nutrients Archives - Page 3 of 19

Posts Tagged 'nutrients'

Combined effects of ocean deoxygenation, acidification, and phosphorus limitation on green tide macroalga, Ulva prolifera

Published 29 June 2023 Science Closed
Tags: algae, biogeochemistry, biological response, growth, laboratory, multiple factors, North Pacific, nutrients, oxygen, photosynthesis, physiology

Highlights

Additive and antagonistic interactions between the three stressors were mainly observed.
Ocean deoxygenation, acidification, and P limitation can dysregulate the Ulva prolifera of photosynthetic efficiency.
Green tide macroalgal Ulva prolifera has a strong acclimation capacity to elevated CO₂, low O₂, and high N/P.
Ulva prolifera could use organic P to support its growth under low inorganic phosphorus conditions.
Increased CO₂ levels can decrease the energy costs associated with CCM, and can support the growth of macroalgal cells.

Abstract

Ocean deoxygenation, acidification, and decreased phosphorus availability are predicted to increase in coastal ecosystems under future climate change. However, little is known regarding the combined effects of such environmental variables on the green tide macroalga Ulva prolifera. Here, we provide quantitative and mechanistic understanding of the acclimation mechanisms of U. prolifera to ocean deoxygenation, acidification, and phosphorus limitation under both laboratory and semi-natural (mesocosms) conditions. We found that there were significant interactions between these global environmental conditions on algal physiological performance. Although algal growth rate and photosynthesis reduced when the nitrogen-to‑phosphorus (N/P) ratio increased from 16:1 to 35:1 under ambient CO₂ and O₂ condition, they remained constant with further increasing N/P ratios of 105:1, 350:1, and 1050:1. However, the increasing alkaline phosphatase activities at high N/P ratios suggests that U. prolifera could use organic P to support its growth under phosphorus limitation. Deoxygenation had no effect on specific growth rate (SGR) but decreased photosynthesis under low N/P ratios of 16:1, 35:1, and 105:1, with reduced activities of several enzymes involved in N assimilation pathway being observed. Elevated CO₂ promoted algal growth and alleviated the negative effect of deoxygenation on algal photosynthesis. The patterns of responses to high CO₂ and low O₂ treatments in in situ experiments were generally consistent with those observed in laboratory experiments. Our results generally found that the strong physiological acclimation capacity to elevated CO₂, low O₂, and high N/P could contribute to its large-scale blooming in coastal ecosystem.

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Simulated upwelling and marine heatwave events promote similar growth rates but differential domoic acid toxicity in Pseudo-nitzschia australis

Published 28 June 2023 Science Closed
Tags: abundance, biogeochemistry, biological response, laboratory, multiple factors, North Pacific, nutrients, otherprocess, physiology, phytoplankton, temperature

Along the west coast of the United States, highly toxic Pseudo-nitzschia blooms have been associated with two contrasting regional phenomena: seasonal upwelling and marine heatwaves. While upwelling delivers cool water rich in pCO₂ and an abundance of macronutrients to the upper water column, marine heatwaves instead lead to warmer surface waters, low pCO₂, and reduced nutrient availability. Understanding Pseudo-nitzschia dynamics under these two conditions is important for bloom forecasting and coastal management, yet the mechanisms driving toxic bloom formation during contrasting upwelling vs. heatwave conditions remain poorly understood. To gain a better understanding of what drives Pseudo-nitzschia australis growth and toxicity during these events, multiple-driver scenario or ‘cluster’ experiments were conducted using temperature, pCO₂, and nutrient levels reflecting conditions during upwelling (13 °C, 900 ppm pCO₂, replete nutrients) and two intensities of marine heatwaves (19 °C or 20.5 °C, 250 ppm pCO₂, reduced macronutrients). While P. australis grew equally well under both heatwave and upwelling conditions, similar to what has been observed in the natural environment, cells were only toxic in the upwelling treatment. We also conducted single-driver experiments to gain a mechanistic understanding of which drivers most impact P. australis growth and toxicity. These experiments indicated that nitrogen concentration and N:P ratio were likely the drivers that most influenced domoic acid production, while the impacts of temperature or pCO₂ concentration were less pronounced. Together, these experiments may help to provide both mechanistic and holistic perspectives on toxic P. australis blooms in the dynamic and changing coastal ocean, where cells interact simultaneously with multiple altered environmental variables.

