Jodi R. Shann

The Effect of Phytotoxins on Competitive Outcome in a Model System

The difficulty of distinguishing allelopathy from resource competition among plants has hindered investigations of the role of phytotoxic allelochemicals in plant communities. The effects of allelopathic substances on competitive outcome when two species differ in their sensitivity to an inhibitor were modelled by applying atrazine, a commonly used herbicide for broadleaf weeds, to corn—soybean mixtures. A target—neighbor design was used, in which differing densities of a neighbor species are planted around one individual of the target species. This design is particularly appropriate to investigations of allelopathy, due to the density—dependent nature of phytotoxic effects. Neighbor density greatly influenced the response to the toxin. At a corn densities of 0, 3, 6, 9, and 12 plants per pot and atrazine treatment of 3.0 mg/kg, the dry mass of the soybean (target) plant increased from 0.2 g with no neighbors to 0.5 g with 9—12 neighboring corn plants. The increased growth of soybean at higher corn densities is contrary to the predicted effects of resource competition and is due to uptake of atrazine by the corn plants, which decreased the amount available to the soybean target. Detoxification of soil by neighbors may explain in part the conflicting assessments of some putatively allelopathic species, such as black walnut (Juglans nigra).

Effects of various mixtures of ferulic acid and some of its microbial metabolic products on cucumber leaf expansion and dry matter in nutrient culture

Cucumber seedlings (Cucumis sativus cv. ‘Early Green Cluster’) ranging from 6 to 16 days of age were treated with various concentrations (0– 1 mM) of caffeic, ferulic,p-coumaric,p-hydroxybenzoic, protocatechuic, sinapic, syringic, and vanillic acids and mixtures of ferulic acid and one or two of the other phenolic acids. Seedlings were grown in full-strength Hoaglands solution which was changed every other day. Phenolic acid treatments were given with each nutrient solution change starting at day 6 or given once when seedlings were 13 or 14 days old. Leaf area, mean relative rates of leaf expansion, transpiration rates, water utilization, and the concentrations of the phenolic acids in nutrient solution were determined at one- or two-day intervals. Seedling dry weight was determined at final harvest. Seedling leaf area and dry weight were linearly related. Since leaf areas can be easily obtained without destructive sampling and leaf area expansion responds rapidly to phenolic acid treatments, it was utilized as the primary indicator of plant response. The resulting data suggested that a number of ferulic acid microbial metabolic products, as well as two other phenolic acids observed in soils (p-coumaric and syringic acid), can reduce seedling dry weight, leaf expansion, and water utilization of cucumber seedlings in a similar manner. The magnitude of impact of each of the phenolic acids, however, varied with phenolic acid and concentration. It appears that the inhibitory activity of these phenolic acids involved water relations of cucumber seedlings, since the phenolic acid treatments resulted in closure of stomata which then remained closed for several days after treatment. The data also demonstrated that the effects of mixtures of phenolic acids on cucumber seedlings may be synergistic, additive, or antagonistic. The type of response observed appeared to be related to the factor measured, the compounds in the nmixture, and the magnitued of inhibition associated with each compounds. The data also indicated that the effects of the various phenolic acids were reversible, since seedling leaf area increased rapidly once phenolic acids were removed from the root environment. Mean relative rates of leaf expansion recovered even in the presence of the various phenolic acids.

Localization and speciation of selenium and mercury in Brassica juncea—implications for Se–Hg antagonism

The occurrence and form of selenium and mercury were investigated in Indian Mustard, Brassica juncea, a selenium accumulating plant, which had been co-exposed to varying concentration levels of these two elements. Plants were grown and exposed in hydroponic solutions. Following exposure, root exudates were collected in fresh solutions and the head-space around the aerial portions of the plants was sampled. These samples and the harvested plant tissues were then processed for determination of Se and Hg-containing compounds. For the plant tissues, roots, stems and leaves were separated and extracted using a sequential procedure that removed water-soluble species, water-soluble proteins, and dodecyl sulfate-soluble proteins. Size exclusion chromatography allowed further fractionation. High molecular-weight selenium/mercury-containing compounds were found primarily in the plant root extract. Evidence suggests that a Se and Hg complex of high molecular weight may be protein associated. For the analysis of exudate solutions, ion-pairing reversed phase chromatography coupled to ICP-MS was used. Multiple selenium and mercury species were detected, with one mercury-containing compound observed eluting near selenocystine. Plant head-space was sampled with solid phase microextraction and analyzed with GC-ICP-MS and GC-TOFMS. Apart from the primary selenium volatiles and elemental mercury, no volatile species simultaneously containing Se and Hg could be detected.

