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.     

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.     

Microbial activity,community structure and potassium dynamics in rhizosphere soil of soybean plants treated with glyphosate

With the advent of glyphosate [N-(phosphonomethyl)glycine] tolerant crops, soils have now been receiving repeated applications of the herbicide for over 10 years in the Midwestern USA. There is evidence that long-term use of glyphosate can cause micronutrient deficiency but little is known about plant potassium (K) uptake interactions with glyphosate. The repeated use of glyphosate may create a selection pressure in soil microbial communities that could affect soil K dynamics and ultimately K availability for crops. Therefore, the objectives of this study were to characterize the effect of foliar glyphosate applied to GR (glyphosate resistant) soybeans on: (1) rhizosphere microbial community profiles using ester linked fatty acid methyl ester (EL-FAME) biomarkers, (2) exchangeable, non-exchangeable, and microbial K in the rhizosphere soil, and (3) concentrations of soybean leaf K. A greenhouse study was conducted in a 2 × 2 × 3 factorial design with two soil treatments (with or without long-term field applications of glyphosate), two plant treatments (presence and absence of soybean plants), and three rates of glyphosate treatments (0×, 1× at 0.87, and 2× at 1.74 kg ae ha^?1, the recommended field rate). After each glyphosate application, rhizosphere soils were sampled and analyzed for microbial community structure using ester linked fatty acid methyl ester biomarkers (EL-FAME), and exchangeable, plant tissue and microbial biomass K. Glyphosate application caused a significant decrease in the total microbial biomass in soybean rhizosphere soil that had no previous exposure to glyphosate, at 7 days after glyphosate application. However, no significant changes were observed in the overall microbial community structure. In conclusion, the glyphosate application lowered the total microbial biomass in the GR soybean rhizosphere soil that had no previous exposure to glyphosate, at 7 days after glyphosate application; caused no changes in the microbial community structure; and did not reduce the plant available K (soil exchangeable or plant tissue K).     

The effects of fresh and stabilized pruning wastes on the biomass,structure and activity of the soil microbial community in a semiarid climate

The incorporation of organic amendments from pruning waste into soil may help to mitigate soil degradation and to improve soil fertility in semiarid ecosystems. However, the effects of pruning wastes on the biomass, structure and activity of the soil microbial community are not fully known. In this study, we evaluate the response of the microbial community of a semiarid soil to fresh and composted vegetal wastes that were added as organic amendments at different doses (150 and 300 t ha⁻¹) five years ago. The effects on the soil microbial community were evaluated through a suite of different chemical, microbiological and biochemical indicators, including enzyme activities, community-level physiological profiles (CLPPs) and phospholipid fatty acid analysis (PLFA). Our results evidenced a long-term legacy of the added materials in terms of soil microbial biomass and enzyme activity. For instance, cellulase activity reached 633 μg and 283 μg glucose g⁻¹ h⁻¹ in the soils amended with fresh and composted waste, respectively. Similarly, bacterial biomass reached 116 nmol g⁻¹ in the soil treated with a high dose of fresh waste, while it reached just 66 nmol g⁻¹ in the soil amended with a high dose of composted waste. Organic amendments produced a long-term increase in microbiological activity and a change in the structure of the microbial community, which was largely dependent on the stabilization level of the pruning waste but not on the applied dose. Ultimately, the addition of fresh pruning waste was more effective than the application of composted waste for improving the microbiological soil quality in semiarid soils.     

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.     

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.     

Improving soil structure by promoting fungal abundance with organic soil amendments

Building soil structure in agroecosystems is important because it governs soil functions such as air and water movement, soil C stabilization, nutrient availability, and root system development. This study examined, under laboratory conditions, effects of organic amendments comprised of differing proportions of labile and semi-labile C on microbial community structure and macroaggregate formation in three variously textured soils where native structure was destroyed. Three amendment treatments were imposed (in order of increasing C lability): vegetable compost, dairy manure, hairy vetch (Vicia villosa Roth). Formation of water stable macroaggregates and changes in microbial community structure were evaluated over 82 days. Regardless of soil type, formation of large macroaggregates (LMA, >2000 μm diameter) was highest in soils amended with vetch, followed by manure, non-amended control, and compost. Vetch and manure had greater microbially available C and caused an increase in fungal biomarkers in all soils. Regression analysis indicated that LMA formation was most strongly related to the relative abundance of the fungal fatty acid methyl ester (FAME) 18:2ω6c (r = 0.55, p < 0.001), fungal ergosterol (r = 0.58, p < 0.001), and microbial biomass (r = 0.57, p < 0.001). Non-metric multidimensional scaling (NMS) ordination of FAME profiles revealed that vetch and manure drove shifts toward fungal-dominated soil microbial communities and greater LMA formation in these soils. This study demonstrated that, due to their greater amounts of microbially available C, vetch or manure inputs can be used to promote fungal proliferation in order to maintain or improve soil structure.     

