Soils Of Argentina Research Articles

Molecular identification of three isolates of Trichoderma harzianum isolated from agricultural soils in Argentina, and their abilities to detoxify in vitro metsulfuron methyl

Metsulfuron methyl (MM) is a sulfonylurea herbicide used worldwide for the control of weeds in cereal crops. In a previous study, three Trichoderma strains (T5, T6, and T7) capable of using MM as a sole carbon and energy source were isolated. In this study, the three strains were identified as Trichoderma harzianum using genetic markers, and the transformation of MM by the T. harzianum strains was quantified using spectrophotometry. Solutions of different phytotoxic doses of MM were incubated with plugs of mycelia of the Trichoderma strains and the resulting mixtures were used to assess MM detoxification. The toxicity of the degradation products was tested with a bioassay using pre-germinated seeds of Lens culinaris Medik. and mycelia. Strain T7 was more efficient in transforming MM at higher concentrations than the T5 and T6 strains. In the bioassay, T5 showed the best performance at higher MM doses. We conclude that both T5 and T7 strains are promising for further studies regarding treatment or amelioration of MM contaminated soils.

Draft Genome Sequence of Cellulolytic and Xylanolytic Paenibacillus sp. A59, Isolated from Decaying Forest Soil from Patagonia, Argentina.

Paenibacillus sp. A59 was isolated from decaying forest soil in Argentina and characterized as a xylanolytic strain. We report the draft genome sequence of this isolate, with an estimated genome size of 7 Mb which harbor 6,424 coding sequences. Genes coding for hydrolytic enzymes involved in lignocellulose deconstruction were predicted.

Draft Genome Sequence of Burkholderia cordobensis Type Strain LMG 27620, Isolated from Agricultural Soils in Argentina.

Bacteria of the genus Burkholderia are commonly found in diverse ecological niches in nature. We report here the draft genome sequence of Burkholderia cordobensis type strain LMG 27620, isolated from agricultural soil in Córdoba, Argentina. This strain harbors several genes involved in chitin utilization and phenol degradation, which make it an interesting candidate for biocontrol purposes and xenobiotic degradation in polluted environments.

Sorption of Zn(II) and Cu(II) by four Argentinean soils as affected by pH, oxides, organic matter and clay content

Increasing heavy metal applications to agricultural soils in the form of phosphatic fertilizers and/or atmospheric deposition have led to extensive research on the chemistry of Zn and Cu in soils. Cu(II) and Zn(II) sorption onto different soil fractions of three Mollisols and one Entisol from the southwest of Buenos Aires Province, Argentina, was studied. Different variables affecting the sorption capacity such as pH, cation exchange capacity, specific surface area (SSA), type and amount of clay minerals present, content of Fe-, Al-, and Mn-oxides and oxohydroxides, organic matter and electric charge parameters were investigated. To assess the monometal sorption, batch equilibrium experiments were performed using Cu(II) and Zn(II) metal solutions over a pH range from 4.0 to 7.0. The increase in metal sorption with increasing pH for both metal cations was attributed to an increase in the negative surface charges. At pH 5.0, Cu(II) showed more affinity than Zn(II) for reactive surface soil sites. Removal of organic matter via H2O2 treatment (<2-mm OMR fraction) dramatically decreased the sorption of both cations; however, Cu(II) was sorbed more than Zn(II). The variation in SSA (obtained by water vapor adsorption) in <2-µm (clay fraction) and <2-mm (whole soil fraction) after Zn(II)/Cu(II) sorption at pH 4 and 6 reflected a different interaction between both cations and binding surface sites. Sorption isotherms correlated better with Langmuir than Freundlich equations. Sorption capacities (q max) in <2-µm fraction, ranged from 166 to 111 mmol kg−1 for Cu(II), and from 62 to 31 mmol kg−1 for Zn(II). This study extends the understanding of the sorption mechanisms of Cu(II) and Zn(II) to agricultural soils from the semi-arid Pampean region of Argentina. An understanding of the local soil environment is important in order to reduce or prevent contamination of this valuable resource, especially from fertilizers and other such anthropogenic additions to the soil.

