Skip to main content
Research article - Peer-reviewed, 2004

The C : N : P stoichiometry of autotrophs - theory and observations

Agren, GI


Evolution has set biochemical constraints on the chemical composition of living organisms. These constraints seem to lead to increases in N : C and P : C ratios with increasing relative growth rate for all types of organisms. The N : P ratio also seems to decrease with relative growth rate for heterotrophs whereas autotrophs may show a more complex behaviour. Here I will show that, from biochemical considerations, N : C should increase linearly and P : C quadratically with relative growth rate in autotrophs with the consequence that N : P increases at low relative growth rates, passes a maximum and then decreases at high relative growth rates. These predictions are verified against observations for a freshwater alga (Selenastrum minutum) and a tree seedling (Betula pendula). Changes in temperature, light or other factors that affect the growth rate of autotrophs interact with nutrient supply in such a way that there are no simple rules for as to how N : P will change

Published in

Ecology Letters
2004, volume: 7, number: 3, pages: 185-191

Authors' information

Swedish University of Agricultural Sciences, Department of Ecology and Environmental Research

UKÄ Subject classification

Environmental Sciences related to Agriculture and Land-use

Publication Identifiers


URI (permanent link to this page)