The effect of glyphosate on soil microbial activity,microbial community structure,and soil potassium

The herbicide, glyphosate [N-(phosphonomethyl) glycine] is extensively used worldwide. Long-term use of glyphosate can cause micronutrient deficiency but little is known about potassium (K) interactions with glyphosate. The repeated use of glyphosate may create a selection pressure in soil microbial communities that could affect the nutrient dynamics such as K. The objective of this study was to determine the effect of single or repeated glyphosate applications on microbial and K properties of soils. A 54 day incubation study (Exp I) had a 3 × 5 factorial design with 3 soils (silt loam: fine, illitic, mesic Aeric Epiaqualf) of similar physical and chemical characteristics, that varied in long-term glyphosate applications (no, low, and high glyphosate field treatments) and five glyphosate rates (0, 0.5×, 1×, 2×, and 3× recommended field rates applied once at time zero). A second 6 month incubation study (Exp II) had a 3 × 3 factorial design with three soils (as described above) and three rates of glyphosate (0, 1×, and 2× recommended field application rates applied monthly). For each study microbial properties [respiration; community structure measured by ester linked fatty acid methyl ester (EL-FAME) analysis and microbial biomass K] and K fractions (exchangeable and non-exchangeable) were measured periodically. For Exp I, glyphosate significantly increased microbial respiration that was closely related to glyphosate application rate, most notably in soils with a history of receiving glyphosate. For Exp II, there was no significant effect of repeated glyphosate application on soil microbial structure (EL-FAME) or biomass K. We conclude that glyphosate: (1) stimulates microbial respiration particularly on soils with a history of glyphosate application; (2) has no significant effect on functional diversity (EL-FAME) or microbial biomass K; and (3) does not reduce the exchangeable K (putatively available to plants) or affect non-exchangeable K. The respiration response in soils with a long-term glyphosate response would suggest there was a shift in the microbial community that could readily degrade glyphosate but this shift was not detected by EL-FAME.     

Repeated application of diluted olive mill wastewater induces changes in the structure of the soil microbial community

Repeated application of diluted olive mill wastewater (OMW) is a common disposal method which allows the application of large amounts of OMW and improves the organic matter and nutrient status of Mediterranean soils. However, there is lack of information regarding the effects of this practice on the soil microbial community. A study was carried out to investigate these effects on the structure of the bacterial and fungal community of a loamy sand (LS) and a sandy loam (SL) soil, using denaturating gradient gel electrophoresis (DGGE) fingerprinting. OMW was daily applied as aqueous solutions of 0, 2 and 4%, in the presence or absence of nitrogen fertilization, for a three-month period. Multivariate analysis of the DGGE profiles showed that OMW applications resulted in marked changes in the fungal community in both soils, while nitrogen fertilization diminished these effects. Small effects were evident for the bacteria only in the LS soil and this was attributed to the higher availability of OMW-derived phenolics in this soil which resulted in a direct impact on bacteria. Nitrogen fertilization alleviated the effects of OMW on the bacterial community. We suggest that the impact of OMW on the structure of the soil microbial communities was mostly a result of its indirect effect on the soil nutritional status, which becomes enriched in organic substrates and poor in available nitrogen.     

Changes in microbial communities and carbohydrate profiles induced by the mycorrhizal fungus (Glomus intraradices) in rhizosphere of olive trees (Olea europaea L.)

The influence of inoculation of olive trees with arbuscular mycorrhizal (AM) fungi, Glomus (G) intraradices, on microbial communities and sugar concentrations, were examined in rhizosphere of olive trees (Olea europaea L.). Analyses of phospholipid and neutral lipid fatty acids (PLFA and NLFA, respectively) were then used to detect changes in microbial community structure in response to inoculation of plantlets with G. intraradices.Microscopic observations studies revealed that the extraradical mycelium of the fungus showed formation of branched absorbing structures (BAS) in rhizosphere of olive tree. Root colonization with the AM fungi G. intraradices induced significant changes in the bacterial community structure of olive tree rhizosphere compared to non-mycorrhizal plants. The largest proportional increase was found for the fatty acid 10Me18:0, which indicated an increase in the number of actinomycetes in mycorrhizal rhizosphere soil, whereas the PLFAs i15:0, a15:0, i16:0, 16:1ω7 and cy17:0 which were used as indicators of bacteria decreased in mycorrhizal treatment compared to non-mycorrhizal control treatment. A highest concentration of glucose and trehalose and a lowest concentration of fructose, galactose, sucrose, raffinose and mannitol were detected in mycorrhizal rhizosphere soil. This mycorrhizal effect on rhizosphere communities may be a consequence of changes in characteristics in the environment close to mycorrhizal roots.     

