Timing is everything: How trees use an inner clock for smarter growth

As climate patterns shift and seasons grow less predictable, trees must adapt in ways science is only beginning to understand. Beneath their bark and branches lies a powerful, invisible system: a circadian clock.

Much like the one that governs human sleep cycles, the tree’s biological clock regulates daily and seasonal activities. It tells the tree when to grow, when to bud, and when to conserve energy.

Now, researchers at Umeå University have unlocked more of this inner world. Their recent study shows how genetic changes to this clock can help trees better align with the rhythm of their environment.

Trees use an inner clock to grow 

Most earlier studies explored plant circadian rhythms under greenhouse conditions. While useful, these environments don’t capture nature’s chaos – temperature swings, shifting daylight, rainfall variation, and insect threats.

In the wild, trees must handle all these factors while maintaining their growth and seasonal behaviors.

To tackle this, researchers at the Umeå Plant Science Centre studied 68 genetically modified Populus trees under both controlled and natural conditions. Over several years, they examined how alterations to specific clock-related genes influenced growth, leaf senescence, and bud activity.

The team’s approach combined advanced statistical modeling with experimental plant biology. Each modified tree had a distinct genetic profile targeting clock components like TOC1, LHY, GI, or EBI1.

The goal was to pinpoint how internal timing shapes external performance. The field experiments added crucial context, allowing the team to track the effects of gene modification under real-world seasonal cues.

Circadian clock controls tree growth

“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,” said Bertold Mariën, lead author of the study.

In both greenhouse chambers and open fields, some trees with altered clock genes grew significantly taller or faster. Others delayed leaf senescence or bud set, effectively prolonging the growth period.

These effects were most pronounced in northern Sweden, where short summers restrict tree development. The researchers observed that the clock doesn’t just set a tree’s internal rhythm – it fine-tunes how trees respond to day-length and environmental signals.

For instance, the lhy-10 and toc1-5 variants displayed faster growth in outdoor conditions, suggesting that their altered clocks helped trees maximize growth within shorter seasons.

These core clock genes are part of a feedback loop that coordinates when cells divide, when leaves expand, and when energy is stored.

Changing genes helps trees grow stronger

“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,” explained study co-author Maria E. Eriksson.

“This is especially useful at higher latitudes like in Northern Sweden where short growing seasons limit timber production.”

Among the most promising findings was the role of EBI1, a gene previously associated with stress resistance in Arabidopsis. Trees with modified EBI1 generally showed faster growth and higher chlorophyll content index (CCI), a sign of delayed leaf aging.

These trees didn’t just grow more – they remained greener for longer. That extended greening can boost photosynthesis and carbon storage.

The study also highlighted how different promoters affected growth. AtGA20ox1 trees, which overproduce gibberellins, grew quickly and developed more biomass.

Interestingly, some trees increased growth even with a shorter growth period, showing that timing can be more important than duration. The type of genetic promoter used, and the tree’s background genotype, both influenced the outcomes.

Clockwork in leaves and roots

The research also supported a shift in how we think about tree development. Traditional views focused heavily on carbon source limitation, assuming trees grow more when photosynthesis is high.

But this study adds weight to an alternative model: growth is also limited by when internal conditions – like water pressure and hormone levels – meet the right thresholds.

The circadian clock seems to act as a gatekeeper, opening and closing growth windows in sync with environmental conditions. For example, the team found that cell division and DNA replication were gated to nighttime, when the risk of DNA damage is lower, and air humidity supports turgor pressure in cells.

Even root clocks may follow different rhythms than leaf clocks, leading to asynchronous growth. Such tissue-specific timing mechanisms further complicate models of tree behavior but also offer new opportunities to improve forestry by targeting these internal dynamics.

Using tree clocks for better forests

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

Integrating the clock into forestry could enable smarter planting schedules, more efficient use of resources, and the development of trees suited to rapidly warming regions. But there’s more. These findings may reshape how global vegetation models are built.

“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,” said Mariën.

That’s because many existing models treat trees as passive responders to light and temperature. They don’t account for how internal clocks modulate those responses. Adding this layer of complexity could significantly improve how we predict carbon uptake and forest health.

Tree timing and forest management

This work is more than a scientific milestone – it’s a step toward a new kind of forestry. The researchers call it chronosilviculture: aligning forest management with biological timekeeping.

Instead of forcing trees into rigid planting cycles, foresters could one day select species or cultivars with clock traits tailored to specific climates or latitudes.

By revealing how the circadian clock acts as nature’s master of ceremony, the Umeå team has given foresters and ecologists a powerful new tool. With climate change pushing ecosystems to their limits, understanding how trees grow with their natural rhythm may be the smartest way forward.

The study is published in the journal npj Biological Timing and Sleep.

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