Herbal Fructus Amomi oil Natural massage Diffusers 1kg Bulk Amomum villosum Essential oil

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The Zingiberaceae family has attracted increasing attention in allelopathic research because of the rich volatile oils and the aromaticity of its member species. Previous research had shown that the chemicals from Curcuma zedoaria (zedoary) [40], Alpinia zerumbet (Pers.) B.L.Burtt & R.M.Sm. [41] and Zingiber officinale Rosc. [42] of the ginger family have allelopathic effects on seed germination and seedling growth of maize, lettuce and tomato. Our current study is the first report on the allelopathic activity of volatiles from stems, leaves, and young fruits of A. villosum (a member of Zingiberaceae family). The oil yield of stems, leaves, and young fruits was 0.15%, 0.40%, and 0.50%, respectively, indicating that fruits produced a larger quantity of volatile oils than stems and leaves. The main components of volatile oils from stems were β-pinene, β-phellandrene and α-pinene, which was a pattern similar to that of the major chemicals of leaf oil, β-pinene and α-pinene (monoterpene hydrocarbons). On the other hand, the oil in young fruits was rich in bornyl acetate and camphor (oxygenated monoterpenes). The results were supported by the findings of Do N Dai [30,32] and Hui Ao [31] who had identified the oils from different organs of A. villosum.

There have been several reports on the plant growth inhibitory activities of these main compounds in other species. Shalinder Kaur found that α-pinene from eucalyptus prominently suppressed root length and shoot height of Amaranthus viridis L. at 1.0 μL concentration [43], and another study showed that α-pinene inhibited early root growth and caused oxidative damage in root tissue through increased generation of reactive oxygen species [44]. Some reports have argued that β-pinene inhibited germination and seedling growth of test weeds in a dose-dependent response manner by disrupting membrane integrity [45], altering the plant biochemistry and enhancing the activities of peroxidases and polyphenol oxidases [46]. β-Phellandrene exhibited maximum inhibition to the germination and growth of Vigna unguiculata (L.) Walp at a concentration of 600 ppm [47], whereas, at a concentration of 250 mg/m3, camphor suppressed the radicle and shoot growth of Lepidium sativum L. [48]. However, research reporting the allelopathic effect of bornyl acetate is scanty. In our study, the allelopathic effects of β-pinene, bornyl acetate and camphor on root length was weaker than for the volatile oils except for α-pinene, whereas leaf oil, rich in α-pinene, was also more phytotoxic than the corresponding volatile oils from the stems and fruits of A. villosum, both findings indicating that α-pinene might the important chemical for allelopathy by this species. At the same time, the results also implied that some compounds in the fruit oil that were not abundant might contribute to the production of the phytotoxic effect, a finding which needs further research in the future.

Under normal conditions, the allelopathic effect of allelochemicals is species-specific. Jiang et al. found that essential oil produced by Artemisia sieversiana exerted a more potent effect on Amaranthus retroflexus L. than on Medicago sativa L., Poa annua L., and Pennisetum alopecuroides (L.) Spreng. [49]. In another study, the volatile oil of Lavandula angustifolia Mill. produced different degrees of phytotoxic effects on different plant species. Lolium multiflorum Lam. was the most sensitive acceptor species, hypocotyl and radicle growth being inhibited by 87.8% and 76.7%, respectively, at a dose of 1 μL/mL oils, but hypocotyl growth of cucumber seedlings was barely affected [20]. Our results also showed that there was a difference in sensitivity to A. villosum volatiles between L. sativa and L. perenne.

The volatile compounds and essential oils of the same species can vary quantitatively and/or qualitatively because of growth conditions, plant parts and detection methods. For example, a report demonstrated that pyranoid (10.3%) and β-caryophyllene (6.6%) were the major compounds of the volatiles emitted from leaves of Sambucus nigra, whereas benzaldehyde (17.8%), α-bulnesene (16.6%) and tetracosane (11.5%) were abundant in the oils extracted from leaves [50]. In our study, volatile compounds released by the fresh plant materials had stronger allelopathic effects on the test plants than the extracted volatile oils, the differences in response being closely related to the differences in the allelochemicals present in the two preparations. The exact differences between volatile compounds and oils need to be further investigated in subsequent experiments.

