Plant Physiology - Lecture Notes - O. M. Tarnopilska 2019

6. Mineral Nutrition of Plants
6.1 Classification of Mineral Elements

The primary products of Photosynthesis serve as the source of the essential set of Organic compounds for plants. They are formed from CO₂ and H₂O during The process of plant aerial Nutrition, with their chemical structures based on C, O₂, and H₂. Through METABOLISM, these primary photosynthetic products are converted into Amino Acids, high-energy compounds, Nucleic Acids, and secondary organic metabolites. Their synthesis requires other non-metals and metals (such as N, P, S, K, Ca, Fe, Cu, Mg, etc.), which essentially encompasses all the elements of the periodic table. Plants obtain these elements from the soil; therefore, growth intensity and agricultural crop yields depend largely on soil nutrition conditions. This is why measures aimed at increasing soil fertility, proper fertilizer management, and adhering to strict agricultural practices are of such paramount importance.

About 68 chemical elements have been detected in plants, 47 of which are consistently present. In 1935, Oleksandr Pavlovych Vinohradov established that the qualitative Elemental Composition of living organisms is generally similar to that of the Earth's crust. Their content in a plant depends on its species, as well as soil and climatic conditions. Organogenic elements (C, H, O, N, S) are the most abundant in plants. When plant residues are burned, these elements are released as gaseous compounds, while Mineral Substances remain as ash. The amount of ash in a plant depends on its ability to concentrate mineral elements, their availability in the soil, Water supply, and other factors. Ash elements are particularly abundant in actively functioning living Tissues.

The content of ash elements varies across different plants and even among different Organs of the same plant. For instance, leaves contain 10-15% ash, tree bark approximately 7%, wood about 1%, herbaceous stems 4-5%, and seeds 3%.

The qualitative composition of ash depends on the metabolic processes taking place within tissues and organs. For example, seeds contain higher amounts of K, P, and Mg, which are essential for the normal Development of the embryo; storage organs accumulate K, which activates starch synthesis; stems are rich in Ca and Si; and leaves contain P, Mg, and K (in young leaves) or Ca (in older ones). Furthermore, elements that predominate in the soil tend to accumulate in greater quantities. Certain species are capable of hyperaccumulating specific elements; for instance, marine Algae accumulate bromine and iodine, while some grasses (such as corn and others) accumulate gold. Depending on their concentration in the Organism, mineral elements are classified into Macronutrients (C, O, H, N, S, K, P, Ca, Mg, Cl, Na, Si, Al), micronutrients (Fe, Cu, Mn, B, Zn, Co, Mo, etc.), and ultramicronutrients (Cs, Se, Cd, Hg, Ag, Au, Ra), whose physiological roles remain largely unexplored. Macronutrients account for 10-10^-2% of the plant's fresh weight, micronutrients for 10^-5-10^-6%, and ultramicronutrients for 10^-6-10^-12%.

Without macro- and micronutrients, normal plant activity is disrupted. At the same time, certain macronutrients such as sodium, silicon, and aluminum do not play a significant role in plant physiology.