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How to Analyze Photosynthesis in Plants: Methods and Tools

Posted by: Scott Trimble
March 26, 2019

Photosynthesis: Why is it important?

Life as we know it would be impossible without photosynthesis. Outside of providing the essential elements that support life on earth, photosynthesis is of special importance to the food and agriculture industry, as well as for ecologists studying climate change. In addition, there are many commercial enterprises which depend heavily on photosynthesis. As a result, there are a plethora of methods to measure photosynthesis. Some modern methods are accurate enough to be useful not just for commercial use, but also in laboratories and research projects.

What is Photosynthesis?

Photosynthesis is the process by which green plants and microbes manufacture food. They need carbon dioxide (CO2) in the air, which enters the plant through leaves, and water (H2O) from the soil, which roots absorb. Light captured by chlorophyll in the leaves combines water and carbon dioxide to produce glucose (C6H12O6) and oxygen (O2).

The equation for photosynthesis is:

6CO2 + 6H2O + Sunlight ----------> C6H12O6 + 6O2

The glucose undergoes various reactions with other minerals to produce sugars, carbohydrates, proteins, fats, volatile compounds, etc.

Without photosynthesis, much of life on Earth wouldn’t exist. Animals depend on it, and so do people.

Disciplines and Industries Using Photosynthetic Analysis

All of our plant and animal-based food depends on photosynthesis, and so do the plants producing wood for timber, fiber for clothes, etc. Photosynthetic analysis is, therefore, important for various industries associated with:

  • Agriculture for the production of grains, fiber, and fodder.
  • Horticulture and floriculture, whether outdoor, indoor or greenhouse-based.
  • Pasture management for animal husbandry.
  • Forestry management for the production of wood and pulp.
  • Biomass energy production.
  • Cyanobacteria and algae cultivation for the production of energy, chemicals, and other bio-products.

Many disciplines of science are engaged in monitoring plant health, such as:

  • Agricultural Sciences
  • Forest Ecology
  • Terrestrial and Marine Ecology
  • Environmental Sciences

The Importance of Photosynthetic Analysis

Photosynthesis is how plants produce the biomass needed to grow and produce flowers and fruit or grain.

  • Scientists and food/biomass producers are interested in improving photosynthesis to maximize production directly from crops or indirectly from animal husbandry through genetics.
  • Indoor and greenhouse farming practices depend partially or completely on artificial lights. Hence, a major portion of research and cultivation is centered on optimizing photosynthesis through the development of appropriate technology.
  • Researchers are interested in the photosynthetic rate of algae and bacteria being used to generate energy and other useful bio-products.
  • Ecological research measures photosynthesis to monitor the health of ecosystems, and to track the effects of climate change.

In all cases, whether in the laboratory or in the field, measuring photosynthesis is a necessity.

Measuring Photosynthesis

Since photosynthesis is a chemical reaction, its levels are monitored by the rate of occurrence. Changes in the levels of its inputs and outputs are used to calculate the photosynthetic rate. Thus, there are various methods to measure photosynthesis:

  • Uptake of CO2 by plants: Since CO2 is needed for photosynthesis, measuring how much of it is taken up by the plants gives us information on how much of photosynthesis is happening.
  • Release of O2: The amount of O2 produced during photosynthesis can be measured.
  • Dry matter content: Dry matter is comprised of all the solids in a plant minus the water content. These solids are all produced as a result of photosynthesis. So, dry matter can be used to measure this process.
  • Carbohydrate production: This is an indirect way of measuring photosynthesis by its products. Parts of a plant can be harvested, dried and weighed at intervals. The difference in weights gives the increase in carbohydrates (sugars) due to photosynthesis.
  • Measure light-dependent photosynthesis using Hill’s reaction: In the first step of photosynthesis, oxygen is produced by chloroplasts by splitting water molecules using energy from light. Using dichlorophenolindophenol (DCPIP) as the terminal electron acceptor of oxygen atoms, Hill’s reaction measures the light-dependent phases of photosynthesis.
  • Chlorophyll fluorescence: When chlorophyll absorbs light, its molecules are raised to an “excited state”. It returns to its normal state by releasing the energy. Part of this is used to power photosynthesis; another portion is emitted as radiation called flourescence radiation. Since flourescence radiation is complementary to photosynthesis it is used to measure it in higher plants as well as algae and bacteria.

Commercial Instruments

Gas exchange is used most often as the way to measure photosynthesis, and there are a few different techniques. CO2 measurement uses infrared light, while O2 measurement requires electrochemical sensors.

  • Infrared Gas Analyzer: CO2 absorbs infrared light. When infrared light is directed at a plant or leaf in a closed space or chamber, there is less CO2 because the plants have used it in photosynthesis. So, there is more infrared light left unabsorbed. (Clarify this please. I understand this to mean that as CO2 levels decrease, less infrared light is absorbed. Is this correct? The incoming and outgoing CO2 from the leaf chamber is measured by infrared spectroscopy with an infrared gas analyzer. The difference gives us the amount of CO2, from which the rate of photosynthesis can be calculated.
  • Electrochemical Gas Sensor: O2 doesn’t absorb infrared light, so it is measured by electrochemical sensors. The gas passes through a membrane to which electrodes are connected. O2 gets changed to water after receiving electrons, in the form of hydrogen ions, (I added this - is it correct? The electrons have to come from somewhere, and you can’t turn oxygen into water without hydrogen.) from the electrode, a process which is measured as an electric current. The amount of current used is proportional to the amount of O2 present from which the rate of photosynthesis can be calculated.

