stoichiometry: one construct, many systems

In chemistry, stoichiometry is the quantitative relationship between the amounts of reactants and products in a chemical reaction, governed by the law of definite proportions and expressed as whole-number mole ratios in a balanced equation. Jeremias Benjamin Richter coined the term in his 1792 Anfangsgründe der Stöchyometrie, and the concept is codified in IUPAC's Compendium of Chemical Terminology. The referent is the exact proportion in which elements combine, measured in moles, the parent idea that ecology later borrowed and extended from the beaker to whole organisms.[1]

Unit

One mole ratio relating reactants and products

Recovery means

Balance the chemical equation; the coefficients give the stoichiometric ratios

Measured by

Determined from balanced equations and measured masses/moles (gravimetric or molar analysis)

Ecological stoichiometry is the study of the balance of multiple chemical elements (chiefly carbon, nitrogen, and phosphorus) in organisms and in the interactions among them, and of how element ratios constrain growth, nutrient cycling, and trophic dynamics. Robert Sterner and James Elser developed it into a general framework in their 2002 book Ecological Stoichiometry, building on Alfred Redfield's ocean element ratios and formalized across scales by Elser and colleagues in Ecology Letters (2000); William Reiners had earlier urged a stoichiometric view of ecosystems in The American Naturalist (1986). The referent is the elemental composition of living things and its ecological consequences, measured as C:N:P ratios, the same ratio-of-elements logic as chemical stoichiometry, scaled up to the biosphere.[2][3][4]

Unit

One organism's (or pool's) elemental ratio, e.g., C:N:P

Recovery means

Measure the elemental content of tissue or a nutrient pool and express it as molar ratios

Measured by

Elemental analysis (CHN analyzers, phosphorus assays) yielding molar C:N:P ratios