## 3 Results  
### Cell Growth and Chlorophyll Fluorescence Change  
Optical density and cell count changes were specific to _M. aeruginosa_, given its colonies form. As shown in Figure 1A(i), a consistent decline in optical density was noted from the beginning up to the sixth month, reaching a low point in the seventh month (OD\({}_{730}\) = 0.74). After seven months of dark treatment, the OD\({}_{730}\) value had ranged from 0.74 (seven-month dark-treated group) to 1.49 (ten-month dark-treated group) with a mean of OD\({}_{730}\) = 1.18 (Figure 1A(i)). A similar pattern was observed in cell count analysis. The number of _M. aeruginosa_ cells per mL declined from 1.43 \(\times\) 10\({}^{7}\) (non-dark-treated group) to 0.72 \(\times\) 10\({}^{7}\) (six-month dark-treated group). After seven months, the range of cell count values fluctuated from 0.11 \(\times\) 10\({}^{7}\) cells (eleven-month dark-treated group) to 0.41 \(\times\) 10\({}^{7}\) cells (twelve-month dark-treated group) with a mean of 0.22 \(\times\) 10\({}^{7}\) cells per mL (Figure 1A(ii)). The cell growth rate \(\mu\) (represented as \(\log_{10}\frac{\mathrm{OD}_{730}}{\mathrm{0.012}}\)) and cell counts maintained a linear regression relationship for samples treated with darkness from the first to the sixth month (\(R^{2}\) = 0.902). However, no significant correlation was found between the seventh and the eleventh months (Figure 1A(iii)). In the experiment, the OD value decreased to 44% of the initial group by the end, whereas the cell count decreased to 8% of its initial group, consistent with the logarithmic relationship shown in Equation (2).  
Similar to the data observed in the relationship between OD\({}_{730}\) and cell counts of _M. aeruginosa_ (Figure 1A(iii)), outlier values were noted for the Fv/Fm and NPQ values of _M. aeruginosa_ at the seventh and eleventh months. Concurrently, _P. foetida_ showed abnormal data in its fourth month. Upon excluding these outliers (the seventh and the eleventh months for _M. aeruginosa_ and the fourth month for _P. foetida_), ChF analysis revealed that the mean value of the maximum Fv/Fm for _M. aeruginosa_ was at 0.75 \(\pm\) 0.04 (Figure 1B(i)), and the mean value of the maximum Fv/Fm for _P. foetida_ was at 0.59 \(\pm\) 0.11 (Figure 1B(ii)); both remained in a healthy level for cyanobacterial photosynthesis capability [29]. The mean NPQ value for _M. aeruginosa_ was 0.57 \(\pm\) 0.10 (Figure 1B(i)), while for _P. foetida_, it was 0.41 \(\pm\) 0.22 (Figure 1B(ii)). The Fv/Fm and NPQ values for _M. aeruginosa_ were higher than _P. foetida_ and classified clearly into two clusters (Figure 1B(iii)).  
Figure 1: Cell counts and chlorophyll fluorescence (ChF) analysis in _Microystis aeruginosa_ and _P. foetida_ re-cultured after the different dark treatment periods. Optical density (**A(i)**) and cell count, the blue dotted line represents the result of linear regression. (**A(ii)**) changes in dark-treated _M. aeruginosa_ and the linear regression relationship between growth rate and cell counts, the points encircled by the yellow circle are outliers in the data, and the blue dotted line represents the result of linear regression on cell counts and growth rate. (**A(iii)**). The Fv/Fm and NPQ values over time for _M. aeruginosa_ (**B(i)**) and _P. foetida_ (**B(ii)**). There is a large gap between the two species in the ratio of Fv/Fm to NPQ values, the yellow and red circles indicate the value ranges of two cyanobacteria species. (**B(iii)**). Error bars represent standard errors.