Blog 3 - Physiology and Growth

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Blog 3 - Physiology and Growth

Is the pecan a C3 or a C4 plant?

The pecan is a C3 plant. A C4 plant has the special ability to close its stomata throughout most of the day. This way the plant will not run out of water very quickly when it is warm and water easily evaporates. Therefore, the C4 characteristic are needed for plants growing in arid regions. (Difference between C3. C4 and CAM plants, n.d.). As we mentioned in blog 1, the pecan is native to South-North America. Therefore, the climate is warm, but not arid.

Is the pecan an annual, biennial or a perennial?

The pecan tree is a perennial for its lifespan is longer than three years.  (Andersen, 2017).

Is the pecan able to fix atmospheric nitrogen?

Legumes have nitrification abilities. It is able to take up the nitrogen out of the air (N2) and fix it into ammonia (CH4). The ammonia is later nitrified and turned into nitrates (NO3-), which the plants can take up as nutrient. The nitrogen fixation is done at the roots. When digging up the crop you will find white little knobs on the roots. This is where the magic happens. (Sheaffer & Moncada, 2011).
The pecan tree is a legume. However, its nitrogen fixation abilities are almost unspoken. Therefore, I assume that the pecan has poor abilities in this domain compared to other legume crops. Alfalfa is the highest scoring nitrogen fixing legume, but the soybean is also doing well. (Sheaffer & Moncada, 2011).

Photosynthesis and respiration

To start to understand the impact of climate change, such as changes in the air temperature and CO2 concentration, it is important to understand both chemical processes.

Photosynthesis
6 CO2 + 6 H2O + light energy à C6H12O6 + 6 O2

1.       Light-depended reactions
The light-depended reactions takes place in the thylakoid. Here, light energy is converted into chemical energy. This is done in two sets of reactions: photosystem I and photosystem II. The chlorophyll molecules absorb the photons (light energy). (Helmenstine, Ph.D., n.d.).
It starts with photosystem II when the energised electrons are passed to the electron transport chain. In the meanwhile, photolysis takes place. The oxidation of water molecules producing free O2 and H electrons. Long story short, ATP synthase is created and phosphorylates the ADP into ATP. The left-over electrons are transported through to photosystem I. The low-energy electrons are re-energised and pushed through another electron chain. Here NADP+ is reduced to NADPH. Photosystem I and photosystem II are located next to one another and work side by side. (Learning Resource, 2016).

Light-independed reactions (Calvin Cycle)
The light-indedepend reactions are called the Calvin Cycle. This takes place in the stoma, the fluid-filled space surrounding the thylakoids. Here glucose is synthetized. (Helmenstine, Ph.D., n.d.).
The ATP and NADPH created in the light-depended reactions are released into the stroma. They will fuel the Calvin cycle. Here CO2 is converted into G3P. The cycle consists of three steps. Step 1 is carbon fixation. The six-molecule chain is broken into two. Step 2 is reduction. Here the NADPH and ATP from the light reaction which reduce the CO2. In the last step the regeneration of RuBP takes place and makes sure the G3P is finally created. The Calvin Cycle has to run six times in order to create one molecule of G3P. The G3P is able to remove the phosphate and add fructose to form the sugar sucrose. This is the molecule that a plant uses to transport carbohydrates. It is also the start molecule to build starch and cellulose. (Learning Resource, 2016).
The Calvin cycle needs input in the form of NADPH or ATP, so it relies on the light-depended reactions but it does not need direct light in order to work. As long as there is a storage or supply of some sort, the cycle will work apart from the light reactions. (Learning Resource, 2016).

Respiration
C6H12O6 + 6 O2 à 6 CO2 + 6 H2O + energy
ATP, which is created in photosystem II is the storage energy for the plant, but it is also created in the mitochondria. See it a bit as human anatomy. Fat is our storage energy and can be stored for further energy usage without needing direct consumption of carbohydrates, in the plants case, NADPH. (Sheaffer & Moncada, 2011).

Respiration is done in three stages:
Stage 1                 In the cytoplasm sugar molecules are broken down so that they can enter the outer layer of the mitochondria. This is called glycolysis.
Stage 2                Several chemical reactions result in the creation of high-energy ATP and electron molecules (for stage 3). This is series of chemical reactions are called the Krebs cycle. CO2 is produced.
Stage 3                A lot of high-energy ATP molecules are formed from high-energy electrons. (Created in stage 2). H2O is produced. Oxygen is needed in the electron transport system because they are the final acceptors of the electrons.
(Sheaffer & Moncada, 2011).
Most of the ATP is created in the stage 3, the electron transport system. (Sheaffer & Moncada, 2011).

Effects of climate change


If the CO2 concentration in the air changes, plants will need to adapt and photosynthesise more, for the CO2 level needed for the chemical reaction is a given. This means that there is also a steady supply of sunlight and water molecules needed in order to process more chemical reactions. If not, the CO2 concentration in the air will rise heat up the earth, for CO2 makes it easier for radiation and warmth is recycled. As result, the overall temperature on earth will rise. Climate change has begun. This will have a great deal of consequences for plants. The temperature will rise, which will provide certain plants problems with water evaporation (transpiration) and water supplies. Dry spells will stretch out longer and storms will become more severe. Ecosystems will have to adapt very quickly and some will not able to keep up. Extreme weather will also influence our food supplies and diets. 

References

Andersen, P. (2017, September 20). The Pecan Tree. Retrieved from University of Florida:                   https://edis.ifas.ufl.edu/hs229
Difference between C3. C4 and CAM plants. (n.d.). Retrieved from Major Differences: http://www.majordifferences.com/2014/04/difference-between-c3-c4-and-cam-plants.html#.WcItIXasnIU
Helmenstine, Ph.D., A. (n.d.). Retrieved from Thought Co: https://www.thoughtco.com/what-is-the-calvin-cycle-608205
Learning Resource. (2016, August 15). Photosynthesis. Retrieved from Youtube: https://www.youtube.com/watch?v=HWqVgpAmf5I
Sheaffer, C. C., & Moncada, K. M. (2011). Introduction to Agronomy. Boston, United States of America: Cengage Learning.

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