What's the function of Potassium in plants?

Amir Tajer

Posted on June 03 2016

Nitrogen, Potassium, and Phosphorus are three main nutrients plants need to be healthy. After Nitrogen, Potassium is the most important nutrient plants need and Potassium is usually the nutrient responsible for the quality of the plant such as shape, color, size, and taste.


Potassium functions in plants:

  • Enzyme Activation
  • Stomata Activity
  • Photosynthesis
  • Transport of Sugars
  • Water and Nutrient Transport
  • Protein Synthesis
  • Starch Synthesis
  • Crop Quality


Enzyme Activation:

Plants need Potassium to activate the enzymes and Potassium is actually responsible for activation of over 60 different enzymes. Potassium also neutralizes the plants pH levels so they would have a desirable pH level for chemical reactions (between 7 to 8). Enzymes are very important to plants because they act as catalysts for chemical reactions such as Adenosine Triphosphate (ATP), which is an important energy source for many chemical reactions in plants.


Stomata Activity:

Stomates are the pores that plants use to breath. Carbon Dioxide, water vapor and oxygen all are transferred between plant and atmosphere through stomates. Potassium regulates the opening and closing of stomates; therefore, it is essential for photosynthesis, water and nutrient transportation, and cooling down the plants. For example, the pores close when there is insufficient supply of water to prevent water loss or they would open to allow gases to move in and out freely. So when there is Potassium deficiency the pores can’t react quickly and sometimes instead of minutes it might take hours for them to close or open causing loss of water vapor and plants would be more susceptible to water stress.



The role of Potassium in photosynthesis is more complex than other functions of Potassium. We talked about Potassium role in both Enzyme activation and stomata activity and probably the most important role of Potassium in photosynthesis is production of ATP. Plants use sun’s energy to combine CO2 and water to form sugars and ATP is the high energy product of that reaction. Also, as we discussed earlier ATP is the energy source for many chemical reactions that occur in plants. When there is potassium deficiency the rate of ATP production and photosynthesis are both reduced.


Transport of Sugars:

After producing sugars in photosynthesis plants must transport the sugars for utilization and storage. The energy used to transport the sugars come in the form of ATP. When there isn’t enough ATP there is not enough energy to transport the sugars and causes the process to break down. Since ATP and Potassium have direct coloration .Therefore, having sufficient amount of Potassium is very important to keep transportation systems functioning adequately.


Water and Nutrient Transport:

“Potassium also plays a major role in the transport of water and nutrients throughout the plant in the xylem. When K supply is reduced, translocation of nitrates, phosphates, calcium (Ca), magnesium (Mg), and amino acids is depressed. As with phloem transport systems, the role of K in xylem transport is often in conjunction with specific enzymes and plant growth hormones. An ample supply of K is essential to efficient operation of these systems.”


Protein Synthesis: 

“Potassium is required for every major step of protein synthesis. The “reading” of the genetic code in plant cells to produce proteins and enzymes that regulate all growth processes would be impossible without adequate K. When plants are deficient in K, proteins are not synthesized despite an abundance of available nitrogen (N). Instead, protein “raw materials” (precursors) such as amino acids, amides and nitrate accumulate. The enzyme nitrate reductase catalyzes the formation of proteins, and K is likely responsible for its activation and synthesis.”


Starch Synthesis:

“The enzyme responsible for synthesis of starch (starch synthetase) is activated by K. Thus, with inadequate K, the level of starch declines while soluble carbohydrates and N compounds accumulate. Photosynthetic activity also affects the rate of sugar formation for ultimate starch production. Under high K levels, starch is efficiently moved from sites of production to storage organs.”


Crop Quality:

“Potassium plays significant roles in enhancing crop quality. High levels of available K improve the physical quality, disease resistance, and shelf life of fruits and vegetables used for human consumption and the feeding value of grain and forage crops. Fiber quality of cotton is improved. Quality can also be affected in the field before harvesting such as when K reduces lodging of grains or enhances winter hardiness of many crops. The effects of K deficiency can cause reduced yield potential and quality long before visible symptoms appear. This “hidden hunger” robs profits from the farmer who fails to keep soil K levels in the range high enough to supply adequate K at all times during the growing season. Even short periods of deficiency, especially during critical developmental stages, can cause serious losses.”