Marine productivity: Footprints of the past and steps into the future
If the address matches an existing account you will receive an email with instructions to retrieve your username. Skip to Main Content. Williams David N. Thomas Colin S. First published: 15 February About this book This landmark publication takes the 50th anniversary of the publication of the seminal paper by the Danish scientist, Einer Steemann Nielsen, as an occasion to assess the development, present state and future of the major aspects in freshwater and marine plankton productivity. Each chapter of this important work has been written by internationally-acknowledged experts in the subject, and the whole has been carefully drawn together and edited to provide a book that is an essential tool and reference for all aquatic scientists.
Raven Fisheries Oceanography Edited by P. A landmark publication in marine and freshwater biology.
Phytoplankton Productivity: Carbon Assimilation in Marine - Ebooks
All major aspects covered in a clear and consise reader-friendly manner. Invaluable for all those working in aquatic sciences. Book will be launched to coincide with major international conference. Asterisks indicate that no data are available. Relative carbon biomass a and ammonium assimilation b of bacterioplankton and phytoplankton in N-poor surface waters in the Baltic Sea. The not assigned biomass reflects the biomass of organisms which were microscopically identified and enumerated but not analysed by SIMS see result section.
Ammonium production resulted partly from N 2 -fixation but mostly from ammonium regeneration of unknown sources d. Dinoflagellates included Dinophysis and Heterocapsa. Mean C-specific C-fixation rates ranged from 0. They were highest for Chaetoceros 0. The remaining phototrophic cells showed lower C-fixation mean: 0. N 2 -fixation rates were 0.
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Added 15 N-ammonium concentrations decreased exponentially over time. Bulk concentrations, however, remained at steady-state since gross consumption and production rates balanced each other Fig. The turnover time through consumption was 1. Ammonium dynamics in surface waters during N-depletion. Gross ammonium production and consumption rates measured in June and August were positively correlated, following a close to ratio dashed line d. S1 since C-fixation rates of the same plankton community measured in a parallel study at lower light were five times as high as those measured herein [ 38 ].
Primary production based on N 2 -fixation and ammonium regeneration often dominates across diverse aquatic environments [ 1 , 2 , 3 ]. At the herein sampled coastal area, ammonium production derived mostly from regeneration and less from recent N 2 -fixation Fig.
Yet, parts of the regenerated ammonium may have its origin in N 2 -fixation hours, days or weeks prior to our sampling. Additional N may have been supplied as DON released from diazotrophs [ 9 , 16 , 18 , 48 ]. Recently, amino acids have been shown to be newly synthetised during N 2 -fixation, and incorporated into bulk PON at rates of 0. By comparison, new production, i. Interestingly, primary production rates were as high as those typically measured during spring Swedish Monitoring Program when new production is based on nitrate.
High primary production rates despite low nutrient concentrations were reconciled by a tight coupling of production and consumption rates, following a close to ratio Fig. The high N-retention through regeneration and re-assimilation in the photic zone combined with low sedimentation losses, e.
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Thus, diazotrophic-derived and regenerated N is effectively retained and accumulated in the upper mixed layer from early towards late summer when the food demand by fish is highest [ 24 ]. As a novelty—compared to numerous black-box-experiments, dating as far back as half a century ago [ 57 ], and also more recent SIMS-based ammonium analyses in freshwater systems [ 58 ], marine sediments [ 59 ] and coral—dinoflagellates symbioses [ 60 ]—we quantified ammonium assimilation for major taxa of the bacterioplankton and phytoplankton in marine waters.
Small heterotrophic bacteria greatly contributed to community biomass and ammonium assimilation Fig. Our SIMS data may underrate single-cell assimilation rates of the picoplankton due to uncertainties in their cellular N-contents and uptake kinetics. Bulk C-fixation was indeed not stimulated by 15 N-ammonium additions, as implied from similar C-fixation rates measured after 15 N 2 and 15 N-ammonium incubations Fig. Numerically inconspicuous taxa not analysed by SIMS might have also contributed to ammonium assimilation disproportionally to their population biomass, as shown for anaerobic bacteria [ 58 ] and diatoms [ 62 ].
The mismatch of ammonium assimilation and consumption might also be explained by nitrification but we could not detect any significant rates of this process. Nitrification was also not detectable in previous studies in N-depleted Baltic Sea surface waters during summer [ 63 , 64 ] and nitrifiers are generally outcompeted by phytoplankton under nitrate-replete regimes [ 65 ].
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Using SIMS, we could analyse in situ assimilation rates across various functional plankton taxa with different or even similar cell sizes. Intriguingly, filamentous N 2 -fixing cyanobacteria did not substantially take up ammonium which is supported by long-term observations of natural isotopic compositions of these cyanobacteria in the Baltic Sea [ 68 ]. In a parallel study to that in June , N 2 -fixation rates were as fast as 0. Therefore, their potential cellular N-turnover was more than one order of magnitude faster by N 2 -fixation than by ammonium assimilation. The low ammonium assimilation by filamentous N 2 -fixing cyanobacteria is also supported by the observation that cyanobacterial colonies release significant amounts of ammonium [ 7 , 8 ] and DON [ 16 , 18 ], depending on their energy reserves.