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Growth performance, antioxidant indexes, and the expression of genes were considerably promoted by dietary supplementation of alanyl-glutamine and vitamin E in juvenile marine medaka in seawater acidification by carbon dioxide

Published 26 June 2023 Science Closed
Tags: biological response, fish, growth, laboratory, molecular biology, morphology, mortality, multiple factors, North Pacific, nutrients, physiology

The experiment was conducted to study the effect of different dietary supplementation of alanyl-glutamine dipeptide (AGD) and/or vitamin E (VE) on the growth performance, antioxidant indexes, and the expression of glutathione peroxidase (GPx) and peroxisome proliferator-activated receptor α (PPAR_Ɑ) genes in juvenile marine medaka (Oryzias melastigma) in seawater acidification. Seven groups of juvenile marine medaka in triplicate were studied in an ecosystem. One of them was in normal seawater (pH 8.1, pH control), and the others were in seawater acidification (pH 7.7) regulated by carbon dioxide (CO₂). The juveniles were separately fed for 10 weeks using one of six different diets. The six diets were one control diet (basic feed) without supplements and the other diets with different amounts of additional AGD and/or VE. The juveniles were sampled randomly for analysis of a whole fish in week 0 and week 10. The results showed that different dietary supplementation of AGD and/or VE could considerably promote the growth performance, antioxidant indexes, and the expression of GPx and PPARα genes of juvenile marine medaka in seawater acidification. The optimal diet was D4, with additional AGD 5 g and VE 50 IU per kg of dried feed.

Continue reading ‘Growth performance, antioxidant indexes, and the expression of genes were considerably promoted by dietary supplementation of alanyl-glutamine and vitamin E in juvenile marine medaka in seawater acidification by carbon dioxide’

Variable food alters responses of larval crown-of-thorns starfish to ocean warming but not acidification

Published 20 June 2023 Science Closed
Tags: biological response, echinoderms, laboratory, morphology, mortality, multiple factors, nutrients, performance, South Pacific, temperature

Phytoplankton abundance is decreasing and becoming more variable as the ocean climate changes. We examine how low, high, and variable phytoplankton food supply affected the survival, development, and growth of larval crown-of-thorns starfish, Acanthaster sp. exposed to combined warming (26, 30 °C) and acidification (pH 8.0, 7.6). Larvae fed a low food ration are smaller, and develop slower and with more abnormalities than larvae fed a high ration. Larvae fed a variable food supply (low, followed by high ration) overcome the negative effects of low food on development rate and occurrence of abnormalities, but are 16–17% smaller than larvae fed the high ration continuously. Acidification (pH 7.6) slows growth and development and increases abnormalities regardless of the food regime. Warming slows growth and development, but these effects are mitigated by high food availability. As tropical oceans warm, the success of crown-of-thorns starfish larvae may depend on the abundance of their phytoplankton prey.

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Phosphate limitation and ocean acidification co-shape phytoplankton physiology and community structure

Published 16 May 2023 Science Closed
Tags: biological response, BRcommunity, multiple factors, nutrients, physiology, phytoplankton, review

A new study reports synergistic inhibitory effects of ocean acidification and phosphate limitation on the nitrogen-fixing capacity of a globally important cyanobacterium species. Inspired by the report, this Comment presents the complexity of how ocean acidification and phosphate limitation affect phytoplankton physiologies and species beyond nitrogen fixation and cyanobacteria, and what future research is needed to address the remaining crucial questions.

Increasing CO₂ emission and climate change have manifold impacts on ocean primary production and carbon sequestration. One of the direct effects comes from ocean acidification due to the dissolution of ~30% of the increased CO₂ into the ocean, whereas indirect impacts mainly stem from warming-driven ocean stratification that impedes upwelling of nutrient-rich deep waters leading to oligotrophication of the vast central ocean basin¹. Between nitrogen and phosphate, the two major productivity-limiting nutrients, phosphate is the ‘ultimate’ limiting nutrient as it has no biogenic source, and its growth-limiting condition in the oceans is more prevalent than previously thought². Nitrogen, in contrast, can be sourced from the atmosphere by diazotrophic bacteria through nitrogen fixation, which is often co-limited by phosphate and iron scarcity².

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Responses of biogenic dimethylated sulfur compounds to environmental changes in the northwestern Pacific continental sea

Published 11 May 2023 Science Closed
Tags: abundance, biogeochemistry, biological response, BRcommunity, community composition, laboratory, molecular biology, multiple factors, North Pacific, nutrients, otherprocess, phytoplankton, prokaryotes

Continental seas are facing rapid environmental shifts, but how biogenic dimethylated sulfur compounds, including dimethylsulfide (DMS), dimethylsulfoniopropionate (DMSP), and dimethylsulfoxide (DMSO), will respond to these environmental changes remains poorly understood. Here we investigated the effects of nutrient input, ocean acidification, and dust deposition on the phytoplankton community and organic sulfur cycle in the East China Sea. Nutrient input promoted phytoplankton growth and increased the concentrations of DMS, DMSP, and DMSO. With sufficient nutrients, especially nitrate, the dissolved DMSP degradation was inhibited, and the bacterial DMSP-cleavage pathway (inferred by dddP gene abundance) was enhanced, causing increased DMS production. The sensitivity of phytoplankton biomass and DMS to ocean acidification varied with different initial nutrient levels, demonstrating insensitivity under eutrophic conditions and negative responses under nutrient-limited conditions. The ocean acidification promoted the dissolved DMSP degradation and bacterial DMSP-demethylation pathway (inferred by dmdA gene abundance) and weakened the DMS production, causing the decreases of DMS and DMSP. The nutrient from dust deposition (2 mg L⁻¹) was identified as the key factor in enhancing phytoplankton biomass and the organic sulfur compounds concentrations, but trace metals input from dust deposition had no significant effect. This study has identified environmental drivers and suppressors of phytoplankton and biogenic dimethylated sulfur compounds in a changing marine environment, which will enable the effective modeling of future climate change.

