Uncoupled phytoplanktonbacterioplankton relationship by multiple drivers interacting at diferent temporal scales in a highmountain Mediterranean lake

Global-change stressors act under diferent timing, implying complexity and uncertainty in the study of interactive efects of multiple factors on planktonic communities. We manipulated three types of stressors acting in diferent time frames in an in situ experiment: ultraviolet radiation (UVR); phosphorus (P) concentration; temperature (T) in an oligotrophic Mediterranean high-mountain lake. The aim was to examine how the sensitivity of phytoplankton and bacterioplankton to UVR and their trophic relationship change under nutrient acclimation and abrupt temperature shifts. Phytoplankton and bacteria showed a common pattern of metabolic response to UVR× P addition interaction, with an increase in their production rates, although evidencing an inhibitory UVR efect on primary production (PP) but stimulatory on bacterial production (HBP). An abrupt T shift in plankton acclimated to UVR and P addition decreased the values of PP, evidencing an inhibitory UVR efect, whereas warming increased HBP and eliminated the UVR efect. The weakening of commensalistic and predatory relationship between phyto- and bacterioplankton under all experimental conditions denotes the negative efects of present and future global-change conditions on planktonic food webs towards impairing C fux within the microbial loop

Saharan dust inputs and high UVR levels jointly alter the metabolic balance of marine oligotrophic ecosystems

The metabolic balance of the most extensive bioma on the Earth is a controversial topic of the global-change research. High ultraviolet radiation (UVR) levels by the shoaling of upper mixed layers and increasing atmospheric dust deposition from arid regions may unpredictably alter the metabolic state of marine oligotrophic ecosystems. We performed an observational study across the south-western (SW) Mediterranean Sea to assess the planktonic metabolic balance and a microcosm experiment in two contrasting areas, heterotrophic nearshore and autotrophic open sea, to test whether a combined UVR × dust impact could alter their metabolic balance at mid-term scales. We show that the metabolic state of oligotrophic areas geographically varies and that the joint impact of UVR and dust inputs prompted a strong change towards autotrophic metabolism. We propose that this metabolic response could be accentuated with the global change as remote-sensing evidence shows increasing intensities, frequencies and number of dust events together with variations in the surface UVR fluxes on SW Mediterranean Sea. Overall, these findings suggest that the enhancement of the net carbon budget under a combined UVR and dust inputs impact could contribute to boost the biological pump, reinforcing the role of the oligotrophic marine ecosystems as CO2 sinks.This work was funded by the Ministerio Español de Ciencia e Innovación (CGL2011–23681 and CGL2015-67682-R), and Campus de Excelencia Internacional del Mar (CeiMar). M.J.C. and J.M.G.-O. were supported by the Spanish Government Fellowship “Formación de Profesorado Universitario” (FPU12/01243 and FPU14/00977, respectively)

Complex interactions in microbial food webs : stoichiometric and functional approaches

