巢湖入湖河流沉积物中有机磷的形态分级研究简

为识别巢湖流域污染物的特征、来源及其沉积物有机磷各形态分布与富营养化的关系,测定了7条巢湖入湖河流沉积物中有机磷各形态的含量,分析不同污染类型入湖河流沉积物中有机磷各形态分布的差异及与其他因素间的相关性。研究发现,不同污染类型入湖河流沉积物中水土保持控制型河流沉积物中有机磷各组分的相对含量顺序为残渣态P_o >富里酸-P_o >HCl-P_o >胡敏酸-P_o >NaHCO₃-P_o,平均的相对比例为7.5：3.1：1.9：1.5：1.0,而城市污染控制型和面源污染控制型河流沉积物中有机磷各组分的相对含量顺序恰好相同,面源污染控制型河流沉积物P_o各形态含量低于城市污染控制型和水土保持控制型河流。中活性P_o和OM、TP、P_i、P_o、TN、NaHCO₃-P_i、NaOH-P_i呈正相关,非活性P_o与P_o、NaOH-P_i呈显著正相关关系,反映了中活性P_o很容易转化为生物可利用磷和非活性P_o,且非活性P_o仍然具有潜在的生物活性。     

Evaluation of various chemical extraction methods to estimate plant-available arsenic in mine soils

Elevated levels of bioavailable As in mining soils, agricultural areas and human habitats may cause potential toxicity to human health, plants and microbe. Therefore, it is essential to determine proper soil chemical extraction method in order to estimate plant-available As in mining soils and protect agricultural and environmental ecosystems by evaluation of environmental risk and implementation of remediation measures. In this study, six single soil chemical extraction processes and four-step sequential chemical extraction protocol were used to determine the relative distribution of As in different chemical forms of soils and their correlations with total As in plants grown in mining areas and greenhouse experiments. The strongest relationship between As determined by single soil chemical extraction and As in plant biomass was found for sodium acetate and mixed acid extractant. The mean percent of total As extracted was: ammonium oxalate (41%)>hydroxylamine hydrochloride (32%)>mixed acid (16%)>phosphate (6%)>sodium acetate (1.2%)>water (0.13%). This trend suggests that most of the As in these soils is inside the soil mineral matrix and can only be released when iron oxides and other minerals are dissolved by the stronger chemical extractant. Single soil chemical extraction methods using sodium acetate and mixed acids, that extract As fractions complexed to soil particles or on the surface of mineral matrix of hydrous oxides of Fe, Mn and Al (exchangeable+sorbed forms) can be employed to estimate and predict the bioavailable As fraction for plant uptake in mining affected soils. In sequential chemical extraction methods, ammonium nitrate and hydroxylamine hydrochloride may be used to provide closer estimates of plant-available As in mining soils.     

Greenhouse evaluation and environmental impact assessment of different urine-derived struvite fertilizers as phosphorus sources for plants

A selection of six urine-derived struvite fertilizers generated by innovative precipitation technologies was assessed for their quality and their effectiveness as phosphorus sources for crops. Struvite purity was influenced by drying techniques and magnesium dosage. In a greenhouse experiment, the urine fertilizers led to biomass yields and phosphorus uptakes comparable to or higher than those induced by a commercial mineral fertilizer. Heavy metal concentrations of the different struvite fertilizers were below the threshold limits specified by the German Fertilizer and Sewage Sludge Regulations. The computed loading rates of heavy metals to agricultural land were also below the threshold limits decreed by the Federal Soil Protection Act. Urine-derived struvite contributed less to heavy metal inputs to farmland than other recycling products or commercial mineral and organic fertilizers. When combined with other soil conditioners, urine-derived struvite is an efficient fertilizer which covers the magnesium and more than half of the phosphorus demand of crops.     

