Centro de Recursos Naturales Renovables de la Zona Semiárida

Bacteria, which prey on other microorganisms, are commonly found in the environment. While some of these organisms act as solitary hunters, others band together in large consortia before they attack their prey. Anecdotal reports suggest that bacteria practicing such a wolfpack strategy utilize antibiotics as predatory weapons. Consistent with this hypothesis, genome sequencing revealed that these micropredators possess impressive capacities for natural product biosynthesis. Here, we will present the results from recent chemical investigations of this bacterial group, compare the biosynthetic potential with that of non-predatory bacteria and discuss the link between predation and secondary metabolism.

Globally, the consumption of various products of animal origin continues to grow, and this pattern is expected to continue for the immediate future. Despite a decrease in total animal numbers, some countries, such as the United States, produce approximately the same amount of beef, prob-

The role that accumulated carbohydrates play in plant regrowth has been discussed for over 60 years. However, few quantitative studies have been published on the importance of carbohydrates for regrowth in early spring after plants have been exposed to periods of either drought or drought plus defoliation. We examined the relationship between total nonstructural carbohydrate (TNC) concentrations and pools (biomass X concentration) and spring regrowth for crested wheatgrass [Agropyron desertorum Fisch. ex Link) Schult.] and bluebunch wheatgrass [Pseudoroegneria spicata (Pursh) A. Love ssp. Spicata; Syn. A. spicatum (Pursh) Scribn. and Smith] with and without clipping under drought, natural, and irrigated conditions. In spring 1985 and early spring 1986, after 1 or 2 years of clipping, crown and root TNC concentrations an IT NC pools per tiller were generally similar for clipped and unclipped plants of both species. Nonstructural carbohydrate concentrations in crowns and roots did not relate to rate or total production of dark regrowth in mid-spring 1985 and early spring 1986. In early spring 1986 following 2 years of repeated treatments, crown and root TNC pools were on average 7 times higher under drought, in both clipped and unclipped plants, than they were under the higher moisture-level treatments for both species. The large pools of TNC in drought-treated plants appeared to enhance the production of dark regrowth when meristematic limitations on growing tillers did not exist in early spring. These results suggest that plants exposed to prolonged periods of drought or drought plus defoliation may have rapid initial regrowth upon alleviation of these stresses because high amounts of TNC may have accumulated in their storage organs during stress. In addition, the results suggest that high TNC availability facilitates growth only when meristematic activity is high.

Pasture-based production systems represent a significant sustainable supplier of animal source foods worldwide. For such systems, mounting evidence highlights the importance of plant diversity on the proper functioning of soils, plants and animals. A diversity of forages and biochemical-primary and secondary compounds- at appropriate doses and sequences of ingestion, may lead to benefits to the animal and their environment that are greater than grazing monocultures and the isolated effects of single chemicals. Here we review the importance of plant and phytochemical diversity on animal nutrition, welfare, health, and environmental impact while exploring some novel ideas about pasture design and management based on the biochemical complexity of traditional and non-traditional forage sources. Such effort will require an integration and synthesis on the morphology, ecophysiology and biochemistry of traditional and non-traditional forage species, as well as on the foraging behavior of livestock grazing diverse pasturelands. Thus, the challenge ahead entails selecting the “right” species combination, spatial aggregation, distribution and management of the forage resource such that productivity and stability of plant communities and ecological services provided by grazing are enhanced. We conclude that there is strong experimental support for replacing simple traditional agricultural pastures of reduced phytochemical diversity with multiple arrays of complementary forage species that enable ruminants to select a diet in benefit of their nutrition, health and welfare, whilst reducing the negative environmental impacts caused by livestock production systems.

