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Soil microorganisms play a vital role in increasing the availability of phosphorus (P) for plants through mineralization of organic P and solubilization of precipitated P compounds. In this two-year study, we analyzed several P-solubilizing microorganisms (PSMs) of the genus Bacillus and their consortiums for the ability to release soluble P from apatite concentrates of various grinding degrees using ryegrass (Lolium multiflorum Lam.) as a model plant. The effects were accessed by analyzing plant growth and nutrient assimilation. The greatest effect on root system development and plant biomass accumulation (dry weight) was observed for the apatite concentrate of standard grinding in combination with Bacillus megaterium BI14 and Bacillus subtilis BI2 and Bacillus velezensis BS89 strains. Although the introduction of apatite concentrates led to an increase in the content of total strontium in soil, the levels of strontium did not exceed the maximum allowable concentration, and the accumulation of mobile strontium by plants was unchanged; importantly, the use of tested PSMs led to a decrease in the strontium content in the green biomass of ryegrass. Our results indicate that biologized apatite concentrates in combination with PSMs represent promising fertilizers that can provide a source of soluble P to be readily assimilated by plants. [ABSTRACT FROM AUTHOR]

[Objective] to provide the suitable turfgrass varieties for soil bioremediation in Hg2+ contaminated region. [Method] The leaf chlorophyll content, Fv/Fm, soluble sugar content, SOD activity, MDA content, leaf relative conductance and N, P and K accumulation characteristics of four tested turgrass varieties were determined by a pot simulation experiment of Hg2+ stress. [Result] With increase of Hg2+concentration, the leaf chlorophyll content, Fv/Fm and N, P and K accumulation declined continuously, soluble sugar content and SOD activity showed a first rising and then declining trend, and MDA content and leaf relative conductance increased continuously. The leaf chlorophyll content, Fv/Fm, soluble sugar content, SOD activity and N, P and K accumulation of four turgrass varieties under 75-100 mg/kg Hg2+ stress reduced significantly compared with CK but MDA content and relative conductance increased significantly. High Hg2+ concentration had the significant effects on leaf cell membrane permeability and N, P and K accumulation of seedlings of four tested turfgrass varieties, which severely inhibited plant growth and causes death of plants. [Conclusion] The annual ryegrass variety (Shengyan) with the strongest tolerance to Hg2+ stress among four tested turfgrass varieties can be selected as the optimized tufgrass variety for bioremediation of Hg2+-contaminated soil. [ABSTRACT FROM AUTHOR]

Lead (Pb) is one of the ubiquitous soil contaminants. The strategy to increase Pb phytoremediation is of highly critical considering the difficulty in phytoextraction of Pb due to its low solubility and high retention on soil particles. The effects of application nano hydroxyapatite (NHAP) on Pb phytoextraction by ryegrass ( Lolium Perenne L.) were evaluated. Ninety pots of Pb-contaminated soil with different Pb concentrations (0–800 mg/kg) were seeded with ryegrass. The effects of NHAP on biomass and Pb uptake were examined. The results indicated that the application of 5 g/kg NHAP to Pb-contaminated soils significantly increased the ryegrass biomass. The removal rates of Pb from the soil by ryegrass were enhanced obviously after NHAP addition. These results suggested that NHAP was suitable for application to in-situ Pb-contaminated soils for remediation. The observation in this study provides useful information about the effects of NHAP on lead removal, which plays an important role in the phytoremediation. [ABSTRACT FROM AUTHOR]

Improvement of soil water capacity is a critical technology to decrease the plant growth restriction by water stress in the arid and semi-arid region. The influences of biochar amended soils (which were incubated for 11 months) on the ryegrass growth at different clipping stages and water stress conditions were determined. Biochar amendment did not influence the plant germination. Better improvement effects on plant height and biomass were found in the Shahuang soil (M soil) with lower fertility than that in the Dark Loessial soil (B soil) at the first clipping stage and under different water stress condition at the second clipping stage. The biochar application rate of 8 g kg-1 appeared to get better improvement effects than the control and 16 g kg-1. This study showed that biochar application could be used as the soil amendment in the Loess Plateau to weaken the restriction of water shortage and promote plant growth. [ABSTRACT FROM AUTHOR]

