Temporal and spatial variations of carbon isotope signature reveal substantial contribution of bracts and internode assimilates to grain filling of japonica rice

Carbon isotope composition (δ13C) of a plant organ is an inherent signature reflecting its physiological property, and thus is used as an integrative index in crop breeding. It is also a non-intrusive method for quantifying the relative contribution of different source organs to grain filling in cereals. Using the samples collected from two-year field and pot experiments with two nitrogen (N) fertilization treatments, we investigated the temporal and spatial variations of δ13C in source organs of leaf, sheath, internode, and bracts, and in sink organ grain. Constitutive nature of δ13C was uncovered, with an order of leaf (−27.84‰)