Growth dynamics of Chinese wingnut (Pterocarya stenoptera) seedlings and its effects on soil chemical properties under simulated water change in the Three Gorges Reservoir Region of Yangtze River

Pterocarya stenoptera is a native deciduous tree species and a candidate for reforestation in the riparian zones of the Three Gorges Reservoir Region of Yangtze River in China. Water treatments of continuous flooding (CF) and periodic flooding–drought (PF) were applied to examine the growth dynamics of 4-month-old P. stenoptera seedlings and its effects on soil chemical properties. Results showed that P. stenoptera seedlings in both CF and PF significantly decreased leaf biomass accumulation and the height and diameter growth as compared to that in control (CK; treatment with well-watered, well-drained soil), respectively. There was no significant difference in stem biomass among the three groups, but root biomass in PF showed severe reduction compared to that in both CK and CF. Total biomass in PF was significantly decreased compared to that in CK, but comparable to that in CF. Furthermore, no significant difference was found between CF and CK in total biomass. Water treatments in the unplanted soil pots significantly influenced soil pH, soil organic matter (OM), total nitrogen (TN), and alkali hydrolysable nitrogen (AN) contents, in contrast to no significant effects in total phosphorus (TP), total potassium (TK), available phosphorus (AP), and available potassium (AK) contents. In P. stenoptera soils, there were significant effects by water treatment, time, and treatment × time in the eight tested soil chemical properties, except treatment in TK and time effect in OM content. Compared to unplanted soils, the growth of P. stenoptera seedlings significantly increased soil pH value and OM, TN, TP, and TK contents, while decreasing AN, AP, and AK contents in CK group, augmented the mean value of each of the tested soil chemical properties with an exception of AK content in CF group, and increased soil pH value and TN, AN, TP, and AP contents with no significant differences in OM, TK, and AK contents in PF group. Given the fact that TN and TP contents significantly increased in P. stenoptera soils as compared to those in unplanted soils, growth of P. stenoptera seedlings should be a successful candidate for restoration within the highly dynamic hydrologic zone of the riparian zones of the Three Gorges Reservoir Region.     

Layer of organic pine forest soil on top of chlorophenol-contaminated mineral soil enhances contaminant degradation

Chlorophenols, like many other synthetic compounds, are persistent problem in industrial areas. These compounds are easily degraded in certain natural environments where the top soil is organic. Some studies suggest that mineral soil contaminated with organic compounds is rapidly remediated if it is mixed with organic soil. We hypothesized that organic soil with a high degradation capacity even on top of the contaminated mineral soil enhances degradation of recalcitrant chlorophenols in the mineral soil below. We first compared chlorophenol degradation in different soils by spiking pristine and pentachlorophenol-contaminated soils with 2,4,6-trichlorophenol in 10-L buckets. In other experiments, we covered contaminated mineral soil with organic pine forest soil. We also monitored in situ degradation on an old sawmill site where mineral soil was either left intact or covered with organic pine forest soil. 2,4,6-Trichlorophenol was rapidly degraded in organic pine forest soil, but the degradation was slower in other soils. If a thin layer of the pine forest humus was added on top of mineral sawmill soil, the original chlorophenol concentrations (high, ca. 70 μg g^?1, or moderate, ca. 20 μg g^?1) in sawmill soil decreased by >40 % in 24 days. No degradation was noticed if the mineral soil was kept bare or if the covering humus soil layer was sterilized beforehand. Our results suggest that covering mineral soil with an organic soil layer is an efficient way to remediate recalcitrant chlorophenol contamination in mineral soils. The results of the field experiment are promising.     