Sorption, desorption and leaching potential of sulfonylurea herbicides in Argentinean soils

The sulfonylurea (SUs) herbicides are used to control broadleaf weeds and some grasses in a variety of crops. They have become popular because of their low application rates, low mammalian toxicity and an outstanding herbicidal activity. Sorption is a major process influencing the fate of pesticides in soil. The objective of this study was to characterize sorption–desorption of four sulfonylurea herbicides: metsulfuron-methyl (methyl 2-[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)carbamoylsulfamoyl)]benzoate), sulfometuron-methyl (methyl 2-[(4,6-dimethylpyrimidin-2-yl)carbamoylsulfamoyl]benzoate), rimsulfuron (1-(4,6-dimethoxypyrimidin-2-yl)-3-(3-ethylsulfonyl-2-pyridylsulfonyl)urea) and nicosulfuron (2-[(4,6-dimethoxypyrimidin-2-yl)carbamoylsulfamoyl]-N,N-dimethylnicotinamide) from different soil horizons of different landscape positions. Sorption was studied in the laboratory by batch equilibration method. Sorption coefficients (Kd-SE) showed that rimsulfuron (Kd-SE = 1.18 to 2.08 L kg−1) and nicosulfuron (Kd-SE = 0.02 to 0.47 L kg−1) were more highly sorbed than metsulfuron-methyl (Kd-SE = 0.00 to 0.05 L kg−1) and sulfometuron-methyl (Kd-SE = 0.00 to 0.05 L kg−1). Sorption coefficients (Kd-SE) were correlated with pH and organic carbon content. All four herbicides exhibited desorption hysteresis where the desorption coefficients (Kd-D) > Kd-SE. To estimate the leaching potential, Koc and ground-water ubiquity score (GUS) were used to calculate the half-life (t1/2) required to be classified as “leacher” or “nonleacher”. According to the results, rimsulfuron and nicosulfuron herbicides would be classified as leachers, but factors such as landscape position, soil depth and the rate of decomposition in surface and subsurface soils could change the classification. In contrast, these factors do not affect classification of sulfometuron-methyl and metsulfuron-methyl; they would rank as leachers.

Abundance and ribotypes of phosphate-solubilizing bacteria in Argentinean agricultural soils under no-till management

Phosphate-solubilizing bacteria (PSB) abundance and ribotypes were examined in the top soil (0–10 cm) of agricultural fields under no-till management sampled in two seasons, summer (February) and late winter (September), in 2010. No-till plots under sustainable agricultural practices (intense crop rotation) or under non-sustainable practices (soybean monocropping) were sampled at four different locations as replicates in a 400-km west–east transect in the most productive agricultural region of Argentina. Natural grasslands were selected close to the cultivated fields for comparative purposes. Culturable heterotrophic bacteria (CHB) were enumerated on nutrient agar plates, and PSB were counted on NBRIP agar plates containing Ca3(PO4)2. The PSB community structure was explored by ribotyping (16S rDNA PCR-restriction fragment length polymorphism). Quantitatively, data showed that the number of CHB and PSB per gram of dry soil was not statistically different among sampled sites, soil management programs or seasons. Qualitatively, ribotyping showed that the most abundant PSB species differed in their fingerprinting patterns among geographical sites, which suggests that local soil conditions impose strong selective constraints. The comparative analysis of PSB ribotypes revealed seasonal differences among February and September isolates for all sampling sites.

Effect of conventional and no-till practices on solute transport in long term field trials