The effect of clipping height on ryegrass regrowth was investigated by examining the roles of several plant hormones. Our study consisted of three treatment conditions: (1) darkness over whole plants, (2) darkness only over stubble leaf sheaths, and (3) light over whole plants. Results showed that under darkness over whole plant, low stubble height resulted in low leaf regrowth biomass. Similar leaf regrowth biomass was observed under conditions of darkness only over stubble leaf sheaths as well as light over whole plants. Each unit weight of stubble at different clipping heights has relatively similar potential of providing stored organic substance for leaf regrowth. Therefore, regrowth index, calculated as newly grown leaf biomass divided by unit stubble weight, was used to evaluate regrowth capacity at different clipping heights under minimal influence of organic substances stored in stubbles. Under light over whole plants and single clipping, low stubble height and high stubble height with root thinning resulted in low leaf biomass and high regrowth index. On the other hand, under light over whole plants and frequent clipping high leaf biomass and regrowth index were observed in high stubble height. In addition, we found that leaf zeatin and zeatin riboside (Z + ZR) affected ryegrass regrowth and that roots regulated leaf Z + ZR concentration. Thus, our results indicate that root-derived cytokinin concentration in leaves influences ryegrass regrowth at different clipping heights. [ABSTRACT FROM AUTHOR]

Abstract: Manganese (Mn) toxicity limits plant growth in acid soils. Although Mn toxicity induces oxidative stress, the role of superoxide dismutase (SOD, EC.1.15.1.1) isoforms in conferring Mn tolerance remains unclear. Seedlings of ryegrass cultivars Nui (Mn-sensitive) and Kingston (Mn-tolerant) were hydroponically grown at 2.4 (optimal) or 750 μM Mn (toxic) concentration, and harvested from 2 to 48 h. Kingston showed higher shoot Mn than Nui at 2.4 μM Mn. At toxic supply, shoot Mn concentration steadily increased in both cultivars, with Kingston having the highest accumulation at 48 h. An early (2 h) increase in lipid peroxidation under Mn excess occurred, but it returned (after 6 h) to the basal level in Kingston only. Kingston exhibited higher SOD activity than Nui, and that difference increased due to toxic Mn. In general, Mn-induced gene expression of Mn- and Cu/Zn-SOD isoforms was higher in Nui than Kingston. Nevertheless, under Mn excess, we found a greater Fe-SOD up-regulation (up to 5-fold) in Kingston compared to Nui. Thus, Fe-SOD induction in Kingston might explain, at least partly, its high tolerance to Mn toxicity. This is the first evidence that Mn toxicity causes differential gene expression of SOD isoforms in ryegrass cultivars in the short-term. [Copyright &y& Elsevier]

Abstract: In this study, a novel experimental setup (one pot placed above another) was used to investigate the residual effects of EDDS application on plant growth and metal uptake. Two plant species, garland chrysanthemum and ryegrass, were grown in the upper pots (mimicking the upper soil layers) and were harvested 7days after EDDS application. During this period the upper pots were watered twice. The lower pots (mimicking the subsoil under the upper soil layers) served as leachate collectors. Thereafter, the two pots were separated, and the same plants were grown in the upper and lower pots in two continuous croppings. Results showed that EDDS application restrained the growth of the first crop and resulted in a dramatic enhancement of Cu accumulation in plants grown in the upper pots. However, no negative growth effects were identified for the second and third crops, which were harvested 81 and 204days after the EDDS application, respectively. In the lower pots, the leachate from the upper pots after EDDS application exhibited the increased total and CaCl2-extractable Cu concentrations in the soil. However, the growth of garland chrysanthemum and ryegrass, and their shoot Cu concentrations were unaffected. These data suggest that the residual risk associated with EDDS application was limited, and that subsoil to which EDDS leachate was applied may exhibit reduced Cu bioavailability for plants due to the biodegradation of EDDS. [Copyright &y& Elsevier]

A pot experiment was conducted in two acidic soils (pH 4.8) with similar properties except for phosphorus (P) status to investigate the influence of different P fertilizers [Kunyang phosphate rock (KPR), monocalcium phosphate (MCP)] on ryegrass growth and different soil P fractions in the two soils. The P treatments were KPR at 50, 100, and 250 mg P kg-1 and MCP at 50 mg P kg-1. Results showed that the application of P fertilizers produced significant increase of ryegrass growth compared with no P application on soil with low P status. Dry weight of ryegrass did not increase after P application, compared with no P application on soil with high P status. Through P fractionation as modified method of Hedley, Stewart, and Chauhan (1982), inorganic resin P, sodium bicarbonate (NaHCO3) P, and sodium hydroxide (NaOH) P increased after MCP treatment compared with no P application. The PR application only increased resin P and hydrochloric acid (HCl) P. Soil organic P fractions were stable and less affected by P application. The average of KPR P dissolved in the two soils across all P rates was low: only about 19% of the averaged amount of KPR P applied, which was due to its low reactivity. This explains the poor agronomic effectiveness of KPR with respect to MCP. [ABSTRACT FROM AUTHOR]

