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Uruguay sits in the Rio de la Plata Grasslands, one of the biggest grassland biomes in the world, with a pronounced biodiversity. Nowadays, intensification of land use has led to the degradation of this ecosystem. A common practice for enhancing productivity of natural grasslands in the region is the overseeding of an exotic legume, alongside phosphorus fertilization. The objective of this study is to measure the impact of a phosphorous fertilization gradient on total plant species richness, the presence of exotic species and the net primary productivity. With the data obtained, we explored possible mechanisms that explain the changes in diversity observed. Two experimental sites were used: PA (in the geomorphological region ‘Sierras del Este’), and GL (in the geomorphological region ‘Cuesta Basaltica’). Eight plots were established, with different amounts of phosphorus fertilization, with overseeding of Lotus angustissimus. A vegetation sampling of each treatment was done on the third year and a half after the establishment of the experiment. Total and exotic species richness was evaluated, alongside the effect of each treatment on the total and the L. angustissimus net primary productivity of the first three years of the experiment. We found that total species richness decreased with increasing amounts of phosphorus fertilization, while exotic species richness increased with increasing amounts of phosphorus fertilization. The total and the L. angustissimus net primary productivity increased with fertilization for PA, but didn’t for GL. This suggests that, in GL, mechanisms regarding the ‘niche dimension’ and the ‘total competition’ hypothesis are taking place. In PA, it isn’t possible to distinguish which mechanisms are the predominant ones behind the species loss observed. We conclude that more studies need to be done on this technology, in search of fertilization thresholds that allow for greater productivity without putting biodiversity in jeopardy.

Fire is a widespread disturbance that affects plant individuals and populations. In fire-prone environments, such as Mediterranean-type ecosystems, many species are stimulated to germinate by fire-related cues, for example heat and smoke. However, little is known about the effect of fire on seed germination of species from herbaceous communities like temperate grasslands. In this study we assessed the germination response to direct (heat shock and smoke) and indirect (light intensity) fire-related cues of five herbaceous and one shrubby species that occur in natural grasslands of eastern Uruguay. All species are native and belong to the Poaceae (2 species) and Asteraceae (4 species) families. Seeds were subjected to smoke and heat shock treatments (50°C, 100°C) under two light intensities (high-light and low-light). We found that direct fire-related cues did not stimulate germination in any of the species studied. Most of the species showed a reduced percentage of germination or a delayed mean germination time, relative to the control treatment, when exposed to heat shock at 100°C or smoke. However, the seeds survived the exposure to high temperatures, indicating that they can tolerate a fire event. Light was found to be a key germination cue. Treated seeds responded to fire-related cues mainly when we simulated the high-light environment after fire. Our results contribute to the growing body of evidence that many species of South American grasslands do not rely on recruitment by seeds after a fire event, but rather on the ability to resprout by means of subterranean or protected basal buds.

Questions: Do the effects of grazing components on vegetation structure differ in their relative importance? Do components interact in their effect on vegetation?. Location: San Jose department, Southern Campos, Uruguay. Methods: In a manipulative field experiment we simulated three different grazing components: trampling, defoliation and urine deposition, over 3 yr in a natural grassland. Defoliation was analysed through two intensity levels and two procedures: uniform and selective cutting. We evaluated the effects of grazing components on species diversity and composition, and frequency of plant functional types. Results: All simulated grazing components had at least some effect on vegetation structure. Additionally, both individual and interactive effects on vegetation attributes were detected. Our study indicates that the relative influence of each grazing component varied according to the attribute