Non-planted Soil Research Articles

Enhancing growth and phytoremediation efficiency of Pennisetum purpureum cv. Mahasarakham in weathered PAH-contaminated soil through thidiazuron application

Polycyclic aromatic hydrocarbons (PAHs) are phytotoxic, which can limit their phytoremediation. When the ability of plants to phytoremediation PAHs is compromised, the application of plant growth regulators can enhance the growth of the plants. This study aimed to determine the best plant growth regulator (1-naphthalene acetic acid, 6-benzyladenine, or thidiazuron) to enhance the phytoremediation ability of sweet grass (Pennisetum purpureum cv. Mahasarakham) when grown in weather PAH-contaminated soil. In a greenhouse study, 0.01 mg/l thidiazuron resulted in the highest growth of sweet grass when compared to the other tested plant growth regulators (dry shoot weight 24.11 ± 1.28 g and dry root weight 0.70 ± 0.02 g). Sweet grass was grown in soil contaminated with PAH, which demonstrated the toxicity to sweet grass by reducing the total chlorophyll (1.01 µg/g fresh weight) and carotenoid (0.28 µg/g fresh weight) contents with proline increased (6.63 µg/g fresh weight). Meanwhile, total chlorophyll, carotenoid, and proline content in leaves of sweet grass grown in non-contaminated soil were 1.68, 0.44, and 5.23 µg/g fresh weight, respectively. When sweet grass was used to phytoremediate PAHs, there were reductions in acenaphthylene (4.69 ± 0.50%), acenaphthene (10.69 ± 1.47%), and phenanthrene (3.61 ± 0.07%), which compared to levels of over 30% in non-planted soil. For the three PAHs, the bioconcentration factors were 1.6 to 2.4, but the translocation factors were below 1, showing limited movement to the aerial parts of the plant, thereby suggesting that the main mechanism is rhizoremediation. Sweet grass is an excellent candidate for PAH remediation, especially when thidiazuron is applied to relieve plant stress.

Assembly processes and co-occurrence of bacterial communities in tree rhizosphere under Pb-Zn contamination

Rhizosphere bacteria are critical for supporting plant performance in stressful environments. Understanding the assembly and co-occurrence of rhizosphere bacterial communities contributes significantly to both plant growth and heavy metal accumulation. In this study, Ligustrum lucidum and Melia azedarach were planted in soils with simulated varying levels of Pb-Zn contamination. The Rhizosphere bacterial communities were investigated by using 16S rRNA gene sequencing. The impacts of Pb-Zn contamination on the diversity and structure of the rhizosphere bacterial community were found to be greater than those of both tree species. The variation in bacterial community structure in both trees was mainly driven by the combinations of Pb-Zn and soil properties. Deterministic processes (non-planted, 82 %; L. lucidum, 73 %; M. azedarach, 55 %) proved to be the most important assembly processes for soil bacterial communities, but both trees increased the importance of stochastic processes (18 %, 27 %, 45 %). The rhizosphere co-occurrence networks exhibited greater stability compared to the non-planted soil networks. Rare taxa played a dominant role in maintaining the stability of rhizosphere networks, as most of the keystone taxa within rhizosphere networks belonged to rare taxa. Dissimilarities in the structure and network complexity of rhizosphere bacterial communities were significantly associated with differences in tree biomass and metal accumulation. These variations in response varied between both trees, with L. lucidum exhibiting greater potential for phytoremediation in its rhizosphere compared to M. azedarach. Our results offer valuable insights for designing effective microbe-assisted phytoremediation systems.

Dissipation kinetics of chlorpyrifos and 3,5,6 trichloro-2-pyridinol under vegetation of different aromatic grasses: Linkage with enzyme kinetics and microbial community of soil