Gas analyzers are used either with a closed system or open system. Open systems are more popular since temperature, humidity, and CO2 concentrations in the chambers can be controlled.

CID Bio-Science’s CI-340 Handheld Photosynthesis System is a portable and handheld tool that measures photosynthesis, respiration, transpiration, stomatal conductance, PAR and internal CO2. It comes with an accompanying software and USB cable for downloading data.

  • It can be used with open and closed systems.
  • This gas anaylzer measures the intake of CO2 and production of H2O during photosynthesis by infra-red spectroscopy.
  • Optional modules allow for control of CO2, humidity, temperature, light intensity, and flourescence radiation.
  • Ten customized leaf chambers can accommodate different sizes and thickness, including cacti and conifers.

photosynthesis analysis

Open and closed IRGA systems. Image credits: (Illustration by Alan Rhodes, Mulkey & Smith 1998)

CID Bio-Science’s F-920 Gas Analyzer,  which measures 0-100% of CO2 and O2, is an example of a tool that can be used with both open and closed systems. It is handheld and light, and functions in a wide range of temperature and humidity conditions. Results are available within six seconds, and a data logger can store 1000s of readings. Data can be transferred through USB or Bluetooth for analysis to computers and other devices.

The company also supplies all the necessary accessories that are needed. These include a choice of

• Eight open system chambers that come in different sizes and for different kinds of leaves.

• Four closed system leaf chambers that in a size range from ¼ to 4 liters.

The Best Time For Measurements

The objective of the measurement and the plant species studied will determine the correct timing for measuring photosynthesis.

  • For maximum rates of photosynthesis, measurements are made around 10:00AM.
  • To get the diurnal range, take measurements from 6:00AM to 6:00PM at a two-hour intervals. This can tell you when the photosynthetic rate is at its maximum.
  • Multiple measurements should always be made at the same time of the day to compare for precision.

Find Out More

You can find out more on the topic of photosynthesis and measuring photosynthesis from the following articles.

Tools are a Measure of Industry

There is a saying, “An artist is only as good as his/her tools". This goes for industries as well. Instruments have to be precise in the field and the laboratory. Precision agriculture, as its name indicates, can be possible only through advanced science and the wide availability of such tools. CID Bio-Science’s gas analyzers are affordable and are accompanied by strong support to make them more attractive. Not surprisingly, CID Bio-Science’s gas analyzers are depended on by researchers as well as producers.

---

Vijayalaxmi Kinhal
Science Writer, CID Bio-Science
Ph.D. Ecology and Environmental Science, B.Sc Agriculture

Sources

Antuña-Jiménez, D., Díaz-Díaz, G., Blanco-López, M.C., Lobo-Castañón, M.J., Miranda-Ordieres, A.J., & Tuñón-Blanco P. (2012). Chapter 1 - Molecularly Imprinted Electrochemical Sensors: Past, Present, and Future. Molecularly Imprinted Sensors , 1-34

Baker, N. R. Chlorophyll fluorescence: a probe of photosynthesis in vivo. Annu Rev Plant Biol. 59:89-113. DOI: 10.1146/annurev.arplant.59.032607.092759

BBC. What is photosynthesis? Retrieved from https://www.bbc.com/bitesize/articles/zn4sv9q

DOE/Sandia National Laboratories (2017, August 21). Biofuels from bacteria: New clean energy source? ScienceDaily. Retrieved from www.sciencedaily.com/releases/2017/08/170821135052.html

Hans Lambers, H., & Bassham, J. A. (2019, February 6). Photosynthesis. Encyclopedia Britannica. Retrieved from https://www.britannica.com/science/photosynthesis

Majer, P. (2013, June). Measuring photosynthesis by gas exchange systems. Retrieved from
https://www.plant-phenotyping-network.eu/lw_resource/datapool/systemfiles/elements/files/ 18af46af-d5f1-11e8-8a88-dead53a91d31/current/document/co2_handout.pdf

NEON Science. (2014, October 22). How we measure photosynthesis. [Video Film]. Retrieved from https://www.youtube.com/watch?v=PlEzyZadA90

Researchgate (2017, Nov, 11). What is the best time of the day to measure leaf physiological responses (Photosynthetic rate, transpiration rate, and stomatal conductance)? Retrieved from https://www.researchgate.net/post/Dear_all_What_is_the_best_time_of_the_day_to_measure_leaf_physiological_responses_Photosynthetic_rate_transpiration_rate_and_stomatal_conductanc

Retrieved from https://www.sciencedirect.com/topics/chemistry/electrochemical-sensors

Science and Plants for Schools. Measuring the rate of photosynthesis. Retrieved from http://www.saps.org.uk/secondary/teaching-resources/157-measuring-the-rate-of-photosynthesis

Featured photo image credit: Whologwhy


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