Juan Manuel Medina-Sánchez

University of Granada | UGR · Department of Ecology

High-mountain lakes and rivers are usually oligotrophic and strongly influenced by atmospheric transport processes. Thus, wet deposition of reactive N species (Nr), mainly in the form of nitrate (NO3⁻), is a major source of N input in these high-mountain ecosystems. Bacterial denitrifiers are thought to be largely responsible for reduction of NO3⁻...

This chapter addresses the question of why the high mountain lakes of Sierra NevadaSierra Nevada(Spain) areSpainunique remote sensorsRemote sensorsof global changeGlobal change. The answers arise from a set of peculiar physico-chemical and biological features shared by most of these water bodies. Their physical characteristics stem from their altit...

Multiple drivers are threatening the functioning of the microbial food webs and trophic interactions. Our understanding about how temperature, CO2, nutrient inputs, and solar ultraviolet radiation (UVR) availability interact to alter ecosystem functioning is scarce because research has focused on single and double interactions. Moreover, the role t...

The Metabolic Theory of Ecology (MTE) predicts that the temperature increases exert a common effect on organisms stimulating metabolic rates, this being stronger for a heterotrophic than for an autotrophic metabolism. However, no available studies within the MTE framework have focused on organisms’ response under fluctuation at high temperature int...

The coastal Atlantic area of Patagonia has a marked variability in physicochemical and biological properties. It is already affected by global change, as evidenced in historical patterns of environmental drivers and in direct anthropogenic influences. Here we focus on the effects of global change on plankton, mostly on phytoplankton, which constitu...

Mixotrophy combines autotrophy and phagotrophy in the same cell. However, it is not known to what extent the phagotrophy influences metabolism, cell composition, and growth. In this work, we assess, on the one hand (first test), the role of phagotrophy on the elemental and biochemical composition, cell metabolism, and enzymes related to C, N, and S...

Who’s cooking, who's cleaning, and who's got the remote control within the waters blanketing Earth? Anatomically tiny, numerically dominant microbes are the crucial “homemakers” of the watery household. Phytoplankton’s culinary abilities enable them to create food by absorbing sunlight to fix carbon and release oxygen, making microbial autotrophs t...

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 res...

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Global-change stressors act under different timing, implying complexity and uncertainty in the study of interactive effects of multiple factors on planktonic communities. We manipulated three types of stressors acting in different time frames in an in situ experiment: ultraviolet radiation (UVR); phosphorus (P) concentration; temperature (T) in an...

Energy (photosynthetically active [PAR] and ultraviolet [UVR] radiation) and matter (organic and inorganic nutrients) fluxes regulate the ecosystem's stability. However, the mechanisms underpinning the potential interplay between resistance and resilience to shifts in nutrient inputs and UVR are poorly understood. To assess how the UVR × nutrients...

Thermal stratification of the water column promotes contrasting conditions with respect to irradiance level and nutrient concentration for phytoplankton growth, demanding more research on which environmental factor has more importance in determining the photosynthetic performance of the communities. For this purpose, two research surveys were perfo...

Mixotrophic protists combine phagotrophy and phototrophy within a single cell. Greater phagotrophic activity could reinforce the bypass of carbon (C) flux through the bacteria‐mixotroph link and thus lead to a more efficient transfer of C and other nutrients to the top of the trophic web. To determine whether foreseeable changes in temperature and...

Algal-bacterial interactions include mutualism, commensalism, and predation. However, how multiple environmental conditions that regulate the strength and prevalence of a given interaction remains unclear. Here, we test the hypothesis that the prevailing algal-bacterial interaction shifted in two years (2005 versus 2015), due to increased temperatu...

Models predict that phytoplankton is bottom-up regulated by resources and top-down controlled by consumers. However, how the strength of these controls varies with UV radiation (UVR) is not well known. In this study, we test the hypothesis that the phosphorus (P) content of phytoplankton affects the role that UVR exerts strengthening or weakening t...

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...

A continuing challenge for scientists is to understand how multiple interactive stressor factors affect biological interactions, and subsequently, ecosystems–in ways not easily predicted by single factor studies. In this review, we have compiled and analyzed available research on how multiple stressor pairs composed of temperature (T), light (L), u...

Wet deposition of reactive nitrogen (Nr) species is considered a main factor contributing to N inputs, of which nitrate (NO3−) is usually the major component in high-mountain lakes. The microbial group of denitrifiers are largely responsible for reduction of nitrate to molecular dinitrogen (N2) in terrestrial and aquatic ecosystems, but the role of...

Evaluating how environmental stressor interactions influence ecosystem structure and functioning is critical to understanding the response of ecosystems to global change. We exposed a species-poor planktonic community to P pulses in the absence and presence of solar ultraviolet radiation (UVR). We used a field-mesocosm study in an oligotrophic mid-...

