Individual growth models support the quantification of isotope incorporation rate, trophic discrimination and their interactions

Two large but independent bodies of literature exist on two essential components of the dynamics of isotopic incorporation: the isotopic incorporation rate (λ) and the trophic discrimination factor (Δ). Understanding the magnitude of these two parameters and the factors that shape them is fundamental to interpret the results of ecological studies that rely on stable isotopes. λ scales allometrically with body mass among species and depends on growth within species. Both are often assumed to be constant and independent of each other but evidence accumulates that might be linked and to vary with growth. We built and analyzed a model (IsoDyn) that connects individual growth and isotopic incorporation of nitrogen into whole body and muscle tissues. The model can assume a variety of individual growth patterns including exponential or asymptotic growths. λ depends on the rate of body mass gains which scales allometrically with body mass. Δ is a dynamic response variable that depends partly on the ratio between fluxes of gains and losses and covaries negatively with λ. The model can be parameterized either from existing large databases of animal growth models or directly from experimental results. The model was applied to experimental results on three ectotherms and one endotherm and compared to the results of the simpler and widely used time model. IsoDyn model gave a better fit with relatively little calibration. IsoDyn clarifies and expands the interpretation of isotopic incorporation data.

Effect of temperature on 13C and 15N incorporation rates and discrimination factors in two North American fishes

The biological parameters needed to interpret isotopic field data on food webs—namely isotopic incorporation and discrimination (Δ13C and Δ15N)—are unknown for many animals. We investigated the effects of temperature on carbon and nitrogen incorporation and discrimination in Creek Chub (Semotilus atromaculatus) and White Sucker (Catostomus commersonii) by rearing wild-caught fish on a distinct diet at 12 °C and 20 °C for 160 days. Mass specific growth rates were higher at 20 °C. Isotopic turnover was mainly influenced by metabolic processes as opposed to growth in both species, especially White Sucker. Cold-reared fish had slower rates of isotopic incorporation and higher isotopic residence times than warm-reared fish. Discrimination factors were generally smaller for Δ15N (range = 1.9 to 3.0) and larger for Δ13C (range = 1.4 to 2.3) than values reported for other fishes. Variable temperature effects on discrimination suggests unmeasured effects of the experimental diet which will require additional experimentation to tease apart. These results support the hypothesis that metabolic rates are correlated with isotopic incorporation rates in animals dependent on environmental temperature.

Fast Carbon Isotope Exchange of Carboxylic Acids Enabled by Organic Photoredox Catalysis

Carbazole/cyanobenzene photocatalysts promote the direct isotopic carboxylate exchange of C(sp3 )-acids with labelled CO2. Substrates that are not compatible with transition metal catalyzed degradation-reconstruction approaches or prone to thermally induced reversible decarboxylation undergo isotopic incorporation at room temperature in short reaction times. The radiolabelling of drug molecules and precursors with [11C]CO2 is demonstrated.

Fast Carbon Isotope Exchange of Carboxylic Acids Enabled by Organic Photoredox Catalysis

Carbazole/cyanobenzene photocatalysts promote the direct isotopic carboxylate exchange of C(sp3 )-acids with labelled CO2. Substrates that are not compatible with transition metal catalyzed degradation-reconstruction approaches or prone to thermally induced reversible decarboxylation undergo isotopic incorporation at room temperature in short reaction times. The radiolabelling of drug molecules and precursors with [11C]CO2 is demonstrated.

Micronutrient-fortified rice can be a significant source of dietary bioavailable iron in schoolchildren from rural Ghana

Iron deficiency and anemia are prominent contributors to the preventable disease burden worldwide. A substantial proportion of people with inadequate dietary iron rely on rice as a staple food, but fortification efforts are limited by low iron bioavailability. Furthermore, using high iron fortification dosages may not always be prudent in tropical regions. To identify alternative fortification formulations with enhanced absorption, we screened different iron compounds for their suitability as rice fortificants, measured in vitro gastric solubility, and assessed dietary iron bioavailability using stable isotopic labels in rural Ghanaian children. Isotopic incorporation in red blood cells indicates that in the two age groups of children investigated (4 to 6 and 7 to 10 years), formulations provided 36 and 51% of the median daily requirement in absorbed iron, respectively. We describe approaches to enhancing iron bioavailability from fortified rice, which can substantially contribute to the prevention of iron deficiency in rice-eating populations.