The dissipation of chlorpyrifos (CP) and its hydrolytic metabolite 3,5,6-trichloro-2-pyridinol (TCP) in the soil is crucial for safe agriculture. However, there is still lacking relevant information about its dissipation under different vegetation for remediation purposes. In the present study, evaluation of dissipation of CP and TCP in non-planted and planted soil with different cultivars of three types of aromatic grass viz Cymbopogon martinii (Roxb. Wats), Cymbopogon flexuosus, and Chrysopogon zizaniodes (L.) Nash was examined in light of soil enzyme kinetics, microbial communities, and root exudation. Results revealed that the dissipation of CP was well-fitted into a single first-order exponential model (SFO). A significant reduction in the half-life (DT50) of CP was observed in planted soil (30–63 days) than in non-planted soil (95 days). The presence of TCP in all soil samples was observed. The three types of the inhibitory effect of CP i.e. linear mixed inhibition (increase in enzyme-substrate affinity (Km) and decrease in enzyme pool (Vmax), un-competitive inhibition (decrease in Km and Vmax), and simple competitive inhibition were observed on soil enzymes involved in mineralization of carbon, nitrogen, phosphorus, and sulfur. The improvement in the enzyme pool (Vmax) was observed in planted soil. Streptomyces, Clostridium, Kaistobacter, Planctomyces, and Bacillus were the dominant genera in CP stress soil. CP contamination in soil demonstrated a reduction of richness in microbial diversity and enhancement of functional gene family related to cellular process, metabolism, genetic, and environmental information processing. Among all the cultivars, C. flexuosus cultivars demonstrated a higher dissipation rate of CP along with more root exudation.

Developing a glyphosate-bioremediation strategy using plants and actinobacteria: Potential improvement of a riparian environment

Glyphosate (Gly) and its principal degradation product, the aminomethylphosphonic acid (AMPA) were found in soils from a riparian environment in Argentina. Sixty-five actinobacteria were isolated from these soils, rhizosphere, and plants (Festuca arundinacea and Salix fragilis). The isolate Streptomyces sp. S5 was selected to be used as bioinoculant in a greenhouse test, in which plants, actinobacteria, and their combinations were assessed to bioremediate the riparian soil. The dissipation of both compounds were estimated. All treatments dissipated similarly the Gly, reaching 87–92 % of dissipation. AMPA, dissipation of 38 % and 42 % were obtained by Salix and Festuca, respectively, while they increased to 57 % and 70 % when the actinobacterium was added to each planted system. Regarding the total dissipation, the higher efficiencies for both compounds were achieved by the non-planted soils bioaugmented with the actinobacterium, with 91 % of Gly dissipated and 56 % for AMPA. According to our study, it could be suggested which strategy could be applied depending on the bioremediation type needed. If in situ bioremediation is necessary, the combination of phytoremediation and actinobacteria bioaugmentation could be convenient. On the other hand, if ex situ bioremediation is needed, the inoculation of the soil with an actinobacterium capable to dissipate Gly and AMPA could be the more efficient and easier alternative.

DNA stable isotope probing on soil treated by plant biostimulation and flooding revealed the bacterial communities involved in PCB degradation

Polychlorinated biphenyl (PCB)-contaminated soils represent a major treat for ecosystems health. Plant biostimulation of autochthonous microbial PCB degraders is a way to restore polluted sites where traditional remediation techniques are not sustainable, though its success requires the understanding of site-specific plant–microbe interactions. In an historical PCB contaminated soil, we applied DNA stable isotope probing (SIP) using 13C-labeled 4-chlorobiphenyl (4-CB) and 16S rRNA MiSeq amplicon sequencing to determine how the structure of total and PCB-degrading bacterial populations were affected by different treatments: biostimulation with Phalaris arundinacea subjected (PhalRed) or not (Phal) to a redox cycle and the non-planted controls (Bulk and BulkRed). Phal soils hosted the most diverse community and plant biostimulation induced an enrichment of Actinobacteria. Mineralization of 4-CB in SIP microcosms varied between 10% in Bulk and 39% in PhalRed soil. The most abundant taxa deriving carbon from PCB were Betaproteobacteria and Actinobacteria. Comamonadaceae was the family most represented in Phal soils, Rhodocyclaceae and Nocardiaceae in non-planted soils. Planted soils subjected to redox cycle enriched PCB degraders affiliated to Pseudonocardiaceae, Micromonosporaceae and Nocardioidaceae. Overall, we demonstrated different responses of soil bacterial taxa to specific rhizoremediation treatments and we provided new insights into the populations active in PCB biodegradation.