considered. N addition was the only treatment that affected plant diversity. Plant functional type composition, in turn, was affected mainly by trampling. N addition and trampling were the component that affected the frequency of the largest number of species. Defoliation selectivity showed effects both in terms of plant functional type and species composition. Exclosure treatment and defoliation intensity had slight effects on grassland structure. Conclusions: This study provides insight on the underlying mechanisms of some observed patterns of grazing on the Campos grasslands. Our results lead us to conclude that all grazing components have to be taken into account to understand vegetation dynamics subjected to grazing. Prevention of woody encroachment by grazing can be attributed to direct and indirect effects of trampling. Trampling should be taken into account to explain increaser species responses. However, mechanisms responsible for other general patterns remain less clear. The importance of selective defoliation in species replacement induced by grazing in these grasslands has yet to be clarified. Fil: Lezama, Felipe. Universidad de la República. Facultad de Ciencias; Uruguay Fil: Paruelo, José. 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. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina

Herbivores alter plant biodiversity (species richness) in many of the world’s ecosystems, but the magnitude and the direction of herbivore effects on biodiversity vary widely within and among ecosystems. One current theory predicts that herbivores enhance plant biodiversity at high productivity but have the opposite effect at low productivity. Yet, empirical support for the importance of site productivity as a mediator of these herbivore impacts is equivocal. Here, we synthesize data from 252 large-herbivore exclusion studies, spanning a 20-fold range in site productivity, to test an alternative hypothesis—that herbivore-induced changes in the competitive environment determine the response of plant biodiversity to herbivory irrespective of productivity. Under this hypothesis, when herbivores reduce the abundance (biomass, cover) of dominant species (for example, because the dominant plant is palatable), additional resources become available to support new species, thereby increasing biodiversity. By contrast, if herbivores promote high dominance by increasing the abundance of herbivory-resistant, unpalatable species, then resource availability for other species decreases reducing biodiversity. We show that herbivore-induced change in dominance, independent of site productivity or precipitation (a proxy for productivity), is the best predictor of herbivore effects on biodiversity in grassland and savannah sites. Given that most herbaceous ecosystems are dominated by one or a few species, altering the competitive environment via herbivores or by other means may be an effective strategy for conserving biodiversity in grasslands and savannahs globally. Fil: Koerner, Sally E.. University of North Carolina at Greensboro. Department of Biology; Estados Unidos Fil: Smith, Melinda D.. State University of Colorado - Fort Collins; Estados Unidos Fil: Burkepile, Deron E.. University of California; Estados Unidos Fil: Hanan, Niall P.. New Mexico State University; Estados Unidos Fil: Avolio, Meghan L.. University Johns Hopkins; Estados Unidos Fil: Collins, Scott L.. University of New Mexico; Estados Unidos Fil: Knapp, Alan K.. State University of Colorado - Fort Collins; Estados Unidos Fil: Lemoine, Nathan P.. State University of Colorado - Fort Collins; Estados Unidos Fil: Forrestel, Elisabeth J.. University of California at Davis; Estados Unidos Fil: Eby, Stephanie. Northeastern University; Estados Unidos Fil: Thompson, Dave I.. University of the Witwatersrand; Sudáfrica. Kruger National Park. South African Environmental Observation Network. Ndlovu Node. Scientific Services; Sudáfrica Fil: Aguado-Santacruz, Gerardo A.. Tecnológico Nacional de México; México Fil: Anderson, John P.. New Mexico State University; Estados Unidos Fil: Anderson, T. Michael. University Wake Forest; Estados Unidos Fil: Angassa, Ayana. Botswana University of Agriculture and Natural Resources; Sudáfrica. Hawassa University; Etiopía Fil: Bagchi, Sumanta. Indian Institute of Science; India Fil: Bakker, Elisabeth S.. Netherlands Institute of Ecology; Países Bajos Fil: Bastin, Gary. Alice Springs; Australia Fil: Baur, Lauren E.. University of New Mexico; Estados Unidos Fil: Beard, Karen H.. State University of Utah; Estados Unidos Fil: Beever, Erik A.. United States Geological Survey; Estados Unidos. State University of Montana; Estados Unidos Fil: Bohlen, Patrick J.. University of Central Florida; Estados Unidos Fil: Boughton, Elizabeth H.. MacArthur Agroecology Research Center; Estados Unidos Fil: Canestro, Don. University of California; Estados Unidos Fil: Cesa, Ariela. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires; Argentina Fil: Chaneton, Enrique Jose. 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. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina Fil: Cheng, Jimin. Northwest A&F University; China Fil: D?Antonio, Carla M.. University of California; Estados Unidos Fil: Deleglise, Claire. Université Grenoble Alpes; Francia Fil: Dembélé, Fadiala. Institut de Formation et de Recherche Appliquee; Sudáfrica Fil: Dorrough, Josh. Ecosystem Mangement Science; Austria Fil: Eldridge, David J.. University of New South Wales; Australia Fil: Fernandez Going, Barbara. University of Texas at Austin; Estados Unidos Fil: Fernández Lugo, Silvia. Universidad de La Laguna; España Fil: Fraser, Lauchlan H.. Thompson Rivers University; Canadá Fil: Freedman, Bill. Dalhousie University Halifax; Canadá Fil: García Salgado, Gonzalo. Dalhousie University Halifax; Canadá Fil: Goheen, Jacob R.. University of Wyoming; Estados Unidos Fil: Guo, Liang. Northwest A&F University; China Fil: Husheer, Sean. New Zealand Forest Surveys; Nueva Zelanda Fil: Karembé, Moussa. Université des Sciences; Malí Fil: Knops, Johannes M. H.. Universidad de Nebraska - Lincoln; Estados Unidos Fil: Kraaij, Tineke. Nelson Mandela University; Sudáfrica Fil: Kulmatiski, Andrew. State University of Utah; Estados Unidos Fil: Kytöviita, Minna Maarit. Universidad de Jyvaskyla; Finlandia Fil: Lezama, Felipe. Universidad de la República; Uruguay Fil: Loucougaray, Gregory. Université Grenoble Alpes; Francia Fil: Loydi, Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Centro de Recursos Naturales Renovables de la Zona Semiárida. Universidad Nacional del Sur. Centro de Recursos Naturales Renovables de la Zona Semiárida; Argentina Fil: Milchunas, Dan G.. State University of Colorado - Fort Collins; Estados Unidos Fil: Milton, Suzanne J.. South African Environmental Observation Network; Sudáfrica Fil: Morgan, John W.. La Trobe University; Australia Fil: Moxham, Claire. Arthur Rylah Institute for Environmental Research; Australia Fil: Nehring, Kyle C.. State University of Utah; Estados Unidos Fil: Olff, Han. University of Groningen; Países Bajos Fil: Palmer, Todd M.. University of Florida; Estados Unidos Fil: Rebollo, Salvador. Universidad de Alcalá; España Fil: Riginos, Corinna. The Nature Conservancy; Estados Unidos Fil: Risch, Anita C.. Swiss Federal Institute for Forest, Snow and Landscape Research; Suiza Fil: Rueda, Marta. Consejo Superior de Investigaciones Científicas. Estación Biológica de Doñana; España Fil: Sankaran, Mahesh. National Centre For Biological Sciences; India. University of Leeds; Reino Unido Fil: Sasaki, Takehiro. Yokohama National University; Japón Fil: Schoenecker, Kathryn A.. Fort Collins Science Center and Colorado State University; Estados Unidos Fil: Schultz, Nick L.. Federation University; Australia Fil: Schütz, Martin. Swiss Federal Institute for Forest, Snow and Landscape Research; Suiza Fil: Schwabe, Angelika. Universitat Technische Darmstadt; Alemania Fil: Siebert, Frances. North West University; Sudáfrica Fil: Smit, Christian. University of Groningen; Países Bajos Fil: Stahlheber, Karen A.. University of Wisconsin Green Bay; Estados Unidos Fil: Storm, Christian. Universitat Technische Darmstadt; Alemania Fil: Strong, Dustin J.. United States Department of Agriculture. Agriculture Research Service; Estados Unidos Fil: Su, Jishuai. Northwest A&F University; China Fil: Tiruvaimozhi, Yadugiri V.. National Centre for Biological Sciences; India Fil: Tyler, Claudia. University of California; Estados Unidos Fil: Val, James. Office of Environment and Heritage; Australia Fil: Vandegehuchte, Martijn L.. University of Ghent; Bélgica. Swiss Federal Institute for Forest, Snow and Landscape Research; Suiza Fil: Veblen, Kari E.. State University of Utah; Estados Unidos Fil: Vermeire, Lance T.. United States Department of Agriculture. Agriculture Research Service; Estados Unidos Fil: Ward, David. Kent State University; Estados Unidos Fil: Wu, Jianshuang. Lhasa National Ecological Research Station; China Fil: Young, Truman P.. University of California at Davis; Estados Unidos. Mpala Research Centre; Kenia Fil: Yu, Qiang. Chinese Academy Of Agricultural Sciences; China. Institute of Agricultural Resources and Regional Planning; China Fil: Zelikova, Tamara Jane. University Of Wyoming; . University of Wyoming; Estados Unidos

