Nutrient uptake plasticity in phytoplankton sustains future ocean net primary production

A global estimate of multiecosystem photosynthesis losses under microplastic pollution

Understanding how ecosystems respond to ubiquitous microplastic (MP) pollution is crucial for ensuring global food security. Here, we conduct a multiecosystem meta-analysis of 3,286 data points and reveal that MP exposure leads to a global reduction in photosynthesis of 7.05 to 12.12% in terrestrial plants, marine algae, and freshwater algae. These reductions align with those estimated by a constructed machine learning model using current MP pollution levels, showing that MP exposure reduces the chlorophyll content of photoautotrophs by 10.96 to 12.84%. Model estimates based on the identified MP-photosynthesis nexus indicate annual global losses of 4.11 to 13.52% (109.73 to 360.87 MT·y-1) for main crops and 0.31 to 7.24% (147.52 to 3415.11 MT C·y-1) for global aquatic net primary productivity induced by MPs. Under scenarios of efficient plastic mitigation, e.g., a ~13% global reduction in environmental MP levels, the MP-induced photosynthesis losses are estimated to decrease by ~30%, avoiding a global loss of 22.15 to 115.73 MT·y-1 in main crop production and 0.32 to 7.39 MT·y-1 in seafood production. These findings underscore the urgency of integrating plastic mitigation into global hunger and sustainability initiatives.

Dissolved oxygen depletion in Chinese coastal waters

Estuarine and coastal environments have experienced dissolved oxygen (DO hereafter) depression and hypoxia due to increasingly intensified anthropogenic eutrophication and climate warming. This review compared diverse systems in Chinese coastal waters that experience DO depletion or hypoxia, aiming to identify essential aspects in advancing the abilities in comprehensively understanding DO dynamics across systems that span wide ranges of physical and biogeochemical environments. The coastal DO depression and relevant ecological consequences around the world are generally overviewed. DO depression in specific systems around Chinese coastal waters, ranging from large estuarine-coastal system to small embayment, are selected to synthetically understand the environment, the controlling processes, the evolution of eutrophication level, and the potential environmental changes under warming trend. Stressed ecosystems would be put at higher risks with high confidence due to increased complexity and uncertainty caused by future socioeconomic transformation and climate warming. This review proposes key aspects to advancing the abilities in predicting, managing, and mitigating DO stress for marine ecosystems in Chinese coastal waters, potentially providing a framework to discuss future DO changes in the coastal waters worldwide.

Spatial‒temporal pattern of primary productivity in the South China Sea under the monsoon regulation: Insights from observations of 2003-2022

Spatiotemporal analysis of Ocean Primary Production (OPP) is highly important for monitoring, conserving, and sustainable development of marine environment and ecosystems. Because of the influence of several factors such as temperature increasing, nutrients, wind and ocean dynamics, the analysis and prediction of the seasonal evolution and interannual trend of OPP have become more difficult and challenging. Taking the South China Sea (SCS) as the study area, this research conducted the comparative analysis of three widely used models in the SCS and identified the Vertical Generalized Production Model (VGPM) as the optimal model (R2 = 0.64, uRMSD = 0.25). We constructed a long-term data analysis framework for OPP, focusing on the typical spatial distribution characteristics in different month and the interannual trends. The framework is based on OPP, wind speed (WS), and sea surface height (SSH) data from 2003 to 2022 and utilizes empirical orthogonal function (EOF) analysis, the seasonal Kendall (SK) test, harmonic analysis, and the monsoon index. The results revealed that the first and second modes drive the patterns of January and August in winter and summer, respectively. Additionally, the fourth mode had dipole pattern in the SCS, capturing the main spatial distribution characteristics of the OPP in the northern SCS and southeastern Vietnam. The results from the SK test and harmonic analysis demonstrated that the most pronounced interannual decreases in OPP are in the northern SCS (lowest to -0.028897 mg∙C∙m-2∙d-1∙a-1), northwestern Luzon Island (lowest to -0.0115123 mg∙C∙m-2∙d-1∙a-1) and southeastern Vietnam (lowest to -0.0121879 mg∙C∙m-2∙d-1∙a-1). Furthermore, we quantified the impact of monsoons on OPP in the SCS, and positive correlations in southeastern Vietnam and dipole patterns in the northern SCS to northwestern SCS were identified. Finally, we evaluated the impacts of the El Niño‒Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) on OPP via their intensity indices. These findings provide insight into the biogeochemical cycling mechanisms in the SCS, with profound implications for local fisheries, the environment, and climate change.

