Semi-arid Region Of Central Argentina Research Articles

Vegetated roofs as a nature-based solution to mitigate climate change in a semiarid city

• Extensive vegetated roofs (EVRs) sequester c. 0.57 kg C/m2 in semi-arid Córdoba, Argentina. • EVRs reduce energy consumption by c. 40% through the year, especially in summer. • EVRs reduce CO2 emissions and offer a sustainable nature-based solution to climate change. Extensive vegetated roofs (EVRs) are effective in storing carbon and suppressing carbon dioxide emissions to reduce energy consumption in buildings significantly. This study aimed to quantify the carbon sequestration capacity of EVRs and estimate their potential in reducing CO 2 emission in Córdoba city in the semiarid region of central Argentina. For carbon sequestration capacity, we sampled plant and soil materials of three EVRs with similar vegetation but different ages and urban environmental stresses. We measured the carbon storage in the aboveground and belowground biomass and the substrate. To estimate the potential of EVRs in reducing energy consumption and thereby trimming CO2 emission, we simulated the energy consumption reduction by a building with EVRs using the EnergyPlus modeling software. We adjusted the actual data of physical parameters obtained in our study to calculate CO 2 emission reduction compared to a control roof. Our results suggested that EVRs in the semiarid climate could sequester carbon in the order of 2.11 CO2eq/m 2 per year The EVRs achieved a reduction in energy consumption of c. 40%, equivalent to decreasing the emission by 68.38 kg CO 2 /m 2 per year. Since the EVRs can provide an integrative and multifunctional solution to reduce atmospheric CO 2 in urban ecosystems, they offer a promising sustainable nature-based solution with the potential to mitigate climate change effects.

Zooplankton community size structure across lakes within a semi-arid landscape: the effect of temperature and salinity

AbstractBody size is a master trait controlling biological communities and ecosystem functioning. Mean population size not only depends on the size of individuals, but also on the size distribution of individuals within the population. Mean community size is additionally influenced by the composition of species (larger- or smaller-sized species). Shallow lakes within semi-arid landscapes are prone to experience large changes in temperature and salinity, which affect the zooplankton size structure. Higher temperatures are expected to result in smaller average body size, while the effect of salinity appears to depend on the range under study. Here we analyze zooplankton body size patterns across shallow lakes from the semi-arid central region of Argentina. All community size descriptors point to decreasing size and a narrow size range at higher temperatures. On the other hand, the maximum average community body size occurred at intermediate (~30 gL−1) salinity levels. The combined effect of both variables resulted in a bell-shaped pattern, with maximum community body size toward lower temperatures and intermediate salinities. Based on future temperature scenarios, one may anticipate an overall decrease in community body size. But such prediction is strongly conditioned by regional and local trends in salinity.

Analysis of biodiversity attributes for extensive vegetated roofs in a semiarid region of central Argentina

Vegetated roofs (VRs) contribute to the resilience of cities by providing multiple ecosystem functions. A wide range of these benefits depends on the plant layer. Here, we hypothesized that increasing biodiversity attributes (i.e., composition, structural, and functional) in VRs will improve their performance under the climate conditions of semiarid regions. We aimed to (i) characterize functional groups of eight species assessed from key functional traits, (ii) evaluate species performance through survival and coverage, comparing biodiversity attributes from mono to polyculture treatments, (iii) analyze the relationship between performance with biodiversity attributes, and (iv) systematize and rank the treatments using an index to select those with the best performance and to recommend them for VRs in semiarid regions. We expect those treatments with higher biodiversity attributes will show better performances than simpler ones. Functional traits as indicators of ecosystem functions of eight species and four life-forms (succulents: Sedum acre, S. lineare, S. reflexum, creeping herbs: Phyla nodiflora, Glandularia x hybrida, tall forb: Grindelia cabrerae, and grasses: Eustachys distichophylla, and Nassella tenuissima) were evaluated through a trial using 22 microcosms during a 12-month experimental study. A principal component analysis and a cluster analysis were used to detect functional groups according to leaf and plant height traits. We used the Kaplan-Meier analysis to assess species survival among the treatments. Final coverage and growth increment (and their coefficients of variation) were used to construct the performance index. The PCA and CA determined five functional groups: I) succulents; II) creeping herbs; III) N. tenuissima; IV) E. distichophylla, and V) G. cabrerae. Four species showed significantly differences in survival rates among the treatments (p < 0.05), and six treatments were characterized as the best ones: with the highest coverage (>93%) and growth increment (81%), and with low CVs. Although some monoculture (Sedum spp., P. nodiflora and, E. distichophylla) reached comparable index values with respect to mixed microcosms, for VRs we recommend those plant mixtures combining biodiversity attributes because they provide both more ecosystem services and higher chances of survival and phenological complementarity in the long term.

