Q.Which one of the following statements can best explain the term critical concentration of an essential elements?

The critical concentration of an essential element is the minimum tissue concentration below which the plant shows deficiency symptoms and its growth is retarded.

For any mineral element considered essential for plant growth, there exists a concentration in plant tissue below which the plant's growth (or a specific physiological function) is measurably slowed or impaired — this threshold is called its critical concentration. As the internal concentration of that element rises through and past this critical value, growth improves until it plateaus at an adequate/optimal level; the …

Increasing Mn concentration beyond the optimum causes Mn toxicity, which blocks the uptake of Fe, Mg, and Ca, so the plant shows deficiency symptoms of these elements.

Manganese is an essential micronutrient, needed in small amounts for photosynthetic water-splitting (the oxygen-evolving complex) and enzyme activation. However, mineral nutrients must be supplied within a narrow optimum range - too little causes deficiency, but too much causes toxicity. When Mn concentration in the growth medium is raised well above the normal requirement, it competitively interferes with the absorption and translocation of other cations, specifically preventing the uptake of iron (Fe), magnesium (Mg), and calcium (Ca) at the root and within the plant. As a result, even though Fe, Mg, and Ca are present in the medium, the plant develops their defici …