Phytotoxic doses of boron in contrasting soils depend on soil water content

Boron (B) affects plant growth in soil at B doses (mg added B kg^-1 soil) that appear in the range of natural background B concentrations. A study was set up to determine B bioavailability by testing B toxicity to plant as affected by soil properties and ageing after soil dosing. Nineteen soils (pH 4.4?C7.8) and 3 synthetic soils (sand-peat mixtures) were amended with 7 doses of H₃BO₃. Barley root elongation was determined immediately after B amendment and after 1 and 5 months ageing. Soil solution B concentrations increased linearly with added B concentrations with almost no detectable adsorption. In contrast, the ratio of aqua regia soluble B/soil solution B in unamended soils (no B added) was 10?C25 times higher than in B amended soils at similar aqua regia soluble B concentrations illustrating a much lower B availability in unamended soils. Soil solution B concentrations did not decrease by ageing. The toxic B doses or soil B concentrations that decreased barley root growth by 10% (EC10 values) varied about tenfold (respectively 3?C27 mg added B kg^-1 and 5?C52 mg B kg^-1) among soils. Corresponding thresholds in soil solution varied less than fourfold (16?C59 mg B l^-1). Soil ageing for 5 months did not significantly change EC10 and EC50 values, expressed either as total soil B or as soil solution B, unless in 1 soil. Variability in EC10 and EC50 values was explained by various soil properties (soil moisture content, background B, %clay, cation exchange capacity), but covariance of these properties with the soil moisture content suggest that B dilution is the critical factor explaining B toxicity. It is concluded that effects of B amendments do not decrease by ageing and that soil solution B or B doses corrected for soil moisture content may be used as an index for B toxicity across different soils.     

Elevated amino sugar nitrogen concentrations in soils: a potential method for assessing N fertility enhancement by actinorhizal plants

No single soil nitrogen (N) assay seems to be adequate to predict N fertility. An amino sugar-nitrogen assay has been proposed as a method to estimate soil N fertility and determine N fertilization requirements of agronomic crops. Such chemical methods of estimating potentially-available soil N are appealing because of their rapidity and simplicity. In this case study an amino sugar-N assay was used in established plantings of actinorhizal woody plants to determine whether they increased soil amino sugar N concentrations in soil and by how much. Amino sugar N is derived primarily from bacterial and fungal cell walls, but not plant cells, and probably reflects N-stimulation of microbial activity in soils. It was hypothesized that actinorhizal plants would increase soil amino sugar N. Mine spoil Entisols supporting Frankia-nodulated autumn olive shrubs (Elaeagnus umbellata) had 104 mg kg^-1 of amino sugar-N while European alder (Alnus glutinosa) trees on the same soil type had amino sugar N concentrations of 98 mg kg^-1 beneath their canopies. Soil adjacent to, and between, the two plantations and lacking N-fixing plants had 54 mg kg^-1 N of soil amino sugars. At another location a cluster of European alder trees increased soil amino sugar concentrations in a fertile Mollisol by a similar amount, 45 mg kg^-1, but by a lesser proportion. This Mollisol had a high amino sugar N background level of 336.5 mg kg^-1 indicating high N fertility. Results indicated that there was no correspondence between amino sugar N concentrations and total N concentrations, nor was there correspondence between amino sugar N concentrations and total soil organic matter concentration on mine spoils. Actinorhizal plants apparently increase the amino sugar N concentration in soils and an amino sugar N assay has potential for development as an additional means of indexing N fertility enhancement by N-fixing trees.     

