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Biogeosciences An interactive open-access journal of the European Geosciences Union
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Volume 12, issue 3
Biogeosciences, 12, 697–712, 2015
https://doi.org/10.5194/bg-12-697-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.
Biogeosciences, 12, 697–712, 2015
https://doi.org/10.5194/bg-12-697-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 04 Feb 2015

Research article | 04 Feb 2015

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

P. Carrillo1, J. M. Medina-Sánchez2, C. Durán1, G. Herrera1, V. E. Villafañe3, and E. W. Helbling3 P. Carrillo et al.
  • 1Instituto Universitario de Investigación del Agua, Universidad de Granada, Granada, Spain
  • 2Departamento de Ecología, Facultad de Ciencias, Universidad de Granada, Granada, Spain
  • 3Estación de Fotobiología Playa Unión and Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) – Casilla de Correos No 15 (9103) Rawson, Chubut, Argentina

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 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). This did not occur in the low-UVR lake (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.

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Under UVR and stratification,the commensalistic algae-bacteria interaction was strengthened in the high-UVR lake, where excretion of organic carbon rates exceeded the bacterial carbon demand,but did not occur in the low-UVR lake.The greater UVR damage to algae and bacteria and the weakening of their commensalistic interaction found in the low-UVR lake indicates these lakes would be especially vulnerable to UVR. These results have implications for the C cycle in lakes of the Mediterranean region.
Under UVR and stratification,the commensalistic algae-bacteria interaction was strengthened in...
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