Soil Pot Experiments Research Articles

Enhanced phytoremediation of petroleum-contaminated soil by biochar and urea

Application of bioremediation in petroleum-contaminated soils is limited by its low efficiency. Although biochar and urea are commonly used soil additives, their potential beneficial effect on the bioremediation of petroleum contamination have rarely been discussed. In this study, biochar and urea were combined to test their effects on the phytoremediation of petroleum-contaminated soil in pot experiments. Our results showed that the degradation rate of total petroleum hydrocarbons reached 49.6%, 38.3%, 42.5%, and 77.9% when the soil was treated with biochar, urea, ryegrass, and their integrated application treatment (PBCN), respectively. A number of soil physicochemical properties (e.g., pH, elements, aggregate distribution, and organic matter composition) altered by the treatments were found to be linked to the accelerated degradation of petroleum hydrocarbons. The activities of soil dehydrogenase, lipase, and urease, and the abundances of 16 s rRNA gene and alkane degradation-related genes could be increased simultaneously when biochar, urea, and ryegrass were co-applied. Furthermore, urea significantly reduced soil bacterial α-diversity, while soil bacterial community dissimilation was mainly driven by urea and ryegrass. Lysobacter, xanthomonadaceae, and longimicrobia could be biomarker species in the PBCN group. Soil bacterial network analysis showed that biochar and urea application decreased the network complexity and robustness, while ryegrass behaved inversely. Lastly, soil metabolomic analysis revealed that root soil metabolites were greatly affected by urea-addition during phytoremediation, and co-application of biochar and urea could activate the putative metabolism pathway of petroleum hydrocarbons in root soil (e.g., naphthalene and anthracene degradation, and pyruvate metabolism). In summary, this study confirmed the enhancement of biochar and urea application in the phytoremediation of petroleum-contaminated soil and explored the internal mechanism of the interactive effect, which can potentially improve the development of eco-friendly and cost-effective in-situ bioremediation technology for petroleum-contaminated soils.

Effects of Different Sulfur Compounds on the Distribution Characteristics of Subcellular Lead Content in Arabis alpina L. var. parviflora Franch under Lead Stress.

Sulfur plays a vital role in the phytoremediation of lead-contaminated soil. The effects of different sulfur forms (S Na2S, and Na2SO4) on lead (Pb) absorption in hyperaccumulator Arabis alpina L. var. parviflora Franch were studied in a soil pot experiment. The subcellular sulfur and lead enrichment characteristics in A. alpina were studied by adding sulfur in different forms and concentrations (0, 75, and 150 mg·kg-1) to Pb-contaminated soil. The results show that the root and shoot biomass increased by 1.94 times under Na2S and Na2SO4 treatment, and the root-shoot ratio of A. alpina increased 1.62 times under the three forms of sulfur treatments, compared with the control. Sulfur content in cell walls and soluble fractions of the root and shoot of A. alpina significantly increased 3.35~5.75 times and decreased 5.85 and 9.28 times in the organelles under 150 mg·kg-1 Na2SO4 treatment. Meanwhile, Pb content in the root and shoot cell walls of A. alpina significantly increased by 3.54 and 2.75 times, respectively. Pb content in the shoot soluble fraction increased by 3.46 times, while it significantly reduced by 3.78 times in the shoot organelle. Pb content in the root organelle and soluble fraction decreased by 2.72 and 2.46 times. Different forms and concentrations of sulfur had no regularity in the effect of Pb and sulfur content in the subcellular components of A. alpina, but the bioconcentration and translocation factors of A. alpina increased compared with the control. Under different concentrations of Na2SO4, there was a significant positive correlation between the contents of sulfur and Pb in the subcellular components of the root of A. alpina (p < 0.05). These results indicate that sulfur application can enhance the Pb resistance of A. alpina by strengthening the cell wall fixation and vacuolar compartmentalization.

