Nitrogen Assimilation Rates Research Articles

Titanium dioxide nanoparticles alleviates polystyrene nanoplastics induced growth inhibition by modulating carbon and nitrogen metabolism via melatonin signaling in maize.

Nanoplastics, are emerging pollutants, present a potential hazard to food security and human health. Titanium dioxide nanoparticles (Nano-TiO2), serving as nano-fertilizer in agriculture, may be important in alleviating polystyrene nanoplastics (PSNPs) toxicity. Here, we performed transcriptomic, metabolomic and physiological analyzes to identify the role of Nano-TiO2 in regulating the metabolic processes in PSNPs-stressed maize seedlings (Zea mays L.). The growth inhibition by PSNPs stress was partially relieved by Nano-TiO2. Furthermore, when considering the outcomes obtained from RNA-seq, enzyme activity, and metabolite content analyses, it becomes evident that Nano-TiO2 significantly enhance carbon and nitrogen metabolism levels in plants. In comparison to plants that were not subjected to Nano-TiO2, plants exposed to Nano-TiO2 exhibited enhanced capabilities in maintaining higher rates of photosynthesis, sucrose synthesis, nitrogen assimilation, and protein synthesis under stressful conditions. Meanwhile, Nano-TiO2 alleviated the oxidative damage by modulating the antioxidant systems. Interestingly, we also found that Nano-TiO2 significantly enhanced the endogenous melatonin levels in maize seedlings. P-chlorophenylalanine (p-CPA, a melatonin synthesis inhibitor) declined Nano-TiO2-induced PSNPs tolerance. Taken together, our data show that melatonin is involved in Nano-TiO2-induced growth promotion in maize through the regulation of carbon and nitrogen metabolism.

Resting cells of Skeletonema marinoi assimilate organic compounds and respire by dissimilatory nitrate reduction to ammonium in dark, anoxic conditions.

Diatoms can survive long periods in dark, anoxic sediments by forming resting spores or resting cells. These have been considered dormant until recently when resting cells of Skeletonema marinoi were shown to assimilate nitrate and ammonium from the ambient environment in dark, anoxic conditions. Here, we show that resting cells of S. marinoi can also perform dissimilatory nitrate reduction to ammonium (DNRA), in dark, anoxic conditions. Transmission electron microscope analyses showed that chloroplasts were compacted, and few large mitochondria had visible cristae within resting cells. Using secondary ion mass spectrometry and isotope ratio mass spectrometry combined with stable isotopic tracers, we measured assimilatory and dissimilatory processes carried out by resting cells of S. marinoi under dark, anoxic conditions. Nitrate was both respired by DNRA and assimilated into biomass by resting cells. Cells assimilated nitrogen from urea and carbon from acetate, both of which are sources of dissolved organic matter produced in sediments. Carbon and nitrogen assimilation rates corresponded to turnover rates of cellular carbon and nitrogen content ranging between 469 and 10,000 years. Hence, diatom resting cells can sustain their cells in dark, anoxic sediments by slowly assimilating and respiring substrates from the ambient environment.

Study of Chlorella sorokiniana Cultivation in an Airlift Tubular Photobioreactor Using Anaerobic Digestate Substrate

