Plants produce their own food through photosynthesis, using energy from light to convert water and carbon dioxide into oxygen and carbohydrates.[1] Understanding the factors involved in photosynthesis and how they interact is essential for ensuring plants photosynthesize effectively, resulting in healthy, high-yielding crops.
In this blog post, we’ll explore the science behind photosynthesis, including the critical role played by nutrients, and discuss how growers can support this vital process.
The photosynthesis equation
Photosynthesis is a light-driven process. Plants capture light energy and use it to convert carbon dioxide (CO2), absorbed through their leaves, and water (H2O), absorbed through the roots, into carbohydrates (CH2O)—their food—and oxygen (O2), which is released back into the atmosphere. The photosynthesis equation is:[2]
6 CO₂ (carbon dioxide) + 6 H₂O (water) ® C6H12O6 (carbohydrates) + 6 O2 (oxygen)
The photosynthesis equation
Photosynthesis is a light-driven process. Plants capture light energy and use it to convert carbon dioxide (CO2), absorbed through their leaves, and water (H2O), absorbed through the roots, into carbohydrates (CH2O)—their food—and oxygen (O2), which is released back into the atmosphere. The photosynthesis equation is:[2]
6 CO₂ (carbon dioxide) + 6 H₂O (water) ® C6H12O6 (carbohydrates) + 6 O2 (oxygen)
The photosynthesis equation
Photosynthesis is a light-driven process. Plants capture light energy and use it to convert carbon dioxide (CO2), absorbed through their leaves, and water (H2O), absorbed through the roots, into carbohydrates (CH2O)—their food—and oxygen (O2), which is released back into the atmosphere. The photosynthesis equation is:[2]
6 CO₂ (carbon dioxide) + 6 H₂O (water) ––> C6H12O6 (carbohydrates) + 6 O2 (oxygen)
In chemical terms, this is an oxidation-reduction[3] process. Oxidation refers to a molecule losing electrons, while reduction refers to a molecule gaining them. In this case, water is oxidized—it is split into oxygen gas and hydrogen ions—while carbon dioxide is reduced by gaining hydrogen ions from water, forming carbohydrates.
This entire process occurs in the leaves in two cycles: light and dark.
Site of synthesis: the leaves
Leaves are adapted to maximize light absorption. At their center is the mesophyll, the tissue that captures light for photosynthesis. The mesophyll contains chloroplasts—tiny organelles filled with chlorophyll,[4] the green pigment that absorbs light energy.
The leaves also regulate carbon dioxide intake through small openings on their undersides called stomata. Each stoma is flanked by guard cells, which control its opening and closing.[5] Stomata open to absorb carbon dioxide and release water into the atmosphere through transpiration. When water is abundant, stomata remain open longer, allowing the plant to absorb more carbon dioxide and increase photosynthesis. However, when water is scarce and transpiration rates rise, the stomata close to conserve water, limiting further carbon dioxide uptake.
Figure 1. The photosynthetic process. Image Source: Daniel Mayer, https://commons.wikimedia.org/w/index.php?curid=20722530.
Light and dark reactions
The light reaction cycle occurs first. Also called the photochemical reaction, it can be thought of as the light-harvesting stage. It begins with different pigments in the plant absorbing specific light wavelengths:
- Chlorophyll a and b absorb blue and red light, giving plants their green color. [6]
- Carotenoids (e.g., β-carotene, lutein and zeaxanthin) absorb blue and green light and help dissipate excess energy from photosynthesis as heat.[7] Carotenoids are responsible for the red, orange and yellow colors seen in autumn as chlorophyll degrades.[8]
These pigments are attached to light-harvesting complexes, which transfer the absorbed light energy to the reaction center—where the chemical processes of photosynthesis begin.[9] The first of these is photolysis, a process in which “chemical bonds are broken as the result of transfer of light energy.”[10]
Figure 1. The photosynthetic process. Image Source: Daniel Mayer, https://commons.wikimedia.org/w/index.php?curid=20722530.
