How Does Cobalt Affect Plant Growth?
Cobalt is a Metal Nutrient

Cobalt is a nutrient that is essential for plant growth and development. Cobalt is a trace element component of various enzymes and proteins necessary for chlorophyll production, enzyme activation, drought resistance, and nitrogen fixation. It is required for the production of chlorophyll and, thus, photosynthesis. It is also needed to produce carbohydrates and is an essential co-factor in other amino acids. In plants, cobalt causes stress at levels above 80 ppm, and it may also be toxic to higher plant life forms. 

Cobalt is a metal that is important for plant growth. Plants need cobalt to produce chlorophyll, the pigment that gives plants their green color. Chlorophyll also helps plants use sunlight to turn carbon dioxide and water into sugars and oxygen.

A study published in the Journal of Plant Nutrition found that adequate concentrations of cobalt in the soil increased dry matter growth, female flowers, and fruit yields. The researchers found a linear relationship between soil cobalt concentration and dry matter production.

Cobalt aids in micro-biotic activity and amplifies nitrogen fixation among symbiotic bacteria. Cobalt is known to be an essential factor in various enzyme and co-enzyme functions that have a significant effect on the growth and metabolism of plants. Cobalt deficiency leads to decreased seed germination and plant biomass.

Cobalt Deficiency and Toxicity in plants

The presence of cobalt deficiency visually presents as a symptom of nitrogen deficiency. The abundance of cobalt in the soil can be toxic and is more common than cobalt deficiency. Roots actively take up cobalt in the cation form of Co2+; however, the movement of this compound throughout the plant is limited and poorly mobile. The toxic concentrations of cobalt result in the loss of leaves, discoloration, and paling of plant leaves and veins. This is a common problem with plants grown in soil with high levels of cobalt. In these soils, the roots take up large amounts of cobalt because it is a plant nutrient. 

Cobalt can also be found in some fertilizers that are used to help plants grow. However, if these fertilizers contain high levels of cobalt, they can lead to toxicity problems for the plant. The most likely occurrence of cobalt toxicity in plants is when plants are watered with water containing high levels of cobalt. To reduce the risks of plant toxicity, it is important to adjust the water pH to be neutral or low. Some common causes for high levels of cobalt are hard stormwater run-off and irrigation systems for agriculture. If you have soil that contains high levels of cobalt, then use a soil test to check your soil’s cobalt levels. The most common occurrence of cobalt toxicity in plants is when plants are watered with water containing high levels of cobalt. Some unique symptoms that may occur (e.g., the sudden death of leaves or flowers) are consistent with other plant toxins, such as copper and nickel. Toxic concentrations of cobalt can result in loss of leaves, discoloration, and paling of plant leaves and veins. Furthermore, excess cobalt on new leaf growth presents with interveinal chlorosis and white leaf margins on leaf tips.

Source: Nair et al., 2022

Figure 1. The nitrogen cycle is an important process that takes place in all living organisms. Nitrogen is a key component of DNA and amino acids, which are the building blocks of life. This cycle involves the conversion of nitrogen from its most common form, atmospheric N2, to a more usable form. Nitrogen fixation is the process by which atmospheric nitrogen (N2) is converted into ammonia (NH3). It can be done by either ammonification or nitrification. Ammonification converts N2 to NH4+ through oxidation, while nitrification converts N2 to NH3 through reduction. Symbiotic bacteria in the root nodules of legumes are responsible for converting atmospheric nitrogen into ammonia through nitrification. Cobalt is essential for symbiotic bacteria in nitrogen fixation because it helps with the reduction reaction during nitrification and provides a necessary cofactor for this process.

Source: Banerjee1 & Bhattacharya, 2021

Figure 2. The uptake and translocation of cobalt in plants have been studied extensively in the past few decades. The uptake of cobalt by plants depends on the concentration of cobalt in soil, plant species, and other environmental factors. In plants, the cobalt is taken up by translocating a protein called cobalamin, in which cobalt is bound to adenosine. The cobalt-cobamamide complex binds to the ATPase at the cytoplasmic membrane, forming an active transport site for uptake. The amount of free cytoplasmic ATP is measured by luminescence, and cellular uptake will occur as long as there is enough input of ATP.

Source: Banerjee1 & Bhattacharya, 2021

Figure 3. Cobalt is a metal used in the production of lithium-ion batteries and is also used in the production of alloys and pigments. The demand for cobalt has increased significantly in recent years due to its use in electric vehicles, smartphones, and other electronic devices. The main cobalt sources are copper and nickel mines, which produce about 60% of the world’s supply. The other 40% comes from recycling scrap metal or as a byproduct from refining copper or nickel ore.

Further Reading

Ashraf, M. and Harris, P.J.C. (2004) Potential Biochemical Indicators of Salinity Tolerance in Plants. Plant Science, 166, 3-16. http://dx.doi.org/10.1016/j.plantsci.2003.10.024

Bradford, K.J. et al., 1982. Plant Physiol. 70:1503-1507.

Cobalt. plant problems. (n.d.). Retrieved December 10, 2021, from https://plantprobs.net/plant/nutrientImbalances/cobalt.html. 

International Plant Nutrition Institute (IPNI). (n.d.). Retrieved December 10, 2021, from http://ipni.net/publication/nutrifacts-na.nsf/0/5D2097137F73C07F85257EA8006297B0/$FILE/NutriFacts-NA-15.pdf.

Naeem, M., Ansari, A. A., & Gill, S. S. (2020). Contaminants in agriculture: Sources, impacts and management. Springer. 

Palit, S. et al., 1994. The Botanical Review 60:149-181.