We find that $Rhizobium$ forms nodules on the roots of leguminous plants. Also,$Frankia$,another microbe,forms nitrogen-fixing nodules on the roots of the non-leguminous plant $Alnus$. 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) Yes,it is necessary for a microbe to be in close association with a plant to provide mineral nutrition in cases of symbiotic nitrogen fixation.
$1$. Symbiotic nitrogen fixation requires a specialized environment where the microbe can function effectively without being inhibited by oxygen.
$2$. For example,$Rhizobium$ bacteria enter the root hairs of leguminous plants and form root nodules.
$3$. Inside these nodules,the bacteria differentiate into bacteroids and produce the enzyme nitrogenase,which fixes atmospheric nitrogen into ammonia.
$4$. The plant provides the bacteria with carbohydrates and a protected environment,while the bacteria provide the plant with fixed nitrogen,demonstrating that close physical association is essential for this mutualistic interaction.