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Fil: Aguiar, Sebastián. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Laboratorio de Análisis Regional y Teledetección; Argentina. Fil: Texeira, Marcos. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Laboratorio de Análisis Regional y Teledetección; Argentina. Fil: Garibaldi, Lucas A. Universidad Nacional de Río Negro. Instituto de Investigaciones en Recursos Naturales, Agroecología y Desarrollo Rural; Argentina. Fil: Garibaldi, Lucas A. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Recursos Naturales, Agroecología y Desarrollo Rural; Argentina. Fil: Jobbágy, Esteban G. Universidad Nacional de San Luis. Instituto de Matemática Aplicada San Luis. Grupo de Estudios Ambientales; Argentina. Fil: Jobbágy, Esteban G. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Matemática Aplicada San Luis; Argentina. Over the past decades, the choices of farmers and societies regarding what to grow and eat are being reshaped drastically, as suggested by the diversification of crop supply within countries and its simultaneous homogenization across them. Such a trend could be supported by parallel shifts in production (i.e. diversification within countries, homogenization across countries) or by the growing redistribution introduced by international trade which can even mask reductions in production diversity (i.e. specialization) within countries. Here we assessed the spatial and temporal trends in crop production, exports, imports, and supply diversity based on data from the Food and Agriculture Organization (FAO) for 152 countries and 49 crops from 1961 to 2013. Within countries, the diversity of crop supply increased at a faster rate than the diversity of production, which grew only slightly. Both were surpassed by the diversification of trade, which, within countries, involved a much faster diversity growth of imports compared to exports. Across countries, crop production homogenized at slower rates than crop supply, indicating that crop trade was important for explaining this decoupling. Mirroring country-based analyses, a crop-perspective indicates that crops are becoming more geographically ubiquitous for all the components of the food balance. However, this pattern had important exceptions, like oil palm which has increased its production concentrating in a few specialized countries. We evaluate our results in the context of the multiple social-ecological trade-offs related to international trade and the resilience of the global food system.

Continental precipitation returns to the atmosphere and the ocean with a delay that is critical in regulating seasonal water supply to ecosystems and societies. We quantify the magnitude and spatial patterns of this seasonal hydrologic buffer, its climatic and terrain drivers, and its apparent benefits to ecosystems using observed precipitation, climate reanalysis evaporation, GRACE seasonal water storage change, and MODIS vegetation index for a 1°× 1° global grid. We found that (1) seasonal hydrologic buffering is widespread and averages 241 mm.yr−1 on land (a quarter of continental precipitation); it supports evaporation 3-to-9 months of the year over all regions except the per-humid tropics and energy limited high latitudes, (2) the seasonal climatic water imbalance, with surplus in some months and deficit in others, drives hydrologic buffering in lower latitudes, while it is controlled by snow/ice storage in high latitudes, (3) the main terrain effect at our scale of analysis is grid-to-grid water transfer via large rivers providing lateral subsidy to lowland basins, and (4) buffering is manifested in global patterns of plant water use, as shown by high evaporation levels in water deficit conditions, particularly under tropical monsoonal climate. Our results highlight the paramount role of seasonal land water storage and redistribution in supporting ecosystem productivity, and provide a reference to understanding likely impacts of global change on the water cycle and ecosystem dynamics in the future. Fil: Kuppel, Sylvain. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Matemática Aplicada de San Luis "Prof. Ezio Marchi". Universidad Nacional de San Luis. Facultad de Ciencias Físico, Matemáticas y Naturales. Instituto de Matemática Aplicada de San Luis "Prof. Ezio Marchi"; Argentina Fil: Fan, Ying. Rutgers University; Estados Unidos Fil: Jobbagy Gampel, Esteban Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Matemática Aplicada de San Luis "Prof. Ezio Marchi". Universidad Nacional de San Luis. Facultad de Ciencias Físico, Matemáticas y Naturales. Instituto de Matemática Aplicada de San Luis "Prof. Ezio Marchi"; Argentina