This study reports the immobilization and performance of a hydrocarbon-degrading Rhodococcus sp. strain (designated as QBTo) on sunflower seed husks (SH) for the bioremediation of soils polluted with crude oil. The SH performance as inoculants carrier was compared with peat, which is a vegetal material traditionally used in carrier-based inoculants production. The stability of the immobilized culture under storage conditions was assessed by viability at different times when stored at 25°C and 10°C. The catabolic activity of immobilized and free QTBo cells introduced into sandy loam soil, freshly contaminated with crude oil, was studied in microcosms. A higher number of viable QTBo cells were recovered from the inoculants formulated with SH (QTBo-SH) after prolonged storage at 10°C and 25°C. The microcosms amended with QTBo-SH inoculants showed a removal of about 66% of total petroleum hydrocarbons (TPH), whereas in those inoculated with QTBo-peat inoculants, the decrease was of about 47%. In the control microcosms (noninoculated) and liquid culture–amended soils, the TPH removal was about 28%. SH is a waste of edible oil industry, nontoxic, and biodegradable and has demonstrated to confer to the immobilized cultures greater potential to survive not only during storage but also in the soil environment, improving bioremediation process.

The aim of this study was to determine the effect of winter cover crop (CC) residues on soil pH and phosphorus (P) availability. Three incubation assays were performed in pots using two CC: vetch (V) (Vicia villosa Roth.) and oats (Oa) (Avena sativa L.). Soil samples were taken from 10 sites at 0–20-cm depth. The rate of residues were 0 (D0), 10 (D1), 20 (D2), 30 (D3), and 40 (D4) g dry matter kg−1 soil and the soil sampling was after 10, 20, 30, 60, 90, and 120 days of incubation. Soil pH, extractable P (Pe), and soil organic matter (SOM) and its fractions were determined. The pH increase was correlated with the rate applied (D1 < D2 < D3 < D4). No differences were found for pH comparing V and Oa residues with low residue rates. Soil pH changes were dependent from initial pH and SOM fractions in different soils across the incubation period. The multiple regression models showed that the pH changes were dependent on initial pH level and SOM fractions with a high R2 (0.81). CC residues and its quantities produced different changes on pH – especially at the beginning of the incubation – which influenced the P availability.

Roth) is native of Europe and Western Asia and it is the second most cultivated vetch worldwide. Hairy vetch is used as forage species in semiarid environments and as a legume cover crop in sub-humid and humid regions. Being an incompletely domesticated species, hairy vetch can form spontaneous populations in a new environment. These populations might contain novel and adaptive traits valuable for breeding. Niche occupancy based on geographic occurrence and environmental data of naturalized populations in central Argentina showed that these populations were distributed mainly on disturbed areas with coarse soil texture and alkaline-type soils. Low rainfall and warm temperatures during pre- and post-seed dispersal explained the potential distribution under sub-humid and semiarid conditions from Pampa and Espinal ecoregions. Conversely, local adaptation along environmental gradients did not drive the divergence among recently established Argentinian (AR) populations. The highest genetic diversity revealed by microsatellite analysis was observed within accessions (72%) while no clear separation was detected between AR and European (EU) genotypes, although naturalized AR populations showed strong differentiation with the wild EU accessions. Common garden experiments were conducted in 2014-16 in order to evaluate populations' germination, flowering, and biomass traits. European cultivars were characterized by low physical seed dormancy (PY), while naturalized AR accessions showed higher winter biomass production. Detected variation in the quantitative assessment of populations could be useful for selection in breeding for traits that convey favorable functions within specific contexts.

Background and aims – Natural montane grasslands in the Southern Pampas of Argentina are expected to show a high potential for recovery after heavy grazing due to their evolutionary history in the presence of large herbivores and their high productivity. The objective of this work is to compare plant diversity, bare soil percentage, biomass and botanical composition between grazed and non-grazed areas at different times following grazing exclusion. Methods – Vegetation was assessed on exclosures established in 2006 and on nearby areas open to grazing by feral horses in December 2006, 2007, 2008 and 2009. In 2009 we added 15 year old exclosures to the analysis. Key results – Species richness declined 24 months after grazing exclusion, mainly due to a decrease in the abundance of forb species. Bare soil percentage was significantly reduced 12 months after exclosures were built. Above-ground biomass showed a 3-fold increase 12 months after grazing exclusion. After three years, species richness and biomass were similar to those corresponding to older exclosures (15-years old). The composition of plant communities also changed following horse exclusion, with three and 15-years old exclosures dominated by perennial grasses typical of late seral stages. Conclusions – Our results support the hypothesis that natural montane grasslands in the Southern Pampas of Argentina may recover fast from grazing by large herbivores without application of specific restoration techniques.

