No evidence of greater biomass allocation to stolons at moderate resource levels in a floating plant

Abstract

Variation in biomass allocation patterns has been considered a strategy in clonal plants to adapt to various environments. It has been predicted that clonal plants allocate more biomass to spacers (i.e., stolon and rhizomes) at moderate resource levels. We tested the prediction in an aquatic clonal plant Salvinia natans by subjecting it to nine nutrient levels under either a low or a high light condition. Biomass, ramet number and mean stolon internode length were overall greater under the moderate nutrient levels and the high light condition. The responses of plant growth and morphology to nutrient availability were unimodal under the high light condition, but bimodal under the low light condition. Floating frond mass ratio was overall smaller in the high than in the low light condition, but the reverse was true for submerged frond mass ratio and stolon mass ratio. Under the high light condition, floating front mass ratio increased with increasing nutrient availability, and a reverse pattern was found for submerged mass ratio and stolon mass ratio. Under the low light condition, the response of floating mass ratio to nutrient availability was hump shaped, but that of submerged mass ratio and stolon mass ratio was U shaped. Therefore, our findings do not support the theoretical prediction that biomass allocation to spacers is the highest at moderate nutrient availabilities, but suggest that nutrient availability and light intensity can interact to influence growth, morphology and biomass allocation of aquatic clonal plants.