Nutrient inputs and ultraviolet radiation (UVR) are global factors affecting the structure and functioning of aquatic ecosystems, particularly clear-water ecosystems. We performed experiments in two model lakes highly exposed to UVR fluxes in order to test the effect that future increases in mineral nutrients transported by dust aerosol might exert...

Autotrophic picoplankton (APP) is responsible for the vast majority of primary production in oligotrophic marine areas, such as the Alboran Sea. The increase in atmospheric dust deposition (e.g. from Sahara Desert) associated with global warming, together with the high UV radiation (UVR) on these ecosystems may generate effects on APP hitherto unkn...

Solar radiation and nutrient pulses regulate the ecosystem’s functioning. However, little is known about how a greater frequency of pulsed nutrients under high ultraviolet radiation (UVR) levels, as expected in the near future, could alter the responses and interaction between primary producers and decomposers. In this report, we demonstrate throug...

The suitability of O2 optodes to resolve the effects of global-change stressors on respiration of microbial planktonic assemblages from oligotrophic ecosystems was tested. With this aim, we first evaluated how O2 measurements with optodes on closed flasks depended on delayed temperature equilibration (hysteresis), which can bias actual measurements...

To understand how atmospheric dust deposition and ultraviolet radiation (UVR) can affect remote, freshwater ecosystems through changes in their microbial metabolism, it is important to have tools that allow us detecting alterations and anticipating potential shifts in the functioning of microbial communities. Ecoenzyme activities (EA) are easy to m...

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...

Processes and environmental factors that alter carbon fixation and fluxes are key to understanding ecosystem function and impacts of global change stressors. We tested the effects of ultraviolet A radiation (UVA) and nutrients on the 14C production of particulate (bacteria, algae and zooplankton size fractions) and dissolved organic carbon. Experim...

From an extensive study, we determined that heterotrophic bacterial production (HBP) variance in Sierra Nevada (Spain) lakes was explained mainly by excretion of organic carbon by algae (EOC), underlining a bacterial dependence on algal carbon. Subsequently, we studied how the interaction among global change factors such as ultraviolet radiation (U...

Some of the most important effects of global change on coastal marine systems include increasing nutrient inputs and higher levels of ultraviolet radiation (UVR, 280-400 nm), which could affect primary producers, a key trophic link to the functioning of marine food webs. However, interactive effects of both factors on the phytoplankton community ha...

Global change models normally do not include interaction effects between different pools of recalcitrant humic organic carbon which can alter carbon cycling via their influence on biological activities. This issue is especially important in northern regions where lakes receive high inputs of allochthonous dissolved organic carbon (DOC) from the ext...

Abstract. 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 r...

Múltiples factores de estrés relacionados con el cambio global [sequía, aumento de la radiación ultravioleta, aerosoles atmosféricos, aumento de la temperatura, cambio en el régimen de mezcla vertical] actúan produciendo un impacto acumulativo sobre los ecosistemas acuáticos, en particular sobre los ecosistemas de alta montaña del sur de Europa. Nu...

We conducted a microcosm experiment aimed at studying the interactive effects of high CO2, nutrient loading and irradiance on the metabolism of a planktonic community sampled in the Western Mediterranean near the coast of Málaga. Changes in the metabolism of phytoplankton and bacterioplankton were observed for 7 d under 8 treatment conditions, repr...

Author(s) 2014. CC Attribution 3.0 License. This discussion paper is/has been under review for the journal Biogeosciences (BG). Abstract Abstract An indirect effect of global warming is the shallowing epilimnion, causing organisms to be exposed to higher levels of ultraviolet (UVR, 280–400 nm) and photosynthetically active radiation (PAR, 400–700 n...

As a consequence of global change, modifications in the interaction among abiotic stressors on aquatic ecosystems have been predicted. Among other factors, UVR transparency, nutrient inputs and shallower epilimnetic layers could alter the trophic links in the microbial food web. Currently, there are some evidences of higher sensitiveness of aquatic...

Because the nature of the main resource that limits bacterioplankton (e.g. organic carbon [C] or phosphorus [P]) has biogeochemical implications concerning organic C accumulation in freshwater ecosystems, empirical knowledge is needed concerning how bacteria respond to these two resources, available alone or together. We performed field experiments...

Consumer growth can be affected by imbalances between the nutrient content of the consumer and its food resource. Although ontogenetic-driven changes in animal composition are well documented, their potential consequences for the organism’s sensitivity to food quality constraints have remained elusive. Here we show that the potential growth respons...

Metabolic and stoichiometric theories of ecology have provided broad complementary principles to understand ecosystem processes across different levels of biological organization. We tested several of their cornerstone hypotheses by measuring the nucleic acid (NA) and phosphorus (P) content of crustacean zooplankton species in 22 high mountain lake...