Where Do All Those Leaves Come From?!



I wanted to link my leaf raking drudgery to some scene

in a famous movie. No go. Raking leaves is so mundane

that I could only find one movie that showed someone

raking leaves – Disney’s The Odd Life of Timothy Green.

And heck, he sprang up from a garden, all those leaves

are his cousins!

It’s Fall if you hadn’t noticed. Apple cider, football, pumpkin, wonderful colors….. and raking leaves. I spent last weekend with a rake in my hand and hate in my heart.

Maybe that’s a little strong. But when you spend time trying to put the little beggars in piles and then have to watch the wind scatter them and blow more leaves off the trees – well, you know it’s exasperating.

My efforts resulted in seven 50 gallon bags stuffed with botanical death. All told, more than 400 pounds of biomass. I stare up at the bare branches and wonder, “where did all that matter come from?”

Matter is made of atoms, so the leaves in the trash bags represent literally trillions upon trillions of atoms joined together in specific molecules. So the question is really, what was the source(s) of those particular atoms?

The tree made the leaves, but it didn’t get smaller due to its effort to produce leaves, so the material in leaves didn’t come from the mass of the tree. They were certainly organized by the tree into those biomolecules (proteins, carbohydrates, DNA and RNA, and fats) that make up the leaves, but they didn’t come from the tree originally.

The tree has roots in the soil and pulls water and nutrients into its trunk via those roots. Could the soil be where all the mass comes from? Consider this. If you have a potted plant, do you have to add soil to it every year? Nope.

Jan Baptiste van Helmont was a successful scientist, even

though it may not look like it at first. He was wrong about

digestion’s stages, but did include a description of

something that sounds a lot like the enzymes we have.

He said that trees didn’t get there mass from the soil, but

said they did get it from water – wrong. However, he said

air was involved and proposed that air was made of gas –

a word he coined.

Six hundred years ago, a scientist named Jan Baptist von Helmont measured this more carefully. He grew a tree in 200 pounds of soil from a seed until it weighed 190 pounds. Then he weighed the soil again. He found all his original dirt except for 2 ounces. I very much doubt that 190 pounds of tree mass came from two ounces of soil.

Everyone knows that trees need water. During a drought, your trees die and your grass turns brown. If water is that crucial, maybe my 400 hundred pounds of dead leaves came from water.

Water is made up of hydrogen and oxygen (H₂O).  Can all the leaves be made from just water? No way; trees (and every other living thing on Earth) are carbon based. The proteins sugars, lipids, and nucleic acids are all built on a backbone of carbon atoms, with oxygen, hydrogen, and nitrogen atoms in some specific spots.

Carbon, hydrogen, oxygen, and nitrogen are the main elements of life. You can’t change one atom into another (with the exception of radioactive elements) so all the mass in my bags of leaves couldn’t have come from just water. Certainly some of the mass came from water, after all, living things are mostly water, but there’s no way the carbon came from water.

When a tree uses sugars to make energy, some water is produced. This is called metabolic water, and we do it too. You can prove this by breathing on a mirror. See that condensation? Much of that is metabolic water. Metabolic water is important in producing the molecules of life, so important that some animals, like the kangaroo rat, can live only on metabolic water, they never drink!

Kangaroo rats can live their lives without drinking even

though they live in Death Valley. Another fun fact – they

have fur-lined cheek pouches for carrying seeds back to

their den. No drinking and fur in their oral cavity – worst

case of dry mouth ever!

So a bit comes from water, even less from soil, and none of the leaf mass springs from the tree itself. What do we have left? Only one choice comes to my mind - and your breathing it right now. 

Air? Really? How could 400 hundred pounds of leaves come from the air? It seems silly, but it’s the basis of life on Earth. Air is 78% nitrogen (N₂), 21% oxygen (O₂), and 0.00397% carbon dioxide (CO₂) – plus some water vapor. This is almost everything a growing tree needs, except for some trace minerals that can be found in that 2 ounces of disappeared soil that von Helmont measured 600 years ago. 

Basically, those things we humans breathe out (CO₂, H₂O, O₂, and N₂) are exactly what plants need to grow. We actually use only a small portion of the oxygen that we breathe in, but we do add some carbon dioxide to the air when we exhale. This is a big reason why talking to your plants makes them grow better; you're increasing the concentration of carbon dioxide in their immediate vicinity.