Fate and bioavailability of arsenic in organo-arsenical pesticide-applied soils. Part-I: incubation study

A laboratory incubation study was conducted to estimate geochemical speciation and in vitro bioavailability of arsenic as a function of soil properties. Two chemically-variant soil types were chosen, based on their potential differences with respect to arsenic reactivity: an acid sand with minimal arsenic retention capacity and a sandy loam with relatively high concentration of amorphous Fe/Al-oxides, considered a sink for arsenic. The soils were amended with dimethylarsenic acid (DMA) at three rates: 45, 225, and 450 mg/kg. A sequential extraction scheme was employed to identify the geochemical forms of arsenic in soils, which were correlated with the "in vitro" bioavailable fractions of arsenic to identify the most bioavailable species. Arsenic bioavailability and speciation studies were done at 0 time (immediately after spiking the soils with pesticide) and after four-months incubation. Results show that soil properties greatly impact geochemical speciation and bioavailability of DMA; soils with high concentrations of amorphous Fe/Al oxides retain more arsenic, thereby rendering them less bioavailable. Results also indicate that the use of organic arsenicals as pesticides in mineral soils may not be a safe practice from the viewpoint of human health risk.     

Residual gasoline saturation in unsaturated soil with and without organic matter

The goal of this study was to investigate the influence of one variable, natural organic matter, on residual gasoline saturation in sandy soils. Capillary pressure-saturation (P_c−S) relationships (air-gasoline) were determined for three physically-similar sandy soils, with different organic carbon contents (0.086%, 0.89% and 1.65%) and residual gasoline saturations were compared. Two initial moisture conditions, residual water saturation and air-dry, were evaluated. One soil type was packed to two different bulk densities. Visualization of the soils using cryo-scanning electron microscopy was performed to aid in better understanding the role of the organic matter in the soil. The results showed that soils with higher organic contents had higher residual gasoline saturations when starting with an initially air-dry soil. Increasing the bulk density of the same air-dried soil resulted in an increase in residual gasoline saturation. In the presence of a residual water saturation, however, residual gasoline saturations were virtually identical for the three soils and independent of bulk density; approximately 5–10 times lower than in soil that was initially air-dry. The presence of the residual water effectively coated the surface of the soil thereby reducing or eliminating gasoline/soil interactions. Some residual water may also be occupying very small pore spaces, making these locations inaccessible to the gasoline.     

巢湖入湖河流沉积物中有机磷的形态分级研究

为识别巢湖流域污染物的特征、来源及其沉积物有机磷各形态分布与富营养化的关系,测定了7条巢湖入湖河流沉积物中有机磷各形态的含量,分析不同污染类型人湖河流沉积物中有机磷各形态分布的差异及与其他因素间的相关性。研究发现,不同污染类型人湖河流沉积物中水土保持控制型河流沉积物中有机磷各组分的相对含量顺序为残渣态Po〉富里酸-Po〉HCl-Po〉胡敏酸-Po〉NaHCO3-Po,平均的相对比例为7．5：3．1：1．9：1．5：1．0,而城市污染控制型和面源污染控制型河流沉积物中有机磷各组分的相对含量顺序恰好相同,面源污染控制型河流沉积物Po各形态含量低于城市污染控制型和水土保持控制型河流。中活性P。和OM、TP、Pi、Po、TN、NaHCO3-Pi、NaOH—Pi呈正相关,非活性Po与Po、NaOH-Pi呈显著正相关关系,反映了中活性Po很容易转化为生物可利用磷和非活性Po,且非活性Po仍然具有潜在的生物活性。     

A study on As, Cu, Pb and Zn (bio)availability in an abandoned mine area (São Domingos, Portugal) using chemical and ecotoxicological tools

The aim of this study was to relate the results obtained by chemical methods, used to assess environmental (bio)availability, with the ecotoxic response and bioaccumulation of trace elements (TE) by the earthworm Eisenia fetida exposed to field-contaminated, metal-polluted soils from a sulphide mine. The extracting solution 0.5 M NH₄CH₃COO, 0.5 M CH₃COOH and 0.02 M EDTA (pH 4.7), was able to predict environmental bioavailability of TE to E. fetida. However, the toxicological bioavailability could not be predicted from the results of the chemical extractions or from the bioaccumulation results: E. fetida reproduction was higher in soils where environmental bioavailability of TE and bioaccumulation values were also higher. In this study, the toxic response of the organism seemed to be more influenced by the overall nutritional status of the soil (e.g. pH, organic matter, plant nutrient availability and cation exchange capacity) than by its TE contamination. In the case of anthropogenic multi-contaminated sites, the different soil characteristics exert an important and confounding influence in the toxic response and the relationship between different bioavailable fractions cannot be easily established, emphasising the need to combine results from chemical methods with those from bioassays when evaluating the bioavailability of TE in these soils.     

