Sugar Poisons Leaves?

By Richard B. Primack

“In my experience I have found nothing so truly impoverishing as what is called wealth.” 

- Henry David Thoreau in his Journal. 

An innovative recent article in Science proposes that earlier leaf senescence of trees in autumn is promoted by summer condition of high light and warm temperature that favor high levels of photosynthesis.   According to this hypothesis, rapidly photosynthesizing leaves will accumulate sugar in their leaves and deplete nitrogen reserves,  promoting early leaf senescence. This early leaf senescence caused by high levels of summer photosynthesis will tend to cancel the later autumn leaf senescence caused by warmer autumn conditions associated with climate change.  

During sunny dry conditions in Boston, black birch leaves undergo leaf senescence in August. 

This study raises several key questions.  Is their “poison sugar hypothesis” a widely applicable result, or just another additional factor that contributes to variation in leaf senescence?  How can we be sure that their result is really due to high photosynthetic rate and not just due to the well-known effects of  summer drought stress? And finally, do their results apply to other species and other places?  

When their wetland habitats dry out during a drought, the leaves of coast pepperbush wilt and undergo early senescence.  

 

Here is a copy of their article from Science.

Christine Rollinson wrote a Perspective about this topic for Science.

Ula Chrobak reported on the story for Popular Science.