Work

Interactive effects of hyposalinity and nitrate loading on growth, physiology, and nitrogen status of the seagrass, Halodule wrightii

Year: 2026

Type: article

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 µ M . 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 δ 15 N 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, δ 15 N 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 µ M 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 .

Source: Frontiers in Marine Science

DOI: 10.3389/fmars.2025.1712666

Authors: Joseph L. Kowalski, Hudson DeYoe, Kirk Cammarata, Kristina Vatcheva

Institutions: The University of Texas Rio Grande Valley, Texas A&M University – Corpus Christi

Language: English

Topic: Marine and coastal plant biology

Subfield: Oceanography

Field: Earth and Planetary Sciences

Domain: Physical Sciences

SDG: Clean water and sanitation

Open Access status: gold

Estimated APC paid: $3,801