Nutrient enrichment and artificial light at night synergistically confer a competitive advantage to alien aquatic species over natives
Many freshwater ecosystems are currently facing the dual challenges of artificial light at night (ALAN) and nutrient enrichment. How these simultaneously acting environmental factors affect competitive outcomes between alien and native aquatic plants has not been thoroughly investigated. Here, we conducted a greenhouse experiment to quantify the competitive outcomes and their determinants of nine pairs of alien and native aquatic plant species in China under fully crossed factorial combinations of ALAN (Ambient vs. ALAN) and nutrient enrichment (Low vs. High). Nutrient enrichment significantly affected competitive outcomes. Specifically, native species tended to have more biomass under low-nutrient conditions, while the reverse was true under high-nutrient, although the trends were not significant. This pattern was even more pronounced in the presence of ALAN. Differential effects of nutrient enrichment and ALAN on interspecific competition of alien and native species may be responsible for variation in competitive outcomes. We found that nutrient enrichment tended to increase the interspecific competition coefficients for native species, whereas an opposite trend for alien species was observed, this effect being most prominent in the presence of ALAN. Our findings suggest that nutrient enrichment and ALAN could synergistically confer a competitive advantage to alien species over native species. Therefore, intervention measures are necessary to minimise nutrient enrichment of freshwater habitats, especially in habitats exposed to light pollution resulting from ALAN.
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