Integrated Waste Management in a Zone of Northern Italy: Compost Production and Use,and Analytical Control of Compost,Soil, and Crop

Agricultural soils of two Italian maize farms were treated for five years with an industrially produced high-quality compost. Cattle manure and the usual mineral fertilizer were used for comparison purposes. The effects of the organic and mineral fertilizer treatments were studied by analyzing the compost and manure, cultured soils, and harvested material. The grain yield was also determined. Organic fertilization improved soil pH, CEC, content of organic matter and NPK. Soil respiration and N mineralization were found to be higher than in the purely mineral-treated soil. Plant K take-up was improved, whereas grain yield was not affected. It was confirmed that organic fertilization, particularly compost use, maintained and increased soil fertility. The study demonstrated the feasibility of using in loco analytical facilities to follow the entire recycling process—from waste to compost production—and the use of the final product in the field.     

Effect of chemophytostabilization practices on arbuscular mycorrhiza colonization of Deschampsia cespitosa ecotype Waryński at different soil depths

The effects of chemophytostabilization practices on arbuscular mycorrhiza (AM) of Deschampsia cespitosa roots at different depths in soils highly contaminated with heavy metals were studied in field trials. Mycorrhizal parameters, including frequency of mycorrhization, intensity of root cortex colonization and arbuscule abundance were studied. Correlations between concentration of bioavailable Cd, Zn, Pb and Cu in soil and mycorrhizal parameters were estimated. An increase in AM colonization with increasing soil depth was observed in soils with spontaneously growing D. cespitosa. A positive effect of chemophytostabilization amendments (calcium phosphate, lignite) on AM colonization was found in the soil layers to which the amendments were applied. Negative correlation coefficients between mycorrhizal parameters and concentration of bioavailable Cd and Zn in soil were obtained. Our results demonstrated that chemophytostabilization practices enhance AM colonization in D. cespitosa roots, even in soils fertilized with high rates of phosphorus.     

Hexabromocyclododecanes in soils and plants from a plastic waste treatment area in North China: occurrence,diastereomer- and enantiomer-specific profiles,and metabolization

Plastic waste is a source of organic contaminants such as hexabromocyclododecanes (HBCDs). HBCDs have been found to cause developmental and reproductive toxicity; it is important to investigate the occurrence and metabolization of HBCDs in the soil environments with plastic waste contamination. This work analyzed HBCDs and their metabolites in soil and plant samples collected from Xinle and Dingzhou—the major plastic waste recycling centers in North China. Results showed that total HBCD concentrations in soils followed the order: plastic waste treatment site (11.0–624 ng/g) > roadside (2.96–85.4 ng/g) ≥ farmland (8.69–55.5 ng/g). HBCDs were detected in all the plant samples with total concentrations ranging from 3.47 to 23.4 ng/g. γ-HBCD was the dominant congener in soils, while α-HBCD was preferentially accumulated in plants. Compositions of HBCD isomers in soils and plants were significantly different (P < 0.05) among sampling sites and among plant species. HBCDs in farmland soil and all plant samples exhibited high enantio-selectivity based on the enantiomeric fractions (EFs). Furthermore, metabolites of pentabromocyclododecenes (PBCDEs) were frequently identified in soils, and mono-OH-HBCDs were the most common ones in plants. This study for the first time provides evidences of HBCD contamination in the soil-plant system caused by plastic waste, their stereo-selectivity, and metabolization behavior, improving our understanding of the environmental behavior and fate of HBCDs.     

