Short-term effects of olive mill waste water (OMW) on chemical and biochemical properties of a semiarid Mediterranean soil

Olive mill waste water (OMW), a by-product of the olive mill industry, is produced in large amounts in Mediterranean countries. Olive mill waste water contains a high organic load, substantial amounts of plant nutrients but also several compounds with recognized toxicity towards living organisms. Moreover, OMW may represent a low cost source of water. Thus, the use of OMW for soil fertigation is a valuable option for its disposal, provided that its impact on soil chemical and biochemical properties is established. Investigations were performed on the short-term influence of OMW on several chemical and biochemical properties of a soil from a continental semi-arid Mediterranean region (Morocco). The soil was amended with 0, 18 and 36 ml 100 g⁻¹ soil of OMW (corresponding to a field rate of 0, 40 and 80 m³ ha⁻¹, respectively) and changes in various functionally related properties such as microbial biomass, basal respiration, extractable C and N, and soil hydrolases and oxido-reductases activities were measured over time. The variations of the main physical and chemical properties as well as the residual phytotoxicity of OMW amended and non-amended soils as assessed by tomato seed germination tests were also monitored. Temporary and permanent changes in several chemical and biochemical soil properties occurred following OMW application, thus being these properties varied in sensitivity to the applied disturbance. A sudden increase of total organic C, extractable N and C, available P and extractable Mn and Fe contents were measured. Simultaneously, a rapid increase of soil respiration, dehydrogenase and urease activities and microbial biomass (at 14 day incubation) of OMW amended soils occurred. In contrast, the activities of phosphatase, β-glucosidase, nitrate reductase and diphenol oxidase decreased markedly. The soil became highly phytotoxic after OMW addition (large decline of soil germination capability), mainly at 80 m³ ha⁻¹ OMW. After 42 days' incubation, however, a complete recovery of the soil germination capability and a residual phytotoxicity of about 30% were observed with 40 and 80 m³ ha⁻¹ OMW, respectively. These findings indicate that the impact of OMW on soil properties was the result of opposite effects, depending on the relative amounts of beneficial and toxic organic and inorganic compounds present. The toxic compounds contained in OMW most likely counteracted the beneficial effect of organic substrates provided, which promoted the growth and activity of indigenous microorganisms.     

Treated Olive Mill Wastewater Effects on Soil Properties and Plant Growth

Olive-oil production has a vital impact on the socioeconomic development in most Mediterranean countries, where 97.5 % of the world oil is produced. However, the olive-oil extraction process generates considerable quantities of an agro-industrial effluent, olive mill wastewater (OMW), which has negative impact on the environment and biological life. The objective of this study was to evaluate the potential use of OMW treated by different technologies in irrigation and determine its effect on the plant growth and soil quality parameters. Different technologies were used to treat the OMW, the resultant treated OMW was used to irrigate the maize planted in the pot experiment. The results indicated that UOMW increased soil salinity and reduced plant growth, while the treated OMW by different technologies improved plant growth and resulted in lower soil pH. The impact on other soil properties varied depending on the techniques used for treatments. Although treated OMW enhanced plant growth compared with the untreated, the plant growth remained lower than that obtained using the potable water with fertilizers, indicating lack of some essential plant nutrients.     

Conserved chemical properties of young humic acid fractions in tropical lowland soil under intensive irrigated rice cropping

Increasing cropping intensity (i.e. number of crops per year) of irrigated rice seems to cause an accumulation of phenolic compounds in the soil organic matter (SOM). We have studied the chemical nature of SOM in a broad range of soil types at different sites with long-term double- and triple-crop irrigated rice trials. Accumulation of phenols, as measured by ¹³C nuclear magnetic resonance spectroscopy, was found in both the mobile humic acid (MHA) and calcium humate (CaHA) fractions at all sites, regardless of soil type, hydrology during the fallow, and with and without inorganic fertilizer or green manures. Although phenols accumulated consistently in MHA and CaHA, the C, N and hydrolysable amino acid concentrations, degree of humification and amounts of MHA and CaHA were significantly altered by crop management, and they varied from site to site. Our results are consistent with the hypothesis that the accumulation of phenols is a characteristic of the anaerobic, or nearly anaerobic, soil conditions that exist at the initial stages of SOM formation in submerged irrigated rice soils. By contrast, other SOM properties are additionally influenced by soil conditions that govern the degradation and turnover of existing SOM. The chemical properties of MHA and CaHA indicated that they are labile, and the quantities of these HA fractions were more sensitive to recent management than were total soil C or N.     

