Carbon, Nitrogen And Phosphorus Stoichimetry Of Freshwater Zooplankton In Guangdong Province, South China

The present thesis studied carbon (C), nitrogen (N) and phosphorus (P) elements stoichiometry of zooplankton species in five freshwater bodies in Guangdong Province, and it aims to provide basic data linking to functions of main zooplankton groups in warming water in China.Zooplankton was sampled in Liuxihe reservoir, Shenzhen reservoir, Yantian reservoir, Dajingshan reservoir and Minghu lake (artificial lake in Jinan university), from April 2010 to March 2011. Five species of copepods and six species of cladoceras were selected for analysis of stoichiometry. The carbon (C), nitrogen (N) and phosphorus (P) contents (% of dry weight) of each species were measured.In general, C, N and P contents of zooplankton species narrowly varied in individuals of each species, but there existed a large inter-specific difference, especially in the P contents. The C, N contents of zooplankton species were relatively constant between species. Cladocerans had higher P contents and lower C, N contents than copepods. The P contents of cladocerans and copepods reanged from 0.48% to 1.38% and from 0.33% to 0.45%, respectively. The average contents of C and N of the six cladoceran species were 47.8±1.0% and 9.7±0.6%, the average contents of C and N of the five species of copepods were 50.8±1.2% and 11.4±0.7%, respecitvley. The C:N (by mass) ratios of all species were nearly constant (slightly changed between 4.4 and 5.2). The C:P, N:P ratio of cladoceras were lower than that of copepods. The C: P, N:P ratio (by mass) of cladocera and copepods ranged from 31.4 to 94.7, from 6.3 to 18.6 and from 113.9 to 153.8, from 25.5 to 33.9, respectively.The C, N, P contents (% of dry weight) of zooplankton species didn't show clear seasonality. The N:P ratio had a small seasonal fluctuation. The elemental composition of a single zooplankton specie didn't change dramatically in spite of the varing environmental conditions of the waterbody.Zooplankton species had a significant correlation among C, N and P contents. The N and C of zooplankton positively correlated, while the P and C, P and N contents negatively correlated. The N:P and C:P ratio (by mass) significantly positively correlated (P<0.01), the N:P and C:P ratios of each zooplankton specie were almost contant between different waterbodies. Zooplankton community structure in similar waterbodies usually shows a persistent variation with enrichment of nutrients, the variation indirectly confirms the stoichiometric demand for zooplankton species. In the eutrophic waterbodies, the selective predation by fish usually shapes zooplankton community to be dominated by copepods, changing the componental distribution of nutrients in the ecosystems and promoting phytoplankton to obtain more phosphorus.