Abstract: Shijiu Lake is located in the middle and lower reaches of the Yangtze River. It is one of the few freshwater lakes linking to the Yangtze River. A survey was carried out in Shijiu Lake and its tributaries in autumn (normal water season) and winter (dry season) in 2012 to explore the species composition and seasonal variation of the protozoa community. At the same time, similarity index was calculated to discuss the protozoa response to habitat homogeneity by comparing with adjacent Gucheng Lake. In total, 57 species of protozoa were collected, and the species number in dry season was less than in normal water season. The similarity indexes were in the grades Ⅰ-Ⅲ among different river sampling sites, namely, the protozoa structure was completely different or mildly similar. The similarity indexes among different lake sampling sites were in the grades ⅡⅣ, being very dissimilar to moderately similar. Species in rivers were very dissimilar in different seasons (0.050-0.267), while species in lake were mildly similar (0.250-0.375). That suggested that seasonal change of protozoan species in river was more obvious than in lake, and the heterogeneity of biological composition was also higher in river than in lake. Protozoa had a good response to water quality, and nitrogen and phosphorus nutrition played an important role in protozoa species composition and distribution. The comparison of Shijiu Lake with Gucheng Lake and other lakes in the middle and lower reaches of the Yangtze River showed that within a certain scale, habitat homogeneity would accelerate biological homogeneity with the increase of habitat scale. But beyond the landscape scale, the regional characteristics of protozoa would gradually emerge, even if habitat is in homogeneity, its biological composition may not be homogeneous. Besides, the biological similarity had a decreasing trend with the increase of distance.

Key words: light quality, tomato, chlorophyll fluorescence, photosynthetic pigment content, photosynthetic characteristics