The tropical rainforest is the most coplex and species rich biome in the world but it is soils are nutrient poor . What is the reason for this

because nutrients cannot be stored in the soil for a long time  

Explanation:

In rainforests, high temperatures and humid conditions lead to the rapid decomposition of the organic matter in the soils, which releases nutrients rapidly. However, rainforest soils are poor in nutrients due to rains that wash dead organic material from them. Moreover, rainwater is filtered naturally into the ground, thereby extracting (leaching) nutrients off the surface.