Roger: 0:02

Talking Trees with Lillie and Jad. Welcome to Talking Trees. Today we explore how plants sense and respond to mechanical forces like wind and pressure at the cellular level. We'll delve into the biological mechanisms behind signal transmission and growth. Adaptation focusing on thigmomorphogenesis and apex development. Adaptation focusing on thigmomorphogenesis and apex development. Integrative models combining biomechanics and mechanobiology are shedding new light on these complex responses. Let's dive in.

Jad: 0:37

Welcome back everyone, especially all you arborists out there. If you've ever looked at a tree and wondered, hmm, is that thing going to stand up to the next big windstorm? Or what's the best way to prune this to keep it healthy, well, today's for you.

Lilly: 0:54

We're going to dive into how trees sense and respond to all the forces they deal with. You know the pushes and pulls, like they've got this inner force meter always checking things out.

Jad: 1:04

We're calling it plant mechanobiology and we've got this awesome research paper as our guide Mechanosensitive Control of Plant Growth. It's a little dense, but don't worry, we'll break it down. Make it practical, like how knowing this stuff can actually help you out in the field every day.

Lilly: 1:20

You know, I think a good place to start is with something called mechanical loads. Basically, these are all the forces acting on a tree.

Jad: 1:25

OK, so like what? Wind? Obviously Gravity.

Lilly: 1:28

Yeah, exactly you got it Like when a big gust of wind slams into the crown right. Or how gravity is always pulling down on those branches. All those external forces create stress and strain, kind of like what you see in a bridge or a building.

Jad: 1:39

So, as arborists, we're not just looking at the tree itself, but also all these invisible forces that are constantly shaping it.

Lilly: 1:46

You got it. And then you've got internal forces too, like turgor pressure. It's the pressure from the water inside the tree's cells. It's what keeps it rigid, kind of like how air pressure keeps a pyre inflated.

Jad: 1:56

So it's like there's this push and pull, external versus internal kind of a constant tug of war going on inside the tree.

Lilly: 2:03

Perfect analogy and getting that balance is key for us to really assess a tree's stability, you know and predict how it's going to react in different situations.

Jad: 2:10

Now, one thing that's always fascinated me is how trees handle bending stress. You know, wind can be a tree's best friend or its worst enemy.

Lilly: 2:19

Oh, absolutely. And when it comes to bending, the stem is the real star of the show. Think of it like a composite beam it's made up of all these different tissues and each one reacts to stress in its own way.

Jad: 2:30

So different tissues have different strengths, different weaknesses.

Lilly: 2:34

Exactly the bark, the wood. They all have their own unique properties that contribute to the stem's overall strength how much it can bend without breaking. But here's the thing and this kind of blew my mind when I first read about it the shape of the stem has a bigger impact on how stress is distributed than the stiffness of the tissues themselves.

Jad: 2:55

Wait, really so the geometry of the stem trumps the material. That's wild.

Lilly: 2:59

It is, isn't it? Think about it You've got a tall, skinny stem and then you've got a short, stocky one. That tall guy is going to experience way more bending stress under the same wind, even if the wood itself is just as strong. That's why you often see trees in those super windy spots, like out in the open, developing those thick tapered trunks. It's like they're adapting to the wind, you know, getting tougher.

Jad: 3:21

So when we're out there pruning, we've got to be thinking about more than just what we're cutting off. We need to think about how those cuts are going to affect the whole shape of the tree, how the stress is going to be distributed after we're done.

Lilly: 3:33

Exactly. Pruning can make a tree stronger or it can weaken it. It all depends on how it's done. We've got to work with the tree, not against it. You know, work with its natural mechanics.

Jad: 3:50

Now we all know that trees grow from the tips of their branches, and right at the very tip of each shoot there's this tiny little powerhouse called the shoot, apical meristem or SAM.

Lilly: 3:54

Oh yeah, the SAM it's like the control center for growth, the brain of the operation that's constantly cranking out new cells that turn into leaves, stems, you name it.

Jad: 4:03

It's kind of hard to believe that something so small can drive all that incredible growth we see in trees.

Lilly: 4:08

I know right, and here's the crazy part it's also under a ton of pressure, like literally. There's this thing called the pressurized vessel model that helps us understand how it works. Imagine the SAM like a tiny little pressure cooker. It's packed with cells all pushing against each other.

Jad: 4:24

So SAM is like a tiny pressurized growth chamber within that chamber, the points with the highest stress.

Lilly: 4:36

they're actually right at the edges where those new leaves are forming. It's like those spots where the SAM is being pulled in different directions, trying to balance growth with, you know, staying strong and not falling apart.

Jad: 4:44

Yeah, it sounds like a tough job being the SAM.

Lilly: 4:46

Yeah.

Jad: 4:47

So how does all of this, this knowledge about the SAM and its stress points, how does it change the way we think about pruning, like when we're deciding between, say, topping a tree versus doing some selective pruning?