The uptake of ferulic and p-hydroxybenzoic acids by Cucumis sativus

Abstract The uptake of ferulic acid (FA) and p -hydroxybenzoic acid ( p -HBA) from solutions (0.1–1.0 mM, pH 4.0–7.0), was determined for intact and ex

Effects of ferulic andp-coumaric acids in nutrient culture of cucumber leaf expansion as influenced by pH

Cucumber seedlings were grown in 5 mM MES [2-(N-morpholino)ethanesulfonic acid] -buffered nutrient solutions adjusted to a pH of 5.5, 6.25, or 7.0. Nutrient solutions were changed on alternate days. Seedlings were treated for a two-day period with various concentrations (0–1 mM) of ferulic acid,p-coumaric acid, or mixtures of these phenolic acids when 16 days old. Leaf growth, dry weight, and water utilization of the seedlings; pH of the solutions; and disappearance of the phenolic acids from nutrient solutions were monitored. Leaf area expansion of cucumber seedlings was inhibited by both ferulic andp-coumaric acid, and the magnitude of these inhibitions was influenced by concentration and pH. Inhibition of leaf area expansion was greater at pH 5.5 and nominal at pH 7.O. Ferulic acid was more inhibitory thanp-coumaric acid. The effect of pH on growth was best described by data for mean relative rates of leaf expansion. For example, the mean relative rates of leaf expansion by both acids at 0.5 mM for the 16- to 18-day growth period (treatment period) were reduced by 45, 31, and 8% for the pH 5.5, 6.25, and 7.0 treatments, respectively. The dry weight of seedlings at harvest (day 22) was significantly reduced for seedlings grown in the pH 5.5 and 6.25 treatments, but not for the pH 7.0 treatment. There was, however, one exception; the dry weight of seedlings treated withp-coumaric acid solutions adjusted to a pH of 5.5 was not significantly reduced. Water utilization by the seedlings was reduced by both ferulic andp-coumaric acid. Again, the impact of ferulic acid was greater thanp-coumaric acid. The effect of ferulic acid on water utlization decreased with increasing pH of the nutrient solution. The pH effects were not so consistent forp-coumaric acid. The effects of equimolar mixtures of the two phenolic acids were additive for all variables measured. There was a linear correlation between mean relative rates of leaf expansion and water utilization.

The role of plants and plant/microbial systems in the reduction of exposure

The activities of plants and plant/microbial associations may offer a viable means of accomplishing the in situ remediation of contaminated soils. Two uses of plants for phytoremediation are reported here. In one set of studies, the ability of plants to foster degradative microorganisms was investigated. Results indicated that the degradation of several chlorinated pesticides increased in rhizosphere soil and that this same increase occurred when unplanted soils were given materials released from plant roots. In current investigations, the potential for plants to remove and accumulate metals from their environment is being considered. This work employs a unique testing system, the target-neighbor method, that allows evaluation of how planting density influences metal uptake. Results of these studies could provide the information needed to manipulate plant density for optimization of metal removal (remediation of metal-contaminated soil) or minimization of the amount of toxic metals in important crops (reduction of human exposure).

Enzyme Activities as Indicators of Municipal Solid Waste Compost Maturity

Composts of municipal solid waste in a commercial scale facility were assayed for enzymatic activities over time. The main enzymes assayed in this study were alkaline phosphatase, acid phosphatase, endo-cellulase, glucosidase, and lipase (C10). The biomass was measured by using lipid phosphate as a measure of the amount of cellular membranes, and metabolism was measured by the amount of 14C-acetate incorporated into the lipid phosphate pool. All tests followed steady trends which show promise for use as possible stability and maturity indicators. Cellulase activity appears to be a good indicator of stability. The lipase activity appears to be a good indicator of compost maturity. A simple test strip (Api-Zyme from Api Analytab Products, Plainview, New York) was also used and compared to the standard enzyme assay methods. Api-Zyme and standard methods gave comparable results. The use of specific enzymatic activities presents an inexpensive and fast method, which may be combined with others, to predict a co...