Effect of five tree crops and a cover crop in multi-strata agroforestry at two fertilization levels on soil fertility and soil solution chemistry in central Amazonia

The spatio-temporal patterns of soil fertility and soil solution chemistry in a multi-strata agroforestry system with perennial crops were analysed as indicators for the effects of crop species and management measures on soil conditions under permanent agriculture in central Amazonia. The study was carried out in a plantation with locally important tree crop species and a leguminous cover crop at two fertilization levels on a xanthic Ferralsol. Soil fertility to 2 m soil depth was evaluated 3.5 years after the establishment of the plantation, and soil solution chemistry at 10, 60 and 200 cm soil depth was monitored over 2 years. Several soil fertility characteristics exhibited spatial patterns within the multi-strata plots which reflected the differing properties of the plant species and their management, including the fertilizer input. Significant differences between species could be detected to 150 cm depth, and between fertilization treatments to 200 cm depth. Favourable effects on nutrient availability in the soil were found for annatto (Bixa orellana) (P, K) and cupuaçu (Theobroma grandiflorum) (Ca, Mg) in comparison with peach palm (Bactris gasipaes) and Brazil nut (Bertholletia excelsa). Nutrient concentrations of the soil solution showed pronounced fluctuations in the topsoil, corresponding to fertilizer applications. Large nutrient concentrations in the soil solution were accompanied by increased concentrations of aluminium and low pH values, caused by exchange reactions between fertilizer and sorbed acidity and reinforced by the acidifying effect of nitrification. The soil solution under the leguminous cover crop Pueraria phaseoloides had relatively large N concentrations during periods when those under the tree crops were small, and this could partly explain why no yield responses to N fertilization were observed at this site.     

Changes in water extractable metals,pH and organic carbon concentrations at the soil-root interface of forested soils

Soluble metals are of nutritional and ecotoxicological interest as they are the most readily available form to the biota. Metal solubility in soils is mostly controlled by pH and the organic matter content. The rhizosphere is generally considered as an environment enriched in organic matter and often more acidic (depending on nutritional status of the plant) than the bulk soil. Yet, there is a lack of consensus on the distribution of metals at the soil-root interface. Consequently, the specific objectives of this paper are to compare the chemical properties and the water extractable metal concentrations of the rhizosphere and the bulk soil of forest soil (1) along a gradient in soil contamination and (2) under different tree species. Two study areas were used: (1) Rouyn-Noranda (Canada) where samples were collected along a gradient in metal contamination at a distance of 0.5, 2 and 8 km downwind from a copper smelter; (2) Saint-Hippolyte (Canada) where the effect of three tree species (Abies balsamea, Acer saccharum and Betula papyrifera) was studied. In the field, the rhizosphere was operationally defined as the soil adhering to the roots after agitation, soil falling from the roots and the rest of the soil composing the bulk soil. Once in laboratory, a second agitation was performed to separate the rhizosphere into an inner and an outer component. Water extractable metal concentrations (Al, Ca, Cd, Co, Cr, Cu, Fe, Li, Mg, Mn, Ni, Pb and Zn) were quantified either with an ICP-AES or a GFAAS. Measurements of pH, electrical conductivity (EC), water-extractable organic carbon (WEOC) and solid phase organic carbon (SPOC) were performed. Results systematically indicate that EC, WEOC and SPOC follow the sequence inner rhizosphere > outer rhizosphere > bulk soil. The pH is always lower in the inner rhizosphere than in the bulk soil, while the outer rhizosphere frequently shows an inconstant behaviour. The results also show a clear gradient following inner rhizosphere > outer rhizosphere > bulk soil for water extractable Al, Ca, Cd, Cu, Fe, Mg, Mn, Ni, Pb and Zn. Li, Co and Cr levels were below method detection limit in all cases. WEOC seems to be the main variable related to the water-extractable metals concentrations. The gradient in metal contamination at Rouyn-Noranda was not as expected in the water extracts with the site at 2 km frequently presenting higher metal concentrations than the sites at 0.5 and 8 km. Moreover, a tree species effect did not clearly immerge for any of the chemical properties studied. However, the water extractable Ca concentrations were higher in the soil under Acer saccharum. The effects of the metal gradient and of the tree species may be more pronounced if stronger extractants are used. The addition of an outer rhizosphere component is useful as its behaviour is not consistently intermediate between the inner rhizosphere and bulk soil.     

