SHORT-TERM RESPONSE OF SOIL MICROORGANISMS TO ESSENTIAL OILS WITH ALLELOPATHIC POTENTIAL EXTRACTED FROM MEDITERRANEAN PLANTS

Essential oils (EOs) with allelopathic compounds have been used to reduce or avoid weed germination and growth. The aim of this study was to evaluate the potential phytotoxic effects of EOs extracted from different Mediterranean plants on soil microbial biomass and activity. EOs were extracted from leaves of Eucalyptus camaldulensis Dehnh (EUC); Eriocephalus africanus L. (ERI); Thymus capitatus (L.) Hoffmanns. & Link (TCP); Citrus reticulata Blanco var. ‘Clemenules’ (TAN) and Citrus limon (L.) Osbeck var. ‘Eureka’ (LEM). Each EO was supplied to pots containing 560 g of soil at three different doses (low, medium, high). After 15, 30, 90, 120 days the supply of EOs, soils were destructively analyses for microbial biomass carbon (MBC) and microbial respiration. EOs extracted from E. camaldulensis (EUC), C. limon (LEM) and T. capitatus (TCP), at the highest concentration decreased MBC up to 30 days since their addition, with no further effects at two last samplings. EOs extracted from ERI and TAN did not affect MBC. Soil respiration was not affected by any experimental factor, whereas the metabolic quotient was increased by EO extracted from TCP. Our results suggested that essential oils with allelopathic potential extracted from mediterranean plants can negatively affect soil microorganisms and, consequently, their use as herbicides should take into account these findings.