Rhizosphere effects on soil bacterial abundance and diversity in the Yellow River Deltaic ecosystem as influenced by petroleum contamination and soil salinization

In this study, we compared the differences of bacterial abundance and diversity between rhizosphere and surrounding bulk soils under soil salinization and petroleum contamination in the Yellow River Delta on a 110-km-distance scale. In comparison with bulk soils, rhizosphere soils were mainly characterized by lower salinity and higher water content in saline soils. For bacterial abundance, the numbers of total bacteria and hydrocarbon degraders were significantly higher in rhizosphere soils than those in bulk soils. Although there was no significant difference in total petroleum hydrocarbon (TPH) concentration between the two types of soils, TPH had distinctly different effects on bacterial abundance in rhizosphere and bulk soils. TPH concentration was the major determinant of total bacterial abundance and had positive effects on abundances of hydrocarbon degraders. However, the abundances of total bacteria and hydrocarbon degraders in bulk soils were primarily determined by soil salinity and water content. Great abundance of rhizosphere bacteria suggested that plant roots could alleviate the stresses from soil salinization and provide more favorable microhabitats for bacterial growth. TPH had positive effects on bacterial diversity of both rhizosphere and bulk soils. Our results support the view that petroleum in the environments functions as both toxic chemicals and carbon sources to soil bacteria. Great abundance and diversity of total bacteria in plant rhizospheres would potentially improve the roles of bacteria in maintaining ecosystem functioning in the degraded ecosystems. Our results would improve our understanding of the relationships between rhizosphere effects and multiple environmental stresses that control the development of bacterial community in fragile anthropologically-affected ecosystems.     

Application of the membrane interphase probe (MIP): an evaluation

Background, aim, and scope

The membrane interphase probe (MIP?) from Geoprobe Systems® has frequently been applied in different countries for the characterization of soil contaminated with volatile organic carbons (VOCs). Experience shows that misinterpretation of the collected data is common. This is mainly due to the lack of understanding and knowledge related to the detectors used, their detection limits, and the sensitivity of the MIP system. It has been noticed that the sensitivity of the system given by the producer and by different users are rather optimistic, e.g., the values given are lower (= better) than those actually experienced in the field. A need for a better understanding of the MIP system sensitivity, combined with a more scientifically based interpretation of the collected data, exists.

Materials and method

Both laboratory tests (using solutions) as well as field measurements were carried out using different detector configurations to allow a better interpretation of the detector signals/system sensitivity and to collect qualitative information. These configurations were: (1) detectors stand alone; (2) the use of a 2-ml sample loop, and (3) a purge and trap system. The configurations (2) and (3) are used in combination with a capillary column to carry out on-site qualitative and semiquantitative analyses.

Results and discussion

With respect to the configuration of “detectors stand alone,” detection limits for toluene (in aqueous solutions) range between 4 ppm (flame ionization detector—FID) and 10 ppm [photo ionization detector (PID)]. For chlorinated aliphatic hydrocarbons (CAHs), observed limits are 10 ppm (FID), 4–50 ppm (PID), and 3–10 ppm [dry electrolytic conductivity detector (DELCD)]. When using the 2-ml sample loop, relatively high concentrations have to be initially present in the soil. Observed detection limits for mono-aromatic hydrocarbons are 5–100 ppm; for CAHs, 1–50 ppm; for alkanes, 250–400 ppm; and for MTBE, 25 ppm. The application of purge and trap results in a better resolution and the detection of lower concentrations. Consequently, a better identification of the pollution with depth is possible. In this case, the detection limits are a function of the concentrations and the flushing time. In relation to the qualitative analyses, it was found that the configuration of the MIP-system with the built-in capillary column and the 2-ml sample loop or the purge and trap preconcentrator, respectively, are useful to carry out on-site analyses, thus allowing a better identification of the pollution in a vertical profile.

Conclusions

The measurements carried out using the MIP with detectors stand-alone or in combination with a loop or trap, or connected to a column, confirm that analysis is indeed very useful to characterize VOC source zones when knowing and understanding its performance. This relates mainly to the detection limits of the MIP system. For a selection of parameters, such limits have been obtained. These values seem to be more realistic than those found in the few references where numbers are given. For the qualitative measurements, it can be concluded that a better resolution is obtained, and pollutants present in lower concentrations will be detected when using the purge and trap. It is advised to determine the optimal flushing time and the detection limit of the expected pollutants in advance.

