"It takes a village to finish (marine) science these days" Paraphrased from Curtis Huttenhower (the Human Microbiome project) The rapidity and complexity of climate change and its potential effects ...on ocean biota are challenging how ocean scientists conduct research. One way in which we can begin to better tackle these challenges is to conduct community-wide scientific studies. This study provides physiological datasets fundamental to understanding functional responses of phytoplankton growth rates to temperature. While physiological experiments are not new, our experiments were conducted in many laboratories using agreed upon protocols and 25 strains of eukaryotic and prokaryotic phytoplankton isolated across a wide range of marine environments from polar to tropical, and from nearshore waters to the open ocean. This community-wide approach provides both comprehensive and internally consistent datasets produced over considerably shorter time scales than conventional individual and often uncoordinated lab efforts. Such datasets can be used to parameterise global ocean model projections of environmental change and to provide initial insights into the magnitude of regional biogeographic change in ocean biota in the coming decades. Here, we compare our datasets with a compilation of literature data on phytoplankton growth responses to temperature. A comparison with prior published data suggests that the optimal temperatures of individual species and, to a lesser degree, thermal niches were similar across studies. However, a comparison of the maximum growth rate across studies revealed significant departures between this and previously collected datasets, which may be due to differences in the cultured isolates, temporal changes in the clonal isolates in cultures, and/or differences in culture conditions. Such methodological differences mean that using particular trait measurements from the prior literature might introduce unknown errors and bias into modelling projections. Using our community-wide approach we can reduce such protocol-driven variability in culture studies, and can begin to address more complex issues such as the effect of multiple environmental drivers on ocean biota.
Since the First Edition was published in 1983, this book has been recognized as the standard in the field. In the time since the book first appeared, there has been tremendous growth in the field ...with unprecedented discoveries over the past decade that have fundamentally changed the view of the marine nitrogen cycle. As a result, this Second Edition contains twice the amount of information that the previous edition contained.
Potential climate-change impacts on the Chesapeake Bay Najjar, Raymond G.; Pyke, Christopher R.; Adams, Mary Beth ...
Estuarine, coastal and shelf science,
2010, 2010-1-00, 20100101, Letnik:
86, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We review current understanding of the potential impact of climate change on the Chesapeake Bay. Scenarios for CO
2 emissions indicate that by the end of the 21
st century the Bay region will ...experience significant changes in climate forcings with respect to historical conditions, including increases in CO
2 concentrations, sea level, and water temperature of 50–160%, 0.7–1.6
m, and 2–6
°C, respectively. Also likely are increases in precipitation amount (very likely in the winter and spring), precipitation intensity, intensity of tropical and extratropical cyclones (though their frequency may decrease), and sea-level variability. The greatest uncertainty is associated with changes in annual streamflow, though it is likely that winter and spring flows will increase. Climate change alone will cause the Bay to function very differently in the future. Likely changes include: (1) an increase in coastal flooding and submergence of estuarine wetlands; (2) an increase in salinity variability on many time scales; (3) an increase in harmful algae; (4) an increase in hypoxia; (5) a reduction of eelgrass, the dominant submerged aquatic vegetation in the Bay; and (6) altered interactions among trophic levels, with subtropical fish and shellfish species ultimately being favored in the Bay. The magnitude of these changes is sensitive to the CO
2 emission trajectory, so that actions taken now to reduce CO
2 emissions will reduce climate impacts on the Bay. Research needs include improved precipitation and streamflow projections for the Bay watershed and whole-system monitoring, modeling, and process studies that can capture the likely non-linear responses of the Chesapeake Bay system to climate variability, climate change, and their interaction with other anthropogenic stressors.
A multi-year study was conducted in the eutrophic Lafayette River, a sub-tributary of the lower Chesapeake Bay during which uptake of inorganic and organic nitrogen (N) and C compounds was measured ...during multiple seasons and years when different dinoflagellate species were dominant. Seasonal dinoflagellate blooms included a variety of mixotrophic dinoflagellates including Heterocapsa triquetra in the late winter, Prorocentrum minimum in the spring, Akashiwo sanguinea in the early summer, and Scrippsiella trochoidea and Cochlodinium polykrikoides in late summer and fall. Results showed that no single N source fueled algal growth, rather rates of N and C uptake varied on seasonal and diurnal timescales, and within blooms as they initiated and developed. Rates of photosynthetic C uptake were low yielding low assimilation numbers during much of the study period and the ability to assimilate dissolved organic carbon augmented photosynthetic C uptake during bloom and non-bloom periods. The ability to use dissolved organic C during the day and night may allow mixotrophic bloom organisms a competitive advantage over co-occurring phytoplankton that are restricted to photoautotrophic growth, obtaining N and C during the day and in well-lit surface waters.