The prediction and description of water and solute movement in soils under different tillage systems is essential to the study of pesticide contamination in soils and groundwater quality. However, the impact of tillage practices in soil physical characteristics varies across locations and types of soil. In this work we analyzed the long-term impact of no till (NT) and conventional tillage (CT) on solute transport within three different Argentinian soils. Bromide transport studies were conducted under controlled conditions in the laboratory using undisturbed soil columns. Samples were taken from long term field trials, with a history of over 16 years of NT and CT practices. The studied soils were: Paraná soil (PAR), a silty clay loam soil (<37% clay), and Mandfredi (MAN) and Pergamino (PER), both silty loam soils (<26% clay). Breakthrough curves were fitted using the non-equilibrium equation model (CDEneq). The following transport parameters were estimated from the fitted curves: velocity (v), hydrodynamic dispersion coefficient (D), dispersivity (λ), mobile water content (β), and mass transfer coefficient (ω). The relationship between the estimated parameters and soil properties was analyzed. Also, the parameters were compared between soils and tillage practices using a mixed linear model. Parameters v and D were positively correlated to soil clay content in NT samples. Such correlation was not observed in CT samples. This would suggest that clay content in soils under conservational tillage, favors the transport of solutes, as it increases v and D. In this study, no differences were found between soils or tillage practice regarding the estimated v parameter. Differences were found for D and λ between CT and NT samples in PAR soil. In this case, the magnitude of solute dispersion was higher in the NT samples. For the other soils (MAN and PER), no difference in D and λ between tillage practices was found. Effects of tillage on solute transport was not substantial in these soils, even when no till management had been applied for over 30 years. Whereas in PAR (the soil with higher clay content), soil management had an important effect on structure, and therefore on solute and water transport. These results suggest that in the PAR clayey soils studied, structure is well preserved under conservational tillage, and this could lead to an increase in the risk of leaching of solutes or chemical substances.

Burkholderia cordobensis sp. nov., from agricultural soils

Two Gram-negative, rod-shaped bacteria were isolated from agricultural soils in Córdoba province in central Argentina. Their 16S rRNA gene sequences demonstrated that they belong to the genus Burkholderia, with Burkholderia zhejiangensis as most closely related formally named species; this relationship was confirmed through comparative gyrB sequence analysis. Whole-cell fatty acid analysis supported their assignment to the genus Burkholderia. Burkholderia sp. strain YI23, for which a whole-genome sequence is available, represents the same taxon, as demonstrated by its highly similar 16S rRNA (100% similarity) and gyrB (99.1-99.7%) gene sequences. The results of DNA-DNA hybridization experiments and physiological and biochemical characterization further substantiated the genotypic and phenotypic distinctiveness of the Argentinian soil isolates, for which the name Burkholderia cordobensis sp. nov. is proposed, with strain MMP81(T) ( = LMG 27620(T) = CCUG 64368(T)) as the type strain.

Persistence and sorption of imazapyr in three Argentinean soils

Imazapyr is a herbicide widely used for weed control in imidazolinone-tolerant sunflower. Imazapyr has a high potential for leaching into groundwater because it is highly water-soluble, persistent in soil, and only weakly sorbed by soils. There is a lack of information available in Argentina concerning groundwater leaching of imazapyr. Therefore, the objective of the present study was to determine the persistence and sorption of imazapyr in 3 Argentinean soils (Tandil, Anguil, and Cerro Azul sites). The presence and concentration of imazapyr were determined and quantified by ultra-performance liquid chromatography and tandem mass spectrometry. The persistence in soils followed the order: Cerro Azul > Tandil > Anguil, with half-life values of 121 d, 75 d, and 37 d, respectively. The half-life of imazapyr was negatively associated with soil pH and iron and aluminum content, and was positively related to clay content. Imazapyr sorption was found to be well described by the Freundlich isotherm. Soil pH and clay, iron, and aluminum contents were the main factors affecting the sorption of imazapyr. The sorption had a limiting effect on the degradation rate. Under certain conditions, the weak sorption and high persistence may increase the movement of imazapyr in the soil profile and the risk of groundwater pollution.

Environmental fate of glyphosate and aminomethylphosphonic acid in surface waters and soil of agricultural basins