Effects of single and combined applications of three root exudates of Sedum plumbizincicola on the phytoremediation efficiency of paddy soil contaminated with Cd

Root exudates are carriers for the transfer of material, energy and information between plant roots and soils. Plants encountering environmental stresses such as heavy metal pollution adapt to the environment by producing and secreting root exudates. In this study, laboratory soil culture experiment and pot experiment with Sedum plumbizincicola were used to study the effects of single and combined application of three root exudates, citric acid, glycine, and fructose, on the Cd-activation and phytoremediation of Cd-contaminated paddy soil. Results from the soil culture experiment showed that for the single application of root exudates, all three root exudates significantly activated the Cd in soil as presented by the increased content of diethylenetriamine pentaacetic acid extracted Cd (DTPA-Cd). In Particular, citric acid (SC) at a relatively low concentration (2 mmol/kg) exhibited the best Cd activation efficiency by increasing DTPA-Cd in the soil by 66.12%. For the combined application of root exudates, citric acid in combination with glycine (SC + G, 1:3) had the best activation effect on the Cd in the soil. In the phytoremediation pot experiment, both the single application of citric acid at a low concentrate (1 mmol/kg) and the combined application of citric acid and glycine (1:1) significantly reduced the total Cd and DTPA-Cd in the soil and increased the biomass and the content of Cd in S. plumbizincicola; thus, the phytoremediation efficiency of Cd-contaminated soil increased by 42.33% and 35.61%. The results from this study suggest that citric acid plays a crucial role in Cd activation and phytoremediation with single or combined applications with glycine. However, the mechanisms under the synergetic interaction between citric acid and glycine require further investigation.

Evaluating the release and metabolism of ricinine from castor cake fertilizer in soils using a LC-QTOF/MS coupled with SIRIUS workflow

Castor cake is a major by-product generated after castor oil extraction and has been widely used as an organic fertilizer. Once applied to soil, a toxic alkaloid ricinine in castor cake may be released into soils and subsequently taken up by crops, which poses a potential threat to food safety and human health. However, the environmental fate of castor cake derived ricinine in agroecosystems remains unclear. In this study, the release and metabolism of ricinine in soils were conducted using soil pot experiments with different castor cake application rates. The analytical methodology of ricinine quantification in soil pore water was first established using solid phase extraction (SPE) coupled with liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QTOF/MS). A non-target screening workflow associated with LC-QTOF/MS and SIRIUS platform was further developed to identify ricinine metabolites in soil pore water. After castor cake application, the ricinine concentrations in soil pore water significantly increased to 297–7990 μg L−1 at 1 day and then gradually decreased to 62.1–3460 μg L−1 at 7 days and 1.70–279 μg L−1 at 14 days for the selected two tested soils with castor cake application rates of 2, 10, and 20 g castor cake/kg soil. In addition, two ricinine metabolites R-194 and R-180 were tentatively identified and one ricinine metabolite N-demethyl-ricinin was confirmed through authentic reference standard for the first time by the developed non-target screening workflow. This study highlights the release and metabolism of toxic alkaloid ricinine in soils once applied castor cake as an organic fertilizer. Ricinine could be released into soil pore water in a short-term after castor cake application and then undergo demethylation, hydroxylation, and hydroxylation followed by methylation metabolisms over time in agroecosystems.

Foliar Spraying of Mannose Alleviates Cadmium Stress by Changing the Subcellular Distribution and Chemical Forms of Cadmium in Wheat Root

Cadmium (Cd)-contaminated soil has been receiving increasing attention worldwide due to the great harm it causes via food-chain enrichment through crops such as wheat. However, there is little research regarding the effects of mannose (MAN) on plants in response to Cd stress. Hence, hydroponic and potted soil experiments were conducted to investigate the mitigation effects of MAN on wheat under Cd stress and the possible mechanism. Compared with Cd treatment alone, foliar spraying of 160 μM MAN significantly reduced the Cd accumulation in shoots and increased the Cd retention in roots. The content of hemicellulose was increased by MAN treatment, and the proportion of Cd retained by hemicellulose in the cell wall of roots was increased. Furthermore, 160 μM MAN significantly reduced the water-extracted and ethanol-extracted Cd in roots, which are easily transported to shoots. In potted soil experiments using Cd-contaminated soil, MAN reduced the Cd content in wheat grain by 26.3%, compared with the control. These findings indicate that foliar spraying of 160 μM MAN resulted in less Cd being transported from roots to shoots by increasing the Cd retention in the cell wall and changing the Cd chemical forms in roots, which promoted wheat growth and reduced the Cd concentration in wheat grain.

