Adaptations to Aquatic Environments

Aquatic plants evolved from terrestrial plants. Like whales and other marine mammals, aquatic plants evolved from land back to aquatic habitats. Aquatic plants modified terrestrial features to withstand emerged, submerged, or floating conditions.

Types of Challenges

Aeration of Roots:

Reproduction: There are two common modes of reproduction sexual and vegetative.  Sexual reproduction is rare; vegetative is more commonly used.
        Sexual Reproduction:

        Vegetative Reproduction:   

Seed germination: Plants have different strategies for seeds.  Major problems are:

Photosynthesis: Gas exchange: As the water gets deeper, the wavelength of light gets shorter until it’s gone. The red and blue wavelengths are lost, and the green (not so good for photosynthesis) remains. Adaptations include:

-C4 provides a possible pathway for recycling CO2 from cell respiration
-plants using C4 have low photorespiration rates and the ability to use even the most
intense sunlight efficiently.
-C4 plants more efficient than C3 plants in rate of carbon fixation and amount of water
used per unit carbon fixed.




Submerged fresh water plants:



Algal blooms can block the sunlight and nutrients to submerged plants.  It also filters out red light loss. 




Aeration of Roots –

Oxygen is transmitted from the leaves to the roots and rhizomes by lacunae (air spaces forming channels in leaves, stems, and roots). Lacunae also have a structural role. Lacunae take up about 60% of the plants volume.

An experiment was done to demonstrate the oxygen gradient in plants. It was found that a plant has 20% oxygen in its leaves, 15% in its stem, 10% in the root parts, and only 2- 5% in the root hairs. The oxygen is taken 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 adjust for respiration. Aquatic plants can respire anaerobically. This has been shown experimentally by bubbling N2 or O2 into the water with rhizomes, and then measuring the ethanol production. At <3% O2, ethanol is produced by Typha, Scirpus, Nuphar, and others. Some aquatic plants have developed air roots along their stems for respiration in water. Aquatic trees have developed pnuematophores, which are extensions of the root system reaching above the water level. Pnuematophores take in oxygen through small holes at their tips.

Other challenges that aquatic plants must adapt to include: flooding, desiccation (drying out) nutrient uptake, and vegetative reproduction.