An official website of the United States government
Abstract Coastal ecosystems are exposed to saltwater intrusion but differential effects on biogeochemical cycling are uncertain. We tested how elevated salinity and phosphorus (P) individually and interactively affect microbial activities and biogeochemical cycling in freshwater and brackish wetland soils. In experimental mesocosms, we added crossed gradients of elevated concentrations of soluble reactive P (SRP) (0, 20, 40, 60, 80 μg/L) and salinity (0, 4, 7, 12, 16 ppt) to freshwater and brackish peat soils (10, 14, 17, 22, 26 ppt) for 35 d. We quantified changes in water chemistry [dissolved organic carbon (DOC), ammonium (), nitrate + nitrite (N + N), SRP concentrations], soil microbial extracellular enzyme activities, respiration rates, microbial biomass C, and soil chemistry (%C, %N, %P, C:N, C:P, N:P). DOC, , and SRP increased in freshwater but decreased in brackish mesocosms with elevated salinity. DOC similarly decreased in brackish mesocosms with added P, and N + N decreased with elevated salinity in both freshwater and brackish mesocosms. In freshwater soils, water column P uptake occurred only in the absence of elevated salinity and when P was above 40 µg/L. Freshwater microbial EEAs, respiration rates, and microbial biomass C were consistently higher compared to those from brackish soils, and soil phosphatase activities and microbial respiration rates in freshwater soils decreased with elevated salinity. Elevated salinity increased arylsulfatase activities and microbial biomass C in brackish soils, and elevated P increased microbial respiration rates in brackish soils. Freshwater soil %C, %N, %P decreased and C:P and N:P increased with elevated salinity. Elevated P increased %C and C:N in freshwater soils and increased %P but decreased C:P and N:P in brackish soils. Freshwater soils released more C and nutrients than brackish soils when exposed to elevated salinity, and both soils were less responsive to elevated P than expected. Freshwater soils became more nutrient‐depleted with elevated salinity, whereas brackish soils were unaffected by salinity but increased P uptake. Microbial activities in freshwater soils were inhibited by elevated salinity and unaffected by added P, but brackish soil microbial activities slightly increased with elevated salinity and P.
more »
« less
This content will become publicly available on April 8, 2026
Impact of salinity on morphology, growth, and pigment profiles of Scenedesmus obliquus HTB1 under ambient air and elevated CO2 (10%) conditions
Certain microalgal species, such as Scenedesmus obliquus strain HTB1, thrive under high CO2 concentrations, making them promising for carbon sequestration to mitigate climate change. Isolated from the Baltimore Inner Harbor, HTB1 grows faster with 10 % CO2 than with ambient air. To investigate its responses to salinity and elevated CO2, two experiments were conducted. In the first, HTB1 was cultured at seven different salinities (0, 17.5, 20, 22.5, 25, 27.5, and 30 ppt) (parts per thousand) under ambient air. Higher salinity caused cell shrinkage, color changes from green to pale white, reduced pigments like zeaxanthin, lutein, and chlorophyll b, but increased canthaxanthin. Growth declined significantly above 22.5 ppt. The second experiment compared HTB1's response to salinity (0, 10, 20 ppt) under air and 10 % CO2. Cultures under 10 % CO2 showed minimal color changes, while those under air shifted from green to brown, with salinity having less inhibitory effects on growth under elevated CO2. Interestingly, lutein and canthaxanthin levels rose with salinity in 10 % CO2. These findings indicate that elevated CO2 mitigates salt stress in HTB1, reducing its impact on growth and promoting adaptive pigment changes. This study sheds light on how salinity and CO2 interact to influence HTB1's morphology, growth, and pigment composition, enhancing our understanding of its resilience and potential applications.
