Background and Aims An increase of population density may result in the spatial and temporal heterogeneity of resources at minor scales than an individual, inducing different modular responses at different positions of a plant, or architectural plasticity. To better understanding how plants respond to density via plasticity in architecture, we conducted a field experiment with an annual species of Abutilon theophrasti.

Key Results Increased density had different effects for different layers of modular traits, and effects also varied with different stages; high density also reduced variations among layers in different traits. No variation due to density or among different layers was found in reproductive mass and branch traits.

Conclusions An increase of density can induce contrasting responses in different layers of a trait and in different traits of a module, indicating trade-offs between layers and between traits, and low to intermediate competition strength was more likely to induce active response in more layers. It suggested that plants are able to deal with competition via several strategies simultaneously, producing an integrated phenotype. These conclusions further contributed to the complexity of plant plasticity to density.

We subjected plants to low, medium and high densities, and harvested them at different stages, when we separated each individual plant into different layers every 10 cm or 20 cm, and measured a series of traits per layer and analyzed variations in them among layers and due to density and stage.