Algal blooms can block the sunlight and nutrients to submerged plants. Lacunae alsohave a structural role. An experiment was done to demonstrate the oxygen gradient in plants. The oxygen istaken in from the air by photosynthesis and travels through the plant and out the root hairs. When low oxygen levels are present, plants use other mechanisms to adjustfor respiration.
Aquatic plants can respire anaerobically.
This has beenshown experimentally by bubbling N2 or O2 into the water with rhizomes,and then measuring the ethanol production. Some aquatic plants have developed air roots along their stems for respiration in water. Aquatic trees havedeveloped pnuematophores which are extensions of the root system reachingabove the water level. Pnuematophores take in oxygen through small holes at their tips.