Ncert Exercises & Solutions

36. We know that plants require nutrients. If we supply these in excess, will it be beneficial to the plants? If yes, how/ if no, why?

Plants can tolerate a Specific amount of micronutrient. A slight lesser amount of it can cause deficiency symptom and a slight higher amount can cause toxicity. The mineral ion concentration which reduces the cry weight of a tissue by 10° is called toxic concentration. Th. concentration is different for different micronutrients as well as for different plant. e.g. Mn²⁺ is toxic beyond

600 μ {gg}^{- 1}

for soyabean and beyond

5300 μ {gg}^{- 1}

for sunflower

It is very difficult to identify the toxicity symptoms of mineral ion. It is because excess uptake of one element can reduces the uptake of other element at a time.
e.g., manganese (Mn²⁺) becomes toxic when absorbed by plants in higher amounts. The toxicity is expressed in form of brown spots surrounded by chlorotic vein.

It is due to the following

(i) Reduction in uptake of Fe³⁺ and Mn²⁺.

(ii) Inhibition of binding of Mn²⁺ to specific enzymes.

(iii) Inhibition of Ca²⁺ translocation in shoot apex.

Thus, excess of Mn²⁺ causes deficiency of iron, magnesium and calcium.

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