Direct pathway of incorporating dietary nitrogen in shell-bound matrix of the planktic foraminifera Trilobatus sacculifer
Journal
Earth and Planetary Science Letters
Journal Volume
654
Start Page
119231
ISSN
0012-821X
Date Issued
2025-03
Author(s)
Fang, Wei-Ning
Branson, Oscar
Yang, Er-Wen
Chen, Wen-Hui
Cai-Li, Ren-Yi
Spero, Howard J.
Fehrenbacher, Jennifer
Vetter, Lael
LeKieffre, Charlotte
Abstract
The stable isotopes of organic nitrogen (N) preserved within the fossil tests of foraminifera have been used to reconstruct past changes in surface ocean nitrogen cycling processes. Modern observations show temporal and spatial covariations of δ15N between planktic foraminifera and particulate organic matter in the surface ocean, suggesting that heterotrophic foraminifera record the N isotopic compositions of their diet. However, little is known about the underlying mechanisms of N translocation from diet into foraminiferal biomass (i.e., intrashell protoplasm) and finally embedded within their mineralized shells. We investigate the pathways of N uptake from diet into foraminiferal calcite tests by feeding the planktic, dinoflagellate-bearing Trilobatus sacculifer with two strains of brine shrimp (Artemia) with different 15N/14N isotopic compositions, and monitoring the δ15N evolution of both biomass and shell-bound matrix. The two feeding groups show comparable results, that δ15N of both the biomass and shell-bound matrix evolve towards their diet sources without expressing trophic enrichment in δ15N. However, we observe that the δ15N of the biomass and shell-bound matrix exhibit distinct mixing behaviors. Biomass δ15N is well modelled as a mixture between the original biomass and newly metabolised dietary intake, suggesting T. sacculifer has a closed N system with minimum N leakage. Meanwhile, shell-bound δ15N quickly approaches the δ15N of the diet, and is offset from the biomass δ15N. This indicates a direct pathway of N incorporation from the diet into shell-bound organics during calcification, without significant exchange with the overall biomass pool.
Subjects
calcification
Foraminifera culturing
Foraminifera-bound δ15N
Nitrogen metabolism
Primary organic sheet
Trophic effects
Publisher
Elsevier BV
Type
journal article