Soil Respiration and N-Mineralization Processes in the Patagonian Steppe Are More Responsive to Nutrient Than to Water Addition

Aims: Soil respiration and N-mineralization are key processes in C and N cycling of terrestrial ecosystems. Both processes are limited by soil temperature, moisture and nutrient content in arid and cold ecosystems, but how nutrient addition interacts with water addition requires further investigation. This study addresses the effects of water and N+P additions on soil respiration and mineralization rates in the Patagonian steppe.Methods: We measured soil respiration and N-mineralization throughout seasons in control, fertilized, irrigated and irrigated-fertilized plots. We also analyzed root density and soil physico-chemical properties.Results: The soil CO2 effluxes in the Patagonian steppe were controlled by soil temperature, soil water content and root density. Increases in water addition had no effects on soil respiration, except when combined with N+P addition. However, soil nutrient enrichment without water addition enhanced soil respiration during the plant growing season. We found a linear positive relationship between root density and soil respiration, without interaction with treatments. N+P addition had negative impacts on N-mineralization, resulting in a strong N-immobilization. However, soil ammonium and nitrate content increased with N+P addition all over the seasons.Conclusion: Moderate increases in the precipitation through small pulses lead to no long-term response of soil processes in arid and cold Patagonian ecosystems. However, soil CO2 effluxes are likely to increase with nutrient additions, such as anthropogenic N deposition, and microbial biomass could retain more nutrients in the soil. Therefore, high levels of N enrichment in arid ecosystems may strengthen the positive feedback between C cycle and climate change.

Occurrence of kleptoparasitic sarcophagid flies (Diptera: Sarcophagidae: Miltogramminae) in natural and human modified sites in Southern South American Andean landscapes

Sarcophagid flies belonging to the subfamily Miltogramminae are mainly kleptoparasites of bees and solitary wasps. Twenty-six locations were surveyed to accomplish the first specific exploration on the diversity of Miltogramminae in southern Andean areas of South America. We evaluated changes in abundance, richness and composition among habitat types to establish the effect of anthropization on the Miltogramminae community. Habitat types were considered as human modified (trails and roads, parks and meadows) and natural sites (watercourses and lake beaches, sandy and shrubby areas), distributed in two ecoregions (Valdivian forest and Patagonian steppe). We found differences in the capture rate and composition of Miltogramminae among habitat types. The species Opsidia intonsa Aldrich was highly dominant in samples, with higher proportional abundance in human modified habitats. Richness of Miltogramminae was higher in natural sites. Comparisons between the ecoregions surveyed indicated the genus Opsidia Coquillett did not show differences in abundance between ecoregions, whereas Senotainia Macquart was more abundant in the Patagonian steppe. The results provide evidence on the significant effects of human influence on landscapes in kleptoparasitic fly diversity. Slight modifications of natural areas (as proliferation of trails or isolated houses) should be addressed to evaluate the conservation of kleptoparasitic Diptera.

Touch me carefully: a step towards understanding morphological diversity in the South American spiny sunflowers (Compositae, Barnadesioideae)

The subfamily Barnadesioideae (Compositae) is endemic to South America, comprising 10 genera and 80 species of mostly spiny herbs, subshrubs, shrubs, trees, or woody vines distributed from Venezuela to Argentina. Three genera, Dasyphyllum (27 species), Chuquiraga (22 spp.) and Barnadesia (19 spp.) contain 85% of the species, while the other seven genera (Archidasyphyllum, Arnaldoa, Doniophyton, Duseniella, Fulcaldea, Huarpea, and Schlechtendalia) are represented by up to three species each. Most species are found in xeric areas in the Andean and Patagonian regions—as in the Páramos, Puna and Patagonian steppe vegetation—with a secondary center of diversity in eastern South America. Previous phylogenetic hypotheses have clarified the relationships within the subfamily, showing that there are many non-monophyletic groups in different taxonomic ranks. As a result, taxonomic changes have been proposed over recent decades in order to reflect classifications comprising only monophyletic groups. In the present study, we provide a generic synopsis of the subfamily Barnadesioideae based on the most recent generic circumscriptions, including a key, expanded morphological descriptions, information on geographical distribution and habitat, photographs and taxonomic notes for all genera.

Geographic distribution modeling and taxonomy of Stephadiscus lyratus (Cothouny in Gould, 1846) (Charopidae) reveal potential distributional areas of the species along the Patagonian Forests

Background Stephadiscus lyratus (Couthouy in Gould, 1846), an endemic Charopidae from southern South America, was described from few dry shells. The distribution of this species is known on scattering occurrences, mainly from material deposited in museum collections. We provide here new information on anatomy, habitat, and microhabitat preferences and estimate the potential geographic distribution of the species to test if it is exclusively endemic to the Subpolar Magellanic Forest. Methods Fieldwork was carried out in the National Parks of the Patagonian Forests. Snails were photographed, measured, and dissected for anatomical studies; shells were studied with scanning electron microscopy. Estimation of the species geographical distribution (EGD) was obtained through correlative ecological niche modeling (ENM). We designed a calibration area a priori with known species points of occurrence in the Magellanic Subpolar Forests and borders of the Patagonian steppe. Seven bioclimatic variables of the WorldClim database were used. The best ENMs were calibrated and selected using a maximum entropy method with Maxent v3.3.3K through the R package “kuenm”. Candidate models were created by combining four values of regularization multiplier and all possible combinations of three feature classes. We evaluated candidate model performance based on significance (partial ROC), omission rates (E = 5%), and model complexity (AICc). From the best models obtained, a final model was transferred to a region “G” consisting of the calibration area plus the Valdivian Temperate Forests and whole Patagonian steppe, where we hypothesize that the species could be present. Finally, we obtained binary presence-absence maps. We quantified the proportion of the occurrence points and distribution range of S. lyratus in different land cover categories. To explore the degree of protection of S. lyratus’EGD, we quantified the proportion of its distributional range within protected areas. Results A be-lobed kidney, a close secondary ureter, the terminal portion of the uterus forming a compact glandular mass, and the vas deferens with a dilatation are new anatomical information that distinguishes this species. Stephadiscus lyratus inhabit cold native forest areas, mainly living on or under humid logs in contact with the ground. The main constraining variables to explain S. lyratus distribution in the EGD were BIO3, BIO12, BIO6, and BIO4. The potential area of distribution obtained almost duplicates their original range (140,454 km2) extending to the Valdivian Temperate forests mainly in Chile. Natural and semi-natural terrestrial vegetation was predominant in the potential area of distribution of S. lyratus. However, only 14.7% of this area occurs within current protected areas from Argentina and Chile. The ectothermic physiological traits of this species, low dispersal capacity, and its narrow habitat requirements turn S. lyratus into a potentially vulnerable species.