Using Geochemical Fingerprints for Assessing Sediment Source Apportionment in an Agricultural Catchment in Central Argentina

In the hilly semi-arid region of central Argentina, where the agricultural frontier expands at the expense of natural ecosystems, soil erosion is one of the most alarming environmental problems. Thus, obtaining knowledge about the dynamics of erosive processes and identifying erosion hotspots constitutes a primary scientific objective. This investigation is focused on estimating the apportionments of main sources of sediments, at the mouth of a small catchment called Durazno del Medio, located in the province of San Luis, Argentina. Elemental Analysis, measured by Energy Dispersive X-ray Fluorescence (EDXRF), was used to select potential geochemical fingerprints of sediment. The unmixing model MixSIAR was applied to approximate the contribution of each identified source in the sediment accumulation areas at the mouth of the catchment. Potential sediment sources were selected using two criteria: (i) a hierarchical approach to identify the main geomorphological units (GUs) and (ii) the main land uses (LU), recognized by examining satellite images and field recognitions. The selected geochemical tracers were able to distinguish sources located in the Crystalline basement hills with loess-patched (CBH) as the main sediment contributors.

Temporal integration of remote‐sensing land cover maps to identify crop rotation patterns in a semiarid region of Argentina

AbstractCrop rotations are key agronomic tools to enhance farm productivity, preserve soil, and ensure provision of ecosystem services. Knowledge of the spatio‐temporal distribution of crops over regions is essential to characterize rotations at field scale and estimate their impacts on several outcomes. Our objectives were to: (a) determine the diversity of cropping systems practiced in a semiarid region of central Argentina during an 8‐yr period and (b) use the generated high‐resolution crop rotation map jointly with estimates of soil erosion to evaluate the potential linkage between cropping sequences and water erosion intensity. Temporally aggregated seasonal land‐cover maps were used to derive spatially explicit crop rotations during 2011–2018 across a 6,000 km2 semiarid agricultural region in Argentina. Soybean (Sy) [Glycine max (L.) Merr.] and maize (Mz) (Zea mays L.) defined the major crop rotations of the study area. Sorghum [Sorghum bicolor (L.) Moench] and peanut (Arachis hypogaea L.) occupied minor areas and thus were assimilated into the dominant summer cropping systems. Only seven sequences of summer crops, most of them including soybean and maize, accounted for &gt;90% of the spatio‐temporal variability. Soybean monoculture was the dominant cropping system (28.5%), followed by a 3‐yr Sy–Sy–Mz rotation (23.9%), and other soybean‐dominated rotation patterns. In winter, the prevailing land cover was stubble (96.6%). The generated high‐resolution maps illustrate the low diversity of crops in the study area. Mapping the spatio‐temporal distribution of land cover allowed for quantification of land transformations and the examination of linkages between soybean monocropping and erosion.

How sowing date affects development and performance of safflower through climate variables

AbstractSafflower (Carthamus tinctorius L.) has unrealized potential as an alternative crop in many semiarid regions including central Argentina. Our objective was to relate how temperature and precipitation conditions with fall (5 June 2012 and 23 Apr. 2013) and winter sowing (13 Aug. 2012 and 20 Aug. 2013) affected phenology, yield, yield components, and oil percent in four winter and eight spring‐type safflower accessions in the semiarid region of central Argentina. Fall sowing was associated with lower temperatures, higher precipitation, lower heat/moisture stress indices and precipitation deficits than winter sowing. Rosette period lasted 55 d longer, and stem elongation to anthesis period 30 d longer in fall than in winter sowing. However, anthesis was advanced only few days in fall sowing and duration of postanthesis development was comparable between sowing regimes and years. Fall sowing plants averaged 3,252 filled grains m–2 and a grain yield of 109.8 g m–2, whereas winter sowing plants averaged 1,443 filled grains m–2 and a grain yield of 49.3 g m–2. Grain yield was 35% higher in winter than in spring‐type accessions, but winter types had lower oil percent (22.0%) than spring‐types (33.3%). In the semiarid region of central Argentina, we recommend fall sowing as it extended the growing season in terms of days preanthesis and presented favorable climatic conditions for safflower development.