Calcium alginate-biochar composite as a novel amendment for the retention and slow-release of nutrients in karst soil

Soil erosion is a prominent environmental problem in karst areas. To reduce the loss of nutrients in karst soil, two kinds of calcium alginate-biochar composites (CA-MBs) were synthesized. Soil column leaching and pot experiments under different treatments were carried out to investigate the retention and slow-release of CA-MBs on nutrients. The results showed that the retention effects of calcium alginate-rice straw biochar composite (CA-MRB300) and calcium alginate-Eupatorium adenophorum biochar composite (CA-MEB600) on nutrients under fertilization were better than that under non-fertilization. The addition of 0.5 wt% CA-MRB300 and CA-MEB600 reduced the loss of nutrients after fertilization, and 0.5 wt% CA-MRB300 reduced the cumulative leaching amount of PO43-, NH4+, NO3-, and K+ by 48.05%, 28.76%, 36.63%, and 9.08%, respectively. Surface precipitation, ion exchange, and physical adsorption were considered to be the main retention mechanisms of different nutrients based on analyzing the physicochemical properties of CA-MBs and their effects on soil physicochemical properties. The addition of 1.5 wt% CA-MRB300 had the best promotion effect on the root length, stem length, and dry weight of soybean under non-fertilization, indicating that CA-MRB300 could be used as a slow-release fertilizer to promote the growth of soybean. This study develops a novel soil amendment to reduce the loss of nutrients in karst soil.

Effects of composite environmental materials on the passivation and biochemical effectiveness of Pb and Cd in soil: Analyses at the ex-planta of the Pak-choi root and leave

Passivation of soil heavy metals using environmental materials is an important method or important in situ remediation measure. There are more studies on inorganic environmental materials for heavy metal passivation, but not enough studies on organic and their composite environmental materials with inorganic ones. In order to reveal the passivation effect of coal-based ammoniated humic acid (CAHA), biochemical humic acid (BHA), biochar (BC) and other organic types and inorganic environmental materials such as zeolites (ZL) on soil heavy metals and their biological effectiveness. The microstructures of these materials were analyzed by Scanning electron microscope (SEM). The main components of the environmental materials were analyzed by Energy dispersive spectrometer (EDS), Fourier transforms infrared spectroscopy (FT-IR) and X-ray diffraction spectrum (XRD) to elucidate the mechanism of passivation of heavy metals in soil by these environmental materials. The study was conducted to investigate the effects of different types of environmental materials and their combinations on the passivation effect and biological effectiveness of Pb and Cd complex contamination in soil by means of soil incubation and pot experiments using single-factor and multifactor multilevel orthogonal experimental designs. Soil incubation experiments proved that the effective state of soil Pb and Cd in T7 was reduced by 13.40% and 11.07%, respectively. The extreme difference analysis determined the optimized formulation of soil lead and cadmium passivation as BHA: CAHA: BC: ZL = 3.5:5:20:10. The pot experiment proved that the application of composite environmental materials led to the reduction of lead and cadmium content and increase of biomass of Pak-choi, and the optimal dosage of optimized composite environmental materials was 23.1 g/kg.

Effects of four endophytic bacteria on cadmium speciation and remediation efficiency of Sedum plumbizincicola in farmland soil.

Cadmium (Cd) pollution in farmland soils severely affects agricultural production safety, thereby threatening human health. Sedum plumbizincicola is a Cd and Zn hyperaccumulator commonly used for the phytoremediation of Cd-contaminated soil. This study was aimed to improve the remediation effect of S. plumbizincicola on Cd-contaminated farmland soil and provide a theoretical basis for the enhancement of endophytic bacteria in the repair of Cd-contaminated soil with S. plumbizincicola. Four kinds of endophytic bacteria, namely Buttiauxella, Pedobacter, Aeromonas eucrenophila, and Ralstonia pickettii, were used, and soil culture experiments and pot experiments were conducted to explore the effects of endophytic bacteria on soil Cd speciation and phytoremediation efficiency of Cd-contaminated farmland soils. Under the experimental conditions, after inoculation with endophytic bacteria, the soil pH was effectively reduced, content of weak acid-extracted Cd and oxidizable Cd increased, and content of reducible Cd and residual Cd decreased. Soil Cd activity was increased, and the availability coefficient of soil Cd increased by 1.15 to 6.41 units compared with that of the control (CK2). Compared with CK2, the biomass of S. plumbizincicola significantly increased by 23.23-55.12%; Cd content in shoots and roots of S. plumbizincicola increased by 29.63-46.01% and 11.42-84.47%, respectively; and bioconcentration factor was 2.13 to 2.72 times that of CK2. The Cd removal rate of S. plumbizincicola monocropping was 48.25%. When S. plumbizincicola was planted with inoculating endophytic bacteria, the Cd removal rate in the soil reached 61.18-71.49%, which was significantly higher than that of CK2 (p < 0.05). The treatment with endophytic bacteria activated soil Cd, promoted the growth of S. plumbizincicola, increased its Cd content, and enhanced the phytoremediation of Cd-contaminated farmland soil. Therefore, endophytic bacteria can be used to improve the remediation efficiency of S. plumbizincicola in Cd-contaminated farmland soils.

