3.1 Photosynthesis parameters
Under the treatments of Mt200 and Mt500, there was no significant change of Fv/Fm compared with the control group (Fig.1A). However, the value decreased significantly under Pal addition. When the alga was incubated with Pal200 and Pal500 for 72 h, the Fv/Fm data decreased from 0.6 to 0.5 (Fig. 1A).
The rETRmax did not vary significantly upon Mt addition (Fig. 1B), although it increased at 24h and decreased afterwards. After 24h, the rETRmaxunder Mt500 reached were 128.5 μmol electrons m-2s-1 and remained higher than the control group. In contrast, Pal addition dramatically reduced the rETRmax values from about 105 to 62.9 μmol electrons m-2s-1 at Pal200 and 56.7 μmol electrons m-2s-1 at Pal500.
3.2 P uptake, cell number andCO2emission rate
When P supply was 3.15 mg/L, the P uptake declined from 3.0 to 2.8 mg/L at Pal500 (Fig. 2A). When the P concentration in the medium was 31.5 mg/L, the P uptake increased significantly under Pal addition. However, the increase of P uptake was much lower under Mt addition (Fig. 2A).
As for the growth of C. reinhardtii , Mt and Pal had contrasting effects. Mt200 and Mt500 respectively increased the cell number from 27.4 to 28.6 and 29.9*107 ml-1 (Fig. 2B). However, the number of cells significantly decreased to 26.1 and 21.0*107 ml-1treated by Pal200 and Pal500, respectively
At Mt200, the respiration showed no evident fluctuation. When Mt was elevated to 500 mg/L, the CO2 emission rate slightly decreased from 35.0 to 32.3 mg C 10-10 cells h-1 (Fig. 2C). Nevertheless, the CO2emission rate showed a persistent increasing trend from Pal0 to Pal500, reaching 46.0 mg C 10-10 cells h-1.