Reorganization of soil microbial community under repetitive disturbance induced by treated olive mill wastewater

Olive mill wastewater (OMW) is a significant agro-industrial byproduct generated across the Mediterranean region. Although it contains valuable organic and mineral nutrients, its high concentration of phenolic compounds and phytotoxic nature hinder direct reuse. This study explores the ecological consequences of repeated applications of biotechnologically treated OMW in soil, emphasizing the structural and functional responses of soil microbial communities. OMW was initially detoxified using the white-rot fungus Pleurotus ostreatus , achieving a 55% reduction in phenolic content, and was subsequently applied to soil in a pot experiment three times over a 45-day period. Changes in microbial community composition (via PLFAs), co-occurrence networks, and enzyme activities were monitored, three and 15 days after each application. The repeated OMW treatments initiated a process of microbial secondary succession, resulting in distinct community structures over time. By the end of the experiment, total microbial biomass exceeded baseline levels by approximately 30%, while the activities of N -acetyl-β-D-glucosaminidase and β-glucosidase increased by 85% and 160%, respectively. Additionally, network architectural properties recovered to pre-disturbance levels. Repeated OMW inputs enriched soil macronutrients and organic carbon while slightly lowering pH. Both pH and organic carbon directly reduced microbial biomass and diversity but indirectly promoted key soil functions through their influence on microbial biomass. Overall, the findings demonstrate that the repeated use of treated OMW can foster microbial community reorganization and functionality. This approach therefore represents a promising strategy for sustainable soil management in olive-growing regions. Nevertheless, validation across broader spatial and temporal scales is recommended. • OMW triggers secondary succession, shaping distinct microbial profiles by stage. • The topology of co-occurrence networks responded to the succession process. • Microbial biomass exceeded the initial levels, reflecting acclimation. • Repeated application of treated OMW can contribute to sustainable soil management.