抄録
Soybean plants grown in a green house were allowed to assimilate 13CO2 for 10 hrs under steady-state conditions at 13 (Exp. 1), 26 (Exp. 2) and 40 (Exp. 3) days after anthesis. The partitioning of labelled carbon into individual plant parts and th significance of carbon assimilated at different growth stages for seed-filling were investigated by periodic sampling of labelled plants until harvesting time (50 days after anthesis). The plants were treated with (+N plants) or without (-N plants) supplement nitrogen 9 days after anthesis. Carbon assimilated 13 days after anthesis (Exp. 1) was most actively used for pod formation. Incorporation of labelled carbon into seeds was continued until harvesting time. Fifty per cent or more of labelled carbon found in the seeds at harvesing time was transported mainly from the leaves, pods and stems + petioles during the late reproductive stage from 26 to 50 days after anthesis (Fig. 2). Carbon assimilated 26 (Exp. 2) and 40 (Exp. 3) days after anthesis was utilized mainly as carbon sources for seed-filling. In these experiments, however, the most of labelled carbon found in the seeds at harvesting time was transported into the seeds directly from the leaves within 4 days after the 13CO2 assimilation (Fig. 2). Contribution of assimilated carbon to seed production was highest in Exp. 2 accounting for 4.37% in -N plants and 4.21% in +N plants. They accounted respectively for 1.25 and 1.66% for Exp. 1, and 2.70 and 2.15% for Exp. 3 (Table. 1). Supplement application of nitrogen increased seed yield at about 7% (as carbon content). This increase was due mainly to the efficient contribution of carbon assimilated during the early stage of seed filling.
