Biomass allocation and allometric relationships of the invasive plant species Plantago virginica grown at different densities

To study the invasive plant species Plantago virginica, whole plant excavation was performed in locations supporting plants at different population densities (30, 100, and 220 plants·m⁻²). Differences and trade-off characteristics of biomass allocation between roots, leaves, and reproductive organs, and allometric relationships correlating with different plant densities were systematically analyzed. The results indicate that biomass and allocation ratios differed significantly (P < 0.05) at the three different densities of P. virginica, revealing that individual organ biomass, single leaf biomass, total biomass, leaf or root allocation ratio, and root to shoot ratio decreased with increasing plant density, revealing obvious density-dependent effects. By contrast, the reproductive allocation ratio and reproduction to leaf ratio increased significantly with increasing density (P < 0.05), indicating that high density prompts P. virginica to allocate more resources for reproduction. Significant allometric relationships among organ biomasses of P. virginica were detected at the three different densities (P < 0.05). Most of these relationships were allometric, with a ≠ 1.0. Increasing plant density of P. virginica could enhance biomass allocation to photosynthetic organs, and reduce reproductive biomass allocation. By adjusting the resource allocation rate and ratio between above ground and underground photosynthetic and reproductive organs, P. virginica could improve its adaptability to increased pressure of intraspecific competition. These results indicate strong resource allocation plasticity, which may be an important contributor to its high invasive capability. These results provide basic data for further elucidation of the reproductive strategies and invasion mechanisms of P. virginica.