Trees hold their breath

Scientists studying Ponderosa pines in a Colorado forest were interrupted by a wildfire – which led them to a surprising discovery.

The researchers were investigating the trees’ photosynthesis, during which they take in CO2 through pores in their needles, called stoma.

When heavy smoke from the wildfire filled the forest, the scientists had their equipment in place and operating, and witnessed something unexpected: the trees held their breath. They closed their stoma, apparently to stop the smoke from entering.

The scientists combed past research for something similar, and found a study from 100 years earlier, that showed coal smoke caused a different species of pine to produce a semi-permeable pitch blocking their stoma, to exclude the smoke while still allowing some CO2 to enter.

In both cases, reduced CO2 meant reduced photosynthesis…which meant the trees produced less glucose.

Glucose powers the growth of new wood -- and new needles to conduct more photosynthesis. So, when the trees close their stoma, it slows growth.

Other scientists estimated that the trees’ growth rate during these smoky conditions fell by up to 15% -- as they traded growth for protection from smoke.

Clearly, over millions of years of evolution, this has proven a successful strategy. Understanding it will help scientists better predict how forests may be shaped by wildfires in the future.