A nursery experiment was conducted to evaluate the potential role of arbuscular mycorrhizal (AM) fungi in encouraging the vegetation cover on bauxite residue (red mud) sites. An alkali tolerant bermudagrass (Cynodon dactylon) adapted to local conditions were grown in red mud with different amendments with and without AM fungi to assess mycorrhizal effects on plant growth, mineral nutrition, metal uptake and neutralization of bauxite residue. Inoculation of AM fungi significantly increased the plant growth, nutrient uptake and reduced Fe, Al accumulation in plant tissue and also improved the soil physico-chemical and biochemical properties. Gypsum and sludge amended treatments inoculated with AM fungi had maximum biomass, nutrient uptake and reduced accumulation of metals. The neutralization of red mud was significant in presence of AM fungi than control. The experiment provided evidence for the potential use of bermudagrass in combination with AM fungi for ecological restoration of bauxite residue sites.

A mixture of common Southern Piedmont (USA) grassland species (Lolium arundinacea, Paspalum dilatatum, Cynodon dactylon and Trifolium repens) was exposed to O₃ [ambient (non-filtered; NF) and twice-ambient (2X) concentrations] and fed to individually caged New Zealand white rabbits (Oryctolagus cuniculus) in a digestibility experiment. Forages and feed refusals were analyzed for concentrations of total cell wall constituents, lignin, crude protein, and soluble and hydrolyzable phenolic fractions. Neutral detergent fiber and acid detergent fiber digestibility by rabbits were significantly lower for 2X than NF forage. Decreased digestibility could not be attributed to lignin concentrations, but was associated with increased concentrations of acid-hydrolyzable and saponifiable phenolics. Exposure of forage to elevated O₃ resulted in decreased digestible dry matter intake by rabbits. Elevated O₃ concentrations could be expected to have a negative impact on forage quality, resulting in decreased nutrient utilization by mammalian herbivores in Southern Piedmont grasslands under projected future climate scenarios.

This research attempted to investigate the plant/soil concentration ratios (CRs) of ¹³⁷Cs and ⁴⁰K in plants that grow on the Anzali Lagoon of the Caspian coast, Iran. The activity concentrations of ¹³⁷Cs and ⁴⁰K were measured in soil samples, annual plants (Echinochloa crus-galli, Digitaria sanguinalis, and Trifolium repens), and perennial plants (Phragmites australis, and Cynodon dactylon). The relationship of activity concentration with soil particle density, and pH of soil samples, CR, and ¹³⁷Cs/⁴⁰K discrimination factor (DF) were determined. The activity concentration of ¹³⁷Cs in the soil, annual plants, and perennial plants ranged between 12- and 124 (Bq/kg dry weight), 2- and 17 (Bq/kg dw), and 2 - and 14 (Bq/kg dw), respectively. The geometric mean (GM) values of DF in annual and perennial plants were 0.57 and 0.55, respectively. The CR for ¹³⁷Cs and ⁴⁰K varied as a non-linear relation in annual plants and perennial plants. This study showed that the CRs for ¹³⁷Cs in annual plants were higher than the CRs for perennial plants.

The reclamation of mine waste deposits is often hindered by the scarcity of natural topsoil. Acid mine drainage sludge (AMDS), as a mass-produced waste in metalliferous mines, is a potential topsoil substitute but had not been validated. In this study, a pot experiment with three plant species was conducted to evaluate the capacity of AMDS to support plant growth, buffer acidification, and immobilize heavy metal(loid)s when reclaiming mine waste rocks. Chemical fertilizer and compost chicken manure were applied to AMDS at different rates to explore their effects on plant growth and the physicochemical properties of AMDS. Results showed that all the plants could survive in AMDS even without fertilization. The contents of heavy metal(loid)s in rhizosphere remained almost unchanged over the experimental period, indicating low leachability of revegetated AMDS. Fertilizers enhanced macronutrients and soil enzyme activities, leading to significant increases in plant biomass. However, owing to manure composting and low richness and diversity of the bacterial community in AMDS, the NH₄⁺-N and bioavailable phosphorus contents were extremely low. Bermuda grass was a suitable pioneer species for reclamation for its better adaptability to nutrient deficiency and heavy metal(loid) stress. Overall, AMDS is a viable soil substitute for mine reclamation due to its capability to support plant growth and environmental safety.

