COMPETITION FOR SPACE BETWEEN EICHHORNIA-CRASSIPES (MART) SOLMS AND PISTIA-STRATIOTES L CULTURED IN NUTRIENT-ENRICHED WATER

The interrelationships between two free-floating aquatic macrophytes, Eichhornia crassipes (Mart.) Solms and Pistia stratiotes L, were investigated using a reciprocal replacement series for the intermixed combinations. The carrying capacity for each species was investigated in monoculture. The plants were cultured in outdoor tanks in Gainesville, Florida, where nutrient-enriched water was replenished at weekly intervals. E. crassipes showed dominance over P. stratiotes when the species were grown together. Interaction between the two species for growth space became apparent within the first month of the experimental period. The luxuriant growth and high plasticity of E. crassipes plants enabled them to grow above the P. stratiotes plants, thus shading and stressing them. Higher concentrations of nitrogen (N) (by about two-fold) were accumulated in the shoots of E. crassipes than in its roots, whereas N accumulation in the roots and shoots of P. stratiotes was similar. The N content of E. crassipes shoots increased throughout the experimental period ∼ six-fold, while the N content of roots increased two-fold. Phosphorus accumulation was equally distributed between the roots and shoots of both species. © 1990.