Response of Soil Microbial Community to a High Dose of Fresh Olive Mill Wastewater

An incubation experiment was designed in order to determine the further microbiological response to an addition (500 m3 ha−1) of fresh olive mill wastewater (FOMWW) in a soil that has been frequently amended with uncontrolled doses of OMWW since the 1990s in an active disposal site (ADS soil). To achieve this aim, the phospholipid fatty acid (PLFA) profiles, microbial biomass C (Cmic), and dehydrogenase (DHA) and urease activities (URA) were monitored at the beginning (T0), 3 h (T1) and 97 d (Tf, i.e., the end) of incubation after FOMWW addition. After the FOMWW addition, an increase in the ratio of fungal to bacterial PLFAs was observed in ADS soil. Moreover, a relative increase of monounsaturated fatty acids (MUFAs) with respect to saturated fatty acids (SATFA) was found in the ADS soil. An increase of the Gram-positive to Gram-negative ratio was observed in this soil at the end of the incubation. While DHA and Cmic increased in the ADS soil after FOMWW addition, URA showed a decrease. Fungi and Gram-positive bacterial biomass experienced an increase after addition of a high dose of FOMWW in laboratory conditions.