Cyanate (OCN⁻) is a reduced nitrogen compound that may be a source of nitrogen and carbon for marine phytoplankton. Cyanate is produced photochemically and through organic matter degradation but its ...distribution in marine systems is poorly defined because, until recently, there was no method to measure its concentration in marine environments. Here, we report results from the first regional oceanographic survey of cyanate distributions and uptake. Cyanate concentrations ranged from below detection (0.4 nM) to 11 nM in the coastal North Atlantic Ocean along the North American continental shelf and were slightly higher in nearshore surface waters than offshore surface waters. Subsurface cyanate maxima were observed at many stations suggesting a nonconservative distribution. Subsurface cyanate peak concentrations were tightly correlated with chlorophyll a concentrations integrated throughout the water column (R² = 0.79). Cyanate N and C uptake were measurable in all regions and seasons sampled. Cyanate N uptake was significantly higher than cyanate C uptake for all cruises (1.3 ± 1.9 nmol L−1 h−1 and 0.4 ± 0.6 nmol L−1 h−1 for N and C, respectively). However, cyanate N uptake was significantly lower in November than in June and August, and cyanate C uptake was significantly higher in November than during June and August. Spatial trends in cyanate distribution and uptake, along with the correlation between depth-integrated Chl a concentrations and cyanate maxima, suggest that cyanate is taken up in the euphotic zone and is likely produced by degradation of phytoplankton-derived organic matter in subsurface waters.
In marine oxygen deficient zones (ODZs), which contribute up to half of marine N loss, microbes use nitrogen (N) for assimilatory and dissimilatory processes. Here, we examine N utilization above and ...within the ODZ of the Eastern Tropical North Pacific Ocean, focusing on distribution, uptake and genes for the utilization of two simple organic N compounds, urea and cyanate. Ammonium, urea and cyanate concentrations generally peaked in the oxycline while uptake rates were highest in the surface. Within the ODZ, concentrations were lower, but urea N and C and cyanate C were taken up. All identified autotrophs had an N assimilation pathway that did not require external ammonium: ODZ Prochlorococcus possessed genes to assimilate nitrate, nitrite and urea; nitrite oxidizers (Nitrospina) possessed genes to assimilate nitrite, urea and cyanate; anammox bacteria (Scalindua) possessed genes to utilize cyanate; and ammonia-oxidizing Thaumarchaeota possessed genes to utilize urea. Urease genes were present in 20% of microbes, including SAR11, suggesting the urea utilization capacity was widespread. In the ODZ core, cyanate genes were largely (∼95%) associated with Scalindua, suggesting that, within this ODZ, cyanate N is primarily used for N loss via anammox (cyanammox), and that anammox does not require ammonium for N loss.
We compared growth kinetics of Prorocentrum donghaiense cultures on different nitrogen (N) compounds including nitrate (NO3-), ammonium (NH4+), urea, glutamic acid (glu), dialanine (diala) and ...cyanate. P. donghaiense exhibited standard Monod-type growth kinetics over a range of N concentraions (0.5-500 μmol N L-1 for NO3- and NH4+, 0.5-50 μmol N L-1 for urea, 0.5-100 μmol N L-1 for glu and cyanate, and 0.5-200 μmol N L-1 for diala) for all of the N compounds tested. Cultures grown on glu and urea had the highest maximum growth rates (μm, 1.51±0.06 d-1 and 1.50±0.05 d-1, respectively). However, cultures grown on cyanate, NO3-, and NH4+ had lower half saturation constants (Kμ, 0.28-0.51 μmol N L-1). N uptake kinetics were measured in NO3--deplete and -replete batch cultures of P. donghaiense. In NO3--deplete batch cultures, P. donghaiense exhibited Michaelis-Menten type uptake kinetics for NO3-, NH4+, urea and algal amino acids; uptake was saturated at or below 50 μmol N L-1. In NO3--replete batch cultures, NH4+, urea, and algal amino acid uptake kinetics were similar to those measured in NO3--deplete batch cultures. Together, our results demonstrate that P. donghaiense can grow well on a variety of N sources, and exhibits similar uptake kinetics under both nutrient replete and deplete conditions. This may be an important factor facilitating their growth during bloom initiation and development in N-enriched estuaries where many algae compete for bioavailable N and the nutrient environment changes as a result of algal growth.
