Roger: 0:02

Talking Trees with Lillian Jad. Welcome to another insightful episode of Talking Trees. Today we're delving into the fascinating world of water transport in trees. Our first article explores how tree roots strategically distribute and redistribute water in the soil to ensure optimal access to water sources in the soil. To ensure optimal access to water sources. The second article dives into the microscopic mechanisms that enable trees to pump water to incredible heights. Finally, the third article analyzes related issues such as cavitation and the repair of damaged vascular bundles. Join us as we uncover the intricate processes that keep our trees hydrated and thriving. Stay tuned.

Jad: 0:53

Hey everyone, welcome to another deep dive with us. We're tackling something today that's pretty fundamental to how trees well, how trees work.

Lilly: 0:57

It really is, yeah.

Jad: 0:58

I mean every arborist out there, heck. Anyone who's ever looked at a tree has to wonder how on earth water gets all the way from the roots up to those leaves, especially when those leaves are, you know, 100 feet in the air.

Lilly: 1:11

Yeah, absolutely. I mean defying gravity like that. That's a pretty neat trick.

Jad: 1:14

It is, and we're diving into some brand new research that's well kind of shaking up how we think about that process. We've got a couple of papers that are let's just say they're making waves.

Lilly: 1:25

Yeah, they're really pushing the boundaries of what we thought we knew. It's exciting stuff.

Jad: 1:28

It is. So, to kick things off, let's start with what we thought we knew, the classic cohesion tension theory. Right, that's what we all learned in Arbery Culture 101.

Lilly: 1:38

Right, exactly that idea of negative pressure, kind of like a chain being pulled upwards, drawing water up through the xylem Like a really long straw, essentially. Yeah, pretty much. But the thing is, there have always been some well, some gaps in that theory.

Jad: 1:52

Like how much pull can water actually withstand before it breaks? And what about those pesky air bubbles that always seem to crop up in the xylem?

Lilly: 2:00

Exactly those are the kind of questions that have been bugging scientists and arborists for quite a while.

Jad: 2:07

So this is where these new papers come in, one by Liu and his team. They actually managed to look inside the xylem of living eucalyptus trees using this super sophisticated NMR imaging.

Lilly: 2:19

Yeah, that in itself is pretty impressive, being able to see what's happening in real time inside a whole tree like that.

Jad: 2:25

And what they found is? Well, it's not quite as simple as that straw analogy we were talking about.

Lilly: 2:29

No, not at all, it turns out, the xylem vessels. They're not just passive conduits.

Jad: 2:34

Meaning they're doing more than just letting the water flow through.

Lilly: 2:38

Right. The real action is happening in the vessel walls. They're structured with these. Get this these tiny skyling nanofibers.

Jad: 2:47

Imagine like a microscopic twisted rope Okay, I'm trying to picture that and those nanofibers, they're actually what, pumping the water upwards.

Lilly: 2:53

You got it. The shape and the properties of those nanofibers. They create this incredible pumping action.

Jad: 3:00

A pump like built into the tree itself. That's wild.

Lilly: 3:04

It is, isn't it? And it kind of reminds me of those Venturi pumps we sometimes use in tree care, the ones that create suction using air or water flow. It's a similar principle, but on a well, on a much tinier scale.

Jad: 3:16

So these nanofibers are like mini Venturi pumps, working away inside the xylem walls.

Lilly: 3:21

Exactly, and what this means is trees can actually push water upwards, they're not just relying on that negative pressure pull.

Jad: 3:29

Okay, my mind is officially blown. So it's not just the cohesion tension theory at work, there's this whole other mechanism happening too.

Lilly: 3:36

Right. It's a total paradigm shift and it helps explain how trees can overcome gravity with well, with much less negative pressure than we thought possible.

Jad: 3:45

And it might solve some of those, those head scratchers we were talking about, like, like how water can get up those super tall trees without, without breaking apart?

Lilly: 3:52

Exactly, it's a really elegant solution, really Nature at its finest.

Jad: 3:56

Absolutely, but hold on, before we get too carried away. I have to ask about something you mentioned earlier, that whole ice like water thing. Where does that fit into all of this?

Lilly: 4:04

Ah yes, that's maybe the most surprising discovery of all Inside those tiniest channels of the mannofibers. Well, they found water in a get this in a solid state almost like ice.

Jad: 4:17

Wait, ice inside a living tree. How is that even possible?

Lilly: 4:21

It's pretty mind-boggling, isn't it? But it's there and this ice-like water. It acts like a super slick lubricant, letting water flow through those tiny channels with almost no friction.

Jad: 4:32

So it's like an express lane for water molecules.