Lilly: 4:59

Well, when you top a tree, you're basically chopping off a big chunk of the crown and that can really mess up the stress distribution in the SAM. You end up with weak, poorly attached growth. But when you do selective pruning you're working with the tree's natural branching patterns and that helps to keep those stress points under control. You end up with healthier growth, a stronger tree.

Jad: 5:20

Okay, so we've got this tiny pressure cooker, the SAM, and it's reacting to all these stress points. But how does a tree actually know, when it's being bent or pushed around, what's the sensing mechanism?

Lilly: 5:33

That's where it gets really cool Trees. They don't have eyes or ears like we do, but they've got this whole system for feeling mechanical strain. It's like a sixth sense for forces.

Jad: 5:42

So they're feeling the force, but how?

Lilly: 5:45

Well, scientists think it involves these special cells maybe hanging out in the areas that get stressed the most, like the parts of a stem that bend a lot or those boundaries around the sand we were talking about.

Jad: 5:54

Makes sense, Put the sensors where the action is right. But how do these cells actually, you know, detect the strain?

Lilly: 6:01

One idea is that it has to do with something called mechanosensitive ion channels. They're these tiny pores in the cell membrane that open and close depending on the pressure or stretching. You can think of them like little gates controlling the flow of ions in and out of the cell.

Jad: 6:16

So like when the cell wall bends or stretches, it pulls on these channels and that triggers a signal.

Lilly: 6:21

Bingo, and those signals they often use calcium ions can then spread throughout the whole plant, that's how they affect all sorts of things, from gene expression to you.

Jad: 6:33

know how the tree grows, so calcium is like the tree's internal alarm system.

Lilly: 6:34

Yeah, kind of it's a really fast signal and it goes everywhere, letting the tree know what's going on. It's a big player in how plants deal with stress.

Jad: 6:41

Okay, so we've got these strain sensing cells, the ion channels and calcium running all over the place, but how does that actually change how a tree grows? How does it know to like, grow thicker in certain places or change its shape to handle the wind?

Lilly: 6:57

Remember those cortical microtubules we were talking about earlier, those tiny scaffolds that tell the cells how to divide and grow? Well, mechanical stress can actually change their orientation. It's like those strain signals are giving the construction crew inside the cells directions you know, telling them where to build and where to reinforce.

Jad: 7:13

So the tree can literally redirect its growth, like depending on which way the force is pushing or pulling it.

Lilly: 7:19

Yeah, exactly, that's one of the big reasons trees can adapt to all kinds of environments. A tree in a sheltered spot might grow tall and slender, while one out in the open battling the wind all the time will end up thick and stocky, more spread out.

Jad: 7:36

It's incredible. It's like the tree is constantly analyzing its surroundings, feeling the forces, and then like coming up with a plan for how to grow.

Lilly: 7:42

It really is, and this brings up an important point Plant mechanobiology isn't just about what happens in a single cell or even a single tissue. It's about how everything works together.

Jad: 7:53

So we need to think about the whole tree, not just the parts.

Lilly: 7:56

Right To really understand how these forces affect a tree. We need to see the bigger picture, how all the different processes are connected.

Jad: 8:03

And that's where like models and simulations come in right.

Lilly: 8:06

Exactly. Scientists are using these really complex computer models to try to figure out how trees respond to different forces. They factor in things like, you know, the properties of the tissues, the shape of the tree, even the wind patterns.

Jad: 8:19

So they're basically building virtual trees and putting them through wind tunnels and stuff.

Lilly: 8:23

In a way, yeah, and then they compare those simulations to what they see happening with real trees out in the world. It helps them understand how trees work, how they might react in different situations.

Jad: 8:32

It's pretty amazing stuff, right, but there's one thing I keep wondering about. We've been talking about how trees respond to stress in the moment, but do they have any memory of what's happened to them before? Can they learn from past storms or injuries and get tougher in the future?

Lilly: 8:48

Now that's a great question, and it's something researchers are still trying to figure out. We know that trees that go through repeated stress they do get stronger over time, so there's got to be some kind of memory involved, but we're not totally sure how it works.

Jad: 9:03

It's like muscle memory, but for trees.

Lilly: 9:05

Huh, yeah. One possibility is that all that stress triggers these changes called epigenetic changes. They don't really change the tree's DNA, but they change how those genes are expressed. You know how they're used.

Jad: 9:17

So, like the tree, is rewriting its own instruction manual based on its experiences.

Lilly: 9:21

Not rewriting it exactly, but more like adding notes or highlighting certain parts, making some instructions more important than others.

Jad: 9:29

Mind blown. So trees aren't just reacting, they're learning, changing their whole growth strategy as they go, becoming more resilient.