Argentinian agricultural production is fundamentally based on a technological package that combines no-till and glyphosate in the cultivation of transgenic crops. Transgenic crops (soybean, maize and cotton) occupy 23million hectares. This means that glyphosate is the most employed herbicide in the country, where 180–200million liters are applied every year.The aim of this work is to study the environmental fate of glyphosate and its major degradation product, aminomethylphosphonic acid (AMPA), in surface water and soil of agricultural basins. Sixteen agricultural sites and forty-four streams in the agricultural basins were sampled three times during 2012. The samples were analyzed by UPLC-MS/MS ESI(+/−).In cultivated soils, glyphosate was detected in concentrations between 35 and 1502μgkg−1, while AMPA concentration ranged from 299 to 2256μgkg−1. In the surface water studied, the presence of glyphosate and AMPA was detected in about 15% and 12% of the samples analyzed, respectively. In suspended particulate matter, glyphosate was found in 67% while AMPA was present in 20% of the samples. In streams sediment glyphosate and AMPA were also detected in 66% and 88.5% of the samples respectively.This study is, to our knowledge, the first dealing with glyphosate fate in agricultural soils in Argentina. In the present study, it was demonstrated that glyphosate and AMPA are present in soils under agricultural activity. It was also found that in stream samples the presence of glyphosate and AMPA is relatively more frequent in suspended particulate matter and sediment than in water.

Denitrifying capacity of rhizobial strains of Argentine soils and herbicide sensitivity

Agrochemical application in soils is a matter of environmental concern, and among soil microorganisms, rhizobia and their action before different pesticides are interesting to study, due to their taxonomic and functional diversity. The objectives of the present work were to assess the capacity of rhizobial populations to use herbicides as source of nutrients, as well as their ability to reduce nitrates and / or denitrify. Eighty-one strains belonging to four populations of different genera of rhizobia (Rhizobium, Mesorhizobium, Ensifer and Bradyrhizobium) were assessed. The effect of glyphosate, 2,4-dichlorophenoxyacetic acid, and atrazine on growth of the strains, as well as the ability of the strains to act on herbicide transformation to reduce nitrate and denitrify, were evaluated. The genera studied showed different responses to pesticides. Bradyrhizobium had the greater capacity to utilize the herbicides and among the compounds evaluated, atrazine was the most used as a source of energy. To conclude, some Bradyrhizobium strains were able both to denitrify and to use the atrazine herbicide. The results obtained in this study increase expectations of the use of rhizobia as inoculants, causing changes at the agricultural and environmental level and allowing an appropriate management of agricultural soil fertilization, efficiency in nitrogen fixation and a faster biodegradation of pesticides in soil.

Fungi degrading metsulfuron methyl in agricultural soils of Argentina

Strains of Mucor, Penicillium and Trichoderma, able to use metsulfuron-methyl (MM) as a sole carbon and energy source, were isolated from agricultural soils in Argentina. This is the first time this ability is recorded in the Mucor or Trichoderma species. When the isolated strains were compared in relation to their capacity to use the herbicide, those of Trichoderma showed the best results. Because of this, they were selected for further assays. The effect of metsulfuron on growth in liquid media was tested. Also, the ability of conidia to germinate in water agar medium containing the target herbicide was evaluated. All the strains could grow from spores using only metsulfuron-methyl as a carbon and energy source. These strains of Trichoderma are promising candidates to be used in the recovery of soils and waters contaminated with this herbicide.

Genotypic Characterization of Azotobacteria Isolated from Argentinean Soils and Plant‐Growth‐Promoting Traits of Selected Strains with Prospects for Biofertilizer Production

The genetic diversity among 31 putative Azotobacter isolates obtained from agricultural and non-agricultural soils was assessed using rep-PCR genomic fingerprinting and identified to species level by ARDRA and partial 16S rRNA gene sequence analysis. High diversity was found among the isolates, identified as A. chroococcum, A. salinestris, and A. armeniacus. Selected isolates were characterized on the basis of phytohormone biosynthesis, nitrogenase activity, siderophore production, and phosphate solubilization. Indole-3 acetic-acid (IAA), gibberellin (GA3) and zeatin (Z) biosynthesis, nitrogenase activity, and siderophore production were found in all evaluated strains, with variation among them, but no phosphate solubilization was detected. Phytohormones excreted to the culture medium ranged in the following concentrations: 2.2–18.2 μg IAA mL−1, 0.3–0.7 μg GA3 mL−1, and 0.5–1.2 μg Z mL−1. Seed inoculations with further selected Azotobacter strains and treatments with their cell-free cultures increased the number of seminal roots and root hairs in wheat seedlings. This latter effect was mimicked by treatments with IAA-pure solutions, but it was not related to bacterial root colonization. Our survey constitutes a first approach to the knowledge of Azotobacter species inhabiting Argentinean soils in three contrasting geographical regions. Moreover, this phenotypic characterization constitutes an important contribution to the selection of Azotobacter strains for biofertilizer formulations.