Plants take carbon dioxide from the air, and using the energy of sunlight, turn it into carbohydrates – this is photosynthesis. But they don’t just use the carbs for energy. The sugars are the carbon basis for synthesizing every biomolecule the plant will need in order to build leaves and wood.

We have covered carbon (from CO₂), hydrogen (from rain and metabolic water), oxygen (from carbon dioxide and metabolic water), but what about the nitrogen in DNA and proteins? Believe it or not, that comes from the air too.

N₂ in the air is hard to tear apart so the nitrogen can be used in building biomolecules. Plants can “fix” carbon themselves, turning gaseous carbon to solid carbon during photosynthesis, but they can’t fix nitrogen. To turn nitrogen into a form they can use, plants rely on nitrogen fixing bacteria in the soil.

Many plants form a symbiotic relationship with nitrogen fixing bacteria, letting them live inside nodules of their roots. Therefore, the nitrogen the trees use comes from the air, even if it passes through the bacteria first.

The top image is from art student Melchiorri. He claims

that the silk mesh stabilizes the chloroplasts and lets them

produce oxygen via photosynthesis even though they aren’t

in a cell. There are problems here, like chloroplasts don’t live

very long. The bottom image is of an artificial leaf that can

produce hydrogen and oxygen gases from water in the

presence of light. Leaves use 1% of available light; this “leaf”

already uses 7x as much of the light.

Most trees don’t harbor nitrogen-fixing bacteria in their roots, they rely on the nitrogen that the bacteria spread around and leave in the soil, or that nitrogen that comes from dead plant material. One exception is the black locust tree. It is estimated that a black locust stand of trees (and their bacteria) can add 40-60 kg (88 –133 lb.s) of nitrogen to the soil every year.

Now I can rake my leaves confident in the knowledge that I'm raking up a true miracle. They can’t weigh too much, they’re basically nothing but air, water vapor and a bit of bacterial waste. So why does my back hurt so much?

Soon, we may have artificial leaves to deal with. One recent project by art school graduate Julian Melchiorri has used chloroplasts embedded in silk protein mesh in order to carry out photosynthesis. These can be used in space, where plants have a harder time growing in zero gravity. This might be our source of oxygen on the way to Mars.

In addition, new research describes a synthetic leaf made form metal films on either side of a silicon mesh can be used to split water as occurs in photosynthesis. These synthetic leaves might be helpful in producing hydrogen and oxygen for use in fuel cells. I just hope we don’t have to rake them up.



Contributed by Mark E. Lasbury, MS, MSEd, PhD
As Many Exceptions As Rules

Pijpers, J., Winkler, M., Surendranath, Y., Buonassisi, T., & Nocera, D. (2011). Light-induced water oxidation at silicon electrodes functionalized with a cobalt oxygen-evolving catalyst Proceedings of the National Academy of Sciences, 108 (25), 10056-10061 DOI: 10.1073/pnas.1106545108

The Friday Five

In this special edition of Friday Five, we’ve collected 5 of the most popular articles from THE ‘SCOPE for 2014!

5. Is homosexuality "natural"?

4. State Fairs and Stiff Beers: Why We Can't Stop Drinking

3. Is It Really Possible For Someone To Turn Into THE HULK? Don’t Make Me Angry.

2. Science Identifies The Catchiest Songs Ever – Did Your Favorite Make The List?

1. Where Do All Those Leaves Come From?!

Contributed by:  Bill Sullivan

Follow Bill on Twitter: @wjsullivan

O Christmas Tree: It’s Not Easy Being Green

Evergreens are a remarkable mainstay in the evolution of plants. Evidence suggests that they have existed more or less in their present form for the past 300 million years. In other words, the evergreens are so resilient and exquisitely adapted to their environment that nature has not tweaked with their genetic recipe since the Permian. The evergreens can survive just about anything nature can throw at them, except humans. Nearly 40 million of these stoic conifers are chopped down each Christmas season in North America alone.

"Christmas Tree" farms cultivate a variety of evergreens that will grace one of 40 million homes each season. This makes it a lot easier than hiking into the forest to cut one down yourself.