Activated Carbon Adsorption of Fuel Oxygenates MTBE and ETBE from Water

In order to assess as to whether treated textile effluent could be safely used to irrigate some winter vegetables, growth room experiments were conducted. Varying levels of treated and untreated textile effluents were applied to germinating seeds of some winter vegetables and their effect was evaluated on germination and early growth stage using seed germination, growth, and biochemical attributes. From the results, it was obvious that textile effluent reduced seed germination and early growth of all vegetables. However, this effect was more pronounced at the highest concentration of textile effluent. Furthermore, treated textile effluent did not show any inhibitory effect on seed germination of all vegetables. Photosynthetic pigments such as chlorophyll a and b, and protein contents were higher in the leaves of all vegetable plants irrigated with treated textile effluent than those of supplied with untreated textile effluents. It has been observed that heavy metals were lower in concentration in treated textile effluent as compared with untreated textile effluent. However, germination and growth responses of all three vegetables were different to treated or untreated textile effluents. Furthermore, the Raphanus sativus ranked as tolerant followed by Brassica campastris and Brassica napus based on germination and growth responses. In conclusion, in view of shortage of water, textile effluent could safely be used for irrigation to vegetables after proper processing.     

Model study on the effect of 15 phenolic olive mill wastewater constituents on seed germination and Vibrio fischeri metabolism

Olive mill wastewaters (OMW) can be a severe problem when disposed of as untreated because of their high organic load, elevated concentration of polyphenols, and moderately low biodegradability. In the present study, the acute toxicity of 15 compounds with low molecular weight (<350 Da), catechol, four benzoic acids, three phenylacetic acids, three phenylethanols, and four cinnamic acids, already isolated from the reverse osmosis in the fractionation of OMW, was assessed on the marine bacterium Vibrio fischeri and on the seeds of two dicotyledonous species Cucumis sativus and Lepidium sativum, and on one monocotyledon Sorghum bicolor. Results of phytotoxicity showed that the most toxic compounds were catechol (EC50s ranging from 0.40 mmol/L for S. bicolor to 1.09 for C. sativus) and hydroxytyrosol, (EC50s ranging from 0.47 mmol/L for S. bicolor to 1.55 for C. sativus) while the toxic potential on bacteria was particularly elevated with EC50 values 1 or 2 orders less than phytotoxicity. These results suggested that the risk of OMW disposal may be more elevated for the water compartment than for the soil.     

Olive oil mill wastewater treatment using a chemical and biological approach

Olive oil mill wastewaters (OMW) are recalcitrant to biodegradation for their toxicity due to high values of chemical oxygen demand (COD), biological oxygen demand (BOD), and phenolic compounds. In the present study OMW, collected in southern Italy, were subjected first to a chemical oxidative procedure with FeCl3 and then to a biological treatment. The latter was performed in a pilot plant where mixed commercial selected bacteria, suitable for polyphenols and lipid degradation, were inoculated. The effect of treatments was assessed through COD removal, reduction of total phenols, and decrease of toxicity using primary consumers of the aquatic food chain (the rotifer Brachionus calyciflorus and the crustacean Daphnia magna). The results showed that the chemical oxidation was efficacious in reducing all parameters analyzed. A further decrease was found by combining chemical and biological treatments.     

