Climate change has shifted the optimal growing location for the plant thale cress, large-scale experiment shows

A large-scale global experiment with thale cress (Arabidopsis thaliana) shows that climate change has led to a shift in the optimal growing location for these plants. The study, led by researchers from Berkeley and Stanford, amongst others, and published today in Science, also suggests that plant populations have the capacity to adapt rapidly to climate change. “That’s encouraging,” says Utrecht plant researcher Martijn van Zanten, who participated in the study together with bioinformatician Basten Snoek. “But this will only be true if there is sufficient genetic variation.”

Snoek and Van Zanten contributed to the project by establishing twelve test plots in the Utrecht University Botanic Gardens with a mixture of thale cress seeds and closely monitoring their development over several years. The seeds were descended from thale cress plants originally collected in the wild at 231 locations across the Northern Hemisphere. These plants came from a wide range of environments and climates, from the subtropics to the Arctic Circle.

Evolution experiment

Prior to the experiment, all plants were grown together in Germany under identical conditions, and their seeds were harvested. Researchers then established twelve plots, each with exactly the same seed mix, at 43 locations across the Northern Hemisphere, covering a wide range of climates. The plants were allowed to grow naturally, while weather and climate conditions were carefully recorded.

How plant populations evolve is predictable and closely linked to the environment.

“Under the influence of weather and climate, some variants in the seed mix, namely those that are less well adapted to local conditions, gradually disappear. Others, by contrast, are doing progressively better after a few generations. This is real-time evolution by natural selection: plants best adapted to the local climate survive and increase in number. Such an experiment has never been done before with plants on this scale,” Van Zanten explains.

Every two weeks

Every two weeks, the researchers collected a flower from each individual plant that was flowering in the plots. Per plot, the flowers were then sequenced, mapping the genetic code of the flowering plants. “This gave us a snapshot of all the variants present in each plot every two weeks,” says Snoek. “This was done at all locations over a five-year period.” The result was an extensive dataset, which was analysed in detail by the lead authors of the study. They examined not only which plant variants persisted at each location, but also which genes and alleles, variants of genes, contributed positively to adaptation to the local climate.

Similar climates, similar evolution

The current study reports on the first three years of the experiment. “This experiment has yielded many new insights,” says Van Zanten. “It shows that thale cress populations in similar climates adapt in similar ways. For instance, after several years, the plots in Madrid closely resembled those in Greece, with the same variants performing well. By contrast, the variants that persisted there differed greatly from those in the far north, while northern locations were more similar to one another. This shows that how plant populations evolve is predictable and closely linked to the environment.” 

Thale cress is widely used in laboratory research. Its entire genome has been sequenced, and the functions of many of its genes are well understood. This allowed the team to show that, during the experiment, natural selection acted on genes involved in, among other things, how the plants respond to high temperatures.
 

If plants move because they perform best at a certain temperature, they will eventually reach a coastline or another barrier beyond which they cannot move.

Optimal growing location shifted

Van Zanten finds the shift in optimal growing locations for plants particularly striking. “The thale cress plants used were collected around thirty years ago. We know what the temperature was at their original locations at the time. Now we see that their descendants perform better in places that were about 1.5 degrees colder back then. We observe this pattern across the entire Northern Hemisphere. It makes the impact of climate change on living nature very tangible.”

Rapid adaptation

The experiment shows that thale cress populations can potentially adapt quickly to new conditions, which could be seen as good news. However, Van Zanten and Snoek add a note of caution. “In this experiment, the populations in the plots started with seeds collected from all over the Northern Hemisphere,” says Van Zanten. “In reality, of course, this is not the case, and there is likely to be much less genetic variation at a given location on which natural selection can act.”

We stood in the blazing sun and in soggy wet snow to collect flowers. It was nice to get my hands and shoes dirty again.

But if temperatures rise and plant populations cannot adapt quickly enough, couldn’t plants simply move along with the warming climate? “If plants move because they perform best at a certain temperature, they will eventually reach a coastline or another barrier beyond which they cannot move. At that point, those plants will be lost.”

Away from computer screen

Snoek and Van Zanten, who frequently collaborate and are now involved in a follow-up study, joined the project after hearing about it from a colleague. Van Zanten: “This is a project where working together allows you to achieve far more than you ever could alone or with a small team.”

Surprisingly, Snoek, a bioinformatician, was only minimally involved in the data analysis for this project. “It was actually a really enjoyable project because it forced me to step away from my computer screen,” he says. “We stood in the blazing sun and in soggy wet snow to collect flowers. It was nice to get my hands and shoes dirty again.”