Evaluation of rhizobacterial isolates from Argentina, Uruguay and Chile for plant growth-promoting characteristics and antagonistic activity towards Rhizoctonia sp. and Macrophomina sp. in vitro

This study was conducted over 3 years in soils of Uruguay and Chile and two years in soils of Argentina. 686 bacterial isolates were phenotypically characterized by testing in relation to the presence of plant growth promoting properties: phosphate solubilization, production of siderophores, starch hydrolysis, production of exopolysaccharides and biological control of Macrophomina phaseolina and Rhizoctonia spp. In all samples analyzed, the number of Gram-positive bacteria exceeded that of Gram negative. Ten bacterial isolates were selected for their plant growth promoting properties and API Test and 16S rRNA gene (rDNA). Six of these isolates belong to the genus Pseudomonas, three to the genus Bacillus and one to Janibacter. This is the first report of a strain from the genus Janibacter with promising plant growth-promoting attributes. The results obtained allow us to improve the microbial germplasm of plant growth promoting bacteria from soils of Chile, Argentina and Uruguay with a view to their potential use in the formulation of mixed inoculants that promote the growth of alfalfa.

Isolation and characterization of atrazine-degrading Arthrobacter sp. strains from Argentine agricultural soils

Three bacterial strains capable of degrading atrazine were isolated from Manfredi soils (Argentine) using enrichment culture techniques. These soils were used to grow corn and were treated with atrazine for weed control during 3 years. The strains were nonmotile Gram-positive bacilli which formed cleared zones on atrazine solid medium, and the 16S rDNA sequences indicated that they were Arthrobacter sp. strains. The atrazine-degrading activity of the isolates was characterized by the ability to grow with atrazine as the sole nitrogen source, the concomitant herbicide disappearance, and the chloride release. The atrazine-degrader strain Pseudomonas sp. ADP was used for comparative purposes. According to the results, all of the isolates used atrazine as sole source of nitrogen, and sucrose and sodium citrate as the carbon sources for growth. HPLC analyses confirmed herbicide clearance. PCR analysis revealed the presence of the atrazine catabolic genes trzN, atzB, and atzC. The results of this work lead to a better understanding of microbial degradation activity in order to consider the potential application of the isolated strains in bioremediation of atrazine-polluted agricultural soils in Argentina.

Five Year Field Evaluation of Prosopis alba Clones on pH 9–10 Soils in Argentina Selected for Growth in the Greenhouse at Seawater Salinities (45 dS m−1)

Prosopis alba seedlings, that grew at the 45 dS m−1 salinity level in a previous study of growth and survival of Argentine and Peruvian Prosopis, were propagated by rooting cuttings and established in a seed orchard/long term evaluation trial on soils with low salinity (EC 5.1–7.5 dS m−1) but high pH (8.9 to 10.2). A pH gradient occurred in the field with values ranging from pH 9.4 in block 1 to pH 10.3 in block 5. After five years growth, almost all of the clones had a mean height greater than 4 m and one clone was more than 5 m. Ten of the 21 tested clones had significantly greater biomass growth than the three seed propagated check varieties. The broad-sense (i.e., clone mean) heritability was estimated to be 0.45 for biomass, 0.53 for diameter and 0.59 for height indicating that strong genetic gains should be possible by selecting and vegetatively propagating the best genotypes. In the block with the highest pH values, two clones that appear to be P. alba × P. ruscifolia hybrids (i.e., P. vinallilo) had the greatest biomass. Correlations between growth during the last two months in the high salinity hydroponic greenhouse selection system and growth in the field were significant (R2 = 0.262) and positive, although the relationship was negative for putative P. vinallilo clones (R2 = 0.938). The several fold increase in biomass of some of the clones over the three check varieties, suggests that the greenhouse screen was successful in identifying superior salt tolerant clones. Apparently whether the greenhouse seedlings had lesser (~1 cm) to greater (~3 cm) height growth was not as important as just having a healthy live apical meristem. The observed salt tolerance of the putative P. vinalillo clones may prove useful as rootstocks for recently described high pod producing P. alba clones.