Lilly: 4:35

Exactly. And here's the thing they only saw this in living trees, not in samples that had been taken out and studied. It really shows you how important it is to look at the whole functioning system. You know when we're studying trees.

Jad: 4:49

It's a reminder that trees are well. They're a lot more complex than we sometimes give them credit for.

Lilly: 4:55

They really are. Every new discovery just opens up. Well, it opens up more questions.

Jad: 4:59

Totally, and this next paper we're looking at it kind of dives into that whole idea of what do they call hydraulic architecture, basically how a tree's plumbing, you know its whole water transport system is set up to be well, as efficient and resilient as possible.

Lilly: 5:16

Right, and a big part of that is this concept of segmentation.

Jad: 5:20

Segmentation OK, break that down for me.

Lilly: 5:22

Sure, so it's this idea that different parts of of the water transport system have different vulnerabilities, let's say, to things like cavitation, kind of like a fuse box in a house. You know you want the less essential circuits to trip burst if there's an overload, so you don't, you know, fry the whole system.

Jad: 5:39

OK, so like a, like a twig might be more likely to I don't know to give out than, say, the main trunk of the tree.

Lilly: 5:45

Exactly In the paper. Actually, it breaks down segmentation into two main types hydraulic segmentation and vulnerability segmentation.

Jad: 5:54

Okay, two types, so hydraulic segmentation first. What's that all about?

Lilly: 5:58

Basically it means that as you go from, say, the base of the trunk up to those the smaller branches and twigs the pathway for water, it gets narrower, harder for water to move through, kind of like a bottleneck effect.

Jad: 6:10

Right. So like a highway that gets narrower and narrower the farther out you go, makes sense. What about that second type, the vulnerability segmentation?

Lilly: 6:20

Right, so that one's all about how susceptible different parts of the xylem are to cavitation. You know those air bubbles forming and blocking the flow. And interestingly they found that the root xylem is actually usually more vulnerable to cavitation than the shoot xylem.

Jad: 6:37

Really, that seems I don't know kind of counterintuitive. Would you want to protect the roots at all costs?

Lilly: 6:41

Well, think about it this way If the roots get damaged, the whole tree's in trouble, right, but if it loses a few twigs or branches, well, that might be a sacrifice worth making to protect the overall system. It's like a built-in safety mechanism.

Jad: 6:54

So it's like the tree's what, hedging its bets, sacrificing some parts to keep the whole thing going. Pretty clever it is. And this whole segmentation idea. It helps explain why trees can survive, even when you know what we were talking about earlier, that whole idea of trees actively managing their water use.

Lilly: 7:25

Ah, good question. So it turns out that cavitation itself might actually trigger signals within the tree, telling those, telling the stomata on the leaves to close up, you know, to reduce water loss.

Jad: 7:38

Oh, wow. So it's like a, like a feedback loop the tree senses a problem and then takes action to prevent, well, to prevent further damage.

Lilly: 7:46

Exactly. It's all about that dynamic balance we were talking about. It's not just water passively flowing through a system. There's this constant communication and adjustment happening. The tree is constantly sensing and responding to changes in its environment.

Jad: 8:02

That's pretty amazing and as arborists you know we see how different species react differently to drought stress. Some are way tougher than others. Does this research shed any light on why that is?

Lilly: 8:13

Absolutely One of the papers, the one by Becker and his team. They looked at this idea of whole plant hydraulic conductance, which is basically how efficiently a tree can move water from roots to leaves, and they found that fast growing pioneer species you know the ones that quickly colonize open areas they tend to have higher conductance than slower growing, more specialized trees.

Jad: 8:36

OK. So it's like some trees are built for I don't know, for speed and efficiency, while others are more about that slow and steady approach.

Lilly: 8:43

Exactly those pioneer species can tolerate a bit more risk, you know, because they're adapted to quickly take advantage of available resources.

Jad: 8:51

And then the paper by Nardini. They focus on oak species, right yeah. What did they find out about drought tolerance in oaks?

Lilly: 9:02

They were looking at Mediterranean oaks, which face some pretty, pretty tough conditions, and they found that those drought-avoiding oaks, the ones that try to keep their tissues hydrated even when it's dry they actually maintain higher root conductance and leaf water content during droughts compared to those drought-pollerant species.

Jad: 9:18

So those drought avoiders are like what the camels of the tree world. They've got their own internal water reserves.

Lilly: 9:24

That's a great analogy. It shows how different species have evolved different strategies, you know, for dealing with water scarcity. Some will go for efficiency, others for resilience.

Jad: 9:34

So for us out there, you know, caring for trees, knowing the trees, its personality when it comes to water management is, knowing a tree's uh, its personality when it comes to water management is, well, it's pretty crucial.

