Measurements of algal growth rates and elemental contents
We enumerated the number of algal cells at the end of incubation using the Fuchs-Rosenthal counting chamber and an optical microscope (Olympus, Tokyo, Japan; eyepiece magnification 10x, objective magnification 10x) (cells mL−1). Then, the algal growth rate was calculated from the difference between the cell number at the start (N 0) and the end of incubation (Nt ) as follows,
\(\text{GR}=\frac{\ln\left(N_{t}\right)-ln(N_{0})}{t}\) (1),
where t = 7 days.
The C and N contents of algal cells collected on GF/F filters (μg mL−1) were measured using a CHN elemental analyzer (2400 Series II CHNS/O Elemental Analyzer, Perkin Elmer, Massachussets, USA). The P content of algal cells was measured by the ascorbic acid-molybdenum blue method after potassium persulfate oxidation . The C, N, and P cell quotas of the algal cell were calculated as:
\(Q_{E}=\frac{\text{Scenedesmus\ }\mathrm{C,\ N,\ or\ P\ biomass}\ (\mathrm{\text{μg}}\ \mathrm{\text{mL}}^{-1})}{\text{Scenedesmus}\mathrm{\text{\ density\ }}(\mathrm{\text{cells\ m}}\mathrm{L}^{-1})}\)(2).