Humans have long been fascinated by the evergreens because these trees and shrubs do not lose their leaves (needles) in autumn like the broadleaf trees. Seemingly in defiance to the harsh winter, the aptly named evergreens stay full and green all year long. Impressed with this act of endurance, early humans thought that evergreens must hold special powers. The ancient Pagans would place evergreen branches over their doors and windows to ward off evil spirits, especially during the winter solstice when the days were at their shortest and the nights at their coldest. Evergreens served as a reminder that the days would lengthen and the crops would grow once again in the spring.

A decorated evergreen is now synonymous with “Christmas Tree”, but this ritual has its “roots” in Paganism. Interestingly, it has even been argued that this passage from the Bible forbids emulating this Pagan practice.

So how do evergreens stay green year round? In winter, shorter days mean less sunlight. As sunlight is required for photosynthesis, plants face a dramatic reduction in energy during winter. To cope with this, broadleaf plants stop making chlorophyll, the molecule that drives photosynthesis and reflects green light. Consequently, the leaves change color and eventually fall off as the tree goes dormant.

By way of comparison, evergreen “leaves” do not have a lot of surface area; they are more resistant to lower temperatures and decreased moisture. Chlorophyll in these needle-like leaves is retained and photosynthesis can still generate energy from light, albeit at a much slower rate than spring or summer.

In addition to keeping chlorophyll, retaining moisture is equally important:  trees cannot extract water from frozen ground, and occasional sunlight in the winter can draw out precious moisture. Evergreen needles have a thick coating of wax and a slender shape, characteristics that help them hold water in and prevent evaporation, respectively.

A recent study has shown that the conifer’s ability to survive arid times involves the coordinated evolution of tissues regulating water supply (xylem) and water loss (stomatal pores) in the needle leaves. A plant hormone called abscisic acid helps keep the leaf’s pores sealed when water isn’t available. Another mechanism allows leaves to dehydrate and resist damage via a water transport system.

Close up image of pine needle – the small pores are stomata, which open and close to regulate gas exchange. When open, water vapor can escape.

Conifers have thousands of needle leaves, which help maximize energy production while not losing water to dehydration. Of course, evergreen needles do not last forever. They do need to be replaced, but conifers do this intermittently and a green appearance is always observed.

Ever since ancient times, the evergreens have been admired for their stamina and hardiness through the winter. They are a source of inspiration reminding us that better times are ahead. In this light, the ritual chopping down of the tree for decoration seems a most bizarre way to honor the mighty evergreen. Consider, instead, a Festivus Pole.
 

Contributed by:  Bill Sullivan

Follow Bill on Twitter.

Brodribb TJ, McAdam SA, Jordan GJ, & Martins SC (2014). Conifer species adapt to low-rainfall climates by following one of two divergent pathways. Proceedings of the National Academy of Sciences of the United States of America, 111 (40), 14489-93 PMID: 25246559

Where Do All Those Leaves Come From?!

I wanted to link my leaf raking drudgery to some scene

in a famous movie. No go. Raking leaves is so mundane

that I could only find one movie that showed someone

raking leaves – Disney’s The Odd Life of Timothy Green.

And heck, he sprang up from a garden, all those leaves

are his cousins!

It’s Fall if you hadn’t noticed. Apple cider, football, pumpkin, wonderful colors….. and raking leaves. I spent last weekend with a rake in my hand and hate in my heart.

Maybe that’s a little strong. But when you spend time trying to put the little beggars in piles and then have to watch the wind scatter them and blow more leaves off the trees – well, you know it’s exasperating.

My efforts resulted in seven 50 gallon bags stuffed with botanical death. All told, more than 400 pounds of biomass. I stare up at the bare branches and wonder, “where did all that matter come from?”

Matter is made of atoms, so the leaves in the trash bags represent literally trillions upon trillions of atoms joined together in specific molecules. So the question is really, what was the source(s) of those particular atoms?

The tree made the leaves, but it didn’t get smaller due to its effort to produce leaves, so the material in leaves didn’t come from the mass of the tree. They were certainly organized by the tree into those biomolecules (proteins, carbohydrates, DNA and RNA, and fats) that make up the leaves, but they didn’t come from the tree originally.

The tree has roots in the soil and pulls water and nutrients into its trunk via those roots. Could the soil be where all the mass comes from? Consider this. If you have a potted plant, do you have to add soil to it every year? Nope.

