How do plants impact the carbon  system? This was my question for project week this year. In my project I measured the carbon dioxide levels of four different phytoplankton cultures, each with the fertilizer variable changed to see which conditions were the best for the most efficient phytoplankton.  Phytoplankton are microscopic plants that live in the ocean, they are at the bottom of the food chain and produce 60% of the world’s oxygen. Also, I measured the carbon dioxide levels of a potted succulent, an unpotted chenopodium and a birthday candle.

First, to measure the carbon dioxide ppm (parts per million) I built an airtight apparatus using water as the seal.  I started with a 9 x 13 pan, placed four tiles on the bottom with a larger tile to cover the four. Then I placed a CO2 sensor hooked up to a Rasberry Pi computer to record the results. After the tiles were in place and the sensors were on the large tile, I placed a fish tank upsidown over it all to finalize the seal with water.  From there, all the different experiments had slight variations of this system. For example, for the birthday candle, I needed to put tinfoil on the top to prevent the fire from warping the plastic. Another example is, for the phytoplankton, I needed to take the lid to one of the culture jugs and poke two holes in, push the air tubes through and connect it to an air pump in the airtight apparatus.

All the phytoplankton cultures had different amounts of miracle grow in them. For phytoplankton culture 1, which had 3/4 tsp of miracle grow. The lowest point of the carbon dioxide ppm lowers every day, the low on day one is 974 then 904 and then 874. This is probably due to the forced air, photosynthesis and cellular respiration. Cellular respiration is when organisms use oxygen to break down food molecules to get chemical energy that a cell requires, causing the plant to emit CO2. Photosynthesis is when plants use light to convert water and carbon dioxide into food and in the process, emit oxygen. This culture had the second darkest color, but the third best productivity in photosynthesis. This means, although color gives hints about the most productive sample, it is not always correct. However, in instances like culture 3 and 4, color was accurate. 

Culture 2, the culture with 2/4 tsp miracle grow was the sample with the third darkest color, had the second most productivity with a low of 591 ppm. In culture 3, which had 1/4 tsp miracle grow, the color was the darkest of all of them and the most productive, reaching a low of 437 ppm.  In culture 4, which had no miracle grow, the color was extremely transparent (basically clear but with some residue). I thought it was all dead due to the fact it looks like clear water.  It was: all the phytoplankton were either dead or severely overpowered by the bacteria performing cellular respiration causing the carbon dioxide levels to go up consistently. 

 

In addition to those experiments, I conducted three experiments, an unpotted plant, a potted plant and a candle. First, with the potted plant, I thought that because the succulent was a plant the carbon dioxide levels would decrease. Instead, there is a steady and significant incline. This is mainly due to cellular respiration from the succulent itself, bacteria in the dirt and possibly the decaying leaves on the surface of the dirt causing carbon dioxide to be released. This experiment is similar to culture 4 because they both go up, one more drastically than the other but up nonetheless. The results of that experiment resulted in the conduction of this one.

The unpotted plant, a chemodium also known as a goosefoot. It was just lying in my backyard, so I picked it up, rinsed the roots and placed it in the isolated area. This plant went up then down, and after many hours, a little bit up again. This happened everyday. Sometimes the movement was more drastic than other days.

I also tried testing fire directly. Fire requires oxygen to keep burning. In the isolation area the fire quickly absorbed all the oxygen, leaving only carbon dioxide and went out. It all happened in 15-20 seconds, too quickly for the CO2 sensor to pick anything up for a few minutes due to the lag. A few minutes later, the results were crazy high, at the max of 5000 for a while.

Plants impact the carbon system because without plants, the world would be overflowing with carbon dioxide causing the carbon system to change drastically. This is because plants breath in more carbon dioxide than they breath out. 

My hypothesis was correct.