EFFECT OF RICE PLANT ROOT TTC-REDUCING ACTIVITY ON THE CHEMICAL FORM OF IODINE IN CULTIVATED SOIL SOLUTIONS

Abstract This study aimed to evaluate the effect of rice plant root activity on the chemical form of stable iodine (I) in a cultivated soil solution. Concentrations of I−, IO3− and organic-I were analyzed 4 days after exposure I− or IO3− solutions to each of the cultivated soil surface. When exposed to I−, its concentration in the cultivated soil was approximately the same as that in the non-planted soil. When the rhizosphere was exposed to IO3−, the I− concentration in the soil increased under cultivation conditions. IO3− remained undetected in the soil solution. The organic-I concentration in the cultivated soil solution was higher than that in the non-cultivated soil. Concentrations of organic-I increased under IO3− addition compared to I− addition. A weak positive correlation was observed between the TTC-reducing activity of plant roots, and the total and organic-I concentrations in the soil solution. It was suggested that the amount of organic I formed from IO3− was determined by the reducing activity of the roots.

Assessing Direct and Residual Effects of Cover Crops on the Soybean Cyst Nematode, Heterodera glycines.

Greenhouse experiments were conducted to determine if cover crops directly decrease population densities of the soybean cyst nematode (SCN), Heterodera glycines, and/or have residual effects on reproduction of the nematode on soybean (Glycine max). Population densities of SCN were not significantly decreased by nine cover crop plants or three cover crop mixes compared with a non-planted soil control in a repeated 60-day-long greenhouse experiment. When susceptible soybeans were grown in the soils after cover crop growth, fewer SCN females formed after three annual ryegrass (Lolium multiflorum) cultivars (Bounty, King, and RootMax), the Daikon radish (Raphanus sativus var. longipinnatus) cultivar CCS779, Kodiak mustard (Brassica juncea), and a mix containing cereal rye, crimson clover (Trifolium incarnatum), plus Daikon radish (cultivars not stated) compared with following the non-planted control. In another repeated experiment, cover crops were grown for 56 days in SCN-infested soil in the greenhouse then exposed to Iowa winter conditions for 28 days to simulate winter termination of the plants. One treatment, a cover crop mix containing 'Bounty' annual ryegrass plus 'Enricher' Daikon radish, had a decrease in SCN population density greater than the non-planted control at the end of the experiment. Significantly fewer SCN females formed on soybeans grown after several cover crops, including the three annual ryegrass cultivars that had the suppressive residual effects in the first experiment. In summary, there were no cover crop treatments that consistently decreased SCN population densities across experiments, and only one cover crop treatment in one experiment significantly reduced SCN population densities more than a non-planted soil control. However, there was a somewhat consistent, adverse, residual effect of cover crops on reproduction of SCN on susceptible soybeans after growth of multiple cover crops.

Soil physicochemical (colloidal) properties affected by ozonated water and organic fertilization.

More has to be investigated on the use of ozonated water (O3) for the improvement of growth medium properties. Accordingly, the objective was to examine the effects of O3 (control, 0.5, 1.0, and 2.0 mg L−1) on soil physicochemical (colloidal) properties using organic fertilization (manure), under non-planted or planted conditions. Different soil physicochemical (colloidal) properties including soil available water (SAW), aggregate stability, soil porosity, pH, salinity (EC), organic carbon (SOC), CaCO3, and cation exchange capacity (CEC) were determined. The experimental treatments and their interactions significantly (P ≤ 0.05) affected soil physicochemical properties including SAW (4.17–10.98%), aggregate stability and porosity (7.77–57.37%), SOC (0.15–2.09%), and CEC (17.68–42.75 Cmol( +)/kg). Interestingly, the single use of O3 or in combination with manure significantly decreased EC. Although O3 significantly decreased SOC in non-planted soils, it significantly increased SOC in planted soils. O3 may enhance soil physicochemical (colloidal) properties, and if combined with manure in a planted soil, such positive effects may be further enhanced.

Rhizosphere effect on removal and bioavailability of PAHs in contaminated agricultural soil