Lilly: 9:37

And that's something we need to think about when we're taking care of trees. If we understand how they learn from stress, maybe we can actually use that knowledge to help them get stronger, you know, to help them live longer.

Jad: 9:47

So we're not just pruning branches, we're shaping memories, influencing the tree's future shaping memories influencing the tree's future.

Lilly: 9:54

Yeah, in a sense we are. We're starting to understand that our actions have these long-term consequences and that we can actually play a role in shaping a tree's destiny.

Jad: 10:01

That's a pretty powerful realization. It feels like we're entering a whole new era of tree care, one that's based on a much deeper understanding of how trees work, how they sense and respond to the world around them.

Lilly: 10:13

And with that understanding comes a responsibility. You know to use that knowledge wisely, to care for trees in a way that supports their health and resilience for years to come.

Jad: 10:23

Okay, so we've covered a lot of ground here, from those tiny sensors in the cells to these big picture ideas about tree memory and adaptation. But I'm curious how does all of this amazing science translate into action for arborists out in the field? How can we use this knowledge to make better decisions when we're actually taking care of trees? I feel like we've been given this secret decoder ring to understand how trees work. We're starting to get how they see the world, how they talk to themselves and how they deal with all the stuff that gets thrown at them.

Lilly: 10:54

And that understanding it gives us so many more options for how we take care of them. We can move beyond, just you know, reacting to problems, we can actually start shaping the tree's future, helping it grow the way we want it to.

Jad: 11:06

So like give us some real-world examples. How can we use this plant?

Lilly: 11:14

mechanobiology stuff, to make better decisions when we're out there working on trees. Well, think about pruning. In the past, we mostly focused on just getting rid of dead branches or, you know, shaping the tree to look a certain way. But now we can actually think about how each cut is going to affect the tree's structure. You know how the stress is going to be distributed. We can actually plan for the long term. Think about how we want the tree to grow.

Jad: 11:36

So we're not just cutting branches, we're actually manipulating forces shaping how the tree responds to its environment.

Lilly: 11:43

Exactly Like we know that some branching angles are just naturally weaker, more likely to break, so when we prune we can try to encourage wider angles, you know, to make the whole branch structure stronger.

Jad: 11:55

It's like we're sculpting the tree's skeleton, making it strong so it can live a long, healthy life.

Lilly: 12:01

That's a great way to put it and this idea. It applies to all sorts of other stuff too, like when we're trying to figure out if a tree is stable. We can't just look at what we see on the outside. We need to think about you know what kind of stress it's been through in the past how the forces are distributed inside and how well it can adapt to change.

Jad: 12:16

It's like we've got this whole extra layer of understanding. Now we're seeing not just the tree as it is right now, but also how it got that way and how it's going to keep growing and changing in the future.

Lilly: 12:31

And that deeper understanding helps us make smarter decisions about how to take care of it. Like, let's say, we see a tree that's showing signs of too much stress. Maybe we can't see any damage yet, but we know it's been through a lot. We might recommend cabling or bracing it to help it out. Or maybe we adjust our pruning strategy based on how much wind the tree is exposed to. We can anticipate how it's going to react, you know, and plan accordingly.

Jad: 12:51

So it's more about prevention, being proactive, instead of just reacting to problems after they happen.

Lilly: 12:56

Exactly that's where the real power of this plant mechanobiology stuff comes in. It helps us become better advocates for trees, not just helping them survive, but helping them thrive.

Jad: 13:06

I mean, it's a pretty exciting time to be an arborist, wouldn't you say?

Lilly: 13:09

Absolutely. We're on the cutting edge of tree care. Science and practice are coming together to give us this whole new level of understanding of how these amazing organisms work.

Jad: 13:21

So if you had to give our listeners just one takeaway message, what would it be? What's the one thing they can do right now to start using these ideas in their work?

Lilly: 13:30

Hmm, I'd say stay curious, never stop watching trees, asking questions, learning new things. The more we learn about plant mechanobiology, the better we'll be at taking care of trees.

Jad: 13:41

Couldn't have said it better myself, and remember everyone. We're all in this together. We're a community of tree lovers, and the more we share our experiences and observations, the more we'll all learn.

Lilly: 13:50

Well said. The more we uncover about how trees sense, respond and adapt, the more we realize how tough, how intricate, how vital they are to our world.

Jad: 14:00

And on that note, I think it's time to wrap up our deep dive into the amazing world of plant mechanobiology. Thanks for joining us today.

Roger: 14:10

Thank you for joining us on this episode of Talking Trees. Today we delved into the fascinating world of plant mechanobiology, exploring how plants sense mechanical forces like wind and pressure at the cellular level. We discussed integrative models that blend biomechanics and mechanobiology to shed light on phenomena like thigmomorphogenesis and apex development. We hope this deep dive inspires you to appreciate the complex interplay between biology, physics and modeling in understanding plant adaptation. Until next time,