Cyanate is a simple reduced nitrogen (N) compound that can be a source of N and carbon (C) for marine organisms and may also be a substrate for dissimilatory N processes such as nitrification and ...anammox. We measured cyanate distributions and cyanate and urea uptake in the Eastern Tropical South Pacific, a region defined by coastal upwelling, high primary productivity, a shallow oxic layer, and rapid N loss from a large oxygen deficient zone (ODZ). Cyanate concentrations ranged from below the limit of detection (0.4 nM) to 45 nM in the oxic upper water column. Below the oxycline, cyanate concentrations were largely below detection except for small cyanate peaks (2–8.3 nM) within the core of the ODZ at some stations. The majority of N taken up in the shallow oxic layer was from ammonium and urea (78% ± 8%); cyanate uptake was <2% of these. Uptake of cyanate fluctuated diurnally with the highest rates of cyanate N uptake in the early afternoon. In the ODZ, rates of cyanate, urea, and ammonium uptake were similar to each other (0.1–14 nmol N L-1 d-1) and to previously reported rates of 29N₂ production supported by cyanate and ammonium (3–14 nmol N₂ L-1 d-1). This suggests a role for cyanate in the metabolism of anaerobic microbes and a potential role for cyanate in the anammox reaction (cyanammox). To our knowledge, these represent the first rates of N uptake in a marine anoxic water column.
The ocean carbon cycle is tightly linked with the cycles of the major nutrient elements nitrogen, phosphorus, and silicon. It is therefore likely that enrichment of the ocean with anthropogenic CO₂ ...and attendant acidification will have large consequences for marine nutrient biogeochemistry, and for the microbes that mediate many key nutrient transformations. The best available evidence suggests that the nitrogen cycle may respond strongly to higher CO₂ through increases in global N₂ fixation and possibly denitrification, as well as potential decreases in nitrification. These trends could cause nitrification to become a nitrogen cycle "bottleneck," by increasing the flux of N₂ fixed into ammonium while decreasing the fraction being oxidized to nitrite and nitrate. The consequences could include reduced supplies of oxidized nitrogen substrates to denitrifiers, lower levels of nitrate-supported new primary production, and expansion of the regenerated production system accompanied by shifts in current phytoplankton communities. The phosphorus and silicon cycles seem less likely to be directly affected by enhanced CO₂ conditions, but will undoubtedly respond indirectly to changing carbon and nitrogen biogeochemistry. A review of culture experiments that examined the effects of increased CO₂ on elemental ratios of phytoplankton suggests that for most cyanobacteria and eukaryotes, C:N and N:P ratios will either remain at Redfield values or increase substantially. Natural plankton community CO₂ manipulation experiments show much more mixed outcomes, with both increases and decreases in C:N and N:P ratios reported at future CO₂ levels. We conclude our review with projections of overall trends in the cycles of nitrogen, phosphorus, and silicon over the next century as they respond to the steady accumulation of fossil-fuel-derived CO₂ in a rapidly changing ocean.
Prochlorococcus and Synechococcus are the most abundant free-living photosynthetic microorganisms in the ocean. Uncultivated lineages of these picocyanobacteria also thrive in the dimly illuminated ...upper part of oxygen-deficient zones (ODZs), where an important portion of ocean nitrogen (N) loss takes place via denitrification and anaerobic ammonium oxidation. Recent metagenomic studies revealed that ODZ Prochlorococcus have the genetic potential for using different N forms, including nitrate and nitrite, uncommon N sources for Prochlorococcus, but common for Synechococcus. To determine which N sources ODZ picocyanobacteria are actually using in nature, the cellular 15N natural abundance (δ15N) and assimilation rates of different N compounds were determined using cell sorting by flow cytometry and mass spectrometry. The natural δ15N of the ODZ Prochlorococcus varied from −4.0‰ to 13.0‰ (n = 9), with 50% of the values in the range of −2.1–2.6‰. While the highest values suggest nitrate use, most observations indicate the use of nitrite, ammonium, or a mixture of N sources. Meanwhile, incubation experiments revealed potential assimilation rates of ammonium and urea in the same order of magnitude as that expected for total N in several environments including ODZs, whereas rates of nitrite and nitrate assimilation were very low. Our results thus indicate that reduced forms of N and nitrite are the dominant sources for ODZ picocyanobacteria, although nitrate might be important on some occasions. ODZ picocyanobacteria might thus represent potential competitors with anammox bacteria for ammonium and nitrite, with ammonia-oxidizing archaea for ammonium, and with nitrite-oxidizing bacteria for nitrite.
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