Synergistic effects of UVR and simulated stratification on commensalistic algal-bacterial relationship in two optically contrasting oligotrophic Mediterranean lakes
Author:
Carrillo P.,Medina-Sánchez J. M.,Durán C.,Herrera G.,Villafañe V. E.,Helbling E. W.
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 nm), which could affect primary and bacterial production as well as the commensalistic algal-bacterial relationship. The combined effects of UVR and reduction in the depth of the upper mixed layer (UML) were assessed on variables related to the metabolism of algae and bacteria, during in situ experiments performed with natural microplanktonic communities from two oligotrophic lakes with contrasting UVR-transparency (clear vs. opaque) of southern Spain. The negative UVR effects on epilimnetic primary production (PP) and on heterotrophic bacterial production (HBP), intensified by high mean irradiances, were higher in the UVR-opaque than in the UVR-clear lake, and stronger on the algae than on the heterotrophic bacterial communities. Under UVR and high mean irradiance, the algal-bacterial relationship was strengthened in the UVR-clear lake, where excreted organic carbon (EOC) rates exceeded the bacterial carbon demand (BCD). This did not occur in the UVR-opaque lake. The greater UVR damage to algae and bacteria and the weakening of their commensalistic interaction found in the UVR-opaque lake indicates that these ecosystems would be especially vulnerable to stressors related to global change. Thus, our findings may have important implications for the carbon cycle in oligotrophic lakes of the Mediterranean region.
Publisher
Copernicus GmbH
Reference58 articles.
1. Aas, P., Lyons, M. M., Pledger, R., Mitchell, D. L., and Jeffrey, W. H.: Inhibition of bacterial activities by solar radiation in nearshore waters and the Gulf of Mexico, Aquat. Microb. Ecol., 11, 229–238, 1996. 2. Amado, A. M., Meirelles-Pereira, F., Vidal, L. O., Sarmento, H., Suhett, L., Farjalla, V. F., Cotner, J. B., and Roland, F.: Tropical freshwater ecosystems have lower bacterial growth efficiency than temperate ones, Front. Microbiol., 4, 1–8, 2013. 3. American Public Health Association (APHA): Standard Methods for the Examination of Water and Wastewater, 18th edn. American Public Health Association, Washington, DC, 1992. 4. Baines, S. B. and Pace, M. L.: The production of dissolved organic-matter by phytoplankton and its importance to bacteria- patterns across marine and fresh-water systems, Limnol. Oceanogr., 36, 1078–1090, 1991. 5. Banaszak, A. T.: Photoprotective physiological and biochemical responses of aquatic organisms, in: UV Effects in Aquatic Organisms and Ecosystems, edited by: Helbling, E. W. and Zagarese, H. E., Royal Society of Chemistry, Cambridge, UK, 329–356, 2003.
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