The rhizosphere effect of ryegrass (Lolium perenne L.) on polycyclic aromatic hydrocarbons (PAHs) dissipation, bioavailability and the structure change of microbial community was investigated using a compartmented device-rhizobox. The PAHs removal efficiency, bioavailability and the change in structure of the microbial community were ascertained using HPLC, Tenax-TA extraction and PCR-DGGE, respectively. The results showed that in the root area (R1) and bulk soil (CK), the removal of 3-ring PAHs were 97.72 ± 0.34% and 95.51 ± 0.75%, 4-ring PAHs were 89.01 ± 1.61% and 78.65 ± 0.47%, 5-ring PAHs were 77.64 ± 4.05% and 48.63 ± 3.19%, 6-ring PAHs were 68.69 ± 3.68% and 36.09 ± 1.78%, respectively. The average removal efficiency of the total PAHs after 80 days followed the order: R1M (91.1%) > CKM (84.9%) > CK (77.6%), indicating that planted soil with inoculation of Mycobacterium sp. as well as non-planted soil inoculated with Mycobacterium sp. could both significantly accelerate the removal of PAHs compared to control soil. The bioavailability ratio of PAHs with 3 and 4 rings tended to decrease (from 59.9% to 14.8% for 3-ring and 7.61% to 5.08% for 4-ring, respectively in R1) while those with 5 rings increased significantly (from 2.41% to 33.78% in R1) during the last 40 days, indicating that bioavailability alteration varies with the number of rings in the PAHs. In addition, PAH bioavailability generally did not show a significant difference between treated soil and control soil. These results suggest that ryegrass rhizosphere effect as well as inoculation of Mycobacterium sp. can accelerate PAH removal in polluted soil. The bacteria community structure demonstrated a complex interplay of soil, bacteria and ryegrass root, and potential PAH degraders were present in abundance. This study provides the exploring data of rhizosphere and bioaugmentation effect on PAH dissipation in agricultural soil, as well as the change of bioavailability and microbial composition thereof.

Effect of Rice Planting on Nitrous Oxide (N2O) Emission under Different Levels of Nitrogen Fertilization

Nitrogen (N) fertilization is one of the most effective practices to increase productivity, and has therefore had a fast global increase. Consequently, the effects of the application of N fertilizer on emissions of N2O have been widely studied, but the effect of rice planting on N2O emission was not adequately quantified. To evaluate the effect of rice cultivation on N2O emissions, different levels of N were applied in a typical temperate rice field, and the N2O fluxes were compared in rice-planted and non-planted soils. Seasonal N2O fluxes responded differently with respect to N fertilization in the two different soil conditions. In non-planted soils, seasonal N2O fluxes ranged within 0.31–0.34 kg N2O ha−1 under 0 kg N ha−1 fertilization, and significantly increased by increasing N fertilization rates, with an average rate of 0.0024 kg N2O kg−1 N for 3 years. In rice-planted soils, seasonal N2O fluxes were also increased by N fertilization but showed large negative N2O fluxes, irrespective of the N fertilization level. This study confirms that the rice reacted as a reducer of N2O emissions, not an emission source, in paddy fields, suggesting that N2O fluxes should be estimated by the static chamber planted with rice to obtain a more precise field environment. The differences of N2O fluxes between the rice-planted and non-planted soils might have been caused by the rice plant’s rhizospheric activities, which may have influenced the N2O consumption potential in the rice plants’ rhizosphere. The N2O consumption potential was significantly increased with increasing N fertilization rates and was highly correlated with rice biomass yields. Therefore, the decrease in N2O fluxes by N fertilization in rice-planted soils might have been caused by a decreasing denitrification potential in paddy soils.

Unveiling of active diazotrophs in a flooded rice soil by combination of NanoSIMS and 15N2-DNA-stable isotope probing

The biological nitrogen fixation in planted and nonplanted paddy soils was quantified using a chamber-based 15N2-labeling technique, and the active diazotrophs of soil were assessed by 15N2-DNA-stable isotope probing (SIP). In addition, the nanometer scale secondary ion mass spectrometry (NanoSIMS) was applied to analysis the 15N-enrichment of soil DNA in SIP fractions. 15N2-labeling experiment showed that BNF was 11.33 ± 1.90 kg N ha−1 in the rice-planted soil and 3.55 ± 1.18 kg N ha−1 in the nonplanted soil after 28-day labeling. The biologically fixed 15N was mainly (> 95%) recovered in the surface layer (0–0.5 cm) in the rice-planted soil. High throughput sequencing of nifH genes extracted from surface soil showed that the presence of rice affected the community composition of diazotrophs. The relative abundance of Nostocales and Stigonematales was significantly higher in rice-planted soil than in nonplanted soil (P < 0.05). After CsCl gradient ultracentrifugation, NanoSIMS images clearly showed that 15N was incorporated into soil DNA in the 15N2-labeling SIP gradient fractions. Analyses of nifH genes in 15N-enriched SIP gradient fractions suggested that Nostocales and Stigonematales were the major contributors to BNF in the rice-soil system. Taken together, these results have highlighted the contributions of cyanobacteria to the BNF in paddy fields and improved our understanding of the close relationship between rice plants and cyanobacteria.