Jan Baptiste van Helmont was a successful scientist, even

though it may not look like it at first. He was wrong about

digestion’s stages, but did include a description of

something that sounds a lot like the enzymes we have.

He said that trees didn’t get there mass from the soil, but

said they did get it from water – wrong. However, he said

air was involved and proposed that air was made of gas –

a word he coined.

Six hundred years ago, a scientist named Jan Baptist von Helmont measured this more carefully. He grew a tree in 200 pounds of soil from a seed until it weighed 190 pounds. Then he weighed the soil again. He found all his original dirt except for 2 ounces. I very much doubt that 190 pounds of tree mass came from two ounces of soil.

Everyone knows that trees need water. During a drought, your trees die and your grass turns brown. If water is that crucial, maybe my 400 hundred pounds of dead leaves came from water.

Water is made up of hydrogen and oxygen (H₂O).  Can all the leaves be made from just water? No way; trees (and every other living thing on Earth) are carbon based. The proteins sugars, lipids, and nucleic acids are all built on a backbone of carbon atoms, with oxygen, hydrogen, and nitrogen atoms in some specific spots.

Carbon, hydrogen, oxygen, and nitrogen are the main elements of life. You can’t change one atom into another (with the exception of radioactive elements) so all the mass in my bags of leaves couldn’t have come from just water. Certainly some of the mass came from water, after all, living things are mostly water, but there’s no way the carbon came from water.

When a tree uses sugars to make energy, some water is produced. This is called metabolic water, and we do it too. You can prove this by breathing on a mirror. See that condensation? Much of that is metabolic water. Metabolic water is important in producing the molecules of life, so important that some animals, like the kangaroo rat, can live only on metabolic water, they never drink!

Kangaroo rats can live their lives without drinking even

though they live in Death Valley. Another fun fact – they

have fur-lined cheek pouches for carrying seeds back to

their den. No drinking and fur in their oral cavity – worst

case of dry mouth ever!

So a bit comes from water, even less from soil, and none of the leaf mass springs from the tree itself. What do we have left? Only one choice comes to my mind - and your breathing it right now. 

Air? Really? How could 400 hundred pounds of leaves come from the air? It seems silly, but it’s the basis of life on Earth. Air is 78% nitrogen (N₂), 21% oxygen (O₂), and 0.00397% carbon dioxide (CO₂) – plus some water vapor. This is almost everything a growing tree needs, except for some trace minerals that can be found in that 2 ounces of disappeared soil that von Helmont measured 600 years ago. 

Basically, those things we humans breathe out (CO₂, H₂O, O₂, and N₂) are exactly what plants need to grow. We actually use only a small portion of the oxygen that we breathe in, but we do add some carbon dioxide to the air when we exhale. This is a big reason why talking to your plants makes them grow better; you're increasing the concentration of carbon dioxide in their immediate vicinity.

Plants take carbon dioxide from the air, and using the energy of sunlight, turn it into carbohydrates – this is photosynthesis. But they don’t just use the carbs for energy. The sugars are the carbon basis for synthesizing every biomolecule the plant will need in order to build leaves and wood.

We have covered carbon (from CO₂), hydrogen (from rain and metabolic water), oxygen (from carbon dioxide and metabolic water), but what about the nitrogen in DNA and proteins? Believe it or not, that comes from the air too.

N₂ in the air is hard to tear apart so the nitrogen can be used in building biomolecules. Plants can “fix” carbon themselves, turning gaseous carbon to solid carbon during photosynthesis, but they can’t fix nitrogen. To turn nitrogen into a form they can use, plants rely on nitrogen fixing bacteria in the soil.

Many plants form a symbiotic relationship with nitrogen fixing bacteria, letting them live inside nodules of their roots. Therefore, the nitrogen the trees use comes from the air, even if it passes through the bacteria first.

The top image is from art student Melchiorri. He claims

that the silk mesh stabilizes the chloroplasts and lets them

produce oxygen via photosynthesis even though they aren’t

in a cell. There are problems here, like chloroplasts don’t live

very long. The bottom image is of an artificial leaf that can

produce hydrogen and oxygen gases from water in the

presence of light. Leaves use 1% of available light; this “leaf”

already uses 7x as much of the light.