Light and dark reactions
The light reaction cycle occurs first. Also called the photochemical reaction, it can be thought of as the light-harvesting stage. It begins with different pigments in the plant absorbing specific light wavelengths:
- Chlorophyll a and b absorb blue and red light, giving plants their green color. [6]
- Carotenoids (e.g., β-carotene, lutein and zeaxanthin) absorb blue and green light and help dissipate excess energy from photosynthesis as heat.[7] Carotenoids are responsible for the red, orange and yellow colors seen in autumn as chlorophyll degrades.[8]
These pigments are attached to light-harvesting complexes, which transfer the absorbed light energy to the reaction center—where the chemical processes of photosynthesis begin.[9] The first of these is photolysis, a process in which “chemical bonds are broken as the result of transfer of light energy.”[10]
This is the oxidation phase of photosynthesis, where the bonds in water are split into oxygen gas and hydrogen ions.[11]
That equation is: [12]
2 H2O + light ® O2 + 4H+
This splitting also releases electrons that contribute to the synthesis of adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide phosphate (NADPH) in the chloroplast.[13] ATP is considered the “energy currency” of all life, as it stores and releases energy,[14] while NADPH is “an essential electron donor in all organisms.”[15] The equation for the light reaction cycle is:[16]
2 H2O + 2 NADP+ (the oxidized form of NADPH) + 3 ADP (adenosine diphosphate) + Pi (inorganic phosphate) ® O2 + 2 NADPH + 3 ATP
ATP and NADPH are both required for the second stage of photosynthesis—the dark reaction, also known as the Calvin cycle. NADP+, ADP and Pi are byproducts of that process. It’s called the dark reaction because it does not require light, although it depends on the products of the light reaction. This is the stage when carbohydrates are formed. As shown in the Calvin cycle equation, NADPH and ATP are used to generate carbohydrates, while NADP+ and ADP are regenerated:[17]
CO2 + NADPH + H+ + ATP ® C6H12O6 + NADP+ + ADP + Pi
This is where the reduction of carbon dioxide occurs: [18]
CO2 + 4 H+ + 4e– ® CH2O + H2O
Because this stage regenerates ADP and NADP+, those molecules become available again for the light reactions. Thus, the light and dark reactions are interdependent.
This is the oxidation phase of photosynthesis, where the bonds in water are split into oxygen gas and hydrogen ions.[11]
That equation is: [12]
2 H2O + light ® O2 + 4H+
This splitting also releases electrons that contribute to the synthesis of adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide phosphate (NADPH) in the chloroplast.[13] ATP is considered the “energy currency” of all life, as it stores and releases energy,[14] while NADPH is “an essential electron donor in all organisms.”[15] The equation for the light reaction cycle is:[16]
2 H2O + 2 NADP+ (the oxidized form of NADPH) + 3 ADP (adenosine diphosphate) + Pi (inorganic phosphate) ® O2 + 2 NADPH + 3 ATP
ATP and NADPH are both required for the second stage of photosynthesis—the dark reaction, also known as the Calvin cycle. NADP+, ADP and Pi are byproducts of that process. It’s called the dark reaction because it does not require light, although it depends on the products of the light reaction. This is the stage when carbohydrates are formed. As shown in the Calvin cycle equation, NADPH and ATP are used to generate carbohydrates, while NADP+ and ADP are regenerated:[17]
CO2 + NADPH + H+ + ATP ® C6H12O6 + NADP+ + ADP + Pi
This is where the reduction of carbon dioxide occurs: [18]
CO2 + 4 H+ + 4e– ® CH2O + H2O
Because this stage regenerates ADP and NADP+, those molecules become available again for the light reactions. Thus, the light and dark reactions are interdependent.