The food web structure in some high mountain lakes deviates from the established tendency of high heterotrophic bacteria: phytoplankton biomass ratios in oligotrophic ecosystems. Thus, the microbial food web in La Caldera Lake is weakly developed, and bacteria constitute a minor component of the plankton community in terms of abundance, biomass and production. Autotrophic picoplankton is absent, and heterotrophic microbial food web is weakly developed compared to a grazing chain dominated by calanoid copepods and a phytoplankton community mainly composed of mixotrophic flagellates. In order to explain the singular food web structure of this lake, functional, stoichiometric and taxonomical approaches are followed to assess, on various temporal and spatial scales, the relevance of stressful abiotic factors (ultraviolet solar radiation and P-limitation) on the structure and functioning of this ecosystem. P-availability was the main factor controlling the algal biomass whereas bacterial P- limitation was a transient phenomenon. The algae-bacteria relationship was predominately commensalistic. In contrast to algae, full-sunlight radiation had no negative effect on bacterial growth but rather enhanced bacterial dependence on the carbon released by algae. The prevalence of the commensalistic-mutualistic relationship and the development of a more complex microbial food web were related to the stoichiometry of algae and bacteria (N:P ratios). The microbial food web only developed at balanced algal and bacterial N:P ratios, with the appearance of ciliates after a nutrient pulse. However, mixotrophic algae dominated the planktonic community under P-deficit conditions, and they were the main factor controlling bacterioplankton. Their regulatory effect has a dual nature: (i) a resource-based control, where bacteria depend on the photosynthetic carbon released by algae, i.e., a commensalistic interaction ("without you I cannot live"); and (ii) a predatory control, where bacteria is a prey for mixotrophs ("with you I die"). Hence, the niche of microheterotrophs (nanoflagellates and ciliates) is occupied by mixotrophs, and there is a resulting simplification of the planktonic structure. With respect to the carbon cycle, mixotrophic bacterivory constitutes a "by-pass" for the flux of C towards the grazing chain, precluding the development of a complex heterotrophic microbial food web. Mixotrophs thereby improve the energetic transfer efficiency in high mountain lakes through a reduction in the number of trophic levels. Antagonistic effects of UVR x P interactions on the algae-bacteria relationship were caused by an enhancement of dual (resource and predation) control. Based on these results, an alternative model for the flux of C in autotrophic high mountain lakes has been proposed.La estructura de la red trófica en algunos lagos de alta montaña, se aleja de los patrones establecidos para ecosistemas oligotróficos que proponen el predominio de la red trófica microbiana sobre la cadena de pastoreo. Así, en la laguna de La Caldera las bacterias son el componente minoritario de la comunidad planctónica en términos de abundancia, biomasa y producción. El picoplancton autótrofo está ausente y la red microbiana heterotrófica se encuentra escasamente desarrollada frente a una cadena de pastoreo dominada por copépodos calanoides y algas mixotróficas. Para comprender los mecanismos que determinan esta estructura trófica hemos seguido diferentes aproximaciones de análisis: funcional, estequiométrica y taxonómica sobre distintas escalas espaciales y temporales, en relación con los principales factores de estrés abiótico (radiación ultravioleta y limitación por fósforo) que controlan el funcionamiento de los ecosistemas de alta montaña. Nuestros resultados indican que la disponibilidad de fósforo, de forma generalizada, controla la biomasa algal y de manera transitoria la bacteriana, estableciéndose entre ambas comunidades una relación comensalista. La radiación solar completa no afecta negativamente el desarrollo de las bacterias y si el de las algas y potencia la relación de dependencia por el carbono orgánico (comensalismo) entre algas y bacterias. El predominio de la relación comensalista-mutualista y el desarrollo del bucle microbiano esta relacionado con la estequiometría (razón N:P) de algas y bacterias. Así, sólo cuando la razón N:P de algas y bacterias es equilibrada para crecer, un pulso de nutrientes permite el desarrollo del bucle microbiano. En condiciones naturales de déficit de P, sin embargo, existe un predominio de "algas" con metabolismo mixotrófico. Las algas mixotróficas ejercen un efecto regulador dual sobre las bacterias que denominamos Ni contigo ni sin ti, (i) control por depredación, donde las bacterias son consumidas por algas mixotróficas ("contigo me muero"), (ii) control basado en los recursos estableciéndose una relación de dependencia de las bacterias sobre del carbono liberado por las algas ("sin ti no puedo vivir"). La mixotrofia supone un simplificación en la cadena trófica microbiana, donde los mixótrofos ocupan el nicho potencial de nanoflagelados y ciliados. Desde un punto de vista energético implica un cortocircuito en el flujo de energía y un incremento en la eficiencia de transferencia energética en ecosistemas ultraoligotróficos y con alta dosis de radiación ultravioleta (RUV). Los efectos de la interacción entre RUV y pulsos de P tienen un efecto antagónico sobre la interacción alga-bacteria, intensificando la interacción comensal-depredadora. A partir de los resultados obtenidos proponemos un modelo alternativo de flujo de energía para ecosistemas autotróficos de alta montaña

Exploring the ring-closing metathesis for the construction of the solomonamide macrocyclic core: identification of bioactive precursors

New synthetic strategies directed toward the novel cyclopeptides solomonamides have been explored utilizing an olefin metathesis as the key reaction. In the various strategies investigated, we worked on minimally oxidized systems, and the olefin metathesis reaction demonstrated efficiency and validity for the construction of the macrocyclic core. The described synthetic strategies toward the solomonamides are well suited for the subsequent access to the natural products and represent flexible and diversityoriented routes that allow for the generation of a variety of analogues via oxidative transformations. In addition, preliminary biological evaluations of the generated solomonamide precursors revealed antitumor activity against various tumor cell lines.This work was financially supported by the Ministerio de Economía y Competitividad (MINECO) (ref BIO2014-56092-R, CTQ2014-60223-R and CTQ2016-76311-R) and Junta de Andalucía and “Fondo Europeo de Desarrollo Regional-FEDER” (P12 CTS-1507). I.C.-S. thanks Ministerio de Educación, Cultura y Deporte for a predoctoral fellowship (FPU programme)

