Survival and life strategy of the foraminiferan Globobulimina turgida through nitrate storage and denitrification

International audienceIn a laboratory experiment, we examined the prolonged survival and behaviour of the benthic foraminiferan Globobulimina turgida under 3 simulated natural conditions: oxygenated with added nitrate, anoxic with added nitrate, and anoxic. The survival rates, adenosine triphosphate (ATP) reserve and intracellular nitrate pool of G. turgida were measured periodically under these conditions. Furthermore, to evaluate the efficiency and energy yield of the respiration system, denitrification rates of individual specimens were quantified using the acetylene inhibition and N 2 O microsensor technique at the start of the experiment. Our results demonstrate that the long-term (56 d) survival rate (64%) and ATP concentrations of G. turgida were not significantly different in oxygenated and anoxic, nitrate-containing conditions (Mann-Whitney test, p > 0.05). Thus, G. turgida can survive prolonged anoxia (3 mo) as long as nitrate is available to sustain its respiration. However, it remains unsure whether growth or reproduction can take place under anoxia. Short-term (21 to 35 d) survival rates were lower in nitrate-free, anoxic conditions (22% recovered alive compared to 62 to 82% in nitrate-oxic or nitrate-anoxic conditions), but foraminifera were observed to survive up to 56 d if respiring from their intra-cellular nitrate pool only. The foraminiferal nitrate pool appears very dynamic, as wide ranges of concentrations were measured in living specimens (0 to 463 mM ind.-1). We postulate that the scatter in the nitrate pool measurements highlights the ability of the foraminifera to actively collect and respire on nitrate, depending on individuals' history of exposure to oxygen and nitrate

Variabilidad espacial de la desnitrificación en una cadena de lagos rica en nitrato y con alimentación subterránea (Ruidera, Centro de España)

Spatial variations of denitrification activity and the relative importance of controlling factors were determined using the isotope pairing technique in a seepage chain of Mediterranean flowthrough lakes (Ruidera lakes) and within a given lake in the chain (Colgada lake), all receiving extremely high nitrogen inputs. The range of denitrification rates measured (28-155 ¿mol N m-2 h-1) were comparable with rates measured with isotope pairing in other freshwater systems. While the bulk of total denitrification was mostly based on NO3- from the overlying water, coupled nitrification-denitrification seemed to be lower in all Ruidera lakes. At the regional scale, i.e. lake district, inter-variability in denitrification (CV = 37 %) was lower than the intra-variability observed in a single lake (CV = 54 %). In fact, a preliminary meta-analysis of data from published studies suggested that denitrification rate variabilities did not differ statistically between the environmental and regional scales. Dissolved oxygen concentration, dissolved organic carbon content and nitrate from the overlying water were found to be the most important factors affecting the spatial heterogeneity of denitrification rate in the lake complex. At the single-lake scale, only phosphorus explained the variability of denitrification rates observed along its main axis. Our study emphasizes the significance of hotspots in denitrification processes, but also highlights the need for further studies on spatial denitrification given that fact that conflicting controlling factors have been found at different scales. To spatially measure denitrification is complicated due to the intrinsic difficulties of the incubation process and hotspots, which makes modelling indispensable.[ES] Mediante la técnica del par isotópico, estudiamos las variaciones espaciales de la actividad desnitrificante y la importancia relativa de sus factores de control en una cadena de lagos mediterráneos de tipo fluvial (lagunas de Ruidera) y en un lago concreto dentro de la misma (Laguna Colgada), todos los cuales reciben cargas elevadas de nitrógeno. El rango de las tasas medidas mediante dicha técnica fue comparable (28-155 µmol N m-2 h-1) al registrado en otros ambientes dulceacuícolas. Gran parte de las tasas se debieron al nitrato presente en el agua sobrenadante al sedimento (62-83 %), resultando de menor importancia los procesos acoplados de nitrificación-desnitrificación en todos los lagos estudiados. A escala del conjunto lacustre, la variabilidad del proceso fue inferior (CV = 37 %) a la presente en un único lago (CV = 54 %). En relación con esto, un meta-análisis preliminar de la variabilidad de la desnitrificación en distintos limnoambientes reveló que no había diferencias significativas entre la escala del ecosistema individual y la regional. Las concentraciones de oxígeno disuelto, carbono orgánico disuelto y nitrato en el agua sobrenadante fueron los factores fundamentales que controlaron las tasas de desnitrificación en el conjunto de lagos, mientras que en la laguna Colgada solo el ortofosfato explicó la variabilidad del proceso registrada en su eje principal. Este estudio recalca la importancia de los micrositios más favorables (hotspots) para el proceso de desnitrificación, pero también apoya la necesidad de más estudios sobre el tema porque los factores que lo controlan a distintas escalas espaciales difieren entre estudios. Las dificultades intrínsecas a la incubación y a la existencia dichos micrositios para medir espacialmente este proceso mediante cualquier técnica hacen imprescindible la modelización del mismoWe gratefully acknowledge the technical staff of Lagunas de Ruidera Natural Park for assistance and lake level data. We are also grateful to the Guadiana Water Authority for data on water discharge to Ruidera lakes. Field and lab help provided by Jos? Mar?a Alonso, Eva L?pez-Del-gado and Meritxell Plensa is also acknowledged. Julio Mateo is thanked for constructing the incubators for the isotope pairing technique improving an earlier design by the Swiss EAWAG (Prof. Bernhard Wehrli). This study has been supported by a predoctoral fellowship to E. Piña-Ochoa and the REN-2002-00558 and CGL-2006-2346/HID Projects of the Spanish Ministry of Education and Science

