Nitrogen and phosphorus effect on Typha domingensis Presl. rhizome growth in a matrix of Schoenoplectus americanus (Pers.) Volkart ex Schinz and Keller

T. domingensis responded to nitrogen addition but not to phosphorus addition. When nitrogen was added, the number of rhizomes and their weight increased. Mesocosms with nitrogen had an average of 8 rhizomes, control mesocosms 5, the differences being significant (P < 0.05). Fresh rhizome biomass per mesocosm (0.58 m2) differed among treatments (P < 0.05): with nitrogen addition it was 110 (±31) g, with phosphorus addition 71 (±39) g, nitrogen and phosphorus 137 (±57) g, control mesocosms 67 (±30) g. The number and weight of rhizomes were highly correlated (Pearson's correlation = 0.84). Because T. domingensis responds to nitrogen additions by increasing the number and biomass of its rhizomes, it might be able to out-compete S. americanus when nitrogen concentrations increase.