BACKGROUND: A plot-scale experiment was conducted to assess the impact of field application rates of glyphosate on soil microbial communities by taking measurements of microbial activity (in terms of substrate-induced respiration and enzyme activity) in parallel with culture-independent approaches to assessing both bacterial abundance and diversity. Two rates of glyphosate, alone or in a mixture with 2,4-dichlorophenoxyacetic acid, were applied directly onto the soil surface, simulating normal use in chemical fallow in no-till systems. RESULTS: No consistent rate-dependent responses were observed in the microbial activity parameters investigated in the field plots that were exposed to glyphosate. Denaturant gradient gel electrophoresis (DGGE) of the overall bacterial community (Eubacteria) and ammonia-oxidising bacteria (AOB) revealed no effects of the high rate of glyphosate on the structure of the communities in comparison with the control. No treatment effects were observed on the abundance of Eubacteria shortly after treatment in 2010, while a small but significant difference between the high rate and the control was detected in the first sampling in 2011. The abundance of AOB was relatively low during the study, and treatment effects were undetectable. CONCLUSIONS: The absence of negative effects on soil microbial communities in this study suggests that glyphosate use at recommended rates poses low risk to the microbiota.

Wild sunflower Helianthus annuus originates from North America and has naturalised in Argentina where it is considered invasive. The present study attempts to assess the genetic diversity using two different molecular marker systems to study the wild genetic patterns and to provide data applicable to conservation and breeding uses. Ten natural populations sampled throughout the wild range and six inbred lines were studied using inter-simple sequence repeat (ISSR) and simple sequence repeats (SSR) markers. A total of 64 ISSR bands and 29 SSR alleles were produced from 106 wild and cultivated plants. We found 9 ISSR private bands and 21 SSR private alleles in wild accessions, but no private bands/alleles were found in cultivated sunflowers. Molecular variability in wild populations was approximately 60% higher than in inbred lines. Local wild sunflowers kept considerable diversity levels in comparison with populations in the centre of origin (approximately 70%) and therefore they might possess a potential for adaptive evolutionary change. Analysis of molecular variance (AMOVA) indicated population structure with nearly 20% of genetic variability attributable to between-population differentiation. Principal coordinate analyses (PCO) grouped wild populations from different geographic locations, and a Mantel test showed low congruence between genetic distance (GD) and geographic distances (GGD); hence, molecular data could not rule out multiple wild introduction events. Low correlations were found between ISSR and SSR GD at individual and population levels; thus, divergent evolutionary groups were not evident in local wild sunflowers. Several genetic diversity criteria were utilised to assign conservation value and certain wild populations emerged as interesting sites for more extensive sampling.

Abstract Gene flow can have several different applied consequences, ranging from extinction to the escape of transgenes to the evolution of weedy or invasive lineages. Here, we describe patterns of hybridization and gene flow involving domesticated and wild sunflowers in Argentina. To address the risks of introgression of variants from the cultivated sunflower into invasive wild Helianthus , we used genotyping‐by‐sequencing ( GBS ) to genotype 182 samples from 11 sites in Argentina, along with previously published data from samples from the native range (North America), to determine the native source populations of the Argentinian samples and to detect admixture. We unexpectedly discovered two distinctive forms of H. petiolaris in Argentina, one from H. petiolaris subsp. petiolaris as expected, but the other from an unknown source. Extensive admixture was observed among Argentinian sunflowers, largely confirming phenotypic predictions. While many hybrids are F1s, there were signals consistent with introgression from the domesticated sunflower into H. petiolaris . Whether this introgression is incidental or a causal driver of invasiveness is not yet clear, but it seems likely that genes found in the domesticated sunflower genome (whether engineered or not) will quickly find their way into wild Argentinian sunflower populations.