Aquatic ecology and society of Ruidera lakes (Central Spain)

El libro intenta ofrecer una visión inicial y facilitar la comprensión de este sistema tan complejo y valioso la actividad humana sobre el territorio, que afecta tanto a la cuenca hidrográfica superficial como a la subterránea, ha sido decisiva para alterar su calidad ecológica. la conservación y recuperación de este ecosistema depende en gran parte de la sociedad castellano-manchega.Ministerio de Ciencia e Innovación. Consejo Superior de Investigaciones CientíficasDepto. de Biología CelularFac. de Ciencias BiológicasTRUEpu

Seasonal nitrogen dynamics in a seepage lake receiving

11 pages, 6 figures, 2 tablesStudies on nitrogen dynamics in seepage lakes are seldom undertaken, yet our understanding of the complex pattern of the nitrogen (N) cycle is complicated by its temporal and spatial heterogeneity. This research investigated temporal variation inNconcentration, considering different forms ofN(NO−3 ,NO−2 ,NH+4 , dissolved organicN, particulate organic N) in a Spanish flowthrough seepage lake (Colgada Lake) receiving high N loads. The study was based on monthly data collected over the period 2003–2005 from lake inputs and outputs, vertical profiles at a single representative site in the middle of the lake and fluxes of NH+4 and NO−3 at the sediment–water interface. The distribution of total N (TN) inputs and outputs did not follow a clear temporal pattern. TN inputs varied from 27.70 to 125 tonnes N month−1, 75–84% of which is NO−3 .Temporal variation of concentration profiles for different N forms measured showed significant differences owing to stratification. Ammonium always entered the sediment, whereas sediments acted as either a sink or source of NO−3 . Fluctuation in N dynamics in this lake was more influenced by external factors, such as the input variability, than by the turnover of nitrogenous substances in the water body. Comparing seasonal N dynamics, there seems to be temporal differences between seepage lakes and drainage lakes. In seepage lakes, dissolved inorganic nitrogen (DIN) peaks were reached in early spring and after overturn, whereas in drainage lakes, the autumn minimum gradually increased to maxima in late winter and during the stratification periodREN 2002-00558 Proyecto del Ministerio de Educación y Ciencia de EspañaPeer reviewe

Biomarkers for dementia in Latin American countries : gaps and opportunities

Limited knowledge on dementia biomarkers in Latin American and Caribbean (LAC) countries remains a serious barrier. Here, we report on the results from an online survey completed by dementia specialists from LAC. It aims to explore the ongoing work, needs, interests, potential barriers, and opportunities for future studies related to biomarkers. The survey was answered by 48 respondents from 10 LAC countries. The results show that neuroimaging is the most commonly used biomarker (73%), followed by genetic studies (40%), peripheral fluids biomarkers (31%) and cerebrospinal fluid biomarkers (29%). Regarding barriers in LAC, we identified that lack of funding appears to undermine the implementation of biomarkers in clinical or research settings, followed by insufficient infrastructure and training. The survey revealed that despite the above barriers, the region holds a great potential to advance dementia biomarkers research as the majority of respondents share an interest in the topic, would like to host studies, and confirmed access to unique populations. Considering the unique contributions that LAC could make to this growing field, we highlight the urgent need to introduce and expand biomarker research and suggest strategies to accelerate such developments. These insights allowed us to propose an action plan that addresses the recommendations towards a biomarker framework recently proposed by regional experts

Biomarkers for dementia in Latin American countries: Gaps and opportunities

Limited knowledge on dementia biomarkers in Latin American and Caribbean (LAC) countries remains a serious barrier. Here, we reported a survey to explore the ongoing work, needs, interests, potential barriers, and opportunities for future studies related to biomarkers. The results show that neuroimaging is the most used biomarker (73%), followed by genetic studies (40%), peripheral fluids biomarkers (31%), and cerebrospinal fluid biomarkers (29%). Regarding barriers in LAC, lack of funding appears to undermine the implementation of biomarkers in clinical or research settings, followed by insufficient infrastructure and training. The survey revealed that despite the above barriers, the region holds a great potential to advance dementia biomarkers research. Considering the unique contributions that LAC could make to this growing field, we highlight the urgent need to expand biomarker research. These insights allowed us to propose an action plan that addresses the recommendations for a biomarker framework recently proposed by regional experts