Production of carbon dioxide and nitrous oxide in alkaline saline soil of Texcoco at different water contents amended with urea: A laboratory study

Soil of the former lake Texcoco is alkaline saline with pH often >10 and electrolytic conductivity (EC) >70 dS m^?1 with rapidly changing water contents. Little is known how fertilizing this area with urea to vegetate the soil would affect emissions of carbon dioxide (CO₂) and dynamics of N. Texcoco soil with electrolytic conductivity (EC) 2.3 dS m^?1 and pH 8.5 (TEXCOCO A soil), EC 2.0 dS m^?1 and pH 9.0 (TEXCOCO B soil) and 200 dS m^?1 and pH 11.2 (TEXCOCO C soil) was amended with or without urea and incubated at 40% of water holding capacity (WHC), 60% WHC, 80% WHC and 100% WHC, while emissions of nitrous oxide (N₂O) and CO₂ and dynamics of ammonium (NH₄⁺), nitrite (NO₂^?) and nitrate (NO₃^?) were monitored for 7 days. An agricultural soil served as control (ACOLMAN soil). The emission of CO₂ increased in the urea amended soil 1.5 times compared to the unamended soil, it was inhibited in TEXCOCO C soil and was >1.2 larger in soil incubated at 40%, 60% and 80% WHC compared to soil incubated at 100% WHC. The emission of N₂O increased in soil added with urea compared to the unamended soil, was similar in TEXCOCO A and B soils, but was <0.2 mg N kg^?1 soil day^?1 in TEXCOCO C soil and generally larger in soil incubated at 60% and 80% WHC compared to soil incubated at 40% and 100% WHC. The water content of the soil had no significant effect on the mean concentration of NH₄⁺, but addition of urea increased it in all soils. The concentration of NO₂^? was not affected by the water content and the addition of urea except in TEXCOCO A soil where it increased to values ranging between 20 and 40 mg N kg^?1. The concentration of NO₃^? increased in the ACOLMAN, TEXCOCO A and TEXCOCO B soil amended with urea compared to the unamended soil, but not in the TEXCOCO C soil. It decreased with increased water content, but not in TEXCOCO C soil. It was found that the differences in soil characteristics, i.e. soil organic matter content, pH and EC between the soils had a profound effect on soil processes, but even small changes affected the dynamics of C and N in soil amended with urea.     

Effects of atrazine on microbial activity in semiarid soil

The effect of an atrazine formulation on microbial biomass, microbial respiration, ATP content and dehydrogenase and urease activity in a semiarid soil and the influence of time on the response of soil microbial activity to the herbicide treatment were assessed. The atrazine formulation was added to soil as aqueous solutions of different concentrations of active ingredient to obtain a range of concentrations in the soil from 0.2 to 1000 mg kg⁻¹. Microcosms of soil with the different herbicide concentrations and untreated control soil were incubated for 6 h, 16 and 45 days. In general, an increase in the measured microbiological and biochemical parameters with atrazine concentration in soil was observed. The increase in microbial activity with atrazine pollution was noticeable after lengthy incubation.     

Mitigation of olive mill wastewater toxicity

The toxicity of olive mill wastewaters (OMW) is commonly attributed to monomeric phenols. OMW were treated in an aerated, stirred reactor containing agricultural soil, where the oxidative polymerization of phenols took place. In 24 h, OMW monomeric phenols decreased by >90%. This resulted in a corresponding reduction in phytotoxicity, as measured by germination tests with tomato and English cress seeds, and in microbial toxicity, as measured by lag phase duration in Bacillus cereus batch growth. Soil germination capability after irrigation with OMW was assessed in long-term pot experiments. The relative germination percentage of tomato was higher when the soil was irrigated with treated OMW rather than with untreated ones, although it was lower than the control (e.g., soil irrigated with distilled water). At longer incubation times, a complete recovery of the soil germination capability was achieved with treated, but not with untreated, OMW.     