Microalgae offer a promising solution for efficiently treating high-nitrogen wastewater and recovering valuable nutrients. To optimize microalgae growth and nutrient assimilation, case-dependent studies are essential to demonstrate the process’s potential. This study aimed to evaluate the treatment capacity of high-nitrogen anaerobic digestion effluent as a nutrient source for a C. sorokiniana microalgal culture in a tubular photobioreactor. The study had two primary objectives: to assess how the concentration and composition of the digestate influence microalgae growth, and to identify the preferred nitrogen forms assimilated by the microalgae during long-term, continuous operation. A 20 L tubular airlift bioreactor was constructed and used in batch mode; various digestate concentrations were examined with ammonia nitrogen levels reaching to 160 mg/L. These experiments revealed a biomass growth rate of up to 130 mg/L/d and an ammonia nitrogen assimilation rate ranging from 8.3 to 12.5 mg/L/d. The presence of phosphorous proved essential for microalgae growth, and the growth entered a stationary phase when the initial phosphorous was fully assimilated. A nitrogen-to-phosphorous (N/P) ratio of 10 supported efficient species growth. While ammonia was the preferred nitrogen form for microalgae, they could also utilize alternative forms such as organic and nitrate nitrogen, depending on the specific digestate properties. The results from the continuous photobioreactor operation confirmed the findings from the batch mode, especially regarding the initial nitrogen and phosphorous content. An important condition for nearly complete ammonia removal was the influent dilution rate, to balance the nitrogen assimilation rate. Moreover, treated effluent was employed as dilution medium, contributing to a more environmentally sustainable water management approach for the entire process, at no cost to the culture growth rate.

Active microbial taxa preferentially assimilate inorganic nitrogen in acidic upland soils using a 15N-DNA-SIP approach

Soil endogenous nitrogen is an essential source of crop nitrogen supply. Nitrogen assimilation is a vital transformation process that maintains nitrogen availability and promotes the mineralization of endogenous organic nitrogen in acidic soils. However, the dominant microbial populations that assimilate NH4+ and NO3− in acidic upland soils were unknown, and their response to long-term fertilization remained unclear. In this study, 15N-labeled NH4+ and NO3− were added to acidic upland soils characterized by long-term (32 years) differentiation in organic matter inputs. Glucose was added to facilitate nitrogen assimilation, and a nitrification inhibitor (dicyandiamide, DCD) was added to distinguish the contribution of NH4+ and NO3− assimilation. Results showed that soil inorganic N assimilation mainly occurred in the first week after inorganic N addition. Soil net inorganic N assimilation rates were 0.006–0.42 mg N kg−1 d−1 in the NH4+, NO3− and NH4++DCD treatments. The analysis of 15N-DNA-based stable isotope probing (SIP) found that the majority of inorganic N assimilation in our soils was conducted by a limited number of active microbial taxa, which accounted for 1.4%–2.0% of the entire bacterial community and 15.7%–28.8% of the fungal community. The dominant bacteria governing inorganic N assimilation in acidic upland soils included Bacillus, Burkholderia–Caballeronia–Paraburkholderia and Micrococcaceae. The primary fungi included Penicillium, Chaetomium, Aspergillus, and Fusarium. No obvious bias was detected in nitrogen assimilation rates and the dominant microbial taxa for NH4+-N and NO3−-N. Compared with unfertilized soil, long-term organic matter input decreased the dominating N assimilating microbial taxa. These findings demonstrate the feasibility of 15N-DNA-SIP technology in soil nitrogen cycling research and suggest the importance of active microbial taxa in acidic agricultural soil nitrogen retention and loss.

Time-resolved systems analysis of the induction of high photosynthetic capacity in Arabidopsis during acclimation to high light.

Induction of high photosynthetic capacity is a key acclimation response to high light (HL) for many herbaceous dicot plants; however, the signaling pathways that control this response remain largely unknown. Here, a systems biology approach was utilized to characterize the induction of high photosynthetic capacity in strongly and weakly acclimating Arabidopsis thaliana accessions. Plants were grown for 5 wk in a low light (LL) regime, and time-resolved photosynthetic physiological, metabolomic, and transcriptomic responses were measured during subsequent exposure to HL. The induction of high nitrogen (N) assimilation rates early in the HL shift was strongly predictive of the induction of photosynthetic capacity later in the HL shift. Accelerated N assimilation rates depended on the mobilization of existing organic acid (OA) reserves and increased de novo OA synthesis during the induction of high photosynthetic capacity. Enhanced sucrose biosynthesis capacity increased in tandem with the induction of high photosynthetic capacity, and increased starch biosynthetic capacity was balanced by increased starch catabolism. This systems analysis supports a model in which the efficient induction of N assimilation early in the HL shift begins the cascade of events necessary for the induction of high photosynthetic capacity acclimation in HL.

