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mass extinctions

How certain plants survive mass extinction events: study

How certain plants survive mass extinction events: study

We often read about Earth’s mass extinction events and how they wiped out vast numbers of animal species, leaving survivors to evolve and repopulate the planet. But it’s rarer to hear about how plants managed these catastrophes.

A new study published last month by a team at University College Dublin, Ireland, in the journal Nature Plants shows how plants with thicker, heavier leaves were more likely to survive the Triassic-Jurassic mass extinction caused by an episode of global warming 200 million years ago – around the time when dinosaurs came to dominate the planet. The extinction event is known to have had a massive impact on life, both on land and in the oceans, with an estimated half of species on Earth going extinct at the time.

“Previously we knew a bit about plant survival in terms of their abundance – whether they are present or absent in fossil record,” says the study’s lead author Wuu Kuang Soh, of University College Dublin, “but we didn’t know how they survived or the intrinsic factors of plants that contributed to their survival.”

By looking at fossilized leaves of two plant groups uncovered in Greenland, the authors suggest that the reason for some plants’ survival is that those with heavier leaves were more resilient to environmental stressors such as high air temperature and rising carbon dioxide.

According to Barry Lomax, a lecturer in Environmental Science at the University of Nottingham, UK, who was not involved in the research, “being able to establish that different plant groups respond differently to stress, and that their capacity to adapt to this stress is reflected in their propensity for survival, is a great piece of detective work.”

New proxy development

The work presented in this study – a joint research effort by University College Dublin and Macquarie University, Australia – relied heavily on the development of a new proxy i.e. a physical characteristic which is used to infer details about some related, but immeasurable, trait. By showing how the thickness of a plant’s leaf cuticle (the protective layer covering a leaf) is related to the leaf mass per unit area (LMA) in modern leaves, the team were able to use their fossils to identify how heavy the paleo leaves were for their size.

Macrofossil of 200 million years old Triassic ginkgo, Sphenobaiera spectabilis. Used with permission of the study authors (Credit: Mark Wildham).

For some scientists, this development itself is the study’s highlight. “I think the key finding of the work is that it gives us another set of tools to unpick how plants have responded to large scale perturbations in the carbon cycle which have influenced climate,” says Lomax.

By using the new proxy for LMA the authors were able to look at changes in two plant groups – Ginkoales (an gymnosperm order – see image) and Bennettitales (a now extinct order of seed plant)– across the Triassic-Jurassic mass extinction, and discover their opposing fates; the former flourishing and the latter experiencing sharp ecological decline.

“We found that plants with higher LMA had a higher chance of survival than plants with lower LMA during this global warming induced mass extinction event” says lead author Soh.

Commenting on the study, Charilaos Yiotis, a plant physiologist at University College Dublin who did not participate in the research, says that “under the greenhouse conditions of the Triassic-Jurassic Boundary – or, may I add, under near-future greenhouse conditions – plants with fast leaf turnover rates (low LMA) are outcompeted by those adopting more “conservative” strategies like robust, low turnover leaves (high LMA).” The turnover rate Yiotis refers to is the time taken for leaves to be produced and then fall.

“The spectrum describes how “fast” or “slow” the plant is turning over its nutrient resources,” adds Dana Royer, a paleobotanist at Weslayan University, Connecticut, who peer-reviewed the paper for Nature. “At the fast-return end (low LMA), plants have high photosynthetic rates, high nutrient contents, short-lived (deciduous, for example) and cheaply built leaves. This is the live-fast-die-young strategy. At the slow-return end (high LMA), plants show the reverse.”

The current mass extinction

The study’s findings are important in relation to the sixth mass extinction event which is currently underway. Scientists believe that a similar extinction process to those in the past is now taking place, as the variety of life on land gives way to the seemingly unstoppable human developments of agriculture, industry, and urbanisation. By looking at the paleo-evidence the authors tentatively suggest that today’s plant communities which host thicker, heavier leaves (high LMA) may be better adapted to deal with the current episode of anthropogenic warming, and therefore have a better chance of future ecological success than plants with lighter leaves (low LMA).

