What were the competitive advantages and the challenges for the aquatic plants to adapt to terrestrial mode of living?
Although it is not certain when plants first arose, it appears that they did so during a time when the Earth's climate was changing. Likely, those areas where plants evolved was subject to periods of flooding and periods of drying, and characteristics that enabled some species to better survive during the dry periods evolved slowly. Adaptation to the drier conditions eventually enabled early plants to colonize the land. To fully appreciate the huge advantages that terrestrial migration had for plant development, it is necessary to understand the differences between aquatic and terrestrial environments with respect to requirements for plant growth.
Advantages of Moving to a Terrestrial Environment: Increased Photosynthesis and Decreased Competition
In order for plants to photosynthesize and produce the proteins, lipids, and carbohydrates necessary for growth, they require light energy. Light energy available to organisms living beneath the water's surface is greatly reduced (Fig 5). The blue and especially red wavelengths of light that are absorbed by photosynthetic pigments do not penetrate deep beyond the surface of the water; therefore, photosynthetic organisms living in an aquatic environment do not receive the full amount of light energy radiated from the sun. Photosynthetic organisms growing on land do not face this problem. Photons emitted from the sun can directly strike light-absorbing surfaces and the full range of useful wavelengths are available for photosynthesis. In the aquatic environment, many large algae compete for sunlight (similar to the competition for sunlight in modern forests). For early plants first moving into terrestrial environments, there was no competition for access to light.
The photic zone.
It is important to remember the fundamental role that plants play within an ecosystem. Plants and other autotrophs are the basis for supporting heterotrophic life. Prior to colonization of the land by plants, there was little basis for support of animal or fungal life. As mentioned above, the vast
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