Rare earth elements in soil and plant systems - A review

The rare earth elements (REEs) form a chemically uniform group and include yttrium (Y), lanthanum (La) and the lanthanides cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). Their average abundance in the Earth’s crust range from 66μg g⁻¹ in Ce to 0.5μg g⁻¹ in Tm and ?0.1μg g⁻¹ in Pm. Recent great improvements in more routine analytical technique, the use of REEs as fertilisers, at least in East Asian agriculture, and the importance of these elements as indicators in both pedological and physiological processes and reactions have contributed to an increased interest in these previously less considered elements in environmental sciences. This review of recent and current literature deals with REEs in primary and secondary soil minerals, concentrations in surface soils, factors influencing adsorption, solubility and transport in soils, including weathering and transformations of REE minerals, and vertical distribution in soil profiles. Reviewed and discussed are also concentrations, distribution and localisation of REEs in plants and plant organs, soil-plant relationships and interactions, effects on plant growth and crop production and their importance in plant physiology and biochemistry. The REEs are found, usually several elements together, as phosphates, carbonates and silicate minerals finely dispersed especially in magmatic and metamorphic rocks. REE concentrations in surface soils of humid climates, such as the A(E)-horizons of Podzols and Laterites, are usually lower than in the parent material, due to higher weathering and leaching rates than of the average soil constituents. Some fractionation may occur due to the formation of more element-specific secondary minerals. Transfer from soil to plant is usually low, but extreme accumulators are found, e.g., among several species of ferns. Roots have generally higher concentrations than shoots. Possible uptakemechanisms of REEs are discussed. Uptake is positively, though often weakly, correlated with soil acidity and easily soluble concentrations of the elements, but rarely well related to their total concentrations in the soil. Under certain conditions, low concentrations of at least some REEs seem to favour plant growth and productivity, but the physiological mechanisms are still not well understood. Some considerations concerning the boundary between essential and non-essential micro nutrients are discussed.     

From geochemical background determination to pollution assessment of heavy metals in sediments and soils

Establishing geochemical background concentrations to distinguish the natural background from anthropogenic concentrations of heavy metals in sediments and soils is necessary to develop guidelines for environmental legislation. Due to the fact that the background concentrations strongly depend on geological characteristics such as mineral composition, grain size distribution and organic matter content, several normalization methods have been developed. Empirical (geochemical), theoretical (statistical) and integrated methods (combining both empirical and theoretical methods) are the main approaches described in literature for determination of geochemical background concentrations. In this review paper, the different approaches as well as the main normalization methods for heavy metal concentrations in sediments and soils will be discussed. Both geochemical background concentrations and added risk level (maximum permissible addition) should be taken into account for setting up legal threshold limits. Moreover, different approaches to evaluate the pollution status of heavy metals in sediments and soils, from Sediment/Soil Quality Guidelines to quantitative indices (Geo-accumulation Index-I_geo, Enrichment Factor-EF, Pollution Load Index-PLI and Risk assessment Code-RAC) will be presented. Although guidelines to establish whether a sediment or soil is polluted or not are generally only related to total metal concentrations, the available/reactive pool i.e., availability/reactivity of metals should be taken into account for sediment/soil pollution assessment.     

Coexisting Bacterial Populations Responsible for Multiphasic Mineralization Kinetics in Soil

Experiments were conducted to study populations of indigenous microorganisms capable of mineralizing 2,4-dinitrophenol (DNP) in two soils. Previous kinetic analyses indicated the presence of two coexisting populations of DNP-mineralizing microorganisms in a forest soil (soil 1). Studies in which eucaryotic and procaryotic inhibitors were added to this soil indicated that both populations were bacterial. Most-probable-number counts with media containing different concentrations of DNP indicated that more bacteria could mineralize low concentrations of DNP than could metabolize high concentrations of it. Enrichments with varying concentrations of DNP and various combinations of inhibitors consistently resulted in the isolation of the same two species of bacteria from soil 1. This soil contained a large number and variety of fungi, but no fungi capable of mineralizing DNP were isolated. The two bacterial isolates were identified as a Janthinobacterium sp. and a Rhodococcus sp. The Janthinobacterium sp. had a low μ_max and a low K_m for DNP mineralization, whereas the Rhodococcus sp. had much higher values for both parameters. These differences between the two species of bacteria were similar to differences seen when soil was incubated with different concentrations of DNP. Values for μ_max from soil incubations were similar to μ_max values obtained in pure culture studies. In contrast, K_s and K_m values showed greater variation between soil and pure culture studies. The results of this study help to confirm predictions that two physiologically distinct bacterial populations are responsible for the multiphasic mineralization kinetics observed in the soil studied.     

