Water movement in trees

[Mark]

Here is an interesting video on water movement in trees.

http://gowood.blogspot.com/2012/12/wood-science-101-7-water-movement-in.html

[noreast maple]

Interesting!! Thanks.

[mustanger]

I really appreciate this posting. Wow! It sure helps answer some questions about sap movement, that I've always wondered about.

[red maples]

Very cool. and that one scientist had GREAT hair!!!!

[Starting Small]

I was glad to see it, I just do not think I will be able to explain it to someone again! Really is amazing how nature works sometimes

[wildlifewarrior]

Interesting but I have some issues, one is he never really discusses how important adhesion is in this whole process, if it wasn't for adhesion of H2O molecules the whole process would be impossible, similarly there is cohesion between the walls of the xylum and the water itself. He did mention capillary action which works on the process of cohesion and adhesion, but with the complex structure of xylem, I imagine that in a tree it could move more than the 1m he mentions. He also never discussed the pressure of the ground and ground water around the roots. I am talking about the actual pressure put on the roots not osmotic pressure.

Now my real question is he continued to mention that it is all coming off of the leaves which is fine for the summer, but what about now when there are no leaves and the trees are transporting the sap up....hmmmmm.

Mike

[DrTimPerkins]

Here is an interesting video on water movement in trees.

http://gowood.blogspot.com/2012/12/wood-science-101-7-water-movement-in.html

Very interesting video. Just be aware that the while the processes of transpiration (mostly when leaves are on trees, although there can be some transpiration through fine twigs as well) and water uptake and sap exudation (during the spring/fall when there are no leaves on trees) have some similarities, there are some important differences as well.

So about the critical lack of bubbles in the xylem system. Correct mostly....but bubbles do spontaneous form all the time. However the xylem system has ways of trapping these bubbles locally to prevent the system from cavitating entirely and stopping transport throughout the tree. Kind of like instantly sticking a finger in a hole that forms in a dam. With the right high-frequency microphones and amplifiers, you can hear the bubbles form (sounds like clicks) inside the tree on a hot sunny day. It is just that the tree has billions of xylem elements (pipes), so they are extremely redundant, with lots of possible pathways for sap to move around a cavitated element, so that even tens of thousands of bubbles forming doesn't impede water movement. In cold temperatures however, water cannot hold dissolved gases very well, so cavitation (bubble formation) occurs much more extensively, pretty much breaking the water transport system in trees in the winter. The sap exudation mechanism in maple trees is thought to be an evolutionary adaptation to "refill" or repair the cavitated vessels, so that when leaves come out again, all the pipes have been fixed and transpiration can begin again.

Also....the Dr. John Sperry they mentioned, an EXCELLENT scientist and expert in water transport in trees, was (back in the late 1980s, early-1990s) a Post-Doc with Dr. Mel Tyree, who happened to be the former Director of the UVM Proctor Maple Research Center, and undoubtedly the foremost expert on water transport in trees.

[wildlifewarrior]

Very well explained Dr. Perkins. That is fantastic info about the bubbles. I was thinking that there must be a way for trees to deal with gases in the xylem. Mainly since we drill into a tree, or woodpeckers, or beetles etc.

Mike