Ester-linked Fatty Acid Methyl Ester Research Articles

Soil Health Assessment to Evaluate Conservation Practices in SemiArid Cotton Systems at Producer Site Scale

Maintaining soil health and sustainable crop production has been challenged by climate variability and wind erosion in semi-arid regions. To understand the initial effects of the transition of tilled cotton systems to no-tillage with winter wheat as a cover crop, we sampled 18 commercial grower sites from 2019 to 2022 in the Southern High Plains (SHP). We evaluated the soil biological component, which often responds rapidly to changes in residue additions or minimized soil disturbance providing an early indication of changes in soil health, especially in the low organic matter soils in this region. After two years, compared to tilled systems, no-till systems had significant increases in ester-linked fatty acid methyl ester (EL-FAME) bacterial and saprophytic and AMF fungal markers, enzyme activities of nutrient cycling, and various SOM pools, under both center-pivot irrigation and dryland. Similar increases were also observed in two dryland sites sampled before and up to two years after transition to no-till. Our study demonstrates the potential of no-tillage and cover crops to improve soil health in cotton production in semiarid regions, and a framework for a soil health assessment that links different soil health indicators with functions related to soil organic matter, soil water, and biogeochemical cycling.

The Impact of Tree Species on Microbial Community Structure and Soil Function on Forest Plantations in the Central Hardwoods Region (CHR)

Interactions between above- and below-ground monoculture forest plantation components are critical to tree growth and development. Within the Central Hardwoods Region (CHR), synergistic relationships between tree species and soil microbial community structure and function have received limited research attention. Soil microbes are integral to forest ecosystems as their activities intrinsically promote soil organic matter decomposition, nutrient cycling, and ecosystem functioning. Here, we examined soils from two perfectly aligned stands of black walnut (BW, Juglans nigra L.) and Northern red oak (RO, Quercus rubra L.) trees. Measurements of selected soil chemical properties, microbial community structure using ester-linked fatty acid methyl ester (EL-FAME), and soil enzyme activities (EAs) were used. Analysis of modifications within microbial communities showed a significant positive response to BW based upon soil EAs and microbial indicators, compared to RO. Seasonal comparisons predictably revealed higher microbial activities during summer. Fungi dominated the soil microbial community structure with a fungal/bacterial ratio of 2:1. Gram-positive rather than Gram-negative bacteria or actinomycetes dominated the bacterial community. The activity of the soil enzymes ß-glucosidase and arylsulfatase increased, but ß-glucosaminidase and acid phosphatase decreased. Additionally, acid phosphatase and arbuscular mycorrhizal fungi revealed strong correlations. The differences observed in biological properties, specifically microbial communities and EAs, highlight the varied responses to BW and RO soil biology and subsequent soil ecosystem functions. These results indicate that variations in microbial abundance and soil functions occur throughout the course of an entire year.

Soil health within transitions from irrigation to limited irrigation and dryland management

AbstractThe decline in groundwater supply in the Texas High Plains is forcing some growers to convert center‐pivot irrigated cropland to dryland production. Transitioning toward reduced water input can lead to declines in soil health. We assessed short‐term changes in soil health indicators in two transition scenarios: (a) from high irrigation method to low irrigation method (center pivot to subsurface drip) and (b) from high irrigation method to dryland (center pivot to dryland), in comparison to continuous center‐pivot management. We monitored changes in chemical and biological indicators in four fields for each transition scenario and in three pivot‐irrigated fields. There were declines in soil water content, potassium (K), sodium (Na), and soil organic carbon with transition from irrigation to reduced irrigation and dryland. Severe drought in the final year revealed reduced amounts of multi‐enzyme activities, total ester‐linked fatty acid methyl ester (EL‐FAME), and total fungi. Transitioning to low water‐input management in this environment complicates efforts to maintain microbial components of soil health. Longer‐term comparisons are needed to detect slow changes in soil health indicators on producers’ fields.