Investigating CH4 and N2O emissions from eco-engineering wastewater treatment processes using constructed wetland microcosms

Methane (CH₄) and nitrous oxide (N₂O) are important greenhouse gases, because of their contribution to the global greenhouse effect. The present study assessed emissions of N₂O and CH₄ from constructed wetland microcosms, planted with Phragmites australis and Zizania latifolia, when treating wastewater under different biological oxygen demand (BOD) concentration conditions. The removal rate was 95% for BOD and more than 80% for COD in all three pollutant concentrations, both plants’ removal rates of pollutants were at almost the same level, and both were found to resist BOD concentrations as high as 200 mg L⁻¹. When BOD concentrations fell below 200 mg L⁻¹, the soil plant units reached an average of 80–92% T-N and T-P removal rates; however, as the concentrations increased to 200 mg mg L⁻¹ or when during the initial phases of winter, the removal rates for T-N and T-P decreased to less than 70%. With NH₃-N removal, the influences of BOD concentrations and air temperature were more obvious. When BOD concentrations increased to 100 mg L⁻¹ after October, an obvious decrease in NH₃-N removal was detected; almost no nitrification occurred beginning in December at BOD concentrations of 200 mg mg L⁻¹. N₂O and CH₄ emissions showed obvious seasonal changes; higher emissions were observed with higher BOD concentrations, especially among Z. latifolia units. The enumeration of methane-oxidizing bacteria and methane-producing bacteria was also conducted to investigate their roles in impacting methane emissions and their relationships with plant species. The pollutant purification potentials of P. australis and Z. latifolia plant units during wastewater treatment of different pollutant concentrations occurred at almost the same levels. The nutrient outflow and methane flux were consistently higher with Z. latifolia units and higher concentrations of BOD. The more reductive status and higher biomass of methanogens may be the reason for the lower nitrification and higher CH₄ emissions observed with Z. latifolia units and higher concentration systems. The Z. latifolia root system is shallow, and the activity of methanotrophs is primarily confined to the upper portion of the soil. However, the root system of P. australis is deeper and can oxidize methane to a greater depth. This latter structure is more favorable as it is better for reducing methane emissions from P. australis soil plant systems.     

Intraspecific and interspecific pair-wise seedling competition between exotic annual grasses and native perennials: plant–soil relationships

Few studies have examined plant–soil relationships in competitive arenas between exotic and native plants in the western United States. A pair-wise competitive design was used to evaluate plant–soil relationships between seedlings of the exotic annual grasses Bromus tectorum and Taeniatherium caput-medusae and the native perennial grasses Elymus elymoides and Pseudoroegneria spicata. Two soils were tested: an arid soil (argid) occupied by E. elymoides and presently invaded by B. tectorum and a high elevation, high organic matter, soil (aquept) where none of the tested species would typically occur. Plant growth proceeded for 85 days at which time above-ground biomass and tissue nutrient concentrations were quantified. Soil also was collected from the rooting zone beneath each species and analyzed for various nutrient pools. The exotic species had significantly greater above-ground biomass than the natives and grew far better in the aquept soil than the argid soil. Growth of B. tectorum, and to some degree, T. caput-medusae was suppressed in intraspecific competition and enhanced, especially in the aquept soil, when competing with the natives. Although not significant, biomass of natives strongly trended downward when competing with the exotic grasses. Overall, concentrations of tissue nutrients were minimally affected by competition, but natives tended to be more negatively affected by competition with exotics. Except for phosphorus (P), all species had significantly greater nutrient concentrations when growing in the aquept soil compared to the argid soil. In both soils, exotics had significant greater tissue concentrations of manganese (Mn), magnesium (Mg), and iron (Fe), while natives had significantly greater nitrogen (N). Species affects on soil nutrient pools occurred mostly in the aquept soil with exotic species significantly decreasing pools of available N, potentially available N, and soil-solution pools of calcium (Ca²⁺), potassium (K⁺), and magnesium (Mg²⁺) relative to natives. Overall, the data suggest that, in the seedling state, B. tectorum is a superior competitor. Moreover, when the natives compete intra- or interspecifically, particularly in the aquept soil, availability of N and other nutrients in their rooting zone is consistently greater than when they compete interspecifically with the exotic grasses. These data suggest the exotics are able to co-opt nutrients in the rooting zone of the natives and perhaps gain a competitive advantage.     