Change in soil properties and the soil microbial community following land spreading of olive mill wastewater affects olive trees key physiological parameters and the abundance of arbuscular mycorrhizal fungi

Olive mill wastewater (OMW) constitutes a major environmental problem for Mediterranean countries, where most of the world olive oil production takes place. The recycling of the OMW and its use as water for irrigation in agriculture, provided that its impact on soil and plant is established, is an attractive possibility for the Mediterranean countries. Investigations were performed on the influence of agronomic application of OMW (amount applied: 30, 60, 100 and 150 m³ ha^?1) in a field of olive trees on trees characters (photosynthesis, root-soluble carbohydrate and root colonisation), soil properties, and soil microbial community structure. Specific attention was paid to arbuscular mycorrhizal (AM) fungi. The soil fatty acid methyl ester (FAME) 16:1ω5 was used to quantify biomass of AM fungi and the root FAME 16:1ω5 analysis was used as index for the development of colonisation in the olive trees roots. A significant increase in organic C, C/N ratio, extractable phosphorus and exchangeable potassium was found after one year of agronomic application of OMW. The development of saprophytic fungi was significantly higher in the OMW amended soils, whereas the abundance of the soil FAME 16:1ω5, root FAME 16:1ω5, photosynthetic rates and the amount of the total root-soluble carbohydrate were decreased significantly after agronomic application of OMW. A principal component analysis (PCA) of the trees characteristics profiles showed discrimination between the nonirrigated and the OMW irrigated olive trees. These findings suggest that the altering functioning of arbuscular mycorrhizas should be considered as potential factors mediating olive trees responses to agronomic application of OMW when the OMW dose applied is higher than 30 m³ ha^?1. To our knowledge, this is the first report of alterations in the soil FAME 16:1ω5 and root FAME 16:1ω5 due to land spreading of OMW.     

土壤含水率监测位置对温室滴灌番茄耗水量估算的影响

土壤水分传感器埋设位置的选择是局部灌溉条件下获得作物根区代表性土壤含水率数据,从而制定滴灌灌溉制度的关键。本文以日光温室滴灌番茄为对象,研究滴灌线源土壤湿润体内含水率分布状况,通过对比距滴灌带不同位置处土壤含水率监测结果估算番茄耗水量的差异,探讨土壤含水率监测的合理位置。结果表明,番茄生育期内14~25 mm的灌水定额主要用于增加0~40 cm土层的土壤含水率,湿润体内日平均土壤含水率分布在75%~100%田间持水率。作物生育期内连续多次滴灌条件下,沿滴灌带单个灌水器形成的湿润土体会充分叠加,形成近似均匀的土壤含水率带状分布,且作物生育期内沿深度方向0~40 cm土层土壤含水率均值无显著性差异,距滴灌带不同水平距离的土壤含水率随时间的变化趋势具有同步特点,无明显的滞后性。以集中80%总根量的土壤深度作为滴灌番茄水分渗漏下界面时,14~25 mm的灌水定额会导致深层渗漏,且深层渗漏量表现出一定的空间变异性。番茄生育期内深层渗漏量约占灌水量的13%。距滴灌带不同位置处的番茄耗水量除在番茄苗期和开花座果期有较大差异外,其余生育阶段的差异均在10%以内。对温室滴灌番茄来说,滴灌高频少量的灌溉特征有利于维持作物根系层适宜的土壤水分状态,监测1个含水率剖面即可满足估算作物耗水量的要求。     

Short-term effects in soil microbial community following agronomic application of olive mill wastewaters in a field of olive trees

Olive mill wastewater (OMW) creates a disposal problem. The large amounts generated, combined with the high phenol and chemical oxygen demand concentrations, are the main difficulties in finding a solution for the management of these wastewaters. We investigated the short-term effect of spreading OMW on the soil surface of an olive grove on the soil microbial communities. Analyse of ester-linked fatty acid methyl ester (EL-FAME) were used to assess variation in soil microbial community structure after agronomic application of OMW. EL-FAME analysis showed significant shifts of specific groups of fatty acids 30 days after application of OMW to a field of olive trees at rates of 0 (control soil), 30, 60, 100, and 150 m³ ha⁻¹ of OMW. In particular, the branched saturated fatty acids indicative of Gram-positive bacteria decreased and the unsaturated fatty acids commonly found in Gram-negative bacteria and fungi increased. The fungal/bacterial ratio measured increased significantly with increasing OMW. Lower cy19/18:1ω7c and cy17/16:1ω7c ratios were found in the amended soil than the control soil, and we interpret that as an indication that nutrient availability may be more limiting in the control soil. Similarly, the relative abundances of monounsaturated fatty acids increased with added OMW, and this is consistent with the presence of high substrate availability in OMW-treated soil. Principal Components Analysis of the FAME profiles showed discrimination between the control soil and OMW amended soil. Differences in fatty acid profiles between OMW-treated soil and control soil suggests that amendment of soil with OMW favors specific groups of organisms. To our knowledge, this is the first report of alterations in the FAME profile in soils due to agronomic application of OMW.     

