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Adjusting trees' internal clocks can help them cope with climate change

A new study from Umeå University has revealed that trees' circadian clocks guide their growth and the timing of seasonal events like the appearance of leaves in spring. The researchers investigated the growth of genetically modified poplars in greenhouse and field conditions, combining statistical learning and plant biology methods. Their findings, in npj Biological Timing and Sleep, suggest that adjusting clock-associated genes could help trees better synchronize with changing climates, offering new opportunities for forestry.

Trees, like humans, have a circadian clock that regulates their daily and seasonal rhythms. Research has suggested that this clock is important to regulate growth and the timing of important seasonal events, like for example, bud formation in autumn and bud opening in spring.

However, most of this research has been done in controlled greenhouse conditions and not outside in the field where plants are exposed to natural environmental conditions. In the field, as in the real world, temperature fluctuations, insect predation and other factors affect plant growth.

To address this, the researchers conducted an extensive study based on 68 poplar or aspen lines with different, modified properties. Among the genes that were modified were many associated with the circadian clock. These trees' growth was studied in multiple greenhouse and field experiments over several years. The results clearly showed that the circadian clock has a strong role in regulating tree growth and the timing of seasonal events in the life of a tree, like the budding of leaves.

"Our study is the first to combine datasets from greenhouse and field studies to show that multiple aspects of the circadian clock system influence tree growth and the timing of life-cycle events," says Bertold Mariën, lead author of the study.

"By applying statistical modeling to these datasets, we were able to pinpoint which circadian clock-associated genes impact tree growth or, for example, the time when leaves appear or change color."

Insights for forestry and climate adaptation

The study provides a new perspective on how trees use their circadian clock to coordinate their growth with the environment. For example, certain genetic modifications in key clock regulators changed the trees' sensing of the day length and allowed trees to continue growing later into the season.

"This study is a proof-of-concept that trees conditioned to a particular length of day at a certain latitude can be adapted to a new latitude, effectively extending their growing season. This is especially useful at higher latitudes, like in Northern Sweden, where short growing seasons limit timber production," explains Maria E. Eriksson, last author of the study.

Additionally, some gene modifications improved the trees' resilience under environmental fluctuations. By focusing on these specific genes, it would be possible to breed tree varieties that are better adapted to rapid changes in the local climate, and to new growing locations, for example in other latitudes.

"In the future, forestry management could be improved by integrating trees' circadian clocks and their natural growth cycles with traditional practices," says Eriksson. "In this way, tree growth and resilience could be optimized in a changing world."

Beyond the implications for forestry, the study also has relevance for global vegetation models that predict forest growth and carbon storage. The importance of the clock in shaping trees' sensitivity to environmental conditions is often underestimated in these models, according to Mariën.

He concludes, "By properly incorporating our findings on the circadian clock into global vegetation models, we can improve predictions of how forests will respond to climate change."