Forest floor manipulation effects on the relationship between aggregate stability and ectomycorrhizal fungi

Forest floor and mineral soil manipulations influence the soil biogeochemical properties important for loblolly pine (Pinus taeda L.) tree growth. The impacts of forest floor manipulations on soil aggregate stability and the presence of ectomycorrhizal fungi (EMF), was assessed to elucidate the relationship between EMF abundance and aggregate stability. The study site consists of a 14-year-old loblolly pine plantation managed by Weyerhaeuser Company in the Lower Coastal Plain, approximately 8 miles east of New Bern, North Carolina, USA. The soil samples were collected from the top 7.62 cm of each soil treatment which includes three levels of forest floor retention: removed, control, and doubled and two levels of forest floor mixing with the mineral soil: mixed and unmixed. Ectomycorrhizal fungi abundance was evaluated by ester-linked fatty acid methyl ester analysis and microbial community functionality was assessed by acid-phosphatase activity measurement. Aggregate stability was assessed using the aggregate mean weight diameter approach. Results indicate that the forest floor manipulations had no significant impact on aggregate stability and EMF abundance. However, a positive relationship between EMF abundance and aggregate stability was identified. Removing the forest floor resulted in a soil bulk density increase of 0.18 g cm−3 compared to doubling the forest floor. Our results demonstrate that some mineral soil properties recover relatively quickly from forest floor manipulations. The study informs forest managers interested in how soil responds to forest floor manipulation and the interaction between EMF and aggregate stability.

Vertical distribution and effect of historical residual organochlorine pesticides on microbial community structure in sediment cores from an abandoned oxidation pond after dredging for 15 years.

The vertical distribution pattern of 19 organochlorine pesticides (OCPs), together with microbial ester-linked fatty acid methyl ester (EL-FAME) profiles were investigated in sediments from an abandoned oxidation pond of Ya-Er lake, China, which had been heavily polluted by hexachlorocyclohexanes (HCHs) and chlorobenzenes in 1980s. Subsurface sediment samples were taken from five sediment cores along the transect running from the lakeshore (0.5~2.7 m in depth) to lakebed (0.1~0.4 m). The total OCP concentration ranged from 29.8 to 941.8 ng g-1 dw. Hexachlorobenzene (HCB), HCHs, and dichlorodiphenyl-trichloroethanes (DDTs) were the three dominant OCP classes, accounting for 26.5-97.4%, 1.8-33.2%, and 0.4-15.5% of the total OCP concentration, respectively. Hot spots of HCB, HCHs, and DDTs were detected at 0.9~2.7 m deep layers of the lakeshore, where was oncethe maindredged sediment backfill site for in-situ remediation of the oxidation pond in 2002-2004. HCHs and HCBstill showed high potential ecological risks. The sources of OCPs were identified and quantified using principal component analysis with absolute principal component scores-multiple linear regression model. The firstthree major sources were persistent residues, recent agricultural input, and historical industrial input, contributing on average 28.2%, 17.9%, and 17.1% of total OCPs, respectively. Redundancy analysis of microbial EL-FAME profiles and nine dominant OCPs revealed that the spatial variation in microbial community structure was significantly corresponded with the OCP composition. This is the first study highlighting the concern on historical industrial inputs of OCPs in subsurface sediments of the lakeshore disposal zone. The findings could help to distinguish the artificial backfill sediments from undisturbed polluted sediments for optimization of further dredging plans.

Comparing biological methods for soil health assessments: EL‐FAME, enzyme activities, and qPCR