Effect of swine and dairy manure amendments on microbial communities in three soils as influenced by environmental conditions

Understanding the impacts of manure amendments on soil microorganisms can provide valuable insight into nutrient availability and potential crop and environmental effects. Soil microbial community characteristics, including microbial populations and activity, substrate utilization (SU) profiles, and fatty acid methyl ester (FAME) profiles, were compared in three soils amended or not amended with dairy or swine manure at two temperatures (18 and 25°C) and two soil water regimes (constant and fluctuating) in laboratory incubation assays. Soil type was the dominant factor determining microbial community characteristics, resulting in distinct differences among all three soil types and some differing effects of manure amendments. Both dairy and swine manures generally increased bacterial populations, substrate diversity, and FAME biomarkers for gram-negative organisms in all soils. Microbial activity was increased by both manures in an Illinois soil but only by dairy manure in two Maine soils. Dairy manure had greater effects than swine manure on SU and FAME parameters such as increased activity, utilization of carbohydrates and amino acids, substrate richness and diversity, and fungal FAME biomarkers. Temperature and water regime effects were relatively minor compared with soil type and amendment, but both significantly affected some microbial responses to manure amendments. Overall, microbial characteristics were more highly correlated with soil physical factors and soil and amendment C content than with N levels. These results indicate the importance of soil type, developmental history, and environmental factors on microbial community characteristics, which may effect nutrient availability from manure amendments and should be considered in amendment evaluations.Mention of trade names or commercial products in this article is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the US Department of Agriculture     

Chemical structure of humic acids in biosolids-amended soils as revealed by NMR spectroscopy

We used NMR spectroscopy to characterize humid acids extracted from soils that had received long-term application of 2 levels of biosolids to evaluate the soil organic matter (SOM) stability in biosolids-amended soils. The study also quantified fulvic acids (FAs), humic acids (HAs) and Fe/Al oxides. The soils were collected in 2004 from 7 fields, in Fulton County, southwestern Illinois, which received biosolids at a cumulative rate of 0 (control), 554 (low biosolids) and 1,066 (high biosolids) Mg ha⁻¹. The application of biosolids increased both FA and HA contents, but biosolids-amended soil and control soil did not differ in FA/HA ratio. Biosolids application had no effect on water-soluble organic carbon content. Biosolids application increased the presence of Fe/Al in the SOM complex and lowered its C/Fe and C/Al ratios. ¹³C NMR spectra showed increased alkyl C and decreased aromatic C content in soil HAs with the application of biosolids, and the extent of such changes was higher with high than low biosolids treatment. Under biosolids application, the soil HAs’ C structure shifts from O-alkyl-dominant to alkyl-dominant. Biosolids application does not decrease SOM stability but rather increases the stability of soil humic substances.     

Quadratic response models for N and P mineralization in domestic sewage sludge for mininig dump reclamation

A valuable feature of sewage sludge used for restoring degraded soils is its supplying capacity for C, N and P. A series of laboratory incubation experiments to quantify the release of N and P from raw (dried) and co-composted urban sewage sludges applied to mine dump soil were conducted. The effect of application dose (0–100 g kg⁻¹) and incubation time (0–30 day) on N and P mineralization as well as the process modelling were carried out by Response Surface Methodology. Models fitted revealed significant interaction effects between factors involved in soil-sludge dynamics, which accounted for 26% total variance in N-mineralization. The response models were used to predict nutrient releases required in properly formulating sludge management guidelines, viz. maximum simultaneous value for extractable inorganic forms of N and P achieved 11 and 18 days after applying 100 g kg⁻¹ of co-compost and dried sludge, respectively. Addition of sludges resulted into mineralization of 18% total N and up to 15% total P, while chemical and biochemical properties of the amended soil were improved paralleling organic matter mineralization. Compared to dried sludge, co-composting sludge lead to a decline of up to 30% and 65% in the availability in soil of N and P, respectively, but at expenses of C losses of only 7%, illustrating that co-composting was superior in turning sludge into an environmentally safe soil amendment.     

Effects of cultivation on soil microbiological properties in a freshwater marsh soil in Northeast China

The Sanjiang Plain has become an intensive area of land use/cover change in China. However, little is known about the effect of cultivation on soil microbiological properties in this freshwater marsh ecosystem. Our objective was to evaluate the effect of cultivation on mineralizable, microbial biomass, and total C in the Sanjiang Plain of Northeast China. Soil microbial biomass C (MBC) was 4346 ± 309 mg kg⁻¹ in undisturbed marsh and 229 mg kg⁻¹ in soil cultivated for 15 years. Undisturbed marsh soil had the highest microbial quotient (3.64%), which declined with increasing cultivation time (R² = 0.97, p < 0.01). Metabolic quotient increased with increasing cultivation time. Soil C mineralization in undisturbed marsh was 3.5 times that in soil cultivated for 1 year, and was 12 times that in soil cultivated for 15 years. Cultivation strongly affected measured soil microbiological properties.     