Decreasing O2 availability reduces cellular protein contents in a marine diatom

Anthropogenic activities and climate change are exacerbating marine deoxygenation. Apart from aerobic organisms, reduced O2 also affects photoautotrophic organisms in the ocean. This is because without available O2, these O2 producers cannot maintain their mitochondrial respiration, especially under dim-light or dark conditions, which may disrupt the metabolism of macromolecules including proteins. We used growth rate, particle organic nitrogen and protein analyses, proteomics, and transcriptomics to determine cellular nitrogen metabolism of the diatom Thalassiosira pseudonana grown under three O2 levels in a range of light intensities at nutrient-rich status. The ratio of protein nitrogen to total nitrogen under ambient O2 level among different light intensities was about 0.54–0.83. At the lowest light intensity, decreased O2 had a stimulatory effect on protein content. When light intensity increased to moderate and high or inhibitory levels, decreased O2 reduced the protein content, with maximum values of 56 % at low O2 and 60 % at hypoxia, respectively. In addition, cells growing under low O2 or hypoxic status exhibited a decreased rate of nitrogen assimilation associated with decreased protein content, which was associated with downregulated expression of genes related to nitrate transform and protein synthesis and upregulated expression of genes related to protein degradation. Our results suggest that decreased O2 reduces the protein content of phytoplankton cells, which might degrade grazer nutrition and thus affect marine food chains under the scenario of increasingly deoxygenated/hypoxic waters in future.

Effect of selenium supplementation on mycorrhizal onion (Allium cepa L.) plants

ABSTRACT Selenium (Se) is a beneficial element for higher plants; however, its involvement in improving the plants availability to soil nutrients has not been adequately addressed. Onion (Allium cepa L.) plants were grown under the sufficient (2 mM) and deficient (0.05 mM) phosphorus (P) supply and inoculated with an arbuscular mycorrhizal fungus (AMF, Diversispora versiformis) in the absence or presence of 20 or 80 µg Se L–1 applied as Na2SeO4 under greenhouse conditions. Phosphorus deficiency impaired both shoot and root growth, while mycorrhisation increased plants biomass and root length by up to two times, accompanied by increased potassium uptake, levels of non-structural carbohydrates, protein and amino acids in the leaves and roots. AMF’s impact on biomass production was enhanced by Se supplementation, and the rates of photosynthesis and nitrogen assimilation were also boosted. Besides, AMF effects on the root activity of phosphatase, the acidification of rhizosphere and the mobilisation of insoluble P in the substrate were significantly exacerbated by Se. Our results showed a strong synergistic effect between Se and AMF in improving the plants performance on P-impoverished soils via enhanced ability to solubilise non-labile P fractions in the substrate and stimulation of carbon and nitrogen metabolism.

Long term outdoor microalgal phycoremediation of anaerobically digested abattoir effluent

Sufficient and reliable long-term field data on the growth, productivity and nutrient removal rates of microalgal based wastewater treatment system is essential to validate its overall techno-economic feasibility. Here, we investigated the semi-continuous microalgal cultivation of Scenedesmus sp. in anaerobically digested abattoir effluent (ADAE) for 13 months in outdoor raceway ponds operated at 20 cm depth. This study was initiated with three different cultures consisting of 1) monocultures of Chlorella sp., 2) Scenedesmus sp., and 3) an equal mixed concentration of both microalgae species. However, after 15 weeks, Scenedesmus sp. was found to be the most dominant microalgae species in all the different cultures, even completely taking over the Chlorella sp. monoculture. Over the course of summer and early autumn, the average weekly biomass productivity of Scenedesmus sp. cultures was 12.5 ± 0.6 g m−2 d−1 which was 16% and 30% higher than productivities recorded in spring and winter, respectively. All available ammoniacal nitrogen (NH3–N) was found to be exhausted during each growth period with an average 33.6% nitrogen assimilation rate. The average rate of phosphate and COD (chemical oxygen demand) removals were 85.2% and 37.5% throughout the cultivation period. No significant differences were found in carbohydrate, lipid and protein content of Scenedesmus sp. during different seasons of the year. Over 53% increase in biomass productivity can be achieved if CO2 is added to control culture pH at pH 6.5. Here, we successfully demonstrated reliability of continuous long-term cultivation of microalgae in ADAE for simultaneous wastewater treatment and algal biomass production.