Bioremediation trial on aged PCB-polluted soils—a bench study in Iceland

Polychlorinated biphenyls (PCBs) pose a threat to the environment due to their high adsorption capacity to soil organic matter, stability and low reactivity, low water solubility, toxicity and ability to bioaccumulate. With Icelandic soils, research on contamination issues has been very limited and no data has been reported either on PCB degradation potential or rate. The goals of this research were to assess the bioavailability of aged PCBs in the soils of the old North Atlantic Treaty Organization facility in Keflavík, Iceland and to find the best biostimulation method to decrease the pollution. The effectiveness of different biostimulation additives (N fertiliser, white clover and pine needles) at different temperatures (10 and 30 °C) and oxygen levels (aerobic and anaerobic) were tested. PCB bioavailability to soil fauna was assessed with earthworms (Eisenia foetida). PCBs were bioavailable to earthworms (bioaccumulation factor 0.89 and 0.82 for earthworms in 12.5 ppm PCB soil and in 25 ppm PCB soil, respectively), with less chlorinated congeners showing higher bioaccumulation factors than highly chlorinated congeners. Biostimulation with pine needles at 10 °C under aerobic conditions resulted in nearly 38 % degradation of total PCBs after 2 months of incubation. Detection of the aerobic PCB degrading bphA gene supports the indigenous capability of the soils to aerobically degrade PCBs. Further research on field scale biostimulation trials with pine needles in cold environments is recommended in order to optimise the method for onsite remediation.     

Integrated waste management in a zone of northern Italy: compost production and use, and analytical control of compost, soil, and crop

Agricultural soils of two Italian maize farms were treated for five years with an industrially produced high-quality compost. Cattle manure and the usual mineral fertilizer were used for comparison purposes. The effects of the organic and mineral fertilizer treatments were studied by analyzing the compost and manure, cultured soils, and harvested material. The grain yield was also determined. Organic fertilization improved soil pH, CEC, content of organic matter and NPK. Soil respiration and N mineralization were found to be higher than in the purely mineral-treated soil. Plant K take-up was improved, whereas grain yield was not affected. It was confirmed that organic fertilization, particularly compost use, maintained and increased soil fertility. The study demonstrated the feasibility of using in loco analytical facilities to follow the entire recycling process-from waste to compost production-and the use of the final product in the field.     

The adaptation of two similar soils to pyrene catabolism

The development of pyrene catabolic activity was assessed in two similar soils (pasture and woodland) amended with 100 mg pyrene kg(-1) In the pasture and woodland soils, significant mineralisation of 14C-pyrene was observed after 8 and 76 weeks soil-pyrene contact times, respectively. In both soils, there were significant decreases (P<0.05) in the lag times and significant increases (P <0.05) in the maximum rates and extents of 14C-pyrene mineralised with increasing soil-pyrene contact time. A microbial inoculum was added to the woodland soil to assess if the previously added, but undegraded 14C-pyrene was bioavailable at 16 and 24 weeks. This resulted in the immediate mineralisation of the previously added 14C-pyrene, indicating that it was bioavailable but that the microbial community in the woodland soil had not developed the ability to mineralise pyrene. The relative contributions of the indigenous microflora to 14C-pyrene mineralisation were assessed by the addition of celective inhibitors, with bacteria seeming to be responsible for the mineralisation of pyrene in both soils. It is suggested that the rate of pyrene-transfer from the soil to the microorganisms was lower in the woodland soil due to its higher organic matter content.     