AbstractSoil health initiatives have categorized assays for enzyme activities (EAs) that measure p‐nitrophenol and ester‐linked fatty acid methyl ester (EL‐FAME) as Tier 2 indicators for biological activity and community structure analysis, respectively. Quantitative polymerase chain reaction (qPCR) assays of functional and taxonomic communities are emerging Tier 3 indicators. To facilitate comparisons of soil biological health between research groups that may employ different methods, we applied these current and emerging indicators to semiarid soils from the Texas High Plains sampled in the growing season and postharvest from 2014 through 2018. Microbial groups via EL‐FAME markers and EAs were strongly correlated (r > .79) with qPCR assays of equivalent taxonomic and functional genes. To further quantify the predictive power of these relationships, we modeled several genes as a function of EA or EL‐FAME markers, combined with other related covariates (e.g., soil texture, pH, irrigation, and soil organic C [SOC]) using a generalized linear model. The latter was trained using data from 2014, which was an average year in terms of temperature and precipitation for the region. Subsequently, the model was tested making predictions for 2015–2018, which represented high variability in climatic conditions, ensuring a thorough assessment of its predictive power. In most cases, soil texture, SOC, and Tier 2 indicators were identified as moderate to strong predictors of the biological responses. Our results suggest that the different approaches for assessing either function or community in these semiarid soils were highly comparable and provided similar information on how microbial communities were responding to both management and climate.

An evaluation of biological soil health indicators in four long‐term continuous agroecosystems in Canada

AbstractThe soil microbial community (SMC) and soil organic matter (SOM) are inherently related and are sensitive to land‐use changes. Microorganisms regulate essential soil functions that are key to SOM dynamics, whereas SOM dynamics define the SMC. To expand our understanding of soil health, we evaluated biological and SOM indicators in long‐term (18‐yr) continuous silage corn (Zea mays L.), continuous soybean [Glycine max (L.) Merr.], and perennial grass ecosystems in Ontario, Canada. The SMC was evaluated via ester‐linked fatty acid methyl ester (EL‐FAME) and amplicon sequencing. Soil organic matter was evaluated via a new combined enzyme assay that provides a single biogeochemical cycling value for C, N, P, and S cycling activity (CNPS), as well as loss‐on‐ignition, permanganate oxidizable C (POXC), and total C and N. Overall, soil health indicators followed the trend of grasses > corn > soybean. Grass systems had up to 8.1 times more arbuscular mycorrhizal fungi, increased fungal/bacteria ratios (via EL‐FAME), and higher microbial diversity (via sequencing). The POXC was highly variable within treatments and did not significantly differ between systems. The novel CNPS activity assay, however, was highly sensitive to management (up to 2.2 and 3.2 times higher under grasses than corn and soybean, respectively) and was positively correlated (ρ > .92) to SOM, total C, and total N. Following the “more is better” model, where higher values of the measured parameters indicate a healthier soil, our study showed decreased soil health under monocultures, especially soybean, and highlights the need to implement sustainable agriculture practices that maintain soil health.

Soil microbial biomass and composition from urban landscapes in a semiarid climate

Soil microbial communities have been used as indicators of changes in soil health agroecosystems. However, few studies have evaluated soil health under turfgrass systems especially in semiarid climates. Our study determined whether microbial biomass and composition in residential soils were controlled by home age along a turfgrass chronosequence and evaluated effects of turfgrass management in structuring soil microbial communities. Soil samples were obtained from nine locations within each home age category: oldest (1950–1970), middle (1971–1990), newer (1991–2010), and newest (2011–present) in summer 2018 and 2019. Soil microbial biomass and composition were assessed using chloroform fumigation extraction method (CFEM) and ester-linked fatty acid methyl ester (EL-FAME) analysis. Soil microbial biomass carbon (MBC) and nitrogen (MBN) were 46–52% and 65–75% higher in oldest homes when compared to newest homes, respectively. Neither total FAMEs nor fungal FAME abundance differed for home age categories, but bacterial FAME abundance increased with home age. Non-parametric analysis determined no microbial abundance differences with management practices or turfgrass species. Pearson correlations indicated soil organic matter and silt content most consistently altered the microbial community. Soil microbial communities within semiarid, urban environments shifted from high fungal to bacterial dominated as landscapes matured, potentially due to long-term effects of irrigation, fertilization, and pesticide use. Our results indicate time after establishment was more important to development of soil microbial communities in semiarid, perennial turfgrass systems than subtle differences in management, suggesting soil health and resource conservation goals in this setting may be achievable with relatively low levels of management over time.

