The autumn-sweet smell of decay

Did You Know? Even in death, different leaves have different smells!

People often talk about colors during the autumn season in temperate zones, but this week our nature study session unexpectedly led us to leaf sniffing!

Like all living organisms, plants are made of a variety of compounds. Some of these are called volatile organic compounds (VOCs), which are gases released into the air from leaves, stems, roots, and flowers. Volatile compounds are used in a variety of plant-animal and plant-plant interactions. Although some are the same among different species, others are unique to some species or species groups. Furthermore, plants may possess the same VOCs but may possess them in different proportions. Some VOCs are released continuously, whereas others are released at the onset of a stimulus (i.e. “something” happens to the plant) such as leaf damage by an herbivore.

The common and unique scents among leaves contribute to the overall earthy-sweet smell of walking through the woods in the fall. As leaf tissues dry and die, some VOCs disperse but others remain trapped in cells. Leaves release trapped VOCs when they are crushed. In addition, decomposition by detritivores, bacteria, and fungi further tear apart tissues and break down sugars and other stable molecules. Again, some of these characteristics are the same among plants and some are different. If you separate leaves of different species from a larger pile and crush them, chances are that for each one you can find a couple of different adjectives or even memories (e.g. “this reminds me of cherries”) to describe the smells wafting towards you.

So go ahead…grab a fistful of fallen leaves, take a big whiff, and mentally wander through the different smells. We promise we won’t tell anyone that you stopped to play and wonder with your inner child!