Plant roots built beachhead for life on land
Plants -- even relatively small ones -- played a crucial role in establishing a beachhead for life on land, according to recent work by an international team from China, the U.S., the U.K., and the University of Saskatchewan.
|A 410-million-year-old soil shows extensive rhizome traces of Drepanophycus, an early vascular plant |
related to modern club mosses [Credit: Jinzhuang Xue, Peking University]
Team member Jim Basinger, a paleobiologist at the U of S, explained that below-ground traces of plant life are not often preserved in the geological record since soils are prone to erosion and disturbance over time.
"Soils are subject to a lot of reworking by physical processes such as erosion and redistribution of sediments, as well as biological processes like invertebrates digging through them," he said. "Rather than protecting the remains of plants, soil environments actually promote destruction of plant remains."
The Yunnan site is doubly unusual in that evidence of both rhizomes and above-ground stems of the plant were preserved.
|Artist’s conception of early Devonian (ca 410 million BCE) riverside landscape with plant community |
dominated by Drepanophycus, an early vascular plant related to modern club mosses
[Credit: Zhenzhen Deng, Peking University]
"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 research team's findings are published the Proceedings of the National Academy of Sciences.
See also: Evidence from China shows how plants colonized the land
Source: University of Saskatchewan [August 30, 2016]