Exogenous application of melatonin to plants is a promising approach for assisted phytoremediation of soil lead (Pb). In this study, we investigated the effects of foliar applications of melatonin to mature bermudagrass (Cynodon dactylon (L.) Pers.), a fast-growing perennial with potential as a non-hyperaccumulator plant for Pb phytoremediation. Following exposure to Pb (3000 mg kg⁻¹) for 30 days, decreases in biomass and chlorophyll production, degradation of thylakoid membranes, reduced photosynthesis and PSII (reaction center of photosystem II) efficiency, and elevated oxidative stress were found. Foliar applications of melatonin to Pb-stressed bermudagrass mitigated these negative effects, restoring photosynthetic pigments and chloroplast ultrastructure, subsequently improving photosynthesis and photochemistry efficiency of PSII. Exogenous melatonin also eliminated the excessive accumulations of reactive oxygen species (ROS) and methylglyoxal (MG) which associated with cellular redox homeostasis by improving ascorbic acid (AsA) and reduced glutathione (GSH) contents, redox status of GSH/GSSG (oxidative glutathione), and key enzymes activities in both AsA-GSH and glyoxalase systems. Ultimately, treating bermudagrass plants with exogenous melatonin elevated biomass production and disproportionally greater Pb translocation to roots and senescent leaves. This collectively resulted in 21% greater recovery of Pb compared to Pb-stressed bermudagrass lacking melatonin application. Overall, results from this study demonstrated the beneficial roles of melatonin for improving the effectiveness of bermudagrass as a non-hyperaccumulator plant for soil Pb phytoremediation.

Vegetation restoration is one of the most effective measures to restore degraded ecosystem in mining wasteland. A field experiment was conducted to study the effects of some site treatments’ three different approaches on the benefits of selective vegetation in the manganese mine. Three different approaches included (1) exposed tailings, the control treatment (tailing site); (2) soil covering of 10-cm thickness (external-soil site), and (3) soil covering of 10-cm thickness, soil ameliorating (adding fowl dung), and seeding propagation of Cynodon dactylon (Linn.) Pers. (rehabilitation site). The results indicated that 18 herb species were taken from 8 families and 4 woody plants in three sites after 1 year. After 3 years, 29 species from 14 families were observed in 3 sites. Meanwhile, compared with tailing site, the plant species of rehabilitation site was more than tailing site, and the plant abundance of external-soil site was similar to rehabilitation site. It was worthy to be mentioned that the plant species of external-soil site and rehabilitation site had a better effect on the plant community coverage of herb layer as compared with tailing site. In summary, the plant species of rehabilitation site had the most species diversity and could be recommended as the ve-restoration modes in manganese tail wasteland.

