Although climate skeptics might find it hard to believe with this year’s endless snow and freezing temperatures in North America, climate change is making warm, sunny early springs increasingly common. And that affects when trees start to leaf out. But how much? A study showed that a plant's genetics can be used to produce more accurate predictions of when its leaves will burst bud in spring.
Montréal/Canada — Simon Joly, biology professor at Université de Montréal and Elizabeth Wolkovich, an ecology professor at University of British Columbia, discovered that when species and individual specimens within a species are very similar genetically, they tend to respond more similarly to environmental signals than those that are genetically dissimilar. He came to this conclusion after responding to a call sent out by Elizabeth Wolkovich, a professor at the University of British Columbia who previously taught at Harvard University and studies how trees respond to climate change. She wanted to include genetics, one of Joly's areas of expertise, in her work to see if it could help better predict budburst.
They chose 10 tree and shrub species that are relatively common in Massachusetts and Quebec, including striped maple, American beech, northern red oak and specific types of honeysuckle, poplar and blueberry. Branches were collected from Harvard Forest in Massachusetts and UdeM's Station de biologie des Laurentides in January, once the trees and shrubs had been cold long enough for leaves to burst bud — given the right conditions.
According to Elizabeth Wolkovich, there are three main environmental signals that affect budburst: the length of time they’ve spent in the cold, warm temperatures and hours of daylight. Once collected, the branches were kept chilled and sent to Harvard's Arnold Arboretum, where they were then placed in special growth chambers with controlled temperatures and hours of daylight. The experiment was carried out with 8- and 12-hour-long days and daytime temperatures of 15 and 20 °C.
The Trees Adapted
The experiment showed that a 5 °C increase in temperature causes leaves to burst bud 20 days earlier than average, though the impact on each species can vary considerably. Furthermore, more hours of daylight moved budburst up by about 12 days. However, these estimates become more accurate once genetic information from the trees and shrubs has been factored in.
This finding held true even though the scientists didn’t find major genetic differences between individual specimens of a single species between the two regions. Tree genes move around relatively quickly through pollen, so some individual specimens in Massachusetts could be genetically more closely related to specimens in Quebec than to other specimens in Massachusetts.
Even though it's still very hard to tell how climate change will affect spring, this study shows that plants react strongly to differences in climate and that their genetics help determine how well they adapt to these changes.
Findings Open the Door to a Wide Range of New Studies
In the future the researchers want to look at whether certain individual specimens within a species are better equipped to adapt to climate change and why. That’s how plant species might be able to adapt to what's coming. But this depends on how extreme the changes to our climate actually are, which remains an open question given current carbon emissions.
Joly also wonders how the ecosystem as a whole, including the insects that eat leaves, will react to higher temperatures. Will they react in the same way as trees? These are the extremely complex questions that people are beginning to ask and that needed to be studied jointly with other researchers from different disciplines.
References: Simon Joly, Dan F. B. Flynn and Elizabeth Wolkovich, "On the importance of accounting for intraspecic genomic relatedness in multi-species studies", Methods in Ecology and Evolution, May 7 2019.