中文摘要：

通过对2个密度的大豆群体在开花初期进行光富集处理，研究了大豆不同粒位籽粒的粒重及其空间分布特征。结果表明：大豆籽粒的单粒重呈现明显的粒位效应。在多粒荚内，基粒的粒重最小。2、3和4粒荚的第2粒位籽粒的粒重比基粒分别高10．6％、14．8％和17．3％。光富集和高密度增加基粒粒重的幅度高于其它粒位的籽粒，增幅为17．7％～27．9％，但并未改变其原有的粒位粒重特征。大豆的不同粒位粒重在主茎上呈明显的“纺锤形”分布，下部节位上的籽粒单粒重略小，而中部节位上的籽粒单粒重较大。多粒荚内不同粒位的粒重空间分布曲线的变异程度小，1粒荚内的籽粒大小受光照和密度影响最大。高密度条件下，上部节位的不同粒位籽粒对光照更加敏感。不同粒位的籽粒大小与灌浆顺序并无直接关系，受荚内同化产物均衡分配机制的调节，粒位数的增加减小了单个籽粒的增重程度。

英文摘要：

Seed size in different seed position and its spatial distribution across main stem were investigated by glyphosate-resistant soybean cuhivar SV19-U2 grown under both ambient and light-enriched conditions at low and high densities. Obvious effect of seed position on seed size was found. Seed size of first-seeded position within several-seeded pod was minimal. In two, three and four-seeded pod, the seed size of second-seeded position was 10.6% , 14.8% and 17.3% larger than that of first-seeded position. Light enrichment and high density increased seed size of first-seeded position by 17.7% -27.9%. The increment in seed size from first-seeded position was greater than that from second-, third- and fourth-seeded position, while the inherent seed size character in different position was not changed. The spatial distribution of seed size from different seed position across main stem showed the ＂spinning shape＂ from top to bottom. Seed size at bottom node position was smaller, and was larger at middle node position. The curve of seed size＇ s spatial distribution across main stem was even and seed size in one-seeded pod was much sensitive to light and density conditions. Under high density, light enrichment imposed more influence on seed size at top node position than at lower node position. The more seed number in a pod could decrease the increment of single seed size. It is proposed that seed size at different position might not be directly related to the sequence of seed filling, and seed size is modulated by assimilate distribution mechanism within pod.