Abstract: Effects of extracts from Phytolacca americana,an invasive alien plant,on seed germination and seedling growth of Melilotus officinalis,Brassica pekinensis,Plantago virginica,and Digitaria sanguinalis were investigated in laboratory.Results show that ethanolic extract from the plant 1000-4000,4000,and 2000-4000 μg·mL^-1in concentration significantly inhibited seed germination of B.pekinensis,P.virginica,and D.sanguinalis,respectively,and water extract 1000-4000 μg·mL^-1in concentration also did significantly that of D.sanguinalis with the highest inhibition rates being 32.22%,46.56%,32.69%,and 28.57%,respectively.The ethanolic extract 250-500 μg·mL^-1in concentration and the water extract 250-4000 μg·mL^-1in concentration increased root length of M.officinalis seedlings and both the ethanolic extract 250-1000 μg·mL^-1in concentration and water extract 250-4000 μg·mL^-1in concentration promoted growth of the seedling in height,and the water extract 500 μg·mL^-1in concentration increased significantly dry weight of the seedlings,with the highest promotion rates being 21.32%,37.89%,12.94%,32.07%,and 18.81%,respectively.The ethanolic extract 1000-4000 μg·mL^-1in concentration and the water extract 4000 μg·mL^-1in concentration both inhibited growth of B.pekinensis roots in length;both the ethanolic and water extracts 2000-4000 μg·mL^-1in concentration did the plants in height,and the water extract 4000 μg·mL^-1in concentration did seedling dry weight of the plant,too,with the highest inhibition rates being 37.00%,20.95%,25.63%,22.30%,and 13.67%,respectively.The water extract 250-1000 μg·mL^-1in concentration significantly promoted seedling root length of P.virginica,and 250-4000 μg·mL^-1in concentration it did seedling height,too,but the ethanolic extract 1000-4000 μg·mL^-1in concentration significantly inhibited growth of its root in length,and 4000 μg·mL^-1in concentration it did seedling height and dry weight of the seedlings,with the highest inhibition rates being 58.06%,29.72%,adn 18.36%,respectively.The ethanolic extract 500-4000,1000-4000 and 2000-4000 μg·mL^-1in concentration inhibited the seedlings of D.sanguinalis in root length,height and dry weight,respectively,and the water extract 4000 μg·mL^-1in concentration did the seedlings in root length,with the highest inhibition rates being 70.31%,44.65%,42.43%,and 35.50%,respectively.Obviously,P.americana has a strong effect of allelopathic inhibition on seed germination and seedling growth of B.pekinensis,P.virginica and D.sanguinalis,but an effect of allelopathic promotion on invasive plant M.officinalis,which directly or indirectly strengthens its invasiveness.

Key words: Phytolacca americana, extract, allelopathic activity, seed germination, seedling growth