Observed declines in upper ocean phosphate-to-nitrate availability

Climate warming is increasing ocean stratification, which in turn should decrease the nutrient flux to the upper ocean. This may slow marine primary productivity, causing cascading effects throughout food webs. However, observing changes in upper ocean nutrients is challenging because surface concentrations are often below detection limits. We show that the nutricline depth, where nutrient concentrations reach well-detected levels, is tied to productivity and upper ocean nutrient availability. Next, we quantify nutricline depths from a global database of observed vertical nitrate and phosphate profiles to assess contemporary trends in global nutrient availability (1972-2022). We find strong evidence that the P-nutricline (phosphacline) is mostly deepening, especially throughout the southern hemisphere, but the N-nutricline (nitracline) remains mostly stable. Earth System Model (ESM) simulations support the hypothesis that reduced iron stress and increased nitrogen fixation buffer the nitracline, but not phosphacline, against increasing stratification. These contemporary trends are expected to continue in the coming decades, leading to increasing phosphorus but not nitrogen stress for marine phytoplankton, with important ramifications for ocean biogeochemistry and food web dynamics.

Nitrogen source and availability regulate plastic population dynamics in the marine diatom Thalassiosira weissflogii

Variation in nitrogen (N) availability significantly influences population dynamics and the productivity of marine phytoplankton. As N availability in the ocean is conditioned by the N source, it is important to understand the capacity of phytoplankton organisms to adjust their physiology and dynamics under different N conditions. We investigated the growth dynamics of Thalassiosira weissflogii, a coastal diatom, in response to different N sources (Nitrate, NO3-; Ammonium, NH4+; urea, CH4N2O) and availabilities (45 and 5 μM). Our findings demonstrate that T. weissflogii can display plastic adjustments in population dynamics to different N sources. These responses evidenced a greater preference for NH4+ and urea than NO3-, particularly under high N availability. The relative growth rate (μ) is higher (1.18 ± 0.01) under NH4+-high treatment compared to NO3--high (1.01 ± 0.01). The carrying capacity (K) varied only among concentrations, indicating equal N utilization efficiency for biomass production. No effects of N source were detected under the low concentration, suggesting that the preference for NH₄⁺ and urea was diminished by limited nitrogen supply due to potential interactions. These results provide valuable insights into the physiological flexibility of T. weissflogii to varying N conditions, shedding light on the ecological success and resilience of this species in highly variable coastal environments.

Endemic, cosmopolitan, and generalist taxa and their habitat affinities within a coastal marine microbiome

The relative prevalence of endemic and cosmopolitan biogeographic ranges in marine microbes, and the factors that shape these patterns, are not well known. Using prokaryotic and eukaryotic amplicon sequence data spanning 445 near-surface samples in the Southern California Current region from 2014 to 2020, we quantified the proportion of taxa exhibiting endemic, cosmopolitan, and generalist distributions in this region. Using in-situ data on temperature, salinity, and nitrogen, we categorized oceanic habitats that were internally consistent but whose location varied over time. In this context, we defined cosmopolitan taxa as those that appeared in all regional habitats and endemics as taxa that only appeared in one habitat. Generalists were defined as taxa occupying more than one but not all habitats. We also quantified each taxon's habitat affinity, defined as habitats where taxa were significantly more abundant than expected. Approximately 20% of taxa exhibited endemic ranges, while around 30% exhibited cosmopolitan ranges. Most microbial taxa (50.3%) were generalists. Many of these taxa had no habitat affinity (> 70%) and were relatively rare. Our results for this region show that, like terrestrial systems and for metazoans, cosmopolitan and endemic biogeographies are common, but with the addition of a large number of taxa that are rare and randomly distributed.