Cover crop biomass and species composition affect soil microbial community structure and enzyme activities in semiarid cropping systems

Cover crops are promoted to increase soil organic carbon (SOC) storage and improve soil biological health in agricultural systems. However, cover crop effects on soil microbial communities – key regulators of SOC and nutrients – and functioning are not clear in semiarid environments. This study investigated the response of soil microbial community structure and enzyme activities to cover crop integration under limited-irrigation winter wheat (Triticum aestivum)-sorghum (Sorghum bicolor)-fallow rotation. The study had a randomized complete block design with eight treatments and three replications. Treatments were pea (Pisum sativum); oat (Avena sativa); canola (Brassica napus L.); and mixtures of pea + oat (POmix), pea + canola (PCmix), pea + oat + canola (POCmix), and pea + oat + canola + hairy vetch (Vicia villosa) + forage radish (Raphanus sativus L.) + barley (Hordeum vulgare L.) (diverse-mix) as cover crops; and a fallow. Soil samples were collected in the summer of 2017 and 2018 from 0 to 15 cm depth of each plot established in fall 2015. Microbial community size and structure were evaluated via ester-linked fatty acid methyl ester (EL-FAME) analysis, which showed that total microbial community size and fungal community were similar between soils under oats and diverse-mix, and were 31% and 41% greater than fallow, respectively. The FAME marker for arbuscular mycorrhizal fungi (AMF) was 84% greater under oats than fallow. The combined enzyme activity of acid phosphatase, β-glucosidase, and β-glucosaminidase was 294 mg p-nitrophenol (PNP) kg−1 soil h−1 under diverse-mix, which was greater than fallow (204 mg PNP kg−1 soil h−1, p = 0.021) in 2018. Cover cropping during fallow period in a crop-fallow rotation could increase total microbial community size, fungal abundance, and enzyme activities associated with carbon (C) and nutrient cycling. Among cover crops, oat and its mixture with legumes (pea and hairy vetch) and brassicas (canola and forage radish) were most effective in improving soil health and biogeochemical cycling in a hot and dry semiarid climate.

A comparison between fatty acid methyl ester profiling methods (PLFA and EL‐FAME) as soil health indicators

AbstractFatty acid methyl ester (FAME) profiling for characterizing microbial community composition typically is conducted via phospholipid fatty acid (PLFA) or ester‐linked fatty acid methyl ester (EL‐FAME) methods. As soil health assessments aim to be utilized across the nation and globe, the robust measurement and interpretation of microbial communities across a range of soils and environments will be necessary. This study compared PLFA and EL‐FAME methods for detecting and interpreting profiles of microbial community composition in croplands across a wide geographic area using a total of 172 soil samples from 14 states representing a wide range of soil properties. Overall, PLFA and EL‐FAME provided comparable biomarkers in terms of microbial community composition. The Spearman's Rank correlation test showed positive correlations (r = 0.37–0.71) between PLFA and EL‐FAME methods for absolute abundance of total FAME and individual microbial groups including fungi (saprophytic fungi [SF], arbuscular mycorrhizal fungi [AMF], and general fungi [F]) and all bacterial groups (Gram positive [GMP], Gram negative [GMN], and Actinobacteria). In both methods, a common set of fatty acids were influential in differentiating samples. The main differences in biomarker abundances between the two methods were that fungal and Actinobacteria biomarkers (e.g., 16:1ω5c [AMF], 18:1ω9c [F], 18:3ω6c [F], and 10Me16:0 [Actinobacteria]) were more abundant or critical in EL‐FAME profiling (large variation among soil samples and sensitive to soil properties), but bacterial biomarkers such as i15:0 (GMP), 16:1ω7c (GMN), 18:1ω7c (GMN), and cy19:0ω7c (GMN) were more dominant and responsive to soil properties in PLFA profiling. The practical advantages of EL‐FAME are lower cost and simpler methodology. Although both methods produced similar microbial profile abundances for important microbial markers, PLFA was more sensitive to the wide range of soil chemical properties in this sample set including pH, clay content, soil organic matter, and active carbon.