In native campos of Uruguay, overseeding legumes coupled with phosphorus (P) fertilization is a technology used to increase animal production. Short-term improvements in both forage productivity and quality are repeatedly reported. However, some evidence suggests that this management may at times lead to the collapse of the native community and invasions by exotic species. Indeed, it is yet unclear to what extent overseeding legumes into native grasslands affects its long-term integrity. This study uses data from a long-term experiment to assess whether increased P fertilizer rates—typically used to encourage legume establishment and growth—are associated with reduced species diversity. In 1996 a grazed native grassland in eastern Uruguay was either left untouched (control) or overseeded with a mix of Trifolium repens and Lotus corniculatus and then fertilized at either a moderate or high rate of P (197 or 394 kg · ha-1 over 13 years, respectively). The three treatments were arranged in a randomi...

Las praderas naturales de la region bas altica de Uruguay estan amenazadas por el incremento de la carga animal y cambios en el uso del suelo. Para evaluar el efecto del pastoreo se han propuesto los grupos funcionales como una herramienta simple para el monitoreo y manejo de la vegetacion. El presente estudio evaluo el efecto del incremento de la carga animal considerando rasgos de 23 especies de gramineas perennes dominantes. Para identificar los grupos funcionales se determino la respuesta al incremento de la intensidad de pastoreo en un experimento con dos cargas de capones (0,78 and 1,56 unidades ganaderas ha-1) cuantificando la cobertura de dichas especies y los valores de sus rasgos. El contenido de MS y el area foliar especifica fueron los rasgos que mejor describieron la respuesta de las gramineas perennes al incremento de la carga animal y podrian ser utilizados como marcadores funcionales. Tres grupos funcionales fueron identificados. El nivel mas bajo de carga animal se relaciono con el grupo funcional A (especies estivales, altas, con baja area foliar especifica y alto contenido de MS) y con el grupo funcional B (especies invernales altas y con niveles intermedios de rasgos foliares). Por otro lado, el nivel mas elevado de carga animal se relaciono con el aumento del grupo funcional C (especies estivales, postradas, con alta area foliar especifica y bajos contenidos de MS). Esta clasificacion de una comunidad con alta diversidad de especies en tres grupos funcionales es un nuevo enfoque para desarrollar metodos simples y generales para el diagnostico del estado de praderas naturales de la region basaltica en Uruguay y generar recomendaciones para su manejo.

Grasslands and their grazers provide some of the most compelling examples for studying the relationship between diversity, productivity, and disturbance. In this study, we analyzed the impact of grazing-induced changes in species composition and community structure upon the productivity of a grassland in the Campos region, Uruguay. We compared three treatments: a continuously grazed area, a 9-year old exclosure to domestic herbivores, and grazing-simulated plots inside the exclosure, which were clipped so that their standing biomass resembled that of the grazed area. We studied the community composition of the grazed and ungrazed situations, and determined biomass and above-ground net primary production (ANPP) of the three treatments during 1 year. Grazed plots had higher species richness and diversity than the exclosure. Grazing resulted in the replacement of some cool-season, tussock grasses by warm-season, prostrate grasses. ANPP was 51% higher under grazing than in the exclosure, but the grazing-simulated plots inside the exclosure were the most productive treatment, 29% higher than the grazed plots. Thus, two components of grazing effect may be postulated for this grassland. The structural component resulted in higher ANPP, probably due to the elimination of standing dead biomass. The species composition component resulted in lower ANPP once the structural component was controlled, probably due to the shift to warm-season phenology and prostrate habit. Our findings contrast with a similar experiment carried out in the neighbouring Flooding Pampa region, which suggests that the relationship between grazing and community structure and function is difficult to generalize.