Assessing the in situ bioavailability of trace elements to snails using accumulation kinetics

The bioavailability of trace elements in soils is conditioned by both physico-chemical and biological parameters. In this study, the accumulation kinetics of cadmium (Cd), lead (Pb), arsenic (As) and antimony (Sb) were determined for 3 industrially impacted sites to assess the bioavailability of these contaminants to the garden snail (Cantareus aspersus). Mono and multivariate regressions allowed the identification of cation exchange capacity (CEC), silts and organic carbon content as the soil parameters modulating the in situ bioavailability of Cd and Pb. For all elements, the total concentrations in the soils were not good predictor (not significant correlation) of the bioavailability to snails. The Cd, As and Sb assimilation fluxes were correlated with the calcium chloride (CaCl₂) extract concentrations, but this correlation was not observed with Pb. The total soil concentration coupled with soil properties best explained the variation in Pb assimilation, whereas their influences on Cd bioavailability were lower, signifying that other parameters such as contamination sources may modulate Cd bioavailability. Here, the As and Sb in situ accumulation kinetics are described for the first time and highlighted a slight bioavailability to snails at the studied sites. The absence of a correlation between the As or Sb assimilation fluxes and total metals in the soil coupled with the absence of influence of soil properties on their bioavailability may result from the speciation of these metalloids, which are known to modulate their mobility in soils. This study highlights the need to consider both physico-chemical and biological aspects of metal and metalloid bioavailability to assess the risk of metal transfer from soil to organisms.     

Species adaptation in serpentine soils in Lesbos Island (Greece): metal hyperaccumulation and tolerance

Serpentine (ultramafic) soils, containing relatively high nickel and other metal concentrations, present a stressful environment for plant growth but also a preferred substrate for some plants which accumulate nickel in their tissues. In the present study we focused on: (1) the relationships between serpentine soils of Lesbos Island (Greece) and serpentinophilic species in order to test their adaptation to the ‘serpentine syndrome’, and (2) the Ni-hyperaccumulation capacity of Alyssum lesbiacum, a serpentine endemic, Ni-hyperaccumulating species, recorded over all its distribution for the first time. We sampled soil and the most abundant plant species from the four serpentine localities of Lesbos Island. Soil and leaf elemental concentrations were measured across all the sites. Our results confirmed our hypothesis that serpentinophilic species are adapted to elevated heavy metal soil concentrations but restricting heavy metal concentration in their leaves. We demonstrated that different A. lesbiacum populations from Lesbos Island present differences in Ni hyperaccumulation according to soil Ni availability. Our results highlighted the understanding of serpentine ecosystems through an extensive field study in an unexplored area. Alyssum lesbiacum and Thlaspi ochroleucum emerge as two strong Ni hyperaccumulators with the former having a high potential for phytoextraction purposes.     