Nitrogen Availability Affects the Metabolic Profile in Cyanobacteria.

Nitrogen is essential for the biosynthesis of various molecules in cells, such as amino acids and nucleotides, as well as several types of lipids and sugars. Cyanobacteria can assimilate several forms of nitrogen, including nitrate, ammonium, and urea, and the physiological and genetic responses to these nitrogen sources have been studied previously. However, the metabolic changes in cyanobacteria caused by different nitrogen sources have not yet been characterized. This study aimed to elucidate the influence of nitrate and ammonium on the metabolic profiles of the cyanobacterium Synechocystis sp. strain PCC 6803. When supplemented with NaNO3 or NH4Cl as the nitrogen source, Synechocystis sp. PCC 6803 grew faster in NH4Cl medium than in NaNO3 medium. Metabolome analysis indicated that some metabolites in the CBB cycle, glycolysis, and TCA cycle, and amino acids were more abundant when grown in NH4Cl medium than NaNO3 medium. 15N turnover rate analysis revealed that the nitrogen assimilation rate in NH4Cl medium was higher than in NaNO3 medium. These results indicate that the mechanism of nitrogen assimilation in the GS-GOGAT cycle differs between NaNO3 and NH4Cl. We conclude that the amounts and biosynthetic rate of cyanobacterial metabolites varies depending on the type of nitrogen.

Integrated Physiological, Transcriptomic, and Metabolomic Analyses Revealed Molecular Mechanism for Salt Resistance in Soybean Roots.

Salinity stress is a threat to yield in many crops, including soybean (Glycine max L.). In this study, three soybean cultivars (JD19, LH3, and LD2) with different salt resistance were used to analyze salt tolerance mechanisms using physiology, transcriptomic, metabolomic, and bioinformatic methods. Physiological studies showed that salt-tolerant cultivars JD19 and LH3 had less root growth inhibition, higher antioxidant enzyme activities, lower ROS accumulation, and lower Na+ and Cl- contents than salt-susceptible cultivar LD2 under 100 mM NaCl treatment. Comparative transcriptome analysis showed that compared with LD2, salt stress increased the expression of antioxidant metabolism, stress response metabolism, glycine, serine and threonine metabolism, auxin response protein, transcription, and translation-related genes in JD19 and LH3. The comparison of metabolite profiles indicated that amino acid metabolism and the TCA cycle were important metabolic pathways of soybean in response to salt stress. In the further validation analysis of the above two pathways, it was found that compared with LD2, JD19, and LH3 had higher nitrogen absorption and assimilation rate, more amino acid accumulation, and faster TCA cycle activity under salt stress, which helped them better adapt to salt stress. Taken together, this study provides valuable information for better understanding the molecular mechanism underlying salt tolerance of soybean and also proposes new ideas and methods for cultivating stress-tolerant soybean.

Potential metabolic mechanisms for inhibited chloroplast nitrogen assimilation under high CO2.