Improvement of Low-Fertility Soils from a Coal Mining Subsidence Area by Immobilized Nitrogen-Fixing Bacteria

Coal mining subsidence leads to reductions in soil fertility. In order to improve soil physical and chemical properties and to promote vegetation restoration, a nitrogen-fixing bacterium named S1 was isolated from the coal mining subsidence area in the Shendong mining area, and a zeolite-immobilized nitrogen-fixing bacterium was studied to improve the soil in the subsidence area. The results show that the immobilized nitrogen-fixing bacteria can significantly improve the ammonium nitrogen and nitrate nitrogen of soil by 50 times and 0.6 times, respectively, at 20 days, and it can also improve organic matter. In pot experiments, it was found that immobilized microorganisms can improve germination rate, plant height and the dry and fresh weight of maize. The results of the above soil culture tests and pot experiments were then compared and analyzed. It was found that plants made obvious use of soil ammonium nitrogen and nitrate nitrogen, and planting the plants was conducive to increases in soil organic matter.

Potential of potent purple nonsulfur bacteria isolated from rice-shrimp systems to ameliorate rice (Oryza sativa L.) growth and yield in saline acid sulfate soil

In rice-shrimp farming systems, the high level of sodium that shrimps are able to grow in may create an adverse environment for rice. This research aimed to isolate purple nonsulfur bacteria (PNSB) from rice-shrimp fields and select strains that were resistant to H+, Al3+, Fe2+ and Mn2+, that can produce plant growth promoting substances such as 5-aminolevulinic acid, exopolymeric substances, indole-3-acetic acid and siderophores. The selected bacteria were applied in a soil pot experiment to determine their ability to enhance rice growth and yield. From 63 PNSB isolated from 21 paddy fields of rice-shrimp systems, four strains were selected for their properties as biofertilizers and plant growth promoters (PGP). They were all identified as strains of Luteovulum sphaeroides. A randomized complete block design incorporating six treatments was used to investigate the ability of the four PNSB strains to ameliorate rice growth and yield in saline acidic soil with saline water irrigation at 4‰. PNSB cultures at 1.90 × 105 CFU g−1 dry soil weight were applied three times, along with normal chemical fertilizers, and all monitored parameters of rice growth and grain yield significantly improved in soil with a toxic Al3+ content of 10.8 meq 100 g−1. A mixed four cultures most effectively increased grain yield (86.8%) compared with no applied PNSB. Remediation of the pot soil was exhibited in decreased exchangeable Na in soil and proline content in leaves. The four PNSB could act as biofertilizers, PGP and bioremediators with potential to enhance rice yield in rice-shrimp systems for sustainable rice cultivation.

English

This study was to explore the beneficial interactive effects of fungal inoculum alone or in conjunction with phosphatic fertilizer on maize (Zea mays L.). We conducted a greenhouse pot experiment in soil which included four treatments such as control, Penecillium oxalicum, Aspergiilus niger, P. oxalicum + A. niger at three different levels of phosphatic fertilizers (0, 100, and 200 mg kg-1). The plant height, fresh weight of root/shoot biomass and dry weight of root/shoot biomass and soil chemical properties were recorded. We evaluated the growth parameters of maize and phosphorus (P) uptake in maize were highest in treatment I3 × F2 (Penecillium+Aspergillus + 200 mg P kg-1) followed by I2 × F2 (Aspergillus + 200 mg P kg-1) over rest of the treatments. The beneficial effect was decreased where alone fertilizer dose was added as compared to those where it was added with the co-inoculation of phosphorus solubilizing fungi (PSF). It was observed that soil pH, total organic carbon and available P significantly changed because of various treatments. Based on these evidences, it could be inferred that increasing the maize growth by fungal culture improves soil P fertility, which is favorable to succeeding crops. Further research is needed to understand the chemistry of co-inoculation of fungal inoculum with phosphatic fertilizer. © 2022 Friends Science Publishers

