Molecular Soil Biology 2026, Vol.17, No.1, 1-11 http://bioscipublisher.com/index.php/msb 4 Figure 1 Changes in cell density of microalga SA-2 under different treatments Note: (a) EDTA-Ca at different concentrations; (b) EDTA-Fe at different concentrations 2.2 Effects of EDTA-Fe and EDTA-Ca treatments on microalgal dry weight The dry weight of microalgae SA-2 was calculated based on the constructed dry weight standard curve (Figure 2a). Changes in dry weight were consistent with changes in cell density. The maximum dry weight of SA-2 was observed at an EDTA-Ca concentration of 0.3 mg/L and an EDTA-Fe concentration of 0.2 mg/L, both reaching 0.9 g/L (Figure 2b; Figure 2c). These results indicate that EDTA-Ca at concentrations below 0.3 mg/L and EDTA-Fe at concentrations below 0.2 mg/L promoted the growth of microalgae. In contrast, EDTA-Ca concentrations above 0.3 mg/L and EDTA-Fe concentrations above 0.2 mg/L inhibited microalgal growth. Figure 2 Changes in dry weight of microalga SA-2 under different treatments Note: (a) Dry weight standard curve; (b) EDTA-Ca at different concentrations; (c) EDTA-Fe at different concentrations 2.3 Effects of EDTA-Fe and EDTA-Ca treatments on microalgal cell viability In this study, the effects of EDTA-Ca and EDTA-Fe treatments on microalgal cell viability were measured on day 12, and micrographs of SA-2 cells under different EDTA-Ca and EDTA-Fe concentration gradients were obtained (Figure 3). The strongest cell viability (96.50%) was observed under 0.3 mg/L EDTA-Ca treatment (Figure 4a), while the highest viability (97.24%) occurred under 0.2 mg/L EDTA-Fe treatment (Figure 4b). These results indicate that EDTA-Ca at concentrations below 0.3 mg/L and EDTA-Fe at concentrations below 0.2 mg/L enhance the cell viability of SA-2. Conversely, EDTA-Ca concentrations above 0.3 mg/L and EDTA-Fe concentrations above 0.2 mg/L inhibit cell viability, leading to increased microalgal cell death. Figure 3 Microscopic images of microalga SA-2 cells under different concentrations of EDTA-Ca and EDTA-Fe treatments
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