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Short-term responses of Corallina officinalis (rhodophyta) to global-change drivers in a stressful environment of Patagonia, Argentina

Published 28 April 2023 Science Closed
Tags: biological response, corals, laboratory, light, multiple factors, nutrients, physiology, primary production, South Atlantic

Over the last two decades, an increasing interest has arisen in the responses of primary producers to global-change drivers and, more recently, in the need to consider how those various drivers may interact. To understand how Corallina officinalis (hereafter Corallina) can be affected by future changing conditions, we investigated the short-term direct effects of co-occurring increased nutrient loads, solar radiation, and lower pH, assessing how these clustered drivers affected Corallina‘s overall physiological performance in a harsh Patagonian coastal environment. To describe the seasonal trend of the physiological parameters in the field, we sampled subtidal Corallina to determine their net oxygen production (NOP), pigments, and carbonate content (CC). Furthermore, we conducted seasonal 10-days experiments, simulating the conditions predicted for the year 2100 by the IPCC (RCP 8.5) —manipulating pH, nutrients, and irradiance—along with the current conditions. The pigments and carotenoids/chlorophyll-a ratio were, in general, constant in the field over the seasons; but the NOP and CC dropped in spring, when the carotenoids peaked. After the experiment, the highest carotenoid/chlorophyll-a ratio was registered in summer under both the currentand the predictedconditions and in winter under the predictedcondition. This lower physiological status was also reflected in almost all other variables. Thus, Corallina may display an acclimatation strategy to cope with high ultraviolet-radiation levels by adjusting its pigment composition to avoid photoinhibition. An understanding of how Corallina, as a habitat-forming species, will respond to future global-change may provide clues about the extent of effects on the ecosystem functions and services.

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Reallocation of elemental content and macromolecules in the coccolithophore Emiliania huxleyi to acclimate to climate change

Published 14 April 2023 Science Closed
Tags: biological response, growth, laboratory, light, multiple factors, nutrients, photosynthesis, physiology, phytoplankton

Global climate change leads to simultaneous changes in multiple environmental drivers in the marine realm. Although physiological characterization of coccolithophores has been studied under climate change, there is limited knowledge on the biochemical responses of this biogeochemically important phytoplankton group to changing multiple environmental drivers. Here, we investigate the interactive effects of reduced phosphorus availability (4 to 0.4 µmol L⁻¹), elevated pCO₂ concentrations (426 to 946 µatm), and increasing light intensity (40 to 300 µmol photons m⁻² s⁻¹) on elemental content and macromolecules of the cosmopolitan coccolithophore Emiliania huxleyi. Reduced phosphorus availability reduces particulate organic nitrogen (PON) and protein contents per cell under 40 µmol photons m⁻² s⁻¹ but not under 300 µmol photons m⁻² s⁻¹. Reduced phosphorus availability and elevated pCO₂ concentrations act synergistically to increase particulate organic carbon (POC) and carbohydrate contents per cell under 300 µmol photons m⁻² s⁻¹ but not under 40 µmol photons m⁻² s⁻¹. Reduced phosphorus availability, elevated pCO₂ concentrations, and increasing light intensity act synergistically to increase the allocation of POC to carbohydrates. Under elevated pCO₂ concentrations and increasing light intensity, enhanced carbon fixation could increase carbon storage in the phosphorus-limited regions of the oceans where E. huxleyi dominates the phytoplankton assemblages. In each type of light intensity, elemental-carbon-to-phosphorus (C:P) and nitrogen-to-phosphorus (N:P) ratios decrease with increasing growth rate. These results suggest that coccolithophores could reallocate chemical elements and energy to synthesize macromolecules efficiently, which allows them to regulate their elemental content and growth rate to acclimate to changing environmental conditions.

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Increased food resources help eastern oyster mitigate the negative impacts of coastal acidification

Published 11 April 2023 Science Closed
Tags: adaptation, biological response, growth, laboratory, mollusks, mortality, multiple factors, nutrients, otherprocess, performance, physiology, respiration

Oceanic absorption of atmospheric CO2 results in alterations of carbonate chemistry, a process coined ocean acidification (OA). The economically and ecologically important eastern oyster (Crassostrea virginica) is vulnerable to these changes because low pH hampers CaCO3 precipitation needed for shell formation. Organisms have a range of physiological mechanisms to cope with altered carbonate chemistry; however, these processes can be energetically expensive and necessitate energy reallocation. Here, the hypothesis that resilience to low pH is related to energy resources was tested. In laboratory experiments, oysters were reared or maintained at ambient (400 ppm) and elevated (1300 ppm) pCO2 levels during larval and adult stages, respectively, before the effect of acidification on metabolism was evaluated. Results showed that oysters exposed to elevated pCO2 had significantly greater respiration. Subsequent experiments evaluated if food abundance influences oyster response to elevated pCO2. Under high food and elevated pCO2 conditions, oysters had less mortality and grew larger, suggesting that food can offset adverse impacts of elevated pCO2, while low food exacerbates the negative effects. Results also demonstrated that OA induced an increase in oyster ability to select their food particles, likely representing an adaptive strategy to enhance energy gains. While oysters appeared to have mechanisms conferring resilience to elevated pCO2, these came at the cost of depleting energy stores, which can limit the available energy for other physiological processes. Taken together, these results show that resilience to OA is at least partially dependent on energy availability, and oysters can enhance their tolerance to adverse conditions under optimal feeding regimes.