Comparative Assessment of PAHs Reduction in Soil by Growing Zea mays L. Augmented with Microbial Consortia and Fertilizer: Modulation in Uptake and Antioxidant Defense Response

Polyaromatic hydrocarbons (PAHs) are found ubiquitously in the environment and are carcinogenic and recalcitrant in nature, hence their fate in crops is imperative to quantify. In present study, the role of petroleum hydrocarbon (PH) degrading microbial consortium and organic fertilizer in the translocation and accumulation of PAHs in a crop plant i.e., Zea mays var. NMH-589 was determined under experimental simulated condition using spiked soil with PAHs mixture (300 µg g−1 phenantherene, 300 µg g−1 anthracene, 200 µg g−1 pyrene, and 200 µg g−1 fluoranthene). After 32 days of treatment, removal of 49.7% of PAHs mixture (k = 0.01552 d−1, t1/2 = 44.6 d) in soil was observed due to growth of maize plant, compared to only 31% removal in non-planted soil (k = 0.0097, t1/2 = 71.456). While growing maize plant amended with organic fertilizer and microbial consortium (Pseudomonas sp. BP10 and Penicillium oxalicum PS10), enhanced the degradation rate of PAHs in soil by 99.4% (k = 0.03107 d−1, t1/2 = 22.3 d). Maximum accumulation of total PAHs mixture in plant tissues (root, shoot, and leaves) was 99.5, 63.5, and 43.5 µg g−1, respectively without any amendment, while the accumulation was lowest i.e., 11.4 µg g−1, 1.2 µg g−1 and not detected, respectively when the soil was amended with microbes and cow-dung manure. Plants also stimulated the microbial count in soil by enhancing their CFU g−1 of soil up to 503%), while the addition of microbial consortium reduced the PAHs stress to plant concurrent with the decrease in antioxidant activities of the plant.

Individual and combined effects of cadmium and polycyclic aromatic hydrocarbons on the phytoremediation potential of Xanthium sibiricum in co-contaminated soil

ABSTRACTSoil contamination with heavy metals and organic pollutants continues to cause major ecological damage and human health problems. Phytoremediation offers a highly promising technology for the recovery of sites contaminated with mixed pollutants. In this study, we performed a greenhouse experiment to investigate the individual and combined effects of cadmium (Cd) and polycyclic aromatic hydrocarbon (PAH) contamination on the growth of Xanthium sibiricum, and also the ability of this species to accumulate and remove Cd and to reduce PAHs over a period of 75 days. Our results demonstrated that individual or combined contamination by Cd and PAHs showed no significant differences to the control treatment except in the high Cd treatment. The reduction of PAH concentration in the soil with the passage of time was similar in the presence or absence of plants. At higher levels of Cd, the removal of pyrene decreased in both planted and non-planted soils; however, this effect might be due to the higher Cd content. Soil dehydrogenase and polyphenol oxidase activities showed that soil contamination did not have a significant effect on the removal of PAHs. Overall, our results suggest that X. sibiricum might be a suitable species for use in the phytoremediation of contaminated soils.

Potentialities of Six Plant Species on Phytoremediation Attempts of Fuel Oil-Contaminated Soils

A field experiment investigating the phytoremediation potential of six plant species—Goosegrass (Eleusine indica), Bermuda grass (Cynodon dactylon), Sessile joyweed (Alternanthera sessilis), Benghal dayflower (Commelina benghalensis), Lovanga (Cleome ciliata), and Chinese violet (Asystasia gangetica)—on soil contaminated with fuel oil (82.5 ml/kg of soil) have been conducted from March to August 2016. The experiments consider three modalities—Tn: unpolluted planted soils, To: unplanted polluted soils, and Tp: polluted planted soil—randomized arranged. Only three (E. indica, C. dactylon, and A. sessilis) of the six species survived while the others died 1 month after the beginning of experimentations. The relative growth indexes showed a strong similarity between the growth parameters of E. indica and C. dactylon, each on polluted and control soils, unlike A. sessilis. Total petroleum hydrocarbons (TPHs) removal efficiency were 82.56, 80.69, and 77% on soil planted with E. indica, C. dactylon, and A. sessilis, respectively; and 57.25% on non-planted soil. According to the bioconcentration and translocation factors, E. indica and A. sessilis are involved on rhizodegradation and phytoextraction of hydrocarbons whereas C. dactylon is only involved into rhizodegradation. Overall, E. indica and C. dactylon out-yielded A. sessilis in the phytoremediation capacity of fuel oil-contaminated soils.

