Allelopathic effect of aqueous extracts from invasive smooth cordgrass (Spartina alterniflora) on lettuce (Lactuca sativa)

Aqueous extracts of the root, stem and leaf of smooth cordgrass (Spartina alterniflora Loisel), at concentrations of 0.065, 0.130, 0.195, 0.260 and 0.325 g·mL^-1, were used as treatment solutions to study their allelopathic effects on seed germination and early seedling growth of (Lactuca sativa L.). Seed germination was significantly inhibited by the root aqueous extract at concentrations ≥ 0.260 g·mL^-1; or by stem and leaf extracts at concentrations ≥ 0.130 g·mL^-1 and ≥ 0.195 g·mL^-1, respectively. All the aqueous extracts of the root, stem and leaf inhibit seed germination of lettuce, which not only reduced the rate of germination but also prolonged the mean period of ultimate germination. The stem and leaf aqueous extracts had more significant inhibitory effects on seedling growth, while the root aqueous extract actually promoted the growth of the seedling hypocotyl at low concentrations (<0.195 g·mL^-1, RI>0). The allelopathic effect of the aqueous extracts is in the sequence of stem > leaf > root. This study suggests that the root, stem and leaf of smooth cordgrass contain water-soluble allelochemicals which can inhibit both seed germination and seedling growth of lettuce. The allelopathic effects are intensified at higher extract concentrations.