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Sediment-seawater exchange altered adverse effects of ocean acidification towards marine microalgae

Published 30 March 2023 Science Closed
Tags: biological response, BRcommunity, community composition, growth, laboratory, metals, multiple factors, North Pacific, nutrients, otherprocess, photosynthesis, physiology, phytoplankton, sediment

Highlights

Five marine microalgal species showed different sensitivities to OA.
OA promoted algal growth except I. galbana after introducing sediments.
N, P and Fe released from sediments mitigated OA-induced toxicity to E. huxleyi.
OA-induced algal community instability was alleviated by the presence of sediments.

Abstract

Ocean acidification (OA) exhibits high threat to marine microalgae. However, the role of marine sediment in the OA-induced adverse effect towards microalgae is largely unknown. In this work, the effects of OA (pH 7.50) on the growth of individual and co-cultured microalgae (Emiliania huxleyi, Isochrysis galbana, Chlorella vulgaris, Phaeodactylum tricornutum, and Platymonas helgolandica tsingtaoensis) were systematically investigated in the sediment-seawater systems. OA inhibited E. huxleyi growth by 25.21 %, promoted P. helgolandica (tsingtaoensis) growth by 15.49 %, while did not cause any effect on the other three microalgal species in the absence of sediment. In the presence of the sediment, OA-induced growth inhibition of E. huxleyi was significantly mitigated, because the released chemicals (N, P and Fe) from seawater-sediment interface increased the photosynthesis and reduced oxidative stress. For P. tricornutum, C. vulgaris and P. helgolandica (tsingtaoensis), the growth was significantly increased in the presence of sediment in comparison with those under OA alone or normal seawater (pH 8.10). For I. galbana, the growth was inhibited when the sediment was introduced. Additionally, in the co-culturing system, C. vulgaris and P. tricornutum were the dominant species, while OA increased the proportions of dominant species and decreased the community stability as indicated by Shannon and Pielou’s indexes. After the introduction of sediment, the community stability was recovered, but remained lower than that under normal condition. This work demonstrated the role of sediment in the biological responses to OA, and could be helpful for better understanding the impact of OA on marine ecosystems.

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Effects of ocean acidification and eutrophication on the growth and photosynthetic performances of a green tide alga Ulva prolifera

Published 17 March 2023 Science Closed
Tags: algae, biological response, growth, laboratory, multiple factors, North Pacific, nutrients, photosynthesis, physiology

With the impact of fossil fuel burning and industrialization, atmospheric CO₂ concentration will reach about 1000 ppmv in 2100, and more and more CO₂ will be absorbed by ocean, resulting in ocean acidification. The Chinese coastal waters are showing unexpectedly high levels of acidification due to a combination of global ocean acidification and severe regional eutrophication, which is caused by natural accumulation or human activities such as aquacultural tail water input, potentially affecting macroalgal blooms. However, little is known about the combined effects of ocean acidification and entrophication on the eco-physiology of bloom-forming macroalgae. This study investigated Ulva prolifera, a dominant species causing green tide in the South Yellow Sea, and explored its growth and physiological responses under the combination conditions of ocean acidification and enriched nutrients. In this study, U. prolifera thalli were cultured under two CO₂ conditions (air and 1000 μatm) and two nutrient conditions (High Nutrient, HN, 135 μmol L^-1 N and 8.5 μmol L^-1 P; Normal Nutrient, NN, 27 μmol L^-1 N and 1.7 μmol L^-1 P). The results showed that eutrophication conditions obviously enhanced the relative growth rate and photosynthetic performance of U. prolifera. Elevated pCO₂ had no significant effect on U. prolifera growth and photosynthetic performance under normal nutrient conditions. However, under eutrophication conditions elevated pCO₂ inhibited U. prolifera growth. Moreover, eutrophication conditions markedly improved the contents of chlorophyll a, chlorophyll b and nitrate reductase activity and inhibited the soluble carbohydrate content, but elevated pCO₂ had no significant effect on them under nutrient-replete conditions. In addition, elevated pCO₂ significantly reduced the carotenoid content under eutrophication conditions and had no effect on it under normal nutrient conditions. These findings indicate that seawater eutrophication would greatly accelerate U. prolifera bloom, which may also be suppressed to a certain extent by ocean acidification in the future. The study can provide valuable information for predicting the future outbreaks of U. prolifera green tide in nearshore regions.

