Change in the δ¹⁵N value of plant amino acids on the phenology of leaf flush and senescence

Abstract

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.