“More specifically, plants that can have leaves with both low and high LMA appear to do well after surviving a catastrophic mass extinction episode,” says Soh. “Our finding is important because it means that plants with flexibility in LMA will be the favourite to flourish during future global warming.”

“A shift to higher LMA is common for plants when they are exposed to high CO2” says Royer, “so the fact that the authors are finding the same response in a “natural” experiment – albeit 200 million years ago – lends support to the idea that we should expect a similar response in our own future.”

Further looking to the future, University College Dublin’s Charilaos Yiotis finds it alarming that most plants of economic importance today would probably never have made it through the Triassic-Jurassic Boundary.

“At a time where humanity’s biggest challenge is to feed an ever-growing human population,” he says, “this study should make us think again about how big a threat climate change is to future food security.”

By Conor Purcell, a Science & Nature Writer with a PhD in Earth Science.

Conor has previously worked with the authors of this paper, but not on the project itself. He can be found on twitter @ConorPPurcell and some of his other articles at cppurcell.tumblr.com.

References

Soh, W.K., Wright, K.L, Bacon, T.I., et al., Palaeo leaf economics reveal a shift in ecosystem function associated with the end-Triassic mass extinction event, Nature Plants, 3, doi:10.1038/nplants.2017.104, 2017.

Editor’s note: This blog post provides a summary to a research paper that is paywalled, unlike other scientific articles featured on GeoLog. The EGU supports and promotes open access, publishing 17 open access journals and having endorsed Open Access 2020, an initiative to promote the large-scale transition to open access publishing. Since research in the realm of palaeontology and evolutionary biology is rarely featured on GeoLog, an exception was made on this occasion to publish a story on a scientific paper not accessible to all. The lead author of the study is happy to be contacted with questions about the research; if you’d like to find out more please email Wuu Kuang Soh (wuukuang@gmail.com).

 

 

March GeoRoundUp: the best of the Earth sciences from around the web

March GeoRoundUp: the best of the Earth sciences from around the web

Drawing inspiration from popular stories on our social media channels, as well as  unique and quirky research news, this monthly column aims to bring you the best of the Earth and planetary sciences from around the web.

Major story

While the March headlines might not have been dominated by a particular story, the state of the Earth’s climate has definitely been the overarching theme of the month.

Ahead of World Meteorological Day (celebrate on the 23rd March) the World Meteorological Organization released its annual report on the State of Global Climate. Compiled from a broad range of sources, the report reiterates the findings of the US government agencies NASA and NOAA, who earlier this year declared that 2016 was the warmest year on record.

Not only were temperatures a remarkable 1.1 °C above the pre-industrial period and 0.06 °C above the previous record set in 2015, global sea ice extent dropped more than 4 million square kilometres below average in November. Boosted by a strong El Niño event global sea levels reached record highs too.

The report comes in the wake of US President Trump’s ‘blueprint’ budget for 2018, where he sets out his spending priorities for the year ahead. Nature put together a piece that highlights what US science would stand to lose if the budget is approved. NASA would experience a 0.8% cut from current levels, largely focused on Earth science missions, and future NOAA satellite programmes are also under threat. Worst hit by the cuts would be the Environment Protection Agency (EPA), with a proposed 31% cut in funding, which would “gut EPA programs tackling climate change and pollution”, according to The Guardian.

But the signals are clear: after the record warming in 2016, temperatures have continued to rise in 2017, affecting ecosystems around the world. An example are the corals of the Great Barrier Reef,  which have suffered from widespread bleaching – a situation where they expel their symbiotic algae, meaning they turn white and can die – for the third consecutive year. A new study on mass bleaching of corals was discouraging news: the only long-term solution to the problem is halting global warming. Improving water quality or enforcing fishing controls provides little relief.

