Competitive performance of two introduced hydrophytes with invasive species Pontederia crassipes Mart.: implications for management of aquatic species invasion

Most aquatic ecosystems are increasingly threatened by the introduction and spread of alien macrophytes, which can alter community structure and ecosystem functioning through competition. This study examined the interactions between the naturalized aquatic macrophyte Pontederia crassipes Mart. (water hyacinth) and two introduced species, Hydrocotyle umbellata L. and Salvinia auriculata Aubl, under open-air experimental conditions. Plants were grown in mixed cultures in two environmental setups, deep water (DW) and constructed wetlands (CW), using water from the El-Mahmoudia Canal to evaluate interspecific competition and growth performance. The results revealed that P. crassipes had a generally positive effect on H. umbellata , while it rapidly declined and died within three months in all mixed cultures, suggesting limited competitive ability under the tested conditions. H. umbellata showed significantly enhanced growth in CW compared to DW, with increased petiole length, laminae index, and rhizoid length, indicating its adaptability and competitive potential in structured aquatic environments. Although S. auriculata exhibited no statistically significant differences between CW and DW, it consistently performed slightly better in CW and demonstrated a competitive edge by displacing P. crassipes in mixed cultures. However, when H. umbellata and S. auriculata were grown together, both species experienced reduced growth, especially in petiole and rhizoid length, highlighting the impact of interspecific competition. These findings suggest that under the experimental conditions examined, P. crassipes showed no clear evidence of a competitive effect, whereas interactions between H. umbellata and S. auriculata should be considered in the management of aquatic plant communities, particularly in constructed wetlands.