| A combined model was constructed for the prediction of cyanobacterial growth based on the relationship between growth and cell characteristics such as cell pigment content, cell phosphorus content, cell carbohydrate content and cell size. And also, the indicator of diversity index may be considered for the early-warning of cyanobacterial blooms; furthermore, the ratio of characteristic pigment to cholorphyll a was suggested to be used to indicate the variation of the structure of phytoplankton community, which should be useful for studying the dynamics of phytoplankton community.Firstly, the effects of irradiance as a physical factor and ambient nitrogen or phosphorus concentrations as chemical factors on the growth of typically bloom-forming Microcystis aeruginosa (FACHB 905), as well as the simultaneous variations of cell pigment content, cell phosphorus content, cell nitrogen content, cell carbohydrate content and cell size with the variation of growth, were studied. The experiments were carried out by adopting uni-algal batch culture, and the typically bloom-forming Microcystis aeruginosa (FACHB 905) was employed. Different phosphorus or nitrogen concentrations in the medium were set, and a gradient of 6 irradiances was employed. Under N-controlled condition, the specific growth rate, cell nitrogen content, and cell cholorphyll a content were affected by N concentration and irradiance intensity, which showed simultaneous and similar variation. There existed interactive effects of irradiance and phosphorus on the growth rate, cell cholorphyll a content, cell phosphorus content, cell carbohydrate content and cell size. The cell characteristics such as cell pigment content, cell phosphorus content, cell nitrogen content, cell carbohydrate content and cell size showed simultaneous variation with growth rate, which indicated that there may exist some relationship between them.The bloom-forming Microcystis aeruginosa (FACHB 912) that was isolated from Lake Taihu was used for the study of the effect of Fe, Cu, Mn and Zn on the growth of cyanobacteria. The experiments were carried out by adopting uni-algal batch culture, and different concentrations of Fe, Cu, Mn and Zn were employed. It was found that Fe, Cu, Mn and Zn were essential micronutrient for the growth of cyanobacteria, which would promote the growth, as well as the cell size and cell content of pigment, carbohydrate, nitrogen, and phosphorus. However, excess concentration of these metals would be toxic and inhibited the growth. The optimal concentrations for the growth of M. aeruginosa were about 12.3μmol Fe/L,0.079μmol Cu/L,3.57μmol Mn/L,0.386μmol Zn/L, higher than which will be toxic. The cell characteristics such as cell pigment content, cell phosphorus content, cell nitrogen content, cell carbohydrate content and cell size showed simultaneous variation with growth rate, which indicated that there may exist some relationship between them.The growth of M. aeruginosa in batch culture showed four phases as lag phase, exponential phase, steady phase, senescence phase. The specific growth rate, division ratio, the microscopic photo perimeter and area of the cell, cell roundness, cell cholorophyll a content showed different variation patterns in the four growth phases, which indicated that the surrounding conditions could impact the growth and cell characteristics. On the other hand, the variation of specific growth rate was in relation to that of cell characteristics such as division ratio, cell size, cell roundness, etc.Based on the variations of growth rate and cell carbohydrate content, it was found that the specific growth rate was inversely proportional to cell carbohydrate content. The growth rate was relatively high when the cell carbohydrate content was low. It can be indicated that high growth occurs when cells are buoyant, which favors blooms. Under P controlled condition, a combined model was constructed for the prediction of cyanobacterial growth, and a better prediction was achieved by the combined model (Adjusted R2=0.698, P<<0.001) than the prediction model using any one factor of cell pigment content, cell phosphorus content, cell carbohydrate content or cell size. Cell characteristics are the reflection of the combined effect of environmental parameters on cells. It will be suitable to be applied in various environments to predict the growth.Finally, a cyanobacterial(Arthrospira platensis) bloom was induced in situ by nutrient manipulation in an enclosure. The succession of the phytoplankton community and the water chemistry variations before the appearance of bloom, as well as their relationship, were investigated. The cell pigment variations were studied simultaneously. The Pearson's correlation analysis showed that there was no significant correlation between water chemistry and green algal or cyanobacterial composition, indicating that water chemistry variations were not suitable to be used as indicators for cyanobacterial-bloom early-warning. However, the diversity index of the phytoplankton community decreased sharply before the bloom appeared. Therefore, the diversity index of phytoplankton community may be considered as an indicator for cyanobacterial-bloom early-warning. In addition, the cell pigment variations represented the changes of community structure, which should be useful for studying the dynamics of phytoplankton community.
|
PDF Full Text Request