Efecto de la disponibilidad de agua sobre una gramínea invasora del caldenal

In the last years, in the semi-arid central region of Argentina, the increase of C3 non-palatable native grass species known generally as “pajas” was observed. One possible cause of the success of these species is the increase in rainfall observed in the region in recent years. The objective of this work was to evaluate the effect of a greater water availability and its seasonal distribution on the biomass and the production of reproductive structures of a non-palatable and highly invasive C3 species ( Jarava ichu ) and a non-palatable C4 species ( Setaria lachnea ). For this, a greenhouse experiment was carried out, consisting in manual irrigation of individuals of both species in pots. Treatments were: dry year, wet year with autumnal peak and wet year with spring peak. The increase in water availability favored the biomass of leaves and stems of J. ichu , independently of the seasonal distribution, with respect to the dry year. On the contrary, the biomass of S. lachnea did not respond to the different treatments (P>0.05). Likewise, the number of panicles was greater for J. ichu under the wet year treatment with spring peak, but there were no differences for S. lachnea . https://doi.org/10.25260/EA.19.29.1.0.763

Potential applications of biochar and terpene-enriched bio-oil produced from a semi-arid native Asteraceae

Biomass of Flourensia oolepis, a native shrub of the semi-arid central region of Argentina, was treated by vacuum pyrolysis to investigate the potential of this species to be used as a source of energy and chemicals. In this study we determined the influence of temperature on the product yields in different plant organs (leaves and stems), characterized the bio-oil, and assessed the bioactivity of biochar aqueous extracts through germination and growth bioassays with Lactuca sativa. The pyrolysis oils showed a predominance of long chain, cyclic and aromatic hydrocarbons in the leaves pyrolysate. The sesquiterpene spathulenol was the major compound in these reactions. Pyrolysis of stems produced mainly phenolic compounds. The effect of phosphoric acid pretreatment on leaves and stems was also evaluated in order to improve bio-oil yield and selectivity to any interesting compound. The results showed that acid treatment enhanced the liquid formation in pyrolysis of leaves giving a high amount of long chain hydrocarbons compared with the untreated organ. The biochar water extracts from leaves exhibited a hormetic type of response, with a promoting growth effect on roots and shoots up to 225%, and only a transient inhibition of germination at higher doses (≥7.5% w/v). Biochar water extracts from stems did not affect seed germination and showed a remarkable promoting effect, stimulating growth at all concentrations tested up to 330%. Although additional testing is required, overall results show F. oolepis as a promissory species for the production of bio-oil and biochar with a wide range of applications, including the potential use as growth regulator.

Posición de las coronas como mecanismo para tolerar el pastoreo en especies forrajeras del pastizal bajo en la región semiárida central de Argentina

Los pastizales naturales cubren importantes extensiones en distintas latitudes del mundo y sobre todo en áreas de clima árido y semiárido. La importancia de estos ecosistemas radica en el uso al que están destinados, que es la producción ganadera. En la región semiárida central de Argentina predominan áreas cubiertas por pastizales naturales (pastizales bajos y samófilos), bosques de Prosopis con pastizal, arbustales y matorrales con pastizal. El pastoreo es uno de los principales factores que producen cambios florísticos y estructurales en esta región donde aún existen diferentes especies que han persistido ante la acción del pastoreo. Resultados preliminares muestran diferencias en la estructura de las plantas cuando se comparan individuos pastoreados y otros provenientes de áreas clausuradas. La hipótesis de este trabajo es que las especies forrajeras que actualmente persisten son capaces de tolerar el pastoreo porque se aclimataron frente a la acción de los herbívoros, produciendo macollos con sus coronas cada vez más enterrados. El objetivo del trabajo fue evaluar en situaciones de pastoreo y de no pastoreo el diámetro de corona y la profundidad de enterrado en poblaciones de Poa ligularis, Piptochaetium napostaense, Digitaria californica y Bothriochloa springfieldii entre especies forrajeras, y en poblaciones de Jarava ichu, Amelichloa brachychaeta y Nassella tenuisima entre las no forrajeras. El trabajo se realizó en la región de colinas y lomas de la Provincia de La Pampa (Argentina) donde se establecieron transectos en áreas pastoreadas y en áreas excluidas del pastoreo. Para todas las áreas bajo pastoreo se determinó la presión de pastoreo a partir del tiempo de pastoreo y la carga animal. Los resultados obtenidos muestran mayor profundidad de enterrado de las coronas de las especies forrajeras en condiciones de pastoreo, mientras que en las especies no forrajeras como las pajas no se observan diferencias. Estos resultados podrían indicar que las especies forrajeras de los pastizales de la Región Semiárida Central de Argentina, que crecen bajo condiciones de pastoreo tienden a favorecer cierto desarrollo en profundidad de las coronas y, con ello, contribuir a la protección de los puntos de crecimientos basales de la acción del pastoreo y condiciones ambientales adversas.

