Publicaciones Cientificas B - Observatorio Cambio Global Sierra Nevada


Climate-driven shifts in algal-bacterial interaction of high-mountain lakes in two years spanning a decade Juan Manuel González-Olalla, Juan Manuel Medina-Sánchez, Ismael L. Lozano, Manuel Villar-Argaiz & Presentación Carrillo - 01/03/2019 - Scientific Reports - Leer más... 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 temperature (T) and Saharan dust depositions in high-mountain lakes of Sierra Nevada (S Spain). Our results support the starting hypothesis that the nature of the prevailing algal-bacterial interaction shifted from a bacterivory control exerted by algae to commensalism, coinciding with a higher air and water T as well as the lower ratio sestonic nitrogen (N): phosphorous (P), related to greater aerosol inputs. Projected global change conditions in Mediterranean region could decline the functional diversity and alter the role of mixotrophy as a carbon (C) by-pass in the microbial food web, reducing the biomass-transfer efficiency up the web by increasing the number of trophic links.
Resource versus consumer regulation of phytoplankton: testing the role of UVR in a Southern and Northern hemisphere lake Villar-Argaiz M, EG Balseiro, BE Modenutti, MS Souza, FJ Bullejos, JM Medina-Sánchez, P Carrillo - 01/02/2018 - Hydrobiologia 816: - Leer más... Models predict that phytoplankton is bot- tom-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 the resource and consumer control on distinct stoichiometric and functional phytoplankton traits. To accomplish this, we coupled field meso- and microcosms in a split-plot design using UVR treatments at the plot level and nutrients and zooplankton (presence/ absence) at the subplot level, in two mountain lakes characterized by their P-sufficient (La Caldera) and P-deficient phytoplankton (Los Cántaros). We found that the addition of nutrients decreased phytoplankton C:P in both lakes, but enhanced primary production and chlorophyll a only under UVR in La Caldera. Also, the effects of zooplankton on phytoplankton varied between lakes and UVR conditions, and increased primary production and chlorophyll a under UVR in La Caldera, but not in Los Cántaros. These results suggest that differences in the stoichiometric aspects associated with the P content in phytoplankton play a key role in how UVR affects resource and consumer controls, with much weaker effects in P-deficient food webs.
Predominant non-additive effects of multiple stressors on autotroph C:N:P ratios propagate in freshwater and marine food webs Villar-Argaiz M, JM Medina-Sánchez, BA Biddanda, P Carrillo - 01/01/2018 - Frontiers in Microbiology 9: Article 69. doi:10.3389/fmicb.2018.00069. - Leer más... 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), ultraviolet radiation (UVR), nutrients (Nut), carbon dioxide (CO2), dissolved organic carbon (DOC), and salinity (S) impact the stoichiometry of autotrophs which in turn shapes the nature of their ecological interactions within lower trophic levels in streams, lakes and oceans. Our analysis from 66 studies with 320 observations of 11 stressor pairs, demonstrated that non-additive responses predominate across aquatic ecosystems and their net interactive effect depends on the stressor pair at play. Across systems, there was a prevalence of antagonism in freshwater (60–67% vs. 47% in marine systems) compared to marine systems where synergism was more common (49% vs. 33–40% in freshwaters). While the lack of data impeded comparisons among all of the paired stressors, we found pronounced system differences for the L × Nut interactions. For this interaction, our data for C:P and N:P is consistent with the initial hypothesis that the interaction was primarily synergistic in the oceans, but not for C:N. Our study found a wide range of variability in the net effects of the interactions in freshwater systems, with some observations supporting antagonism, and others synergism. Our results suggest that the nature of the stressor pairs interactions on C:N:P ratios regulates the “continuum” commensalistic-competitive-predatory relationship between algae and bacteria and the food chain efficiency at the algae-herbivore interface. Overall, the scarce number of studies with even more fewer replications in each study that are available for freshwater systems have prevented a more detailed, insightful analysis. Our findings highlighting the preponderance of antagonistic and synergistic effects of stressor interactions in aquatic ecosystems—effects that play key roles in the functioning of feedback loops in the biosphere—also stress the need for further studies evaluating the interactive effects of multiple stressors in a rapidly changing world facing a confluence of tipping points.

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