more »
« less
- Award ID(s):
- 2344228
- PAR ID:
- 10644337
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- Algal Research
- Volume:
- 88
- ISSN:
- 2211-9264
- Page Range / eLocation ID:
- 104027
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Coastal wetlands are globally important stores of carbon (C). However, accelerated sea-level rise (SLR), increased saltwater intrusion, and modified freshwater discharge can contribute to the collapse of peat marshes, converting coastal peatlands into open water. Applying results from multiple experiments from sawgrass (Cladium jamaicense)-dominated freshwater and brackish water marshes in the Florida Coastal Everglades, we developed a system-level mechanistic peat elevation model (EvPEM). We applied the model to simulate net ecosystem C balance (NECB) and peat elevation in response to elevated salinity under inundation and drought exposure. Using a mass C balance approach, we estimated net gain in C and corresponding export of aquatic fluxes ( ) in the freshwater marsh under ambient conditions (NECB = 1119 ± 229 gC m−2 year−1; FAQ = 317 ± 186 gC m−2 year−1). In contrast, the brackish water marsh exhibited substantial peat loss and aquatic C export with ambient (NECB = −366 ± 15 gC m−2 year−1; FAQ = 311 ± 30 gC m−2 year−1) and elevated salinity (NECB = −594 ± 94 gC m−2 year−1; FAQ = 729 ± 142 gC m−2 year−1) under extended exposed conditions. Further, mass balance suggests a considerable decline in soil C and corresponding elevation loss with elevated salinity and seasonal dry-down. Applying EvPEM, we developed critical marsh net primary productivity (NPP) thresholds as a function of salinity to simulate accumulating, steady-state, and collapsing peat elevations. The optimization showed that ~150–1070 gC m−2 year−1 NPP could support a stable peat elevation (elevation change ≈ SLR), with the corresponding salinity ranging from 1 to 20 ppt under increasing inundation levels. The C budgeting and modeling illustrate the impacts of saltwater intrusion, inundation, and seasonal dry-down and reduce uncertainties in understanding the fate of coastal peat wetlands with SLR and freshwater restoration. The modeling results provide management targets for hydrologic restoration based on the ecological conditions needed to reduce the vulnerability of the Everglades' peat marshes to collapse. The approach can be extended to other coastal peatlands to quantify C loss and improve understanding of the influence of the biological controls on wetland C storage changes for coastal management.more » « less
-
Cyanobacterium Microcoleus anatoxicus, isolated from a coastal stream in northern California, produces both anatoxin-a (ATX) and dihydroanatoxin- a (dhATX), responsible for dog deaths, but its environmental preferences are unknown. We tested the effect of environmentally relevant stressors, e.g., salinity enrichment and nitrogen (N) depletion, on mat formation and toxicity of M. anatoxicus during the stationary growth phase in culture. Microcoleus anatoxicus showed broad salinity tolerance and the potential to enter estuaries and produce toxins in mesohaline conditions. Maximum growth was observed in oligohaline waters with salinity of 4.6 ppt. Moderate salinity stress (up to 7.8 ppt) did not affect dhATX production significantly. In contrast, higher salinity above 9.3 ppt had a detrimental effect on cell growth and significantly suppressed dhATX production. Formation of a common polysaccharide sheath covering multiple filaments was characteristic with increased salinity and may provide protection against osmotic stress. Microcoleus anatoxicus grown for 40 days in N-depleted medium formed mats with significantly elevated dhATX and increased ATX concentrations. Phycobilisome degradation was a possible acclimation response to N-limitation, as indicated by distinctly keritomized and pale cells in these cultures. In both experiments, most of the anatoxins were extracellular,probably due to toxin leaking during the stationary growth phase.more » « less
-
Ball, Marilyn (Ed.)Abstract Temperature and salinity are important regulators of mangrove range limits and productivity, but the physiological responses of mangroves to the interactive effects of temperature and salinity remain uncertain. We tested the hypothesis that salinity alters photosynthetic responses to seasonal changes in temperature and vapor pressure deficit (D), as well as thermal acclimation _of leaf respiration in black mangrove (Avicennia germinans). To test this hypothesis, we grew seedlings of A. germinans in an outdoor experiment for ~ 12 months under four treatments spanning 0 to 55 ppt porewater salinity. We repeatedly measured seedling growth and in situ rates of leaf net photosynthesis (Asat) and stomatal conductance to water vapor (gs) at prevailing leaf temperatures, along with estimated rates of Rubisco carboxylation (Vcmax) and electron transport for RuBP regeneration (Jmax), and measured rates of leaf respiration at 25 °C (Rarea25). We developed empirical models describing the seasonal response of leaf gas exchange and photosynthetic capacity to leaf temperature and D, and the response of Rarea25 to changes in mean daily air temperature. We tested the effect of salinity on model parameters. Over time, salinity had weak or inconsistent effects on Asat, gs and Rarea25. Salinity also had little effect on the biochemical parameters of photosynthesis (Vcmax, Jmax) and individual measurements of Asat, gs, Vcmax and Jmax showed a similar response to seasonal changes in temperature and D across all salinity treatments. Individual measurements of Rarea25 showed a similar inverse relationship with mean daily air temperature across all salinity treatments. We conclude that photosynthetic responses to seasonal changes in temperature and D, as well as seasonal temperature acclimation of leaf R, are largely consistent across a range of salinities in A. germinans. These results might simplify predictions of photosynthetic and respiratory responses to temperature in young mangroves.more » « less
-
This review focuses on recently characterized traits of the aquatic floating plant Lemna with an emphasis on its capacity to combine rapid growth with the accumulation of high levels of the essential human micronutrient zeaxanthin due to an unusual pigment composition not seen in other fast-growing plants. In addition, Lemna’s response to elevated CO2 was evaluated in the context of the source–sink balance between plant sugar production and consumption. These and other traits of Lemnaceae are compared with those of other floating aquatic plants as well as terrestrial plants adapted to different environments. It was concluded that the unique features of aquatic plants reflect adaptations to the freshwater environment, including rapid growth, high productivity, and exceptionally strong accumulation of high-quality vegetative storage protein and human antioxidant micronutrients. It was further concluded that the insensitivity of growth rate to environmental conditions and plant source–sink imbalance may allow duckweeds to take advantage of elevated atmospheric CO2 levels via particularly strong stimulation of biomass production and only minor declines in the growth of new tissue. It is proposed that declines in nutritional quality under elevated CO2 (due to regulatory adjustments in photosynthetic metabolism) may be mitigated by plant–microbe interaction, for which duckweeds have a high propensity.more » « less