Experimental monitoring and post-occupancy evaluation of a non-domestic solar building in the central region of Argentina

Previous experience in designing and monitoring bioclimatic buildings in central Argentina suggests that their thermal behavior is a matter of concern and that further research is needed. Thus, the objectives of this work are: to describe the design and the post-occupancy evaluation of a new non-domestic solar building in a continental semiarid region of central Argentina (37°38′ latitude S, 63°34′ longitude, 175m above sea level), to analyze the building's hygrothermal and energy performance, and to estimate the PMV and PPD. The design guidelines were: to minimize the consumption of conventional energy in thermal-lighting conditioning, to use traditional technology, to maximize the thermal comfort, and to reach an extra-cost lower than 10%. The post-occupancy monitoring of the building was performed along one complete year (August 9th 2011–August 18th 2012). Data-loggers were installed in each functional area to sense the indoor temperature and relative humidity at time steps of 10min. A meteorological station was installed near the building. The experimental results showed that during winter the average temperature in the areas of permanent use was 20.3°C (average outdoor temperature: 10.1°C) and the heating energy consumption was around 73.5kWh/m2. During summer the average indoor temperature in the building was 26.9°C, 1.7°C below the outdoor temperature average (28.6°C); cooling systems were turned on when the indoor temperature reached 28°C, at approximately 11:30 AM, when the outdoor air temperature exceeded 30°C. Mechanical cooling consumed around 59% of the daily electricity consumption. The PDD results obtained for winter and summer representative days meet the requirements of ISO Norm 7730. Heating and cooling energy saving was around 63% and 76.5% respectively. The monitoring showed that the thermal behavior and energy performance met the expectations of both designers and users, and it is considered satisfactory and promising for low-energy consumption buildings.

Annual variation of 7Be soil inventory in a semiarid region of central Argentina

Reliable information on environmental radionuclides atmospheric entrance, and their distribution along the soil profile, is a necessary condition for using these soil and sediment tracers to investigate key environmental processes. To address this need, 7Be content in rainwater and the wet deposition in a semiarid region at San Luis Province, Argentina, were studied. Following these researches, in the same region, we have assessed the 7Be content along a soil profile, during 2.5 years from September 2009 to January 2012. As expected, the specific activity values in soil samples in the wet period (November–April) were higher than in the dry period (May–October). During the investigated period (2009 – beginning 2012) and for all sampled points, the maximum value of the 7Be specific activity (Bq kg−1) was measured at the surface level. A typical decreasing exponential function of 7Be areal activity (Bq m−2) with soil mass depth (kg m−2) was found and the key distribution parameters were determined for each month. The minimum value of areal activity was 51 Bq m−2 in August, and the maximum was 438 Bq m−2 in February. The relaxation mass depth ranges from 2.9 kg m−2 in March to 1.3 kg m−2 in August. 7Be wet deposition can explain in a very significant proportion the 7Be inventory in soil. During the period of winds in the region (September and October), the 7Be content in soil was greater than the expected contribution from wet deposition, situation that is compatible with a higher relative contribution of dry deposition at this period of the year.

