FROM ECOLOGICAL STOICHIOMETRY TO BIOGEOCHEMICAL CYCLES: “STRUCTURAL” CARBON AS AN EXAMPLE

In his seminal elucidation of stoichiometry as a basis for ecological analysis, Reiners (1986, The American Naturalist, v. 127, p. 59-73) recognized the importance of “stiff, non-protoplasmic structures” as a source of significant variation in the chemical composition of organisms. Reiners also emphasized that biological structural materials are a principal source of decay-resistant organic and skeletal constituents in soils and sediments, with broad implications for biogeochemical cycles extending to global spatial scales and geologic temporal scales. Conspicuous examples of these biogeochemical implications are the relationships among the burial in sediments of carbonate and organic carbon compounds and the concentrations of carbon dioxide and oxygen in Earth’s atmosphere. These relationships are mediated by chemical reactions in which charge balance is a pivotal component of stoichiometry. The burial of carbonates affects the relative contributions of weak acid anions (particularly bicarbonate and carbonate ions) to the charge balance of dissolved ions in the oceans. The burial of organic carbon causes the charge balance of Earth’s present-day atmosphere and oceans to be dominated by oxidized species, while the charge balance in sediments and soils is strongly influenced by reactions involving reduced species. In developing an analytical framework based on stoichiometry, Reiners and other ecologists have found common cause with biogeochemists in their focus on the constraints and insights provided by rigorous consideration of mass balance. A parallel emphasis on charge balance provides additional constraints and insights in the analysis of a broader range of ecological and biogeochemical problems.