Carbon supports life on earth as we know it.
In fact, we humans are 18.5 % carbon.
Our plant friends produce carbon through a process called photosynthesis.
Through photosynthesis plants provide that delicious oxygen that humans and other animals need and love.
So, understanding how much photosynthesis is happening,
tells us a lot about how healthy the plants are in an ecosystem.
Now, we know photosynthesis is happening all around us.
We see plants growing and reproducing every day,
but how do us science minded humans measure how much photosynthesis is happening
in plants, in order to grow and produce oxygen?
How we measure photosynthesis is the topic of this video.
So let's first talk about that carbon generating process called photosynthesis.
The "photo" part in photosynthesis relates to light.
Plants use energy from light to grow.
Now "synthesis" relates the biosynthesis, or the process in which plants synthesize
light, carbon dioxide or CO2, and water to grow.
Now to support growth plants absorb CO2 from the atmosphere
through small pores in their leaves called stomata.
Using energy from sunlight, CO2 and water are synthesized to create sugar.
This sugar is then converted into energy
that plants need to grow through a process called respiration.
So the delicious CO2 that plants absorbed,
mixed with some Sun and water, creates the perfect cocktail to produce that energy that plants need to grow.
And if that's not important enough
through photosynthesis, plants also provide clean air for us to breathe.
But how do we actually measure photosynthesis?
Well one way to measure photosynthesis is to measure how much CO2 plant leaves absorb.
Because we know the plant that is actively absorbing CO2 is also performing photosynthesis.
But how do we actually measure CO2 uptake by a plant?
Well let's first place a leaf in a closed chamber that's filled with CO2 rich air.
Think about it, if the leaf in the chamber is alive, it will uptake CO2 to produce the energy that it needs to grow.
Now one way to measure the CO2 in that chamber is to use a light.
The method of using light to measure things in science is called spectroscopy.
Spectroscopy methods measure how much matter, like CO2, absorbs, reflects and transmits light.
Now CO2 loves to absorb infrared light.
So if we fill a chamber with a lot of CO2
and we shine infrared light into the chamber a lot of that light will get absorbed.
Now on the other hand, if the chamber doesn't have a lot to CO2 in it
only a small amount to that light gets absorbed.
Now equip the chamber with a detector that can measure the amount of light
that makes it to that end in the chamber.
The detector is calibrated,
which means that it relates the amount of light recorded in the box
to a specific amount to CO2.
So more light recorded means less CO2 in the chamber
and less light recorded means more CO2 in the chamber.
This chamber system is called an Infrared Gas Analyzer.
Infrared gas analyzers are commonly used to measure CO2 uptake.
So now that we understand the basics of spectroscopy,
how do we measure CO2 uptake individual leaf?
Well, we can use our infrared gas analyzer chamber system.
First, add a reference chamber on the left. We'll flow CO2 rich air through this reference chamber
and use the infrared light detector to measure how much CO2 is in the air.
Next, add a second sample chamber on the right.
Air flows from the reference chamber to the chamber with a leaf in it
and into the sample chamber. The sample chamber uses infrared light detector to measure
the amount of CO2 in the air
after the leaf absorbs what it needs to grow. We can control the volume
air moving through the chambers using a flow meter.
So we know how much air is in each chamber.
Here comes the interesting part...
we can calculate the difference in the amount of CO2 measured in our reference chamber
compared to the CO2 measured in our sample chamber.
the difference between CO2 in the two chambers is the flux.
which represents the amount the CO2 taken up by the leaf inside the chamber for photosynthesis.
The measurement of the difference in CO2 between the two chambers is called Net Assimilation or ANet.
So, the infrared gas analyzer can be used to estimate how much photosynthesis is occurring
but if that's not powerful enough it can also be used to measure how
temperature and moisture changes in our climate impact carbon uptake.
We can also add additional meters to the set up to control things like
temperature and humidity in the chamber.
So we can adjust the temperature of the chamber and measure how that affects CO2 uptake of our plant.
These measurements can also be combined with other
techniques that measure and estimate carbon over large areas.
For example, the National Ecological Observatory Network, or the NEON project,
uses an infrared gas analyzer installed on its towers across United States
to measure carbon in the atmosphere.
NEON will also be combining this atmospheric carbon data with airborne remote sensing
to model carbon across entire forests and over larger landscapes.
And so, to sum this all up
plants use CO2 to perform photosynthesis --
to grow and provide oxygen.
We can measure CO2 uptake with spectroscopy
or light measures, using an infrared gas analyzer.
These measurements can help us understand both
how healthy plants are in an ecosystem and also how changes in climate affect plant growth.
And that, my friends, is how and why we measure photosynthesis.
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