The fitness of the environments of air and water for photosynthesis, growth, reproduction and dispersal of photoautotrophs: an evolutionary and biogeochemical perspective

Life has evolved to exploit aquatic and terrestrial environments, but these present very different challenges and opportunities for photoautotrophs. This paper outlines how the physical and chemical ‘fitness’ of air and water have interacted with the evolution of the physical structures and physiological properties of aquatic and terrestrial algae and plants and altered the biogeochemistry of the planet. The two environments are particularly different for photosynthesis and the consequences of water stress in air and potential carbon and light stress under water are discussed, as are the consequences of the lower density of air compared to water for investment in support. The properties of air and water also affect mineral nutrition, reproduction and dispersal of photoautotrophs and the nature of competition between different types of plants. Furthermore, the pivotal role of photoautotrophs in global biogeochemical cycles and major feedbacks are emphasized. They have altered the environment dramatically, changed the availability of essential resources and created niches that can be exploited by new or different species or types of organism. Recent rapid anthropogenic changes, particularly in CO2, are noted and discussed in relation to the security of human requirements.