-Here is a brief description of the nitrogen cycle:

Nitrogen exists in N2 gas form in the atomsphere. However, N2 form can’t be used by organisms. Therefore, there are N-fixing bacteria that convert N2 into usable forms such nitrate or ammonium. Plants integrate the nitrogen into its molecules such as amino acids, and consumers get their nitrogen from the plants. After the organisms died, some decomposers convert the nitrogen in bio tissues back to ammonia. Then, there are bacteria converting this ammonia into nitrites and then nitrates. Then some denitrifying bacteria converts the nitrates back to N2 gas form and the cycle is completed.

So the nitrogen cycle affects plant growth mainly by the availbilty of useable nitrogen forms (nitrate or ammonium) to the plants. Nitrogen is a macronutrient for plant life, and nitrogen shortage is a big survival challenge faced by all plants. Many N-fixing bacteria in the nitrogen cycle actually form a symbiosis relationship with plants to provide usable N forms to the plants. Nitrites, a unusable N form, is harmful to plants.

-Here is a brief description of the water cycle:
Water exists mainly in water bodies (oceans, rivers, reservoirs, ponds). Water evaporates into the air, and from land water can also goes into the air from organisms and things like land moisture. In the air, water forms clouds and then fall down to ground and water bodies again as precipitation. Organisms also release water into the ground and water bodies. Water then evaporates or goes into a water bodies or retained on land in the forms of moistures of things like that.

So the water cycle affects plants mainly by availibity, too. Too little or too much water can be harmful to the plants. Water can also carry solutes such as ions and toxins, and these solutes can affect plant life, too.

Hope that helped. Good luck!