Distribution and biological aspects of the introduced speciesMoina macrocopa (Straus, 1820) (Crustacea, Cladocera) in the semi-arid central region of Argentina

Moina macrocopa is common in eutrophic water bodies. Two subspecies have been described: M. macrocopa macrocopa (Straus, 1820), whose original distribution was restricted to the Old World, and M. macrocopa americanaGoulden, 1968, recorded only in North America. In 1994, the species was found in Bolivia, and in 1997 it was found in the northeast of Argentina. As the specimens belonged to M. macrocopa macrocopa in both cases, the authors suggested that it may have been introduced from the Old World by anthropogenic means. The aim of this study was to assess the distribution of M. macrocopa in La Pampa (Argentina), and provide information on its population characteristics under natural conditions. The species was recorded in six out of more than 100 water bodies surveyed; the specimens belong to M. macrocopa macrocopa. Although this species is not considered halophilic, the water bodies where it was found present high salinity (5.7 to 21.8 g.L–1). All are shallow, temporary and hypertrophic due to the agricultural activities carried out in their basins. Densities were between 1 and 312.6 ind.L–1. Size varied between 0.6 and 1.8 mm and some specimens were larger than those of other places. The parthenogenetic fraction predominated and the number of eggs ranged between 2 and 23. No correlations were found between density, size, or number of eggs and the environmental parameters studied. The presence of M. macrocopa in Pampean lakes could be due to the introduction of fish from hatcheries in the province of Buenos Aires, where it is used as food. Considering that the invasive character ofM. macrocopa has been recognized and that this study found that it is tolerant to a wide range of environmental conditions, attention should be paid to a possible displacement of its native congeneric species, typical of saline and temporary water bodies in central Argentina.

Spatial and temporal patterns of richness and abundance in the anuran assemblage of an artificial water reservoir from the semiarid central region of Argentina

AbstractThis constitutes the first study of anuran fauna composition of an artificial permanent water reservoir, in a semiarid ecosystem of San Luis. Species richness, relative abundance, spatial distribution and pattern of summer activity were estimated in the anuran community of the Embalse La Florida, an artificial water reservoir in the semiarid central region of the sierras of San Luis, Argentina. This reservoir represents one of the few sources of water available for reproduction and early development of amphibian species in the zone. We identified anurans using call surveys during two summers at fifteen sites, belonging to four zones around the shorelines of the reservoir. Eight amphibian species (Rhinella arenarum, Melanophryniscus stelzneri, Leptodactylus bufonius, Leptodactylus mystacinus, Odontophrynus americanus, Odontophrynus occidentalis, Pleurodema tucumanum and Hypsiboas cordobae) were recorded at the shores of the embalse. The highest species richness (seven) was detected in the preserve located on the north shore. Species richness analyzed by month or survey was not correlated with weather variables. The highest relative abundance of anurans was detected at the highly modified campsites area, which may provide stable food and refugia. Relative abundance of all anuran species was positively correlated with precipitation. This permanent water reservoir may act as an important site of amphibian fauna concentration, which is important to monitor and preserve.

Effect of post-fire defoliation on bud viability and plant mortality of Piptochaetium napostaense (Speg.) Hack. and Poa ligularis Ness.

The objective of this work was to evaluate the effects of post-fire defoliation on axillary bud viability and mortality of Piptochaetium napostaense (Speg.) Hack. and Poa ligularis Nees. at different phenological stages. Both species are cool-season perennial native grasses highly preferred by cattle in the semi-arid region of central Argentina. The following treatments were established for each species: no defoliation (control), early-season defoliation (vegetative stage) and late-season defoliation (internode elongation stage). Ten plants were assigned randomly to each treatment. Fire treatment was applied at the end of the annual growing cycle of both species. Our results would suggest that early-season defoliation during the first year after fire might reduce axillary bud viability in P. napostaense and P. ligularis. In addition, P. napostaense was more susceptible to early-season defoliation than P. ligularis. Post-fire defoliation, principally early-season defoliation, might increase plant mortality in P. napostaense, but it does not seem to affect P. ligularis. Therefore, a period with no grazing after fire might be the key factor to protect axillary buds, and subsequently permit the re-establishment of the photosynthetic canopy through the production of new tillers, favouring mainly the persistence of P. napostaense in the community.

