Biphasic mineral nutrition of the submersed aquatic macrophyte Potamogeton pectinatus L.

The mineral nutrition of a clone of the submersed aquatic macrophyte Potamogeton pectinatus L. was examined in relation to the ability of the roots to mobilize N, P, K, S, Ca, Mg, dissolved inorganic C and micronutrients to the shoots from a constant small volume of sediment in the absence of one or more of these nutrients in the water phase. Survival, biomass production and shoot nutrient concentration values were measured after 35 days of growth under controlled conditions. Flower production and shoot morphology were also noted.The roots of P. pectinatus were capable of mobilizing sufficient P, N, S, K and micronutrients from the sediment to the shoots to meet normal growth requirements. In the absence of K from the water phase, Na replaced it, but the vigor of the plants suffered somewhat by the substitution. The roots were not capable of mobilizing sufficient Mg, Ca, or dissolved inorganic C from the sediment to the shoots to meet normal growth requirements. Survival and normal growth occurred with a minimum of 2 ppm Ca, 10 ppm Mg, and 0.5 meq HCO₃^? in the water phase. Water-phase Ca was necessary to prevent the toxicity of other cations such as Mg when present in the water phase.A seasonal periodicity in biomass production occurred under standardized environmental conditions, suggesting an internal regulation independent of obvious external signals.