| Several series of batch cultures were carried out in the laboratory to study: 1. the effects o iron, light and nitrogen nutrients on the growth of different marine algae (Skeletonema costatum, Chaetoceros curoisetus, Prorocentrum dentatum, Platymonas helgolandica var. tsingtaoensis) 2. interactions between iron, light, nitrate and ammonium on the growth of the algae and their biochemical composition. Based on the experiments, phytoplankton uptake of iron under different light and N nutrients conditions (nitrate and ammonium concentration levels and N:P ratios) was intensively studied and discussed together with the effect of EDTA addition. Furthermore, two sets of multi-species culture were executed to test the influences of iron, light and N nutrients on phytoplankton species composition and their competition to iron and N nutrient sources.The iron enrichment experiment shows that in the range of 0 to 5 ×10-6 mol/L FeCls, iron addition had significantly stimulated the growth of algae, with increase of growth rates and the contents of chlorophyll a. When 5×10-6 mol/L iron was added, the maximum growth rates of Skeletonema costatum and Chaetoceros curoisetus increased upto 2 times of those without iron addition. As one of the most essential factors for phytoplankton photosynthesis, light intensity is very critical for algae growth. The results from my experiments shows that the increase of light intensity had increased the growth of algae and the growth rate reached the highest under the light intensity of 4000 Lux. 800 Lux of light intensity had very severe limitation to alga growth. Although the growth of algae was slower under the light intensity of 1500 Lux compared to that under 4000 Lux light intensity, it is observed that alga cell density reached to the same level under 1500 Lux as that under 4000 Lux, indicating that the light intensity of 1500 Lux could be the sufficient light condition for alga growth. EDTA may plays an important role on the transformation of hydrous ferric oxide to soluble iron. Thehydrous ferric oxide was selected as iron source for the growth of algae. EDTA was added with different concentration: 0, 5×10-6 mol/L, 5×10-5mol/L, 1×10-4mol/L. From the measurements, it is found that all additions of EDTA stimulated the growth of algae. The growth rate of algae increased most significantly when 5 x 10'5 mol/L EDTA was added, while the stimulation was not such significant when the concentration of added EDTA increased to 1×10-4 mol/L.The experimental results also show that algae grew fastest when N:P ratios in the water were close to Redfield ratio (N:P=16), when the cell density and chlorophyll a concentrations reached the highest compared to other series with N:P of 80 and 4. Phytoplankton iron uptake and growth with different N sources of nitrate and ammonium were meanwhile studied, respectively. Iron addition significantly enhance algae nitrogen uptake, and algae grew better and reached higher chlorophyll a concentrations with iron addition of 5 ×10-6 mol/L, compared to the addition of 5×10-7 mol/L. However, the effect of iron addition is not so significant when ammonium was the main N source for algae growth as it is under nitrate condition. The uptake rate of iron by micro algae is faster under nitrate condition than under ammonium condition. While the growth rate and the concentration of chlorophyll a are larger under ammonium condition than under nitrate condition. This indicates that phytoplankton growing under ammonium condition have less requirement of iron than that under nitrate condition. The uptake rate of nutrients by marine micro algae was faster in higher iron concentration than in lower iron concentration condition. Iron can affect the relationship between ammonium and nitrate assimilations (the f-ratio). In the case of similar concentration of nitrogen and ammonium, preference for ammonium over nitrate will occur.Under the condition of high light (4000Lux) and no iron addition, Platymonas helgolandica var. tsingtaoensis inhibited the growth...
|
PDF Full Text Request