Conclusions
Our results showed an increase in phenotypic integration, plasticity and
among-individual variation with density, and the positive correlations
between integration and plasticity became stronger with higher densities
but weaker over time in fertile soil, while the correlations among the
three processes became stronger over time in infertile soil. These
suggested certain shared or cooperation mechanisms for integration,
canalization and plasticity in traits. Soil conditions and growth stage
may affect the responses to density in correlations among the three
processes via effects on plant size and competition intensity.
Phenotypic integration may play a more important role in plant
adaptation to environmental stresses, and the decrease in canalization
level may not be harmful. The released variations among individuals due
to attenuated canalization and enhanced integration may facilitate plant
reaction and adaptation to environmental stresses, and inversely
plasticity may lead to higher level of phenotypic integration and
reduced canalization, especially when plants experience intense
competition.