Abstract:

We studied the activity and breeding pattern of dominant lizard species in the Arid Chaco, the southernmost subregion of the Chaco ecoregion (Chancaní Reserve, Córdoba province, Argentina). Lizards were captured with pitfall traps over a 4-year period. In total, 1449 individuals belonging to 11 of the 12 lizard species recorded in the area were trapped. Of these, we selected six species for a detailed analysis: Teius teyou and Stenocercus doellojuradoi accounted for 63% of the captures, Tropidurus etheridgei, Liolaemus chacoensis and Homonota fasciata accounted for 32%, and 5% comprised Leiosaurus paronae and the remaining five species. All the studied species were active during the warm–rainy season (September to March). Monthly lizard captures were highly correlated with monthly mean temperature and rainfall. No captures occurred during the remaining months of the year. All reproductive tactics known for the Chaco lizards were observed in Chancaní, including single clutch in a short breeding season in summer or autumn, as well as an extended breeding season with multiple clutches. Stenocercus doellojuradoi and L. paronae showed a singular reproductive timing, suggesting the occurrence of egg retention. Compared with sub-tropical Chaco sites, the Arid Chaco only differs in the lack of winter activity, resulting from the lower temperature and rainfall regime of our study site.

Author affiliation: Pelegrin, Nicolas. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Cordoba. Instituto de Diversidad y Ecologia Animal; Argentina

Author affiliation: Bucher, Enrique Hugo. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Cordoba. Instituto de Diversidad y Ecologia Animal; Argentina

Abstract:

It has been proposed that aridity and grazing are convergent selective forces: each one selects for traits conferring resistance to both. However, this conceptual model has not yet been experimentally validated. The aim of this work was to experimentally evaluate the effect of aridity and grazing, as selective forces, on drought and grazing resistance of populations of Trichloris crinita, a native perennial forage grass of the Argentinean Arid Chaco region. We collected seeds in sites with four different combinations of aridity and grazing history (semiarid/subhumid × heavily grazed/lightly grazed), established them in pots in a common garden, and subjected the resulting plants to different combinations of drought and defoliation. Our results agreed with the convergence model. Aridity has selected T. crinita genotypes that respond better to drought and defoliation in terms of sexual reproduction and leaf growth, and that can evade grazing due to a lower shoot : root ratio and a higher resource allocation to reserves (starch) in stem bases. Similarly, grazing has selected genotypes that respond better to drought and defoliation in terms of sexual reproduction and that can evade grazing due to a lower digestibility of leaf blades. These results allow us to extend concepts of previous models in plant adaptation to herbivory to models on plant adaptation to drought. The only variable in which we obtained a result opposite to predictions was plant height, as plants from semiarid sites were taller (and with more erect tillers) than plants from subhumid sites; we hypothesize that this result might have been a consequence of the selection exerted by the high solar radiation and soil temperatures of semiarid sites. In addition, our work allows for the prediction of the effects of dry or wet growing seasons on the performance of T. crinita plants. Our results suggest that we can rely on dry environments for selecting grazing-resistant genotypes and on high grazing pressure history environments for selecting drought-resistant ones.

Author affiliation: Quiroga, R. Emiliano. Instituto Nacional de Tecnología Agropecuaria; Argentina

Author affiliation: Golluscio, Rodolfo. Universidad de Buenos Aires. Facultad de Agronomía; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Author affiliation: Blanco, Lisandro Javier. Instituto Nacional de Tecnología Agropecuaria; Argentina

Author affiliation: Fernández, Roberto J.. Universidad de Buenos Aires. Facultad de Agronomía; Argentina

Abstract:

