| Critical Concentration | Deficient |
|---|---|
| A concentration of a nutrient measured in tissue, just below the level that gives maximum growth is defined as critical concentration. e.g., N, P and K are known as critical elements. |
The concentration that is below the critical concentration and the deficiency of nutrient element can lead to a gradual fall in the plant growth is called deficient. |
| Critical concentration | Deficient | |
|---|---|---|
| Zn | 0.5-1% | less than 0.5% |
| Fe | 3.5-5% | less than 3.5% |
Carnivorous plants exhibit nutritional adaptation. Citing an example explain this fact.
Plant can tolerate a specific amount of micronutrients. A slight lesser amount of it can cause deficiency symptoms and a slight higher amount can cause toxicity. The mineral ion concentration which reduces the dry weight of the tissues by $10 \%$ is called toxic concentration.
This concentration is different for different micronutrients as well as for different plants, e.g., $\mathrm{Mn}^{2+}$ is toxic beyond $600 \mathrm{ogg}^{-1}$ for soyabean and beyond $5300 \mathrm{ogg}^{-1}$ for sunflower.
It has also been observed that the toxicity of one micronutrient causes the deficiency of other nutrients. To overcome such problems, farmers should use these nutrients in prescribed concentration so that the excess uptake of one element do not reduce the uptake of other element.
It is observed that deficiency of a particular element showed its symptoms initially in older leaves and then in younger leaves.
(a) Does it indicate that the element is actively mobilised or relatively immobile?
(b) Name two elements which are highly mobile and two which are relatively immobile.
(c) How is the aspect of mobility of elements important to horticulture and agriculture?
(a) The plants try to supply more nutrients to its younger leaves than the older leaves. When nutrients are mobile, the deficiency symptoms are shown by the older leaves first because that particular nutrient reaches the top first and lower leaves does not get that nutrient.
(b) Highly mobile elements are P, K and Mn. Less mobile elements are $\mathrm{Ca}^{+}$and $\mathrm{K}^{+}$.
(c) The aspect of mobility of essential elements is important in horticulture and agriculture in the following ways
(i) A crop in which older leaves are harvested if show deficiency symptoms, will decrease its economic value.
(ii) The crops in which flowers, fruits and inflorescence are harvested, the immobile nutrients will not reach to the apex/tip because of immobility, so this will reduce the yield.
We find that Rhizobium forms nodules on the roots of leguminous plants. Also Frankia another microbe forms nitrogen fixing nodules on the roots of non-leguminous plant Alnus.
(a) Can we artificially induce the property of nitrogen-fixation in a plant, leguminous or non-leguminous?
(b) What kind of relationship is observed between mycorrhiza and pine trees?
(c) Is it necessary for a microbe to be in close association with a plant to provide mineral nutrition? Explain with the help of one example.
(a) Artificial induction in leguminous and non-leguminous plants have been tried by scientists. It's success rate is very low because gene expression is highly specific phenomenon.
Even if desired gene is introduced, it may not work because conditions for its expressions are very specific.
(b) Symbiotic mutualistic relationship (mutualism) is found between the pine roots and mycorrhiza as both are benefitted mutually.
(c) Yes, microbe has to be in close association, to develop a physical relationship for example Rhizobium gets into the root and involve root tissues, then only helps in nitrogen-fixation.