Hidden tree survival strategy

Most plants seem passive. They stand in place, soak up sunlight, and grow. But beneath that stillness lies a constant stream of decisions. Now, research shows trees are far shrewder about survival than scientists realized.

A study from the University of Basel in Switzerland has uncovered a surprising strategy. When water is scarce, trees shut down their food-making machinery before conditions turn dire. They’re not waiting for a crisis. They’re preventing one.

The stomata tradeoff

But there’s a cost. Open stomata also release water vapor. A single mature tree can lose several hundred liters of water this way in a single day.

Leaves are covered with microscopic pores called stomata. When open, these pores let carbon dioxide in for photosynthesis. This process turns sunlight into sugar.

For decades, researchers assumed trees pushed photosynthesis as firmly as possible, closing stomata only when drought became severe. The new findings flip that assumption.

Nighttime refills control morning behavior

The Basel team monitored trees at their forest laboratory in Hölstein. They discovered that what happens overnight determines what happens the next day.

In darkness, water travels from the roots to the cells throughout the tree. This refills tissues and builds internal pressure called turgor. Without turgor, cells cannot expand and growth stops.

Here’s the surprise: if overnight refilling falls short, trees refuse to open their stomata come morning. This even happens under ideal sunlight.

“For the first time, we were able to show that a tree does not even open its stomata in the morning if it cannot absorb enough water overnight,” explained Professor Ansgar Kahmen, co-author of the study.

Growth trumps sugar production

This behavior seems counterintuitive. Why skip a sunny day of photosynthesis?

The answer lies in priorities. Sugar means nothing if a tree cannot use it. Growth requires turgor pressure, and turgor involves water. A tree loaded with sugar but unable to expand gains nothing.

“So the aim is not to optimize photosynthesis and maintain it for as long as possible, but to use the products of photosynthesis as efficiently as possible for growth,” Kahmen said.

In other words, trees play defense before offense.

Every species follows the same rule

Study lead author Richard L. Peters, now at the Technical University of Munich, found this pattern held across the board.

“What is remarkable is that our early stomatal closure observations apply to all tree species, whether deciduous or coniferous,” Peters noted.

This consistency suggests the strategy evolved long ago. This is a fundamental survival mechanism shared across the tree kingdom.

Climate predictions need revision

The discovery carries weight beyond botany. Forests absorb enormous amounts of carbon dioxide, slowing climate change. Climate models rely on assumptions about how much carbon trees capture each year.

If trees close their stomata earlier and more often than models predict, those calculations are off. As droughts intensify worldwide, forests may store considerably less carbon than current projections suggest.

“Climate models that assume a certain growth in carbon storage volume would therefore have to be adapted,” Peters said.

Trees aren’t passive pillars. They’re making daily gambles about water, growth, and survival. Those decisions shape the future of our atmosphere.

The complete study was published in the journal Nature Plants.

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