We investigated the role of selenium (Se) against aluminium (Al) stress in ryegrass by evaluating the growth responses and the antioxidant properties of plants cultured hydroponically with Al (0 or 0.2 mM) and selenite (0–10 µM Se). Al addition significantly reduced the yield and length of shoots and roots, and most Al was accumulated in the roots. Al also enhanced lipid peroxidation and activated the peroxidase (POD), ascorbate peroxidase (APX) and superoxide dismutase (SOD) enzymes in the roots. Se application up to 2 µM improved root growth and steadily decreased thiobarbituric acid reactive substances (TBARS) accumulation in plants treated with 0 and 0.2 mM Al. However, above 2 µM, Se induced stress in plants grown with or without Al. Significant changes in antioxidant enzymes activities were also found as a result of the added Se. At low Se addition levels POD was activated, whereas APX activity decreased irrespective of added Al. Furthermore, Se supplied up to 2 µM greatly decreased root SOD activity in Al-stressed plants. Our study provides evidence that Se alleviated the Al-induced oxidative stress in ryegrass roots through the enhancement of the spontaneous dismutation of superoxide radicals and the subsequent activation of POD enzyme. [ABSTRACT FROM AUTHOR]

The osmotic role of nitrate during aftermath growth of Lolium perenne L. cv. Réveille was investigated. Plants were grown from seed in a controlled environment using a liquid medium with 1.0 mM NH4NO3 as nitrogen source. Eight‐week‐old plants were cut 4.0 cm above the root system and then harvested over a 14‐day period of regrowth on the same initial nutrient solution, except that nitrate was 15N labelled. Throughout the experimental period, nitrate storage and reduction in roots were low. In stubble and especially in leaves, nitrate accumulated during the first 6 days of regrowth whereas nitrate reduction mainly occurred after this period. Analyses of carbohydrate, chloride and potassium contents in stubble and leaves showed that the accumulation of nitrate osmotically compensated for the decrease in soluble sugars during the first 6 days of regrowth. The cumulative osmotic potential of sugars, chloride and nitrate in differently treated plants was studied in stubble and leaves. Compared with uncut plants, the lower carbohydrate concentrations found in cut plants regrowing on 1.0 mM NH4NO3 were compensated for by an accumulation of nitrate. During aftermath growth on low nitrogen nutrition (0.2 mM NH4NO3), chloride replaced nitrate, supporting the proposed osmotic function of nitrate. It is concluded that nitrate is involved in the osmotic adjustment of ryegrass during regrowth after cutting. [ABSTRACT FROM AUTHOR]

• Alkyl chain length affected the uptake of imidazolium based ILs by ryegrass. • A higher uptake efficiency was observed for ILs with a shorter chain length. • A longer alkyl chain length of ILs had a more negative effect on the plant growth. • ILs contents in the roots and leaves decreased with increasing alkyl chain lengths. Imidazolium based ionic liquids (ILs) have been extensively used in the various industrial fields, however, the dependence of their structure on toxicity and bioavailability by plants is not clear. Thus, in this study, uptake of imidazolium based ILs with different alkyl chain lengths (e.g., [C 2 mim]+ and [C 8 mim]+) by ryegrass and their toxicity to plant growth were investigated. Results show that the two ILs could be removed by ryegrass with high efficiencies, and a higher uptake efficiency and accumulation was observed for [C 2 mim]+ with shorter chain length compared with that for [C 8 mim]+. A higher growth inhibition of ryegrass by [C 8 mim]+ was observed compared with that by [C 2 mim]+, indicating the long alkyl chain length of ILs had a negative effect on the plant growth. ILs taken up by ryegrass was retained in the roots and their translocation from roots to shoots was restricted. The IL concentration in roots was 0.68 mg/g-fresh weight for [C 2 mim]+ and 0.08 mg/g- fresh weight for [C 8 mim]+ when the ryegrass was exposed to 10 mg/L ILs. This study proved that plant assimilation of ILs depended on their alky chain lengths, which would be useful for understanding the fate of ILs with various structures in phytoremediation for ILs-contaminated water. [ABSTRACT FROM AUTHOR]