| As one of the main tree species grained in south China, Eucalyptus grandis has the characteristics, such as fast-growing, adaptability to climate change, regenerate fast and high economic benefits. While the violate compounds of Eucalyptus grandis exist ecological problems. However, most research was focus on the the effects of water-soluble phenolic acids on the eucalyptus with allelopathic effects of plantations at present. As a result, the allelopathic effects of plantation forests have not been comprehensively and systemically determined that means any related ecological benefits cannot be fully evaluated. Based on previous studies, three volatile allelochemicals found in the early studies with relatively high concentrations in the soil (Octane,2,4-di-tert-butyl phenol, and 2,2’-methylene bis (6-tert-butyl-4-methyl phenol)) were selected to understand the effects on the seed germination, seedling growth, physiological indexes (MDA, TTC) of three target plants and the community structure of microbial for this study. The result would be expected to clarify the mode of allelopathic effects of volatile allelochemicals in the eucalyptus plantations, and served as a scientific basis for rational and scientific-management of the eucalyptus plantations.1. The results showed that the inhibitory effect of 2,4-di-tert-butyl phenol on the target plants was the strongest. The three volatile allelochemicals showed inhibitory effects on the seed germination, root length, seedling height and the seedling/root fresh weight ratio of Vigna radiata, Raphanus sativus and at high concentrations, but showed insignificant inhibitory effects or stimulative effects at low concentrations. In general, all the three volatile allelochemicals exhibited gradually decreasing stimulative effects on the seedling’s MDA content when the concentration of the substance decreased. At the same time, they exhibited a gradually decreasing inhibitory effects on the seedlings roots’ vitality (TTC), even stimulative effects on the seedlings root’s vitality at low concentrations (n-octane and 2,2’-methylene bis (6-tert-butyl-4-methyl phenol)). However,2,2’-methylene bis (6-tert-butyl-4-methyl phenol) exhibited a certain degree of inhibition on the V. radiata seedling’s MDA content at the lower concentrations tested.2. This study investigated soil bacteria and fungus communities by Illumina MiSeq sequencing of 16S rRNA gene and 18S rRNA gene with three volatile allelochemicals as the exogenous addition in soil of eucalyptus plantations. The results exhibited that all of the bacterial and fungal sequences were affiliated with 17 and 6 distinct classes respectively. The bacterial groups in this study dominated by Crenarchaeota, Chloroflexi, Planctomycetes, Actinobacteria, Euryarchaeota, Parvarchaeota, Gemmatimonadetes, Nitrospirae, OD1, WS3, Armatimonadetes and fungal dominated by Ascomycota, Basal fungi, Basidiomycota, LKM11, LKM15.3. With the decrease of 2,4-di-tert-butyl phenol concentrations, the band number of bacterial and fungal exhibited increasing of inhibition. But bands of bacteria at high concentrations and low concentrations n-octane exhibited stimulative effects and inhibitory effects respectively, but the change was oppositive in fungus. The 2,2’-methylene bis (6-tert-butyl-4-methyl phenol) also exhibited a similar pattern as bacteria at n-octane, and showed gradually decreasing inhibitory effects as the concentration of the substance decreased in fungus.4. From the advantage bacterial communities composition, with the reduced concentration of 2,4-di-tert-butyl phenol, in the phylum classification level, except Proteobacteria exhibited increasing promotive stimulative, others exhibited decreasing inhibitory stimulative; in the genus classification level, except Pseudomonas, Achromobacter, Azoarcus and Azohydromonas exhibitied promotive stimulative, others exhibited inhibitory stimulative, but the inhibitory stimulative of Bacillus, Nitrospira, Rhodoplanes and Methanosarcina is not controlled with reduced concentration. With the reduced concentration of octane, all phylum exhibited different stimulative; except Pseudomonas exhibitied promotive stimulative, others exhibited inhibitory stimulative. With the reduced concentration of 2,2’-methylene bis (6-tert-butyl-4-methyl phenol), Proteobacteria, Firmicutes, Planctomycetes and Chloroflexi exhibited inhibitory stimulative, others exhibitied promotive stimulative; Pseudomonas and Achromobacter exhibited inhibitory stimulative, while Azohydromonas and Azoarcus exhibited promotive stimulative.From the advantage fungal communities composition, with the reduced concentration of 2,4-di-tert-butyl phenol, Ascomycota and Basidiomycota exhibited promotive stimulative, and LMK15 showed inhibitory stimulative at high concentration while showed promotive stimulative at low concentration, but Basal-fungi exhibited inhibitory stimulative; in the genus classification level, except Panorbis-viscosus showed promotive stimulative at high concentration while showed inhibitory stimulative at low concentration, and Natantispora-retorquens exhibited promotive stimulative, but it does not have effects on Penicillium, and others exhibited inhibitory stimulative. With the reduced concentration of octane, Ascomycota exhibited promotive stimulative, while Basal-fungi exhibited inhibitory stimulative. With the reduced concentration of 2,2’-methylene bis (6-tert-butyl-4-methyl phenol), Ascomycota and Basidiomycota showed promotive stimulative, while Basal-fungi and LMK15 showed inhibitory stimulative; in the genus classification level, the majority of the fungal communities exhibited promotive stimulative.5. From the richness and diversity of bacteria and fungi, with the reduced concentration of 2,4-di-tert-butyl phenol, the richness and diversity of soil bacteria exhibited inhibitory stimulative; except the Shannon-weiner and Simpson index of fungi exhibited increasing promotive stimulative, the other index of fungi exhibited inhibitory stimulative. With the reduced concentration of octane, all the richness and diversity of bacteria exhibited decreasing inhibitory stimulative; in addition to chaol, the other index of fungi showed promotive stimulative at high concentration while showed inhibitory stimulative at low concentration. With the reduced concentration of 2,2’-methylene bis (6-tert-butyl-4-methyl phenol), the richness and diversity of soil bacteria showed promotive stimulative at high concentration while showed inhibitory or no stimulative at low concentration; all the richness and diversity of fungi exhibited promotive stimulative.From the PCoA and cluster analysis, according to the different types of violate compound, the bacterial and fungal groups respectively together, while different concentrations were insignificant at this time.In summary, three relatively abundant volatile compounds (2,4-di-tert-butyl phenol, octane, and 2,2’-methylene bis (6-tert-butyl-4-methyl phenol)) existed in the soil of a Eucalyptus grandis plantation were studied and their allelopathic effects on seed germination, seedling growth exhibited inhibitory stimulative, and showed inhibitory stimulative at high concentration while showed promotive stimulative at low concentration. Under 2,4-di-tert-butyl phenol and octane, soil bacteria and fungi exhibited inhibitory stimulative. Soil bacteria and fungi showed insignificant effects by 2,2’-methylene bis (6-tert-butyl-4-methyl phenol). The effects of 2,4-di-tert-butyl phenol exhibited significant inhibitory stimulative. These results have significance to cognitive the allelopathy mechanisms of Eucalyptus grandis. |
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