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Aquatic productivity under multiple stressors

Published 13 March 2023 Science Closed
Tags: biological response, light, multiple factors, nutrients, oxygen, photosynthesis, phytoplankton, review, temperature

Aquatic ecosystems are responsible for about 50% of global productivity. They mitigate climate change by taking up a substantial fraction of anthropogenically emitted CO₂ and sink part of it into the deep ocean. Productivity is controlled by a number of environmental factors, such as water temperature, ocean acidification, nutrient availability, deoxygenation and exposure to solar UV radiation. Recent studies have revealed that these factors may interact to yield additive, synergistic or antagonistic effects. While ocean warming and deoxygenation are supposed to affect mitochondrial respiration oppositely, they can act synergistically to influence the migration of plankton and N₂-fixation of diazotrophs. Ocean acidification, along with elevated pCO₂, exhibits controversial effects on marine primary producers, resulting in negative impacts under high light and limited availability of nutrients. However, the acidic stress has been shown to exacerbate viral attacks on microalgae and to act synergistically with UV radiation to reduce the calcification of algal calcifiers. Elevated pCO₂ in surface oceans is known to downregulate the CCMs (CO₂ concentrating mechanisms) of phytoplankton, but deoxygenation is proposed to enhance CCMs by suppressing photorespiration. While most of the studies on climate-change drivers have been carried out under controlled conditions, field observations over long periods of time have been scarce. Mechanistic responses of phytoplankton to multiple drivers have been little documented due to the logistic difficulties to manipulate numerous replications for different treatments representative of the drivers. Nevertheless, future studies are expected to explore responses and involved mechanisms to multiple drivers in different regions, considering that regional chemical and physical environmental forcings modulate the effects of ocean global climate changes.

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Predicting effects of multiple interacting global change drivers across trophic levels

Published 8 March 2023 Science Closed
Tags: biological response, community composition, communitymodeling, metals, modeling, multiple factors, nutrients, otherprocess, predation, review, temperature, toxicants

Global change encompasses many co-occurring anthropogenic drivers, which can act synergistically or antagonistically on ecological systems. Predicting how different global change drivers simultaneously contribute to observed biodiversity change is a key challenge for ecology and conservation. However, we lack the mechanistic understanding of how multiple global change drivers influence the vital rates of multiple interacting species. We propose that reaction norms, the relationships between a driver and vital rates like growth, mortality, and consumption, provide insights to the underlying mechanisms of community responses to multiple drivers. Understanding how multiple drivers interact to affect demographic rates using a reaction-norm perspective can improve our ability to make predictions of interactions at higher levels of organization—that is, community and food web. Building on the framework of consumer–resource interactions and widely studied thermal performance curves, we illustrate how joint driver impacts can be scaled up from the population to the community level. A simple proof-of-concept model demonstrates how reaction norms of vital rates predict the prevalence of driver interactions at the community level. A literature search suggests that our proposed approach is not yet used in multiple driver research. We outline how realistic response surfaces (i.e., multidimensional reaction norms) can be inferred by parametric and nonparametric approaches. Response surfaces have the potential to strengthen our understanding of how multiple drivers affect communities as well as improve our ability to predict when interactive effects emerge, two of the major challenges of ecology today.

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Fresh and saline submarine groundwater discharge as sources of carbon and nutrients to the Japan Sea

Published 7 February 2023 Science Closed
Tags: biological response, chemistry, field, multiple factors, North Pacific, nutrients, phytoplankton

Highlights

Fresh groundwater was comparable to the discharge from rivers and the main source of carbon, phosphate, and nitrate to coastal waters.
Groundwater-derived alkalinity fluxes were 7 times greater than river inputs, buffering the coastal ocean.
Nutrient and chlorophyll observations revealed the strong influence of groundwater discharge on primary productivity.

Abstract

Submarine groundwater discharge (SGD) is an important pathway for carbon and nutrients to the coastal ocean, sometimes exceeding river inputs. SGD fluxes can have implications for long-term carbon storage, ocean acidification and nutrient dynamics. Here, we used radium (²²³Ra and ²²⁶Ra) isotopes to quantify SGD-derived fluxes of dissolved inorganic (DIC) and organic (DOC) carbon, nitrate (NO₃⁻), nitrite (NO₂⁻), ammonium (NH₄⁺) and phosphate (PO₄³⁻) in a spring-fed coastal bay in the Japan Sea. The average coastal water residence times using ²²³Ra/²²⁶Ra ratios was 32.5 ± 17.9 days. Fresh and saline SGD were estimated using a radium mixing model with short- and long-lived isotopes. The volume of fresh SGD entering the bay (4.6 ± 4.6 cm day⁻¹) was more than twice that of the volume of saline SGD (1.9 ± 2.1 cm day⁻¹). Fresh SGD (mmol m² day⁻¹) was the main source of DOC (2.7 ± 2.6), DIC (13.9 ± 13.7), PO₄³⁻ (0.3 ± 0.3) and NO₃⁻ (6.6 ± 6.5) to the coastal ocean, whereas saline SGD was the main source of NH₄⁺ (0.2 ± 0.2). Total SGD-derived carbon and nutrient fluxes were 4 – 7 and 2–16 times greater than local river inputs. Positive correlations between chlorophyll-a, ²²⁶Ra and δ¹³C-DIC indicate that SGD significantly (p < 0.05) enhances primary productivity nearshore. Overall, fresh SGD of nitrogen and carbon to seawater drove chlorophyll-a, decreased DIC/Alkalinity ratios, and modified the carbonate biogeochemistry of the coastal ocean.

