Where is the water? A new way to ‘see’ the water in tall trees 

Tall trees can experience water limitations even when soil water is readily available. Why is this? We can think of the water conducting tissues in a tree (the xylem) like a straw, and the transpiration (water loss) through the leaves like the suction power to pull water up the straw. The longer the straw (xylem), the more suction power (transpiration) that is needed, and there is a limit on how long the straw could be based on the maximum suction power. Tall trees must maintain high transpiration rates to keep water flowing up from the roots, which means that the upper canopy of tall trees is often water-stressed, and may have difficulty retaining water. So how do tall trees retain water in their upper canopy?


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