Effects of citric acid on antioxidant system and carbon-nitrogen metabolism of Elymus dahuricus under Cd stress

Exogenous citric acid (CA), which acts as an important intermediate product of the tricarboxylic acid (TCA) cycle, can enhance the TCA cycle activity and activate the branched operation of the TCA cycle, thus providing energy required for resistance to adverse conditions. However, the effects of CA application on TCA cycle-related metabolism under cadmium (Cd) were less reported. To investigate the effects of CA on the Cd tolerance of Dahurian wildrye grass (Elymus dahuricus), the growth, Cd accumulation, antioxidant systems and metabolic pathways of leaves and roots were investigated by a potted soil experiment with Cd (50 mg/kg) and CA (4 mmol/L) treatments. The results showed that Cd stress seriously affected growth and induced the production of reactive oxygen in clover leaves and roots, leading to membrane peroxidation and activation of the antioxidant defense system. Exogenous CA could not only effectively relieve the inhibition of Cd stress on growth and reduce the amount of reactive oxygen by increasing the antioxidant capacities but could also promote an increase in root Cd content. Metabolomic results showed that the application of CA increased the contents of sugars, sugar alcohols, and resistant substances, and promoted the metabolism of amino acids including γ-aminobutyric acid (GABA). These alterations contributed the significant enhancement of the Cd resistance, which may be related to the changes in the TCA cycle activity and the metabolism of the shikimic acid pathway in leaves and roots as well as GABA shunt in roots.

Arsenic Accumulation and Physiological Response of Three Leafy Vegetable Varieties to As Stress.

Arsenic (As) in leafy vegetables may harm humans. Herein, we assessed As accumulation in leafy vegetables and the associated physiological resistance mechanisms using soil pot and hydroponic experiments. Garland chrysanthemum (Chrysanthemum coronarium L.), spinach (Spinacia oleracea L.), and lettuce (Lactuca sativa L.) were tested, and the soil As safety threshold values of the tested leafy vegetables were 91.7, 76.2, and 80.7 mg kg−1, respectively, i.e., higher than the soil environmental quality standard of China. According to growth indicators and oxidative stress markers (malondialdehyde, the ratio of reduced glutathione to oxidized glutathione, and soluble protein), the order of As tolerance was: GC > SP > LE. The high tolerance of GC was due to the low transport factor of As from the roots to the shoots; the high activity of superoxide dismutase, glutathione peroxidase, and catalase; and the high content of phytochelatin in the roots. Results of this work shed light on the use of As-contaminated soils and plant tolerance of As stress.

Competitiveness of Bradyrhizobium japonicum inoculation strain for soybean nodule occupancy

The competitiveness of Bradyrhizobium japonicum inoculation strain against indigenous rhizobia was examined in a soil pot experiment. The effect of inoculation strain was evaluated under different soil conditions: with or without previously grown soybean and applied commercial inoculant. Molecular identification of inoculation strain and investigated rhizobial isolates, obtained from nodules representing inoculated treatments, was performed based on 16S rDNA and enterobacterial repetitive intergenic consensus (ERIC) sequencing. Inoculation strain showed a significant effect on the investigated parameters in both soils. Higher nodule occupancy (45% vs. 18%), nodule number (111% vs. 5%), nodule dry weight (49% vs. 9%), shoot length (15% vs. 7%), root length (31% vs. 13%), shoot dry weight (34% vs. 11%), shoot nitrogen content (27% vs. 2%), and nodule nitrogen content (9% vs. 5%) was detected in soil without previously grown soybean and applied commercial inoculant. Soil had a significant effect on the shoot, root and nodule nitrogen content, while interaction of experimental factors significantly altered dry weight and nitrogen content of shoots, roots and nodules, as well as number of nodules. Nodulation parameters were significantly related with shoot dry weight, shoot and nodule nitrogen content. Symbiotic performance of inoculation strains in the field could be improved through co-selection for their competitiveness and effectiveness.

