Abstract
BackgroundAllelopathy (negative, plant-plant chemical interactions) has been largely studied as an autecological process, often assuming simplistic associations between pairs of isolated species. The growth inhibition of a species in filter paper bioassay enriched with a single chemical is commonly interpreted as evidence of an allelopathic interaction, but for some of these putative examples of allelopathy, the results have not been verifiable in more natural settings with plants growing in soil.Methodology/Principal findingsOn the basis of filter paper bioassay, a recent study established allelopathic effects of m-tyrosine, a component of root exudates of Festuca rubra ssp. commutata. We re-examined the allelopathic effects of m-tyrosine to understand its dynamics in soil environment. Allelopathic potential of m-tyrosine with filter paper and soil (non-sterile or sterile) bioassays was studied using Lactuca sativa, Phalaris minor and Bambusa arundinacea as assay species. Experimental application of m-tyrosine to non-sterile and sterile soil revealed the impact of soil microbial communities in determining the soil concentration of m-tyrosine and growth responses.Conclusions/SignificanceHere, we show that the allelopathic effects of m-tyrosine, which could be seen in sterilized soil with particular plant species were significantly diminished when non-sterile soil was used, which points to an important role for rhizosphere-specific and bulk soil microbial activity in determining the outcome of this allelopathic interaction. Our data show that the amounts of m-tyrosine required for root growth inhibition were higher than what would normally be found in F. rubra ssp. commutata rhizosphere. We hope that our study will motivate researchers to integrate the role of soil microbial communities in bioassays in allelopathic research so that its importance in plant-plant competitive interactions can be thoroughly evaluated.
Highlights
One of the fascinating but controversial processes in plant ecology is the mediation of competitive interactions among plants by plant-released metabolites, a mechanism referred to as ‘‘allelopathy.’’ In spite of the established role of soil microbial communities in interfering with the allelopathic activity of a metabolite [1,2,3,4], most studies use bioassays that do not incorporate a microbial component in their experimental designs
Conclusions/Significance: Here, we show that the allelopathic effects of m-tyrosine, which could be seen in sterilized soil with particular plant species were significantly diminished when non-sterile soil was used, which points to an important role for rhizosphere-specific and bulk soil microbial activity in determining the outcome of this allelopathic interaction
Growth bioassays Root growth of all the three assay species was suppressed when grown either on filter paper moistened with m-tyrosine (Flettuce = 56.65, df = 6, 284; P,0.001; Flittleseed canarygrass = 301.1; df = 6, 318; P,0.001; Fbamboo = 16.97, df = 6, 230, P,0.001) or in sterile soil treated with m-tyrosine (Flettuce = 50.1; df = 6, 216; P,0.001; Flittleseed canarygrass = 290.7; df = 6, 258, P,0.001; Fbamboo = 16.58; df = 6, 237; P,0.001) (Fig. 2 upper and middle panel)
Summary
One of the fascinating but controversial processes in plant ecology is the mediation of competitive interactions among plants by plant-released metabolites, a mechanism referred to as ‘‘allelopathy.’’ In spite of the established role of soil microbial communities in interfering with the allelopathic activity of a metabolite [1,2,3,4], most studies use bioassays that do not incorporate a microbial component in their experimental designs. The negative effect on the growth of a plant of a certain species in a filter paper bioassay enriched with a single chemical is frequently used as evidence for an allelopathic interaction; we argue here that such evidence is insufficient and consider three recent examples: (6)-catechin, 8-hydroxyquinoline, and m-tyrosine. The growth inhibition of a species in filter paper bioassay enriched with a single chemical is commonly interpreted as evidence of an allelopathic interaction, but for some of these putative examples of allelopathy, the results have not been verifiable in more natural settings with plants growing in soil
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