What resource will plants compete for in a rain forest? their nutritions & food and also water

The competition for resources like nutrients and water on the floor of the tropical rainforest is fierce. Extensive systems of tree roots soak up much of the nutrients and water. In a mature rainforest, the lower layers of the forest tend to be open because the lack of sunlight and nutrients limits plant growth  

Each plant strives to get enough sunlight to live. Since water is plentiful, most of the competition is for sunlight and nutrients.