Taking Ecological Function Seriously: Soil Microbial Communities Can Obviate Allelopathic Effects of Released Metabolites

Allelopathy (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.On 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.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. 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

Community Impacts of Prosopis Juliflora Invasion: Biogeographic and Congeneric Comparisons

We coordinated biogeographical comparisons of the impacts of an exotic invasive tree in its native and non-native ranges with a congeneric comparison in the non-native range. Prosopis juliflora is taxonomically complicated and with P. pallida forms the P. juliflora complex. Thus we sampled P. juliflora in its native Venezuela, and also located two field sites in Peru, the native range of Prosopis pallida. Canopies of Prosopis juliflora, a native of the New World but an invader in many other regions, had facilitative effects on the diversity of other species in its native Venezuela, and P. pallida had both negative and positive effects depending on the year, (overall neutral effects) in its native Peru. However, in India and Hawaii, USA, where P. juliflora is an aggressive invader, canopy effects were consistently and strongly negative on species richness. Prosopis cineraria, a native to India, had much weaker effects on species richness in India than P. juliflora. We carried out multiple congeneric comparisons between P. juliflora and P. cineraria, and found that soil from the rhizosphere of P. juliflora had higher extractable phosphorus, soluble salts and total phenolics than P. cineraria rhizosphere soils. Experimentally applied P. juliflora litter caused far greater mortality of native Indian species than litter from P. cineraria. Prosopis juliflora leaf leachate had neutral to negative effects on root growth of three common crop species of north-west India whereas P. cineraria leaf leachate had positive effects. Prosopis juliflora leaf leachate also had higher concentrations of total phenolics and L-tryptophan than P. cineraria, suggesting a potential allelopathic mechanism for the congeneric differences. Our results also suggest the possibility of regional evolutionary trajectories among competitors and that recent mixing of species from different trajectories has the potential to disrupt evolved interactions among native species

Interaction of 8-Hydroxyquinoline with Soil Environment Mediates Its Ecological Function

Background: Allelopathic functions of plant-released chemicals are often studied through growth bioassays assuming that these chemicals will directly impact plant growth. This overlooks the role of soil factors in mediating allelopathic activities of chemicals, particularly non-volatiles. Here we examined the allelopathic potential of 8-hydroxyquinoline (HQ), a chemical reported to be exuded from the roots of Centaurea diffusa. Methodology/Principal Findings: Growth bioassays and HQ recovery experiments were performed in HQ-treated soils (non-sterile, sterile, organic matter-enriched and glucose-amended) and untreated control soil. Root growth of either Brassica campestris or Phalaris minor was not affected in HQ-treated non-sterile soil. Soil modifications (organic matter and glucose amendments) could not enhance the recovery of HQ in soil, which further supports the observation that HQ is not likely to be an allelopathic compound. Hydroxyquinoline-treated soil had lower values for the CO2 release compared to untreated non-sterile soil. Soil sterilization significantly influenced the organic matter content, PO 4-P and total organic nitrogen levels. Conclusion/Significance: Here, we concluded that evaluation of the effect of a chemical on plant growth is not enough in evaluating the ecological role of a chemical in plant-plant interactions. Interaction of the chemical with soil factors largel

Ecological phytochemistry of Cerrado (Brazilian savanna) plants

The Cerrado (the Brazilian savanna) is one of the vegetation formations of great biodiversity in Brazil and it has experienced strong deforestation and fragmentation. The Cerrado must contain at least 12,000 higher plant species.We discuss the ecological relevance of phytochemical studies carried out on plants from the Cerrado, including examples of phytotoxicity, antifungal, insecticidal and antibacterial activities. The results have been classified according to activity and plant family. The most active compounds have been highlighted and other activities are discussed. A large number of complex biochemical interactions occur in this system. However, only a small fraction of the species has been studied from the phytochemical viewpoint to identify the metabolites responsible for these interactions