Resilience of the microbial communities of semiarid agricultural soils during natural climatic variability events

The microbial community carries out important processes that support plant growth and maintain soil health. However, extreme climatic variability such as higher temperatures and prolonged drought may cause fluctuations in the microbial community abundance, composition, and activity, thus affecting essential functions they govern including nutrient cycling and soil organic matter (SOM) dynamics. This study evaluated five agricultural lands under continuous cotton (Gossypium hirsutum L.) production from the Texas High Plains semi-arid region during the growing season and post-harvest from 2014 to 2018. Although sites differed in irrigation practices and soil textural class (e.g. from sandy loam to clay), all responded similarly to a decrease in precipitation, and increase in temperatures from 2015 to 2016. Microbial abundance via ester linked-fatty acid methyl ester (EL-FAME) analysis during the growing season of 2016 decreased by 82% in the sandiest soil, and by 38% in the soil with highest clay, when compared to 2015, a year of record precipitation for this region (e.g., 693 vs. 465 mm). Similarly, enzyme activities were reduced by as much as 87% (depending on the site) in the 2016 growing season when compared to 2015. The significant decreases in the soil microbial component could be explained by extremely low soil moisture (e.g., gravimetric water content averaged 2% in drylands, and 6% in irrigated sites) associated to low precipitation and high soil temperatures during the 2016 growing season (6.7 °C warmer than 2015). Furthermore, these conditions resulted in shifts in microbial community composition, especially significant decrease (p < 0.05) of saprophytic fungal markers by 59% (e.g., from an average of 26.8 to 10.9 nmol g−1 soil). However, after 2016 all biological parameters showed increasing trends, thus demonstrating a remarkable recovery and higher resilience than expected for semiarid soils, which experience extremes in temperature, frequent droughts and have low SOM (<1%).

Time-Dependent Changes in Morphostructural Properties and Relative Abundances of Contributors in Pleurotus ostreatus/Pseudomonas alcaliphila Mixed Biofilms.

Pleurotus ostreatus dual biofilms with bacteria are known to be involved in rock phosphate solubilization, endophytic colonization, and even in nitrogen fixation. Despite these relevant implications, no information is currently available on the architecture of P. ostreatus-based dual biofilms. In addition to this, there is a limited amount of information regarding the estimation of the temporal changes in the relative abundances of the partners in such binary systems. To address these issues, a dual biofilm model system with this fungus was prepared by using Pseudomonas alcaliphila 34 as the bacterial partner due to its very fast biofilm-forming ability. The application of the bacterial inoculum to already settled fungal biofilm on a polystyrene surface coated with hydroxyapatite was the most efficient approach to the production of the mixed system the ultrastructure of which was investigated by a multi-microscopy approach. Transmission electron microscopy analysis showed that the adhesion of bacterial cells onto the mycelial cell wall appeared to be mediated by the presence of an abundant layer of extracellular matrix (ECM). Scanning electron microscopy analysis showed that ECM filaments of bacterial origin formed initially a reticular structure that assumed a tabular semblance after 72 h, thus overshadowing the underlying mycelial network. Across the thickness of the mixed biofilms, the presence of an extensive network of channels with large aggregates of viable bacteria located on the edges of their lumina was found by confocal laser scanning microscopy; on the outermost biofilm layer, a significant fraction of dead bacterial cells was evident. Albeit with tangible differences, similar results regarding the estimation of the temporal shifts in the relative abundances of the two partners were obtained by two independent methods, the former relying on qPCR targeting of 16S and 18S rRNA genes and the latter on ester-linked fatty acid methyl esters analysis.