Most trees don’t harbor nitrogen-fixing bacteria in their roots, they rely on the nitrogen that the bacteria spread around and leave in the soil, or that nitrogen that comes from dead plant material. One exception is the black locust tree. It is estimated that a black locust stand of trees (and their bacteria) can add 40-60 kg (88 –133 lb.s) of nitrogen to the soil every year.

Now I can rake my leaves confident in the knowledge that I'm raking up a true miracle. They can’t weigh too much, they’re basically nothing but air, water vapor and a bit of bacterial waste. So why does my back hurt so much?

Soon, we may have artificial leaves to deal with. One recent project by art school graduate Julian Melchiorri has used chloroplasts embedded in silk protein mesh in order to carry out photosynthesis. These can be used in space, where plants have a harder time growing in zero gravity. This might be our source of oxygen on the way to Mars.

In addition, new research describes a synthetic leaf made form metal films on either side of a silicon mesh can be used to split water as occurs in photosynthesis. These synthetic leaves might be helpful in producing hydrogen and oxygen for use in fuel cells. I just hope we don’t have to rake them up.


Contributed by Mark E. Lasbury, MS, MSEd, PhD
As Many Exceptions As Rules



Pijpers, J., Winkler, M., Surendranath, Y., Buonassisi, T., & Nocera, D. (2011). Light-induced water oxidation at silicon electrodes functionalized with a cobalt oxygen-evolving catalyst Proceedings of the National Academy of Sciences, 108 (25), 10056-10061 DOI: 10.1073/pnas.1106545108

Autumn Leaves: More Than Just Pretty Colors

This post originally appeared on the Telegram and Gazette 9/2012

The green tree leaves of summer are already starting to give way to the bright yellows and reds of autumn. We should have a brilliant display of colors throughout the fall.

 

As you may remember from your high school science class, what gives green leaves (and green plants in general) their color is a compound called chlorophyll, which absorbs light energy from the sun. As the summer comes to an end, the change in temperature and change in the amount of daylight trigger processes in the leaves that cause chlorophyll to break down. As this inducer of green color disappears, the color effects of other compounds, carotenoids and anthocyanins specifically, are unmasked. Carotenoids are the compounds that give carrots their orange color and bananas their yellow color. Anthocyanins can give plants bluish, purplish, or reddish tints. Red cabbage, cranberries, and red raspberries are just a few examples of produce that have high levels of anthocyanins.

For the most part, scientists thought that the changing of leaf color in autumn was simply an effect of the disappearance of chlorophyll and signaled that the leaves were about to fall.  Over the past several years, however, researchers have found that the appearance of yellow, orange, and red leaves may have additional ecological impacts.

In 2005, researchers Martin Schaefer and Gregor Rolshausen proposed that the changing leaf color actually acts as a defensive signal against consumption by herbivores (plant-eating organisms).  The "Defense Indication hypothesis," as they termed it, is based on their own work as well as on observations that support their ideas, but were made by other researchers.  Their hypothesis (or, idea that will be tested through experiments and observations) is based on the fact that the signaling pathway that causes the production of anthocyanins also causes the production of defensive compounds to which herbivores have an aversion. After enough time, it is thought that herbivores learn to associate the defensive compounds with the colored leaves and avoid them altogether.

The very hungry caterpillar ate lots of stuff, but not orange, red, or yellow leaves.

Further, the biochemical pathways that cause chlorophyll to break down become active along with pathways that cause the production of compounds called anti-feedants, which make the leaves difficult to digest. If herbivores repeatedly consume autumn-colored leaves and then become sick due to the anti-feedants, they learn to associate the red, yellow, and orange colors with a negative eating experience and avoid those colored leaves in the future.

While the primary cause of autumn leaf colors is the loss of chlorophyll, this paper discusses just one example of how the color change has a significant impact on other organisms. Like so many things in nature, one change often has the potential to ripple through the environment and bring about widespread ecological effects.

 

Contributed by:  Kelly Hallstrom

Visit Kelly’s blog, You Don’t Have To Be A Rocket Scientist
Follow Kelly on Twitter.

Schaefer HM, & Rolshausen G (2006). Plants on red alert: do insects pay attention? BioEssays : news and reviews in molecular, cellular and developmental biology, 28 (1), 65-71 PMID: 16369938