How ancient trees tracked their changing environments

Image: David Doran

Image: David Doran

A rare example of plant behaviour has been captured in amber, thanks to scientists using special technology to analyse organic fragments of a conifer pod dating back 200 million years. Researchers say it’s the oldest instance of tree “record-keeping” that they’ve been able to date.

The scientists used a technique called Raman spectroscopy to study over 5.8 million “record markers” of an ancient pine cone that they found in South America.

This single piece of DNA was capable of containing nine different chemical gradients, telling them how “loving” a plant it was, and how many fat cells it had.

Researcher David Doran, from the University of Florida, is fascinated by the extraordinary behaviour of trees in the past.

“Plants are weird,” he said. “We know more about the animal kingdom than the world’s plants, and yet we’re all deadly creatures.

“Trees in the Cambrian were incredibly flexible. They had this amazing ability to contort their growth, branch networks, molecular machinery and the size of their capillary structures,” he said.

Doran said finding this evidence of plant behaviour is a sign of our environment’s changing shape.

“Twenty million years ago, there was just one storm coming out of the Indian Ocean and then there was this huge reforestation around the globe. Trees had evolved in order to defend themselves from a single catastrophic flood, and if they were not saved then nature would do its best to help them in this extinct lifestyle,” he said.

“Now we’re seeing a different paradigm where we’re seeing trees adapting, and many dying, because of climate change. Plant evolution is really following the balance of land resources and climate change around the world. “

Doran said climate change could provide a future window into plant life in the past and make it easier to understand the relationship between trees and the environment.

“The search for fossil evidence is important for understanding how complex societies and ecosystems evolved,” he said.

“So knowing where, and what happened to these plants can tell us how people relate to the environment as the climate changed.”

Image: David Doran

The research, which will be published in the journal Scientific Reports, builds on previous research by Doran and colleagues at UVa.

Image: David Doran

Their analysis of white pine cones in the same amber revealed an incredible number of post-mortem pregnancies in the Cambrian, suggesting the plants had powerful reproductive systems and were able to encourage and allow normal plant growth in the context of changing environments.

In the new study, the researchers sought a certain extent of determination about the shape of the sexual appearance of the tree by analysing the spectres in which the plant’s DNA was mapped.

When the pigment produced by different parts of the plant was recombined, it could produce a “chromogenic sign” that indicated what kind of shape the plant took.

The team found a long list of possible post-mortem pregnancies, indicating an incredible level of sexual differentiation in the plant.

This would have been essential for sustaining normal growth if a male and female were going to mate.

The tree in the amber would have been a member of the genus Mahocephila, which was “fought over” by other trees of the same genus in the early Cambrian. It was larger than other Mahocephila plants and grew taller and wider in the early Cretaceous.

Most of the historic site was destroyed in volcanic activity, but the scientists hope they can still find new evidence for other species in that ash.

“We’re trying to identify what plant colonies once stood around this volcano and what plant territories those colonies could have held,” said Doran.

This research was supported by the National Science Foundation.

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