Physico – biochemical properties of tomato (Solanum lycopersicum) grown in heavy – metal contaminated soil

The present study was undertaken to investigate the effect of soil contamination with heavy metals on physico-biochemical properties of tomato fruit. The deleterious effect of soil contamination on the quality and quantity of tomato plant yield was determined. Harvested tomato fruit characteristics including fruit length, diameter, volume and fresh and dry weights, total soluble solids, titratable acidity, lycopene and carbohydrates contents were measured in tomato fruits cultivated in soil contaminated with industrial effluents. In addition, some secondary metabolites (total phenols and flavonoids), micro- and macronutrients were also detected. Residual heavy metals (Cd, Co, Ni and Pb) were examined in the harvested fruits. The obtained results were compared with those of tomato fruits cultivated in non-contaminated soil. Results demonstrate that soil contamination with heavy metals have a negative effect on tomato fruits characteristics, titratable acidity, total soluble solids, lycopene, ascorbic acid, micro-elements and carbohydrates content. Moreover, fruits originated from plants grown in contaminated soil possess high phenols and flavonoids contents and higher heavy metals content compared to control fruits. It is recommended that fruits cultivated in that area not to be eaten by large quantities, to avoid excessive accumulation of heavy metals in the human body.

Abbreviations: (AsA): Ascorbic acid; (DTPA): diethylenetriamine penta acetic acid; (TA): Titratable acidity; (TSS): Total soluble solids     

Olive mill wastewater effects on the microbial communities as studied in the field of olive trees by analysis of fatty acid signatures

The aim of this work was to study the effects of spreading olive mill wastewater (OMW) on the soil surface of an olive grove on the soil microbial communities. Analyses of ester-linked fatty acid methyl esters (EL-FAME) were used to assess variations in the soil microbial community structure following land spreading of OMW. Our data provide evidence that agronomic application of OMW has important effects on soil microbial community. Bacteria were relatively more reduced by these treatments than fungi and actinomycetes as revealed by an increased index of fungal/bacterial FAME and actinomycetes/bacterial FAME. Specific FAME markers indicated a significant reduction in the Gram-positive bacteria. However, the relative proportion of the Gram-negative bacteria was not significantly different after agronomic application of OMW. The ratios of cyclopropyl/monoenoic precursors decreased and the total monounsaturated/total saturated fatty acids increased in the OMW amended soils, suggesting that the microbes inhabiting the control soil are more carbon limited than the OMW amended soils. The changes in the FAME pattern of the soil organisms possibly were related (i) to an altered substrate quantity, that is the availability of substrates after the treatments, (ii) the complex nature of OMW which also contains high molecular-mass recalcitrant polyphenols.     