The NtNRAMP1 transporter is involved in cadmium and iron transport in tobacco (Nicotiana tabacum)

Plant natural resistance-associated macrophage protein (NRAMP) plays an important role in maintaining intracellular metal homeostasis and coping with environmental heavy metal stress. Until now, studies on NRAMP in tobacco have been limited. In this study, NtNRAMP1 was cloned from tobacco cultivar TN90, and the highest expression level was observed in the roots, which was strongly induced by Fe deficiency. Heterologously expressed NtNRAMP1 significantly increased the Cd sensitivity of the yeast Δycf1 mutant. Three overexpressed NtNRAMP1 lines were generated to reveal the biofunction of NtNRAMP1. In the soil pot experiments under natural conditions, the contents of Fe and total chlorophyll were increased in the leaves of transgenic tobacco compared with the WT. To reveal the characteristics of NtNRAMP1 in metal transport, transgenic plants were cultured in hydroponic solution with 50 μM Cd and 200 μM Fe. Compared with the WT, the Cd concentrations in transgenic plants increased by 1.26–2.02-fold in the roots. Interestingly, the Cd content in the shoots of transgenic plants was slightly reduced compared with that of the WT. Overexpression of NtNRAMP1 did not promote Fe uptake from the external environment into the roots but enhanced the transfer of Fe from the roots to shoots. Additionally, Fe overload in the leaves of transgenic tobacco resulted in increased levels of MDA and H2O2 while Fe toxicity may be relieved by POD. In conclusion, overexpression of NtNRAMP1 in tobacco could promote Cd uptake and Fe transport from the roots to shoots while disturbing Fe homeostasis in the leaves of transgenic tobacco.

The effects of bio-based superabsorbent polymers on the water/nutrient retention characteristics and agricultural productivity of a saline soil from the Yellow River Basin, China

To investigate the effects of superabsorbent polymers (SAPs) on the water/nutrient retention characteristics and agricultural productivity of a saline soil from the Yellow River Basin, soil column leaching and pot experiments were carried out. Three types of SAPs were used: a commercial SAP (CSAP), a starch-grafted SAP (SGSP), and a modified SGSP (MSSP). Six treatments were set up in the leaching experiment, including MS (MSSP alone was applied), CF (chemical fertilizer alone was applied), CF+CS (chemical fertilizer and CSAP were applied), CF+SS (chemical fertilizer and SGSP were applied), CF+MS (chemical fertilizer and MSSP were applied), and CF+ 70%MS (chemical fertilizer and MSSP were applied, but MSSP dosage was 70% of that in CF+MS). Six treatments were set up in the pot experiment as well, including CK (no fertilizer or SAP was applied), MS, CF, CF+CS, CF+SS, and CF+MS. Results of the leaching experiment showed that water and nutrient leaching loss from the saline soil was reduced by 12.6–22.7% and 14.2–65.0%, respectively, in the treatments with SAP application. In addition, both soil pore number and soil porosity were significantly increased in the 0–10 cm soil layer. In the pot experiment, maize yield was increased by 25.9–32.1% and fertilizer use efficiency was significantly increased with the application of SAP. Taken together, SAP application in the saline soil improved soil moisture and nutritional conditions and promoted crop growth. This work provides a reference for improving crop productivity and water management of the large area of saline soils in the Yellow River Basin.

Two strains of Luteovulum sphaeroides (purple nonsulfur bacteria) promote rice cultivation in saline soils by increasing available phosphorus

Saline soils reduce available phosphorus, retarding plant growth, and rice is particularly affected. We evaluated the ability of purple nonsulfur bacteria to resist the acidic-sodium conditions in saline acid sulfate soil and saline soil, and their ability to enhance rice growth and grain yield by releasing normally unavailable phosphorus. Two P-solubilizing Luteovulum sphaeroides strains were applied to rice seedlings in a soil pot experiment. Single cultures and a mixed (1:1) culture of the strains increased rice growth and grain yield up to 10% in saline acid sulfate soil and 18% in saline soil. After harvest, both inoculated soils showed significantly increased pHH2O but significantly decreased electrical conductivity. The increase in Pavail in both inoculated soils resulted in higher accumulations of P in the rice plants. The need for chemical P fertilizer was reduced by 50% of the recommended application. Both inoculated soil types showed significant increases in NH4+ and potassium. Sodium concentrations in both inoculated soil types were significantly lower than in controls. Proline content in rice from both inoculated soil types was also significantly lower. Rice grain yields were proportional to the inoculated bacterial populations.