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No effect of ocean acidification on growth, photosynthesis, or dissolved organic carbon release by three temperate seaweeds with different dissolved inorganic carbon uptake strategies

Published 27 January 2023 Science Closed
Tags: algae, biological response, BRcommunity, chemistry, growth, Indian, laboratory, morphology, multiple factors, nutrients, photosynthesis, physiology, respiration

In a future ocean, dissolved organic carbon (DOC) release by seaweed has been considered a pathway for organic carbon that is not incorporated into growth under carbon dioxide (CO₂) enrichment/ocean acidification (OA). To understand the influence of OA on seaweed DOC release, a 21-day experiment compared the physiological responses of three seaweed species, two which operate CO₂ concentrating mechanisms (CCMs), Ecklonia radiata (C. Agardh) J. Agardh and Lenormandia marginata (Hooker F. and Harvey) and one that only uses CO₂ (non-CCM), Plocamium cirrhosum (Turner) M.J. Wynne. These two groups (CCM and non-CCM) are predicted to respond differently to OA dependent on their affinities for C_i (defined as CO₂ + bicarbonate, HCO₃⁻). Future ocean CO₂ treatment did not drive changes to seaweed physiology—growth, C_i uptake, DOC production, photosynthesis, respiration, pigments, % tissue carbon, nitrogen, and C:N ratios—for any species, regardless of C_i uptake method. Our results further showed that C_i uptake method did not influence DOC release rates under OA. Our results show no benefit of elevated CO₂ concentrations on the physiologies of the three species under OA and suggest that in a future ocean, photosynthetic CO₂ fixation rates of these seaweeds will not increase with C_i concentration.

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Ocean acidification and ammonium enrichment interact to stimulate a short-term spike in growth rate of a bloom forming macroalga

Published 10 January 2023 Science Closed
Tags: algae, biological response, growth, laboratory, multiple factors, North Pacific, nutrients, photosynthesis, physiology

Introduction: The coastal macroalgal genus, Ulva, is found worldwide and is considered a nuisance algal genus due to its propensity for forming vast blooms. The response of Ulva to ocean acidification (OA) is of concern, particularly with nutrient enrichment, as these combined drivers may enhance algal blooms because of increased availability of dissolved inorganic resources.

Methods: We determined how a suite of physiological parameters were affected by OA and ammonium (NH₄⁺) enrichment in 22-day laboratory experiments to gain a mechanistic understanding of growth, nutrient assimilation, and photosynthetic processes. We predicted how physiological parameters change across a range of pCO₂ and NH₄⁺ scenarios to ascertain bloom potential under future climate change regimes.

Results: During the first five days of growth, there was a positive synergy between pCO₂ and NH₄⁺ enrichment, which could accelerate initiation of an Ulva bloom. After day 5, growth rates declined overall and there was no effect of pCO₂, NH₄⁺, nor their interaction. pCO₂ and NH₄⁺ acted synergistically to increase NO₃^– uptake rates, which may have contributed to increased growth in the first five days. Under the saturating photosynthetically active radiation (PAR) used in this experiment (500 μmol photon m^-2 s^-1), maximum photosynthetic rates were negatively affected by increased pCO_2, which could be due to increased sensitivity to light when high CO₂ reduces energy requirements for inorganic carbon acquisition. Activity of CCMs decreased under high pCO₂ and high NH₄⁺ conditions indicating that nutrients play a role in alleviating photodamage and regulating CCMs under high-light intensities.

Discussion: This study demonstrates that OA could play a role in initiating or enhancing Ulva blooms in a eutrophic environment and highlights the need for understanding the potential interactions among light, OA, and nutrient enrichment in regulating photosynthetic processes.

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Species-dependent effects of seawater acidification on alkaline phosphatase activity in dinoflagellates

Published 14 December 2022 Science Closed
Tags: abundance, biological response, laboratory, molecular biology, multiple factors, nutrients, otherprocess, physiology, phytoplankton

Global climate change is widely shown to cause ocean acidification (OA) and projected to intensify nutrient limitation. Phosphorus (P) is an essential nutrient for phytoplankton to grow. While dissolved inorganic phosphate (DIP) is the preferred form of P, phytoplankton have evolved alkaline phosphatase (AP) to utilize dissolved organic phosphorus (DOP) when DIP is deficient. Although AP is known to require pH>7, how OA may affect AP activity and hence the capacity of phytoplankton to utilize DOP is poorly understood. Here, we examine the effects of pH conditions (5.5 to 11) on AP activity from six species of dinoflagellates, an important group of marine phytoplankton. We observed a general pattern that AP activity declined sharply at pH 5.5, peaked between pH 7 and 8, and dropped at pH>8. However, our data revealed remarkable interspecific variations in optimal pH and niche breadth of pH. Among the species examined, Fugacium kawagutii and Prorocentrum cordatum had an optimal pH at 8, Alexandrium pacificum, Amphidinium carterae, Effrenium voratum, and Karenia mikimotoi showed an optimal pH of 7. However, whereas A. pacificum, F. kawagutii and K. mikimotoi had a broad pH range for AP (7-11), A. carterae, E. voratum, and P. cordatum exhibited a narrow pH range. The response of AP activity of A. carterae to pH changes was verified using purified AP heterologously expressed in Escherichia coli. These findings suggest that OA will likely differentially impact the capacity of different phytoplankton species to utilize DOP in the projected acidified and nutrient-limited future ocean.

