An alternative mechanism for shade adaptation: implication of allometric responses of three submersed macrophytes to water depth

Allometric scaling models describing size-dependent biological relationships are important for understanding the adaptive responses of plants to environmental variation. In this study, allometric analysis was used to investigate the biomass allocation and morphology of three submerged macrophytes (Potamogeton maackianus, Potamogeton malaianus and Vallisneria natans) in response to water depth (1.0 and 2.5 m) in an in situ experiment. The three macrophytes exhibited different allometric strategies associated with distinct adjustments in morphology and biomass allocation in response to varying water depths. In deeper water, after accounting for the effects of plant size, P. maackianus and P. malaianus tended to enhance light harvesting by allocating more biomass to the stem, increasing shoot height and specific leaf area. V. natans tended to allocate more biomass to the leaf than to the basal stem (rosette), showing a higher leaf mass ratio and shoot height in deeper water. The three species decreased biomass allocation to roots as water depth increased. The main effect of water depth treatments was reduced light availability, which induced plastic shoot or leaf elongation. This shows that macrophytes have evolved responses to light limitation similar to those of terrestrial plants.