Assertion : Excess Mn in soil, can adversely decrease Mg , Fe and Cu concentrations in the soil. Reason : Mn increases rate of photosynthesis, thereby increasing absorption of Mg , Fe and Ca from soil.

Step-by-step solution

Manganese ( Mn ) is a micronutrient. Excess of it in soil can cause manganese toxicity characterized by brown spots surrounded by chlorotic veins. It occurs due to (i) reduction in uptake of iron and magnesium (ii) inhibition of binding of magnesium to specific enzymes (iii) inhibition of calcium translocation into shoot apex. Therefore excess of manganese (Mn) causes deficiency of iron (Fe), magnesium ( Mg ) and calcium ( Ca ) . Hence the toxicity symptoms of Mn are actually combined deficiency symptoms of Fe, Mg