Some Pseudomonas fluorescens strains, consistently isolated from the rhizosphere of wild plants grown in a soil that was highly polluted with illegal waste of smelter residues, were utilised for Mirabilis jalapa seed bioinoculation to verify their effects on seed germination and on promoting a higher heavy metal accumulation in the plant rhizosphere and/or uptake in the leaves. The high content of heavy metals in the soil induced a decrease in either the leaf dry weight or photosynthetic pigment concentration during all vegetative phase of M. jalapa. Bioinoculation with P. fluorescens strains significantly increased the germination of seeds and the root length in the contaminated soil. In some bacterial strain/seed combination, bioinoculation significantly increased the accumulation of heavy metals in M. jalapa rhizosphere. For Cd, the concentration of this metal in the rhizospheres of bioinoculated plants ranged from 270 to 910 μg g-1 of dry weight compared with 200 μg g-1 of dry weight for the non-coated plants. Two P. fluorescens strains, AA27 and MO49, which were isolated from Artemisia annua and Melilotus officinalis, respectively, induced a significantly higher rhizosphere availability also for Cr, Cu, Ni and Zn. However, despite the relevant accumulation of the heavy metals in the plant rhizosphere, generally the metal uptake into the leaves was rather low. Both analysis of variance and principal component analysis confirmed this finding. However, one P. fluorescens strain, CD1, which was isolated from the multi-metal accumulator Cynodon dactylon, significantly promoted the M. jalapa leaf uptake for Cr, Cu and Zn. The plant metal uptake assessment, confirmed the per se capability of M. jalapa to effectively uptake Cd (30 %) and Cu (12.72 %) from the rhizosphere to the leaves, whereas the uptake for the other metals was low: Ni (2.66 %), Zn (2.46 %), Cr (1.75 %), Pb (0.73 %). © 2013 Springer Science+Business Media Dordrecht.

Phytoremediation is a method in which plants, soil microorganisms, amendments, and agronomic techniques interact to enhance contaminant degradation. We hypothesized that bermudagrass (Cynodon dactylon L) and an appropriate amount of N fertilizer would improve remediation of pyrene-contaminated Captina silt loam soil. The soil was contaminated with 0 or 1,000 mg pyrene/kg of soil and amended with urea at pyrene-C:urea-N (C:N) ratios of 4.5:1, 9:1, 18:1, or unamended (36:1). Either zero, one, two, or three bermudagrass sprigs were planted per pot and -33 kPa moisture potential was maintained. Pyrene concentrations, inorganic-N levels, shoot and root parameters, and pyrene degrader microbial numbers were measured following a 100-day greenhouse study. At a C:N ratio of 4.5:1, the presence of plants increased pyrene biodegradation from 31% for the no plant treatment to a mean of 62% for the one, two, and three plant treatments. With no plants and C:N ratios of 4.5:1, 9:1, 18:1, and 36:1, the mean pyrene biodegradation was 31, 52, 77, and 88%, respectively, indicating that increased inorganic-N concentration in the soil reduced pyrene degradation in the treatments without plants. Additionally, none of the one, two, or three plant treatments at any of the C:N ratios were different with a mean pyrene degradation value of 69% after 100 days. Pyrene resulted in reduced shoot and root biomass, root length, and root surface area, but increased root diameter. The pyrene degrading microbial numbers were approximately 10,000-fold higher in the pyrene-contaminated soil compared to the control. At the highest N rate, bermudagrass increased pyrene degradation compared to the no plant treatment, however, in the unvegetated treatment pyrene degradation was reduced with added N.

Wastewater land application is a cost-effective method to treat and dispose wastewater; however, it may cause soil salinization. Salt mass balance and the potential soil salinization caused by the wastewater land application were investigated in the crop root zone in a wastewater land application system at the City of Littlefield, TX, USA from October 7, 2005 to September 28, 2007 using a lysimeter system. This study showed that, after 2 years of wastewater land application, the ranges of soil salinity were still lower than the threshold (8,500 μS/cm) for Bermuda grass assuming a 10% yield reduction. The leached salt mass showed large spatial and temporal variation. The average values of electrical conductivity of the saturated paste extract of the soil samples increased from 1,433 μS/cm in June 2006 to 1,840 μS/cm in June 2007. The average values of the soil sodium adsorption ratio between June 2006 and June 2007 increased from 11 to 14 resulting in a potential risk of soil dispersion and decreasing the soil infiltration rate. Although the measured leaching fractions in nearly all sampling periods, except one, were higher than the leaching requirement, salt accumulations in the root zone were still found with only two exceptions. Since the time required for reaching equilibrium between cumulative salt mass input and cumulative salt mass output varies from 1 year to a few years, or even longer, the long-term investigation is recommended for the study of salt mass balance in the root zone of this wastewater land application system.