- ArtículoRestringidoReproductive traits in four spontaneous Pappophorum vaginatum populations in arid Argentina(2021)Arid zones, where native rangelands are common, are essentials for millions of people livelihood. These areas support 50% of the world’s livestock and are where 44% of the world’s food is grown. In rangelands of Central Argentina, Pappophorum vaginatum is basically the unique, warm-season perennial grass species palatable to grazing livestock. Our major objective was to determine variability in reproductive characteristics among four spontaneous, overgrazed populations (i.e., P1, P2, P3, P4) of that species to identify promissory materials for domestication. Studies were conducted during three consecutive growing seasons within the southwestern part of the Phytogeographical Province of the Monte, in southwestern Buenos Aires, Argentina. Measured reproductive characteristics were related to flowering initiation, seed production and natural reseeding potential. Significant differences were found for flowering initiation and natural reseeding potential, but not for viable anthecia per plant among the four populations of P. vaginatum. This species fructified from the beginning to the end of the studied growing seasons with a great anthecia production per plant. The light weight of these anthecia and their awns would favor a great wind dispersal and most likely the establishment of new seedlings of P. vaginatum. This suggests that sexual reproduction might have a relatively greater importance than asexual reproduction (i.e., tillering) in the persistence of the overgrazed P. vaginatum in the plant communities of the studied region. Se-lection of plant materials with a late flowering initiation will allow to extend the forage production of a better quality. The variability among and within populations found on this study support the idea that would be promissory to start selection programs to obtain improved germplasm to reincorporate to grasslands of the south of the Phytogeographical Region of the Monte (Argentina) not only to increase livestock production but to recover and maintain biodiversity.
- ArtículoAcceso AbiertoLimitaciones del test de tetrazolio para determinar viabilidad de yemas y semillas(2021)La técnica convencional de tinción conocida como test de tetrazo-lio no es la más apropiada para la determinación de la viabilidad de los tejidos vegetales, sino que debería complementarse con el colorante azul de Evans.
- ComunicacionEmbargadoPlant Species and Defoliation Efects on Soil Nitrogen Mineralization in a Semiarid Rangeland of Argentina(2021)The objective of this study was to evaluate the efects of moderate defoliation and grass species on soil nitrogen (N) mineralization in a semiarid grassland of northeastern Patagonia, Argentina. Studied species were Poa ligularis and Nassella tenuis (desirable/preferred by cattle) and Amelichloa ambigua (undesirable/non preferred). Two defoliations were made to a 5 cm stubble height during the growing season. Hypotheses were that (1) net N mineralization and N availability in the soil are increased by a moderate defoliation and greater species forage quality, and (2) potential N mineralization is higher in the soil beneath the desirable than undesirable species. In 2013 and 2014, in situ net N mineralization was estimated using the tube incubation technique under feld conditions. Potential N mineralization was estimated by long-term laboratory incubations. Defoliation treatments did not afect the soil inorganic N dynamics. The soil under A. ambigua showed a greater in situ net N mineralization than other species, but only in 2013. Poa ligularis presented the highest initial inorganic N and potentially mineralizable N values. However, the opposite was recorded in this specie for the mineralization constant rate. These results demonstrated that moderate defoliations did not afect soil N availability, and presence of the desirable perennial grasses increased the potential N mineralization pool. Sustainable management practices that promote the persistence of these species in plant community are important to maintain soil fertility on semiarid grasslands.
- ArtículoAcceso AbiertoThree-Dimensional Reconstruction of Halamphora coffeaeformis Frustule from Scanning Electron Micrographs(2020)The diatom Halamphora coffeaeformis represents an alternative feedstock of oils for the biodiesel production. In addition, its siliceous cell wall (named frustule) presents possible industrial applications that have not been reported in the literature yet. Thus, the main objective of this study was to perform a three-dimensional reconstruction of H. coffeaeformis´ frustule from scanning electron micrographs, in order to have a study model. For this, the biomass of the species growing in a photobioreactor was harvested and treated as follows: a) some samples were dehydrated and subjected to a critical point; and b) other samples were treated with H2O2 in order to analyse the frustule´s ornamental pattern. All samples were metallized with gold, using an Argon plasma metal evaporator (Pelco model3) and they were observed with a LEO Scanning Electron Microscope, model EVO 40 XVP 2004. The frustules were elliptical to lanceolate with protracted ends. Valves presented convex dorsal margin and straight ventral margin. Dorsal striae were biseriate and radiate; ventral striae were short, uniseriate, radiate at the center and convergent at the ends of the valves. The raphe was straight and close to the ventral margin. The micrographs were analysed and separated into layers with the Adobe Photoshop CS6 software. The layers were vectorised with the Inkscape software and loaded and assembled in the Tinkercad software. The final aspects of the digital model were moulded on the page https://stephaneginier.com/sculptgl/. Finally, 3D printing was done with a CoLiDoTM 3.0 L printer, obtaining a three-dimensional replica representative of the H. coffeaeformis´ morphology . This replica will serve as a model for studies of its frustules related to nanotechnology and /or catalyst support applications.
- ArtículoAcceso AbiertoSoil microbial structure and activity in a semiarid rangeland of Patagonia, Argentina: Plant species and defoliation effects(2021)Natural grasslands are an important renewable resource for livestock production. Grazing in these areas alters the plant community composition, litter quality, and soil microbial structure and activity. Three cool-season species were studied in a semiarid rangeland area of Argentina: Poa ligularis and Nassella tenuis (desirable/ preferred for livestock) and Amelichloa ambigua (undesirable/non preferred). The objective was to analyze the effect of moderate defoliation and plant species on the structure and activity of soil microbial communities associated with their roots. In winter 2012, soil samples (0–10 cm) were taken underneath marked plant canopies of the three species (n = 8). Immediately thereafter, half of the plants (n = 4) were defoliated (5 cm stubble height) and the other half remained undefoliated (controls). The defoliation treatment was conducted again in the spring. Soil samples were taken 30 days after each defoliation event. The study was repeated in 2013, using a different plant set. Bacterial community structure and soil microbial activity were analyzed using PCR-DGGE analysis and basal soil respiration, respectively. Moderate and early defoliations allowed compensatory growth in the defoliated plants. Variations in the soil genetic profiles of A. ambigua suggest a higher dependence on its rhizospheric bacterial communities. Defoliation treatments did not substantially affect basal soil respiration but showed strong links between desirable species and soil microbial activity. Sustainable management practices that promote the persistence of these species are important for the development of microbial communities that respond quickly to stress conditions, favoring decomposition processes that maintain soil fertility in semiarid grasslands.