Ecological stoichiometry: 'elementary recipe of everything'
If you've ever put too much sugar in your coffee, you'll know how important the right proportions are. That's also true for ecology: interactions in ecosystems depend to a large extent on the elemental ratios of carbon (C), nitrogen (N) and phosphorus (P). Ratios Matter is a new, threemonthly newsletter about this elemental balance and its impact on interacting organisms.
One of the editors of Ratios Matter is NIOO-researcher Dedmer van de Waal (Department of Aquatic Ecology). "All life on earth consists of the same elementary building blocks", he explains. "In particular carbon, nitrogen and phosphorus."
These elements can be found in key molecules such as sugars (lots of C), proteins (lots of N) and DNA (lots of P). The exact ratio of the elements determines whether, for instance, plants are suitable as food for herbivores, and how effective fertilizers are in increasing crop yields.
As the Ratios Matter website puts it: "You grow these plants in specific types of soil and add certain fertilizers because they need specific amounts of key nutrients like nitrogen and phosphorus to grow. If there is a very high ratio of nitrogen to phosphorus in the soil, adding more nitrogen will not help the plant grow."
Stoichiometry
The application of the laws of definite proportions and of the conservation of mass and energy to chemical activity is called 'stoichiometry': stoicheion is the ancient Greek word for 'element'. In a nutshell, Jim Elser has commented on Twitter, "stoichiometry refers to elemental recipe of everything!"
In ecology, says van der Waal, studying the chemical balance between elements is particularly important "to understand the complex relationships between organisms, and between organisms and their environment."
Ecological stoichiometry is a fast-growing area, and Ratios Matter has been created by researchers from Canada, the US, Argentina, Germany, Belgium and The Netherlands to bring together "conference announcements, summaries of new manuscripts, job openings, and interesting stories behind the science."
Turtles
One such story, from the first issue of the newsletter, is about turtles: a species "unique in morphology, physiology, life history and ecology", according to the authors of an article published earlier in Freshwater Biology.
The article notes that 82% of dry mass is found in a turtle's skeleton. Phosphorus content by dry mass is 8.5%, much higher than in humans and most other vertebrae.
This leads to the conclusion that thanks also to the animals' longevity and slow growth, "uptake and retention of P by turtles may be very important as a store for P" in freshwater systems: turtle stoichiometry!
Algae
Dedmer van de Waal's own research also gets a mention in the first issue of Ratios Matter: "if you go swimming in summer you'll often see signs warning against blue-green algae in lakes and ponds, or telling you not to collect mussels because of toxic algae in the seawater."
Van de Waal looks specifically at the stoichiometry of these harmful algae: "we study the balance of elements in the algae's toxins and link them to that of their producers and of the entire ecosystem - i.e. a lake or an ocean."
Van de Waal received the International Society for the Study of Harmful Algae (ISSHA) Patrick Gentien Young Scientist Award late last year for this research.
- More information and the first issue of the newsletter: https://ratiosmatter.wordpress.com/