Allelopathic effects of native and exotic Prosopis congeners in Petri dishes and potting soils: assessment of the congeneric approach

The congeneric approach assesses the relative role of exotic invasive plants compared to native plants on associated species. However, most studies on seed germination have been conducted in Petri dishes that do not reflect natural soil conditions. Here, we compared the effects of different litter extracts of the exotics Prosopis juliflora (Sw.) DC. and Prosopis pallida (Willd.) Kunth, as well as native Prosopis cineraria (L.) Druce, on seed germination and seedling dry weight of two weedy plants (Amaranthus graecizans L. and Sisymbrium irio L.) and the native Senecio flavus (Decne.) Sch.Bip. in both Petri dishes and potted soil experiments. The results indicate that non-treated seeds (control) of the three species attained more than 95% germination in the Petri dishes (in vitro). The increase in the litter concentrations of both invasive Prosopis species inhibited the native Senecio flavus germination and significantly reduced germination and seedling weight of the weedy A. graecizans and Sisymbrium irio. Nevertheless, the native P. cineraria extracts had significant depressive effects on seed germination and seedling growth of the native Senecio flavus but limited effects on the weedy A. graecizans and Sisymbrium irio. The results support a greater impact of exotic than native congener on native plants. To better assess allelopathic effects, it is recommended to not rely on germination in Petri dishes.

New Evidence of Model Crop Brassica napus L. in Soil Clean-Up: Comparison of Tolerance and Accumulation of Lead and Cadmium.

The potential of the model crop Brassica napus L. (rapeseed) for the phytoremediation of soils polluted with metals was investigated at laboratory scale. The first step consists in the evaluation of the seed germination and growth of the Brassica napus L. plant in a controlled environment, followed by the determination of the photosynthetic pigments content represented by chlorophyll a and b and carotenoids. The degree of metal accumulation in rapeseed has been evaluated by the bioaccumulation factor (BAC), the bioconcentration factor (BCF) and the translocation factor (TF). Phytotoxicity tests were performed in Petri dishes with filter papers moistened with metal solutions in the range of 0 to 300 mg/L Pb(II) or Cd(II). At the highest concentration of the lead and cadmium treatments (300 mg/L), B. napus L. showed the lowest germination degree (56.67% and 43.33%, respectively). According to Tukey test results, Pb(II) concentrations of up to 300 mg/L do not significantly affect the length of the hypocotyls, whereas, in the case of Cd(II), the mean of the radicle and hypocotyl lengths of the seedlings are significantly affected compared to the mean of the control. In soil pot experiments, important changes have been obtained in the pigment content, especially in the case of cadmium. For both metals and for each treatment (100 to 1500 mg/kg Pb(II) and 1 to 30 mg/kg Cd(II)), a TF < 1 indicates an ineffective metal transfer from root to shoot. Finally, rapeseed can be considered a tolerant plant and a suitable candidate for Pb(II) and Cd(II) accumulation and for the phytostabilization of contaminated soil under the experimental conditions adopted in the present study.

Assessment of Ecotoxicity of Incinerated Sewage Sludge Ash (ISSA)

Combustion in fluidised bed boilers is one of the most commonly used methods of treatment of municipal sewage sludge. Fly ash (FA) and air pollution control (APC) residues are the solid by-products generated by flue gas treatment. There are significant differences in the chemical composition of these wastes. FA is composed of mainly SiO2, P2O5, CaO and metals such as Zn, Ti, Cu, Cr, Pb and Ni. APC residues mainly contain SO3 and Na2O. The leachability tests that were carried out indicate that these wastes display very low leachability of heavy metals (for example leachability of Pb was equal 0.0004 mg·dm−3 in both wastes, leachability of Cd was equal 0.0012 mg·dm−3 in FA an 0.00004 mg·dm−3 in APC). On the other hand, very high sulphate concentrations (49,375 mg·dm−3) were found in water extract for the APC residues. In order to determine the toxicity of these wastes for plants, pot experiments with different additions of waste to the soil were carried out (on Lepidium sativum and Sinapis alba). Tests based on seeds germinations (on Lepidium sativum) in water extracts from waste (in different concentrations) were also performed. The results obtained indicate the very high toxicity of APC residues. Complete inhibition of germination and growth of the test plants was found for all concentrations of the tested waste in water extract and for all additions of waste to the soil in pot experiments. Seed germination tests on water extracts from FA did not show any toxicity of this waste. Pot tests with FA showed their toxicity only with a high (30%) addition in soil.