The available proportions of carbon, nitrogen, phosphorus, sulfur, and other elements can limit how effectively acquired energy becomes new biomass.
Thus:
available energy alone does not determine growth
Growth also requires the correct matter, redox balance, and elemental ratios. Ecological stoichiometry explicitly links elemental supply, organismal demand, food webs, and ecosystem metabolism. (PubMed Central (PMC))
Operational definition
Growth and metabolism constraint.
A limitation caused by mismatch between the relative quantities of elements or nutrients available to an organism and the ratios required for biomass, metabolism, or reproduction.
For example, abundant carbon and free energy cannot produce unlimited biomass when nitrogen, phosphorus, sulfur, iron, or another essential component is insufficient.
The defining principle is:
growth is limited by the required resource in shortest effective supply
rather than by energy availability alone. Carbon fixation occurs through multiple biochemical pathways, while ecological stoichiometry links elemental supply ratios to biomass formation, food-web transfer, and ecosystem metabolism. (PubMed Central (PMC))