School of Earth, Environmental, & Marine Sciences Faculty Publications
Document Type
Article
Publication Date
1-11-2026
Abstract
The study goal was to examine the interactive physiological effects of two freshwater inflow stressors, nitrate pulses coupled with salinity decrease, on the seagrass Halodule wrightii. A microcosm experiment was designed to approximate an observed freshwater inflow event. Over a 13-day period plants were subjected to three sequential salinity drops (S35→ S23→ S15→ S5) with nitrate-nitrogen added simultaneously at 0, 30 or 60 µM. For comparisons, the Control was no salinity change and no nitrate added denoted by S35/No N. Measurements of H. wrightii shoot production, photosynthesis, respiration, quantum efficiency, %N, C:N ratios and δ15N values which were made after each salinity drop revealed differing effects of low versus high N levels under S35 compared to reduced salinity. Compared to the Control at the experimental endpoint, leaf net photosynthesis: respiration (P:R) ratio decreased 3-fold for hyposalinity + High N addition (S5/High N) largely due to increased respiration. Leaf %N increased and C:N ratio decreased concomitantly with both stressors, with S5/High N having the highest %N and lowest C:N ratio. While the magnitude of the effect was related to the amount of added N at S35, there were different effects of Low versus High N at low salinity (S5). The trends of P:R ratio, leaf %N and C:N ratio are consistent with increased respiration, uptake of added N, and depletion of carbon reserves. However, δ15N suggested that added NO3- was taken up by leaves at S35, but not at S5. The increased %N at S5 may be due to translocation of amino acid N from rhizomes-roots to leaves. Metabolic networks were hypothesized to be regulated differently at 30 versus 60 µM NO3- under conditions of hyposalinity. These findings add to the growing evidence that simultaneous stressors typical of substantial freshwater inflow events, hyposalinity and nitrate loading, could adversely affect H. wrightii.
Recommended Citation
Kowalski, Joseph L., Hudson DeYoe, Kirk Cammarata, and Kristina Vatcheva. "Interactive effects of hyposalinity and nitrate loading on growth, physiology, and nitrogen status of the seagrass, Halodule wrightii." Frontiers in Marine Science 12 (2025): 1712666. https://doi.org/10.3389/fmars.2025.1712666
Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 International License.
Publication Title
Frontiers in Marine Science
DOI
10.3389/fmars.2025.1712666
Comments
Copyright © 2026 Kowalski, DeYoe, Cammarata and Vatcheva. 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) and the copyright owner(s) 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.