Friday, June 18, 2010

The Role of Nutrients in Plants - the Micronutrients

The previous two days of this blog were devoted to the macronutrients that are required by plants and the roles they play to plant growth.  The 6 macronutrients were nitrogen, phosphorus and potassium (the main three) along with calcium, magnesium and sulfur.

Today we will look at the 8 micronutrients.  Just these nutrients are prefaced with the term micro it doesn't mean that these nutrients aren't just as important as the micronutrients.  They are just as important.  Below is a description of these nutrients and their responsibilities for the growth of plants.

Iron (Fe)

• Catalyzes the production of chlorophyll.
• Involved in some respiratory and photosynthetic enzyme systems.
• Involved in the reduction of nitrates and sulfates.

Zinc (Zn)
• Involved in plant carbon metabolism.
• A necessary component of several enzyme systems that regulate various metabolic activities within plants.
• Part of an enzyme that regulates the equilibrium among carbon dioxide, water, and carbonic acid.
• Part of two enzymes that play a role in protein metabolism.
• Essential for the formation of chlorophyll and function of normal photosynthesis.
• Needed to form auxins, which are growth-promoting substances in plants.
• Associated with water relations in plants and improves water uptake.

Manganese (Mn)
• Involved in the production of amino acids and proteins.
• An activator of several enzymes.
• Plays an essential role in respiration and N metabolism.
• Necessary for the reduction of nitrates and helps make them usable by plants.
• Plays a role in photosynthesis and in the formation of chlorophyll.

Boron (B)
• Important in sugar translocation and carbohydrate metabolism.
• Particularly needed at the location of active cell division.
• Plays an important role in flowering, pollen-tube growth, fruiting processes, N metabolism, and hormone activity.
• Maintains Ca in a soluble form, thus insuring its proper utilization.
• Deficiencies may be aggravated by severe drought conditions, heavy lime applications, or irrigation with alkaline water.

Copper (Cu)
• Part of several enzyme systems.
• Has a role in photosynthesis and chlorophyll formation.
• May have an important function in root metabolism. (Cu appears to be concentrated more in the rootlets of plants than in leaves or other tissues. Cu in citrus fibrous roots may be 5 to 10 times greater than in leaves.)
• Regulates several biochemical processes within the plant.
• Important in the utilization of proteins in the growth processes of plants. (The photosynthesis rate of Cu-deficient plants is abnormally low.)
• May also be involved in oxidation-reduction reactions in plants.
• Heavy fertilization with N tends to increase the severity of Cu deficiency.

Molybdenum (Mo)
• Assists in the formation of plant proteins.
• Helps starch, amino acid, and vitamin formation.
• Considered a catalyst that aids the conversion of gaseous N to usable forms by nitrogen-fixing microorganisms.
• A constituent of the plant enzyme that converts nitrate to ammonia.

Chlorine (Cl)
Although the essentiality of Cl has been established for most higher plants, its need for fruit crops has not yet been demonstrated. The plant requirement for Cl is quite high as compared with other micronutrients, but its exact role in plant metabolism is still obscure. Chlorine is:
• Associated with turgor in the guard cells through the osmotic pressure exerted by imported K ions.
• Involved with oxygen production in photosynthesis.
• Involved in chlorophyll and photosynthesis because its deficiency causes chlorosis, necrosis, unusual bronze discoloration of foliage, and reduction in growth.

Nickel (Ni)
Within the last decade, Ni has been established as an essential element in higher plants. Although well-defined enzymatic functions are known to be associated with Ni in legumes, apparently the need for Ni exists in other plants as well. No one has ever seen a Ni deficiency in soil-grown plants.

The University of Missouri Extension publication "Micro and Secondary Nutrients in Missouri" (EC929) would be a great resource. You can contact your local county extension office or MU Extension Publications Office to order a copy.

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