Impact of habitat environment on Potamogeton perfoliatus L. morphology and its within-plant variability in Lake Balaton

Plastic effect of environmental factors acting on an aquatic submerged plant, Potamogeton perfoliatus L. at the plant-level (nutrient availability) and the leaf-level (light intensity) at different sites in Lake Balaton was studied. Light-dependent morphological traits (foliar morphology and internode length) of P. perfoliatus were measured and analysed across the environmental gradients of the lake. The size of leaves was influenced by both trophic state and light environment: nutrient surplus increased the size of leaves by similar to 29%, whereas a more heterogeneous light environment resulted in 15% larger leaves. The light environment influenced shoot morphology (internode length) to a greater extent than nutrient surplus (38% vs. 19%). Contrary to this, within-plant morphological variability was significantly higher (41%) at the nutrient limiting sites as a result of diversification effect of the leaf-level environmental factor, light. Foliar parameters and within-plant variability showed correlation only with the total N content of the sediment. Appearance of P. perfoliatus is shaped by counteracting effects: within-plant differentiation, promoted by leaf-level environmental sensitivity and within-plant homogenization triggered by perception of the surroundings at plant-level. Both light attenuation, stimulating an increase of morphological variability, and nutrient surplus, initiating the stabilization of morphological parameters, could have adaptive advantages. The variability of leaf size leads to diversification of foliar parameters, thus increasing the efficiency of light harvest at low-nutrient sites and making responses to changes in the light environment more dynamic. These results suggest that leaf-level-induced diversification is counteracted by the standardization effect triggered by plant-level environmental factors.