Interaction Between Reed Canary Grass and Purple Loosestrife in a Replacement Series

Abstract

Both reed canary grass (Phalaris spp.) and purple loosestrife (Lythrum salicaria) are common invasive plants in Canadian wetlands that can erode biodiversity of native plants. A replacement series study was conducted in a conservatory greenhouse to examine effects of replacement ratio and watering regimes on competitive ability between reed canary grass and purple loosestrife. The ratio of reed canary grass to purple loosestrife was in a 4:0, 3:1, 2:2, 1:3, 0:4 sequence based on the final number per pot. The dry weight of plants was used to quantify their competitive ability. The results showed that the plants in waterlogged and mesic treatments had similar biomass, indicating watering regime did not have a significant impact on competition. Different replacement ratios had a significant impact on biomass accumulation. The 1:3 reed canary grass: purple loosestrife treatments had the highest total biomass, the highest reed canary grass biomass, and the lowest purple loosestrife biomass. Reed canary grass always had higher dry weight per plant than purple loosestrife in intercropping treatments. The per plant biomass of reed canary grass increased as more reed canary grass was being replaced by purple loosestrife in areplacement series, suggesting growth of reed canary grass was more affected by intraspecific competition than competition with purple loosestrife. These results indicate that reed canary grass is more competitive than purple loosestrife and the attempt of supressing growth of purple loosestrife using slightly elevated water level is not viable. If we want to maintain a high level of biodiversity in wetland ecosystems, we should consider control of reed canary grass and purple loosestrife simultaneously.