The Study On The Phytoplankton Community In The Rice Fields Cultivating Ducks And Fishes

Rice field is the most important artificial wetland on the earth and is the most disturbing ecosystem with abundant biological populations. In the present study, we investigated the constitution of phytoplankton community in the rice field which cultivate ducks and fishes together at Experimental Base of Huazhong Agricultural University from June to August in 2005. The experiment has three test groups and a control group. During the experiment period, we sampled 5 times and analyzed the phytoplankton community through the species composition, density, biomass, similarity index, diversity index and dominance index. The influences of ducks and fishes on phytoplankton community in the rice fields were analyzed.In total, 38 genus and 150 species including subspecies were observed in this experiment, which were composed by 57 species of Euglenophyta, 46 of Chlorophyta, 31 of Bacillariophyta and 13 of Cyanophyta. The group R and The group F had 79 and 85 taxonomic units, respectively. Furthermore, there were 86 and 100 taxonomic units detected in group D and DF, respectively.The maximum average density of total 5 samples of the phytoplankton was 4.113×10~6 ind/L in group DF, followed by group F with 3.418×10~6 ind/L and group R with 1.963×10~6 ind/L, but the minimum was 0.651×10~6 ind/L in group D. Correspondingly, the maximum average biomass of total 5 samples of the phytoplankton was 17.80 mg/L in group DF, significantly higher (P<0.05) than that in the other 3 groups which was 9.37 mg/L in group F and 6.99 mg/L in group R, as well as the lowest of 2.41mg/L in group D.The similarity of the whole phytoplankton community between the group DF and the other 3 groups was less than that among the other 3 groups. The highest similarity was found in Bacillariophyta, followed by Cyanophyta but the lowest in Euglenophyta. The similarity of Cyanophyta was in accordance with the whole phytoplankton community, as well as that of Chlorophyta. The similarity of Bacillariophyta was lower between the group F and the other 3 groups than that among the other 3 groups. The similarity of Euglenophyta was the same as in Bacillariophyta but change to group R. The activities of the ducks and fishes in the rice field had most greatly impact on the similarity of Euglenophyta, secondly on that of Chlorophyta but minimal on Bacillariophyta.The maximum average diversity factor of the phytoplankton was 1.56 in group DF, followed by 1.47 in group D and 1.26 in group R, while the minimum was 1.26 in group D. There were obviously different influences of the activities of ducks and fishes on the Margalef diversity factor of the phytoplankton community. The ducks activities increased the Margalef diversity factor but the fishes' activities decreased it.The dominant element of the phytoplankton composition in group R and group F was macroscopic algae, the same as in the initial stage of group D and group DF, but the macroscopic algae in the late stage of group D and group DF. The component with the dominant phytoplankton biomass changed from Euglena and Nitzschia to Cosmarium in group R, and from Euglena to Euglena and Pandorina in group D and group DF. The component with the dominant phytoplankton biomass was Euglena and Nitzschia in the first and second sampling in the initial stage in group F, whereas Pandorina in the third and fifth sampling, and Cosmarium in the fourth sampling.The result showed that the cultivating of ducks in the rice fields promoted the growth and reproduction of the macroscopical algae but inhibited that of the microscopical algae. The density and biomass of the phytoplankton in the rice fields cultivating fishes was more than those of the rice fields without fishes. The species and quantity of group DF were so obviously higher than the other three groups that the group DF was the most suitable rice fields for the growth and reproduction of the phytoplankton, while the group D was in the opposite of the group DF. The system that the rice fields cultivating ducks and fishes affected the species and quantity of the phytoplankton in it by changing the illumination and nitrition of the rice fields' water body.