Write the effects of toxicity of micronutrients.

(N/A) $\Rightarrow$ The requirement of micronutrients is always in low amounts.
$-\quad$ Their moderate decrease causes deficiency symptoms.
$\Rightarrow$ Their moderate increase causes toxicity.
$\Rightarrow$ Any mineral ion concentration in tissues that reduces the dry weight of tissues by about $10\%$ is considered toxic.
$\Rightarrow$ Such critical concentrations vary widely among different micronutrients.
$\Rightarrow$ Toxicity symptoms are often difficult to identify.
$\Rightarrow$ Toxicity levels for any element also vary among different plants.
$\Rightarrow$ Many times,an excess of one element may inhibit the uptake of another element.
$\Rightarrow$ Example: Toxicity of Manganese $(Mn)$:
$\Rightarrow$ The appearance of brown spots surrounded by chlorotic veins.
$\Rightarrow$ Manganese competes with Iron $(Fe)$ and Magnesium $(Mg)$ for binding with enzymes.
$\Rightarrow$ Manganese inhibits Calcium $(Ca)$ translocation to the shoot apex.
$\Rightarrow$ Therefore,an excess of Manganese may,in fact,induce deficiencies of Iron,Magnesium,and Calcium.
$\Rightarrow$ Thus,what appears as symptoms of Manganese toxicity may actually be the deficiency symptoms of Iron,Magnesium,and Calcium.