Effect of post-fire defoliation on growth of two native grasses in the Caldenal, Argentina

Plant growth in semiarid rangelands may be affect - ed by time grazing is excluded during the post-fire regeneration period. The objective of this field work was to study the effect of post-fire defoliation at different phenological stages (vegetative (early-season defoliation) and internode elongation (late-season defoliation)) on growth of Piptochaetium napostaense and Poa ligu- laris, two very important perennial native grasses in the temperate semi-arid region of central Argentina (Caldenal). In general, the post-fire defoliation treatments did not affect the number of green leaves on tillers of P. napostaense. Early-season post-fire defoliation generally reduced the number of green leaves on tillers of P. ligularis in comparison to those in control plants. Late-season defoliation, however, usually increased the number of green leaves on tillers of P. ligularis. Nevertheless, very few significant (p 0.05) than values on non-defoliated plants, respectively. Immediately after early- and late-season defo- liation treatments, relative growth rates for tiller height and total green length were reduced (p<0.05) on plants of both species with respect to control plants. Our results suggest that a one-year-period without severe defoliations after fire would be at least necessary for not risking the persistence of these perennial grasses in the Calde- nal community.

A study of the effect of the interaction between site-specific conditions, residue cover and weed control on water storage during fallow

In the semiarid central region of Argentina the probability that rainfall meets crop requirements during growing season is less than 10%, therefore fallowing has been the most important practice to assure water availability during the growing season. Various site-specific and management factors have been identified as crucial for defining fallow efficiency (FE) and final available water contents (AW). The objective of the present study was to improve our knowledge about the interactions between residue cover, weed control, soil profile depth and water storage capacity (WSC) on FE. In 10 sites covering the environments of calcareous plains and sandy plains of the semiarid central region of Argentina and with different WSC, experiments with 3 different levels of residue cover (H, M, L) and with and without weed control (C and W respectively) during fallow were set up. A completely randomized block design with four repetitions and splits plots to consider weed control was used. Soil texture and organic matter were determined in samples of the A horizon (0.20 m). Bulk density, field capacity, permanent wilting point and soil water contents (monthly frequency) were measured at depth intervals of 0.20 m to the depth of the calcite layer or to 2.00 m depth. Soil temperature was taken in weekly intervals at 0.05 m depth and weed plants, separated by species, were counted at the end of fallow in 4 repetitions of 0.25 m 2 in each treatment. An empirical model was developed to predict final AW under these experimental conditions. Model parameters were: Residue level, weed control, WSC, profile depth, and rainfall during fallow. Site-specific conditions (WSC and profile depth) affected water storage during fallow; soils with highest values for both parameters showed highest final AW. Weed density was the most important factor that controlled AW, with on average 35 mm less AW in W than in C treatments. Residue level had a positive effect on final AW in both C and W treatments, with a difference of 18.5 mm between H and L. An interaction between residue level and weed density was observed, indicating weed suppression in H treatments. This was also confirmed by correspondence analysis between residue level and weed species which revealed that different species were related to each level. High residue levels also decreased soil temperature, thus affecting germination of post-fallow crops. The empirical model had an overall average prediction error of 13.7% and the regression between measured and predicted values showed a determination coefficient of 0.77.

Carbon contents and aggregation related to soil physical and biological properties under a land-use sequence in the semiarid region of central Argentina

Land-use change affects vast areas of the semiarid region of central Argentina, where agriculture becomes predominant over mixed farming systems, and large areas of permanent pastures (PAS) are being converted to agricultural land. This land-use change causes loss of soil structure, but very little is known about the effect of changes in aggregate size distribution on soil physical, chemical and biological properties. We decided to use dry sieved aggregates since this technique is commonly used in semiarid regions. The study was carried out at Anguil, La Pampa, Argentina. The soil was a sandy loam Entic Haplustoll with a carbonate-free A-horizon. The PAS site had been under weeping love grass for more than 40 years. Parts of this PAS were turned to cultivation in 1989 (CULT14) and in 2001 (CULT2). Sampling was carried out at 0.6 m intervals to 0.18 m depth. Bulk density (BD), organic carbon (OC), and water holding capacity and infiltration were determined on these samples. Dry aggregate size distribution and OC content of the size fractions were determined on large undisturbed samples. Samples of pooled aggregate size fractions >4, 1–4, and <1 mm, as well as corresponding samples of non fractionated soil were incubated and respiration was measured by CO 2 evolved. The soil of CULT2 had 29% lower contents of large (>4 mm) and 37% higher contents of very small (<1 mm) aggregates than PAS. The intermediate size aggregates were not affected by the short-term effect of tillage. OC loss in CULT2 was 16% regarding PAS. Longer term effects of cultivation were characterized by 30% loss of intermediate size aggregates, 22% increase of bulk density, 74 and 19% decrease in water infiltration and water retention, respectively of CULT14 compared to PAS. A 32% decrease of OC was observed after 14 years of cultivation. Intermediate size aggregates had highest OC contents and no difference between treatments was found, except for a lower value of large aggregates in CULT14. Respiration rates and total CO 2 evolved was related to OC contents of fractions; however, PAS respired more from its small aggregates than expected from their OC content. The results showed that OC turnover and loss of aggregation was very fast in this soil, but soil hydraulic properties were affected in the longer term. Dry aggregates were found to useful for studying soil degradation, and they showed similar trends as those indicated in the literature for water stable aggregates.

