Abstract:Seedlings of Hydrilla verticillata (SHV) were planted in the waters with turbidity of 30NTU, 60NTU or 90NTU. The turbidity of the water was controlled by sand particles smaller than 100μm, and the effect of water turbidity on the growth (such as intemode length, stem height, branch number, leaf width, leaf length, fresh weight and sediment adhesion) of SHV was examined. The photosynthetic fluorescence characteristics of the leaves were determined in situ by a developed, submersible, pulse-amplitude modulated (PAM) fluorometer (diving-PAM). The rapid light responding curves of the leaves were also determined. The experimental results indicated that intemode length and the stem height of SHV increased significantly, whereas branch number and growing rate of biomass decreased remarkably as the water turbidity increased after planted in turbid water for 40 days. When the plants grow to water surface, the light intensity is inceasing. The plants development were restricted on the 60th day. But the growth of upper branch was promoted, and biomass of H. verticillata was enhanced remarkably. At the same time the silts amount attached on H. verticillata observably were added with water turbidity increasing. Compared with plants in the control water, the leaf width of H. verticillata leaves were wider 71.4%(P<0.01), 57.1% (P<0.01) and 48.6% (P<0.01) with turbidity of 30 NTU, 60NTU or 90NTU respectively on 100th day, and their leaf length were 113.0% (P<0.01), 85.5%(P<0.01) and 75.1%(P<0.01) of the control leaves, respectively. The plant biomass under the high silts turbid water decreased significantly. Fv/Fm of Canopy leaves in the turbid waters with turbidities of 60NTU and 90NTU only reduced 5.5% (P<0.05) and 2.9% (P>0.05), and their rETRmax only reduced 2.0% (P>0.05) and 16.8% (P<0.01). It was shown that SHV can grow and develop normally when they are introduced into shallow silt water.