Microbes as Targets and Mediators of Allelopathy in Plants

Abstract

Studies of allelopathy in terrestrial systems have experienced tremendous growth as interest has risen in describing biochemical mechanisms responsible for structuring plant communities, determining agricultural and forest productivity, and explaining invasive behaviors in introduced organisms. While early criticisms of allelopathy involved issues with allelochemical production, stability, and degradation in soils, an understanding of the chemical ecology of soils and its microbial inhabitants has been increasingly incorporated in studies of allelopathy, and recognized as an essential predictor of the outcome of allelopathic interactions between plants. Microbes can mediate interactions in a number of ways with both positive and negative outcomes for surrounding plants and plant communities. In this review, we examine cases where soil microbes are the target of allelopathic plants leading to indirect effects on competing plants, provide examples where microbes play either a protective effect on plants against allelopathic competitors or enhance allelopathic effects, and we provide examples where soil microbial communities have changed through time in response to allelopathic plants with known or potential effects on plant communities. We focus primarily on interactions involving wild plants in natural systems, using case studies of some of the world's most notorious invasive plants, but we also provide selected examples from agriculturally managed systems. Allelopathic interactions between plants cannot be fully understood without considering microbial participants, and we conclude with suggestions for future research. Allelopathy and Soil MicrobesAllelopathy, generally, is considered as a form of negative chemical communication between organisms, whereby one participant (the donor) in an interaction produces a compound(s) that is released in the environment in ecologically relevant quantities that negatively impacts the fitness of other participants (the receivers); the effect presumably benefits fitness of the donor. While the concept of allelopathy extends back to at least Theophrastus in the third century B.C., who invoked this phenomenon as an explanatory mechanism of plant growth, abundance, or community structure in natural systems, the concept has fluctuated in popularity over time (see Willis, 2007 for review). Allelopathy often has been subjected to criticisms of ecological relevance that other phenomena, such as resource competition, have not, thus explaining why it has fallen out of favor during certain time periods. However, studies of allelopathy in terrestrial systems have experienced a tremendous "rebirth" in the last 20 years as interest has risen in describing biochemical mechanisms responsible for structuring plant communities, determining agricultural and forest productivity, and explaining invasive behaviors in introduced organisms. More rigorous observational and experimental approaches, along with better analytical techniques, have

Allelopathy: driving mechanisms governing its activity in agriculture

“…Plants of the Brassicaceae, Chenopodiaceae, Caryophyllaceae and Cyperaceae families are tolerant to some fungal pathogens and show no symbiotic associations with mycorrhizal fungi, due to the allelochemicals released by their roots (Schreiner & Koide 1993). When released into the soil, these allelochemicals can also inhibit the germination of spores, as well as the symbiotic association between mycorrhizal fungi and surrounding host plants (Stinson et al 2006;Javaid 2007;Cipollini et al 2012).…”

No allelopathic effect of the invader Acacia dealbata on the potential infectivity of arbuscular mycorrhizal fungi from native soils

“…The allelopathic effect of A. dealbata was assessed by collecting natural leachates that represent natural concentrations of chemical compounds, a requirement to be able to interpret allelopathy within an ecological context [13].…”

“…Mycorrhizal fungi form symbiosis with 90% of plant species, which are dependent on this association for growth and survival [12]. Changes in native mycorrhizal communities by invasive exotic species usually have negative effects on native plant species leading to a rapid degradation of the invaded ecosystem [6e8, 13,14].…”

Proximate Composition And Preliminary Allelopathic Effect Of A Tropical Fern, Cyclosorus Afer On Oryza Sativa

“…The release of chemicals from some plant organs by a number of processes in simulated and natural conditions which could pose harmful or beneficial effect on neighboring plants is regarded as allelopathy (Ferguson and Rathinasabapathi, 2009). These chemicals do produce some changes in the environment directly through phytotoxicity, or indirectly by interfering with soil microbes (Einhelling, (1986), Cipollini et al, (2012), Kraus et al, (2003). Proximate composition of plants is referred to as the gross components (Protein, fat, carbohydrate, ash, etc.)…”