Response strategies of Acer davidii to varying light regimes under different water conditions

Phenotypic plasticity is crucial for adaptation of plants to complex environmental gradients. It is not clear as to how phenotypic plasticity in response to a certain environmental factor is affected by another ecological factor. Water and light are important factors affecting the phenotype of plants. The interactive effects between drought and shade on plants differ markedly among studies. To address these questions, we subjected Acer davidii Franch. seedlings to five water regimes, combined with two light intensities. Drought decreased all growth and biomass parameters, and all leaf and root traits measured, and increased the root to shoot ratio and root biomass ratio. Shade decreased the shoot height, the diameter at ground height, the root surface area, and all biomass parameters, and increased leaf water content, leaf area ratio, specific leaf area, and total chlorophyll concentration. Significant interactive effects were found on all biomass parameters, half of the growth parameters, and most of the leaf and root traits; shade generally alleviated the negative effects on A. davidii seedlings to some extent. The simplified relative distance phenotypic plasticity indices (RDPIs) of A. davidii responding to light increased with the increase in soil water content whereas no significant trend was observed between the RDPIs and the light regime. The RDPIs of all growth parameters, average leaf area, and all biomass allocation parameters in response to water were greater than those of light. Phenotypic plasticity of one environmental factor might be affected by another across complex environmental conditions.