玛河流域扇缘带盐穗木土壤速效养分的"肥岛"特征

比较了玛河流域扇缘带盐穗木灌丛在单生条件下及与猪毛菜共生条件下的土壤速效养分的"肥岛"特征。结果表明,盐穗木灌丛周围土壤的"肥岛"现象主要体现在土壤表层,沿立地点向外每隔0.6m逐渐减弱,且沿土层深度增加逐渐减弱。盐穗木在单生条件下,灌丛土壤碱解氮和速效钾在立地中心有明显的富集现象。在从立地原点向外3m的表层土壤中,两种养分分别从 2.75 g/kg和56.67 mg/kg下降至1.66 g/kg和29.0 mg/kg,且沿土壤剖面向下呈现显著性降低趋势(P<0.05),但均显著性高于裸地的同类值。而速效磷含量整体呈现亏损状态,其平均值较裸地速效磷含量低25.33%,表明盐穗木种群具有促进氮和钾的富积、但消耗磷的生态功能。在盐穗木-猪毛菜共生条件下,无论是在土壤表层还是沿土壤剖面,3种速效养分的含量整体上显著性高于裸地。共生条件下土壤的碱解氮含量整体低于单生条件下的值,而速效磷和速效钾的含量则是共生大于单生。研究表明,盐穗木单一种群条件下土壤速效磷的亏损状态可在猪毛菜共生条件下出现逆转,两者具有互补效应。该结论为干旱盐碱化地区植物与土壤关系研究提供了新的理论潜力。     

Methods for Detection of Anticarsia gemmatalis Nucleopolyhedrovirus DNA in Soil

Two methods, phenol-ether and magnetic capture-hybridization (MCH), were developed and compared with regard to their sensitivities and abilities to extract the DNA of the insect baculovirus Anticarsia gemmatalis nucleopolyhedrovirus (AgMNPV) from soil and to produce DNA amplifiable by PCR. Laboratory experiments were performed with 0.25 g of autoclaved soil inoculated with different viral concentrations to optimize both methods of baculovirus DNA extraction and to determine their sensitivities. Both procedures produced amplifiable DNA; however, the MCH method was 100-fold more sensitive than the phenol-ether procedure. The removal of PCR inhibitors from the soil appeared to be complete when MCH was used as the viral DNA isolation method, because undiluted aliquots of the DNA preparations could be amplified by PCR. The phenol-ether procedure probably did not completely remove PCR inhibitors from the soil, since PCR products were observed only when the AgMNPV DNA preparations were diluted 10- or 100-fold. AgMNPV DNA was detected in field-collected soil samples from 15 to 180 days after virus application when the MCH procedure to isolate DNA was coupled with PCR amplification of the polyhedrin region.     

Lack of Complete Exposure Pathways for Metals in Natural and FGD Gypsum

Use of wallboard made from synthetic gypsum generated via flue-gas desulfurization (FGD) by coal-fired power plants (FGD gypsum) raised questions concerning the potential for exposure to residual trace metals. Because gypsum is widely used (e.g., in wallboard), any issue with metals could have far-reaching implications. A conceptual site model evaluated potential human health exposure pathways for metals in gypsum, through consideration of data for 21 metals including samples of natural (mined) gypsum, and of FGD gypsum. Because there are no screening values for gypsum, comparisons were made to background soil concentrations and to risk-based concentrations for metals in soil termed preliminary remedial action goals (PRGs), which assume more frequent and prolonged contact with particulate soil than would be likely for gypsum, and thus provide a health protective means for evaluation of exposure. Additional screenings evaluated occupational exposure and agricultural use of gypsum. Maximum metal concentrations in natural and FGD gypsum samples were either consistent with background concentrations or much lower than PRGs for residential or agricultural soil, or workplace air, and thus exposure pathways for these media were considered incomplete. Separate analyses of mercury volatilization were conducted, and this pathway was also found to be incomplete.     

The occurrence and ecology of microbial chain elongation of carboxylates in soils

