Question

Assertion: In tropical rainforests, O-horizon and A horizon of soil profile are shallow and nutrient poor.

Reason: Excessive growth of microorganisms in the soil depletes its organic content.
A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion.
B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion.
C. Assertion is correct but Reason is incorrect.
D. Both Assertion and Reason are incorrect.

Answer 1

Hint: The hot, moist biome where rainfall occurs full year-long is called tropical rainforest. They are referred to as dense canopies of vegetation and form various layers. They are mainly found in Central and South America, Southeast Asia, Australia, islands of New Guinea, etc. The microorganisms’ growth is a very complex and coordinated process.

Complete answer:
The O-horizon and A-horizon in the tropical rainforest are poor in nutrient content and consist of the shallow soil profile. Due to annual rainfall in the tropical rainforest, the nutrient content in the soil is not very good. The dead organic matter in these areas decomposes faster because of high temperature and moisture.

The process of mineral leaching on the topsoil takes place rapidly while the nutrient cycling process also occurs. The layers of soil in the tropical rainforests are very thick and red latosols. So microorganisms or bacteria are not responsible for low nutrient content in the soil but leaching is the main reason for low nutrient in the soil of tropical rainforest.

The role of microorganisms is to decompose or depletes organic matter to form carbon dioxide and minerals which in turn produce nutrients like nitrogen. So excessive growth of microorganisms can deplete more organic matter. The organisms that decompose organic matter are known as decomposers or saprophytes.

Hence, the correct answer is option (B).

Note: Tropical rainforest is the area where rains occur all the year and the temperature is very high in that area. The soil nutrient content is very low and biodiversity is very high in the species of tropical rainforest. It is one of the wettest ecosystems in the whole world. Leaching is the reason for a bad soil profile in tropical rainforest rather than excessive microorganisms’ growth.