Incorporation of urea-derived 13C into microbial communities in four different agriculture soils

The objective of this study was to investigate changes in the composition of the soil microbial community brought about by urea application and differences in the incorporation of urea-derived C into the soil phospholipid fatty acid (PLFA) pool at differing soil pH. We selected four soils which ranged in pH from 3.9 to 7.8. ¹³C-labeled urea was applied at two concentrations 100 and 200 mg N kg^?1 which represents commonly used and high levels of application. Significant hydrolysis of applied urea occurred within 2 h; less than 2 % of urea-C was retained in the soil with one exception, the fluvo-aquic soil at pH 7.8 amended with 200 mg kg^?1 urea-N 3 days after urea application. According to principal component analysis (PCA), the effect of urea and incubation time on microbial community composition was far weaker than differences between the four soils due to their large differences in basic properties; the scores of PC2 were significantly correlated with pH values. The incorporation of ¹³C-urea to PLFAs increased with soil pH; this may be related to increases in the speciation of inorganic C into bicarbonate.¹³C label was primarily incorporated into 16:1ω5c, 16:0, and cy19:0 in red soil, pH 3.9; and into 16:1ω7c, 16:0, and 16:1ω5c in fluvo-aquic soil, pH 7.8. A wider range of PLFAs became labeled in the two paddy soils at pH 5.2 and 6.7. This suggests that the profile of PLFAs labeled from the application of ¹³C-urea may be affected by redox potential.     

土壤微生物群落对高剂量的新鲜橄榄油厂废水的响应

An incubation experiment was designed in order to determine the further microbiological response to an addition (500 m³ ha^-1) of fresh olive mill wastewater (FOMWW) in a soil that has been frequently amended with uncontrolled doses of OMWW since 90s in an active disposal site (ADS soil). To achieve this aim, the phospholipid fatty acid (PLFA) profiles, microbial biomass C (C_mic), and dehydrogenase (DHA) and urease activities (URA) were monitored at the beginning (T₀), 3 h (T₁) and 97 d (T_f, i.e., the end) of incubation after FOMWW addition. After the FOMWW addition, an increase in the ratio of fungal to bacterial PLFAs was observed in ADS soil. Moreover, a relative increase of monounsaturated fatty acids (MUFAs) with respect to saturated fatty acids (SATFA) was found in the ADS soil. An increase of the Gram-positive to Gram-negative ratio was observed in this soil at the end of the incubation. While DHA and Cmic increased in the ADS soil after FOMWW addition, URA showed a decrease. Fungi and Gram-positive bacterial biomass experienced an increase after addition of a high dose of FOMWW in laboratory conditions.     

Linking dynamics of soil microbial phospholipid fatty acids to carbon mineralization in a C natural abundance experiment: Impact of heavy metals and acid rain

A ¹³C natural abundance experiment including GC-c-IRMS analysis of phospholipid fatty acids (PLFAs) was conducted to assess the temporal dynamics of the soil microbial community and carbon incorporation during the mineralization of plant residues under the impact of heavy metals and acid rain. Maize straw was incorporated into (i) control soil, (ii) soil irrigated with acid rain, (iii) soil amended with heavy metal-polluted filter dust and (iv) soil with both, heavy metal and acid rain treatment, over a period of 74 weeks. The mineralization of maize straw carbon was significantly reduced by heavy metal impact. Reduced mineralization rate of the added carbon likely resulted from a reduction of the microbial biomass due to heavy metal stress, while the efficiency of ¹³C incorporation into microbial PLFAs was hardly affected. Since acid rain did not significantly change soil pH, little impact on soil microorganisms and mineralization rate was found. Temporal dynamics of labelling of microbial PLFAs were different between bacterial and fungal PLFA biomarkers. Utilization of maize straw by bacterial PLFAs peaked immediately after the application (2 weeks), while labelling of the fungal biomarker 18:2ω6,9 was most pronounced 5 weeks after the application. In general, ¹³C labelling of microbial PLFAs was closely linked to the amounts of maize carbon present in the soil. The distinct higher labelling of microbial PLFAs in the heavy metal-polluted soils 74 weeks after application indicated a large fraction of available maize straw carbon still present in the soil.