Nutrient impact on photosynthesis
Plants require more than just carbon dioxide and water to create food. Nutrient uptake directly affects photosynthesis by influencing chlorophyll production, enzyme activity, stomatal function and overall plant metabolism. The following nutrients are especially critical:
- Nitrogen is a primary component of chlorophyll.[19]
- Phosphorus transfers energy through the pyrophosphate bond in ATP.[20]
- Potassium regulates stomatal opening, which affects carbon dioxide absorption.[21] When potassium is deficient, stomata remain closed, limiting carbon dioxide assimilation and reducing photosynthesis.
- Calcium influences stomatal regulation.[22]
- Magnesium is the central element of the chlorophyll molecule.[23]
- Iron plays a role in plant respiratory and photosynthetic reactions and supports chlorophyll synthesis and maintenance.[24] An iron deficiency often results in chlorosis— yellowing of the leaves is the telltale symptom.
Maintaining the right nutrient balance is critical to sustaining photosynthesis. For instance, although phosphorus is essential, excess levels can antagonize iron uptake, leading to deficiency symptoms like chlorosis. Nutrient homeostasis—the proper balance of macro- and micronutrients—is necessary for optimal photosynthesis.[25]
Maintaining the right nutrient balance is critical to sustaining photosynthesis. For instance, although phosphorus is essential, excess levels can antagonize iron uptake, leading to deficiency symptoms like chlorosis. Nutrient homeostasis—the proper balance of macro- and micronutrients—is necessary for optimal photosynthesis.[25]
Maximizing photosynthesis
The rate at which a plant photosynthesizes is influenced by several factors, including light intensity, carbon dioxide availability, temperature, water supply and nutrient levels. Plant species, overall health, growth phase and maturity also play a role.[26]
Hydroponic growers can help maximize photosynthesis in their cannabis plants by:
- Supplementing carbon dioxide: Ensuring adequate carbon dioxide levels is critical to fueling photosynthesis.
- Providing the right light spectrum and intensity: Chlorophyll absorbs blue and red light within the 400–700 nanometer range.
- Managing transpiration: Excessive transpiration causes stomata to close, limiting carbon dioxide absorption. Measure and manage VPD to influence transpiration.
- Maximizing light absorption: Because photosynthesis occurs in the leaves, it’s essential that every leaf receives light. Creating a uniform plant canopy and providing canopy lighting help maximize light exposure.
While photosynthesis creates enough food for survival, growers may want to supplement carbohydrates to ensure plants always have energy to continue growing and flowering.
Finally, don’t forget the importance of a balanced nutrient supply. Choosing a complete fertilizer line like Emerald Harvest ensures nutrients are delivered in the right ratios for immediate plant uptake, giving plants the fuel they need to feed themselves.
Emerald Harvest Team
[1] Brittanica. 2025. “Photosynthesis.” Last updated April 8. https://www.britannica.com/science/botany.
[2] Brittanica. n.d. “What is the Basic Formula for Photosynthesis?” Accessed April 29, 2025. https://www.britannica.com/question/What-is-the-basic-formula-for-photosynthesis.
[3] Redox
[4] Clark, Mary Ann, Matthew Douglas, and Jung Choi. 2018. “Photosynthesis.” In Biology 2e, OpenStax. https://oertx.highered.texas.gov/courseware/lesson/6359/student-old/?task=2.
[5] Dashoff, Jared. 2022. “Scientists Discover Mechanism Plants Use to Control ‘Mouths’.” U.S. National Science Foundation, December 7. https://www.nsf.gov/science-matters/scientists-discover-mechanism-plants-use-control
[6] OpenEd CUNY. 2007. “The Light-Dependent Reactions of Photosynthesis.” Accessed April 29, 2025. https://opened.cuny.edu/courseware/lesson/645/student-old/?task=3.
[7] Ibid.
[8] Chaney, William R. 1997. “Why Leaves Change Color – The Physiological Basis.” The Department of Forestry and Natural Resources Frequently Asked Question Series. https://www.extension.purdue.edu/extmedia/fnr/fnr-faq-5.pdf.