Effect of biochar amendment on the alleviation of antibiotic resistance in soil and phyllosphere of Brassica chinensis L.

The increasing prevalence of antibiotic resistance is a global threat to public health. Antibiotic resistance genes (ARGs) in soil have been demonstrated to be able to enter food chain. Strategies to mitigate the spread of antibiotic resistance from soil to crops are of great importance for food safety and human health. Soil amendment with biochar is a widely used approach to improve soil fertility. However, the impact of biochar on mitigating antibiotic resistance of soil and organically produced vegetables that are eaten raw is largely unknown. To gain insights into this impact, pot experiments planting Brassica chinensis L. in soil amended with biochar were conducted and antibiotic resistance genes (ARGs) were characterized by HT-qPCR targeting almost all major classes of ARGs and 10 mobile genetic elements (MGEs) marker genes. A total of 131 ARGs and 9 MGEs in soil and phyllosphere samples were identified. After biochar amendment, the abundance of ARGs was significantly decreased in non-planted soil. By comparison, no significant decrease of ARGs was found in rhizosphere and phyllosphere, indicating that vegetable planting affected antibiotic resistome in biochar-amended soil. To understand this effect, bacterial phylogeny structures within soil and phyllosphere were analyzed and found to correlate with their respective resistome, indicating that planting can influence the effect of biochar on soil antibiotic resistome by altering microbial community compositions. Structure equation models further revealed that a higher bacterial diversity corresponded to a decreased ARGs content. These results suggested that biochar amendment alone was not sufficient enough to alleviate ARGs level in planted soil and crops, instead, maintaining or increasing soil microbial diversity is potentially more useful in mitigating ARG spread and accumulation.

Above- and belowground fluxes of methane from boreal dwarf shrubs and Pinus sylvestris seedlings

The contribution of boreal forest plants to the methane (CH4) cycle is still uncertain. We studied the above and belowground CH4 fluxes of common boreal plants, and assessed the possible contribution of CH4 producing and oxidizing microbes (methanogens and methanotrophs, respectively) to the fluxes. We measured the CH4 fluxes and the amounts of methanogens and methanotrophs in the above- and belowground parts of Vaccinium myrtillus, Vaccinium vitis-idaea, Calluna vulgaris and Pinus sylvestris seedlings and in non-planted soil in a microcosm experiment. The shoots of C. vulgaris and P. sylvestris showed on average emissions of CH4, while the shoots of the Vaccinium species indicated small CH4 uptake. All the root-soil-compartments consumed CH4, however, the non-rooted soils showed on average small CH4 emission. We found methanotrophs from all the rooted and non-rooted soils. Methanogens were not detected in the plant or soil materials. The presence of plant roots seem to increase the amount of methanotrophs and thus CH4 uptake in the soil. The CH4 emissions from the shoots of C. vulgaris and P. sylvestris demonstrate that the plants have an important contribution to the CH4 exchange dynamics in the plant-soil systems.

Improvement of phytoremediation of an aged petroleum hydrocarbon-contaminated soil by Rhodococcus erythropolis CD 106 strain

ABSTRACTThe aim of this study was to assess the impact of soil inoculation with the Rhodococcus erythropolis CD 106 strain on the effectiveness of the phytoremediation of an aged hydrocarbon-contaminated [approx. 1% total petroleum hydrocarbon (TPH)] soil using ryegrass (Lolium perenne). The introduction of CD 106 into the soil significantly increased the biomass of ryegrass and the removal of hydrocarbons in planted soil. The fresh weight of the shoots and roots of plants inoculated with CD 106 increased by 49% and 30%, respectively. After 210 days of the experiment, the concentration of TPH was reduced by 31.2%, whereas in the planted, non-inoculated soil, it was reduced by 16.8%. By contrast, the concentration of petroleum hydrocarbon decreased by 18.7% in non-planted soil bioaugmented with the CD 106 strain. The rifampicin-resistant CD 106 strain survived after inoculation into soil and was detected in the soil during the entire experimental period, but the number of CD 106 cells decreased constantly during the enhanced phytoremediation and bioaugmentation experiments.The plant growth-promoting and hydrocarbon-degrading properties of CD 106, which are connected with its long-term survival and limited impact on autochthonous microflora, make this strain a good candidate for improving the phytoremediation efficiency of soil contaminated with hydrocarbons.

