The soil of the rainforest is nutrient poor. How do plants that have roots in the rainforest floor obtain the nutrients they need? They absorb most of the nutrients they need from recently deceased plants and animals that fall on the forest floor.
They absorb most of the nutrients they need from the air.
They trap insects and gain nutrients they need by digesting the insects.
They have adapted to the poor soil of the rainforest and require fewer nutrients that they gain from the soil.