A matter of ratio(s): how to relate to the elements in your life

It's elementary, my dear Watson! All life on earth is composed of the same, vital elements. Carbon (abbreviated as capital C) is crucial for our energy supply in the form of carbs, fats and sugars. Nitrogen (N) is an important part of proteins, the 'workhorse' molecules of life. And phosphorus (P) is a component of DNA as well as a key to the growth and repair of tissue, including our bones. Without elements we would - literally - be nowhere.

The relatively new field of science that studies these elements and their relationships to obtain a better understanding of ecology is called 'ecological stoichiometry'.

One of the interesting things about elements is that they never just disappear. What is true for chemical reactions - the amount of each element must be the same before and after the arrow -  applies equally to ecological processes in that respect.

Salad sandwich

If you eat a salad sandwich, for instance, you'll absorb some proportion of its elements and secrete the rest. By breathing, or by going to the toilet. But the overall ratio of the elements in the sandwich will always be equal to the ratio of the elements you have absorbed and the ratio of the elements you have secreted taken together.

The exact ratio or balance of elements determines the nature of ecological interactions to a large extent: e.g. what sort of  fertiliser would work best on a particular type of soil, or how suitable are particular plants as food for herbivores?

"That's what's so exciting", says ecologist Dedmer van de Waal from the Netherlands Institute of Ecology (NIOO-KNAW). "In ecological stoichiometry, we get to apply natural laws to cells, organisms and even entire ecosystems in order to understand how they work."

Online book

Van de Waal is one of the editors of a new ebook about ecological stoichiometry, together with the original founders of the field and others. The book is available online through the open access scientific journal Frontiers.

In all, 145 scientists were involved, including 16 from the Netherlands. Articles in the book cover the ratio of elements in a wide range of organisms: from bacteria and soil fungi to cereal grains, tadpoles and antelopes.

The scale on which contributors operate varies just as wildly. Some are concerned with processes within a single cell no larger than a few micrometres (a micrometre is one thousandth of a millimetre), while others look at entire ecosystems that are many square kilometres in size.

Popular field

Van de Waal: "Our ebook shows how wide the range of ecological stoichiometry really is. Nearly all ecosystems and organisms are included, even our own intestines!"

A website that collects the articles included in the book has already had more than 90,000 visitors. It demonstrates that this relatively new field of science - which has only existed in its current form since 2002 - is fast becoming "very popular indeed", concludes Van de Waal.

It's only the start, argues the editorial that opens the book: "Since pretty much everything that is a thing is, at its core, elemental, novel applications of the stoichiometric framework await."

Sneak peek

The book offers readers a sneak peek at what some of these applications may be: a more sustainable use of fertilisers in agriculture, for instance, or more effective ways to balance our diet and stay healthy.

Even attempts to recover valuable substances from waste flows may benefit: an area of application that is perhaps as unexpected as it is welcome.

"It goes beyond understanding ecosystems", stresses Van de Waal. "Ecological stoichiometry may offer solutions to some of the most socially relevant issues of our time."

Photograph of eating giraffe: Slawek K (Unsplash)

• You can download the ebook from the website of the journal Frontiers