Helianthus annuus and H. petiolaris (Asteraceae) are wild sunflowers native to North America but have become naturalized in central Argentina covering an area of about 5 million hectares. Wild H. annuus has been recognized as invader species in several countries, but no research has been done to study the ecological determinants of their distribution. In a survey covering seven provinces between 31°58′–38°S and 60°33′–69°W, we described the ecology of the main wild populations. Wild Helianthus populations were located in three of the 18 ecological regions of Argentina, on five Mollisol and seven Entisol soil groups. The associated plant communities were comprised 60 species belonging to 16 families, all being frequent components of the native flora. Disease symptoms were seldom observed in wild populations, with Alternaria helianthi being the most commonly observed pathogen. Population size varied from less than 100 to more than 100,000 plants, covering from 100 to more than 60,000 m 2 with densities most frequently up to 3 plants/m 2 , but reaching 80 plants/m 2 at certain sites. Intermediate plant phenotypes between wild species and cultivated sunflower were found in one-third of the populations providing evidence of intense gene flow. Hybrid swarms were found at three localities with population sizes between 100 and 10,000 individuals.

Abstract Helianthus annuus is an invasive alien species naturalised in the central region of Argentina where it shares an extended area with the sunflower crop. As this species has also invaded several other sunflower crop growing areas in the world, it severely restricts the use of new technologies, for example herbicide tolerance by genetic modification. The natural seed dormancy of the wild Helianthus strains from the centre of origin in North America is well known, but the seed dormancy of the invasive biotypes is still unknown. Dormancy is a fitness trait related to the establishment, dispersion and persistence of invasive weeds. Four experiments were designed to investigate the effect of the pericarp, light, temperature, the after‐ripening period and hybridization with the DK3880CL sunflower crop ( F1 ) on the seed dormancy of five invasive H. annuus biotypes. The results showed that pericarp scarification increased imbibition of the whole achene by 19%. Light stimulation only increased germination in the wild biotype without any effect on the domesticated sunflower. A period of 12 months after‐ripening at 5°C reduced seed dormancy in the wild biotype and its progeny; the optimal temperature for seed germination at this period was found to be 15°C. Mechanical scarification was the best treatment for overcoming seed dormancy with a differential germination, in the biotypes with the highest response, superior to 63%. Hybridization with domesticated sunflower had a minimal or no effect on seed dormancy but the germination rate was improved in three F1 crosses. Wild biotype dormancy appears to be governed by the maternal pericarp and intrinsic hormone regulation. An increased germination rate of some progenies could constitute an advantage during seedling establishment but only in winters without any frost.

Abstract BACKGROUND Conventional techniques used for determination of extractable poly(hydroxyalkanoate)s ( PHAs ) present in cells are laborious and destructive. Fourier transform infrared ( FTIR ) spectroscopy is an indirect analytical method to study molecular structures and has been used for the detection and quantification of PHA in intact cells. However, obtain a fine powder with pure PHA to prepare KBr pellets is a difficult task. The objective of this study was to develop a cheap alternative for quantifying the extractable intracellular PHA , based on a pulverizable solid as a standard material ( PEM : Pre Extraction Material) produced by Bacillus megaterium BBST4 strain, instead of pure PHA produced by the same strain. Through statistical analysis the correlation between sample content and its FTIR spectra were determined. The proposed methodology employs typical MID‐FTIR equipment and KBr pellets for spectra determination. RESULTS Small root‐mean‐standard errors of prediction of the amount of extractable PHA were obtained using partial least square regression ( PLSR1 ). In order to simplify the determination process, a simple linear regression analysis ( SLRA ) was also developed, and satisfactory correlations were found. CONCLUSIONS Results from PLSR1 and SLRA , calibrated with the proposed standard, indicate that it is a simple, fast and reliable alternative of fitting for determining the extractable PHA in unknown lyophilized cell samples. © 2015 Society of Chemical Industry

