Plant Physiology and Growth

Plant Physiology and Growth

C3 & C4 Plants

  Have you ever wonder what the difference between C3 and C4 plants is?

C3 plants use the Calvin cycle in order to photosynthesize, most of the plants in the world are C3 plants

• The first product of C3 plants is a three-carbon compound (Phosphoglyceric Acid)
• Carbon dioxide fixation takes place at only one place
• C3 plants photosynthesize only when the stomata are open

C4 plants in addition to using the Calvin cycle also use the C4 cycle. Less than 5% of the plants in the world are C4 plants.

• C4 plants do not do photorespiration
• The first product in the plants is a four-carbon compound (Oxaloacetic Acid)
•  Carbon dioxide fixation takes place twice (mesophyll cells, bundle sheath cells)
• C4 plants photosynthesize when stomata are closed too
• C4 plants are more efficient in photosynthesis than C3

Picture 1:https://www.naturalproductsinsider.com/specialty-nutrients/duckweed-innovative-protein-source

C3 plants have a different photosynthetic response to light, C3 need 1/3- ½ of full sunlight for saturation while c4 need more than full light for saturation. C4 plants can stand higher temperatures and have higher optimal growth.

Duckweed is a C3 plant, it has a temperature preference of 25-30 degree Celcius. (Rooijakkers, 2016)

   Perennial Crops

Duckweed is a  perennial crop, a typical characteristic would be the small flowering of the plant. 

• Perennial plants normally live longer than two years. Since duckweed is a plant that can almost double its size within one day and grows exponentially it lives many years. (Missouri Botanical Garden, n.d.)
• Usually, perennials bloom in spring and summer, duckweed does so too. Once autumn arrives the plant produces spores, these go to the bottom of the water surface and reemerge back again during spring. (Ecopond, 2019)

   Reproduction

The crop reproduces vegetatively as explained before. The plant has a fast reproduction that originates in the meristem.  (Landolt E, 2013) Once a frond matures it produces new buds that are attached to the mother frond, this helps the plant to reproduce very rapidly, reaching almost exponential growth.   (Landolt E, 2013) 

Very rarely, when duckweed flowers there is a chance of sexual reproduction.  

   Flowering 

• Flowering in Lemna minor is extremely rare and was recorded only on special occasions. (Краснодар, 2002)
• The plant flowers in summer when the light intensity is higher
• Duckweeds flowers can be wind-pollinated, or insect-pollinated but if this does not occur, the plant is able to self-fertilize 
• The tiny flowers have two stamens and one pistil. (Dr. Appenroth, 2012)

Picture 2:https://www.mobot.org/jwcross/duckweed/flowering-dormancy.htm

Nitrogen Fixation

Like every other plant, duckweed needs a lot of nutrients. The plant is known to be a water purifier, therefore it does not take nitrogen from the air but from the water. 

The fronds and roots are the ones in charge of assimilating nitrogen. In the water, duckweed can find nitrogen in the form of nitrate and ammonium. Nevertheless, studies show that different nitrogen-fixing bacteria can be found in duckweed as well.

Nitrogen fixation can be measured by acetylene conversion into ethylene. (Iqbal, Javed, & Baig, 2019)  Studies that observed the conversion of acetylene indicated there is possible nitrogen fixation. However, this topic still needs more observation.

Global Warming and Increase of CO2 Concentrations

Many studies show that when food crops are exposed to high levels of CO, they produce lower amounts of key nutrients according to the 'Carbon Brief Organization'.   (Dunne Daisy, 2018)   It is estimated that the CO2 level now is 409ppm and is expected to increase to 550ppm in the following years.

In the case of Lemna Minor, studies were conducted in order to see the response of Lemna minor to an increase in CO2, these showed that when increasing CO2, photorespiration in plants decreased. The leaf area ration decreased as well in the presence of more CO2 because the dry weight per frond increased, this is presumed to be caused by nonfunctional stomata.  (Andersen, Dons, Nilsen, & Haugstad, 1985)

References:

Andersen, I. H., Dons, C., Nilsen, S., & Haugstad, M. K. (1985). Growth, photosynthesis and photorespiration of Lemna gibba: response to variations in CO2 and O2 concentrations and photon flux density. Photosynthesis Research, 6(1), 87–96. https://doi.org/10.1007/BF00029048

Dr. Appenroth. (2012). Duckweed Flowering and Dormancy. Retrieved September 20, 2019, from https://www.mobot.org/jwcross/duckweed/flowering-dormancy.htm

Dunne Daisy (2018). Rising CO2 leveld could push 'hundreds of illions' into malnutrition by 2050, from https://www.carbonbrief.org/rising-co2-levels-could-push-hundreds-of-millions-into-malnutrition-by-2050

Ecopond. (2019). Eco Pond | News and Tips. Retrieved September 20, 2019, from https://www.ecopond.co.uk/news/duckweed-problems-information-and-advice

Iqbal, J., Javed, A., & Baig, M. A. (2019). Growth and nutrient removal efficiency of duckweed (lemna minor) from synthetic and dumpsite leachate under artificial and natural conditions. PLOS ONE, 14(8), e0221755. https://doi.org/10.1371/journal.pone.0221755

Landolt E. (2013). Measuring Duckweed Growth. Retrieved September 20, 2019, from https://www.mobot.org/jwcross/duckweed/duckweed-measuring-growth.htm

Missouri Botanical Garden. (n.d.). Lemna minor - Plant Finder. Retrieved September 20, 2019, from http://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?kempercode=a622

Rooijakkers, P. (2016). Photosynthesis model to predict duckweed growth at the Ecoferm greenhouse. Retrieved from http://edepot.wur.nl/389579

Краснодар. (2002). Duckweed Biology. Retrieved September 20, 2019, from https://www.mobot.org/jwcross/duckweed/Russe/biology-e.htm