PLANT NUTRITION: MACRONUTRIENTS, MICRONUTRIENTS, DEFICIENCIES - BIOLOGY - 2025

The plant nutrition is the set of chemical processes by which nutrients extracted from the ground floors that support for the growth and development of organs. It also makes special reference to the types of mineral nutrients that plants require and the symptoms of their deficiencies.

The study of plant nutrition is particularly important for those who are in charge of the care and maintenance of crops of agricultural interest, since it is directly related to the measures of yield and production.

Field sown with corn (Source: pixabay.com/)

Since prolonged cultivation of vegetables causes erosion and mineral impoverishment of the soils, the great advances in the agricultural industry are related to the development of fertilizers, whose composition is carefully designed according to the nutritional requirements of the cultivars of interest.

The design of these fertilizers requires, without a doubt, a vast knowledge of plant physiology and nutrition, since as in any biological system, there are upper and lower limits in which plants cannot function properly, either by lack or excess of some element.

How are plants nourished?

The roots play a fundamental role in plant nutrition. Mineral nutrients are taken from the “soil solution”, and are transported either by the simplistic (intracellular) or apoplastic (extracellular) route to the vascular bundles. They are loaded into the xylem and transported to the stem, where they fulfill various biological functions.

Chicory root

The uptake of nutrients from the soil through the syplast in the roots and their subsequent transport to the xylem by the apoplastic pathway are different processes, mediated by different factors.

Nutrient cycling is thought to regulate ion uptake into the xylem, while influx into the root sympathetic may be dependent on temperature or external ion concentration.

The transport of solutes to the xylem generally occurs by passive diffusion or passive transport of ions through ion channels, thanks to the force generated by the proton pumps (ATPases) expressed in the paratracheal cells of the parenchyma.

On the other hand, transport to the apoplast is driven by differences in hydrostatic pressures from the transpiring leaves.

Many plants use mutualistic relationships to nourish themselves, either to absorb other ionic forms of a mineral (such as nitrogen-fixing bacteria), to improve the absorption capacity of their roots, or to obtain greater availability of certain elements (such as mycorrhizae)..

Essential elements

Plants have different needs for each nutrient, since not all are used in the same proportion or for the same purposes.

An essential element is one that is a constituent part of the structure or metabolism of a plant, and whose absence causes severe abnormalities in its growth, development or reproduction.

In general, all elements function in cellular structure, metabolism, and osmoregulation. The classification of macro- and micronutrients has to do with the relative abundance of these elements in plant tissues.

Macronutrients

Among the macronutrients are nitrogen (N), potassium (K), calcium (Ca), magnesium (Mg), phosphorus (P), sulfur (S) and silicon (Si). Although essential elements participate in many different cellular events, some specific functions can be pointed out:

Nitrogen

This is the mineral element that plants require in greater quantities and it is usually a limiting element in many soils, which is why fertilizers generally have nitrogen in their composition. Nitrogen is a mobile element and is an essential part of the cell wall, amino acids, proteins and nucleic acids.

Although the atmospheric nitrogen content is very high, only plants of the Fabaceae family are capable of using molecular nitrogen as the main source of nitrogen. The forms assimilable by the rest are nitrates.

Potassium

This mineral is obtained in plants in its monovalent cationic form (K +) and participates in the regulation of the osmotic potential of cells, as well as an activator of enzymes involved in respiration and photosynthesis.

Calcium

It is generally found as divalent ions (Ca2 +) and is essential for cell wall synthesis, especially the formation of the middle lamella that separates cells during division. It also participates in the formation of the mitotic spindle and is required for the functioning of cell membranes.

It has an important role as a secondary messenger in several plant response pathways both through hormonal and environmental signals.

It can bind to calmodulin and the complex regulates enzymes such as kinases, phosphatases, cytoskeletal proteins, signaling proteins, among others.

Magnesium

Magnesium is involved in the activation of many enzymes in photosynthesis, respiration, and DNA and RNA synthesis. In addition, it is a structural part of the chlorophyll molecule.

Match

Phosphates are particularly important for the formation of the sugar-phosphate intermediates of respiration and photosynthesis, as well as being part of the polar groups on the phospholipid heads. ATP and related nucleotides possess phosphorus, as well as the structure of nucleic acids.

Sulfur

The side chains of the amino acids cysteine ​​and methionine contain sulfur. This mineral is also an important constituent of many coenzymes and vitamins such as coenzyme A, S-adenosylmethionine, biotin, vitamin B1 and pantothenic acid, essential for plant metabolism.