Abstract Question Does climate change affect vegetation and seed bank composition in desert grasslands? Location Sevilleta National Wildlife Refuge, New Mexico, USA. Methods Vegetation and seed bank species composition were recorded in black grama ( Bouteloua eriopoda ) and blue grama ( Bouteloua gracilis ) grasslands. At each site, two rainfall manipulations and ambient controls were established in 2013 ( n = 10). Treatments included extreme drought (−66% rainfall reduction during the growing season) and delayed monsoon (precipitation captured during July–August and reapplied in September–October). Above‐ground species composition was assessed, and composite soil samples were collected in 2017, five years after the experiment started. Seed bank was evaluated using the seedling emergence method. Results Rainfall treatments increased the above‐ground vegetation and seed bank richness in the blue grama community, but not in the black grama community. Vegetation cover was reduced by both rainfall manipulations, but seed bank density increased or remained the same compared with controls. In above‐ground vegetation, cover of annual and perennial forbs increased, and dominant perennial grasses decreased under drought. In the soil seed bank, species composition was similar among all treatments and was dominated by annual and perennial forbs. Conclusions The seed bank was more resistant to drought than above‐ground vegetation. Because seed banks can enhance long‐term community stability, their drought resistance plays an important role in maintaining ecosystem processes during and following drought in these grassland communities.

Seed dormancy could be a factor related to natural reseeding of hairy vetch (Vicia villosa ssp. villosa Roth.), a winter annual species cultivated for seed, pasture, hay, green manure and cover crop. The presence of combinational dormancy (physical dormancy + physiological dormancy, PY + PD) in hairy vetch was explored by a model using laboratory and field measures. At the stage of natural dispersal, dry seeds of hairy vetch were stored under laboratory conditions at 5, 10, 20 and 30°C (±2°C) or buried at 5 cm depth in an experimental field. Germination at 5, 8, 10, 15, 20 and 25°C was assessed at regular intervals up to 295 days after harvest. Following the hypothesis of the existence of a combinational dormancy mechanism, model development was based on the estimation of: (i) the fraction of non-PY seed as a function of after-ripening thermal-time accumulation, and (ii) seed population thermal parameters associated with a given level of PD. The developed model adequately described the after-ripening thermal-time requirements for PY + PD release of V. villosa. Based on model predictions, under a semi-arid thermal regime, &amp;gt;45% of vetch seeds shed during the summer season would be able to germinate during early autumn. Thus, the seed-bank size threshold at the end of the first growing season should be &amp;gt;65 seeds m–2 in order to reach a minimum stand of 30 plants m–2 necessary for a productive pasture.

presents mainly facultative genotypes that reproduce by diplosporous apomixis, retaining a percentage of sexual pistils that increase under drought and other stressful situations, indicating that some regulators activated by stress could be affecting the apomixis/sexual switch. Water stress experiments were performed in order to associate the increase in sexual embryo sacs with the differential expression of genes in a facultative apomictic cultivar using cytoembryology and RNA sequencing. The percentage of sexual embryo sacs increased from 4 to 24% and 501 out of the 201,011 transcripts were differentially expressed (DE) between control and stressed plants. DE transcripts were compared with previous transcriptomes where apomictic and sexual genotypes were contrasted. The results point as candidates to transcripts related to methylation, ubiquitination, hormone and signal transduction pathways, transcription regulation and cell wall biosynthesis, some acting as a general response to stress and some that are specific to the reproductive mode. We suggest that a DNA glycosylase EcROS1-like could be demethylating, thus de-repressing a gene or genes involved in the sexuality pathways. Many of the other DE transcripts could be part of a complex mechanism that regulates apomixis and sexuality in this grass, the ones in the intersection between control/stress and apo/sex being the strongest candidates.

