Fundamental connections among organism C:N:P stoichiometry, macromolecular composition, and growth
Vrede, T., Dobberfuhl, D. R., Kooijman, S. A. L. M. and Elser, J. J. 2004
Fundamental connections among organism C:N:P stoichiometry, macromolecular
composition, and growth.
Ecology, 85: 1217 - 1229.
Abstract
Whereas it is acknowledged that the C:N:P stoichiometry of consumers
and their resources affects both the structure and the function of
food webs, and eventually influences broad-scale processes such as
global carbon cycles, the mechanistic basis for the variation in
stoichiometry has not yet been fully explored. Empirical evidence
shows that the specific growth rate is positively related to RNA
concentration both between and within taxa in both unicellular and
multicellular organisms. Since RNA is rich in P and constitutes a
substantial part of the total P in organisms, a high growth rate is
also connected with a high P content. We argue that the reason for
this pattern is that the growth of all biota is closely linked with
their protein synthesis rate, and thus with the concentration of
ribosomal RNA. Dynamic energy budget theory supports the positive
relationship between RNA and specific growth rate in microorganisms,
whereas the predictions concerning multicellulars only partially
agrees with the observed pattern. In a simple model of consumer
growth, we explore the consequences of various allocation patterns of
RNA, protein, carbohydrates/ lipids, and other biochemical
constituents on organism potential growth rate and C:N:P
stoichiometry. According to the model the percentage of N and
especially percentage of P per dry mass increases with increasing
specific growth rate. Furthermore, the model suggests that
macromolecule allocation patterns and thus N:P stoichiometry are
allowed to differ substantially at low growth rates whereas the
stoichiometry at high growth rates is much more constricted at low
N:P. The model fits empirical data reasonably well, but it is also
acknowledged that complex life cycles and associated physiological
constraints may result in other patterns. We also use a similar
approach of modeling organism growth from basic biochemical principles
to illustrate fundamental connections among biochemical allocation and
C:N stoichiometry in autotroph production, which is based on
allocation patterns between carbohydrates and rubisco. Similar to the
RNA protein model, macromolecular composition and C:N ratios are more
constrained at high than at low growth rates. The models and the
empirical data together suggest that organism growth is tightly linked
with the organisms biochemical and elemental composition. The
stoichiometry of growth impinges on nutrient cycles and carbon fluxes
at the ecosystem level. Thus, focus on the biological basis of
organism C:N:P stoichiometry can mechanistically connect growth
strategy and biochemical and cellular mechanisms of biota to major
ecological consequences.