Aerial roots tighten when they hit the ground.

Sometime ago I read about fig roots tightening as they hit the ground, acting like tent ropes, pulling tight to help hold the tree steady. Claus Mattheck in his book ‘Design in Nature: Learning from Trees’, references a paper by zimmerman et al. saying “the anchored aerial roots tighten themselves up so much that they can easily raise a pot of soil in which they are anchored.” As more roots grow down they cross over each other, welding together to¬†form a network of support for the tree.

 

Fig aerial roots tighten
An aerial root that has pulled tight, and a couple of smaller roots that are still lose and twisted.

 

Recently I noticed some of my plants displaying this behaviour and it made me think about how cleaver it is! How does the root know when it has hit the ground? What makes it decide to start tightening? How does the root go about tightening?

The root may realise it is now in the dark and pull tight, but I’ve seen aerial root tips covered in hessian¬†to keep them moist and they don’t pull tight, so it’s probably not light related. If it is the dark that triggers the root to tighten then the root would need to remember it had previously been in the light, understand that it’s environment had changed and it should now tighten. I really have no idea what mechanism is triggering the root to change its behaviour!

Once the root has noticed it is in the ground, how does it then go about tightening the root? It seems to me that the plant would need to kill off cells in the root, like removing links in a loose necklace, causing the root to shorten and therefore tighten. Some how selecting cells that are now excessive and using ‘Apoptosis’ to kill off the cells. What ever mechanism the root uses to tighten it is surely a complicated process that needs to be driven by some intelligence.

Most people still find it hard to believe animals are intelligent, so to expect someone to accept plants are intelligent, is a bit of a stretch. In fact it’s hard to find many biologists or even botanists that accept plants are intelligent so I don’t suggest you bring it up if you want to get a job in science – maybe I should take my own advice!

Anthony Trewavas in his excellent (but complicated to read) book writes about plants using swarm intelligence. Individual parts of the plant communicating and working together as a team. Other references, starting with Darwin, refer to the tips of roots having a section near the tip, that acts like a brain. Hopefully the next generation of biologist will be more open-minded and start to unlock how these amazing processes are driven.