In arid environments, water availability is the main limiting factor for primary production, and it is expected that not only drought-resistance, but also plant strategies for soil water use will be under natural selection. Our aim was to investigate the strategies of soil water use and the responses to water shortage that lead to variability in drought resistance in Trichloris crinita plants (a native forage grass of northwestern Argentina) from sites with contrasting aridity. We established a common-garden experiment with plants from relatively “arid” and “humid” sites (326 and 625 mm mean annual precipitation, respectively). During 6 weeks, plants were subjected to two contrasting watering levels: control and drought. We found different water use strategies and drought resistance between plants from arid and humid sites: the former used water more conservatively and grew more under drought. During the first 2 weeks of the drought treatment, plants from arid sites dried out the soil slower than those from humid sites. Plants from arid sites subjected to drought showed less leaf senescence and a greater leaf elongation rate and biomass of green leaves than those from humid sites. This variability in adaptation to drought in T. crinita plants could be used to select plant materials for arid land revegetation or to be incorporated into breeding programs for forage purposes.

Author affiliation: Quiroga, R. Emiliano. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Catamarca-La Rioja. Estación Experimental Agropecuaria Catamarca; Argentina

Author affiliation: Fernandez Alduncin, Roberto Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina

Author affiliation: Golluscio, Rodolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina

Author affiliation: Blanco, Lisandro J.. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Catamarca-La Rioja. Estación Experimental Agropecuaria La Rioja; Argentina

Abstract:

En los pastizales del Chaco Árido argentino se ha perdido biodiversidad y productividad a causa del sobrepastoreo por animales domésticos. El objetivo de este trabajo fue evaluar algunos tratamientos de rehabilitación que podrían aumentar la densidad de gramíneas forrajeras en un pastizal sobrepastoreado de la región. A partir de la idea de que la compactación del suelo, la falta de semillas en el banco y la falta de mantillo son factores que limitan el establecimiento de las plántulas, realizamos un experimento factorial a campo que combinó poceado del suelo, agregado de semillas y acción conjunta de reducción de competencia y agregado de mantillo de arbustos. Durante cuatro años evaluamos la densidad de plántulas y plantas de las gramíneas agregadas y del total de gramíneas forrajeras. Sólo el agregado de semillas aumentó la densidad de plántulas y plantas de estas especies. Durante el primer año registramos mayor densidad de plántulas en las parcelas con agregado de semillas (principalmente <i>Pappophorum spp.</i>) y una mayor densidad de plantas adultas durante los primeros dos años (atribuible al establecimiento casi exclusivo de <i>P. philippianum</i>). A partir del tercer año (año seco) se observó una disminución de 70-80% en la densidad de plantas en todos los tratamientos, si bien persistieron las diferencias debidas al agregado de semillas. Nuestros resultados sugieren que, además de las condiciones climáticas adversas, la falta de semillas en el banco del suelo restringe la recuperación de los pastizales sobrepastoreados en el Chaco Árido, y que <i>Pappophorum philippianum</i> sería una especie promisoria a utilizar con fines de rehabilitación.

Overgrazing by domestic cattle has caused loss of plant diversity and primary productivity in rangelands of the Arid Chaco (Argentina). The objective of our study was to evaluate a number of rehabilitation strategies that might increase the density of forage grasses in an overgrazed rangeland in this region. Based on the hypothesis that soil compaction, lack of seeds and litter cover constrain plant establishment we performed a field factorial experiment, that combined soil pitting, seed addition and the combined effect of competition release and litter addition. During four years, we evaluated seedling and plant density of added grasses and all forage grasses. Seed addition was the only factor that increased seedling and plant density, with <i>Pappophorum spp</i>. and <i>P. philippianum</i> accounting for the main variation in seedling and plant density, respectively. During the third year (a dry year), there was 70-80% decrease in plant density in all treatments, although the differences due to the addition of seeds was still apparent. Our results suggest that, in addition to adverse climatic conditions, the lack of seeds in the soil bank restricts the recovery of overgrazed rangelands in the Arid Chaco. <i>Pappophorum philippianum</i> seems to be a promising species for the rehabilitation of these rangelands.