Lilly: 9:42

Absolutely. It's not just about what species it is, it's about understanding how that species is, uh, adapted to handle water stress, and then you know, adjusting our care accordingly.

Jad: 9:53

It's like we're learning to speak the tree's language a little bit. You know figuring out what they need to thrive.

Lilly: 9:58

Exactly, and it all starts with understanding those fundamental processes we've been talking about.

Jad: 10:04

This whole conversation just makes me appreciate. You know just how diverse and complex trees really are and how much we still don't know about them Right.

Lilly: 10:12

Every time we think we've got them figured out, they throw us a curveball. It's what keeps it interesting.

Jad: 10:16

Absolutely. But before we move on, I think it's worth highlighting one more fascinating aspect of this whole topic the role of water storage in trees. You know it's like their internal reservoir, helping them buffer against those fluctuations in water availability.

Lilly: 10:33

Right Water storage. It's crucial for their survival, especially in those more challenging environments.

Jad: 10:40

And it's funny, you know, we used to think that once a xylem conduit cavitated, that was pretty much it game over for that part of the system.

Lilly: 10:47

Right like a blown fuse. But, as we were talking about earlier, research has shown that embolism repair is actually pretty common, meaning trees can actually refill those cavitated conduits.

Jad: 11:00

So it's not a one-way street. That changes things. How does that tie into water storage?

Lilly: 11:05

Well, it means that cavitation might actually be a key part of the water storage process, not just a sign of, you know, damage.

Jad: 11:12

Okay, now that's intriguing. Tell me more about that.

Lilly: 11:14

Sure. So I'm out in a tree. You know, on a scorching hot day, Transpiration is going full blast, the demand for water in the leaves just skyrockets and the water potential in the xylem it drops.

Jad: 11:27

The tree needs access to water and it needs it fast Right, like a sudden rush hour on the tree's internal highway Exactly.

Lilly: 11:35

And this is where cavitation can actually come into play. Remember how those helical nanofibers in the xylem walls can actually adjust their structure.

Jad: 11:43

Yeah, yeah.

Lilly: 11:44

Well, when water is scarce, they contract narrowing the water channels.

Jad: 11:48

Right, like the trees tightening its belt, trying to conserve water.

Lilly: 11:51

Precisely. But that contraction also it increases the tension within those channels, making them more vulnerable to cavitation. So some of those conduits cavitate, releasing water into the system, almost like a safety valve releasing pressure.

Jad: 12:07

So the tree is temporarily sacrificing some transport capacity to get that quick burst of water to those thirsty leaves.

Lilly: 12:15

Exactly. It's a short-term solution, but it's crucial for survival, and here's the key Because those embolisms can be repaired relatively quickly. The tree can restore its transport capacity when conditions improve when conditions improve.

Jad: 12:29

Wow, that's a brilliant system. It's like the tree has this built-in backup plan, making sure there's a steady supply of water even during those peak demand times.

Lilly: 12:38

Exactly, and the rehearage by Zwinicki and Holbrook. It really highlights this dynamic interplay between cavitation embolism repair and water storage. It shows how these processes all work together to keep the tree functioning even under stress.

Jad: 12:53

It's like we're seeing a whole new level of complexity in how trees manage their water resources.

Lilly: 12:58

It is, and it's that complexity that allows them to be so resilient to thrive in such a wide range of environments. It really challenges that old idea of xylem as just a passive pipeline, doesn't it?

Jad: 13:10

It definitely does. Okay, so I'm ready to get into the nitty gritty here. What kind of tissues are we talking about? When it comes to water storage, where is this water actually being stored?

Lilly: 13:22

Well, think of it like this Trees have both short-term and long-term water storage compartments. For short-term needs, they rely on the water that's stored within the sapwood, both inside living cells and within the lumens of those cavitated xylem conduits we were talking about.

Jad: 13:41

So the sapwood is like the tree's checking account, where it keeps the cash for everyday expenses.

Lilly: 13:45

That's a perfect analogy. It's readily accessible water that can be drawn upon quickly to meet those fluctuating demands.

Jad: 13:54

And what about the long-term storage? Where does that water come from?

Lilly: 13:56

That's where tissues like the pith and bark come into play. They act like the tree's savings account, holding larger reserves of water that can be tapped into during prolonged drought.

Jad: 14:07

Ah, so it's like the tree's squirreling away funds for a rainy day, Rather a not so rainy day.

Lilly: 14:13

Exactly. These tissues are particularly important for trees that are growing in arid or semi-arid environments. Where water availability can be well. It can be pretty unpredictable.

