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Aquatic Microbial Ecology

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AME 64:285-298 (2011)  -  DOI:

Dynamics of extracellular enzyme activities in seawater under changed atmospheric pCO2: a mesocosm investigation

C. Arnosti1,*, H. P. Grossart2, M. Mühling3,4, I. Joint4, U. Passow5,6

1Department of Marine Sciences, University of North Carolina, Chapel Hill,27599 North Carolina, USA
2Leibniz Institute of Freshwater Ecology and Inland Fisheries, 16775 Neuglobsow, Germany
3Institute of Biological Sciences, TU Bergakademie Freiberg, 09599 Freiberg, Germany
4Plymouth Marine Laboratory, Prospect Place, The Hoe, Plymouth, PLI 3DH, UK
5Alfred-Wegener Institute for Polar and Marine Research, 27575 Bremerhaven, Germany
6Marine Sciences Institute, University of California, Santa Barbara, 93106 California, USA

ABSTRACT: As part of the PeECE II mesocosm project, we investigated the effects of pCO2 levels on the initial step of heterotrophic carbon cycling in the surface ocean. The activities of microbial extracellular enzymes hydrolyzing 4 polysaccharides were measured during the development of a natural phytoplankton bloom under pCO2 conditions representing glacial (190 µatm) and future (750 µatm) atmospheric pCO2. We observed that (1) chondroitin hydrolysis was variable throughout the pre-, early- and late-bloom phases, (2) fucoidanase activity was measurable only in the glacial mesocosm as the bloom developed, (3) laminarinase activity was low and constant, and (4) xylanase activity declined as the bloom progressed. Concurrent measurements of microbial community composition, using denaturing-gradient gel electrophoresis (DGGE), showed that the 2 mesocosms diverged temporally, and from one another, especially in the late-bloom phase. Enzyme activities correlated with bloom phase and pCO2, suggesting functional as well as compositional changes in microbial communities in the different pCO2 environments. These changes, however, may be a response to temporal changes in the development of phytoplankton communities that differed with the pCO2 environment. We hypothesize that the phytoplankton communities produced dissolved organic carbon (DOC) differing in composition, a hypothesis supported by changing amino acid composition of the DOC, and that enzyme activities responded to changes in substrates. Enzyme activities observed under different pCO2 conditions likely reflect both genetic and population-level responses to changes occurring among multiple components of the microbial loop.

KEY WORDS: Enzyme · Carbon cycle · pCO2 changes · Microbial loop

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Cite this article as: Arnosti C, Grossart HP, Mühling M, Joint I, Passow U (2011) Dynamics of extracellular enzyme activities in seawater under changed atmospheric pCO2: a mesocosm investigation. Aquat Microb Ecol 64:285-298.

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