Abstract:

We tested if the microbial functional redundancy concept (theory relating changes in ecosystem functioning by species loss) apply for changes in the ammonium-oxidizing community (nitrifi er bacteria) due to: a) grazing disturbance, b) seasonal variations (dry season vs. wet season), c) habitat type (soil vs. organic residues), and d) ecological conditions (two eco-regions), in an arid region of central-western of Argentina. We determined: a) abundance of culturable nitrifi er bacteria, b) nitrifi cation activity and effi ciency, and c) nitrifi er community genetic structure by PCR-DGGE (richness and similarity index). Grazing did not change the nitrifi er abundance, activity and richness, while seasonally and eco- region effects were scarce. Contrarily, the habitat type affected nitrifi er activity, which was higher in organic residues than in soil. All similarity indexes were low (average 0.50, range 0.76-0.18) which suggest high species diversity in these arid eco-regions. Our results indicate that the nitrifi cation process in arid region of Argentina is redundant but it applies only for each habitat. To our knowledge, this is the fi rst functional redundancy study on microbial ecological process in disturbed arid zones, in which we report an important species replacement but without modifi cations in microorganism abundance and activity.

Nosotros testeamos si el concepto de redundancia funcional microbiana (teoría que relaciona los cambios en el funcionamiento del ecosistema y la pérdida de especies) se aplica para la comunidad de microorganismos oxidadores de amonio (bacterias nitrificadoras) afectada por el pastoreo, la estacionalidad (estación seca y húmeda), el tipo de hábitat (suelo y restos orgánicos), y las condiciones ecológicas (eco-región del Chaco Árido y el Monte), en la región árida del centro-oeste de Argentina. Se determinó: a) la abundancia de bacterias nitrificadoras cultivables, b) la actividad y eficiencia de la nitrificación, y c) la estructura genética de la comunidad de nitrificadores mediante PCR- DGGE (riqueza e índice de similitud). El pastoreo no modificó la abundancia de nitrificadores, la actividad y la riqueza, mientras que el efecto de la estacionalidad y la eco-región fue escaso. Contrariamente, el tipo de hábitat afectó la actividad nitrificadora, la cual fue más alta en los restos orgánicos que en el suelo. Todos los índices de similitud fueron bajos (promedio = 0.5; rango entre 0.76-0.18), lo cual sugiere una alta diversidad de especies en estas regiones áridas. Nuestros resultados indican que el proceso de nitrificación en la región árida central de Argentina es redundante, pero que se puede aplicar solo para cada tipo de hábitat. En nuestro conocimiento, este es el primer estudio de redundancia funcional sobre procesos ecológicos microbianos en zonas áridas disturbadas, en el cual se detectó un importante remplazo de especies, sin modificaciones en la abundancia y actividad de los microorganismos.

Author affiliation: Noe, Laura Belen. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico y Transferencia de Tecnologia a la Producción; Argentina;

Author affiliation: Abril, Adriana. Universidad Nacional de Córdoba. Facultad de Ciencias Agropecuarias. Departamento de Recursos Naturales. Cátedra de Microbiología Agrícola; Argentina;

Abstract:

Soil evaporation is a dominant water flux of flat dry ecosystems, reducing available water for plant transpiration. Vegetation plays a key role at controlling evaporation, especially by altering soil surface micro-meteorological conditions. Here, we explored the vegetation cover effect on soil evaporation, differentiating the effects of canopy cover (shadow) and of surface cover (litter) in forests and pastures of Dry Chaco rangelands (San Luis, Argentina). We measured daily soil evaporation using irrigated micro-lysimeters installed at regularly spaced (2 m) patches along transects in native dry forests (n = 54 patches) and pastures (n = 27 patches). In each forest patch, we established a pair of micro-lysimeters, one with litter (3 cm depth, representing high litter cover conditions of the site) and one with bare soil, but in pastures, only one micro-lysimeter with bare soil was installed at each patch (representing the typical no litter cover conditions of pastures of the study site). We found that, when soil water was not limiting, litter cover had the strongest effect in reducing evaporation rates, with a 4- and 6.4-fold reduction respect to bare soil micro-lysimeters in the forest and pasture, respectively. Evaporation decreased sharply with declining incident radiation fraction in bare soil micro-lysimeters from 5.6 mm/day (full radiation) to 3.5 mm/day (full canopy shadow; R2 = 0.50). Litter-covered micro-lysimeters showed lower and more stable evaporation rates, decreasing only from 1.35 to 1.03 mm/day under the same radiation conditions (R2 = 0.10). In accordance with J.T. Ritchie evaporation model, we identified a threshold of ~10.5 mm of cumulative evaporation at which evaporation switched from energy to water limitation in all situations, as revealed by declining evaporation rates and raising surface temperatures. Under typical wet–summer conditions, the pasture, the forest with bare soil, and the forest with litter would need on average a drying cycle of 1.5, 2.5, and 9.5 days, respectively, to reach that threshold. Simulations showed that, considering the distribution of rainfall events at our study site, litter would maintain evaporation in the energy-limited mode most of the time (68.8% of summer days), potentially favouring transpiration. The ecohydrological key role of soil litter controlling evaporation highlights the importance of an accurate assessment of management practices controlling the evaporation/transpiration partition in dry ecosystems.