Gelatinous filter feeders increase ecosystem efficiency

Gelatinous filter feeders (e.g., salps, doliolids, and pyrosomes) have high filtration rates and can feed at predator:prey size ratios exceeding 10,000:1, yet are seldom included in ecosystem or climate models. We investigated foodweb and trophic dynamics in the presence and absence of salp blooms using traditional productivity and grazing measurements combined with compound-specific isotopic analysis of amino acids estimation of trophic position during Lagrangian framework experiments in the Southern Ocean. Trophic positions of salps ranging 10-132 mm in size were 2.2 ± 0.3 (mean ± std) compared to 2.6 ± 0.4 for smaller (mostly crustacean) mesozooplankton. The mostly herbivorous salp trophic position was maintained despite biomass dominance of ~10-µm-sized primary producers. We show that potential energy flux to >10-cm organisms increases by approximately an order of magnitude when salps are abundant, even without substantial alteration to primary production. Comparison to a wider dataset from other marine regions shows that alterations to herbivore communities are a better predictor of ecosystem transfer efficiency than primary-producer dynamics. These results suggest that diverse consumer communities and intraguild predation complicate climate change predictions (e.g., trophic amplification) based on linear food chains. These compensatory foodweb dynamics should be included in models that forecast marine ecosystem responses to warming and reduced nutrient supply.

Is our understanding of aquatic ecosystems sufficient to quantify ecologically driven climate feedbacks?

The Earth functions as an integrated system-its current habitability to complex life is an emergent property dependent on interactions among biological, chemical, and physical components. As global warming affects ecosystem structure and function, so too will the biosphere affect climate by altering atmospheric gas composition and planetary albedo. Constraining these ecosystem-climate feedbacks is essential to accurately predict future change and develop mitigation strategies; however, the interplay among ecosystem processes complicates the assessment of their impact. Here, we explore the state-of-knowledge on how ecological and biological processes (e.g., competition, trophic interactions, metabolism, and adaptation) affect the directionality and magnitude of feedbacks between ecosystems and climate, using illustrative examples from the aquatic sphere. We argue that, despite ample evidence for the likely significance of many, our present understanding of the combinatorial effects of ecosystem dynamics precludes the robust quantification of most ecologically driven climate feedbacks. Constraining these effects must be prioritized within the ecological sciences for only by studying the biosphere as both subject and arbiter of global climate can we develop a sufficiently holistic view of the Earth system to accurately predict Earth's future and unravel its past.

Nitrogen uptake rates and phytoplankton composition across contrasting North Atlantic Ocean coastal regimes north and south of Cape Hatteras

Understanding nitrogen (N) uptake rates respect to nutrient availability and the biogeography of phytoplankton communities is crucial for untangling the complexities of marine ecosystems and the physical, biological, and chemical forces shaping them. In the summer of 2016, we conducted measurements of bulk microbial uptake rates for six 15N-labeled substrates: nitrate, nitrite, ammonium, urea, cyanate, and dissolve free amino acids across distinct marine provinces, including the continental shelf of the Mid-and South Atlantic Bights (MAB and SAB), the Slope Sea, and the Gulf Stream, marking the first instance of simultaneously measuring six different N uptake rates in this dynamic region. Total measured N uptake rates were lowest in the Gulf Stream followed by the SAB. Notably, the MAB exhibited significantly higher N uptake rates compared to the SAB, likely due to the excess levels of pre-existing phosphorus present in the MAB. Together, urea and nitrate uptake contributed approximately 50% of the total N uptake across the study region. Although cyanate uptake rates were consistently low, they accounted for up to 11% of the total measured N uptake at some Gulf Stream stations. Phytoplankton groups were identified based on specific pigment markers, revealing a dominance of diatoms in the shelf community, while Synechococcus, Prochlorococcus, and pico-eukaryotes dominated in oligotrophic Gulf Stream waters. The reported uptake rates in this study were mostly in agreement with previous studies conducted in coastal waters of the North Atlantic Ocean. This study suggests there are distinct regional patterns of N uptake in this physically dynamic region, correlating with nutrient availability and phytoplankton community composition. These findings contribute valuable insights into the intricate interplay of biological and chemical factors shaping N dynamics in disparate marine ecosystems.

Biogenic Phosphonate Utilization by Globally Distributed Diatom Thalassiosira pseudonana

Phosphonates are a class of organic phosphorus (P) compounds that contribute ~25% of dissolved organic P. Recent studies reveal the important role of phosphonates mediated by prokaryotes in the marine P redox cycle. However, its bioavailability by eukaryotic phytoplankton is under debate. 2-Aminoethylphosphonic acid (2-AEP) and 2-amino-3-phosphonopropionic acid (2-AP3) are two biogenic phosphonates in the marine environment. Here, Thalassiosira pseudonana, a common diatom species in the ocean, is able to recover growth from P starvation when provided with 2-AEP and 2-AP3. Moreover, 2-AEP cultures exhibited a more similar growth rate at 12 °C than at 25 °C when compared with inorganic P cultures. The cellular stoichiometry of 2-AEP groups was further determined, the values of which are in-between the P-depleted and DIP-replete cultures. This study provides evidence that biogenic phosphonates could be adopted as alternative P sources to support diatom growth and may provide physiological adaptation.

