Abstract: A simulation experiment under natural condition was conducted to study the dynamics of biomass accumulation, biomass allocation percentage, biomass ratio, and morphological traits of Allium cepa var. proliferum at different plant densities (36, 49, 64, 121 allocatione to and 225 individuals·m^-2), aimed to analyze the effects of density-dependence on the biomass allocation pattern of A. cepa var. proliferum. With increasing plant density, the biomass allocation to above-ground part, leaf, and sheath increased, but less to  below-ground part and bulb, while the blomass allocation to root biomass remained constant. The biomass ratios of above- to below-ground parts, sheath to leaf, root to sheath, bulb to root, bulb to leaf, bulb to sheath, and bulb to shoot exhibited apparent density-dependence, but the ratios of root to leaf and root to shoot remained unchanged. With the growth of plant, the ratios of sheath to leaf and bulb to root increased gradually, ratios of root to sheath, root to leaf, and root to shoot were in reverse, ratios of bulb to leaf, bulb to sheath, and bulb to shoot increased after an initial decrease, and the ratio of above- to below-ground parts decreased after an initial increase. Plant density had significant negative effects on specific leaf area (P<0.001), positive effects on leaf area and root length (P<0.05), but less effects on specific root length (P>0.05). All the results suggested that intraspecific competition exerted great influence on the resource allocation inside plant bodies. In response to different plant densities, the biomass allocation patterns displayed plasticity. With the increase of plant density, the photosynthates allocated more to above-ground vegetative organs, with the cost of decreasing the photosynthates allocation to below-ground asexsual reproductive organ. It was appeared that the “optimal partitioning theory” was only applicable at the absence of plant competition between individual plants. When the competition between plants was present, the population density and density-dependent regulation were the important factors determining plant biomass allocation pattern.

Key words: Rice (Oryza sativa L), Allelopathy, Dynamic inheritance, Genotype譭nvironment interaction, Genetic variances, Heritability