Photosynthesis is the most important process for plants to produce energy. But how can we relate photons of light to plant yield? Based on research, we know that one mole of photosynthetic photons is required to produce one gram of dried biomass (yield).
1 gram/mol
To understand how light supports a given amount of biomass, we need to learn about: photosynthesis, quantum yield, conversion efficiency, respiration and harvest index.
Photosynthesis
Photosynthesis is the process by which plants use water and carbon dioxide (CO2) to produce energy. These simple molecules can produce energy with the help of light. Plants use photons of light to convert carbon dioxide and water into carbohydrates and release oxygen in the process.
However, how much light is required?
By understanding quantum yield, we can measure the number of photons required to produce plant biomass.
It refers to the fixed moles of carbon per mole of photons absorbed (mol mol-1). We know that the minimum amount of photons required to produce carbohydrates is 10. In other words, the quantum requirement for 1 molecule of carbohydrate is 10 photons. But 10 is a quantum requirement that we can achieve at low light intensities.
At Utah State University, Dr. Previous research by Bugbee has shown that under high CO2 levels (1600 ppm) and light intensity around 400 μmol m-2 s-1, common crops such as tomatoes and spinach require 12 photons of light (Quantum yield = 1 mol / 12 mol photons). = 0.08 mol mol-1).
Based on the research, we can conclude that about 12 photons of light are required to produce 1 molecule of carbohydrates.
In understanding how photons are used to produce plant biomass, we need to consider conversion efficiency.
Competence
How efficient can photosynthesis be? Efficiency is equal to output divided by input.
Efficiency = Output / Input
Carbohydrates equal 30 g per mole (CH2O, Atomic weight C=12, H2=2, O=16). Remember, it takes 12 moles to produce carbohydrates. The efficiency is then calculated as follows.
Efficiency = 30 grams / 12 moles = 2.5 g
Plant respiration is a process in which carbohydrates are used to produce energy.
Plant Respiration and Yield
When working with plants we often hear the expression "net photosynthetic rate". Net photosynthetic rate refers to the total fixation rate of carbon without accounting for CO2 lost during respiration. This is the correct way to measure photosynthesis.
When trying to relate photons to yield, we need to consider that a certain percentage of carbohydrates will be used for plant respiration. This process will of course affect how carbohydrates are used in plant biomass or yield.
In the production of plant biomass, we also need to learn about the respiratory efficiency of the plant. Previous research has shown that the respiration efficiency in plants is around 60%.
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To take into account the effect of respiration and photosynthesis efficiency, we need to calculate the photon conversion efficiency.
The photon conversion efficiency is equal to the respiration efficiency times the photosynthesis efficiency.
Photon conversion efficiency = (2.5) x (60%) = 1.5
This calculation gives us the total biomass of 1.5 grams produced for each photon of light. This means that in a perfect scenario where all the emitted photons are absorbed by the plant, 1.5 grams of biomass will be produced for each photon of light. Since perfect scenarios are indeed difficult or impossible to achieve, our assumption is: One mole of photosynthetic photons is required to produce one gram of dried biomass.
1 gram/mol
When we understand how plants use light, we can better analyze the system and learn the importance of light on our crops. With good design we can optimize the light incidence in our plant growing systems. Also, by learning about the influence of light, it is possible to estimate how much it might cost to produce different crops in closed production areas. However, in order to calculate this, we need to know the concept of the harvest index.
Harvest Index
The harvest index is the ratio of the usable or edible product to the total plant biomass. For example, many crops are considered to have a harvest index of around 50%. This is because we grow a plant and harvest its fruit. We therefore consume about half of the total plant biomass. This includes cucumbers (cucumbers), tomatoes, etc. Might be a good guess. Leafy greens such as lettuce have a higher rate of 80%, and we consume almost the entire plant.
Harvest index can be really important when trying to correlate light, yield and light cost in indoor production areas. For example: Under ideal conditions, the cost of photons would be around 5% of the market price for lettuce, based on the number of photons and the harvestable crop. This rate is around 18% with plants with a lower harvest index such as tomatoes.
The plant material harvested is low compared to the total plant biomass produced. Therefore, the production and light cost of the plant will be higher. For this reason, most indoor plants focus on leafy greens. Therefore, optimization of the light effect on the crop is very important for crop production systems.
Of course, we can also use artificial lighting as additional lighting. Additional lighting that we will use in addition to the free sunlight; We can improve the growth and quality of plants by increasing the incidence and quality of light intensity.
Photosynthesis and the use of photons can be complex issues. However, if we really want to have control over our crops, we must pay attention and understand photosynthesis, which is the most important process for obtaining energy in plants, and with it our crops.