Exchange fluxes of VOSCs between rice paddy fields and the atmosphere in the oasis of arid area in Xinjiang, China

Investigations about VOSCs (volatile organic sulfur compounds) have been received increasing attention for their significant contribution to the nonvolcanic background sulfate layer in the stratosphere and the earth’s radiation balance and as a potential tool to understand the carbon budget. In this study, COS and CS2 were always recorded throughout the entire rice cultivation season of 2014. COS fluxes appeared as emission in non-planted soil and as uptake in planted soil, the corresponding results were obtained as 2.66 and −2.35 pmol·m−2·s−1, respectively. For CS2, both planted and non-planted paddy fields acted as sources with an emission rate of 1.02 pmol·m−2·s−1 and 2.40 pmol·m−2·s−1, respectively. COS emission or uptake rates showed a distinct seasonal variation, with the highest fluxes at the jointing-booting stage. COS and CS2 fluxes increased with increasing N fertilizer use because of improved plant and microbial growth and activity. Plots treated with both N and S reduced COS and CS2 fluxes slightly compared with plots with only-N treatment. Light, soil moisture or temperature showed no significant correlation with COS and CS2 fluxes, but revealed the important impacts on the magnitude and direction of gases fluxes. The results also showed that the (available) sulfur contents in soil and roots had a certain effect on VOSCs emission or uptake. Our results highlight the significance of biotic and abiotic production and consumption processes existing in the soil.

Influence of inoculating earthworms on removal of pyrene in soils growing Festuca arundinacea

ABSTRACTThe aim of this study was to examine the potential of inoculating earthworms (Pheretima sp.) in order to enhance phytoremediation of polycyclic aromatic hydrocarbons (PAH) present in soils with the use of tall fescue (Festuca arundinacea). In particular, experiments with or without inoculating earthworms for removal of pyrene was investigated. Results showed that planting of F. arundinacea enhanced the removal of pyrene at initial content over 70 days approximately 54%–80% but only 12%–24% occurred in non-planted soils. After inoculating earthworms, the dissipation rates of pyrene in planted soils were increased up to 61%–86%, which was 6%–12% higher than those in corresponding soils without inoculating earthworms. Among all possible pathways, the contribution of plant--microbial interactions on removal of pyrene was predominant, either with (46%) or without inoculating earthworms (52%), is the primary mechanism of contaminant removal. Data suggest inoculating earthworms may be a feasible way for reinforcing removal of PAH in contaminated sites.

Potential for Lead Release from Lead-Immobilized Animal Manure Compost in Rhizosphere Soil of Shooting Range

This study aimed to clarify the magnitude of lead release from lead-sorbed animal manure compost (AMC) in rhizosphere soil compared with nonplanted soil of shooting range. The presence of buckwheat caused reduction in rhizosphere soil pH and enhancement in the level of water-soluble organic carbon compared with those of nonplanted soil. In addition, the presence of buckwheat altered the lead phases and increased the relative amount of the soluble exchangeable fraction, resulting in increase in the CaCl2-soluble lead level. In contrast, the presence of Guinea grass did not change the lead bioavailability or phases compared with nonplanted soil. Lead release tests in solution showed that between solution pH 5 and solution pH 7 the amount of lead released from the compost was higher in the rhizosphere soil of buckwheat than in nonplanted soil, whereas there was no significant difference between the rhizosphere soil of Guinea grass and nonplanted soil. These results suggest that the increase in the quantity of exchangeable lead resulting from the rhizosphere effect induces lead immobilized by the AMC to be remobilized. Therefore, AMC should be applied to soils that contain plants that are unable to alter the lead phases in the shooting range soil. Efforts should be particularly made to ensure that lead cannot be transformed to the exchangeable phase.