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ORIGINAL RESEARCH article
Front. Mar. Sci.
Sec. Marine Biology
Volume 11 - 2024 |
doi: 10.3389/fmars.2024.1455706
Varying photosynthetic quotients strongly influence net kelp primary production and seasonal differences increase under warming
Provisionally accepted- 1 Institute for Applied Ecology and Phycology, University of Rostock, Rostock, Germany
- 2 Helgoland Biological Research Institute (BAH), Helgoland, Bremen, Germany
- 3 Department of Geography, Faculty of Mathematics and Natural Sciences, University of Kiel, Kiel, Schleswig-Holstein, Germany
- 4 Department Maritime Systems, Interdisciplinary Faculty, University of Rostock, Rostock, Mecklenburg-Vorpommern, Germany
- 5 Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research (AWI), Bremerhaven, Bremen, Germany
- 6 Department of Ecology and Geology, Faculty of Science, Malaga University, Malaga, Spain
Reliable net primary production (NPP) estimations of kelp forests are important to evaluate their C-fixation potential. Oxygen evolution can be converted to C-fixation using photosynthetic quotients (PQs). Although high variability in PQs is known, the consequences for NPP are understudied in kelp species. The present study aimed (i) to quantify the variability of PQs, (ii) to model NPP and (iii) to assess the impact of warming on both. The kelp, Laminaria hyperborea, was studied near the island of Helgoland (North Sea, Germany) along a depth gradient (2, 4, 6 m below mean low water spring tide) across all four seasons. Blade discs were cultivated during at least 6 days per season under simulated ambient photon flux density (PFD) and temperature conditions and, in parallel, in a warming scenario (+ 4°C). PQs were calculated from parallel oxygen production and 14C-fixation measurements at saturating PFD at the end of the incubation period. Seasonal PQs varied between 1.7 and 4.4, with highest values in summer due to increased oxygen production. The warming scenario stimulated C-fixation in most seasons, lowering the PQ in comparison to ambient temperature conditions, while collection depth had no significant effect on PQs. The seasonal PQs were used to model daily NPP rates for kelp standing stock at 4 m depth. These daily NPP rates were compared between temperature treatments and with daily NPP rates based on fixed PQs. The warming scenario had a stimulating effect on daily NPP rates in the high-light season spring. In the low-light season autumn, warming resulted in negative daily NPP rates, as the high respiration rates could not be compensated by gross photosynthesis. Overall, annual NPP rate under warming conditions (347 g C m–2 yr–1) was 14% higher than the annual NPP rate under ambient conditions (303 g C m–2 yr–1). Modelling daily NPP with fixed PQs, which neglects the seasonal variation of the PQs, led to a high overestimation of up to 255%. We, therefore, recommend modelling NPP rates not with a fixed PQ, but with seasonal PQs determined under different temperature scenarios in order to obtain reliable future predictions.
Keywords: Net Primary Production, Laminaria hyperborea, 14 C-fixation, oxygen production, Photosynthetic quotient, Helgoland, Warming scenario
Received: 27 Jun 2024; Accepted: 09 Sep 2024.
Copyright: © 2024 Franke, Kroth, Karsten, Bartsch, Iñiguez and Graiff. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence:
Kiara Franke, Institute for Applied Ecology and Phycology, University of Rostock, Rostock, Germany
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