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Impact of ocean acidification and ocean warming on the oxidation of dissolved Fe(II) in coastal and open Southern Ocean water

Published 8 December 2022 Science Closed
Tags: Antarctic, biological response, chemistry, field, growth, laboratory, metals, multiple factors, nutrients, phytoplankton, temperature

The Southern Ocean is the largest region where major nutrients such as nitrate, silicate and phosphate are present in excess, yet the crucial micronutrient element iron (Fe) is scarce. It is well established that the Southern Ocean is key in exporting carbon to greater depths through biomass production by phytoplankton, but Fe is metabolically required for photosynthesis. Changes in uptake of carbon and heat to the ocean will impact ocean acidification and ocean warming. These anthropogenically linked processes are projected to lead to a drop in ocean pH by 0.2 units and an increase in the ocean’s temperature by 2°C by the end of the century and are already known to have tremendous ecological impacts on the ocean’s flora and fauna. However, little is known about how changes in ocean temperature and pH could alter the nutrient composition in future oceans.

Regarding nutrients, this work focuses on the dissolved (d) element Fe. It is essential for photosynthesis, but also a limiting element in the Southern Ocean due to limiting sources leading to low availability. Iron exists in two redox states in seawater. While the species dFe(III) is stable in seawater and occurs in relatively higher concentrations, its redox partner dFe(II) is tied to several physico-chemical processes impacting its oxidation time and overall presence. The importance of dFe(II) also lies with its accessibility for phytoplankton in its reduced oxidative state. The overall aim of this study was to investigate changes in concentration, speciation, and availability of the ‘more’ bioavailable, rapidly oxidizing Fe species dFe(II) under a changing Southern Ocean scenario.

Chapter 2 addressed the redox behaviour of dFe(II) and dFe(III), where several questions were explored for further experimental planning. The main question was how the coastal and open ocean systems differ in their dFe(II) concentrations and how ocean acidification and ocean warming impact Fe redox chemistry in both systems. I therefore performed controlled acidification and temperature alteration experiments in coastal and open ocean water taken from the Tasmanian coast and the Southern Ocean. This large dataset enabled us to project for future ocean dFe(II) concentrations and oxidation rates. I observed that a reduction in ocean pH by 0.2 units doubles the dFe(II) oxidation time in the open ocean and tripled in coastal water through model-based experiments. In contrast to these high impacts from pH, an increase in temperature by 1°C accelerated the oxidation by ~ 1.1 times (13% in coastal water and 8% in open ocean water). Therefore, realistic changes in temperature are likely to have small impacts on the oxidation of dFe(II) in both water systems compared to the proposed changes in pH.

For phytoplankton, these results pose contradicting outcomes, and studies display mixed results once parameters such as ocean warming, and acidification are combined. An increase in temperature might lead to less or no growth once a certain temperature threshold is crossed. Similarly, a decrease in pH is also thought to impact phytoplankton physiology. It also depends on the severity of acidification and the phytoplankton species itself. Ocean warming could reduce phytoplankton growth, despite increased Fe availability due to higher solubility in warmer water. Regarding ocean acidification, on the other hand, dFe(II) could become available for an extended time, therefore enabling further uptake of dFe(II) by phytoplankton for that time. When comparing mixed effects of ocean acidification and warming, a reduction in pH might have a greater impact on the dFe(II) oxidation than just temperature. Temperature changes, however, might be a greater concern in the near future before ocean acidification becomes relevant.

Due to this projection of temperature being a more imminent concern, I targeted the limiting element Fe in its less investigated form dFe(II). I observed how temperature alone impacts growth of two Southern Ocean phytoplankton species. I therefore ran an dFe(II)-enrichment incubation experiment in Chapter 3 with differing temperatures (3°C, 5°C, and 7°C) in coastal and open ocean water from the Southern Ocean using the well-studied haptophyte Phaeocystis antarctica and the diatom Fragilariopsis cylindrus. These enrichment experiments with altered temperatures overall confirmed that phytoplankton growth was elevated once 5 nM dFe(II) were added. In other words, freely available dFe(II) was present, almost regardless of the temperature increase from 3°C to 7°C. This could implicate that an increase in temperature has beneficial effects on growth in the case of higher concentrations of freely available dFe(II). However, these values of future dFe(II) concentrations and oxidation rates under acidified and warmer scenarios are only laboratory-based projections, to better understand the dFe(II) presence and demand by phytoplankton species in a future Southern Ocean.

