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Myriophyllum aquaticum is a semi-submerged exotic macrophyte that was introduced to China for many years. This species may be found in an emergent form in aquatic environments or in an amphibious form under drained conditions. Nuisance growth of this species has often been attributed to excessive amounts of nutrients. Therefore, we tested the following hypotheses: (1) high nutrient availability facilitates the establishment of M. aquaticum and (2) fragment type interacts with nutrient availability to determine the colonization and regeneration capacities of M. aquaticum. Two types of fragments were grown in water solutions with two levels of phosphorous. After 3 weeks, the survival rates showed no significant difference between the phosphorous treatments. However, emergent fragments showed higher RGR in the low and high phosphorous treatments than amphibious fragments. In addition, emergent fragments also showed higher regeneration capacities, indicating higher invasiveness in emergent fragments compared to amphibious fragments. Moreover, the high phosphorous concentration caused emergent fragments to produce more branches, indicating that nutrient availability may increase M. aquaticum propagule pressure. Our study highlights that nutrient supply increased emergent fragment establishment and shaped the invasion dynamics of macrophytes, which could help predict the spread and potential impact of exotic macrophytes in natural aquatic ecosystems. [ABSTRACT FROM AUTHOR]

The success of invasive macrophytes is due to the ability of introduced fragments to survive, regenerate and colonise freshwaters. In this study, carried out in an experimental garden, we evaluated: (i) the ability of Myriophyllum aquaticum fragments with or without an apex, to survive and colonise and (ii) the effects of a macrophyte bed on the colonisation success of two non-native species ( Ludwigia grandiflora, M. aquaticum). Fragments of M. aquaticum with apical stems had the highest survival rate (85 vs. 62%) and colonisation abilities (i.e. 9% of rate of anchorage with a macrophyte bed). The anchorage rate of L. grandiflora was stimulated by the presence of the non-native Elodea canadensis and the relative growth rate of M. aquaticum fragments was higher in the presence of a L. grandiflora bed. Facilitation may enhance the colonisation of some non-native species during the first stage of invasion (colonisation and regeneration). However, the presence of a macrophyte bed limits the chances of L. grandiflora rooting in the sediment. This result suggests that spatial competition may occur at the beginning of growth in shallow waters. Competitive or facilitative interactions between neighbouring species depend both on the introduced species and on macrophyte bed composition. [ABSTRACT FROM AUTHOR]