Differences in microbial diversity and microbial community structure in soil samples to which volatile oils had been added were related to competition among microorganisms as well as to any toxic effects and the duration of volatile oils in the soil. Vokou and Liotiri [51] found that the respective application of four essential oils (0.1 mL) to cultivated soil (150 g) activated respiration of the soil samples, even the oils differed in their chemical composition, suggesting that plant oils are used as a carbon and energy source by occurring soil microorganisms. Data obtained from the current study confirmed that the oils from the whole plant of A. villosum contributed to the obvious increase in the number of the soil fungal species by the 14th day after oil addition, indicating that the oil may provide the carbon source for more soil fungi. Another study reported a finding: soil microorganisms recovered their initial function and biomass after a temporary period of variation induced by the addition of Thymbra capitata L. (Cav) oil, but the oil at the highest dose (0.93 µL oil per gram of soil) did not allow soil microorganisms to recover the initial functionality [52]. In the current study, based on the microbiological analysis of the soil after being treated with different days and concentrations, we speculated that the soil bacterial community would recover after more days. In contrast, the fungal microbiota cannot return to its original state. The following results confirm this hypothesis: the distinct effect of high-concentration of the oil on the composition of soil fungal microbiome was revealed by principal co-ordinates analysis (PCoA), and the heatmap presentations confirmed again that the fungal community composition of the soil treated with 3.0 mg/mL oil (namely 0.375 mg oil per gram of soil) at the genus level differed considerably from the other treatments. Presently, the research about the effects of the addition of monoterpene hydrocarbons or oxygenated monoterpenes on soil microbial diversity and community structure is still scarce. A few studies reported that α-pinene increased soil microbial activity and relative abundance of Methylophilaceae (a group of methylotrophs, Proteobacteria) under low moisture content, playing an important role as a carbon source in drier soils [53]. Similarly, volatile oil of A. villosum whole plant, containing 15.03% α-pinene (Supplementary Table S1), obviously increased the relative abundance of Proteobacteria at 1.5 mg/mL and 3.0 mg/mL, which suggested that α-pinene possibly act as one of the carbon sources for soil microorganisms.

The volatile compounds produced by different organs of A. villosum had various degrees of allelopathic effects on L. sativa and L. perenne, which was closely related to the chemical constituents that A. villosum plant parts contained. Although the chemical composition of the volatile oil was confirmed, the volatile compounds released by A. villosum at room temperature are unknown, which need the further investigation. Moreover, the synergistic effect between different allelochemicals is also worthy of consideration. In terms of soil microorganisms, to explore the effect of the volatile oil on soil microorganisms comprehensively, we still need to conduct more in-depth research: extend the treatment time of volatile oil and discern variations in chemical composition of the volatile oil in the soil on different days.

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Allelopathy is often defined as any direct or indirect, positive or negative effect by one plant species on another through the production and release of chemical compounds into the environment [1]. Plants release allelochemicals into the surrounding atmosphere and soil through volatilization, foliar leaching, root exudation, and residue decomposition [2]. As one group of important allelochemicals, volatile components enter the air and soil in similar ways: plants release volatiles into the atmosphere directly [3]; rainwater rinses these components (such as monoterpenes) out of the leaf secretory structures and surface waxes, providing the potential for volatile components into the soil [4]; plant roots could emit herbivore-induced and pathogen-induced volatiles into the soil [5]; these components in the plant litter are also released into the surrounding soil [6]. At present, volatile oils have been increasingly explored for their use in weed and pest management [7,8,9,10,11]. They are found to act by spreading in their gaseous state in the air and by transformation into other states into or onto the soil [3,12], playing an important role in inhibiting plant growth by interspecies interactions and altering the crop–weed plant community [13]. Several studies suggest that allelopathy may facilitate the establishment of dominance of plant species in natural ecosystems [14,15,16]. Therefore, dominant plant species can be targeted as potential sources of allelochemicals.

In recent years, allelopathic effects and allelochemicals have gradually received more and more attention from researchers for the purpose of identifying appropriate substitutes for synthetic herbicides [17,18,19,20]. In order to reduce agricultural losses, herbicides are increasingly used to control the growth of weeds. However, the indiscriminate application of synthetic herbicides has contributed to increased problems of weed resistance, the gradual degradation of the soil, and hazards to human health [21]. Natural allelopathic compounds from plants can offer considerable potential for the development of new herbicides, or as lead compounds toward identifying new, nature-derived herbicides [17,22].

Amomum villosum Lour. is a perennial herbaceous plant in the ginger family, growing to a height of 1.2–3.0 m in the shade of trees. It is widely distributed in South China, Thailand, Vietnam, Laos, Cambodia, and other Southeast Asian regions. The dry fruit of A. villosum is a kind of common spice because of its attractive flavor [23] and it represents a well-known traditional herbal medicine in China, which is widely used to treat gastrointestinal diseases. Several studies have reported that the volatile oils rich in A. villosum are the main medicinal components and aromatic ingredients [24,25,26,27]. Researchers found that essential oils of A. villosum exhibit contact toxicity against the insects Tribolium castaneum (Herbst) and Lasioderma serricorne (Fabricius), and strong fumigant toxicity against T. castaneum [28]. At the same time, A. villosum has a detrimental impact on the plant diversity, biomass, litterfall and soil nutrients of primary rainforests [29]. However, the ecological role of volatile oil and the allelopathic compounds are still unknown. In the light of previous studies into the chemical constituents of A. villosum essential oils [30,31,32], our objective is to investigate whether A. villosum releases compounds with allelopathic effects into the air and soil to help establish its dominance. Therefore, we plan to: (i) analyze and compare the chemical components of volatile oils from different organs of A. villosum; (ii) evaluate the allelopathy of volatile oils extracted and volatile compounds from A. villosum, and then identify the chemicals that had allelopathic effects on Lactuca sativa L. and Lolium perenne L.; and (iii) preliminarily explore the effects of oils from A. villosum on the diversity and community structure of microorganisms in the soil.