Wednesday, 31 August 2016

Evolution Planting Life on Land

A 410-million-year-old soil shows extensive rhizome traces of Drepanophycus, an early vascular plant related to modern club mosses.
Photo credit: Jinzhuang Xue, Peking University
Belowground rhizomes in paleosols: The hidden half of an Early Devonian vascular plant

Evolution and ecology are one and the same really because ecology is all about how species adapt and interrelate to form a complete system of interdependent organisms. Without evolution none of the interdependent organism could fit into their particular niche and compete with other organisms for resources. So, evolution created ecosystems and ecosystems drive evolution.

But in the early days of life on Earth, before life emerged from the oceans where it had first evolved and diversified, there was no ecosystem as such on land, so how did the first emerging life manage to eke out an existence and what reason did it have to go there in the first place?

Now scientists believe they may have found how an early plant, related to the club mosses, may have created its own ecosystem by interaction between its rhizomes and silt-laden floods. Rhizomes are underground stems by which many plants spread to form large colonies. Plants like this could have lived in shallow water prone to frequent drying so rather than them leaving the water, the water left them high and dry at times. It is but a small step then to spread out into 'dry' land prone to frequent flooding.

According to information provided by the University of Saskatchewan:

The team found that early in the history of Earth’s terrestrial biosphere, a small plant called Drepanophycus, similar to modern club mosses, was already deeply rooted. This kept soils from washing away and even allowed build up as the resilient above-ground parts of the plants caught silt during floods. These plants – typically a metre long at most – helped form deep, stable soils where other plants could thrive.

“Rhizomes have been around for a long time, but their role in stabilizing sediment has not been recognized, since they have generally been assumed to be shallow or surficial,” Basinger said, explaining that the Yunnan paleosols show rhizomes extending deeply into the soil – something that was assumed to have not happened until much later, when trees appeared...

“This effect was a feature of rhizomes of small and non-woody plants at a time early in the colonization of land,” Basinger said, adding this would have paved the way for more complex forest ecosystems to follow.

These ancient groves would have looked quite alien to modern eyes. Drepanophycus was a lycopsid, one of the oldest lineages of land plants. Descendants of these early lycopsids grew many metres tall, covering vast tracts of land and sharing the landscape with tree ferns and primitive woody plants to form early forests, long before forests familiar to us would evolve. Lycopsids live on today as the diminutive club mosses.

The team of paleobiologists from Peking University, China and the University of Saskatchewan, examined red stone formations from the Xujiachong Formation of Yunnan, China which is derived from early sediment laid down some 410 million years ago. Their findings were published in PNAS a few days ago

The roots and rhizomes of early vascular plants, and their interactions with soils, are poorly documented. Here we report on the complex, belowground rhizome systems of an Early Devonian plant, and their contribution to the formation of the earliest record of rooted red-bed soils in Asia. Our specimens predate the earliest trees with deep roots from the Middle Devonian by 20 million years. We propose that plant rhizomes have long functioned in terrestrial ecosystems, playing important roles in shaping Earth’s environments by reducing soil erosion rates and thereby increasing the stability of land surface and resilience of plant communities.

The colonization of terrestrial environments by rooted vascular plants had far-reaching impacts on the Earth system. However, the belowground structures of early vascular plants are rarely documented, and thus the plant−soil interactions in early terrestrial ecosystems are poorly understood. Here we report the earliest rooted paleosols (fossil soils) in Asia from Early Devonian deposits of Yunnan, China. Plant traces are extensive within the soil and occur as complex network-like structures, which are interpreted as representing long-lived, belowground rhizomes of the basal lycopsid Drepanophycus. The rhizomes produced large clones and helped the plant survive frequent sediment burial in well-drained soils within a seasonal wet−dry climate zone. Rhizome networks contributed to the accumulation and pedogenesis of floodplain sediments and increased the soil stabilizing effects of early plants. Predating the appearance of trees with deep roots in the Middle Devonian, plant rhizomes have long functioned in the belowground soil ecosystem. This study presents strong, direct evidence for plant−soil interactions at an early stage of vascular plant radiation. Soil stabilization by complex rhizome systems was apparently widespread, and contributed to landscape modification at an earlier time than had been appreciated.

Jinzhuang Xue, Zhenzhen Deng, Pu Huang, Kangjun Huang, Michael J. Benton, Ying Cui, Deming Wang, Jianbo Liu, Bing Shen, James F. Basinger, and Shougang Hao
Belowground rhizomes in paleosols: The hidden half of an Early Devonian vascular plant
PNAS 2016
113: 9451-9456.

The interesting things about this find is that it is the earliest evidence of extensive vascular plant colonisation and even at that early time the root and rhizome structures were already well adapted being up to a metre long and penetrating deeply into the soil that they had probably help to create. This may have been the earliest formation of extensive flood plains onto which other life forms such as worms and arthropods could then move. It is also significant in that it is rare for plant remains in soil to be preserved this well. Soils is biologically active and subject to rapid erosion, so plant remains tends not to survive.

Biologically this is interesting in that it shows how first plant, and then animal life could have colonised an otherwise barren land in stages, building and creating ecosystems as it did so.

Imagine the struggle a dedicated creationist fraud or ID hoxer is going to have explaining how this find fits in with the daft notion that everything was created as is in a few days! Why are there no worms in the soil, no bones of mammals, reptiles or birds, no tree roots or flowering plants, in fact, nothing at all apart from traces of this primitive clubmoss, exactly matching how scientists believe the land was colonised and the order of evolution of the plants we now see.

That's the things about evolutionary biology; newly-discovered facts like this always fit neatly into the scientific explanation like a hand into a glove, and they inevitably look completely out of sync with ancient creation myths based on the ignorant guesses of people who knew no better. This is why people who value truth and base their opinions on verifiable evidence don't agree with creationism.

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