Past and Recent Effects of Livestock Activity on the Genetic Diversity and Population Structure of Native Guanaco Populations of Arid Patagonia

Extensive livestock production and urbanization entail modifications of natural landscapes, including installation of fences, development of agriculture, urbanization of natural areas, and construction of roads and infrastructure that, together, impact native fauna. Here, we evaluate the diversity and genetic structure of endemic guanacos (Lama guanicoe) of the Monte and Patagonian Steppe of central Argentina, which have been reduced and displaced by sheep ranching and other impacts of human activities. Analyses of genetic variation of microsatellite loci and d-loop revealed high levels of genetic variation and latitudinal segregation of mitochondrial haplotypes. There were indications of at least two historical populations in the Monte and the Patagonian Steppe based on shared haplotypes and shared demographic history among localities. Currently, guanacos are structured into three groups that were probably reconnected relatively recently, possibly facilitated by a reduction of sheep and livestock in recent decades and a recovery of the guanaco populations. These results provide evidence of the genetic effects of livestock activity and urbanization on wild herbivore populations, which were possibly exacerbated by an arid environment with limited productive areas. The results highlight the importance of enacting conservation management plans to ensure the persistence of ancestral and ecologically functional populations of guanacos.

The Sensitivity of River Catchments to Dissolved Organic Carbon Release During Rain Events - A Study of Eight Catchments in Southern Patagonia

Understanding the role of catchment properties is crucial for anticipating soil-derived dissolved organic carbon (DOC) export to aquatic systems, especially under changing climatic conditions. We present natural variations in DOC concentrations and fluxes in eight catchments differing in size (3 – 300 km 2 ), morphology (very steep to flat), and landscape type (Patagonian steppe, forest and peatland) along a steep precipitation gradient in remote pristine southern Patagonia, Chile. Discharge, precipitation and water chemical parameters were used to differentiate the mechanisms controlling DOC release in different catchment types. The results show large differences between catchments in terms of DOC concentrations (2 - 47 mg L -1 ) and fluxes (1 to 44 tons km -2 yr -1 ) but also in response to changes in precipitation. Small steep and forested catchments are the most reactive in terms of DOC export; specifically, changes in discharge produce fast, high and exponential increases in DOC release. DOC leaching by surface run-off through the organic soil layer is the main source of DOC during high precipitation events, and steep catchments became short-term hotspots for DOC export. In the flat catchments of the Patagonian steppe, the generally lower precipitation rates favour temporal accumulation of DOC in soils, and seasonal high discharge events produce one-off increases in DOC fluxes. Although peatlands constitute a large and continuous source of DOC export, the influence of discharge variation on DOC fluxes in peatland-dominated catchments appears to be low, despite the large carbon pools. Thus, in DOC catchments with similar precipitation regimes, morphology is the dominant factor determining ecosystem responses, where the steepest catchments show the highest sensitivity to rain events in terms of DOC export. Morphology and hydrological buffer capacity rather than the size of the carbon pools or precipitation intensity determine the export of DOC from catchments during strong rain events.

Alien plant species on roadsides of the northwestern Patagonian steppe (Argentina)

The introduction of alien species represents one of the greatest threats to biodiversity worldwide. Highway construction increases the dispersal and invasion of exotic plant species. This study examined the assembly process of the plant communities to determine whether the roadsides of the Patagonian steppe represent a reservoir and dispersal source of invasive exotic species. We analyzed the composition of exotic and native species and functional groups present in the established vegetation and seed banks of roadsides and reference areas nearby. The type of dispersal of exotic and native species at the roadsides was also evaluated. Total cover and that of exotic and native species was lower at the roadsides than in the reference areas; however, at the roadsides the cover and seed abundance of exotic species was higher than that of native species. In the roadsides vegetation, native shrubs such as Acaena splendens predominated, along with exotic perennial herbs and grasses which were mainly represented by Rumex acetosella. In the seed bank the predominant species were exotic perennial herbs, also represented by R. acetosella, annual exotic species such as Epilobium brachycarpum and Verbascum thapsus, and annual native species such as Heliotropium paronychioides. No exotic shrubs were found either at the roadsides or in the reference areas. The species at the roadsides did not present a dominant type of dispersal. The abundance of exotic species at the roadsides, both in the aboveground vegetation and the seed bank, may be due to the stressful environment and the characteristics of the species themselves, such as the ability to form seed banks. This work revealed that the roadsides of the Patagonian steppe constitute reservoirs of invasive exotic species, highlighting the importance of identifying them and controlling their spread, with a view to generating ecosystem management programs.