Rainwater harvesting (RWH) has been essential for the establishment of human settlements in many dry regions of the world that lacked suitable surface or groundwater resources. A vast fraction of the South American Dry Chaco ecoregion still relies on RWH to support, not only livestock production, but domestic and industrial uses as well. As a result, water capture and storage infrastructure is widely disseminated throughout the region. In this paper we characterized the most typical RWH systems in two contrastingly developed sub-regions of Dry Chaco, ranging from extensive ranching to intensive beef and dairy production (central Argentina and western Paraguay, respectively). In each sub-region, we quantified RWH systems density, spatial distribution and associations with landscape features; furthermore, we illustrated how the daily dynamic of water stock in a typical RWH system contributes to assess their capture and storage efficiency. We found that randomly distributed low sophisticated RWH systems prevailed in central Argentina, while clustered distributed high sophisticated ones were more common in western Paraguay. RWH systems density was ten times higher in western Paraguay (0.94 vs. 0.098 units/km2), showing an exponential association with land cleared fraction and proximity to villages. The daily dynamic of water stock of the RWH impoundment showed that water harvest events were exponentially associated with precipitation magnitude events (R2 = 0.86), while annual water losses were explained by infiltration and evaporation fluxes (59 vs. 41%, respectively). Across both sub-regions, RWH accounts for less than 1% of the annual precipitation, playing a minor role on the regional water balance; however at a local level, they can affect several hydrological fluxes including the onset of groundwater recharge and the mitigation of extreme runoff events. Fil: Magliano, Patricio Nicolás. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico San Luis. Instituto de Matemática Aplicada de San Luis; Argentina Fil: Murray, Francisco. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico San Luis. Instituto de Matemática Aplicada de San Luis; Argentina. Instituto Nacional de Tecnología Agropecuaria; Argentina Fil: Baldi, Germán. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico San Luis. Instituto de Matemática Aplicada de San Luis; Argentina Fil: Aurand, Santiago. Instituto Nacional de Tecnología Agropecuaria; Argentina Fil: Paez, Ricardo Andrés. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico San Luis. Instituto de Matemática Aplicada de San Luis; Argentina Fil: Harder, Wilbert. Servicio Agropecuario Paraguayo; Paraguay Fil: Jobbagy Gampel, Esteban Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico San Luis. Instituto de Matemática Aplicada de San Luis; Argentina

Like in other semiarid areas of the world, farming systems in semiarid Chaco tend to use water-conservative crop systems to minimize production risks associated to water stress. While this strategy aims to stabilize crop yields and farmers income, the underutilization of water resources in wet years may result in heavy deep drainage water losses which could potentially lead to the development of dryland salinity. Conversely, more intensive crop systems that consume water exhaustively present lower drainage rates but are more prone to crop failure. We employed a monthly soil water balance approach to analyze the productive and ecohydrologic effects of five different farming systems across the region (winter, spring, summer, late-summer and a winter?summer double crop system) and to assess the possibility of minimizing emerging trade-offs between them through flexible water-informed cropping sequences. Our results indicate that water stress diminishes as crop systems are delayed towards the rainy season (winter > spring > summer > late-summer), but the productively safer late-summer strategy is the one with highest drainage rates. In most of the region, the relatively high production risk and insignificant drainage probability generally determine the convenience of conservative late-summer systems. However, in areas (or years) with higher amount and/or seasonality of rainfall, more intensive double-crop systems are necessary to minimize the likely high drainage fluxes. As rainfall is highly variable from one year to the other, the knowledge of soil water content at the onset of the season is useful to predict part of the available water offer and to asses expected production and ecohydrologic risks. In the most drainage-prone areas the implementation of flexible sequences that alternate conservative and intensive crop systems depending on soil water status, significantly reduced mean annual drainage with an acceptable increase in mean water stress index. Fil: Giménez, Raúl. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico San Luis. Instituto de Matemática Aplicada de San Luis; Argentina. Universidad Nacional de San Luis; Argentina Fil: Mercau, Jorge L.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico San Luis. Instituto de Matemática Aplicada de San Luis; Argentina. Universidad Nacional de San Luis; Argentina Fil: Houspanossian, Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico San Luis. Instituto de Matemática Aplicada de San Luis; Argentina. Universidad Nacional de San Luis; Argentina Fil: Jobbagy Gampel, Esteban Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico San Luis. Instituto de Matemática Aplicada de San Luis; Argentina. Universidad Nacional de San Luis; Argentina

Combining decomposition data with process-based biogeochemical models is essential to quantify the turnover of organic carbon (C) in surface litter and soil organic matter (SOM). Long-term decomposition may be suitably analyzed by linear models (i.e., all fluxes defined by first-order kinetics), which allow the derivation of analytical expressions to estimate the loss of C and the overall apparent decay rate (kapp) through time. Here we compare eight linear models (four discrete-compartment models with one or two C pools, two models with a single time-dependent decay rate, and two models based on a continuous distribution of decay rates) and report their analytical solutions for two types of decomposition experiments: i) studies that evaluate the decomposition of a single input of fresh litter (i.e., a single cohort, as in litterbag and C labeling experiments), and ii) studies that evaluate the decomposition of soil samples with compounds of different ages (i.e., multiple cohorts, as in long-term incubations or isotope dilution experiments). We fitted analytical mass loss functions to both types of datasets and evaluated the performance of the models. For single-cohort data, continuous-decay models provide the best balance between accuracy and parsimony (R2 ¼ 0.99, lowest Akaike and Bayesian information criteria), while for multiple-cohort data the two-pool models tend to perform better (R2 ¼ 0.96), perhaps because of the strong separation of time scales in the decomposition data considered. Differences among some models are marginal, suggesting that decomposition data alone do not point to a single ‘best’ model. All models resulted in apparent decay rates that decreased markedly through time, in contrast with the assumption of constant k adopted in the single-pool exponential decay model. We also show how model parameters estimated from single cohort samples can be used to model multiple cohort decomposition, unifying both types of experimental data in one theory. Based on our results, it is possible to distinguish the temporal changes in C loss that are attributable to initial chemical composition or abiotic factors, from those associated with the presence of multiple ages in the substrate. Fil: Manzoni, Stefano. University Of Duke. Nicholas School Of Environment; Estados Unidos Fil: Piñeiro, Gervasio. University Of Duke. Nicholas School Of Environment; Estados Unidos. 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: Jackson, Robert B.. University Of Duke. Nicholas School Of Environment; Estados Unidos Fil: Jobbagy Gampel, Esteban Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Matemática Aplicada de San Luis "Prof. Ezio Marchi". Universidad Nacional de San Luis. Facultad de Ciencias Físico, Matemáticas y Naturales. Instituto de Matemática Aplicada de San Luis ; Argentina Fil: Kim, John H.. University Of Duke; Estados Unidos Fil: Porporato, Amilcare. University Of Duke. Nicholas School Of Environment; Estados Unidos

