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In this episode of Talking Trees, we explore the function of the assimilation apparatus in trees—namely, the leaves and needles that drive photosynthesis and support tree vitality.
We discuss:
The structure and role of leaves and needles in gas exchange and energy production
How morphological and anatomical adaptations help trees survive environmental stress
The importance of the assimilation apparatus as a bioindicator for pollution and climate stress
Why arborists should consider these traits when selecting species for urban landscapes
This episode offers a blend of tree physiology and practical arboriculture, highlighting how understanding assimilation can guide better decisions in tree care and urban planning.
Talking Trees with Lillie and Jad. Welcome to Talking Trees. Today we explore the essential role of leaves in vascular plants, the powerhouses of photosynthesis and their diverse morphology and anatomy. We'll dive into research revealing how environmental stressors like pollution and permafrost shape the assimilation apparatus and root conductivity, and examine innovative methods for assessing urban impacts on plant health. Let's get started.
Jad:
Welcome back everybody. We're diving into something you see every single day as arborists.
Lilly:
Yeah, leaves, leaves.
Jad:
But we're going to go deeper than just the basics today.
Lilly:
Yeah.
Jad:
We've got some research articles and even some stuff from Wikipedia.
Lilly:
Oh, wow.
Jad:
To really kind of break down leaf anatomy and function and all the amazing stuff that we can see when we really start looking at leaves.
Lilly:
It's easy to overlook them.
Roger:
Yeah.
Lilly:
But you know, they're incredibly complex and they can actually tell us a lot about a tree.
Jad:
Exactly.
Lilly:
Its health, its history and even its relationship to the environment around it.
Jad:
Totally, and we all know like the basic parts of the leaf right.
Lilly:
Right.
Jad:
Pedial lamina stipules. But the really cool stuff is how that varies from tree to tree.
Lilly:
Yeah, and that all comes down to how that specific tree has adapted to survive in its own environment. I mean, its form follows function.
Jad:
Like evolution in action Right.
Lilly:
Exactly so, you know, you think about like a willow tree.
Jad:
Okay.
Lilly:
With those long, narrow leaves, that kind of droop down. Yeah, that shape lets the leaves move in the wind, so it reduces stress on the branches.
Jad:
Which makes sense, because you look at something like a pine tree Right which has needles Totally different. They're built for completely different things.
Lilly:
Yeah, they got to withstand snow loads, you know.
Jad:
Yeah.
Lilly:
Especially up in those colder environments.
Jad:
And then you've got your succulents.
Lilly:
Oh yeah.
Jad:
With their thick leaves that are designed to hold water. It's just amazing how each leaf shape is a response to its environment.
Lilly:
Direct response.
Jad:
Yeah, and it reminds me of those window plants I saw in a documentary one time.
Lilly:
Yeah.
Jad:
That grow in the desert and they have just a little window at the top. That's right Of the leaf.
Lilly:
And the rest is buried underground.
Jad:
Yeah.
Lilly:
Fenestraria.
Jad:
It's amazing.
Lilly:
Yeah.
Jad:
It's incredible how these plants have evolved to survive in such harsh conditions. It really shows you how much we can learn as arborists, absolutely.
Lilly:
If we just look at the shape of the leaf, yeah, morphology is really important to understand the tree's needs and its vulnerabilities.
Jad:
It's like each leaf is a clue.
Lilly:
It is how to care for that tree.
Jad:
Exactly, yeah.
Lilly:
So now we've got to look at the inside of the leaf to really get how it works.
Jad:
Okay, so let's do it.
Lilly:
We've got three main tissue systems.
Jad:
Okay.
Lilly:
The epidermis, the mesophyll and the vascular tissue.
Jad:
Okay, so break those down for me.
Lilly:
All right. So first up, the epidermis is the outer layer. Okay, it's like the skin of the leaf.
Jad:
Protecting it.
Lilly:
It protects the leaf from damage and from losing too much water. Gotcha.
Jad:
And then in the middle we have the mesophyll.
Lilly:
Okay, and this is where the magic happens, the magic of photosynthesis. You got it. The mesophyll is full of cells with chloroplasts.
Jad:
Right.
Lilly:
Those tiny organelles that capture sunlight and turn it into energy for the tree.
Jad:
So the mesophyll is divided into two layers, okay, the palisade layer, yep, and the spongy layer.
Lilly:
So the palisade layer is right underneath the epidermis.
Jad:
Mm-hmm.
Lilly:
And it's tightly packed.
Jad:
Okay.
Lilly:
With cells that are full of chloroplasts.
Jad:
So they're maximizing light absorption.
Lilly:
Exactly like a super efficient solar panel. Cool. And then underneath that we've got the spongy layer.
Jad:
Okay.
Lilly:
And that has more airspace between the cells.
Jad:
Why is that important?
Lilly:
Because gas exchange needs to happen there.
