Sediment accretion and nutrient enrichment enhance the growth and vegetative propagation of Phalaris arundinacea growing within a Carex thunbergii stand

Sediment accretion (burial) and nutrient enrichment may exert a synergistic influence on the growth and distribution of macrophytes in floodplain wetlands; however, this phenomenon has rarely been examined. In this study, we investigated the effects of sediment accretion and nutrient enrichment on the growth and vegetative propagation of <i>Phalaris arundinacea</i> within a <i>Carex thunbergii</i> stand (one <i>P. arundinacea</i> ramet within 25 C<i>. thunbergii</i> ramets) using a factorial sediment burial (0, 3, and 6 cm) and nutrient addition (low, medium, and high) experimental design. High sediment burial (6 cm) without nutrient addition decreased the aboveground and total biomass of <i>C. thunbergii</i> but did not affect <i>P. arundinacea</i>, indicating that <i>P. arundinacea</i> is more tolerant to sediment burial than <i>C. thunbergii</i>. Moderate sediment burial (3 cm) with nutrient addition enhanced the aboveground and total biomass of <i>P. arundinacea</i> but did not affect <i>C. thunbergii</i>, indicating that <i>P. arundinacea</i> may gain a growth advantage over <i>C. thunbergii</i> under moderate sedimentation. High sediment burial with nutrient addition increased the number of rhizomes and ramets produced by <i>P. arundinacea</i> but did not affect <i>C. thunbergii</i>, indicating that the relative abundance of <i>P. arundinacea</i> may increase within the <i>Carex</i> community under high sedimentation conditions. Based on these results, it can be concluded that an increased sedimentation rate facilitates the invasion of <i>P. arundinacea</i> into <i>Carex</i> grasslands, and this invasion is further enhanced by nutrient enrichment. Therefore, management measures should be taken to reduce the sediment load and nutrient input to prevent <i>Carex</i> grasslands invasion by <i>P. arundinacea</i> and maintain the ecological function of floodplain wetlands.