Jad: 14:24

So, as arborists, this is crucial information for us. Right Understanding a tree's water storage capacity, it can inform our irrigation strategies and help us select, you know, species that are well-suited to particular sites, especially with a changing climate.

Lilly: 14:42

And that requires a deep understanding of its physiological processes, just like we've been talking about today.

Jad: 14:48

Right, right, okay. So we've got the sapwood and bark as key players in water storage, but what about those cavitated xylem conduits? How do they fit into all of this?

Lilly: 14:59

Well, as we discussed, those cavitated conduits can be refilled, which means they can act as both transport channels and temporary storage compartments.

Jad: 15:06

So it's like a dual-purpose system, pretty efficient, if you ask me.

Lilly: 15:09

Nature is all about efficiency, and this dual purpose system allows trees to maximize their water use while also maintaining a reserve for times of need. It's a win-win.

Jad: 15:24

I'm starting to see how all these pieces of the puzzle fit together Cavitation, embolism, repair, water storage it's all interconnected, working in this dynamic balance to keep the tree functioning.

Lilly: 15:35

Exactly, and that's the beauty of studying trees. It's about understanding those connections, seeing how the whole system works in harmony.

Jad: 15:43

And that understanding is essential for providing the best possible care for our trees, especially as they face increasing challenges from drought and climate change.

Lilly: 15:53

Couldn't agree more. It's about moving beyond just treating symptoms and really focusing on supporting the trees, the trees natural resilience.

Jad: 16:00

Well said.

Lilly: 16:01

But I think we've laid a solid foundation for understanding how trees manage their water resources and hopefully sparked some new ideas for for how we can apply this knowledge in our work as arborists.

Jad: 16:15

So we've been really digging into how trees manage water, all the way from those microscopic nanofibers to those big picture strategies they use. But now I want to talk about, well, what can we learn from all this?

Lilly: 16:26

It's a big question, right Like all this amazing research. It's not just about understanding trees for the sake of it's, about finding well finding solutions to some of our problems.

Jad: 16:35

You know the human ones exactly is that whole biomimicry thing, you know, taking inspiration from nature to to solve those problems that it feels like it's really, it's really catching on yeah, yeah, it is.

Lilly: 16:46

And this research on trees, it's a perfect example of why I mean we were just talking about those, those bio-inspired fiber pumps, the ones based on that helical venturi mechanism. Imagine like scaling that up, creating pumps that are, you know, super efficient, use hardly any energy and can work in like the toughest conditions all thanks to trees.

Jad: 17:06

That's huge, especially with, you know, water scarcity being such a big problem in so many places. We need all the help we can get.

Lilly: 17:13

Absolutely. And it's not just pumps right. Think about irrigation systems that work like trees do, regulating that water flow, or building materials that use those principles of water storage and damage repair that we've been talking about. It's pretty exciting stuff.

Jad: 17:28

It's like trees are holding the blueprints for a more sustainable future. If we can, you know, just pay attention.

Lilly: 17:33

I love that Trees have had what millions of years to perfect these systems for managing water, and we're just starting to figure them out.

Jad: 17:41

And it's not even just the technology right, it's that whole mindset of how trees deal with stress, how they adapt. Those are lessons we can use in so many ways, like in urban planning or how we manage resources.

Lilly: 17:54

You got it. It's a whole shift in how we think, learning from trees. It forces us to think about systems, about how everything's connected and about you know that long-term resilience.

Jad: 18:06

How it's all connected.

Lilly: 18:07

It's been a pretty wild ride, hasn't it?

Jad: 18:09

It has and hopefully our listeners are walking away with you know a whole new appreciation for how amazing trees are and maybe even a little bit of inspiration to keep learning, keep asking questions and just keep exploring all those secrets that trees are still holding on to.

Lilly: 18:26

I hope so. Trees are full of surprises, that's for sure, and the more we understand them, the better we'll be able to care for them and protect that vital role they play in our world.

Jad: 18:34

Well said Well. On that note, I think it's time to wrap up this deep dive. A huge thank you to you for sharing your expertise and insights with us.

Lilly: 18:43

The pleasure was all mine. I always love talking about the amazing world of trees.

Jad: 18:48

And to our listeners. We encourage you to check out the research we've talked about today. We'll have links to those papers on our website and, as always, keep those trees healthy and thriving.

Roger: 19:00

Thank you for joining us on this journey through the remarkable water transport systems of trees. From root strategies to microscopic mechanisms and the challenges of cavitation, we've explored the intricate ways trees stay hydrated. If you enjoyed this episode, please share our podcast with your friends and leave us a review. Your support helps us continue to bring you captivating stories from the world of trees. Until next time, stay curious and keep appreciating the wonders of nature. See you in the next episode of Talking Trees.