Soil organic matter and microbial community responses to semiarid croplands and grasslands management

Livestock integration in cropping systems and conversion of croplands into grazing lands has been increasingly considered to improve agricultural sustainability, yet their roles in soil health and resilience are not clear due to the complex interactions of soil, climate, and agricultural systems. A study was conducted to evaluate the effects of cropland and grassland management systems on soil organic carbon (SOC) and total nitrogen (N) across the soil profile (0–20, 20–40, 40–60, and 60–80 cm) and microbial community size, structure, and activity in the soil surface (0–20 cm) as indicators of soil health. Cropland systems compared included conventional-tilled winter-grazed cropland (CTGC) and no-tilled and strip-tilled croplands (NTC and STC) without livestock grazing. Grassland systems included grazed grassland (GGL) and ungrazed grassland (UGL). Grassland soils accumulated 18% greater SOC and 13% greater total N than cropland soils in the 0–80 cm profile. Microbial community size (sum of ester-linked fatty acid methyl esters [El-FAME]) in the surface 0–20 cm was 90% greater, and enzyme activities were 131–155% greater in the grasslands than in the croplands. Within grasslands, cattle (Bos taurus) grazing increased microbial community size by approximately 42%, which was mainly due to greater fatty acid methyl esters (FAME) markers for gram-positive bacteria (51%) and Actinobacteria (73%). Grazed cropland had 95% more β‑glucosaminidase activity than ungrazed croplands. This study suggests light grazing and grassland restoration has potential to improve soil health and resilience through an increase in SOC and microbial community responses related to nutrient cycling.

Microbial Inoculants Development for Bioremediation of Gasoline and Diesel Contaminated Soil

In this study, we describe the development of microbial inoculants for the bioremediation of hydrocarbon-contaminated soils through the enrichment of hydrocarbonoclastic populations in municipal solid waste compost (MSWC). Respirometric analyses were performed along with quantification of total heterotrophic bacteria and ester-linked fatty acid methyl ester (EL-FAME) profiling of the microbial communities of the inoculants. CO2-emission rate increased sharply when the compost received application of water plus gasoline or diesel. After 8 (compost diesel) and 12 days (compost gasoline), we observed a significant increase in the number of heterotrophic bacteria. In inoculants receiving gasoline, FAME markers of fungi predominated throughout the incubation period (18 days). By the end of the incubation period, an increase in FAMEmarker for gram-positive bacteria and a decrease for gram-negative bacteria and actinobacteria were observed. In biodegradation trials (data not shown), the inoculants were very efficient, removing over 99% of hydrocarbons from a heavy soil (73% clay) contaminated with either diesel or gasoline (17,000 mg·Kg﹣1 and 15,000 mg·Kg﹣1, respectively). Inoculants based on MSWC enriched in hydrocarbonoclastic microorganisms may be an effective alternative to improve bioremediation in hydrocarbon-contaminated soils.

Native vegetation in reclamation: Improving habitat and ecosystem function through using prairie species in mine land reclamation

In the Appalachian region, coal mining has impacted 600,000ha historically. While a return to forest would be a preferable postmining land use, due to the difficulty and higher costs of reforestation, many sites are reclaimed into non-native grasslands. The typical seed mix for these grasslands is low diversity and consists of exotic, cool season grasses and forbs. For this study, we combined several species in standard reclamation mixes with prairie species native to North America to create a higher diversity planting on three mine sites in southeastern Ohio. Vegetation and soil microbial properties were assessed within two years after site establishment. Results were encouraging. The mix that included native plants met reclamation standards of ground cover two years after planting, indicating these alternative mixes can be successful. The first year species richness and diversity were higher in native planted areas when compared with traditional, the second year they were equal between treatments. Soil beta-glucosidase activities tended to be lower or higher in the native planted areas, in contrast to soil organic matter, which was generally higher under native prairie mix. Microbial biomass, Actinobacteria, and gram negative bacteria estimated by ester-linked Fatty acid methyl esters occasionally appeared to be higher under native prairie mix indicating that the experimental mix may have a positive effect on soil microbial biomass after almost two years of establishment. Incorporating hardy native prairie plants into reclamation seed mixes can increase the value of the ecosystem for pollinators and wildlife, and potentially improve soil conditions more quickly than non-native plantings alone.