Jad:
So that's where the carbon dioxide comes in and the oxygen goes out. That's right. It's amazing how all these layers work together.
Lilly:
It's pretty incredible.
Jad:
Yeah.
Lilly:
A real symphony of form and function. So, and speaking of efficient systems, yeah, we can't forget about the vascular tissue.
Jad:
The veins.
Lilly:
The veins.
Jad:
Yeah, tissue the veins, the veins. Yeah, the leaf's highways.
Lilly:
That's a good way to put it.
Jad:
Transporting water and nutrients.
Lilly:
Exactly. They bring water and minerals to the cells and carry away the sugars that are made during photosynthesis.
Jad:
And they provide support.
Lilly:
They do. They help the leaf keep its shape.
Jad:
So I remember from botany class that there are different types of venation patterns there are it's? Parallel and reticulate. You got it yeah.
Lilly:
So parallel venation is common in monocots. Okay, like grasses.
Jad:
Right.
Lilly:
And the veins run alongside each other. Yeah, but reticulate venation is more common in dicots.
Jad:
Okay.
Lilly:
It's much more intricate. The veins branch out and create a network.
Jad:
I was reading the Wikipedia article on leaves. Oh yeah, and they had all this crazy terminology.
Lilly:
They really go deep.
Jad:
For the different vein patterns Right. You've got pinnate palmate.
Lilly:
Yeah, and then like brocadidromis.
Jad:
Brocadidromis.
Lilly:
Pipidromis.
Jad:
Peptidromis A lot. Yeah, they're mouthful, but basically they're just describing how the veins are connected within the leaf. To make the most of the water and nutrient flow.
Lilly:
So even those tiny veins play a big role.
Jad:
They do, yeah, and especially in tough urban environments. Right that efficiency can really make a difference between a tree thriving or just barely surviving. That brings us to the research articles. Yes, that we want to talk about. Okay, one of them was looking at how leaf anatomy actually changes in response to stress. It was from the IOP conference series Earth and Environmental Science.
Lilly:
That's the one, and they looked at trees in cities and industrial areas.
Jad:
Right where they're exposed to pollution hordes of challenges, Limited root space, all kinds of stuff, but they're exposed to pollution.
Lilly:
Exactly, horts of challenges, limited root space, all kinds of stuff, yeah, but they found that trees are really adaptable.
Jad:
That's good.
Lilly:
It is their leaves can actually change their structure to deal with those tough conditions.
Jad:
So what kind of changes?
Lilly:
Like what did they see? So they found that birch trees in the city.
Jad:
Okay.
Lilly:
Had thicker mesophyll layers compared to birch trees in more natural environments.
Jad:
Like bulking up.
Lilly:
Yeah, like they were bulking up.
Jad:
To withstand the stress.
Lilly:
Yes to withstand the stress.
Jad:
So in a way, that's a good sign right.
Lilly:
It is a sign that they're adapting.
Jad:
They're fighting back. And then you also had an article about the chemical composition of leaves.
Lilly:
Right.
Jad:
What was that one?
Lilly:
So this one was from the Urban Trees Assimilation Efficiency Journal and it looked at the balance of sugars and starches and fiber inside the leaves.
Jad:
Okay.
Lilly:
And how that changes throughout the year.
Jad:
So it's not just a set thing.
Lilly:
No, it's not static.
Jad:
Okay.
Lilly:
It changes as the tree needs change.
Jad:
So what does that mean for us?
Lilly:
As arborists. How can we use that knowledge? Well, they found that this balance can actually tell us how healthy a tree is.
Jad:
Oh, wow.
Lilly:
And how well it's adapted to its environment.
Jad:
That's really useful. It is.
Lilly:
So you know if we understand what a healthy balance looks like.
Jad:
Right.
Lilly:
We might be able to spot signs of stress or even disease early on.
Jad:
Just by.
Lilly:
By looking at changes in the leaf color.
Jad:
Okay.
Lilly:
The texture or even how quickly those fallen leaves decompose.
Jad:
That's fascinating.
Lilly:
It is.
Jad:
It's like we've got this whole other tool Right To help us diagnose problems.
Lilly:
It's another tool in our toolkit.
Jad:
Yeah.
Lilly:
To help us make better decisions about how to care for trees.
Jad:
So we've got two really interesting research articles here.
Lilly:
Yeah.
Jad:
Both looking at how leaves adapt to stress, but you also mentioned something from Wikipedia about leaves.
Lilly:
Right.
Jad:
What was that?
Lilly:
So the Wikipedia article gives a great overview, okay, of leaf morphology.
Jad:
Yeah.
Lilly:
And it covers some really interesting points about leaf evolution and ecology. Cool, it also goes into a lot of detail about the different types of leaves.
Jad:
Right, we did touch on that with those complex vein patterns.
