Other than light and CO2 plants need 14 element (nutrients) to grow. 7 metal and 7 none metals. If just one is missing the plants will not grow. but these elements need to be soluble in water for the plants to use them. In soil plants release eek acids that break down rock and soil making the element water soluble. But in an aquatic environment the acids released by the roots are often sweptsdd away by the current. But often water is naturally slightly acidic. So the aquatic plants mostly absorb nutrient from the water. flowing past them.
In an aquarium the nutrients can come from fish waist or they are already in the tap water you used to fill the tank. People then often use fertilizers to supplement the nutrients. Or people us nutrient rich soil as their substate. Some people need use a soil plus fertilizer. While others use just fertilizers Nutrients in the substate can however eventually run out. Also not all fertilizers have all the 14 nutrients. Manufactures often assume some are in your tap water. So just using a fertilizer is not a guaranty of success. The hard part with plants is figuring out what combination of fish waist, soil, and or fertilizer will give you good plant growth without algae. Getting everything right can be difficult.
Plants need Nitrogen, Potassium, Calcium, Magnesium, Posphate, Sulfur, chlorine, Iron, Boron, Zinc, Copper, molybdenum, and nickel. This is in addition to the carbon, oxygen, and hydrogen the plants can extract from water and air.