Radial growth and biological rotation age of Prosopis caldenia Burkart in Central Argentina

Prosopis caldenia Burkart (caldén) is the most important woody species in the caldenales, the open xerophytic woodlands covering approximately 33 000 km 2 in the semiarid central region of Argentina. Dendrochronological techniques were used to estimate mean radial growth and the biological rotation age of P. caldenia in San Luis, Central Argentina. Inter-annual variations in ring widths were measured on cross-sections from dominant and co-dominant trees at four sampling sites from across the natural distribution of P. caldenia in the province of San Luis. For a period of 65 years, the mean cumulative radial growth between these four stands varied from 174.9 to 246.09 mm, whereas the mean annual radial growth ranged from 2.7 to 4.0 mm yr −1. Biological rotation ages were estimated based on the temporal evolution of the annual basal area mean and current increments. At the four stands, the biological rotation age occurs at ages equal to or greater than 66 years. In comparison with the introduced species presently used for commercial reforestation in the region, P. caldenia shows similar rates of radial growth, is better-adapted to the extreme climatic variability of semiarid Central Argentina, and its wood largely exceeds in quality the wood of those species used for commercial reforestation.

Dormancy and germination in three Acacia (Fabaceae) species from central Argentina

We studied dormancy and germination requirements of seeds of Acacia aroma, A. caven and A. furcatispina from a semi-arid region of central Argentina. Imbibition experiments were performed to determine the rate of water uptake in seeds. To determine optimal temperature for germination, seeds were incubated at three temperature regimes (15/5, 25/15 and 35/20°C) with a 12/12 h daily photoperiod or in total darkness. Additionally, differences in dormancy and germination in seed colour morphs of A. aroma were studied. Seeds of A. aroma and A. caven had impermeable coats, while those of A. furcatispina did not. Seeds of the three species showed the same pattern of germination. Germination percentages were significantly lower at 15/5°C than at 25/15 or 35/20°C. The germination temperature pattern found for these species is probably related to the summer seasonal nature of rainfall in the study area. In A. aroma, seeds of the two colour morphs showed a similar pattern of dormancy and germination.

Thermal response of solar and conventional school buildings to design- and human-driven factors

The objectives of this work are (I) to describe the design and building technology details of a solar school built in a continental semiarid region of central Argentina, (II) to show data from energy, hygrothermal and environmental monitoring, and (III) to compare the behavior of a solar and a conventional school building in response to design and human management factors. Both buildings are located on 36° 24′ latitude and 63° 25′ longitude. With respect to the solar school, good outdoor climate conditions during the study period in winter, plus unnecessary auxiliary heating, have led to indoor temperature increasing beyond 24 °C under real use conditions. Similarly, overheating of functional areas in autumn and spring was the result of temperate outdoor conditions, uncontrolled use of auxiliary heating and internal gains. Even without incoming sunlight, indoor temperature reached 27 °C on some days in summer, while outdoor temperature peaked to 35 °C. Based on the parameters of ISO 7730, more than 10% of people experienced discomfort when temperature exceeded 25 °C. In contrast, an average indoor temperature of 16 and 21 °C was recorded, respectively, for the conventional and the solar building. However, the consumption of natural gas for heating was 50% less in the solar school. Furthermore, this consumption could also be smaller if we take into account that a large proportion of people expressed discomfort at noon because of overheating during the winter time. This demonstrated once more that proper use of heating devices is a very important factor to be considered in solar designs. The work allowed a good validation of methods to assess energy gains and losses during the winter.