Tiny creatures at the bottom of the food chain called diatoms suck up nearly a quarter of the atmosphere’s carbon dioxide, yet research by Michigan State University scientists suggests they could become less able to “sequester” that greenhouse gas as the climate warms.
Litchman analyzed data from lakes and oceans across the United States, Europe and Asia and found a striking difference between the size of diatoms in freshwater and in marine environments. In oceans, diatoms grow to be 10 times larger on average than in freshwater and have a wider range of sizes.
One factor that affects growth is nutrient availability, Litchman said. The research shows that limitations by nitrogen and phosphorus exert different selective pressures on cell size. The availability of these nutrients depends on the mixing of water from greater depths. Using a mathematical model, Litchman and her colleagues found that when those nutrients are constantly limited and mixing is shallow, smaller diatoms thrive.
But when nitrate comes and goes, as often happens in roiling oceans, diatoms evolve larger to store nutrients for lean times. Deep mixing also benefits large diatoms. Depending on how intermittent the nitrate supply is and how deep the ocean mixes, there can be a wide range of diatom sizes. Size matters for the creatures that eat them and also for carbon sequestration, as large diatoms are more likely to sink when they die.
Changing climate could alter the mixing depths and delivery of nutrients to diatoms and their subsequent sizes with a cascade of consequences, Litchman said.
Zoology professor Elena Litchman, who works at MSU's Kellogg Biological Station
Litchman analyzed data from lakes and oceans across the United States, Europe and Asia and found a striking difference between the size of diatoms in freshwater and in marine environments. In oceans, diatoms grow to be 10 times larger on average than in freshwater and have a wider range of sizes.
One factor that affects growth is nutrient availability, Litchman said. The research shows that limitations by nitrogen and phosphorus exert different selective pressures on cell size. The availability of these nutrients depends on the mixing of water from greater depths. Using a mathematical model, Litchman and her colleagues found that when those nutrients are constantly limited and mixing is shallow, smaller diatoms thrive.
But when nitrate comes and goes, as often happens in roiling oceans, diatoms evolve larger to store nutrients for lean times. Deep mixing also benefits large diatoms. Depending on how intermittent the nitrate supply is and how deep the ocean mixes, there can be a wide range of diatom sizes. Size matters for the creatures that eat them and also for carbon sequestration, as large diatoms are more likely to sink when they die.
Changing climate could alter the mixing depths and delivery of nutrients to diatoms and their subsequent sizes with a cascade of consequences, Litchman said.
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