纳米氧化镁促进番茄植株生长的机理

  【目的】  探讨具有抗菌作用剂量的纳米氧化镁 (MgONPs) 对番茄早期生长发育的影响,并明确其被吸收和在植株体内的运输特性,为MgONPs在植物营养和病害防控领域的应用提供理论依据。  【方法】  以番茄为模式植物,利用MgONPs (50～250 μg/mL) 处理番茄种子和幼苗,测定种子萌发率、MgONPs处理幼苗30天后的植株生物量、植物组织细胞形态、叶绿素含量和相对含水量等指标,并用电感耦合等离子发射光谱仪和透射电子显微镜 (TEM) 测定植株对MgONPs的吸收状况。  【结果】  50～250 μg/mL的MgONPs对番茄种子的发芽无抑制作用,而对番茄幼苗生长具有显著的促进作用,其中250 μg/mL剂量作用最显著;此剂量处理后的番茄根长、根干重、地上部分干重和径围分别为20.33 cm、0.11 g、0.20 g、1.65 cm,对照分别为15.63 cm、0.03 g、0.15 g和1.16 cm;番茄叶绿素含量提高了47.37%,相对含水量提高了13.14%。且MgONPs促进了镁元素的吸收,MgONPs处理后番茄叶片中的镁含量较清水组提高了35.16%;透射电子显微镜 (TEM) 照片发现,MgONPs处理后叶片叶绿体周围有纳米颗粒的聚集;扫描电子显微镜 (SEM) 照片和石蜡切片观察证实,MgONPs未破坏番茄植株的组织和细胞形态,明确了在一定浓度下MgONPs对番茄植物细胞无毒副影响。  【结论】  MgONPs在土壤中的分散程度虽然不如在去离子水中,但是依然表现出对番茄生长的显著促进作用,且对种子发芽和幼苗生长无任何不利影响。施入土壤后,MgONPs能被番茄根系吸收,通过维管束系统向上运输至叶片中,从而显著增加叶绿素含量和相对含水量,最终促进了幼苗的生长和干物质积累。在本试验条件下,高浓度 (250 μg/mL) 的MgONPs促进番茄生长的效果好于低浓度。     

Effects of soil application of olive mill wastewaters on the structure and function of the community of arbuscular mycorrhizal fungi

Recycling of olive mill wastewaters (OMW) into agricultural soils is a controversial issue since benefits to soil fertility should counterbalance potential short-term toxicity effects. We investigated the short-term effects of OMW on the soil-plant system, regarding the diversity, structure and root colonization capacity of arbuscular mycorrhizal (AM) fungi and the respective growth response of Vicia faba L, commonly used as green manure in olive-tree plantations. A compartmentalized pot system was used that allowed the establishment of an AM fungal community in one compartment (feeder) and the application of three OMW dose levels in an adjacent second compartment (receiver). At 0, 10, and 30 days after OMW treatment (DAT), V. faba pre-germinated seeds were seeded in the receiver compartment. At harvest, shoot and root dry weights, AM fungal root colonization, soil hyphal length and P availability were recorded in the receiver compartment. In addition, OMW effects on AM fungal diversity in plant roots were studied by DGGE. A transient effect of OMW application was observed; plant growth and AM fungal colonization were initially inhibited, whereas soil hyphal length was stimulated, but in most cases differences were absent when seeding was performed 30 DAT. Similarly, changes induced in the structure of the root AM fungal community were of transient nature. Cloning and sequencing of all the major DGGE bands showed that roots were colonized by Glomus spp. The transient effects of OMW on the structure and function of AM fungi could be attributed to OMW-derived phytoxicity to V. faba plants or to an indirect effect via alteration of soil nutritional status. The high OMW dose significantly increased soil P availability in the presence of AM fungi, suggesting efficient involvement of AM fungi in organic-P minerilization. Overall our results indicate that soil application of OMW would cause transient changes in the AM fungal colonization of V. faba plants, which, would not impair their long-term plant growth promoting ability.     

DETERMINATION OF OLIVE MILL WASTEWATER TOXIC EFFECTS ON THREE MINT SPECIES GROWN IN HYDROPONIC CULTURE

The effects of two olive mill wastewater (OMW) dilutions upon physiological function and metabolic components of three mint species grown in hydroponic culture were studied. Visible symptoms, chlorosis and stunted growth, were pronounced in peppermint and spearmint; toxicity symptoms in menthe douce were few. Peppermint and spearmint displayed loss of calcium (Ca), magnesium (Mg), and potassium (K); menthe douce revealed accumulation of Ca, sodium (Na), and iron (Fe), under OMW. The loss of Ca negatively affected the development and stability of cell wall and membrane; the Mg deficiency negatively affected the photosynthetic apparatus and carbon fixation. Fv′/ Fm′ was slightly affected under OMW, whereas, Φ_PSII, q _P and Rfd displayed significant reductions. No clear effect of OMW on phenols and carbohydrates among the species were found. Ascorbic acid content in peppermint dropped dramatically; the reduction was lower for spearmint and menthe douce. The OMW resistant species, menthe douce, developed a mechanism to control the physiological and the biochemical status.     