Gas Chromatographic Determination of 1,4-Dioxane in Benzene

401-404The term ‘petrochemicals’ implies the basic chemicals derived from refinery petroleum cuts. They are produced by the separation of the byproducts from the cracking of hydrocarbon streams. The basic petrochemicals, which are produced in large volumes, are divided into two classes, olefins and aromatics. Olefins include ethylene, propylene and 1,3-butadiene. Aromatics such as benzene, toluene and xylenes are obtained from refinery and petrochemical light naphtha streams. Aromatics are produced in the reforming process and in stream cracking. Extraction or various extractive distillation processes are used to isolate and separate aromatics from the naphtha streams. Typical extraction processes are based on tetra- ethylene glycol, sulpholane, N,N’-methyl pyrrolidone or morpholine. They produce a mixture of aromatics that are subsequently separated by distillation. Glycols used in extraction processes contain small amounts of 1,4-dioxane, which gets distilled over with benzene when aromatics are separated by distillation. In view of the hazardous properties, it is necessary to determine the levels of 1,4-dioxane in glycols and benzene. Determination of 1,4-dioxane in glycols at low p p m levels has already been reported. The detailed studies carried out for the gas chromatographic determination of 1,4-dioxane in benzene including column selection and linearity are reported in the present communication

Community Impacts of <em>Prosopis juliflora</em> Invasion: Biogeographic and Congeneric Comparisons

<div><p>We coordinated biogeographical comparisons of the impacts of an exotic invasive tree in its native and non-native ranges with a congeneric comparison in the non-native range. <em>Prosopis juliflora</em> is taxonomically complicated and with <em>P. pallida</em> forms the <em>P. juliflora</em> complex. Thus we sampled <em>P. juliflora</em> in its native Venezuela, and also located two field sites in Peru, the native range of <em>Prosopis pallida.</em> Canopies of <em>Prosopis juliflora</em>, a native of the New World but an invader in many other regions, had facilitative effects on the diversity of other species in its native Venezuela, and <em>P. pallida</em> had both negative and positive effects depending on the year, (overall neutral effects) in its native Peru. However, in India and Hawaii, USA, where <em>P. juliflora</em> is an aggressive invader, canopy effects were consistently and strongly negative on species richness. <em>Prosopis cineraria</em>, a native to India, had much weaker effects on species richness in India than <em>P. juliflora</em>. We carried out multiple congeneric comparisons between <em>P. juliflora</em> and <em>P. cineraria</em>, and found that soil from the rhizosphere of <em>P. juliflora</em> had higher extractable phosphorus, soluble salts and total phenolics than <em>P. cineraria</em> rhizosphere soils. Experimentally applied <em>P. juliflora</em> litter caused far greater mortality of native Indian species than litter from <em>P. cineraria</em>. <em>Prosopis juliflora</em> leaf leachate had neutral to negative effects on root growth of three common crop species of north-west India whereas <em>P. cineraria</em> leaf leachate had positive effects. <em>Prosopis juliflora</em> leaf leachate also had higher concentrations of total phenolics and L-tryptophan than <em>P. cineraria,</em> suggesting a potential allelopathic mechanism for the congeneric differences. Our results also suggest the possibility of regional evolutionary trajectories among competitors and that recent mixing of species from different trajectories has the potential to disrupt evolved interactions among native species.</p> </div

Total phenolic content (mean + SE) of soil amended with <i>Prosopis cineraria</i> (gray bar) and <i>P. juliflora</i> (black bar) leaf leachates and unamended soil (control, white bar). (A)

<p>Different letters above bars indicate significant differences (ANOVA, post-ANOVA Tukey’s test; p<0.05). <b>(B)</b> Total phenolic content (mean ± SE) of soil treated with no litter (white circles), <i>P. cineraria</i> (gray circles) or <i>P. juliflora</i> leaf litter (black circles) at rate of 12 mg/g soil, and incubated at 30–34°C under 12 h/12 h light/dark cycle for 0, 1, 2, 3, 4, 6, 8, 10 and14 days.</p

Root length (proportion of control, %) of <i>Brassica campestris</i> (upper panel), <i>B. juncea</i> (middle panel) and <i>Sorghum bicolor</i> (lower panel) seedlings grown in soil treated with different amounts (60, 150 and 300 µL/g soil) of <i>Prosopis cineraria</i> (gray bars) or <i>Prosopis juliflora</i> (black bars) leaf leachate.

<p>Soil treated with distilled water served as untreated control (white bars). Error bars represent +1SE of mean. F and P values are shown for two way ANOVAs.</p