Author affiliation: Magliano, Patricio Nicolás. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Matemática Aplicada de San Luis ; Argentina

Author affiliation: Giménez, Raúl. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Matemática Aplicada de San Luis ; Argentina

Author affiliation: Houspanossian, Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Matemática Aplicada de San Luis ; Argentina

Author affiliation: Paez, Ricardo Andrés. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Matemática Aplicada de San Luis ; Argentina

Author affiliation: Nosetto, Marcelo Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Matemática Aplicada de San Luis ; Argentina

Author affiliation: Fernandez Alduncin, Roberto Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía; Argentina

Author affiliation: Jobbagy Gampel, Esteban Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Matemática Aplicada de San Luis ; Argentina

Abstract:

Intra- and interspecific coexistence has been recorded in several species of scorpions, reflecting different levels of aggregation and sociability. Some species of scorpions avoid temporal or spatial overlap of their surface activities, which may differ depending on species, age group or gender, and thus reduce intra- and interspecific competition and predation. We examined the surface activity of males, females and juveniles (sex-age class) of the scorpion Brachistosternus ferrugineus (Thorell, 1876) in an area of Arid Chaco, and also its microhabitat preference and behavior by each sex-age class. The month-by-month activity of each sex-age class was different, but all the classes were observed each month. The most frequently used microhabitat was soil (64.8%), while leaf litter and vegetation were used in similar proportions. The behavior most frequently observed was ambush (68.3%), followed by walking and less frequently feeding, doorkeeping and courting. Each sex-age class performed one particular behavior with more frequency than the others. Analyzing combinations of microhabitat, behavior and sex-age class, we found the juveniles were associated with feeding on vegetation, males with walking on leaf litter, while females were related to ambush on soil. No marked temporal distribution between sex-age classes was observed. However, the spatial distribution and frequency of behaviors were highly dependent on developmental stage and sex. These differences may facilitate understanding of the coexistence of different age-sex classes of B. ferrugineus.

Author affiliation: Nime, Mónica Fernanda. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Diversidad y Ecología Animal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Diversidad y Ecología Animal; Argentina

Author affiliation: Casanoves, Fernando. Unidad de Bioestadística del Centro Agronómico Tropical de Investigación y Enseñanza; Costa Rica

Author affiliation: Mattoni, Camilo Ivan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Diversidad y Ecología Animal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Diversidad y Ecología Animal; Argentina

Abstract:

Breeding biology in Phyllomedusa sauvagii is related to vegetation since the species encloses its eggs in leaves above water. Considering that arid environments may represent high risks of death by desiccation for amphibians with this reproductive mode, we evaluated plant characteristics associated with sites used for oviposition in semi-permanent ponds in the Arid Chaco region of Argentina. Plant characteristics were used to fit a statistical habitat selection model that allows the prediction of nest presence. The results show that P. sauvagii needs substrate with specific features for oviposition that would help to reduce the probability of eggs and tadpoles desiccation.

