent lycopods." (Kearsey et al 2018)

Stigmaria

Stigmaria are the roots, or undergound rooting structures, of extinct lycopod trees, including Lepidodendron and Sigillaria. These swamp forest trees grew to 50 metres and were anchored by an extensive network of branching underground structures with "rootlets" attached to them. Analysis of the morphology and anatomy of these stigmarian systems suggests they were shoot-like and so they are called rhizomes or rhizophores.
The stigmarian rhizomes are typically covered with a spiral pattern of circular scars where "rootlets" were attached. Since the stigmarian systems are shoot-like, these "rootlets" may be modified leaves, adapted to serve the function of roots. However, some paleontologists argue that the "rootlets" were true roots, with a complex branching structure and root hairs, comparable to the roots of the closest living relative of Lepidodendron, the quillworts (genus Isoetes). The stigmaria would have helped to create 'early soil’, catching particles, stopping mud moving and absorbing water and nutrients

Later Carboniferous

‘During the later part of the Carboniferous Period (Pennsylvanian), 318 to 299 million years ago, great forests grew on the land, and giant swamps filled low-lying areas. Usually when a dead plant or animal decays, microbes decompose it and combine its carbon with oxygen in the air to produce carbon dioxide (or swamp gas methane if anoxic fermentation) a greenhouse gas. But as great masses of dead plants became buried under swamps and out of contact with oxygen, the level of carbon dioxide in the atmosphere actually dropped. The world became cooler.

Several elements contributed to increased nutrient influx and eutrophication of the oceans, including enhanced weathering due to uplift during Variscon Orogony, the evolution of plants and phosphorus from volcanic ashes’. The production of volcanic ashh during the Variscon Orogony over a hundred million years , mainly in late Carboniferous and provided the elements plants need.

For much more

Upper/Late Carboniferous vegetation in Palaeozoic Palaeobotany of Britain 1996

Paleobotany: The Biology and Evolution of Fossil Plants By Edith L. Taylor, Thomas N. Taylor, Michael Krings

Volcanic

The most abundant elements found in volcanic magma are silicon and oxygen, so most ash contain a lot of silica. Low energy eruptions of basalt produce a dark coloured ash containing ~45–55% silica, often in iron (Fe) and magnesium (Mg). More explosive eruptions produce ash nearly 70% silica, while other types of ash are between these figures.

The principal gases released during volcanic activity are water, carbon dioxide, sulphur dioxide, hydrogen, hydrogen sulphide and carbon monoxide. These sulphur and halogen gases and metals are removed from the atmosphere by processes of chemical reaction, dry and wet deposition, and by adsorption onto the surface of volcanic ash. A range of chloride and fluoride compounds are readily mobilised from fresh volcanic ash, due to rapid acid dissolution of ash particles within eruption plumes.

Volcanic ash is a mixture of rock, mineral, and glass particles expelled from a volcano during a volcanic eruption. The particles are very small—less than 2 millimetres in diameter. Due to their tiny size and low density, these particles can travel long distances, carried by wind. They tend to be pitted and full of holes, which gives them a low density. Pitted and full of holes – it is ideal as base for aggregates. Along with water vapor and other hot gases, volcanic ash is part of the dark ash column that rises above a volcano when it erupts.

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