Interrelationships between the growth of Hydrilla verticillata (L.f.) Royle and sediment nutrient availability

On sediment planted with Hydrilla verticillata (L.f.) Royle compared with control (unplanted) sediment we measured >90% and >30% reductions in concentrations of exchangeable N and extractable P following two consecutive 6-week periods of growth. Diminished N availability, owing to prior plant uptake, resulted in a 30% reduction in Hydrilla growth. Concomitant increases (>30%) in the concentration of exchangeable K suggest that this element, obtained via foliar uptake from overlying water, may be exchanged by roots of Hydrilla for ammonium in sediment. We postulate that under N-limiting conditions, K translocation in this species from shoots to roots potentially increases the availability of sediment N. An important implication of these findings is that under some circumstances the growth of Hydrilla may be self-limiting.