Rapid breakdown of brominated flame retardants by soil microorganisms

Polybrominated diphenyl ethers (PBDEs) have been extensively and successfully used as fire retardants in a multitude of products. However, due to their aromatic components and toxicological properties, they are assumed to be persistent environmental pollutants and a popularly-used commercial mixture, DE-71, has been removed from American and European marketplaces. However, our current work shows mixed bacterial cultures, derived or extracted from soils experimentally contaminated with DE-71, were capable of utilizing these as a sole carbon source. Most notably, almost complete loss of parent compounds takes place within a few minutes. Determining pathways was hindered by both the speed of the microbial degradation and the low water solubility of the congeners, complicating detection. The bacterial enrichment communities have been characterized using DGGE analysis and DNA sequencing. Element-specific detection was coupled to ion chromatography and only one degradation product detectable by ICP-MS, the bromide ion, was found. Additionally, samples were analyzed by GC/TOF-MS using a mass-defect-based digital noise filtering technique to facilitate observation of bromine-containing unknowns and ESI-MS was used to identify the non-volatile brominated unknown peaks. However, low concentrations (100 μg L−1 initial fortification and substantially lower levels of theorized by-products) prohibited successful compound identification.

Investigation of selenium-containing root exudates of Brassica juncea using HPLC-ICP-MS and ESI-qTOF-MS

Selenium-containing root exudates were investigated in a known selenium accumulator model plant. Indian mustard (Brassica juncea) plants were grown hydroponically and supplemented with selenite (SeO(3)(2-)) in a 25% Hoaglands nutrient solution. Additive concentrations were 0, 1, 5 and 20 microg mL(-1) Se with five replicate plants per treatment level. Plants were exposed to the respective Se solutions for two weeks, then placed in deionized water for two more weeks. The hydroponic solutions were collected for analysis after the first two weeks of selenium supplementation (day 14) and twice during the deionized water period (days 21 and 28). Separation by ion-pairing high performance liquid chromatography was followed by inductively coupled plasma-mass spectrometry (ICP-MS) for selenium specific detection. Chromatographic peaks unable to be identified by retention-time matching were collected for analysis by electrospray ionization mass spectrometry (ESI-MS). Additional chemical experiments were performed for structural elucidation. Several selenium-containing compounds were identified in the exudate-containing solution and two were identified as selenocystine and the selenosulfate (SSeO(3)(2-)) ion. The presence of dimethylselenide (CH(3)SeCH(3)) is also observed but cannot be attributed exclusively to plant exudation because plants were not grown in sterile conditions. Further, the incorporation of fortified selenoamino acids into peptide structures was found to occur under neutral pH conditions, suggesting that exuded enzymes might facilitate such a reaction. Finally, physiological differences resulting from selenium supplementations were noted and discussed.

Management Practices and Phytoremediation by Native Grasses

Using native species for phytoremediation may be more ecologically beneficial and cost-effective than monoculture planting approaches. This study evaluated the effect of various soil amendments and management on the potential of Midwestern prairie grasses to remediate field soil contaminated with polycyclic aromatic hydrocarbons (PAHs) and other pollutants. A greenhouse investigation was conducted using six different grass species native to Ohio. Plants were grown in buckets containing topsoil and a layer of field-collected contaminated soil. Buckets were amended with commercial compost, fertilizer, or a combination of both. Replicates were watered every fourth day (frequently) or every sixth day (infrequently). Chlorophyll content were measured monthly for five months during the growing season. After five months, cores were sampled from each treatment and the total petroleum hydrocarbon (TPH) and PAH concentration of the soil determined. Native Ohio grasses reduced TPH contamination at least 87% with frequent irrigation and 90% with infrequent irrigation from buckets containing both compost and fertilizer. PAHs were dissipated to concentrations below detection limit of 1 ppm except for benzo (123) perylene and indeno (123-cd) pyrene. Results of this study suggest that it may be effective to allow contaminated sites to re-vegetate with native grasses.