The main difference between submerged and emergent plants is that submerged plants grow entirely underwater, while emergent plants grow partially or completely above the water surface. Both types of plants are important for aquatic ecosystems, but they have different adaptations, benefits, and challenges. In this article, we will explore the characteristics, examples, and roles of submerged and emergent plants in freshwater and marine habitats.
Submerged plants, also known as submersed or aquatic plants, are plants that grow with their roots, stems, and leaves completely submerged in water. They can be rooted to the bottom of the water body, such as pondweed and eelgrass, or they can be free-floating, such as duckweed and water hyacinth. Submerged plants have several adaptations that allow them to survive and thrive underwater, such as:
Thin, flexible, and ribbon-like leaves that reduce water resistance and increase surface area for photosynthesis.
Reduced or absent cuticle (a waxy layer that prevents water loss) and stomata (openings that allow gas exchange) on the leaves, since water is readily available and diffuses through the leaf surface.
Air-filled spaces or tissues (aerenchyma) in the stems and leaves that provide buoyancy and transport oxygen from the surface to the roots.
Specialized reproductive structures, such as flowers that can pollinate underwater or seeds that can float or disperse by water currents.
Submerged plants provide many benefits for aquatic ecosystems, such as:
Producing oxygen and organic matter through photosynthesis, which supports the food web and the water quality.
Providing habitat, shelter, and food for many aquatic animals, such as fish, invertebrates, amphibians, and waterfowl.
Stabilizing the sediment and preventing erosion by anchoring the soil with their roots.
Filtering the water and removing excess nutrients, pollutants, and toxins by absorbing them through their roots and leaves.
However, submerged plants also face some challenges, such as:
Limited light availability, especially in deep or turbid water, which affects their growth and photosynthesis.
Competition with other plants, algae, and animals for space, light, and nutrients.
Herbivory by aquatic animals, such as snails, insects, and fish, that feed on their leaves, stems, and roots.
Invasion by exotic or invasive species, such as Eurasian watermilfoil and hydrilla, that can outcompete and displace native submerged plants.
Emergent plants
Emergent plants, also known as emergent macrophytes or wetland plants, are plants that grow with their roots and some portions of their stems and foliage submerged in water, while their upper portions are visible above the water surface. They can grow along the edges of water bodies, such as lakes, rivers, and ponds, or in shallow water, such as marshes, swamps, and bogs. Emergent plants have several adaptations that allow them to cope with wet and variable conditions, such as:
Thick, sturdy, and erect stems that support the weight and height of the plant above the water.
Waxy, hairy, or serrated leaves that repel water and prevent waterlogging and fungal infections.
Well-developed cuticle and stomata on the leaves that regulate water loss and gas exchange.
Hollow or porous stems and roots that transport oxygen from the air to the submerged parts of the plant.
Diverse reproductive strategies, such as flowers that can pollinate by wind or insects, seeds that can germinate in wet or dry soil, or vegetative propagation by rhizomes, stolons, or tubers.
Emergent plants provide many benefits for aquatic ecosystems, such as:
Creating a transition zone between land and water, which increases the biodiversity and complexity of the ecosystem.
Providing habitat, nesting, and breeding sites for many terrestrial and aquatic animals, such as birds, mammals, reptiles, and amphibians.
Protecting the shoreline and reducing wave action and flooding by absorbing and dissipating the water energy.
Improving the water quality and reducing nutrient loading and sedimentation by filtering and trapping the runoff and pollutants from the land.
However, emergent plants also face some challenges, such as:
Exposure to varying water levels, temperature, and salinity, which affect their growth and survival.
Competition with other plants, especially woody plants, for light, space, and nutrients.
Herbivory by terrestrial and aquatic animals, such as deer, rodents, and waterfowl, that feed on their stems, leaves, and seeds.
Invasion by exotic or invasive species, such as purple loosestrife and phragmites, that can dominate and degrade the wetland habitats.
Conclusion
Submerged and emergent plants are two types of plants that grow in aquatic environments, but they have different adaptations, benefits, and challenges. Submerged plants grow entirely underwater, while emergent plants grow partially or completely above the water surface. Both types of plants are important for the structure and function of aquatic ecosystems, but they also face threats from human activities and invasive species. Therefore, it is essential to conserve and manage these plants and their habitats for the benefit of the environment and society.