Agronomic and Taxonomic Consequences of Agricultural Use of Marginal Soils in Argentina

Expansion of the agricultural frontier over marginal soils leaves a significant environmental imprint on the southern semiarid region of the Argentina pampas. A chronosequence of anthropogenic soils in a cultivated area was investigated to determine the role of human actions on the development of a highly compacted horizon below the plow layer observed during a detailed soil survey in Villarino County. A model area of 300 ha (6 × 0.5 km) representative of the county soilscapes was used to (i) characterize the main physical, chemical, and morphological features of the soils in the chronosequence, and (ii) discuss taxonomical issues that can be improved on to facilitate information transfer. Based on our observations, we propose a new diagnostic feature to classify these soils according to USDA Soil Taxonomy guidelines placed at a taxonomical level above series. Our investigation confirmed that soil morphology is modified within 27 yr of cultivation. Tillage leads to the development of a noncemented plowpan immediately below the Ap, here called ACd, with distinctive morphological features. The ACd is compact and massive with extremely hard rupture resistance when dried. Cultivation-induced alterations were considered important enough to classify the soils into unique soil series. Given the widespread environmental and financial costs and implications of soil compaction, and the genetic connotations of the plowpan, we propose the densipan as a diagnostic horizon and a new class densic to be use at the family level. Advantages of its use will lead to increased utility and precision in published soil maps and improved communication and understanding among stakeholders.

Variability in salt tolerance of native populations of Elymus scabrifolius (Döll) J. H. Hunz from Argentina

AbstractElymus scabrifolius is a native C3 South American grass species. It is valued as forage species adapted to various environments in Argentina and is also a potential source of traits for wheat‐breeding programmes. Efficient utilization of native genetic resources requires extensive collection and characterization of available material. The purpose of this study was to identify and characterize variability in salt tolerance within E. scabrifolius populations in Argentina. Specimens of E. scabrifolius were collected from a wide range of soils in Argentina, and most populations were found in saline environments with high sodium levels. Intraspecific variability in salt tolerance was estimated, and its relation to the salinity level of the populations’ natural environment was assessed. A principal component analysis based on growth data distinguished lines from saline and non‐saline habitats only under salt conditions. Results suggest that selecting under stressed environments is a reasonable strategy for breeding E. scabrifolius. Lines of saline origin had higher biomass under both control and saline conditions, suggesting that higher gains from selection would be obtained if germplasm from this origin was used, and tillering may be the most useful indirect selection criterion for improving salt tolerance. The association between salt tolerance, ion content and osmotic adjustment was also assessed. Salt‐sensitive lines accumulated high sodium levels in leaves. However, osmotic adjustment did not correlate with the maintenance of leaf elongation rates under salinity in the genotypes included in this study.

Molecular diversity of peanut‐nodulating rhizobia in soils of Argentina

RSalpha sequencing is a valuable tool for identification of bacterial strains, and for evaluating the genetic structure of indigenous rhizobial populations. The purpose of this study was to evaluate, qualitatively, the presence or absence of RSalpha fragment in peanut-nodulating strains isolated from plants grown at four sites in central Argentina. RSalpha fragment was found in only three of 26 indigenous strains, and in one of three inoculant strains analyzed. In contrast to results from studies of other symbiotic nitrogen-fixing bacteria, such as soybean-nodulating strains, no correlation was found between generation time and presence of RSalpha sequence. Phylogenetic analysis of the 16S rRNA gene sequence grouped peanut-nodulating strains into two clusters, Bradyrhizobium japonicum vs. B. elkanii, and showed divergence among strains positive for RSalpha sequence. Our results confirm the genetic diversity previously reported for various peanut-nodulating rhizobial strains, and indicate that the RSalpha fragment is not applicable as a marker or tool for competition assays at the field or ecological level.

Isolation and characterization of new atrazine degrading bacterial strains and consortia from Argentinean agricultural soils

Isolation and characterization of new atrazine degrading bacterial strains and consortia from Argentinean agricultural soils