Assessing attention deficit by binocular rivalry

Objective: To determine whether the frequency and duration of the periods of suppression of a percept in a binocular rivalry (BR) task can be used to distinguish between subjects with attention deficit hyperactivity disorder (ADHD) and controls. Method: 122 participants (6 to 15 years) were assigned to three groups: ADHD Combined (ADHD-C), ADHD-Predominantly Inattentive (ADHD-I) and controls. They each performed a BR task and two measures were recorded: alternation rate and duration of exclusive dominance periods. Results: ADHD-C group presented fewer alternations and showed greater variability than did the control group; results for the ADHD-I group being intermediate between the two. The duration of dominance periods showed a differential profile: in control group it remained stable over time, whereas in the clinical groups it decreased logarithmically as the task progressed. Conclusions: The differences between groups in relation to the BR indicators can be attributed to the activity of involuntary inhibition

Increased nutrients from aeolian-dust and riverine origin decrease the CO2-sink capacity of coastal South Atlantic waters under UVR exposure

Increases in ultraviolet radiation (UVR) levels due to the ongoing stratification of water bodies and higher nutrient concentrations either through riverine or aeolian-dust-inputs are expected in the near future in coastal surface waters. Here, we combined remote-sensing data of particulate organic carbon (POC; 1997–2016 period), observational data of solar radiation (1999–2015 period), and a mid-term experimental approach with coastal plankton communities from South Atlantic Ocean (SAO) to test how the interaction between increased nutrients by riverine and aeolian-dust inputs and high UVR may alter the community dynamics and the CO2 sink capacity of these ecosystems in the future. Our results show a decline ∼ 27% in the sink capacity of the coastal ecosystems regardless of the nutrient source considered and under high UVR levels. This decreased CO2 uptake was coupled with a high dynamic photoinhibition and dark recovery of photosystem II and shifts in the community structure toward the dominance by nano-flagellates. Moreover, remote-sensing data also evidences an incipient tipping point with decreasing POC values in this area over the annual planktonic succession. Therefore, we propose that to continue this climate and human-mediated pressure, these metabolic responses could be strengthened and extended to other productive coastal areas.Fil: Cabrerizo, Marco J.. Universidad de Granada; España. Fundación Playa Unión. Estación de Fotobiología Playa Unión; ArgentinaFil: Carrillo, Presentación. Universidad de Granada; EspañaFil: Villafañe, Virginia Estela. Fundación Playa Unión. Estación de Fotobiología Playa Unión; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Medina Sánchez, Juan Manuel. Universidad de Granada; EspañaFil: Helbling, Eduardo Walter. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Fundación Playa Unión. Estación de Fotobiología Playa Unión; Argentin

The effects of UV radiation on photosynthesis estimated as chlorophyll fluorescence in Zygnemopsis decussata (Chlorophyta) growing in a high mountain lake (Sierra Nevada, Southern Spain)