BACKGROUND: Weeping lovegrass (Eragrostis curvula [Shrad.] Nees) is a perennial grass found in semi-arid regions that is well adapted for growth in sandy soils and drought conditions. E. curvula constitutes a polymorphic complex that includes cytotypes with different ploidy levels (from 2x to 8x), where most polyploids are facultative apomicts, although both sexual reproduction and full apomixis have been reported in this species. Apomixis is thought to be associated with silencing of the sexual pathway, which would involve epigenetic mechanisms. However, a correlation between small RNAs and apomixis has not yet been conclusively established. RESULTS: Aiming to contribute to the elucidation of their role in the expression of apomixis, we constructed small RNA libraries from sexual and apomictic E. curvula genotypes via Illumina technology, characterized the small RNA populations, and conducted differential expression analysis by comparing these small RNAs with the E. curvula reference transcriptome. We found that the expression of two genes is repressed in the sexual genotype, which is associated with specific microRNA expression. CONCLUSION: Our results support the hypothesis that in E. curvula the expression of apomixis leads to sexual repression.

Abstract Invasive bivalves continue to spread and negatively impact freshwater ecosystems worldwide. As different metrics for body size and biomass are frequently used within the literature to standardise bivalve‐related ecological impacts (e.g. respiration and filtration rates), the lack of broadly applicable conversion equations currently hinders reliable comparison across bivalve populations. To facilitate improved comparative assessment among studies originating from disparate geographical locations, we report body size and biomass conversion equations for six invasive freshwater bivalves (or species complex members) worldwide: Corbicula fluminea, C. largillierti , Dreissena bugensis, D. polymorpha , Limnoperna fortunei and Sinanodonta woodiana , and tested the reliability (i.e. precision and accuracy) of these equations. Body size (length, width and height) and biomass metrics of living‐weight (LW), wet‐weight (WW), dry‐weight (DW), dry shell‐weight (SW), shell free dry‐weight (SFDW) and ash‐free dry‐weight (AFDW) were collected from a total of 44 bivalve populations located in Asia, the Americas and Europe. Relationships between body size and individual biomass metrics, as well as proportional weight‐to‐weight conversion factors, were determined. For most species, although inherent variation existed between sampled populations, body size directional measurements were found to be good predictors of all biomass metrics (e.g. length to LW, WW, SW or DW: R 2 = 0.82–0.96), with moderate to high accuracy for mean absolute error (MAE): ±9.14%–24.19%. Similarly, narrow 95% confidence limits and low MAE were observed for most proportional biomass relationships, indicating high reliability for the calculated conversion factors (e.g. LW to AFDW; CI range: 0.7–2.0, MAE: ±0.7%–2.0%). Synthesis and applications . Our derived biomass prediction equations can be used to rapidly estimate the biologically active biomass of the assessed species, based on simpler biomass or body size measurements for a wide range of situations globally. This allows for the calculation of approximate average indicators that, when combined with density data, can be used to estimate biomass per geographical unit‐area and contribute to quantification of population‐level effects. These general equations will support meta‐analyses, and allow for comparative assessment of historic and contemporary data. Overall, these equations will enable conservation managers to better understand and predict ecological impacts of these bivalves.

Studying the levels and patterns of genetic diversity of invasive populations is important to understand the evolutionary and ecological factors promoting invasions and for better designing preventive and control strategies. Wild sunflower (Helianthus annuus L.) is native to North America and was introduced, and has become invasive, in several countries, including Argentina (ARG). Here, using classical population genetic analyses and approximate Bayesian computation (ABC) modeling, we studied the invasion history of wild sunflower in ARG. We analyzed 115 individuals belonging to 15 populations from ARG (invasive range) and United States (US, native range) at 14 nuclear and 3 chloroplast simple sequence repeat markers along with 23 phenotypic variables. Populations from ARG showed similar levels of nuclear genetic diversity to US populations and higher genetic diversity in the chloroplast genome, indicating no severe genetic bottlenecks during the invasion process. Bayesian clustering analysis, based on nuclear markers, suggests the presence of 3 genetic clusters, all present in both US and ARG. Discriminant analysis of principal components (DAPC) detected an overall low population structure between central US and ARG populations but separated 2 invasive populations from the rest. ABC modeling supports multiple introductions but also a southward dispersal within ARG. Genetic and phenotypic data support the central US as a source of introduction while the source of secondary introductions could not be resolved. Finally, using genetic markers from the chloroplast genome, we found lower population structure in ARG when compared with US populations, suggesting a role for seed-mediated gene flow in Argentina.