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How Do Trees Adjust Their Growth According to Seasonal Changes?

Image: Tree in spring vs autumn representing seasonal growth cycle. Credit: OpenAI (2024), DALL-E.

If you’ve ever wondered why trees seem to know when to stop growing in the fall and when to start again in the spring, you’re not alone. The answer lies in a combination of two key factors: temperature and daylight. Over millions of years, trees have developed sophisticated mechanisms that allow them to sense changes in these factors and adjust their growth cycles accordingly.

As autumn arrives, and the days grow shorter and cooler, trees begin to shut down their growth processes and enter a state called dormancy. This period of rest helps them conserve energy through the cold winter months. Then, when spring comes around with longer days and warmer temperatures, trees awaken from dormancy and resume growth, taking advantage of the favorable conditions.

Younger Trees Grow Longer, Older Trees Slow Down Sooner

While this general growth pattern is well known, scientists have discovered something intriguing: younger trees in natural forests tend to grow later into the autumn and break dormancy earlier in the spring compared to older trees. This extended growth period gives young trees a competitive edge, allowing them to capture more sunlight and store more nutrients to fuel their early growth years. But how do young trees manage to keep growing longer than their older counterparts?

A Breakthrough Discovery: Small RNA-Protein Module

Collaborative work by researchers at Umeå Plant Science Centre, Sweden (Prof. Ove Nilsson lab) and Huazhong Agricultural University, China (Prof. Jihua Ding lab) published in PNAS demonstrates that a small RNA-protein module controls extended growth capacity in young trees.

In young trees, high levels of a particular small RNA prevent proteins from stopping growth. As these trees age, the levels of this small RNA decrease, allowing the growth-inhibiting proteins to become more active. As a result, older trees stop growing earlier in the fall and remain dormant longer into the spring. This explains why older trees seem to lose their ability to extend their growing season as they age.

Why Is This Important?

This discovery not only helps us understand how trees regulate their growth with age but also provides insight into how trees adapt to seasonal changes. As global temperatures continue to fluctuate due to climate change, understanding these mechanisms could be crucial for forestry and conservation efforts. It may also pave the way for future research on how trees could adapt to rising temperatures and unpredictable weather patterns.

By understanding these natural processes, we can appreciate just how finely tuned trees are to their environment—and how important it is to protect and study them as our climate changes.

Reference

1. Age-dependent seasonal growth cessation in Populus, Xiaoli Liao, Yunjie Su, Maria Klintenäs, Yue Li, Shashank Sane, Zhihao Wu, Qihui Chen, Bo Zhang, Ove Nilsson Ove. https://www.pnas.org/doi/10.1073/pnas.2311226120.

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