Compartmental Analysis of the Partitioning of Photo-assimilated Carbon in Nodulated Soybean Plants during the Light Period

Kouchi, H., Yoneyama, T. and Akao, S. 1986. Compartmental analysisof the partitioning of photo-assimilated carbon in nodulatedsoybean plants during the light period.—J. exp. Bot. 37:994–1005. Dynamics of the partitioning of photo-assimilated carbon invegetative nodulated soybean (Glycine max L.) plants in thelight period was investigated by compartmental analysis basedon data from steady-state ¹³CO₂ assimilation experiments. Themodel assumes a total of 18 compartments consisting of activeand temporary storage pools for soluble materials, starch andstructural materials in leaves, stems plus petioles, roots andnodules together with respired carbon from the roots and nodules.Carbon flow between compartments was described by 22 rate parameters.The rate parameters were evaluated by a non-linear least squaresearch method to optimize the fitness of the simulated resultswith the experimental tracer distribution. The compartment model was well applicable to interpret the carbonpartitioning in whole plants. The analysis showed that: (I)The largest carbon flux during the light period was to storagematerials (starch and temporary storage soluble pools) in theabove-ground parts. The total flux to storage pools was considerablylarger than the transporting flux to below-ground parts. (2)The main carbon flux to the nodules was via direct phloem pathwaysfrom the shoot and not via the compartment of root soluble materials.This flux was 72% of the total carbon flux from the shoot tothe nodulated root system. (3) A large amount of carbon wasreturned to the shoot from below-ground parts. The total returnof carbon flux to the shoot (85% from nodules) was equivalentto 54% of the total influx of carbon to below-ground parts.Direct carbon transfers between roots and nodules were relativelysmall. Key words: Compartmental analysis, carbon partitioning, root nodules, Glycine max L., ¹³CO₂, assimilation