The effect of increased UV radiation on photosynthesis estimated as in vivo chlorophyll fluorescence i.e. optimal quantum yield (Fv/Fm) and electron transport rate (ETR) in the green filamentous alga Zygnemopsis decussata (Streptophyta, Zygnematales) growing in the high mountain lake "La Caldera" (Sierra Nevada, Spain) at 3050 m altitude was evaluated. Two sets of in situ experiments were conducted: (1) On July 2006, Fv/Fm was measured throughout the day at different depths (0.1, 0.25, 0.5 and 1 m) and in the afternoon, ETR and phenolic compounds were determined. In addition, in order to analyze the effect of UV radiation, Fv/Fm was determined in algae incubated for 3 days at 0.5m under three different light treatments: PAR+UVA+UVB (PAB), PAR+UVA (PA) and PAR (P). (2) On August 2007, Fv/Fm was determined under PAB, PA and P treatments and desiccation/rehydration conditions. Fv/Fm decreased in algae growing in surface waters (0.1 m) but also at 1 m depth compared to that at 0.5 m depth. The decrease of Fv/Fm at noon due to photoinhibition was small (less than 10%) except in algae growing at 1 m depth (44%). The maximal electron transport rate was 3.5-5 times higher in algae growing at 0.25-0.5 m respectively than that at 0.1 and 1 m depth. These results are related to the accumulation of phenolic compounds: i.e. the algae at 0.25-0.5 m presented respectively about a 3-5 times higher concentration of phenolic compounds than that of algae at 0.1-1 m depth. The protection mechanisms seem to be stimulated by UVB radiation, since Fv/Fm was higher in the presence of UVB (PAB treatment) compared to PA or P treatments. UVA exerts the main photoinhibitory effect, not only at midday, but also in the afternoon. UVB radiation also had a protective effect in algae grown under desiccation conditions for three days. During re-hydration, the rapid increase of Fv/Fm (after 1 h) was higher in the UVB-grown algae than in algae grown under UVA radiation. After 5 h, Fv/Fm values were similar in algae submitted to desiccation/rehydration under PAB and P treatments as they were in the control (submerged algae). The combined effect of desiccation and UVA produced the greatest decrease of photosynthesis in Z. decussata. Thus UVB, in contrast to other species, may support the recovery process. Z. decussata can acclimate to severe stress conditions in this high mountain lake by the photoprotection mechanism induced by UVB radiation through dynamic photoinhibition and the accumulation of phenolic compounds (UV screen and antioxidant substances).This research was supported by the Spanish Ministries of Environment (PN2003/25) and Education and Science (CGL2005/01564, AGL2005/02655, CGL 2008/01127, CGL 2008/05407) and Consejería de Innovación, Ciencia y Empresa, Junta de Andalucía (Excelencia project P07-CVI-02598)

Multiple interacting environmental drivers reduce the impact of solar UVR on primary productivity in Mediterranean lakes

Increases in rainfall, continental runoff, and atmospheric dust deposition are reducing water transparency in lakes worldwide (i.e. higher attenuation Kd). Also, ongoing alterations in multiple environmental drivers due to global change are unpredictably impacting phytoplankton responses and lakes functioning. Although both issues demand urgent research, it remains untested how the interplay between Kd and multiple interacting drivers affect primary productivity ( Pc). We manipulated four environmental drivers in an in situ experiment—quality of solar ultraviolet radiation (UVR), nutrient concentration (Nut), CO2 partial pressure ( CO2), and light regime (Mix)—to determine how the Pc of nine freshwater phytoplankton communities, found along a Kd gradient in Mediterranean ecosystems, changed as the number of interacting drivers increased. Our findings indicated that UVR was the dominant driver, its effect being between 3–60 times stronger, on average, than that of any other driver tested. Also, UVR had the largest difference in driver magnitude of all the treatments tested. A future UVR × CO2 × Mix × Nut scenario exerted a more inhibitory effect on Pc as the water column became darker. However, the magnitude of this synergistic effect was 40–60% lower than that exerted by double and triple interactions and by UVR acting independently. These results illustrate that although future global-change conditions could reduce Pc in Mediterranean lakes, multiple interacting drivers can temper the impact of a severely detrimental driver (i.e. UVR), particularly as the water column darkens.Ministerio de Economía y Competividad (MINECO)European Union (EU) MICROSENSCGL2011-23681 METAS-CGL2015-67682-RMedio Ambiente, Rural, y Marino PN2009/067Junta de Andalucía CVI-02598 P09-RNM-5376Fundación Playa Unión (Argentina)Juan de la Cierva-Formacion from the Ministerio de Ciencia, Innovación y Universidades FJCI2017-32318Postdoctoral contract "Contrato Puente" from Plan Propio (FP7/2017) of the University of GranadaMETAS projec

Interactive effects of vertical mixing, nutrients and ultraviolet radiation: in situ photosynthetic responses of phytoplankton from high mountain lakes in Southern Europe

