Why can aquatic plants adapt to water?

Aquatic plants have aerenchyma tissue to transport oxygen from the surface to the roots, recycle carbon dioxide from cellular respiration to do photosynthesis, and keep the plant buoyant in water. Aquatic plants also use bicarbonate, which is more plentiful under water, as a carbon source.

Is bicarbonate same as carbon dioxide that aquatic plants get?

Is bicarbonate same as carbon dioxide that aquatic plants are getting?

It is a form of carbon dioxide. Just like in the human body, it acts as an electrolyte to the blood. Thus it helps in cellular respiration for plants that would help in photosynthesis.