Meijun Chen

Short-term bacterial community composition dynamics in response to accumulation and breakdown of Microcystis blooms

Short-term bacterial community composition (BCC) dynamics in response to accumulation and breakdown of Microcystis blooms were examined by conducting in situ mesocosm experiments with varying levels of Microcystis sp. biomass, ranging from 15 to 3217 μg/L as measured by chlorophyll-a concentration in the freshwater water column. The BCC was assessed by means of terminal restriction fragment length polymorphism (T-RFLP) of 16S ribosomal RNA genes followed by cloning and sequencing of selected samples. The results showed that the composition of both free-living and particle-attached bacterial communities changed during the accumulation and breakdown phases of a Microcystis bloom, and differences were also evident with different levels of Microcystis biomass. The relative abundance of bacteria affiliated with Micrococcineae and Legionellales increased in general after amendment with Microcystis. Significant correlation between the relative abundance of Micrococcineae and breakdown of Microcystis biomass was also observed. Canonical correspondence analysis (CCA) showed that the changes in the free-living and particle-attached bacterial community were mostly related to the changes in the concentrations of chlorophyll-a, dissolved organic carbon (DOC), dissolved oxygen (DO) and pH, which were mainly induced by the breakdown of Microcystis biomass. Overall, our study revealed the following: i) accumulation of Microcystis blooms and their breakdown have strong impacts on bacterial community composition; ii) there might be saprophytic association between Micrococcineae and decomposition of Microcystis biomass; iii) it is necessary to reveal potential associations between Legionellales organisms and Microcystis blooms in eutrophic freshwater lakes.

Microbial eukaryotic community in response to Microcystis spp. bloom, as assessed by an enclosure experiment in Lake Taihu, China

Mesocosm experiments were carried out to examine the potential impacts of Microcystis blooms on microbial eukaryotic community composition (MECC). Four treatment additions of differing Microcystis spp. biomass were performed in enclosures, as indicated by chlorophyll a concentrations from 15 to 3217 μg L(-1) in the water column. Dialysis bags were used in enclosures to measure MECC dynamics without influence from predation and irradiance. Samples were taken on days 0, 1 and 4 for MECC analysis, based on changes in the chemical parameters during simultaneous monitoring. The MECC were determined by terminal restriction fragment length polymorphism (T-RFLP), followed by cloning and sequencing of 18S rRNA genes of selected samples. T-RFLP and clone library analysis revealed that MECC in enclosures and dialysis bags shifted strongly during Microcystis spp. decomposition. Members belonging to fungi became the dominant organisms in enclosures with a high biomass of Microcystis spp. Canonical correspondence analysis indicated that temporal changes in MECC were mostly related to changes in the pH and concentrations of dissolved oxygen and dissolved organic carbon, which were induced by the addition of Microcystis spp. The experiment suggests that accumulation of Microcystis biomass can strongly impact MECC, and there might be a saprophytic association between fungi and the decomposition of Microcystis biomass.

Effect of suspended solids on interaction between filter-feeding fish Aristichthys nobilis and zooplankton in a shallow lake using a mesocosm experiment

ABSTRACT Suspended solids (SS) resulting from sediment resuspension (SR) can impact ecosystems through direct and indirect effects on freshwater organisms and their interactions. This study was conducted to determine whether the SS can affect the interaction between filter-feeding fish (Aristichthys nobilis) and zooplankton using a mesocosm experiment with sediments from Lake Taihu, a large shallow lake in China. SR using pump was divided into three intensities: strong, weak and no SR representing different concentrations of SS. Zooplankton abundance was significantly higher in the no-fish treatments than in the fish treatments under all three SR conditions. SR intensity had significantly negative effect on zooplankton abundance. There were interactions between fish and SR intensity on abundances of copepod, rotifer, total zooplankton and dominant zooplankton species except cladoceran abundance. The results indicate that SS had a lesser effect on zooplankton predation by filter-feeding fish, which suggests that zooplankton communities in shallow lakes can be affected by the filter-feeding fish even under high level of SS condition.

Effect of Temperature and Food on Development and Growth of Daphnia similoides (Cladocera: Daphniidae) from Lake Donghu

ABSTRACT Growth, reproduction, and life history parameters of Daphnia similoides from a subtropical eutrophic Chinese lake (Lake Donghu) were measured at four temperatures (10, 15, 25 and 35°C) and two food concentrations (0.2 and 2 mg carbon L−1 of a green alga) in the laboratory. D. similoides had five juvenile instars and up to 28 adult instars. The number of adult instars was greater at the low food level than at the high food level. The number of adult instars with maximal number of offspring, the cumulative number of offspring per female, development time, and body lengths of females and offspring were higher or longer at the low temperatures than at the high temperatures. Body length of females was significantly correlated with offspring number per adult instar at all combinations of temperature and food. Innate capacities of increase (0.13–1.01) linearly increased with temperature.