Colony-forming cyanobacteria such as the Baltic Sea strains and the widespread Trichodesmium may indeed re-assimilate only parts of their newly released N [ 69 ] while the remaining parts may benefit attached microbiota and co-occurring plankton [ 20 , 23 , 25 , 70 ]. Single-cell ammonium and C-assimilation rates were highly variable, often differing by one order of magnitude among diverse taxa and even single species Fig.
Such phenotypic heterogeneity in metabolism can result from i diffusion-limited nutrient assimilation in chain- or colony-forming species in which cells are exposed to distinct chemical microenvironments [ 44 ], ii variable substrate preferences of cells within the same population [ 71 , 72 ] or iii metabolic versatility within cell populations to cope with substrate fluctuations [ 73 ].
Colony-forming picocyanobacteria and Pseudanabaena have been considered as potential N 2 -fixers [ 74 , 75 ]. However, recent SIMS-based analyses did not confirm substantial N 2 -fixation with rates as low as 0. Instead, they seem to preferably assimilate ammonium at rates of 0. Total ammonium assimilation was dominated by autotrophic picocyanobacteria and heterotrophic bacteria Fig.
Their assimilation rates agreed well with recent studies on a single-cell level for both taxa [ 23 ] and on a community level for prokaryotes [ 76 ] and specifically heterotrophic bacteria [ 77 , 78 ]. Such fast assimilation rates may substantially support higher trophic levels, since picocyanobacteria are actively grazed by zooplankton in the Baltic Sea [ 81 , 82 ]. Heterotrophic bacteria usually regenerate ammonium through the degradation of dissolved organic matter DOM , i.
Still, their ammonium assimilation rates were high, comparable to those of phototrophic, non-N 2 -fixing cells Fig. Potentially, some cells received their 15 N-enrichment not directly from 15 N-ammonium assimilation but rather from 15 N-DON released after 15 N-assimilation by the bacterioplankton or phytoplankton.
However, only parts of the recently released DON may be bioavailable [ 87 ] and DON turnover times are rather long, in the order of days [ 18 , 88 , 89 ]. We thus consider the 15 N-enrichment in cells due to recently excreted 15 N-DON as minor during our 3-h incubations. Such combination of high BGE, high substrate C:N ratio and low bacterial C:N ratio implies net N assimilation rather than release by heterotrophic bacteria [ 93 ]. Regenerated ammonium can also derive from, e. Teasing these processes apart is challenging but should be targeted in future studies, to untangle the herein reported large fraction of ammonium regeneration of unknown sources Fig.
Small cells are generally believed to grow faster than large cells at low steady-state nutrient concentrations because of their higher cell surface-to-volume ratios [ 94 ]. Chaetoceros even showed N-assimilation rates similar to those predicted by theoretical diffusion-limited ammonium supply. N-assimilation rates of Chaetoceros based on ammonium during June 0. Diatoms may thus compete well for dissolved inorganic N not only in upwelling, nitrate-rich areas but also in the N-poor regions.
In fact, diatom diversity is comparable in oligotrophic and nutrient-rich areas with Chaetoceros as the most abundant and diverse genus [ 95 ], and diatoms have been shown to compete well for N released from N 2 -fixation [ 20 , 23 ]. Assimilation rates measured by SIMS are a relative measure of the elemental turn-over within cells, independent on cell sizes. Those rates may reflect single-cell growth rates, yet they may not necessarily correlate to actual biomass built-up.
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Rates obtained from SIMS analyses assume that the CN-biomass is evenly distributed in cells, which may not always hold true. For instance, nutrient-storing vacuoles can cover large parts of the cell volume in diatoms but account for proportionally little biomass—a structural feature which may overestimate N-growth rates of diatoms when using SIMS [ 96 ]. In conclusion, our experimental conditions resembled growth conditions for plankton communities—including N-depletion, ammonium regeneration and N 2 -fixation—that currently predominate in marine waters and may even intensify in the future [ 98 , 99 , ].
Under these conditions, eukaryotic diatoms showed a fast C-turnover and N-turnover on a single-cell level but minor population biomass. In contrast, prokaryotic picoplankton of different trophic levels, i. Harrison WG.
Nutrient recycling in production experiments. ICES Mar. Glibert PM. Primary production and pelagic nitrogen cycling. Nitrogen cycling in coastal marine environments. Chapter 7 - Nitrogen uptake and assimilation. Nitrogen in the marine environment. San Diego: Academic Press; Pluses and minuses of ammonium and nitrate uptake and assimilation by phytoplankton and implications for productivity and community composition, with emphasis on nitrogen-enriched conditions. Limnol Oceanogr. Chapter 8-Nitrogen regeneration. Carbon, nitrogen and O 2 fluxes associated with the cyanobacterium Nodularia spumigena in the Baltic Sea.
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