Chain elongation is a growth-dependent anaerobic metabolism that combines acetate and ethanol into butyrate, hexanoate, and octanoate. While the model microorganism for chain elongation, Clostridium kluyveri, was isolated from a saturated soil sample in the 1940s, chain elongation has remained unexplored in soil environments. During soil fermentative events, simple carboxylates and alcohols can transiently accumulate up to low mM concentrations, suggesting in situ possibility of microbial chain elongation. Here, we examined the occurrence and microbial ecology of chain elongation in four soil types in microcosms and enrichments amended with chain elongation substrates. All soils showed evidence of chain elongation activity with several days of incubation at high (100 mM) and environmentally relevant (2.5 mM) concentrations of acetate and ethanol. Three soils showed substantial activity in soil microcosms with high substrate concentrations, converting 58% or more of the added carbon as acetate and ethanol to butyrate, butanol, and hexanoate. Semi-batch enrichment yielded hexanoate and octanoate as the most elongated products and microbial communities predominated by C. kluyveri and other Firmicutes genera not known to undergo chain elongation. Collectively, these results strongly suggest a niche for chain elongation in anaerobic soils that should not be overlooked in soil microbial ecology studies.Subject terms: Soil microbiology, Microbial ecology     

Diversity and distribution of entomopathogenic nematodes (Nematoda: Steinernematidae, Heterorhabditidae) and their bacterial symbionts (gamma-Proteobacteria: Enterobacteriaceae) in Jordan

Until now, only a few systematic surveys of entomopathogenic nematodes (EPN) have been conducted in Middle Eastern countries. Many of the recovered EPN species in this region have shown to own distinctive qualities that enable their survival in unique environments, such as high temperatures and low moisture levels tolerance. These new species and strains, with unique environmental tolerances, are more suitable for their consideration in pest management programs in xerophytic regions. With this background in mind, we recently conducted a survey of EPN in Jordan. This study records for the first time the diversity and distribution of these nematodes and their bacterial symbionts in this country. Jordan’s three geographic regions: (1) the highlands, (2) Jordan valley and (3) the desert region were sampled. Within each region, natural habitats and agricultural regions characteristic to each region were considered for sampling purposes. Four EPN species including three Steinernema and one Heterorhabditis were recovered. Nematodes were identified using a combination of molecular markers and classic morphological diagnostic tools. Bacterial symbionts were identified by analysis of 16S rRNA sequences. Abiotic characteristics such as soil type, soil pH, and elevation were also recorded. We herein report the diversity of EPN species in Jordan and discuss their potential in Biocontrol and IPM programs for this country.     

海南稻田土壤硒与重金属的含量、分布及其安全性

采集了海南省18个市(县)代表性的稻田土壤耕作层(0—20cm)样品280个,研究了硒(Se)和5种有毒重金属元素(Hg、Cd、Cr、Pb和As)的含量、分布及其相关关系,并对Se和重金属的安全性进行评价,可为合理区划清洁且富Se稻田提供理论依据。结果表明:海南稻田土壤中Hg、Cd、Cr、Pb和As平均含量均低于国家土壤环境质量一级标准值和全国土壤背景值,以绿色食品产地环境技术条件限量标准为标准,用单项污染指数法和内梅罗综合污染指数法评价海南稻田土壤重金属的污染状况,结果都是清洁的。但以海南省土壤背景值做参比值,Hakanson潜在生态危害指数达到211.54,属于强生态危害,从潜在生态危害系数来看,Hg(102.61)和Cd(98.89)达到强生态危害,分别比海南省土壤背景值增加1.56和2.3倍,今后应注意控制Hg和Cd污染源。稻田土壤Se含量从痕量到1.532mg/kg之间,平均值为0.211mg/kg,占47.5%的稻田土壤Se含量处于中等及以上水平(>0.175mg/kg)。Se含量高的稻田土壤主要集中在东北部的海口及其周边的澄迈、定安、文昌和琼海,还有东南部的万宁和保亭。由于重金属平均含量还比较低,可暂时忽略重金属污染,故可在上述Se含量高的稻田土壤上种植富Se水稻。稻田土壤Se含量与Hg、Cd和As含量呈极显著或显著正相关,因此今后应加强研究稻田土壤Se与Hg、Cd和As的有效性及其相互作用,以便生产出绿色的富Se优质大米。     

Mineral Elements in Root of Wild Saposhnikovia divaricata and Its Rhizosphere Soil