Atmospheric deposition and river runoff stimulate the utilization of dissolved organic phosphorus in coastal seas

In coastal seas, the role of atmospheric deposition and river runoff in dissolved organic phosphorus (DOP) utilization is not well understood. Here, we address this knowledge gap by combining microcosm experiments with a global approach considering the relationship between the activity of alkaline phosphatases and changes in phytoplankton biomass in relation to the concentration of dissolved inorganic phosphorus (DIP). Our results suggest that the addition of aerosols and riverine water stimulate the biological utilization of DOP in coastal seas primarily by depleting DIP due to increasing nitrogen concentrations, which enhances phytoplankton growth. This "Anthropogenic Nitrogen Pump" was therefore identified to make DOP an important source of phosphorus for phytoplankton in coastal seas but only when the ratio of chlorophyll a to DIP [Log10 (Chl a / DIP)] is larger than 1.20. Our study therefore suggests that anthropogenic nitrogen input might contribute to the phosphorus cycle in coastal seas.

Elemental stoichiometry of the key calcifying marine phytoplankton Emiliania huxleyi under ocean climate change: A meta-analysis

The elemental composition of marine microorganisms (their C:N:P ratio, or stoichiometry) is central to understanding the biotic and biogeochemical processes underlying key marine ecosystem functions. Phytoplankton C:N:P is species specific and flexible to changing environmental conditions. However, bulk or fixed phytoplankton stoichiometry is usually assumed in biogeochemical and ecological models because more realistic, environmentally responsive C:N:P ratios have yet to be defined for key functional groups. Here, a comprehensive meta-analysis of experimental laboratory data reveals the variable C:N:P stoichiometry of Emiliania huxleyi, a globally significant calcifying phytoplankton species. Mean C:N:P of E. huxleyi is 124C:16N:1P under control conditions (i.e. growth not limited by one or more environmental stressors) and shows a range of responses to changes in nutrient and light availability, temperature and pCO2 . Macronutrient limitation caused strong shifts in stoichiometry, increasing N:P and C:P under P deficiency (by 305% and 493% respectively) and doubling C:N under N deficiency. Responses to light, temperature and pCO2 were mixed but typically shifted cellular elemental content and C:N:P stoichiometry by ca. 30% or less. Besides these independent effects, the interactive effects of multiple environmental changes on E. huxleyi stoichiometry under future ocean conditions could be additive, synergistic or antagonistic. To synthesise our meta-analysis results, we explored how the cellular elemental content and C:N:P stoichiometry of E. huxleyi may respond to two hypothetical future ocean scenarios (increased temperature, irradiance and pCO2 combined with either N deficiency or P deficiency) if an additive effect is assumed. Both future scenarios indicate decreased calcification (which is predominantly sensitive to elevated pCO2 ), increased C:N, and up to fourfold shifts in C:P and N:P. Our results strongly suggest that climate change will significantly alter the role of E. huxleyi (and potentially other calcifying phytoplankton species) in marine biogeochemical processes.

Effects of phytoplankton physiology on global ocean biogeochemistry and climate

The similarity of the average ratios of nitrogen (N) and phosphorus (P) in marine dissolved inorganic and particulate organic matter, dN:P and pN:P, respectively, indicates tight links between those pools in the world ocean. Here, we analyze this linkage by varying phytoplankton N and P subsistence quotas in an optimality-based ecosystem model coupled to an Earth system model. The analysis of our ensemble of simulations discloses various feedbacks between changes in the N and P quotas, N2 fixation, and denitrification that weaken the often-hypothesized tight coupling between dN:P and pN:P. We demonstrate the importance of particulate N:C and P:C ratios for regulating dN:P on the global scale, with marine oxygen level being an important control. Our analysis provides further insight into the potential interdependence of phytoplankton physiology and global climate conditions.

Bacteria are driving the ocean's organosulfur cycle

Bacteria are key players in the marine sulfur cycle, from the sunlit ocean surface to the dark abyssal depths. Here, we provide a brief overview of the interlinked metabolic processes of organosulfur compounds, an elusive sulfur cycling process that exists in the dark ocean, and the current challenges that limit our understanding of this key nutrient cycle.