How do the plants in a rainforest contribute to the water cycle?

They remove water from the soil and put it into the atmosphere in a process called transpiration.

Water is removed from the soil and transported to the leaves in a liquid form, and during photosynthesis is converted to a gaseous form and released out the stomata of the leaves. Plant respiration can contribute much more moisture to the atmosphere than simple evaporation in an area like a rainforest.