Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
Biogeosciences, 14, 1527-1539, 2017
https://doi.org/10.5194/bg-14-1527-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
24 Mar 2017
New insights on resource stoichiometry: assessing availability of carbon, nitrogen, and phosphorus to bacterioplankton
Ana R. A. Soares1, Ann-Kristin Bergström2, Ryan A. Sponseller2, Joanna M. Moberg1, Reiner Giesler4, Emma S. Kritzberg3, Mats Jansson2, and Martin Berggren1 1Department of Physical Geography and Ecosystem Science, Lund University, Lund, 22362, Sweden
2Department of Ecology and Environmental Science, Umeå University, Umeå, 90187, Sweden
3Department of Biology/Aquatic Ecology, Lund University, Lund, 22362, Sweden
4Climate Impacts Research Centre, Department of Ecology and Environmental Science, Umeå University, 98107 Abisko, Sweden
Abstract. Boreal lake and river ecosystems receive large quantities of organic nutrients and carbon (C) from their catchments. How bacterioplankton respond to these inputs is not well understood, in part because we base our understanding and predictions on total pools, yet we know little about the stoichiometry of bioavailable elements within organic matter. We designed bioassays with the purpose of exhausting the pools of readily bioavailable dissolved organic carbon (BDOC), bioavailable dissolved nitrogen (BDN), and bioavailable dissolved phosphorus (BDP) as fast as possible. Applying the method in four boreal lakes at base-flow conditions yielded concentrations of bioavailable resources in the range 105–693 µg C L−1 for BDOC (2 % of initial total DOC), 24–288 µg N L−1 for BDN (31 % of initial total dissolved nitrogen), and 0.2–17 µg P L−1 for BDP (49 % of initial total dissolved phosphorus). Thus, relative bioavailability increased from carbon (C) to nitrogen (N) to phosphorus (P). We show that the main fraction of bioavailable nutrients is organic, representing 80 % of BDN and 61 % of BDP. In addition, we demonstrate that total C : N and C : P ratios are as much as 13-fold higher than C : N and C : P ratios for bioavailable resource fractions. Further, by applying additional bioavailability measurements to seven widely distributed rivers, we provide support for a general pattern of relatively high bioavailability of P and N in relation to C. Altogether, our findings underscore the poor availability of C for support of bacterial metabolism in boreal C-rich freshwaters, and suggest that these ecosystems are very sensitive to increased input of bioavailable DOC.

Citation: Soares, A. R. A., Bergström, A.-K., Sponseller, R. A., Moberg, J. M., Giesler, R., Kritzberg, E. S., Jansson, M., and Berggren, M.: New insights on resource stoichiometry: assessing availability of carbon, nitrogen, and phosphorus to bacterioplankton, Biogeosciences, 14, 1527-1539, https://doi.org/10.5194/bg-14-1527-2017, 2017.
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