Skip to main content
Dryad logo

The dynamics and stoichiometry of dissolved organic carbon release by kelp: Carbon fixation, DOC release and nutrient uptake data

Citation

Weigel, Brooke; Pfister, Catherine (2020), The dynamics and stoichiometry of dissolved organic carbon release by kelp: Carbon fixation, DOC release and nutrient uptake data, Dryad, Dataset, https://doi.org/10.5061/dryad.djh9w0vxp

Abstract

Canopy-forming kelps are foundational species in coastal ecosystems, fixing tremendous amounts of carbon, yet we know little about the ecological and physiological determinants of dissolved organic carbon (DOC) release by kelps. We examined DOC release by the bull kelp, Nereocystis luetkeana, in relation to carbon fixation, nutrient uptake, tissue nitrogen content, and light availability. DOC release was approximately 3.5 times greater during the day than at night. During the day, N. luetkeana blades released an average of 16.2% of fixed carbon as DOC. Carbon fixation increased with light availability but DOC release did not, leading to a lower proportion of fixed carbon released as DOC at high light levels. We found no relationship between carbon fixation and DOC release rates measured concurrently. Rather, DOC release by N. luetkeana blades declined with marginal significance as blade tissue nitrogen content increased and with experimental nitrate addition, supporting the role of stoichiometric relationships in DOC release. Using a stable isotope (13C) tracer method, we demonstrated that inorganic carbon is rapidly fixed and released by N. luetkeana blades as 13DOC, within hours. However, recently fixed carbon (13DOC) comprised less than 20% of the total DOC released, indicating that isotope studies that rely on tracer production alone may underestimate total DOC release, as it is decoupled from recent kelp productivity. Comparing carbon and nitrogen assimilation dynamics of the annual kelp N. luetkeana with the perennial kelp Macrocystis pyrifera revealed that N. luetkeana had significantly higher carbon fixation, DOC production and nitrogen uptake rates per unit dry mass. Both kelp species were able to perform light-independent carbon fixation at night. Carbon fixation by the annual kelp N. luetkeana is as high as 2.35 kg C m-2 yr-1, but an average of 16% of this carbon (376 g C m-2 yr-1) is released as DOC. As kelp forests are increasingly viewed as vehicles for carbon sequestration, it is important to consider the fate of this substantial quantity of DOC released by canopy-forming kelps.

Methods

This dataset is derived from the publication "The dynamics and stoichiometry of dissolved organic carbon release by kelp," and it contains all values for replicate measurements of carbon fixation, DOC release, 13-DOC release, and nutrient uptake rates by Nereocystis luetkeana and Macrocystis pyrifera kelp blades. All methods are listed in the Methods section of the published manuscript, and detailed equations used to calculate carbon fixation via 13C-bicarbonate assimilation, DOC and 13-DOC release and nutrient uptake can be found in the manuscript Appendix S1: Sections S1-S4. 

Usage Notes

In the table, the first row contains a description of each data column, while the second row contains a description of the units. Note that for the Squaxin Island nitrate addition experiment, DOC release and 13-DOC release measurements on the same kelp blade at both 3 hours and 8 hours are listed in the table.

Funding

National Geographic Society, Award: Early Career Grant

National Oceanic and Atmospheric Administration, Award: NA16OAR431055

National Science Foundation, Award: 1556874

Washington State Department of Natural Resources, Award: 93099282

Washington State Department of Natural Resources, Award: 93099282