Dry subtropical regions, originally hosting xerophytic vegetation, are currently characterized by diverse land cover/use patterns. Using existing biophysical and socio-economic databases, we explored how human contexts influenced land cover, vegetation composition and agricultural production in five distant regions. On average, cultivated areas represented a minor proportion (

Grazing modifies the structure and function of ecosystems, affecting soil organic carbon (SOC) storage. Although grazing effects on some ecosystem attributes have been thoroughly reviewed, current literature on grazing effects on SOC needs to be synthesized. Our objective was to synthesize the effects of grazing on SOC stocks in grasslands, establishing the major mechanistic pathways involved. Additionally, and because of its importance for carbon (C) biogeochemistry, we discuss the controls of soil organic nitrogen (N) stocks. We reviewed articles analyzing grazing effects on soil organic matter (SOM) stocks by comparing grazed vs. ungrazed sites, including 67 paired comparisons. SOC increased, decreased, or remained unchanged under contrasting grazing conditions across temperature and precipitation gradients, which suggests that grazing influences the factors that control SOC accumulation in a complex way. However, our review also revealed some general patterns such as 1) root contents (a primary control of SOC formation) were higher in grazed than in their ungrazed counterparts at the driest and wettest sites, but were lower at sites with intermediate precipitation (~400 mm to 850 mm); 2) SOM C:N ratios frequently increased under grazing conditions, which suggests potential N limitations for SOM formation under grazing; and 3) bulk density either increased or did not change in grazed sites. Nearly all sites located in the intermediate precipitation range showed decreases or no changes in SOC. We grouped previously proposed mechanisms of grazing control over SOC into three major pathways that can operate simultaneously: 1) changes in net primary production (NPP pathway), 2) changes in nitrogen stocks (nitrogen pathway), and 3) changes in organic matter decomposition (decomposition pathway). The relative importance of the three pathways may generate variable responses of SOC to grazing. Our conceptual model suggests that rangeland productivity and soil carbon sequestration can be simultaneously increased by management practices aimed at increasing N retention at the landscape level. El pastoreo modifica la estructura y el funcionamiento de los ecosistemas, alterando las reservas de C orgánico del suelo (COS). A pesar de que existen revisiones de los efectos del pastoreo sobre la productividad primaria o los cambios en la composición de especies, no se dispone de una síntesis detallada de los efectos del pastoreo sobre el COS. A su vez, discutiremos los controles de las reservas de nitrógeno orgánico del suelo, debido a su importancia en la regulación del ciclo del C. El objetivo de este trabajo fue sintetizar los efectos del pastoreo sobre el COS y analizar los mecanismos a través de los cuales opera. Realizamos una revisión de los artículos que evalúan, mediante comparaciones de sitios pastoreados y no pastoreados, los efectos del pastoreo sobre el COS, incluyendo 67 comparaciones pareadas. La revisión bibliográfica mostró que: 1) el C en las raíces y otros órganos subterráneos fue mayor en zonas pastoreadas que en las no pastoreadas en sitios secos y húmedos, pero menor en sitos con precipitaciones intermedias; 2) el pastoreo aumentó la relación C:N del suelo, sugiriendo limitaciones de N para la formación de materia orgánica del suelo; y 3) la densidad aparente del suelo fue mayor o igual en los sitios pastoreados, respecto a los no pastoreados. Los efectos del pastoreo sobre el COS operarían a través de tres vías: 1) por medio de cambios en la productividad primaria neta, 2) a través de alteraciones en los stocks de NOS, o 3) aumentando la descomposición del COS. El pastoreo afectaría el COS a través de los tres mecanismos simultáneamente, y la respuesta del COS al pastoreo dependerá de la importancia relativa de cada uno. Finalmente, el modelo conceptual propuesto sugiere que la productividad de la biomasa y la cantidad de carbono almacenado en el suelo podrían aumentarse simultáneamente mediante manejos que apunten a incrementar la retención de N a escala de paisaje. Fil: Piñeiro, Gervasio. 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: 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 Fil: Oesterheld, Martin. 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: Jobbagy Gampel, Esteban Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Matemática Aplicada de San Luis "Prof. Ezio Marchi". Universidad Nacional de San Luis. Facultad de Ciencias Físico, Matemáticas y Naturales. Instituto de Matemática Aplicada de San Luis ; Argentina