Recommendations and perspectives

This study indicates that there is still a need for further measurements and discussion between users. Finally, additional data should result in a better interpretation of the collected field data.     

Using glomalin as an indicator for arbuscular mycorrhizal hyphal growth: an example from a tropical rain forest soil

Glomalin concentrations of extra-radical arbuscular mycorrhizal (AM) hyphae were estimated by deploying hyphal in-growth cores containing glomalin-free sand in field soils in a tropical forest and in pot cultures. In field soils, glomalin was 0.044±0.013 μg m⁻¹ hyphae. In pot cultures glomalin concentrations were lower (range 0.0068-0.036 μg m⁻¹), and varied significantly among species. Using this technique, preliminary estimates of extraradical AM hyphal production on Inceptisols were 1.91 Mg ha⁻¹yr⁻¹ and on Oxisol were 1.47 Mg ha⁻¹ yr⁻¹, but they could range between 0.9-5.7 Mg ha⁻¹ yr⁻¹. These rates of hyphal production are approximately 10% (range 5-33%) of estimated above ground primary production of the forest.     

Comparative effectiveness of selected adsorbant materials as potential amendments for the remediation of lead-, copper- and zinc-contaminated soil

Bonemeal, coir, compost, green waste compost, peat and wood bark all potentially could be used as amendments to remediate heavy metal contamination in soils. Their ability to sorb Pb, Cu and Zn was evaluated in the laboratory, using metal solutions ranging from 0 to 5 mmol/L as contaminants. The effects on sorption of metal concentration, background salt concentration and metal competition were evaluated. Single metal sorption by the six amendments was significantly different at metal concentrations of 1.5–5 mmol/L, with green waste compost, coir, compost and wood bark having the highest capacities to adsorb Pb, Cu and Zn. Langmuir sorption maxima were approximately 87 mg Pb/g (coir and green waste compost), 30 mg Cu/g (compost and green waste compost) and 13 mg Zn/g (compost and green waste compost) (equivalent to approx. 0.5 mmol/g of Pb and Cu, and 0.2 mmol/g Zn), all in a background solution of 0.001 M Ca(NO₃)₂. A higher background salt concentration and a combination of all three metals led to significant reduction in the amounts of Pb, Cu and Zn sorbed by all the amendments tested. Competing heavy metal cations in solution decreased Pb sorption to about 50–60% of that from a solution containing Pb alone; Cu sorption was reduced to about 30–40%; the effect of competition on Zn sorption was variable. Overall, in both single metal and competitive sorption, the order of strength of binding was Pb>Cu>>Zn.     

Use of organic amendment as a strategy for saline soil remediation: Influence on the physical, chemical and biological properties of soil

The effectiveness of adding two organic wastes (cotton gin crushed compost, CGCC, and poultry manure, PM) to a saline soil (Salorthidic Fluvaquent) in dryland conditions near Seville (Guadalquivir Valley, Andalusia, Spain) was studied during a period of 5 years. Organic wastes were applied at rates of 5 and 10 t organic matter ha⁻¹. One year after the assay began, spontaneous vegetation had appeared in the treated plots, particularly in that receiving a high PM dose. After 5 years the plant cover in this treated plot was around 80% (compared with the 8% of the control soil). The effect on the soils physical and chemical properties, soil microbial biomass, and six soil enzymatic activities (dehydrogenase, urease, protease, β-glucosidase, arylsulfatase, and phosphatase activities) were ascertained. Both added organic wastes had a positive effect on the physical, chemical and biological properties of the soil, although at the end of the experimental period, the soil physical properties, such as bulk density, increased more significantly in the CGCC-amended soils (23%) and the exchangeable sodium percentage (ESP) decreased more significantly in the CGCC-amended soils (50%) compared to the unamended soil. Water soluble carbohydrates and soil biochemical properties were higher in the PM-amended soils compared to the CGCC-amended soils (by 70% for water soluble carbohydrates, and by 34, 18, 37, 39, 40 and 30% for urease, protease, β-glucosidase, phosphatase, arylsulfatase and dehydrogenase activities, respectively). After 5 years, the percentage of plant cover was >50% in all treated plots and 8% in the control soil.     