VERMICOMPOSTING AS A NITROGEN SOURCE IN GERMINATING KIDNEY BEAN IN TRAYS

This study assessed the effectiveness of vermicompost as a germination media and nitrogen source for kidney bean Phaseolus vulgaris L. Five treatments were tested, based on the addition of increasing quantities of barren soil to vermicompost, and irrigated with four treatments of increasing urea-water solution. Chemical analysis of the different mixtures of vermicompost and barren soil were made. Percentage germination, plant growth, and foliar nitrogen assimilation were measured. Bean seeds in vermicompost germinated earlier than those planted in barren soil, but germination was less than 60% in trays with 85% and 100% vermicompost. Plants in vermicompost were taller and appeared to be healthier-looking. Plants with 0%, 50% and 85% vermicompost concentrations assimilated about 4 mg·L^?1 more nitrogen than other treatments (25% and 100%). Plants in the 85% vermicompost mixture had the best response to nitrogen assimilation.     

A Comparison of Five Bioassays to Monitor Toxicity During Bioremediation of Pentachlorophenol-Contaminated Soil

Five bioassays were used to measure toxicity during bioremediation of a soil contaminated with pentachlorophenol (PCP; 335 ppm), polycyclic aromatic hydrocarbons (PAHs; 1225 ppm) and petroleum hydrocarbons (19 125 ppm). Different bioremediation treatments were tested in soil microcosms including amendment with phosphorus and/or PCP-degrading Pseudomonas sp. UG30, either as free cells or encapsulated in κ-carrageenan. Soil toxicity was monitored using the solid-phase Microtox test, SOS-chromotest, lettuce seed germination, earthworm survival and sheep red blood cell (RBC) haemolysis assays. PCP levels were reduced in all treatments after 210 days. The RBC lysis assay, Microtox test and SOS-chromotest indicated reduced toxicity in most of the microcosms by day 210. Trends depicted by lettuce seed germination and earthworm survival LC50 values varied with each treatment. For example, in soil amended with phosphorus, both the seed germination and earthworm survival LC50 data suggested increased soil toxicity. However, for soil treated with encapsulated Pseudomonas sp. UG30 cells, the earthworm survival LC50 data indicated reduced toxicity while seed germination LC50 values showed little change from values obtained prior to bioremediation. Our results show that toxicity trends in a contaminated soil during bioremediation differ according to the assay used.     

Effects of olive oil mill wastewater on chemical,microbiological, and physical properties of soil incubated under four different climatic conditions

The objective of this study was to understand the degradation of the organic matter of olive mill wastewater (OMW) and its phytotoxic and water repellent effects in dependence on four different climatic conditions. We hypothesized that warm conditions with sufficient soil moisture ensure optimal biological activity and thus minimize negative effects of the OMW treatment. Therefore, OMW-treated soil was incubated for 60 days under four climatic conditions. During incubation, we monitored pH, contents of nitrate, manganese and phenolic compounds, soil respiration, soil water repellency, and δ¹³C. Additionally, calorific value and thermal stability of the soil organic matter at the beginning and end of incubation were determined. Soil samples of the wet-cold and moist-warm incubation were tested for phytotoxicity using a seed germination bioassay with Lepidium sativum. As a function of climatic conditions, positive and negative effects, e.g., addition of nutrients, phytotoxicity, and soil water repellency, were observed. Under dry-hot conditions, the soil was still water repellent after 60 days of incubation whereas the wet-hot, moist-warm, and wet-cold incubation show that soil would stay wettable if soil moisture before OMW treatment would be sufficient. Thus, the impact of OMW treatment on soil quality strongly depends on the environmental conditions which should favor an enhancement of microbial activity to minimize negative effects.     

The fate of organic matter brought into soil by olive mill wastewater application at different seasons

Purpose

Application of olive mill wastewater (OMW) to soil may cause positive or negative effects. The present study aims at a better understanding of the fate of organic matter brought into soil by OMW application under different environmental conditions.

