At what cost can grasses endure cold temperatures?

Iceland is an island with high volcanic activity (remember 2010 when an ash cloud from an erupted volcano brought all air traffic over Europe to a standstill for weeks?). The volcanic activity heats up streams to boiling point and the soils close by also become very hot.  In some places in Iceland, soils can have temperatures reaching up to 40-60 °C, and grasses can still grow and thrive there.

Grasses in Iceland are exposed to geothermal heating. This photo is taken at the field site in Hengill. Photo: Aelys Humphreys.

- Some plant species in Iceland can even occur on soils that have temperatures of up to 70 °C, says Johan Ehrlén, Aelys’ colleague, who also leads a project in Iceland examining how geothermal soil heating influences flowering time of different plants species.

Aelys Humphreys is soon off to another field trip to Iceland. Photo: Jan-Niklas Nuppenau.

Aelys Humphreys and her research team are interested in knowing if the grasses that are exposed to geothermal heating lose their original cold tolerance. They also want to investigate at what pace grasses can adapt to and flourish at different temperatures.

- Most grass species that occur on heated soils in Iceland are widespread in the Northern Hemisphere, even globally. So we know they are able to tolerate freezing temperatures and winter. But winter on the heated soils is very different because those soils never freeze. We are interested in whether the plants that grow on these soils have lost the ability to survive freezing temperatures and a northern winter. If we do find differences between plants on heated and non-heated soils, we are also interested in the genetics underlying those differences and how quickly they can evolve, says Aelys Humphreys.

Organisms will often lose traits that they no longer need since adaptation to certain conditions can come at a high cost. Therefore, there could be a tradeoff between tolerance to heat and frost. In this case, if cold tolerance is not needed in the warmer soils the plant might lose that trait all together. Such a tradeoff could affect the long term fitness of a plant. For example, a plant from a heated soil might produce fewer flowers or seeds if it is transferred to a cold environment.

How long does it take for a species to adapt to new temperatures?

- We study four species of cool season grasses that are widely spread across the world – in for example northern Europe, but also in similar climates in Chile and New Zeeland. All four study species have populations that are adapted to both warm and cold temperatures. One of the grasses we study is a turf grass, used on golf courses, says Aelys Humphreys.

The research team will investigate if there is any evidence of rapid adaptation to new climatic conditions in these grasses, by examining differences in epigenetic patterns of cold tolerance genes. If, for example, there is a lot of DNA methylation on the cold tolerance genes it implies that the cold tolerance is lost (or at least not being expressed). Invasive species are a good example of where rapid spread into diverse environments can happen very quickly and is thought to be facilitated by epigenetic variation. For example, different DNA-methylation patterns have been associated with expansion into new climates in Japanese knotweed and crofton weed.

The field site Hengill. Photo: Jan-Niklas Nuppenau.

On a mission to collect seeds

The research team’s mission for this field trip to Iceland will be to collect leaf material and seeds from plants that grow on geothermally heated as well as non-heated soils.

- Last year we found the grasses we were interested in, the only setback was that we were a bit too early in the season to find mature seeds, says Jan-Niklas Nuppenau, a PhD candidate in Aelys Humphreys’ team.

The seeds they hope to find this year will then be grown in a garden here in Stockholm and also in Umeå, so that the plants will be exposed to two different winter conditions. Then the researchers will find out how well the plants from heated soils survive compared to those from non-heated soils – if at all.

- We will also leave climate loggers in Iceland to see how cold it actually gets on the respective cold and heated sites. Most previous reports have focused on the differences in temperature during the growing season, that is, during spring and summer, but there has been less focus on how winter conditions differ between geothermally heated and non-heated sites, says Aelys Humphreys.

Jan-Niklas Nuppenau. Photo: Aelys Humphreys.

What will happen to grasses during unpredictable climate change?

The effect that an increase in temperature will have on plants is usually discussed in the climate change debate. Often though, it’s forgotten that winter temperatures will also be affected by climate change:

- Some projections have suggested that snow fall might become less regular and predictable, says Aelys Humphreys.

Therefore, it’s crucial to understand how the temperature ranges might shift, how grasses acquire their cold tolerance and respond to different winter conditions. To survive winter can be a challenge for all flowering plants. This is also one possible explanation why there are more species of flowering plants in the tropics.

Hoping for good weather

How is it then to do fieldwork in Iceland? Last year Aelys Humphreys and Jan-Niklas Nuppenau were there, but only for 4 days of fieldwork. They had exceptional luck with the weather. So Jan-Niklas Nuppenau feels he can't give a good answer just yet:

- Collecting grasses at 20 °C under blue skies with a light breeze and sheep running around in an amazing landscape with thermal springs scattered in a lovely valley is easy and pleasant. Apart maybe from the sulfuric smell I could not point out a thing to complain about. However, it felt a bit unreal, since just hours later I got to know what it could be like as well.

Sheep grazing at the field site Hengill. Photo: Jan-Niklas Nuppenau.

Jan-Niklas Nuppenau continues to tell how he went hiking for three days after the field trip ended, with the weather changing completely to 4 °C and horizontal rain, with wind gusts making it hard to stand upright. He finishes:

- It was okay to walk but doing field work under those conditions would have been a challenge.

Aelys Humphreys. Photo: Jan-Niklas Nuppenau.