Author affiliation: García, Cecilia Graciela. Universidad Nacional de Cordoba. Facultad de Cs.exactas Fisicas y Naturales. Centro de Zoologia Aplicada; Argentina. Universidad Nacional de Jujuy. Facultad de Ingenieria. Centro de Investigaciones Basicas y Aplicadas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Author affiliation: Lescano, Julián Norberto. Universidad Nacional de Cordoba. Facultad de Cs.exactas Fisicas y Naturales. Centro de Zoologia Aplicada; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Cordoba. Instituto de Diversidad y Ecologia Animal; Argentina

Author affiliation: Leynaud, Gerardo Cristhian. Universidad Nacional de Cordoba. Facultad de Cs.exactas Fisicas y Naturales. Centro de Zoologia Aplicada; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Cordoba. Instituto de Diversidad y Ecologia Animal; Argentina

Abstract:

The human population in the arid Chaco forests of Argentina is composed mainly of stockmen carrying out ancestral practices. Plant uses in this biogeographic region are relatively well known, but the forest perception by local populations was not studied so far. A total of 77 stockmen and other local salaried people were interviewed with semi-structured interviews, and herbarium specimens were produced with the informants. A Likert scale was used to obtain perceptions of the forest value. We registered 124 plant species, particularly forage woody plants, which have a variety of uses. More than 100 species overlapped with a survey of the region more than one century ago. Stockmen carry out ancestral practices such as cutting, collecting, and storing dry fruit, creating elaborate cercos, and know substantially more forage plants. The results suggest that the local population as a whole has a positive perception of the forests, regardless of their main occupation, and needs the forest to reinforce stockmen’s traditions (criollos) through daily activities.

Author affiliation: Trillo, Cecilia. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Cátedra de Diversidad Vegetal II; Argentina

Author affiliation: Colantonio, Silvia. Universidad Nacional de Córdoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Instituto Multidisciplinario de Biología Vegetal (p); Argentina

Author affiliation: Galetto, Leonardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Instituto Multidisciplinario de Biología Vegetal (p); Argentina. Universidad Nacional de Córdoba; Argentina

Abstract:

Summary 1. Carbon storage in vegetation and soil underpins climate regulation through carbon sequestration. Because plant species differ in their ability to capture, store and release carbon, the collective functional characteristics of plant communities (functional diversity) should be a major driver of carbon accumulation in terrestrial ecosystems. 2. Three major components of plant functional diversity could be put forward as drivers of carbon storage in ecosystems: the most abundant functional trait values, the variety of functional trait values and the abundance of particular species that could have additional effects not incorporated in the rst two components. 3. We tested for associations between these components and carbon storage across 16 sites in the Chaco forest of Argentina under the same climate and on highly similar parental material. The sites differed in their plant functional diversity caused by different long-term land-use regimes. 4. We measured six plant functional traits in 27 species and weighted them by the species abundance at each site to calculate the community-weighted mean (CWM) and the functional divergence (FDvar) of each single trait and of multiple traits (FDiv). We also measured plant and soil carbon storage. Using a stepwise multiple regression analysis, we assessed which of the functional diversity components best explained carbon storage. 5. Both CWM and FDvar of plant height and wood-specic gravity, but no leaf traits, were retained as predictors of carbon storage in multiple models. Relationships of FDvar of stem traits and FDiv with carbon storage were all negative. The abundance of ve species improved the predictive power of some of the carbon storage models. 6. Synthesis. All three major components of plant functional diversity contributed to explain carbon storage. What matters the most to carbon storage in these ecosystems is the relative abundance of plants with tall, and to a lesser extent dense, stems with a narrow range of variation around these values. No consistent link was found between carbon storage and the leaf traits usually associated with plant resource use strategy. The negative association of trait divergence with carbon storage provided no evidence in support to niche complementarity promoting carbon storage in these forest ecosystems.

Author affiliation: Conti, Georgina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Instituto Multidisciplinario de Biología Vegetal (p); Argentina

Author affiliation: Diaz, Sandra Myrna. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Instituto Multidisciplinario de Biología Vegetal (p); Argentina