| Salvinia natans (L.) All. is a free-floating fern distributed mainly in static aquatic habitats. It has a strong accumulation capacity of metals, such as chromium, cadmium and other heavy metals from pollution water. It also can accelerate the transformation of nitrogen and phosphorus from eutrophic water. In this paper, field sampling and laboratory treatment was used to research the morphological plasticity of S. natans in different densities. The effects of cooking oil fume condensate (COFCs) and aniline on its vegetative growth and physiologic characteristics were also studyed. Some results had gained as follows:1. In different densities, S. natans showed a obvious phenotypic plasticity. The dry weights and the length of submerged leaves, dry weight of floating leaves, number of upturned branches, lateral buds of S. natans were positively related to its density. Ratio of floating leaf length to width also changed significantly under different density conditions.2. The mortality of S. natans was closely related to the concentration of COFCs: when the concentration of COFCs was less than 0.04 g/L, it would not lead S. natans dead. When the concentration of COFCs rised to 0.08 g/L, dead individual began appeared. Especially when the concentration was above 0.28 g/L, it could lead to all individuals died within a certain period of time, the higher of COFCs concentration, the sooner of the individual dead.3. COFCs could also speed up the floating leaves of Salvinia to turn yellow, and the number of yellow leaves positively related to the treatment time and concentration of COFCs. COFCs also affected new grow floating leaves, new grow floating leaves in the control group from the first 16th days began to appear yellow, while the high concentration groups were in the first three days.4. COFCs could significantly inhibit the growth of stem of S. natans. At the end of the experiment, stem length of S. natans in the control group was significantly higher than that of other groups, the lower of COFCs content, the less of the effects. COFCs had no significant effect on the axillary buds in a short period. However, with the treatment lasting, COFCs could significant inhibit the formation of axillary buds, the higher the concentration, the less of axillary buds number. COFCs contained some of the ingredients which could be as a nutrient for the growth of S. natans at the very beginning, but with the extension of experiment time, these ingredients still played a significant inhibitory effect on the relative growth rate. Biomass accumulation of submerged leaves, floating leaves, stems were negatively correlated with the concentration of COFCs.5. COFCs could increase the pH values of water body, the effect was positively related to the concentration of COFCs. It didn't show an obvious effect on the water conductivity.6. COFCs could significantly inhibit the activity of catalase (CAT). High concentration could promote the actvity of superoxide dismutase (SOD), but at a concentration of less than 0.38 g/L, there was no difference with the control group. When the concentration of COFCs was between 0.08 g/L and 0.48 g/L, it could significantly promote the activity of peroxidase (POD), the higher concentration could inhibit the activity of POD.7. Aniline could significantly affected the pH value and conductivity of water body, but the growth of S. natans was not significantly affected. This result suggested that S. natans had a high tolerance to aniline.On natural conditions, S. natans could change its morphological characteristics to adapt the high density condition. Because of the high sensitive to COFCs, S. natans could be used as an indicator for COFCs pollution in aquatic environments. S. natans showed an obvious tolerance to aniline, indicating that the plant had a potential to be used in the restoration of environments polluted by aniline.
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