DOI: 10.5061/dryad.djh9w0vxp
title: The dynamics and stoichiometry of dissolved organic carbon release by kelp: Carbon fixation, DOC release and nutrient uptake data

description: 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.
description: 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 <i>Nereocystis
 luetkeana </i>and <i>Macrocystis pyrifera </i>kelp
 blades. All methods are listed in the Methods section of the published
 manuscript, and detailed equations used to calculate carbon fixation via
 <sup>13</sup>C-bicarbonate assimilation, DOC and 13-DOC
 release and nutrient uptake can be found in the manuscript Appendix S1:
 Sections S1-S4. 
description: 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.