Abstract: Allelopathy is a plant-plant interaction mediated by the allelochemicals, which directly or indirectly influence plant growth. As the major part in response to allelochemicals, root morphological traits play an important role in allelopathy research. The global pattern of effects of exogenous allelochemicals on root morphology is not well known. We carried out a meta-analysis based on 61 studies to assess the effects of allelochemicals, including phenols, terpenoids, nitrogen-containing allelochemicals, on root morphology, especially on root length. We found that the allelochemicals significantly inhibited root length, but had little effect on root biomass, root surface area, and root volume. Phenols exhibited the most inhibitory effects on root length, while the allelochemicals had more inhibitory effect on root length of herbs than woody species as well as crops and other species. There was a linear relationship between phenols concentrations and their effect size. We quantified the dose-effect relationship of four phenolic acids, ferulic acid, p-hydroxybenzoic acid, vanillic acid and cinnamic acid. The inhibitory effect of flavonoids on root length was significantly higher than that of phenolic acids. Together, these findings suggested that the responses of target plant root traits to allelochemicals depended on allelochemicals type and dose, species identity, and culture conditions. Future studies need to decipher the mechanism underlying the allelochemicals on root traits of morphology, physiology and architecture under soil environment.

Key words: meta-analysis, allelochemical, phenol, root length, morphological trait