Answer:
The carbon and water cycle I know, but I can't help with the nitrogen cycle. Sorry.
Step-by-step explanation:
Carbon cycle - The role that plants play in the carbon cycle is that they take in our carbon dioxide and put out oxygen, which we breathe. So we give the plant air and they give us air.
Water cycle - The role that plants play in the water cycle is when it rains, the plants absorb some of the water in their roots, thus making them strong and therefore helping the ground not become a mud hole.
Sorry that I can't help with the nitrogen cycle. But I hope what I was able to help you with helps!