Comparison of fatty acid methyl ester methods for characterization of microbial communities in forest and arable soil: Phospholipid fraction (PLFA) versus total ester linked fatty acids (EL-FAME)

Phospholipid fatty acid (PLFA) and ester-linked fatty acid methyl ester (EL-FAME) extraction methods have been commonly used for estimating microbial biomass and characterizing microbial community composition in soil. However, to our knowledge, there is currently no comparison of these two methods across different ecosystems. A regression analysis for 8 different soils showed that there were significant linear relationships between PLFA and EL-FAME extracts (r2=0.97, 0.98 and 0.72, respectively) for determining the fungal (18:2ω6,9) and bacterial abundance and fungal-to-bacterial ratio (F:B ratio). However, regression lines of forest soils for fungal abundance and F:B ratio had a slight but significantly higher intercept than those of arable soils, i.e. higher EL-FAME:PLFA ratio for fungi in forests than those in arable soils. This might be due to that EL-FAME extracts may have additional factors such as physiological status of fungi and the inclusion of substantial amount of humic substances that affect quantitative determination of fungal biomass. Overall, EL-FAME method is simple and would produce similar results to PLFA method for bacteria in both quantitative and qualitative assessments when comparing different soils across ecosystems. However, for fungi, PLFA method would be more suitable than EL-FAME method.

A Multi-biological Assay Approach to Assess Microbial Diversity in Arsenic (As) Contaminated Soils

ABSTRACTMicrobial genetic, structural and functional diversity was assessed in response to arsenic (As) pollution in a former gold mine soil. Ester-linked fatty acid methyl ester (EL-FAME), quantitative PCR (qPCR), denaturating gradient gel electrophoresis (DGGE), enzyme activities and MicroResp techniques were used.Multivariate analysis showed that As bioavailability in soil was an important driver affecting microbial diversity. Microbial biomass assessed by EL-FAMEs and qPCR generally decreased under higher bioavailable As, as well as enzyme activities and C substrate utilization. Conversely, actinomycetes and fungal biomass increased along with total As content suggesting the selection of more resistant species.

Effect of Long Term Fertilization on Microbial Biomass, Enzyme Activities, and Community Structure in Rice Paddy Soil

The effects of long-term fertilization on soil biological properties and microbial community structure in the plough layer in a rice paddy soil in southern Korea were investigated in relation to the continuous application of chemical fertilizers (NPK), straw based compost (Compost), combination these two (NPK + Compost) for last 40 years. No fertilization plot (Control) was installed for comparison. Though fertilization significantly improved rice productivity over control, the long-term fertilization of NPK and compost combination was more effective on increasing rice productivity and soil nutrient status than single application of compost or chemical fertilizer. All fertilization treatments had shown significant improvement in soil microbial properties, however, continuous compost fertilization markedly increased soil enzyme and microbial activities as compared to sole chemical fertilization. Results of microbial community structure, evaluated by EL-FAME (ester-linked fatty acid methyl esters) method, revealed big difference among Control, NPK, and Compost. However, both Compost and Compost+NPK treatments belonged to the same cluster after statistical analysis. The combined application of chemical fertilizer and organic amendments could be more rational strategy to improve soil nutrient status and promote soil microbial communities than the single chemical fertilizer or compost application.

Agronomic application of olive mill wastewaters with rock phosphate increase the 10Me18:0 fatty acid marker of actinomycetes and change rhizosphere microbial functional groups under long-term field conditions

The objectives of this study were to determine the long-term effects of agronomic application of olive mill wastewaters (OMW) with rock phosphate (RP) in a field of olive trees on the soil microbial community structures. Ester-linked fatty acid methyl ester (EL-FAME) profiles were used for characterizing the numerically dominant portion of soil microbial communities. EL-FAME analysis showed significant shifts of specific groups of fatty acids after application of OMW with RP. In particular, the FAME 10Me18:0 indicative of actinomycetes increased and the FAME 18:1ω9 and 18:2ω6 commonly found in fungi decreased. The soil microbial cells reacted to the addition of OWM and RP with an increase in the percentage of cy17:0 and cy19:0 cyclopropane fatty acids. Other changes in FAME composition included the increase of saturated/unsaturated ratio. It seems that alterations of fatty acid composition, after agronomic application of OMW and RP, are responsible for the substantial maintenance of cell membrane integrity, physiological functions and growth.

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

Abstract 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.