Size and XAD fractionations of trihalomethane precursors from soils

Soil organic matter is an important source of allochthonous dissolved organic matter inputs to the Sacramento-San Joaquin Delta waterways, which is a drinking water source for 22 million people in California, USA. Knowledge of trihalomethane (THM) formation potential of soil-derived organic carbon is important for developing effective strategies for organic carbon removal in drinking water treatment. In this study, soil organic carbon was extracted with electrolytes (deionized H2O and Na- or Ca-based electrolytes) of electrical conductivity bracketing those found in Delta leaching and runoff conditions. The extracts were physically and chemically separated into different fractions: colloidal organic carbon (0.45-0.1 microm), fine colloidal organic carbon (0.1-0.025 microm), and dissolved organic carbon (DOC) (<0.025 microm); hydrophobic acid (HPOA), transphilic acid, and hydrophilic acid. Two representative Delta soils, Rindge Muck (a peat soil) and Scribner Clay Loam (a mineral soil) were examined. Results showed that less than 2% of soil organic carbon was electrolyte-extractable and heterogeneous organic fractions with distinct THM reactivity existed. Regardless of soil and electrolytes, DOC and HPOA fractions were dominant in terms of total concentration and THMFP. The amounts of extractable organic carbon and THMFP were dependent on the cation and to a lesser extent on electrical conductivity of electrolytes. Along with our previous study on temperature and moisture effects on DOC production, we propose a conceptual model to describe the impacts of agricultural practices on DOC production in the Delta. DOC is mainly produced in the surface peat soils during the summer and is immobilized by accumulated salt in the soils. DOC is leached from soils to drainage ditches and finally to the Delta channels during winter salt leaching practices.     

Lead contamination in tea garden soils and factors affecting its bioavailability

The consumption of heavy metals is detrimental to human health and most countries restrict the concentration of metals such as lead (Pb) in food and beverages. Recent tests have detected high Pb concentrations in certain commercial brands of tea leaves and this finding has raised concerns for both producers and consumers. To investigate what factors may be contributing to the increase in Pb accumulation in the tea leaves we collected tea leaves and soils from tea producing areas and analyzed them for Pb concentration, pH and organic matter content. The result showed the Pb concentration of 47% investigated tea leaves samples was beyond 2 mg kg(-1), the permissible levels given by China. The total Pb concentration in the surface and subsurface soil layers averaged 36.4 and 32.2 mg kg(-1), respectively which fall below of the 60 mg kg(-1) limit provided for organic tea gardens in China. The pH of the tea garden soils was severely acidic with the lowest pH of 3.37. Soils under older tea gardens tended to have a lower pH and a higher Pb bioavailability which was defined as the amount of lead extracted by CaCl2 solution than those under younger tea gardens. We found that the concentration of bioavailable Pb and the percentage of bioavailable Pb (bioavailable Pb relative to total Pb concentration) were positively correlated with soil H+ activity and soil organic matter content, and the organic matter accumulation contribute more effects on Pb bioavailability in these two factors. We conclude that soil acidification and organic matter accumulation could contribute to increasing Pb bioavailability in soil and that these could increase Pb uptake and accumulation in the tea leaves.     

From agricultural use of sewage sludge to nutrient extraction: A soil science outlook

The composition of municipal wastewater and sewage sludge reflects the use and proliferation of elements and contaminants within society. In Sweden, official statistics show that concentrations of toxic metals in municipal sewage sludge have steadily decreased, by up to 90 %, since the 1970s, due to environmental programmes and statutory limits on metals in sludge and soil. Results from long-term field experiments show that reduced metal pollution during repeated sewage sludge application has reversed negative trends in soil biology. Despite this Swedish success story, organic waste recycling from Swedish towns and cities to arable land is still limited to only about 20 % of the total amount produced. Resistance among industries and consumers to products grown on land treated with sewage sludge may not always be scientifically grounded; however, there are rational obstacles to application of sewage sludge to land based on its inherent properties rather than its content of pollutants. We argue that application of urban organic wastes to soil is an efficient form of recycling for small municipalities, but that organic waste treatment from large cities requires other solutions. The large volumes of sewage sludge collected in towns and cities are not equitably distributed back to arable land because of the following: (i) The high water and low nutrient content in sewage sludge make long-distance transportation too expensive; and (ii) the low plant availability of nutrients in sewage sludge results in small yield increases even after many years of repeated sludge addition. Therefore, nutrient extraction from urban wastes instead of direct organic waste recycling is a possible way forward. The trend for increased combustion of urban wastes will make ash a key waste type in future. Combustion not only concentrates the nutrients in the ash but also leads to metal enrichment; hence, direct application of the ash to land is most often not possible. However, inorganic fertiliser (e.g. mono-ammonium phosphate fertiliser, MAP) can be produced from metal-contaminated sewage sludge ash in a process whereby the metals are removed. We argue that the view on organic waste recycling needs to be diversified in order to improve the urban–rural nutrient cycle, since only recycling urban organic wastes directly is not a viable option to close the urban–rural nutrient cycle. Recovery and recycling of nutrients from organic wastes are a possible solution. When organic waste recycling is complemented by nutrient extraction, some nutrient loops within society can be closed, enabling more sustainable agricultural production in future.     

