Differential impact on soil microbes of allelopathic compounds released by the invasive Acacia dealbata Link

Abstract

Acacia dealbata Link, an Australian tree legume, is one of the most invasive species in south-eastern Europe. The invasive success of A. dealbata is partially attributed to its ability to release allelopathic compounds that affect native plant species, but the allelopathic effect on soil microbes has been little explored. Here, we used natural leachates to assess the bioactivity of these allelochemicals on soil microorganisms in native Mediterranean pine and mixed forests. Soil samples were treated either with acacia canopy leachate or the corresponding canopy leachate. Soil microbial communities were analyzed using Biolog Ecoplates™ and PCR–DGGE. Allelochemicals naturally released by A. dealbata clearly modified soil bacterial functional diversity in the pine forest where acacia leachate significantly increased the consumption of carbohydrates and amino acids and reduced the utilization of carboxylic acids. Acacia leachates also lead to a significant reduction in bacterial richness and diversity in the pine forest soil. However, the soil microorganisms of mixed oak forest were insensitive to allelochemical activity. Our results show that the allelopathic effects of A. dealbata on soil microbes depend on ecosystem type and that soil bacteria are more sensitive than soil fungi to the allelochemicals released by A. dealbata. We conclude that the higher sensitivity of pine forest soil microbiota to allelochemicals introduced by A. dealbata can contribute to the process of invasion.