Lilly:
We did. But the Wikipedia article goes even further. Okay, you know. It talks about how leaves are connected to the rest of the tree and the environment around it.
Jad:
Yeah, they're not just these isolated things.
Lilly:
They're not. They're part of a much bigger system.
Jad:
They're constantly interacting with their surroundings. That's right, yeah.
Lilly:
Responding to light and temperature, humidity. Humidity and even pests.
Jad:
Or pathogens.
Lilly:
Exactly.
Jad:
Yeah.
Lilly:
And understanding these interactions.
Jad:
Is crucial.
Lilly:
Is so important for arborists. Yeah these interactions is crucial, is so important for arborists. Yeah, we need to be able to see how the environment is affecting the leaves Right and, ultimately, the health of the whole tree.
Jad:
So it sounds like this Wikipedia article it does Gives us a really good way to think about leaves more holistically.
Lilly:
It helps us to see the bigger picture.
Jad:
Yeah, and it ties in with the research we've been talking about it talking about. By combining that broad overview with the specific insights from the research, we can really start to get a much deeper understanding of how these work. But there's one more article you wanted to talk about, yes, from the Ukrainian Journal of Ecology. That's right. What's that one all about?
Lilly:
So this one's really interesting, okay. It specifically looks at the chemical composition of leaves and how that relates to a tree's ability to adapt to those tough urban environments. It goes into the balance of sugars, starches and fiber.
Jad:
Okay.
Lilly:
And how those components can tell us about the tree's health.
Jad:
So it's similar to that urban trees assimilation efficiency article.
Lilly:
It is. There are some similarities.
Jad:
Okay.
Lilly:
But this one has a slightly different focus. So it's similar to that urban trees assimilation efficiency article shifts over the growing season and how those shifts show us how the tree is adapting.
Jad:
So it's like we're seeing the chemical processes inside the leaf.
Lilly:
Exactly as it responds, as it's responding.
Jad:
To those urban conditions.
Lilly:
So that urban environment.
Jad:
That's really cool.
Lilly:
It is, and it gives us another way to assess tree health.
Jad:
So what are some of the key takeaways?
Lilly:
From this article.
Jad:
Yeah, that our listeners should keep in mind.
Lilly:
Well, one of the key takeaways From this article, yeah, that our listeners should keep in mind Well one of the most interesting things they found is that the balance of those components. It's not static, it's dynamic.
Jad:
What does that mean?
Lilly:
It means it changes throughout the growing season as the tree responds to what's happening around it.
Jad:
So those changes can tell us how well the tree is adapting Exactly. That's really helpful.
Lilly:
It is.
Jad:
So if we see a weird pattern, yeah, unusual. In those components. It could mean the tree is struggling.
Lilly:
It could be a sign that something's not right Right, but of course we always need to look at the whole picture.
Jad:
Yeah.
Lilly:
Not just one thing in isolation.
Jad:
Right.
Lilly:
But this research gives us another piece of the puzzle when we're trying to figure out how healthy a tree is.
Jad:
It's amazing how these research articles are all giving us this more holistic view. They are Of leaf. Before we move on, I wanted to go back to that Wikipedia article.
Lilly:
Okay.
Jad:
And talk about Agnes Arbor's partial shoot theory of leaf development.
Lilly:
Oh yeah, that's a fascinating one.
Jad:
Yeah, what is that?
Lilly:
It basically says that leaves are modified shoots.
Jad:
Okay.
Lilly:
You know they come from the same place as the shoot tips.
Jad:
So instead of turning into a stem right.
Lilly:
They turn into a leaf Exactly, and this idea is supported by studies that show how compound leaves with all those leaflets actually branch out like shoots do.
Jad:
That's really interesting.
Lilly:
It is. It shows that even something as simple as a leaf can have a really long evolutionary history and a complete way of developing.
Jad:
It really makes you appreciate how much we still have to learn about nature.
Lilly:
It really does.
Jad:
Every time we look closer at something, it just opens up all these new questions, a whole new world, and this episode has shown us Right that even something as simple as a leaf can teach us so much.
Lilly:
It's full of surprises.
Jad:
It is.
Lilly:
So keep asking questions.
Jad:
Stay curious.
Lilly:
Stay curious and never stop learning.
Jad:
We hope you learn something new.
Lilly:
And that you'll see leaves in a whole new light.
Jad:
Until next time.
Lilly:
Happy treeing, happy treeing.
Jad:
Happy treeing everyone.
Roger:
Thank you for joining us on this episode of Talking Trees. Today, we examined the critical functions and adaptive mechanisms of leaves in vascular plants, with a focus on environmental impacts such as pollution and permafrost. With a focus on environmental impacts such as pollution and permafrost, we also reviewed innovative approaches for assessing urban effects on plant physiology. We appreciate your attention and look forward to further discussions in our upcoming episodes. You
