Cultivating microalgal biofilms on three soils under exogenous phosphorus and iron

Biological crusts serve as the initiator of soil development and play a crucial role in soil ecological restoration. In this study, microalgae biofilms were cultivated on three simulated problem soils (saline soil, limestone, and tufa sand) with the addition of phosphogypsum and pyrite tailings. During the 50-day culture period, chlorophyll-a and exopolysaccharide contents rosed in saline soil and limestone compared to the control group, with significant increases in limestone. The biofilms on tufa sand were little affected by the amendments. The influence of soil properties on microalgal growth was manifested in the later stage rather than the initial 25 days of treatment. Biofilm growth was mainly affected by available iron in saline soil and soil macronutrients in limestone. Exogenous phosphorus and iron promote microalgae biofilm formation that is determined by soil types. These findings provide a reference in soil remediation and ecological restoration.