Materials and methods

Single OMW application to soil was conducted in spring, dry summer, summer with irrigation, and in winter. Two days and 18–24 months after the application, soil samples from two depths were analyzed for thermal soil organic matter (SOM) properties, total organic carbon, water-extractable dissolved soil organic carbon, and its specific ultraviolet absorbance at 254 nm.

Results and discussion

After winter and irrigated summer treatments, OMW was largely leached from the upper horizon within 2 days. Application in spring and summer dry initially increased the thermolabile fraction and the calorific value of SOM, however, in a different degree due to different transport, transformation, and immobilization mechanisms. At the long term, SOM content was still elevated after summer dry treatment. The reduction of the thermostable fraction in spring treatment indicates a priming effect of the labile OMW constituents.

Conclusions

Application in winter or with irrigation cannot be recommended for the investigated site. Under hot and dry conditions, SOM content increased most persistently due to stronger mineral-organic interactions. Favorable conditions for biodegradation during OMW application in spring reduced the effects on SOM quantity in the long term. However, a possible priming effect and the persistence of changes in thermal properties need to be further investigated for repeated applications.

     

The influence of the root-knot nematode Meloidogyne incognita, the nematicide aldicarb and the nematophagous fungus Pochonia chlamydosporia on heterotrophic bacteria in soil and the rhizosphere

Plant‐pathogenic nematodes are a major cause of crop damage worldwide, the current chemical nematicides cause environmental damage, but alternatives such as biological control are less effective, so further understanding of the relationship between nematodes, nematicides, biological control agents and soil and rhizosphere microorganisms is needed. Microbial populations from roots of cabbage and tomato plants infested with the root‐knot nematode Meloidogyne incognita were compared with those from plants where the nematode was controlled by the nematicide aldicarb, or a nematophagous fungus with biological control potential, Pochonia chlamydosporia. The total numbers of culturable bacteria and fungi in rhizosphere soil were similar in all three treatments for both plants, around 100‐fold more than in control soil in which there were no plants. However, there were clear differences in the catabolic diversity, assessed by Biolog EcoPlate? carbon substrate utilization assays, between microbial populations from unplanted soil and the rhizosphere. In cabbage, a poor host for M. incognita, the rhizosphere population from P. chlamydosporia‐treated plants was distinct from the population from untreated and aldicarb‐treated plants. In tomato, a host susceptible to the nematode, the catabolic diversity of populations from aldicarb‐ and P. chlamydosporia‐treated plants was similar and differed from the untreated, nematode‐infested plants. The genetic diversity of the fast‐growing heterotrophic bacteria in the tomato rhizosphere, indicated by PCR fingerprinting with ERIC primers, was very different in the infested roots, whereas the profiles of isolates from both aldicarb‐ and P. chlamydosporia‐treated roots were similar. Evidently, nematodes have a greater impact on the rhizosphere population of a susceptible host, tomato, than a poor one, cabbage, and nematode‐infested roots are colonized by a different subpopulation of soil microbes from that on plants where infection is controlled, illustrating differences in root morphology and physiology.     

碳含量对再生水灌溉土壤氮素迁移转化规律的影响

为深入了解碳含量对再生水灌溉系统中氮素迁移转化的影响,该研究进行了碳含量影响下的再生水灌溉系统氮素迁移转化规律试验。利用不同碳含量的再生水灌溉种植在土柱中的黑麦草,测定各试验周期内灌溉水、土壤溶液和排水中不同形态氮的含量,分析不同生育期作物干物质产量和氮含量。结果表明,随灌溉水进入系统的氮素约有34%可被作物吸收利用,62%可通过反硝化作用去除或调节土壤氮库中的氮量,随水分下渗到根系层以下并随排水排出系统的氮量仅占灌溉水中氮量的3%～4%。从作物长势、干物质量和氮的利用量看,高碳处理优于低碳处理。试验条件下,再生水中碳含量较高时有利于氮素的转化、作物吸收利用以及氮的反硝化作用。研究结果对于以灌溉利用为目的的污水处理,具有一定的指导意义。