How Amino Acids Aid Plant Growth
Amino acids are a well-known additive for successfully growing plants and crops. Kyle Ladenburger looks at how they work and some of the additional benefits amino acids provide in the garden.
Amino acids are commonly referred to as the building blocks of life. This is an apt description since they represent the primary structural component in the cells of every protein in not only our bodies but in plants as well. Proteins are built through the specialized sequencing of amino acids to create a wide array of things within the plant, from specific enzymes to vital organs. Amino acids truly make complex lifeforms possible.
Plants have the ability to obtain carbon and oxygen from the air and hydrogen from the soil water creating carbon hydrate, which is then combined with nitrogen, leading to the synthesis of amino acids. This process constantly occurs during the entire lifespan of the plant. All types of plants create an abundance of amino acids that are used in a large array of metabolic and structural processes.
However, throughout the years, studies have shown plants can greatly benefit from the external application of supplemental amino acids and they can do so in a variety of ways. Some are more understood than others. In this article I will highlight a few of the known ways in which plants can utilize externally applied amino acids and how they can be used in our own gardens. But first, it’s important to understand how amino acids can become available to a plant and in which forms they can best be used.
How Amino Acids Become Available for Plants
Since amino acids are the building blocks of proteins and proteins are a key component in the cells of living creatures, when the process is basically reversed by the decomposition of organic matter one of the byproducts remaining are amino acids.
In the soil, dead plant and animal proteins are slowly broken down by specialized microorganisms into their constituent amino acids and short-chain polypeptides with the help of protein-specific enzymes such as Protease. This process takes time and when the amino acids are actually available to the plant is extremely difficult to determine.
Also, it is important to note plants can only utilize supplemental amino acids that are in the L-amino acid form. Those that are in the D-amino acid form cannot be assimilated by the plant and are therefore left to be synthesized within the plant itself.
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So, what do we do when organic decomposition takes too long and we know that the plants can only utilize amino acids in the L-amino acid form? Well, luckily human ingenuity and strong science has led to the ability to not only mimic but also drastically speed up the process of enzymatic digestion.
In the manufacturing of amino acid-based fertilizers and biostimulants, a process called “enzymatic hydrolysis” is used to speed up the digestion of the plant or animal proteins. Through enzymatic hydrolysis the proteins are treated with specific enzymes at the optimal temperature and pH to break them down into amino acids and short-chain polypeptides. The end result is referred to as a protein hydrolysate; of which the two most common products on the market today are soy protein hydrolysate and fish protein hydrolysate. These substances have a full profile of available amino acids in the “L” form and a modest nutrient content as well.
Seaweed extracts also contain a broad array of amino acids, with the cold-processed seaweed products believed to be the most beneficial. It’s important to remember that all dried plant or animal-based organic fertilizer will contain amino acids as well, but further decomposition is required before they can benefit the plant. Another thing to keep in mind is all the L-amino acids can be synthetically produced in a laboratory or factory setting and these are also used in many fertilizer formulations.
Sourcing Water-Soluble Nitrogen via Amino Acids
The most understood benefit of using amino acids in plant growth and development is that they are a water-soluble source of one of the most important elemental nutrients: nitrogen. Proteins comprise a large portion of organic matter and a major component of proteins and, subsequently, amino acids, is nitrogen.
As the organic matter is broken down further by proteolytic enzymes, either in the soil or during the manufacturing process, the nitrogen contained in the amino acids becomes available as a water-soluble nitrogen source that plants can readily uptake. This nitrogen can then be utilized by the plant to create, among other things, more amino acid and protein-based growth structures.
Furthermore, as the water-soluble amino acid derived nitrogen remains in the soil for longer periods of time, specialized microorganisms will continue the process of mineralization, effectively converting the nitrogen into other low molecular weight forms such as ammonium and nitrate, both of which are readily available to plant roots. This process is part of the nitrogen cycle and helps maintain a balanced ratio of positive and negatively charged nitrogen molecules in the soil.