Mineral elements are important components of medicinal herbs, and their concentrations are affected by many factors. In this study, Ca, Mg, Na, K, Fe, Mn, Cu, and Zn concentrations in wild Saposhnikovia divaricata and its rhizosphere soil collected from seven locations at two different times in China were measured, and influences of rhizosphere soil on those minerals in plant were evaluated. The results showed that mean concentrations of eight minerals in plant samples decreased in the order: Ca > Mg > Na > K > Fe > Zn > Mn > Cu, and those in the soil samples followed the following order: Na > Fe > Ca > K > Mg > Mn > Zn > Cu. Mean concentrations of Ca, Na, Mg, and K in plants were higher than those in soils, while higher mean concentrations of the other four minerals were found in soils. It was found that there was a positive correlation of Mg, Na, and Cu concentrations in the plant with those in the soil respectively, but a negative correlation of Mn concentration in plant with that in the soil. Except Ca, K, and Mn, the other five minerals in plant were all directly affected by one or more chemical compositions of soil. The results also indicate that pH value and concentrations of total nitrogen, Mg, Mn, and Cu in soil had significant correlations with multimineral elements in plant. In a word, mineral elements uptake of S. divaricata can be changed by adjusting the soil fertility levels to meet the need of appropriate quality control of S. divaricata.     

Smelling the tree and the forest: elm background odours affect egg parasitoid orientation to herbivore induced terpenoids

Parasitic insects use herbivore induced plant volatiles as signals for host location. However, their responses to these volatiles in the background of natural habitat odours need further evaluation for developing successful biological control strategies. Field elms (Ulmus minor Miller (Ulmaceae)) release a blend of volatiles in response to oviposition of the elm leaf beetle, Xanthogaleruca luteola Müller (Coleoptera: Chrysomelidae), a major urban and forest pest in the USA and Australia. This induced blend attracts the beneficial egg parasitoid Oomyzus gallerucae Fonscolombe (Hymenoptera: Eulophidae). Our olfactory assays showed that an odorous background of non-attractive host plant volatiles from feeding damaged elms or (Z)-3-hexenyl acetate masks the attractive effect of the host-induced (E)-β-caryophyllene to O. gallerucae. Quantitative GC–MS analyses revealed decreased concentrations of (Z)-3-hexenyl acetate accompanied by highly increased concentrations of sesquiterpenes in oviposition and feeding treated elms compared to undamaged elms. This finding hints to how the parasitoid might distinguish between different odorous backgrounds. It is corroborated by the outcome of our field study in natural elm stands, where the egg parasitoid parasitized more host egg masses due to an artificially induced blend of elm terpenoids.     

Effects of litters with different concentrations of phenolics on the competition between Calluna vulgaris and Deschampsia flexuosa

We hypothesized that the outcome of competition between ericaceous plants and grasses is strongly affected by the concentrations of phenolics in the litter that they produce. To test the effect of phenolic-rich litter on soluble soil nitrogen concentrations, plant nitrogen uptake and inter-specific competition, we conducted a greenhouse experiment with the shrub Calluna vulgaris and the grass Deschampsia flexuosa and their leaf litters. Two litters of C. vulgaris were used, with equal nitrogen concentration but different (high and low) concentrations of total phenolics. The D. flexuosa leaf litter contained lower concentrations of phenolics, but higher concentrations of nitrogen than the C. vulgaris litters. The plants were grown in monocultures and in mixed cultures. Inorganic and dissolved organic nitrogen were measured monthly during the experiment. After four months, we measured above- and belowground biomass and the nutrient concentrations in above- and belowground plant parts. In monocultures, C. vulgaris produced more shoot and root biomass on its own litter than with no litter. Growth of Calluna was reduced on grass litter. D. flexuosa plants produced most biomass on their own litter type, whether in monocultures or in mixed cultures. Addition of Calluna litter stimulated the growth of D. flexuosa both in monoculture and in mixtures. The grass plants outcompeted Calluna both on shrub litter and on grass litter but not when grown without litter. The two C. vulgaris litter types that differed in their concentration of phenolics did not differ in their effects on the competition between the two species or on the production of inorganic and dissolved organic nitrogen. We conclude that the nitrogen content of the litter is more important as a plant feature driving competition between shrubs and grasses than the concentrations of phenolics.