Silicon

Despite the fact that only a particular requirement for this mineral has been demonstrated in the Equisoceae family, there is evidence that the accumulation of this mineral in the tissues of some species contributes to growth, fertility and resistance to stress.

Seedling (Source: pixabay.com/)

Micronutrients

The micronutrients are chlorine (Cl), iron (Fe), boron (B), manganese (Mn), sodium (Na), zinc (Zn), copper (Cu), nickel (Ni) and molybdenum (Mo). Like macronutrients, micronutrients have essential functions in plant metabolism, namely:

Chlorine

Chlorine is found in plants as the anionic form (Cl-). It is necessary for the photolysis reaction of water that takes place during respiration; participates in photosynthetic processes and in the synthesis of DNA and RNA. It is also a structural component of the ring of the chlorophyll molecule.

Iron

Iron is an important cofactor for a wide variety of enzymes. Its fundamental role involves the transport of electrons in oxide reduction reactions, since it can be easily reversibly oxidized from Fe2 + to Fe3 +.

Its primary role is perhaps as part of the cytochromes, vital for the transport of light energy in photosynthetic reactions.

Boron

Its exact function has not been specified, however evidence suggests that it is important in cell elongation, nucleic acid synthesis, in hormonal responses, membrane functions and in the regulation of the cell cycle.

Manganese

Manganese is found as a divalent cation (Mg2 +). It participates in the activation of many enzymes in plant cells, in particular decarboxylases and dehydrogenases involved in the tricarboxylic acid cycle or Krebs cycle. Its best known function is in the production of oxygen from water during photosynthesis.

Sodium

This ion is required by many plants with C4 metabolism and crassulaceous acid (CAM) for carbon fixation. It is also important for the regeneration of phosphoenolpyruvate, the substrate of the first carboxylation in the aforementioned routes.

Zinc

A large number of enzymes require zinc to function, and some plants need it for chlorophyll biosynthesis. Enzymes of nitrogen metabolism, energy transfer and the biosynthetic pathways of other proteins need zinc for their function. It is also a structural part of many genetically important transcription factors.

Copper

Copper is associated with many enzymes that participate in oxidation-reduction reactions, since it can be reversibly oxidized from Cu + to Cu2 +. An example of these enzymes is plastocyanin, which is responsible for the transfer of electrons during the light reactions of photosynthesis.

Nickel

Plants do not have a specific requirement for this mineral, however, many of the nitrogen-fixing microorganisms that maintain symbiotic relationships with plants need nickel for the enzymes that process gaseous hydrogen molecules during fixation.

Molybdenum

Nitrate reductase and nitrogenase are among the many enzymes that require molybdenum for their function. Nitrate reductase catalyzes the reduction of nitrate to nitrite during nitrogen assimilation in plants, and nitrogenase converts nitrogen gas to ammonia in nitrogen-fixing microorganisms.

Diagnosis of deficiencies

Nutritional alterations in vegetables can be diagnosed in several ways, among them the foliar analysis is one of the most effective methods.

Internerval chlorosis in Liquidambar styraciflua (Jim Conrad, via Wikimedia Commons)

Chlorosis or yellowing, the appearance of dark colored necrotic spots and their distribution patterns, as well as the presence of pigments such as anthocyanins, are part of the elements to be considered during the diagnosis of deficiencies.

It is important to consider the relative mobility of each item, since not all are transported with the same regularity. Thus, the deficiency of elements such as K, N, P and Mg can be observed in the adult leaves, since these elements are translocated towards the tissues in formation.

On the contrary, young leaves will show deficiencies for elements such as B, Fe and Ca, which are relatively immobile in most plants.

References

1. Azcón-Bieto, J., & Talón, M. (2008). Fundamentals of Plant Physiology (2nd ed.). Madrid: McGraw-Hill Interamericana of Spain.
2. Barker, A., & Pilbeam, D. (2015). Handbook of plant nutrition (2nd ed.).
3. Sattelmacher, B. (2001). The apoplast and its significance for plant mineral nutrition. New Phytologist, 149 (2), 167-192.
4. Taiz, L., & Zeiger, E. (2010). Plant Physiology (5th ed.). Sunderland, Massachusetts: Sinauer Associates Inc.
5. White, PJ, & Brown, PH (2010). Plant nutrition for sustainable development and global health. Annals of Botany, 105 (7), 1073–1080.