But it’s not all bad news when it comes to the global climate and the Earth’s environment. Despite being a record-breaking year in terms of temperatures, 2016 was also the year that saw a dramatic drop in the amount of new coal fueled power plants being built. With cities worldwide battling poor air quality and pollution, this is certainly encouraging news.

What you might have missed

Earlier this month a BBC News crew experienced the fickle nature of volcanoes first hand. The team were visiting Mt. Etna (Sicily) to film a report on volcano monitoring, and  arrived on the Italian island to discover Europe’s most active volcano had just started to erupt again.

Etna’s slow-moving lava is not usually considered dangerous. “But about 20 minutes after arriving, a burst of white steam emerged from the lava – it didn’t make much of a noise or look especially threatening – but the guides started asking people to move. Then, moments later, there was an explosion,” writes Rebecca Morelle, one of the reporters on the team. As they ran down the mountain to safety, the team and tourists, were “pelted with deadly, hot debris.” Read the full account of their ordeal and watch a spectacular video here.

It has also been a big month for palaeontology. Up until now the shape of a dinosaur’s hip determined were along the dinosaur family tree it was placed. Lizard-hipped dinosaurs fell into one group (Saurischia), while those with a more bird-like hip configuration are known as Ornithischia. Now, a team of researchers have proposed a radically new classification system. They found that 21 other anatomical features divide the dinosaurs differently. The new tree puts theropods together with Ornithischian, indicating they probably share a common ancestor. The new theory might face an uphill struggle to debunk the long-lasting consensus on the history of dinosaurs, but many in the field agree that given the thoroughness of the study it is certainly an idea worth considering.

Scientists from the Museum and Cambridge University have proposed radical changes to the dinosaur family tree. Credit: Natural History Museum.

And while we are on the subject of dinosaurs, this brilliant interactive map of every fossil found on Earth (created by @PaleoDB) is a great resource!

Way out in space, the bounty of insights from the Rosetta mission continues. From September 2014, the mission scientists have kept a watchful eye on a 70 m-long, 1 m-wide fracture on the prominent cliff-edge subsequently named Aswan, in the Seth region of the comet, on its large lobe. A few days later, new images of the area revealed that the crack had disappeared and been replaced by a new cliff face, at the bottom of which were many new meter-sized boulders. The discovery allowed the scientists to make the link between the newly created cliff face and outbursts of dust and gas.

You might think the use of infographics to visualise data is a relatively new thing, but you’d be mistaken. This collection of 1800s educational diagrams, of scientific discoveries, from the moon’s surface to the longest rivers, is simply stunning and incredibly effective.

Emslie and Reynolds compare mountains and volcanoes, including mountains in the Alps and Andes. Featured in Geological Diagrams. Courtesy David Rumsey Historical Map Collection

Links we liked

  • Something for the weekend? Why not try your hand at baking a scientifically accurate (sort of!) cake planet?
  • New research suggests that by the middle of the century, more than half of humanity will live in water-stressed areas. Badly managed resources play a crucial role in water shortages globally
  • For a lighthearted, yet very informative, take on mass extinctions this story in The Atlantic is not to be missed
  • A German coal-mine, which has provided power for the country’s industry sector for the past half century, will get a new lease on life when it’s turned into a into a pumped-hydro-storage station, acting like a giant battery that stores solar and wind energy

The EGU story

This time of year, EGU’s biggest story is our annual General Assembly, starting only a few weeks from now. This month, we published the meeting programme, which includes some 1000 sessions and over 17,500 abstracts! On the blog, we published guides on how-to make the best of your oral, poster or PICO presentation at the General Assembly, revealed the finalists of the Communicate Your Science Video Competition, and provided tips on making the most of your time in Vienna without breaking the bank. We look forward to seeing you all in the Austrian capital in the last week of April!

And don’t forget! To stay abreast of all the EGU’s events and activities, from highlighting papers published in our open access journals to providing news relating to EGU’s scientific divisions and meetings, including the General Assembly, subscribe to receive our monthly newsletter.