Effect of Water Exchange Rate on Interspecies Competition Between Submerged Macrophytes: Functional Trait Hierarchy Drives Competition

Aims: Although the relative contributions of the “competition-trait similarity” and “competition-trait hierarchy” hypotheses in predicting competitive outcomes in response to environmental variation has recently been investigated in terrestrial plants, their validity in aquatic plants remain poorly understood, particularly in terms of variation in the water exchange rate (WER). Methods: To this end, this study investigated the influence of WER variation on interspecies competition and functional traits in two pairs of submerged macrophytes (Vallisneria natans vs. Myriophyllum aquaticum and V. natans vs. Myriophyllum spicatum) under three levels of WER using the replacement series experiment. Results: Results showed that V. natans was a stronger competitor than either Myriophyllum species in static waterbodies. However, the relative competitive ability of V. natans consistently decreased with increasing WER and decreasing its planting proportion, which would eventually change it from a stronger to weaker competitor. Between species pairs, most functional traits showed competently opposite patterns to increasing WER and decreasing the planting proportion of V. natans. Conclusions: Our results indicate that WER affected the outcome of interspecies competition between submerged macrophyte species, and moreover, the relative competition ability of each species within a pair was linked strongly to species’ competition-trait hierarchy than to competition-trait similarity.