Elevation in the δ¹⁵N value of amino acids (δ¹⁵N_AAs) from the diet to its consumer (i.e. ‘inter’-trophic discrimination factor: TDF) has been widely used to illustrate the trophic hierarchy among organisms in ecological food webs. However, there is ‘intra’-trophic discrimination factor (TDF’) within a single organism, which is attributable to the catabolism of storage compounds for adjusting the energy balance between supply and demand, independent of the TDF between two separate organisms. The δ¹⁵N_AAs values of the deciduous plant Cerasus lannesiana reveal that the TDF’ is 0.1 ± 1.0‰ (mean ± 1σ) for leaf senescence from spring to autumn, whereas that is gradually decreased from 5.3‰ to 0.9‰ for leaf flush in early spring. These results imply that plants can use sufficient photosynthetically-fixed energy for the leaf senescence, but use a large amount of catabolically-released energy (from deamination of storage amino acids) for the leaf flush under no / less photosynthetic activities. Thus, we predict that the metabolic energy fluxes can be considered in the isotope ecology, as such TDF’ potentially propagates into the δ¹⁵N_AAs values in consumers that particularly feed on buds and flush leaves.

The sterol compositions in sediments from an oxic pond of Bungaku-no-ike (Hachioji, Tokyo, Japan) using tetramethylammonium hydroxide (TMAH) thermochemolysis and gas chromatography-mass spectrometry (GC-MS) analysis were determined. In the sediments, four 5α(H)-stanols (cholestanol, campestanol, sitostanol, and brassicastanol) and their corresponding Δ⁵-sterols were identified. We detected high concentrations of cholestanol (1.08 – 1.07 µg / g), campestanol (0.97 – 1.37 µg / g), and sitostanol (2.78 – 3.88 µg / g) and high values of those 5α(H)-stanol / Δ⁵-sterol ratios (0.76 – 0.85, 0.80 – 0.60, and 0.29, respectively) in the sediments. In contrast, the concentrations of brassicastanol is low (0.16 – 0.28 µg / g) with low brassicastanol / brassicasterol ratios (0.11 – 0.16). The 5α(H)-stanols are known to be typically formed by bacterial reduction of Δ⁵-sterols under anoxic condition. However, the pond was confirmed to be in an oxidative condition (dissolved oxygen in bottom water, 5.5 ± 0.5 mg / L). From these results, the high 5α(H)-stanol / Δ⁵-sterol ratios, except the brassicastanol / brassicasterol, in the pond suggest that the source(s) of the 5α(H)-stanols may be terrigenous matter containing high 5α(H)-stanols resulting from preferential degradation of the Δ⁵-sterols. In any cases, our study indicates that there is some possibility of 5α(H)-stanol inputs even though the sampling location is not anoxic conditions, and thus, the redox indicator using the 5α(H)-stanol / Δ⁵-sterol ratio should pay attention to source effects.