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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).

 

 

Geosciences Column: From the desolate to the diverse, a story of volcanic succession

When a volcano erupts and spews lava onto the surrounding terrain, it is merciless in its destruction. All that is green on the land is engulfed in flame, or buried by an insurmountable mass of molten rock. Whatever charred remains of what lies beneath it will not see the light of day once the lava cools, turning the landscape into a barren black mass of solid basalt.

But volcanoes around the world are not barren basaltic masses. On the contrary, many volcanic slopes are teeming with life. Much of the Hawaiian archipelago is a tropical paradise, its older lava fields thick with forest and foliage. Likewise, Iceland’s flotilla of fiery peaks hasn’t rendered the land completely barren. So how does life return to the scene after an eruption?

Hardy grass on Surtsey’s black sands. (Credit: Ragnar Sigurdsson (arctic-images.com via imaggeo.egu.eu)

Hardy grass on Surtsey’s black sands. (Credit: Ragnar Sigurdsson (arctic-images.com via imaggeo.egu.eu)

The answer lies in a process known as succession. One by one, starting with the hardiest life forms, the lava is recolonised by wind-blown spores and seeds that have managed to make it from areas unharmed by the latest eruption. Over time, the growing community of plants attracts animals that bring further seeds to the site, either clinging desperately to their fur, or deployed stealthily in their droppings.

A long-term investigation of two very different volcanoes has revealed what allows the earliest arrivals to take hold: Surtsey, an isolated volcanic island in the North Atlantic, and Mount St. Helens, a once towering and peak in Washington State. The findings are published in Biogeosciences, an open access journal of the European Geosciences Union.

Surtsey’s arrival in 1963 (left, credit: NOAA) and Mount St Helens during the 1980 eruption (right, credit: Austin Post/USGS)

Surtsey’s arrival in 1963 (left, credit: NOAA) and Mount St Helens during the 1980 eruption (right, credit: Austin Post/USGS)

Surtsey emerged off the Icelandic coast in 1963 amid billowing plumes of ash and steam. Erupting from underwater, Surtsey created its own island – a fresh field of lava that has been consistently monitored since 1990. Mount St Helens erupted violently in 1980, after a catastrophic landslide triggered a volcanic blast so large that the volcano’s entire north flank, together with 370 square kilometres of forest, were obliterated. The resulting fields of pumice, tephra and lava provided a blank canvas for life to start afresh in the area.

Surtsey and Mout St Helens differ in terms of their age, the way they’re isolated, their climate and their size. But, despite these differences, scientists Roger del Moral and Borgþór Magnússon found the way vegetation first established itself followed the same fundamental principles, regardless of where it set up camp.

It’s all down to two different filters: isolation and stress. Isolation creates the biggest filter; meaning only the most well-travelled species can take hold. Then stress further sorts the species that can survive – well-travelled weaklings wouldn’t stand a chance in a place with incredibly poor fertility.

Birds make life a little easier for all involved, particularly in coastal areas, where an entire colony of birds can become established. These birds import nutrients from the surrounding sea by consuming fish from and depositing their waste on land. On Surtsey, these nutrient imports have meant the richest plant life has developed where the bird colonies are.

On Mount St Helens, winds carrying nutrient-laden dust created the first fertile material. This let a group of flowering plants known as lupines take hold and, after several cycles of lupine blooms, the ground became much more fertile. The areas where lupines bloom are now the most species rich.

Vegetation on Surtsey (top, credit: Borgþór Magnússon) and Mount St Helens (bottom, credit: Roger del Moral). Images on the left are areas where the rate of succession is slow, those on the right detail areas with a faster succession rate.

Vegetation on Surtsey (top, credit: Borgþór Magnússon) and Mount St Helens (bottom, credit: Roger del Moral). Images on the left are areas where the rate of succession is slow, those on the right detail areas with a faster succession rate.

In a world where environments are rapidly changing and species are having to move into new territories to adapt, these findings can help shed light on how plants could keep pace with the change as they shift from one site to the next.

By Sara Mynott, EGU Communications Officer

Reference:

del Moral, R. and Magnússon, B.: Surtsey and Mount St. Helens: a comparison of early succession rates, Biogeosciences, 11, 2099-2111, doi:10.5194/bg-11-2099-2014, 2014.

 

Imaggeo on Mondays: Iceland’s highlands

This week’s Imaggeo on Mondays provides a little insight into what you might find beneath your feet as you explore the Icelandic highlands… 

Autumn mountain vegetation, Central Highland, Iceland. (Credit: Ragnar Sigurdsson/arctic-images.com via imaggeo.egu.eu)

Autumn mountain vegetation, Central Highland, Iceland. (Credit: Ragnar Sigurdsson/arctic-images.com, distributed via imaggeo.egu.eu)

You can stumble upon wild blueberries, better known to botanists as vaccinium uliginosum, in cool temperate regions of the Arctic, as well as other mountainous areas including the Pyrenees, Alps, and Rockies. They thrive in wet acidic soils – the sort you might find in heathlands, moorlands and stretches of Arctic tundra, and can carpet the ground beneath coniferous forests too!

Here’s a close-up! (Credit: Kim Hansen via Wikimedia Commons)

Here’s a close-up! (Credit: Kim Hansen via Wikimedia Commons)

Imaggeo is the EGU’s open access geosciences image repository. Photos uploaded to Imaggeo can be used by scientists, the press and the public provided the original author is credited. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. You can submit your photos here.