Silicon has a surprisingly large number of functions in plant life, and is especially important under stressful conditions. The role of silicon can be compared with the role of secondary organic metabolites, which perform protective functions in plants. Seeing all the variety of roles that silicon plays in plants against various stresses, today world scientists admit that they are still far from developing a “unified theory” of silicon in biology and agriculture.
Functions of silicon in a plant
Silicon has a significant effect on plant growth and development, increases yields and improves product quality. At the same time, the positive effect of silicon is especially noticeable in plants under stress conditions. Silicon gives plants mechanical strength, strengthens the cell walls, ensuring the rigidity of various plant organs.
Silicon in optimal doses promotes better metabolism of nitrogen and phosphorus in tissues, increases the consumption of boron and a number of other elements; provides a reduction in the toxicity of excess amounts of heavy metals. Optimization of silicon nutrition of plants leads to an increase in leaf area. In such conditions, more durable cell walls are formed in plants, as a result of which the danger of lodging crops, as well as damage to them by diseases and pests, is reduced.
One of the important functions of active forms of silicon is to stimulate the development of the root system. Studies on cereals, citrus fruits, vegetables and fodder grasses have shown that when the silicon nutrition of plants is improved, the number of secondary and tertiary roots increases by 20–100% or more. The deficiency of silicon nutrition is one of the limiting factors in the development of the root system of plants. It was found that the optimization of silicon nutrition increases the efficiency of photosynthesis and the activity of the root system.
Item Features
The first thing to notice is that almost all plants (with rare exceptions) can be grown without silicon in a nutrient medium. Even siliceous plants such as rice and wheat.
Another feature is that silicon accumulates in plants in large amounts, which often exceed the absorption of the main macronutrients (nitrogen, phosphorus and potassium). The range of silicon concentrations in plants is much wider than that of other nutrients. So, the silicon content ranges from 0,1-10% of dry weight, while, for example, for nitrogen this range is 0,5-6%, for potassium: 0,8-8%, phosphorus: 0,15, 0,5-XNUMX%. That is, the spread of silicon concentration is an order of magnitude larger than that of other elements.
It is very important to note that when grown under artificial favorable conditions, plants practically do not need silicon.
There are three groups of plants according to the silicon content in dry matter:
- silicon content more than 5% (rice, reed, etc.);
- silicon content more than 1% (barley, rye, etc.);
- the silicon content is less than 1% (for example, dicotyledons – cucumber, sunflower, etc.).
Silicon form in plant tissues
In plant tissues, silicon is in the form of water-soluble compounds such as orthosilicic acid (H4SiO4), orthosilicon ethers, as well as in the form of insoluble mineral polymers and crystalline impurities. As part of the organic matter of plant tissues, Si forms orthosilicon esters of hydroxyamino acids, hydroxycarboxylic acids, polyphenols, carbohydrates, sterols, as well as derivatives of amino acids, amino sugars and peptides. The most important soluble forms of silicon in plants and the soil-plant system are monosilicic and polysilicic acids. These inorganic compounds are always present in natural aqueous solutions. Moreover, there is a close relationship between them.