Global change, together with human activities, has resulted in increasing amounts of organic material (including nutrients) that water bodies receive. This input further attenuates the penetration of solar radiation, leading to the view that opaque lakes are more "protected" from solar ultraviolet radiation (UVR) than clear ones. Vertical mixing, however, complicates this view as cells are exposed to fluctuating radiation regimes, for which the effects have, in general, been neglected. Furthermore, the combined impacts of mixing, together with those of UVR and nutrient inputs are virtually unknown. In this study, we carried out complex in situ experiments in three high mountain lakes of Spain (Lake Enol in the National Park Picos de Europa, Asturias, and lakes Las Yeguas and La Caldera in the National Park Sierra Nevada, Granada), used as model ecosystems to evaluate the joint impact of these climate change variables. The main goal of this study was to address the question of how short-term pulses of nutrient inputs, together with vertical mixing and increased UVR fluxes modify the photosynthetic responses of phytoplankton. The experimentation consisted in all possible combinations of the following treatments: (a) solar radiation: UVR + PAR (280–700 nm) versus PAR (photosynthetically active radiation) alone (400–700 nm); (b) nutrient addition (phosphorus (P) and nitrogen (N)): ambient versus addition (P to reach to a final concentration of 30 μg P L−1, and N to reach N:P molar ratio of 31); and (c) mixing: mixed (one rotation from surface to 3 m depth (speed of 1 m 4 min−1, total of 10 cycles)) versus static. Our findings suggest that under ambient nutrient conditions there is a synergistic effect between vertical mixing and UVR, increasing phytoplankton photosynthetic inhibition and excretion of organic carbon (EOC) from opaque lakes as compared to algae that received constant mean irradiance within the epilimnion. The opposite occurs in clear lakes where antagonistic effects were determined, with mixing partially counteracting the negative effects of UVR. Nutrient input, mimicking atmospheric pulses from Saharan dust, reversed this effect and clear lakes became more inhibited during mixing, while opaque lakes benefited from the fluctuating irradiance regime. These climate change related scenarios of nutrient input and increased mixing, would not only affect photosynthesis and production in lakes, but might also further influence the microbial loop and trophic interactions via enhanced EOC under fluctuating UVR exposure.This work was supported by Ministerio Español de Medio Ambiente, Rural y Marino (PN2009/067) and Ciencia e Innovación (GLC2008-01127/BOS and CGL2011-23681), Junta de Andalucía (Excelencia CVI-02598), Agencia Nacional de Promoción Científica y Tecnológica (PICT 2007-1651) and Fundación Playa Unión; GH and CD were supported by the Spanish Government – Formación de Profesorado Universitario Grant

Synergistic effects of UVR and simulated stratification on commensalistic phytoplankton–bacteria relationship in two optically contrasting oligotrophic Mediterranean lakes

An indirect effect of global warming is a reduction in the depth of the upper mixed layer (UML) causing organisms to be exposed to higher levels of ultraviolet (UVR, 280–400 nm) and photosynthetically active radiation (PAR, 400–700 nm). This can affect primary and bacterial production as well as the commensalistic phytoplankton–bacteria relationship. The combined effects of UVR and reduction in the depth of the UML were assessed on variables related to the metabolism of phytoplankton and bacteria, during in situ experiments performed with natural pico- and nanoplankton communities from two oligotrophic lakes with contrasting UVR transparency (high-UVR versus low-UVR waters) of southern Spain. The negative UVR effects on epilimnetic primary production (PP) and on heterotrophic bacterial production (HBP), intensified under increased stratification, were higher in the low-UVR than in the high-UVR lake, and stronger on the phytoplanktonic than on the heterotrophic bacterial communities. Under UVR and increased stratification, the commensalistic phytoplankton–bacteria relationship was strengthened in the high-UVR lake where excretion of organic carbon (EOC) rates exceeded the bacterial carbon demand (BCD; i.e., BCD : EOC(%) ratio 100). The greater UVR damage to phytoplankton and bacteria and the weakening of their commensalistic interaction found in the low-UVR lake indicates that these ecosystems would be especially vulnerable to UVR and increased stratification as stressors related to global climate change. Thus, our findings may have important implications for the carbon cycle in oligotrophic lakes of the Mediterranean region.This study was supported by the Ministerio Español de Medio Ambiente, Rural y Marino (PN2009/067), Ciencia e Innovación (CGL2011-23681), Junta de Andalucía (Excelencia CVI-02598 and P09-RNM-5376), Consejo Nacional de Investigaciones Científicas y Técnicas – CONICET (PIP no. 112-201001-00228), and Fundación Playa Unión. G. Herrera and C. Durán were supported by a Formación de Profesorado Universitario grant from the Spanish government. The authors are indebted to the staff of Sierra Nevada National Park and Lagunas de Ruidera Natural Park for permission to work, to E. Jiménez-Coll for the bacterial production analysis, and to D. Nesbitt for writing assistance in English