Moneesh Upmanyu is a professor of Mechanical and Industrial Engineering at Northeastern University. He studies the structural properties of different materials and how they respond to stimuli, for use in things like microelectronics or robotics systems. Currently, he is studying how and why the leaves of rhododendrons plants curl up in cold temperatures.
The rhododendron is an attractive, blooming specimen in many landscapes and is fairly low maintenance when planted properly. When Upmanyu saw the rhododendron bush for the first time, its thick green leaves were curled up into thin tubes dangling limply from their stems. It looked dead or dying. However, a few days later, the plant seemed to have revived and leaves were spread out flat and lifted upwards towards the sun. It was a warmer day. In a recent paper, along with his colleagues examined the mechanical aspects of how rhododendron leaves curl and droop.
Temperature drop leads to the movement of water from stem into leaf here, causing the stem to droop. The water is distributed through the leaf unevenly, and as it freezes, it causes the top of the leaf to expand and the underside to contract. This makes the leaf curl. That was not the end though. When researchers cut strips from rhododendron leaves, separating them from the midrib, they curled and twisted loosely in all directions. However, with curling restricted by the midrib, those forces are redirected into just one direction, causing a much tighter curl. Rhododendrons retain their green leaves throughout winter, despite growing in tough, alpine conditions.I In the coldest weather, however, they can’t use it and their metabolism shuts down. As the deciduous trees around them lose their leaves, extra sunlight reaches the rhododendrons. That radiation can damage the leaves. By curling and drooping, rhododendron leaves drastically reduce the amount of sunlight hitting them when they can’t use it. Understanding how these mechanisms work in rhododendrons could potentially help scientists engineer crops that are more resistant to cold weather. Moreover, Upmanyu is also interested in how these same principles can be applied to engineering.
Shahjadi Jemim Rahman