Spatial and temporal variation in nitrogen fixation and its importance to phytoplankton in phosphorus-rich lakes
Date
2018-11-27
Authors
Hayes, Nicole M.
Patoine, Alain
Haig, Heather A.
Simpson, Gavin L.
Swarbrick, Vanessa J.
Wiik, Emma
Leavitt, Peter R.
Journal Title
Journal ISSN
Volume Title
Publisher
Wiley
Abstract
- Limnological theory posits that phosphorus (P) limits primary production in freshwater lakes, in part because fixation of atmospheric nitrogen (N2) can compensate for limitations in nitrogen (N) supply to phytoplankton. However, quantitative estimates of the degree to which N2 fixation satisfies planktonic N demand are rare.
- Here we used biweekly sampling during summer in seven lakes over 2 decades to estimate both planktonic N2 fixation and phytoplankton N demand. We further assessed the ability of biologically fixed N to satisfy N needs of primary producers in productive hardwater lakes.
- Phytoplankton N requirements, derived from estimates of phytoplankton productivity and N content, were moderately synchronous (S = 0.41) among lakes (ca. 0.1–9.2 mg N m–3 hr–1). In contrast, rates of N2 fixation determined using isotopic natural abundance method (NAM; 0.002–3.2 mg N m–3 hr–1), or heterocyte-based calculations (0.10–1.78 mg N m–3 hr–1), varied asynchronously (SNAM = –0.03 and SHeterocyte = –0.11) among basins, accounted for a median of 3.5% (mean 11.3% ± 21.6) of phytoplankton demand, and were correlated to the abundance of Nostocales cyanobacteria when analysed using generalised additive models.
- Overall, the total mass of fixed N accounted for a median of only 3.0% of the spring standing stock of total dissolved N in study lakes (mean 7.5 ± 12.1%), with higher relative importance of fixed N in highly productive downstream lakes. Thus, while fixed N helps sustain primary productivity, particularly in years with high rates of N2-fixation, it does not appear to eliminate N limitation of phytoplankton growth in these P-rich hardwater lakes.
Description
© 2018 The Authors. Freshwater Biology published by John Wiley & Sons Ltd. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium,
provided the original work is properly cited.
Keywords
Citation
Hayes, NM, Patoine, A, Haig, HA, et al. Spatial and temporal variation in nitrogen fixation and its importance to phytoplankton in phosphorus-rich lakes. Freshw Biol. 2019; 64: 269– 283. https://doi.org/10.1111/fwb.13214