In Chapter 4, a one-month field study onboard the RV Investigator was conducted east of the Australian continent along the East Australian Current (EAC) into nutrient-rich but Fe poor water in the Southern Ocean. I observed the overall distribution of dFe(II) and hydrogen peroxide in this understudied region. The findings suggest that dFe(II) concentrations are very low in the observed area of the open Southern Ocean (< 0.1 nM) compared to coastal waters (> 0.5 nM), likely driven by differences in terrestrial Fe inputs. Hydrogen peroxide was generally higher in the southern stations within the upper 200 m (~60 nM) while the dFe(II) : dFe ratios are 10 % higher than reported for previous Southern Ocean studies. High biological activity in the upper water extending to the frontal mixing zone where the two major currents meet (EAC and STF), may further have led to the observed low dFe concentrations and high H22O22 concentrations. Occasional higher dFe(II) peaks found in this area in surface water may be the result of several external sources such as rain or vertical transport from seamounts but also due to biological or physico-chemical impacts such as photochemical reduction or uptake by phytoplankton.

Overall, the work in this study advances our understanding of the coupled effects of the climate change parameters ocean acidification and ocean warming on the dFe(II) oxidation, with implications for its availability to phytoplankton and overall sources in the region east and south-east of Tasmania in coastal and open ocean water. The experimental approaches taken suggest a higher impact of ocean acidification compared to ocean warming and a potential benefit for phytoplankton species preferring dFe(II).

Continue reading ‘Impact of ocean acidification and ocean warming on the oxidation of dissolved Fe(II) in coastal and open Southern Ocean water’

Thalassiosira weissflogii grown in various Zn levels shows different ecophysiological responses to seawater acidification

Published 15 November 2022 Science Closed
Tags: biological response, growth, metals, multiple factors, nutrients, physiology, phytoplankton

Highlights

Zn deficient encouraged cellular silicon and sinking rate under normal pCO₂.
Higher pCO₂ decreased cellular silicon and sinking rate of Zn-deficient T. weissflogii.
Higher pCO₂ increased cellular silicon and sinking rate in Zn-replete T. weissflogii.
Silica and carbon cycle could be impacted by acidification and Zn levels.

Abstract

The presence of zinc (Zn), a vital element for algal physiological functions, coupled with the silicification of diatoms implies that it plays an integral role in the carbon and silicon cycles of the sea. In this study, we examined the effects of different pCO₂ and Zn levels on growth rate, elemental compositions and silicification by Thalassiosira weissflogii. The results showed that under normal pCO₂ (400 μatm), cultures of T. weissflogii were depressed for growth rate and silica incorporation rate, but encouraged for cellular silicon content, Si/C, Si/N, and sinking rate when Zn deficient (0.3 pmol L⁻¹). However, cellular silicon and sinking rate of Zn-deficient and Zn-replete (25 pmol L⁻¹) T. weissflogii were decreased and increased at higher pCO₂ (800 μatm), respectively. Thus, acidification may affect diatoms significantly differently depending on the Zn levels of the ocean and then alter the biochemical cycling of carbon and silica.

Continue reading ‘Thalassiosira weissflogii grown in various Zn levels shows different ecophysiological responses to seawater acidification’

Cascading effects augment the direct impact of CO₂ on phytoplankton growth in a biogeochemical model

Published 11 November 2022 Science Closed
Tags: abundance, biological response, BRcommunity, communitymodeling, globalmodeling, light, modeling, multiple factors, nutrients, otherprocess, phytoplankton, predation, temperature, zooplankton

Atmospheric and oceanic CO₂ concentrations are rising at an unprecedented rate. Laboratory studies indicate a positive effect of rising CO₂ on phytoplankton growth until an optimum is reached, after which the negative impact of accompanying acidification dominates. Here, we implemented carbonate system sensitivities of phytoplankton growth into our global biogeochemical model FESOM-REcoM and accounted explicitly for coccolithophores as the group most sensitive to CO₂. In idealized simulations in which solely the atmospheric CO₂ mixing ratio was modified, changes in competitive fitness and biomass are not only caused by the direct effects of CO₂, but also by indirect effects via nutrient and light limitation as well as grazing. These cascading effects can both amplify or dampen phytoplankton responses to changing ocean pCO₂ levels. For example, coccolithophore growth is negatively affected both directly by future pCO₂ and indirectly by changes in light limitation, but these effects are compensated by a weakened nutrient limitation resulting from the decrease in small-phytoplankton biomass. In the Southern Ocean, future pCO₂ decreases small-phytoplankton biomass and hereby the preferred prey of zooplankton, which reduces the grazing pressure on diatoms and allows them to proliferate more strongly. In simulations that encompass CO₂-driven warming and acidification, our model reveals that recent observed changes in North Atlantic coccolithophore biomass are driven primarily by warming and not by CO₂. Our results highlight that CO₂ can change the effects of other environmental drivers on phytoplankton growth, and that cascading effects may play an important role in projections of future net primary production.

Continue reading ‘Cascading effects augment the direct impact of CO₂ on phytoplankton growth in a biogeochemical model’

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