Response of Exotic Invasive Weed Alternanthera philoxeroides to Environmental Factors and Its Competition with Rice

A greenhouse experiment was conducted to determine the influence of the environmental factors such as low-temperature, drought stress, salt-alkali and flooding on the survival rate, propagation rate, fresh biomass and viability of the Alternanthera philoxeroides and its competitive ability against rice by using bioassay method. A high viability of 84% was found when the stems were treated at 4 degrees C and then grew under normal conditions, while no viable plant was noted when the stems were treated at -20 degrees C and grew under normal conditions. Compared to the fresh stem with water content of 93.5%, the survival rate, number of propagated stems and fresh biomass of A. philoxeroides derived from the stems with water content of 30.2% were reduced by 45%, 33% and 74% respectively. The treatments of 0.1% salt-alkaline solution led to loss of viability of A. philoxeroides. The stems of A. philoxeroides could grow in wet soil with different depths of water-layer. The A. philoxeroides at density of 23-180 plants/m(2) reduced the rice grain yield by 43-50% at the rice plant density of 100 plants/m(2).