Some freshwater plants are expected to undergo radical changes as bicarbonate concentrations increase in lakes due to acidification, deforestation and use of nitrogen fertilisers according to a new study led by The University of Western Australia.
Study lead author Adjunct Professor Ole Pedersen, from UWA’s School of Agriculture and Environment, said unlike land-based plants, photosynthesis in many aquatic plants relied on bicarbonate as well as carbon dioxide to compensate for the lack of carbon dioxide in water.
The study, published in Science, found that plants that had the ability to use bicarbonate increases in hard water lakes with greater bicarbonate concentrations while in streams where the carbon dioxide concentration was higher than in air, there were fewer bicarbonate users.
Globally, photosynthesis in land-based plants is influenced by climatic factors such as adaptations to variation in air temperature and water availability.
Professor Pedersen said in water, carbon dioxide often limited photosynthesis because it moved 10,000 times slower than in air which meant rapid photosynthesis could deplete carbon dioxide in dense plant stands.
“In order to meet the requirements of water plants, CO2 concentrations must be 10 to 20 times higher than in air,” he said. “This never happens in lakes, where microscopic algae may reduce the CO2 content to 10 per cent of that in air.”
“The implications of this study are that species richness and composition of water plants are expected to change with ongoing and future changes of bicarbonate concentrations in lakes that are caused by human-induced changes such as acidification, forest cover and use of nitrogen fertilisers.
“The changes can be dramatic since carbon dioxide users are generally small compared to the much bigger bicarbonate users.
“So a change in the balance between the two plant types alters the three-dimensional structure of the underwater meadows that protect small animals and young fish from predators.”