Assessment of soil contamination by potentially toxic elements in the aljustrel mining area in order to implement soil reclamation strategies

Land pollution due to past mining activities is a major environmental issue in many European countries. The Aljustrel mine (SW Portugal), located in the western sector of the Iberian Pyrite Belt (IBP) presents a negative visual and environmental impact as a consequence of the mining activity that has developed since the Roman era. Its impacts are also a restraint on the life quality of the population. The exposure of pyrite and other sulphides to air are responsible for the pollution observed in soils, surface water and stream sediments. This paper investigates the pollution load of potential toxic elements in soil samples collected around the Aljustrel mining area. The aim is to assess the levels of soil contamination with respect to average concentrations of toxic elements in the region and to understand the partitioning and availability of pollutants in the area. The results showed severe soil contamination (mainly As, Cd, Cu, Pb and Zn). The concentrations of As (up to 3936 mg kg⁻¹) and certain heavy metals (up to 5414 mg kg⁻¹ Cu, 61·6 mg kg⁻¹ Cd, 20 000 mg kg⁻¹ Pb and 20 000 mg kg⁻¹ Zn) are two orders of magnitude above the regional South Portuguese Zone (SPZ) background values. The median concentrations of As, Cd, Cu, Pb and Zn exceed the values established for world soils, the European Union, Portugal and Andalusia. The results suggest that the distribution patterns of Co, Cr and Ni element concentrations in the Aljustrel area are primarily influenced by the lithology and geochemistry nature of bedrock. The soil background of this geological domain is characterized by relatively high heavy metal contents, essentially derived from the parent rocks. Copyright © 2010 John Wiley & Sons, Ltd.     

Enzyme activity as an indicator of soil quality changes in degraded cultivated Acrisols in the Mexican Trans‐volcanic Belt

Soils located at the Mexican Trans‐Volcanic Belt (MTB) have a worrying degree of degradation due to inappropriate management practices. Early indicators of soil changes are very useful to alert about negative impacts of wrong managements on these volcanic soils. The aim of this work was to evaluate the short‐term effects (4 years) of different agricultural practices on soil organic matter (SOM) quality and to validate the potential of the selected biochemical properties as optimal early indicators of soil quality in Mexican cultivated Acrisols. During 2002–2005 four agronomic management systems: conventional (Tc); improved conventional (Ti); organic (To) and fallow (Tf) were assayed in plots located at the MTB. An uncultivated soil under grass cover (Sg) was used as reference. Soil samples were collected at 0–10 cm depth and were analysed chemically (soil organic C, total N, water‐soluble C and humic C), and biochemically (total and extra‐cellular enzyme activity). After 4 years, soil organic C, total N, water‐soluble C, and dehydrogenase activity had higher values in To, followed by Ti treatment. A similar response pattern was observed in the extra‐cellular enzyme activity. The highest total enzyme activity was found in Sg, followed by Ti and To treatments, and the lowest values appeared in Tc and Tf. To and Ti increased SOM contents of the degraded Acrisols studied, while Tc and Tf managements decreased the quality of these soils. The results showed that the assayed soil enzymes can be used as indicators of quality changes of these Mexican volcanic soils. Copyright © 2010 John Wiley & Sons, Ltd.     

基于Century模型和1:500 000土壤数据库的华东旱地土壤有机碳动态模拟

Changes in soil organic carbon (SOC) in agricultural soils influence soil quality and greenhouse gas concentrations in the atmosphere. Dry farmland covers more than 70% of the whole cropland area in China and plays an important role in mitigating carbon dioxide (CO2) emissions. In this study, 4109 dry farmland soil polygons were extracted using spatial overlay analysis of the soil layer (1:500000) and the land use layer (1:500000) to support Century model simulations of SOC dynamics for dry farmland in Anhui Province, East China from 1980 to 2008. Considering two field-validation sites, the Century model performed relatively well in modeling SOC dynamics for dry farmland in the province. The simulated results showed that the area-weighted mean soil organic carbon density (SOCD) of dry farmland increased from 18.77 Mg C ha1 in 1980 to 23.99 Mg C ha1 in 2008 with an average sequestration rate of 0.18 Mg C ha1 year?1. Approximately 94.9% of the total dry farmland area sequestered carbon while 5.1% had carbon lost. Over the past 29 years, the net SOC gain in dry farmland soils of the province was 19.37 Tg, with an average sequestration rate of 0.67 Tg C year1. Augmentation of SOC was primarily due to increased consumption of nitrogen fertilizer and farmyard manure. Moreover, SOC dynamics were highly differentiated among dry farmland soil groups. The integration of the Century model with a fine-scale soil database approach could be conveniently utilized as a tool for the accurate simulation of SOC dynamics at the regional scale.     

