[Estimation of Winter Wheat Photosynthesized Carbon Distribution and Allocation Belowground via ¹³C Pulse-labeling]

Evaluating the allocation of carbon (C) photosynthesized by winter wheat belowground is essential for C sequestration in soil and crop production. During the four growth stages of winter wheat, i. e., tillering, elongation, anthesis, and grain-filling, the method of ¹³CO₂ pulse-labeling for the wheat was adopted. Destructive samplings were undertaken at 28 d after each labeling and the total C and ¹³C contents of shoots, roots, soil, and rhizosphere respiration were determined. Results showed that the majority of the fixed ¹³C was recovered in the aboveground (straw and grain), ranging from 51.6% to 90.8% in all growth stages. The allocation of ¹³C photosynthesized belowground (roots, soil, and rhizosphere respiration) decreased as the wheat growth advanced, while the ¹³C transferred to the aboveground increased. Of the total ¹³C input belowground, 22.9%-65.3% was respired by the rhizosphere, 24.3%-59.3% remained in the roots, and 10.4%-17.8% was incorporated into the soil organic carbon by rhizodeposition. Respired ¹³C within the last 2 d of the whole chase period (28 d) only accounted for 0.7%-2.7% of the total respired ¹³C, indicating that 28 days were long enough to ensure a complete distribution of photosynthesized C within all the wheat and soil pools. For the whole growth season of winter wheat, the photosynthesized C allocated aboveground, to roots, soil organic carbon, and rhizosphere respiration was 78.5%, 6.0%, 3.1%, and 12.4% of the net assimilated C, respectively. Based on local wheat production, the total C transferred belowground was quantified as 1.72 t·hm^-2, with 0.99 t·hm^-2 respired as rhizosphere respiration, 0.48 t·hm^-2 retained in roots, and 0.25 t·hm^-2 incorporated into soil organic carbon.