Effect of DOR Incubated with Saprobe Fungi on Hydrolytic Enzymes Activities and Chemical Properties of Rhizospheric Soil of Lettuce

Abstract

The dry olive residue (DOR), a by-product of the olive mill industry, is produce in large quantities in Mediterranean countries. The phytotoxic and antimicrobial properties of this residue adversely impact on soil qualities. The objective of this study was to investigate the evolution of soil enzymes activities (acid phosphatase, β-glucosidase, protease and urease) and chemical properties (pH, phenols, total organic carbon (TOC) and soluble carbohydrates) after the agronomic application on lettuce of either un-treated DOR or DOR incubated with inmobilized Panus tigrinus or Fusarium lateritium. A decrease of total phenols and phytotoxicity on lettuce plants in presence of treated DOR related to the un-treated residue was detected. We observed a decrease of all hydrolytic enzymes, except protease, after the soil incubation with un-treated DOR for 15 days. It appears that the high concentration of phenolics compounds inhibited the activities of these enzymes. However, the microbial activity was stimulated by the addition of DOR incubated with the saprobe fungi as indicated by the increase of soil enzyme activities detected. The protease activity was always higher than the control soil irrespective of the type of amendant. The TOC and phenols of rhizospheric soil of lettuce increased after 15 and 30 days of agronomic application of untreated or treated residue and a general decrease of the soluble carbohydrates contents was found after 30 days of soil incubation. The DOR detoxified by saprobe fungi has been seen to have a positive effect to restore the loss rhizospheric soil functionality detected after the addition of un-treated residue.