Conversion factor (k factor) for estimation of soil microbial biomass potassium by the chloroform-fumigation extraction method

The conversion factor, k_K, for estimation of microbial biomass potassium (K) by the chloroform-fumigation extraction method was determined for some arable soils: upland field soils under different fertilization conditions, an upland field soil under a greenhouse condition, and a paddy field soil under a flooded condition. The k_K value varied with land utilization (paddy or upland) or fertilization (chemical or organic fertilizer). Value of k_K was different between paddy field soil (0.28–0.38) and upland field soil (0.41–0.73). This study indicates that the value could be useful for the estimation of microbial biomass K in soil by the chloroform-fumigation extraction method and further investigation of the amounts of biomass K in different types of soils under conditions with varied field managements will be necessary.     

Assessment of the usefulness of particle size distribution measured by laser diffraction for soil water retention modelling

Particle size distribution (PSD) is a major soil characteristic, which is essential and commonly used for the development of pedotransfer functions (PTFs) to estimate the water retention of soils. The laser diffraction method (LDM) became a popular alternative to the standard sieve‐hydrometer method (SHM) of PSD measurement. Unfortunately, PSDs determined with LDM and SHM methods differ sometimes substantially. Moreover, it is claimed that the laser diffraction method underestimates finer fractions in favor of coarser fractions. Several authors have tried to elaborate on methods to recalculate LDM PSD into its SHM counterparts, but no universal methodology has been developed to this date. In this paper, we use PSD determined by LDM directly for PTF development and compare it with the classical PTF approach based on PSD measured by SHM. Four different PTF models based on LDM particle size distribution data were developed, with different PSD characteristics taken as the models' input variables. The possibility of using alternative PSD characteristics, such as deciles, area moment mean and volume moment mean, for PTF development was examined. The accuracy of PTF models constructed on the basis of LDM‐measured PSD was comparable with that of the developed models using texture data obtained from SHM, giving approximately the same RMSE and R² values. Our study shows that LDM‐measured particle size distribution may be directly used for PTF developments without any recalculations to their sieve‐hydrometer counterparts.     

Modification of the Cataldo method for the determination of nitrate in soil extracts by potassium chloride

The simple and sensitive colorimetric method developed by Cataldo et al. for the determination of nitrate in solution was modified to apply it for 2 M KCI soil extracts. The color intensity was decreased markedly when the KCI concentration of the sample solution increased, in contrast, the sensitivity was improved when the ratio of mixing volume of the sample and salicylic acid-sulfuric acid reagent was changed, and when the sample volume was increased. The modified method showed almost the same accuracy as the steam distillation method with MgO and Devarda alloy.     

