Abstract: Using water lettuce (Pistia stratiotes), water hyacinth (Eichhornia crassipes) and southern naiad (Najas guadelupensis) as apple snails’ (Pomacea canaliculata) food, we determined the temperature, pH, dissolved oxygen and the concentrations of ammonium nitrogen, nitrite nitrogen, nitrate nitrogen, and soluble phosphate of aquaculture liquid at 1, 3, 5, 7, 9 days when different number snails were bred (0, 2, 4, 8, 16, 32). Then, a manipulative experiment was carried out to test the effects of aquaculture liquid of apple snails on the growth and mortality of Bellamya aeruginosa and P. canaliculata. It was found that apple snails’ breeding numbers and types of feeding food had very significant influence on dissolved oxygen, ammonium nitrogen, nitrate nitrogen and soluble phosphate (P<0.01). Dissolved oxygen was significantly decreased with the increase of breeding numbers and cultivation time, while the concentrations of ammonium nitrogen, nitrate nitrogen and dissolved phosphate increased significantly (P<0.05). The nitrite nitrogen concentration was significantly affected only by breeding numbers (P<0.05). In the manipulative experiment, on base of relative growth and mortality rate, apple snails’ aquaculture liquid had significantly different influence on P. canaliculata and B. aeruginosa (P<0.05); the growth rate of P. canaliculata decreased while B. aeruginosa had negative growth. Furthermore, the mortality rate of B. aeruginosa became greater with the increasing concentration of aquaculture liquid. This study indicates that apple snails can change the physical and chemical properties of breeding water quality through their aquaculture liquid. The aquaculture liquid of P. canaliculata can restrain the growth of B. aeruginosa and hasten its mortality, which may be an important invasive mechanism of apple snails. Our study not only enriches the theory of invasion ecology, but also possibly provides experimental basis for ecological risk assessment of apple snails.

Key words: biochar, Lou soil, soil water thermal properties, soil aggregate, mean weight diameters.