How Scarcity and Overbundance of Co2 Affects Plants

Written by: Liam Kastell

Introduction

       Most plants function with around the same amount of carbon dioxide(CO2). CO2 is a major part of photosynthesis (Figure 1). The image below shows how photosynthesis occurs, which is impossible without the inclusion of carbon dioxide. There is a giant overabundance of CO2 in the world. This is due to carbon dioxide being thoroughly distributed through the atmosphere 

Figure 1

and the ocean from burning fossil fuels and other, natural processes. There are some exceptions, though, such as coral and one of the smallest flora known to man. One can insinuate that one of the the smallest plants uses the least amount of carbon dioxide due to less internal functions. This is also because the lower atmosphere contains less amounts of CO2 than other plant-growing areas (such as the ocean). The ocean contains 19 times more CO2 than the land, which means that compared to sea-dwelling flora all plants that grow on land are living with a deficit of CO2. The small plants use even less carbon dioxide than most land-dwelling plants.

 CO2's Effect

Figure 2

     A scarcity of carbon dioxide for plants would kill most plant species. This is because most plants need CO2  to survive, being a vital part of photosynthesis, as stated in the above paragraph. Which is supported by the chart to the right (Figure 2), which shows that when CO2 is less than anywhere lower than 900 parts per million (ppm), photosynthesis rates suffer. Carbon dioxide shortages cause death in plants or loss of health. Most smaller plants or other photosynthetic organisms are almost immune to these effects due to being small enough to not need a lot of carbon dioxide. Bigger plants (or organisms), though, would end up withering and dying in an environment that had a CO2 famine.

     Conversely, an overabundance of carbon dioxide has the opposite effect. This is shown, again, by the graph above (Figure 1). Up until 900 ppm, an increase of carbon dioxide increases the rate of photosynthesis. One can determine that by the facts presented, carbon dioxide and the rate of photosynthesis have a direct relationship up until a point. Once CO2 reaches the 900 ppm barrier, the rate of photosynthesis stops increasing. This occurs due to most plants reaching maximum saturation for carbon dioxide at around this point, causing it to not increase past it. At this level of CO2 little plants would be overloaded past the point of saturation, while most big plants would be fully saturated.

The Small Plants

Figure 3

Figure 4

      One of the smallest plants currently known to  man is Lemna Minor, or a type of duckweed (Figure 4). This weed ranges from 1 mm to 8 mm.  Insinuating that the plant uses less energy than  normal plants because of it's size, we can assume  that it takes in less carbon dioxide to produce the  amount of energy it needs. This species is found mainly in North America and Canada,  while excluding some states such as Georgia and  Nevada. This is exemplified by the map to the  left (Figure 3). Lemna Minor provides an  important role in its environment, which is proven when an author at Go Botany stated,
" Common duckweed can be used to remove excess nutrients or toxic metals from water bodies (called phytoremediation) because it is an efficient bio-accumulator, is fast-growing and hardy[...] ". The quote states that Lemna minor cleans water for other organisms and serves as nature's "filter".

    Another plant that functions akin to Lemna Minor is moss.  It can be pictured below (Figure 5). Mosses, also known as a bryophyte, are small plants that use their seta, or photosynthetic stalks, during early production and then terminate them later in life. Later in their life cycles, moss default to chloroplasts that they have built up over the course of using the seta as an alternative form to photosynthesis. Moss is found in many places around the world and is turned into peat and harvested in some countries like Europe, North America, and Asia. Bryophytes are small plants, which means that individually they use up a lot less carbon than most plants. 

Figure 5

      In a hypothetical scenario, such as colonizing a planet with an atmosphere that contained a lot less carbon dioxide than our own earth or a region that has low CO2 levels, these plants would be a perfect starting point. This is due to these plants not needing a lot of carbon dioxide to survive. Essentially, by being small plants individually, small colonies of these plants are perfectly adapted to conditions in regions with low CO2. Although there is no current location like this that humans know of, if one were to come up in the future, people could look to these plants as just the type of flora to plant there. Of course, this could only be achieved if the plants evolved a smaller colony mentality, but one can predict that natural selection and evolution would resolve any pending problems one would have in this type of situation.

                                Conclusion

     In conclusion, the effect CO2 levels affect all plants throughout the world in different ways. Small plants just happen to be able to function in carbon dioxide scarce conditions due to their tiny size. Carbon allows photosynthesis to occur, which allows plants like Lemna Minor and the moss convert carbon dioxide and water into glucose and oxygen, albeit in smaller amounts. Carbon dioxide is just a cog in the photosynthesis machine which limits the rate of photosynthesis based on its current level. Smaller plants have an advantage over bigger plants because, due to their size, they reach their maximum photosynthetic rate much quicker. Lemna Minor and moss are both very prominent, small plants that photosynthesize all throughout the world, but are limited by the amount of carbon dioxide in the air to do so.

Sources

Articles:

1. Lemna Minor Information: https://gobotany.newenglandwild.org/species/lemna/minor/
2. Lemna Minor Map: http://bonap.net/NAPA/TaxonMaps/Genus/County/Lemna (main site is .org but redirects to a .net link)
3. Lemna Minor Map http http://www.bonap.org/MapKey.html
4. CO2 Information: http://www.waterencyclopedia.com/Bi-Ca/Carbon-Dioxide-in-the-Ocean-and-Atmosphere.html
5. Moss Information: http://bryophytes.plant.siu.edu/bryojustified.html

Pictures:

1. Figure 1: https://students.ga.desire2learn.com/d2l/lor/viewer/viewfile.d2lfile/1798/12577/h20-c02-light-glucose-oxygen.png
2. Figure 2: http://newfs.s3.amazonaws.com/taxon-images-1000s1000/Araceae/lemna-minor-ta-dcameron.jpg
3. Figure 3: http://bonap.net/MapGallery/County/Lemna%20minor.png
4. Figure 4: http://generalhorticulture.tamu.edu/lectsupl/Physiol/P26F3.GIF
5. Figure 5: http://www.microscopy-uk.org.uk/mag/imgmar03/Moss2.jpg