[9] Trafton, Anne. 2017. “How Photosynthetic Pigments Harvest Light.” MIT News, January 11. https://news.mit.edu/2017/photosynthetic-pigments-harvest-light-artificial-photosynthesis-0111.
[10] Speight, James G. 2017. “Chemical Transformations in the Environment.” In Environmental Organic Chemistry for Engineers. Butterworth-Heinemann. https://doi.org/10.1016/B978-0-12-804492-6.00007-1.
[11] Nature Education. 2014. “Photosynthetic Cells.” Accessed April 29, 2025. https://www.nature.com/scitable/topicpage/photosynthetic-cells-14025371/.
[12] Johnson, Matthew P. 2016. “Photosynthesis.” Essays in Biochemistry 60 (3): 255-273. https://doi.org/10.1042/EBC20160016
[13] Nature Education. 2014. “Photosynthetic Cells.” Accessed April 29, 2025. https://www.nature.com/scitable/topicpage/photosynthetic-cells-14025371/.
[14] Dunn, Jacob, and Michael H. Grider. 2023. “Physiology, Adenosine Triphosphate.” StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK553175/.
[15] Spaans, Sebastiaan K., Ruud A. Weusthuis, John van der Oost, and Serve W. M. Kengen. 2015. “NADPH-Generating Systems in Bacteria and Archaea.” Frontiers in Microbiology 6: 742. https://doi.org/10.3389/fmicb.2015.00742.
[16] Boundless. 2025. “The Light-Dependent Reactions of Photosynthesis – Processes of the Light-Dependent Reactions.” In General Biology. LibreTexts.
[17] University of Vermont. 2005. “Lecture 17 Photosynthesis II. Calvin Cycle.” Accessed May 5, 2025. https://www.uvm.edu/~dstratto/bcor011_handouts/Vayda_lecture_notes/17%20photosynth%202%2010%2010%2005.pdf.
[18] Johnson, Matthew P. 2016. “Photosynthesis.” Essays in Biochemistry 60 (3): 255-273. https://doi.org/10.1042/EBC20160016.
[19] Uchida, R. 2000. “Essential Nutrients for Plant Growth: Nutrient Functions and Deficiency Symptoms.” In Plant Nutrient Management in Hawaii’s Soils, Approaches for Tropical and Subtropical Agriculture, edited by J. A. Silva and R. Uchida. University of Hawaii at Manoa. https://www.ctahr.hawaii.edu/oc/freepubs/pdf/pnm3.pdf.
[20] Grusak, Michael A. 2001. “Plant Macro- and Micronutrient Minerals.” In Encyclopedia of Life Sciences. Nature Publishing Group. https://doi.org/10.1038/npg.els.0001306.
[21] Ibid.
[22] Ruiz, L. P., C. J. Atkinson, and Terence Arthur Mansfield. 1993. “Calcium in the Xylem and Its Influence on the Behaviour of Stomata.” Philosophical Transactions of the Royal Society B 241: 67-74. http://doi.org/10.1098/rstb.1993.00092.
[23] Huber, Don M., and Jeff B. Jones. 2012. “The Role of Magnesium in Plant Disease.” Plant and Soil 368: 73-85. https://doi.org/10.1007/s11104-012-1476-0.
[24] Rout, Gyana R., and Sunita Sahoo. 2015. “Role of Iron in Plant Growth and Metabolism.” Reviews in Agricultural Science 3: 1-24. https://doi.org/10.7831/ras.3.1.
[25] Rudolph, Cameron. 2021. “New MSU Research Shows Photosynthesis Controlled by Nutrient Signaling in Plants.” Michigan State University, December 13. https://www.canr.msu.edu/news/new-msu-research-shows-photosynthesis-controlled-by-nutrient-signaling-in-plants.
[26] Brittanica. 2025. “Photosynthesis.” Last updated April 8. https://www.britannica.com/science/botany.