Protective Barriers Around Nutrients
Amino acids have also been shown to have chelating or complexing properties when combined with other elemental nutrients, primarily secondary and micronutrients. Chelates and complex properties are created by a chemical reaction between a metal cation (such as iron, manganese, copper, or zinc) and a chelating or complexing agent which in this case is the amino acid. The reaction creates a protective shield around the positively charged cation preventing it from typical negative reactions such as precipitation from solutions or becoming tied up or electrically bound to the negatively charged soil particles.
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Simply speaking, a fertilizer molecule that is protected by either being chelated or complexed with an amino acid will remain more stable and available to the plant roots for a longer period of time. This increases the likelihood of being taken in by the plant leading to stronger, healthier growth.
There are several amino acids that have the ability to chelate or complex a positively charged nutrient cation but the two that have been shown to do so most effectively are L-Glycine and L-Glutamic Acid. They have the ability to form the strongest protective barrier around the nutrients. Both the nutrient molecule and its protective amino acid shell are taken into the plant via either the roots or through the stomata when applied through a foliar application.
Once inside the plant, the nutrient is released from the amino acid and utilized in whatever way necessary. The amino acid can either end up being used for its nitrogen or metabolically by the plant. On a fertilizer label an amino acid chelated or complexed ingredient will be represented by the name of the mineral nutrient followed by the amino acid used, such as Copper Glycinate for example.
Amino Acids and Plant Defense Mechanisms
More recently, several studies have been performed or are still on-going that look at how amino acids affect plant development beyond simple nutrition. These studies and trials have been primarily focused on how applied amino acids act as biostimulants and how they influence a plant’s primary and secondary metabolism.
Many of these studies have shown amino acids to have a positive effect on a plants ability to withstand and recover more quickly from external antagonism and abiotic stressors such as heat, drought, frost, as well as attacks from pests and disease. Certain amino acids have exhibited the ability to directly affect the stress physiology of a plant and aid in the strengthening of the plant’s own natural immune system.
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Some amino acids act as signaling molecules that, during periods of abiotic stress, initiate and activate downstream metabolic pathways that help the plant develop plant defense mechanism in order to ward off or minimize the damage of an external stress point. Other amino acids have been shown as precursor molecules leading to the development of internally produced compounds such as plant growth hormones that work in many ways to increase plant growth and development during times of high stress.
L-glutamate and L-proline have demonstrated an ability to be directly integrated into a plant’s primary and secondary metabolism to aid in defense against external stress factors including water retention and stomatal control, both of which are of great importance during drought conditions. These would be considered signaling molecules. A good example of an amino acid that acts as a precursor molecule is L-tryptophan.
L-tryptophan is a precursor molecule that, when applied as a supplement, leads to the development of Indole Acetic Acid or IAA — a plant growth hormone that affects several parts of the plant. One that is notable for this topic is its ability to promote stem elongation. This is helpful in conditions where a plant is receiving an uneven supply of light. The IAA can elongate the cells in the stems of the plant that don’t receive enough light and allow them to grow or stretch more dramatically to reach the light they desire.
Limiting Traditional Fertilizer Use
There is a current trend amongst growers to try and limit the amount of traditional fertilizers they use on their plants and I see that trend continuing well into the future. The use of products not primarily for their nutrient content but also for their biostimulant properties is a major component that many growers are integrating into their plant management programs.
Amino acids are a perfect example of a material that can supply important essential nutrients but can also be used as a natural tool to defend against external stresses without the need of chemical pesticides and products of that type. When a plant can naturally fortify itself against unwanted external forces, it is allowed to use the nutrients already available for straight forward growth and production, not just wasting them on recovering from unforeseen circumstances.
Amino acids are a great tool for any grower to have in their arsenal and a perfect representation of what the future of growing might look like.
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Written by Kyle Ladenburger | Director of Regulatory Affairs for Age Old Organics & ENP Turf, Freelance Garden Writer