Moderate phosphorus application enhances Zn mobility and uptake in hyperaccumulator Sedum alfredii

While phytoextraction tools are increasingly applied to remediation of contaminated soils, strategies are needed to optimize plant uptake by improving soil conditions. Mineral nutrition affects plant growth and metal absorption and subsequently the accumulation of heavy metal through hyper-accumulator plants. Microcosm experiments were conducted in greenhouse to examine the effect of different phosphorus (P) sources on zinc (Zn) phytoextraction by Sedum alfredii in aged Zn-contaminated paddy soil. The Zn accumulation, soil pH, microbial biomass and enzyme activity, available Zn changes. and Zn phytoremediation efficiency in soil after plant harvest were determined. Upon addition of P, Zn uptake of S. alfredii significantly increased. Mehlich-3 extractable or the fractions of exchangeable and carbonate-bound soil Zn were significantly increased at higher P applications. Soil pH significantly decreased with increasing P application rates. Soil microbial biomass in the P-treated soils was significantly higher (P?<?0.05) than those in the control. Shoot Zn concentration was positively correlated with Mehlich-3 extractable P (P?<?0.0001) or exchangeable/carbonate-bound Zn (P?<?0.001), but negatively related to soil pH (P?<?0.0001). These results indicate that application of P fertilizers has the potential to enhance Zn mobility and uptake by hyperaccumulating plant S. alfredii, thus increasing phytoremediation efficiency of Zn-contaminated soils.     

Carbon deposition in soil rhizosphere following amendments with compost and its soluble fractions, as evaluated by combined soil-plant rhizobox and reporter gene systems

We determined the organic carbon released by roots of maize plants (Zea mays L.) when grown in soils amended with compost and its soluble fractions. In rhizobox systems, soil and roots are separated from the soil of a lower compartment by a nylon membrane. Treatments are applied to the upper compartment, while in the lower compartment luminescent biosensors measure the bioavailable organic carbon released by roots (rhizodeposition). The rhizobox-plants systems were amended with a compost (COM), its water extract (TEA), the hydrophobic (HoDOM) and hydrophilic (HiDOM) fractions of the dissolved organic matter (DOM) extracted from the compost. After root development, the lower untreated compartments were sampled and sliced into thin layers. The bioavailable organic carbon in each layer was assessed with the lux-marked biosensor Pseudomonas fluorescens 10586 pUCD607, and compared with total organic carbon (TOC) analyses. The TOC values ranged between 8.4 and 9.6 g kg(-1) and did not show any significant differences between bulk and rhizosphere soil samples in any treatment. Conversely, the biosensor detected significant differences in available C compounds for rhizosphere soils amended with various organic materials. Concentrations of available organic compounds in the first 2 mm of soil rhizosphere were 1.69 (control), 1.09 (COM), 2.87 (HiDOM), 4.73 (HoDOM) and 2.14 (TEA)micromol Cg(-1) soil g(-1) roots. The applied rhizobox-biosensor integrated method was successful in detecting and quantifying effects of organic amendments on organic carbon released by maize plant roots. This approach may become important in assessing the carbon cycle in agricultural soils and soil-atmosphere compartments.