Trees 'remember' where they come from

Kurt Kleiner

Genetically identical trees respond differently to their environment depending on what part of the country they come from. The surprising finding could have implications for gardeners and foresters, and might help predict how forests will respond to climate change.

“The findings were really quite stunning,” says Malcolm Campbell, professor of cell and systems biology and vice principal, research at University of Toronto Scarborough. “Our results show that there is a form of molecular ‘memory’ in trees where a tree’s previous personal experience influences how it responds to the environment.”

Campbell and his colleagues were interested in something called the “nursery effect,” which had long been noted by foresters and gardeners. Although many plants are genetically identical clones, it seemed that plants from different nurseries often grew differently in identical environments.

Poplar clones

Campbell decided to look at poplar trees.  Like many plants, poplars can reproduce themselves through their roots or through fragments of branches. These new trees are genetically identical clones of their parent trees.

Campbell’s graduate student, Sherosha Raj, obtained three different types of genetically identical poplars from Alberta, Saskatchewan and Manitoba. The trees were grown in identical conditions. Then half were subjected to drought, and half continued to be watered.

In two of the three varieties, the poplars responded differently to drought conditions depending on what part of the country they came from. The trees seemed to “remember” their previous environments.

Fundamental changes

Campbell’s group showed that the differences were at the fundamental level of gene activation. Identical plants from different parts of the country activated different sets of genes when exposed to drought.

The results suggest that there is more diversity in stands of seemingly identical poplar forests than previously thought. Genetically identical stands of trees might still respond differently to drought, disease, or pests.

The research was published in the journal Proceedings of the National Academy of Sciences.

Campbell’s research team included co-first author Katharina Bräutigam, Erin Hamanishi and Olivia Wilkins, all of the University of Toronto, and researchers at the University of British Columbia, Simon Fraser University and the University of Alberta. The research was supported by competitive research funds from the Natural Sciences and Engineering Research Council (NSERC) of Canada and in kind contributions from Alberta Pacific Forest Industries and Agriculture and Agrifood Canada.