施氮水平对太行山前平原冬小麦-夏玉米轮作体系土壤温室气体通量的影响

应用静态明箱-气相色谱法对4 个施氮肥水平N0 [0 kg(N)·hm^-2]、N200 [200 kg(N)·hm^-2]、N400 [400kg(N)·hm^-2]、N600 [600 kg(N)·hm^-2]的夏玉米-冬小麦季轮作体系2008~2010 年的土壤温室气体(CH₄、CO₂ 和N₂O)排放通量进行研究, 同时观测5 cm 土层土壤温度并记录降水量。结果表明: 太行山前平原冬小麦-夏玉米轮作农田生态系统为CH₄ 吸收汇, CO₂ 和N₂O 排放源。随着氮肥施入量的增加土壤对CH₄ 的吸收速率降低, 而CO₂ 和N₂O 的排放速率增加。冬小麦季施氮处理土壤对CH₄ 的吸收速率显著低于无氮肥的N0 处理, 而N600处理土壤CO₂ 和N₂O 排放速率显著高于N0 处理(P<0.05)。施肥和灌溉会直接导致土壤CO₂ 和N₂O 的排放通量增加, 同时土壤对CH₄ 的吸收峰值减小。土壤温度升高和降水量增加以及干湿交替加剧均会造成N₂O 和CO₂排放速率增加。同时在持续干燥和低温条件的冬季不施氮处理观测到土壤对N₂O 的吸收现象。N0、N200、N400 和N600 处理土壤CH₄ 年排放总量(kg·hm^-2·a^-1)分别为-1.42、-0.75、-0.82、-0.92(2008~2009 年)和-2.60、-1.47、-1.35、-1.76(2009~2010 年), N0、N200、N400 和N600 处理土壤CO₂ 年排放总量(kg·hm^-2·a^-1)分别为15 597.6、19 345.6、21 455.9、29 012.5(2008~2009 年)和10 317.7、11 474.0、13 983.5、20 639.3(2009~2010年), N0、N200、N400 和N600 处理土壤N₂O 年排放总量(kg·hm^-2·a^-1)分别为1.05、2.16、5.27、6.98(2008~2009年)和1.49、2.31、4.42、5.81(2009~2010 年)。     

A model for estimating soil moisture changes as an aid to irrigation scheduling and crop water-use studies: II. Field test of the model

Abstract. A model was developed to estimate daily evapotranspiration and root zone soil moisture changes appropriate for scheduling irrigation, incorporating a modified version of the Penman-Monteith equation.
The model was field tested during 1992–94, for potatoes and sugarbeet, by comparing modelled root zone soil moisture changes with field measurements taken using neutron probes. The study confirmed the accuracy of the model when predicting crop water use and soil moisture change. Linear regression of measured versus modelled data exhibited a slope of 0.99 and an intercept close to and not significantly different from zero. The relationship accounted for 80% of the variation.     

Applicability of a combined staining method with fluorochromes for the visualization of microbial cells in a soil thin section

Staining of microbial cells in a soil thin section provides useful information about the role of soil as an ecological niche by relating the in situ distribution of microorganisms to the state of pores under undisturbed conditions. For technical improvement, we developed a procedure consisting of a combined staining method with 5-sulfofluorescein diacetate (SFDA), a metabolic type fluorochrome, and magnesium salt of l-anilino-8-naphthalene sulfonic acid (Mg-ANS), an adsorption type fluorochrome, in order to detect and differentiate the living microbial cells from the dead ones in a single soil thin section. Using images under a fluorescence microscope, we also examined the applicability of SFDA for staining microbial cells embedded in soil thin sections, which had seldom been attempted. Through this study, we confirmed the following facts: i) combined staining with SFDA and Mg-ANS can be achieved without major modification of the general procedure for thin section preparation, ii) staining with SFDA can be applied to soil thin sections, and iii) detection of in situ distribution and differential identification of the living and dead microbial cells may be possible by the proposed combined staining method.     

蔬菜清洁生产技术补贴支付意愿影响因素研究——以蔬菜残体堆肥化技术应用调查为例

蔬菜残体堆肥化技术是一项重要的清洁生产技术,由于技术应用成本较高且耗时、费力,导致技术推广存在障碍。通过补贴政策激励农户采纳技术行为,是弥补因"政策失灵"造成生态效益外溢的有效手段。本研究运用意愿价值评估方法引导获取农户对于堆沤池建设费用的支付意愿,运用Logistic二元选择模型,基于河北省藁城区142份农户调查数据,探明支付意愿影响因素的方向和强度。研究结果表明:生产经营的显性成本是影响技术补贴支付意愿的重要因素;个别劳动时间与信息来源是影响支付意愿的内部制约因素;以技术补贴为主的政策手段是影响支付意愿重要激励因素;对于土壤污染的认知因素与支付意愿呈反向关系。基于此,提出引导农户应用堆肥化技术的政策建议包括:推进蔬菜生产安全优质高效技术创新;充分发挥蔬菜专业合作组织服务作用;完善蔬菜清洁生产技术补贴政策机制,提高农业生态补贴政策效能。