To be or not to be what you eat: regulation of stoichiometric homeostasis among autotrophs and heterotrophs

Abstract

Homeostasis of element composition is one of the central concepts of ecological stoichiometry. In this context, homeostasis is the resistance to change of consumer body composition in response to the chemical composition of consumer's food. To simplify theoretical analysis, it has generally been assumed that autotrophs exhibit flexibility in their composition, while heterotrophs are confined to a constant (strictly homeostatic) body composition. Yet, recent studies suggest that heterotrophs are not universally strictly homeostatic. We examined the degree to which autotrophs and heterotrophs regulate stoichiometric homeostasis (P:C, N:C, N:P, or %P and %N). We conducted a quantitative review and meta‐analysis using 132 datasets extracted from 57 literature sources which examined the dependence of organismal stoichiometry on resource stoichiometry. Among individual datasets, there was a wide range of responses from strictly homeostatic to non‐homeostatic. Even within heterotrophic organisms, varying levels of homeostasis were observed. Comparing the degree of homeostasis between organisms based on large‐scale habitat types using meta‐analysis indicated some significant differences between groups. For example, aquatic macroinvertebrates were significantly more homeostatic in terms of P:C than terrestrial invertebrates. Our meta‐analysis also confirmed that, with regard to N:P, heterotrophs are significantly more homeostatic than autotrophs. Furthermore, our analysis indicated that the homeostasis parameter 1/H, despite being a potentially useful predictive metric, has to be utilized with caution since it oversimplifies some important aspects of the responses of organisms to elemental imbalances. This critical evaluation of stoichiometric homeostasis contributes to a better understanding of many food‐web interactions, which are commonly driven by elemental imbalances between consumers and their resources.

Aquatic heterotrophic bacteria have highly flexible phosphorus content and biomass stoichiometry

“…The ranges of C: P biomass and N:P biomass observed in this study cover nearly the entire range of measurements recorded in previous studies for bacterial cultures and assemblages (Figure 2; Supplementary Table 6) and nearly match the ranges of C:P biomass and N:P biomass observed in vascular plant tissues (Elser et al, 2000;Sterner and Elser, 2002;Reich and Oleksyn, 2004). Furthermore, the bacterial assemblage (of multiple strains) exhibited greater stoichiometric plasticity than has been documented in any other species or assemblage, including terrestrial and aquatic primary producers (Sterner and Elser, 2002;Persson et al, 2010). These experiments demonstrate that previous assumptions of low and invariant C:P biomass (Tanaka et al, 2009;Fanin et al, 2013) and high relative P content for bacteria (Wolfe-Simon et al, 2010) do not represent the physiological flexibility of bacteria in natural assemblages.…”

Growth rate, protein:RNA ratio and stoichiometric homeostasis of submerged macrophytes under eutrophication stress

“…Most of previous studies on stoichiometric homeostasis have made comparisons between autotrophs and heterotrophs (Persson et al, 2010), or among heterotrophs (Karimi and Folt, 2006;Villar-Argaiz et al, 2002), whereas comparisons across plant species are relatively lacking. Yu et al (2011) and Xing et al (2015) made comparisons across vascular plants species in the Inner Mongolia grassland and across submerged macrophytes species in Yunnan plateau lakes, respectively.…”

“…Generally, autotrophic organisms are considered to be nonhomeostatic or weakly homeostatic, whereas heterotrophs are thought to be strictly homeostatic (Persson et al, 2010;Sterner and Elser, 2002). Previous studies have also documented that stoichiometric homeostasis of plants is lower than that of animals and bacteria, but higher than that of plankton and fungi Sterner and Elser, 2002;Xing et al, 2015;Yu et al, 2011).…”

Impact of food type on respiration, fractionation and turnover of carbon and nitrogen stable isotopes in the marine amphipod Gammarus aequicauda (Martynov, 1931)

“…Food ingestion was impossible to control during this experiment, and as Specific Dynamic Action, SDA, can last for 48 to 72 h depending on the species, it can be assumed that measurements were performed on individuals at really every stage of the SDA cycle (McGaw and Curtis, 2013), explaining a part of the high variability observed. Aquatic invertebrates present a much higher stoichiometry homeostasis than other organisms (Persson et al, 2010), however, our G. aequicauda fed with the animal treatment were able to grow and store C reserves as shown by C:N ratio increases during the experiment.…”