Improving photosynthesis is considered a major and feasible option to dramatically increase crop yield potential. Increased atmospheric CO2 concentration often stimulates both photosynthesis and crop yield, but decreases protein content in the main C3 cereal crops. This decreased protein content in crops constrains the benefits of elevated CO2 on crop yield and affects their nutritional value for humans. To support studies of photosynthetic nitrogen assimilation and its complex interaction with photosynthetic carbon metabolism for crop improvement, we developed a dynamic systems model of plant primary metabolism, which includes the Calvin–Benson cycle, the photorespiration pathway, starch synthesis, glycolysis–gluconeogenesis, the tricarboxylic acid cycle, and chloroplastic nitrogen assimilation. This model successfully captures responses of net photosynthetic CO2 uptake rate (A), respiration rate, and nitrogen assimilation rate to different irradiance and CO2 levels. We then used this model to predict inhibition of nitrogen assimilation under elevated CO2. The potential mechanisms underlying inhibited nitrogen assimilation under elevated CO2 were further explored with this model. Simulations suggest that enhancing the supply of α-ketoglutarate is a potential strategy to maintain high rates of nitrogen assimilation under elevated CO2. This model can be used as a heuristic tool to support research on interactions between photosynthesis, respiration, and nitrogen assimilation. It also provides a basic framework to support the design and engineering of C3 plant primary metabolism for enhanced photosynthetic efficiency and nitrogen assimilation in the coming high-CO2 world.

Dissolved Nitrogen Acquisition in the Symbioses of Soft and Hard Corals With Symbiodiniaceae: A Key to Understanding Their Different Nutritional Strategies?

Nitrogen is one of the limiting nutrients for coral growth and primary productivity. Therefore, the capacity of different associations between corals and their algal symbionts (Symbiodiniaceae) to efficiently exploit the available nitrogen sources will influence their distribution and abundance. Recent studies have advanced our understanding of nitrogen assimilation in reef-building scleractinian (hard) coral-Symbiodiniaceae symbioses. However, the nutrient metabolism of other coral taxa, such as Alcyoniina (soft corals), remains underexplored. Using stable isotope labeling, we investigated the assimilation of dissolved nitrogen (i.e., ammonium, nitrate, and free amino acids) by multiple species of soft and hard corals sampled in the Gulf of Aqaba in shallow (8–10 m) and mesophotic (40–50 m) reefs. Our results show that dissolved nitrogen assimilation rates per tissue biomass were up to 10-fold higher in hard than in soft coral symbioses for all sources of nitrogen. Although such differences in assimilation rates could be linked to the Symbiodiniaceae density, Symbiodiniaceae species, or the C:N ratio of the host and algal symbiont fractions, none of these parameters were different between the two coral taxa. Instead, the lower assimilation rates in soft coral symbioses might be explained by their different nutritional strategy: whereas soft corals may obtain most of their nitrogen via the capture of planktonic prey by the coral host (heterotrophic feeding), hard corals may rely more on dissolved nitrogen assimilation by their algal symbionts to fulfill their needs. This study highlights different nutritional strategies in soft and hard coral symbioses. A higher reliance on heterotrophy may help soft corals to grow in reefs with higher turbidity, which have a high concentration of particles in suspension in seawater. Further, soft corals may benefit from lower dissolved nitrogen assimilation rates in areas with low water quality.

Effects of stepwise changes in dissolved carbon dioxide concentrations on metabolic activity in Chlorella for spaceflight applications

This paper assesses the impacts to the growth rate, health, oxygen production, and carbon dioxide fixation and nitrogen assimilation of Chlorella vulgaris while sparging the culture with various influent concentrations of carbon dioxide. Selected concentrations reflect a cabin environment with one crew member (0.12% v/v) and four crew members (0.45% v/v). Stepwise, sustained changes in influent carbon dioxide concentration on day four of the eight-day experiments simulated a dynamic crew size, reflective of a planetary surface mission. Control experiments used constant influent concentrations across eight days. Significant changes in growth rate (0.12%-to-0.45%: 57% increase; 0.45%-to-0.12%: 59% reduction) suggest a positive correlation between metabolic activity of C. vulgaris and environmental carbon dioxide concentration. Statistical tests illustrate that algae are more sensitive to reductions in influent carbon dioxide. No specific correlation of the nitrogen assimilation rate to influent carbon dioxide, suggesting a nitrogen-limited or irradiance-limited system. Photosynthetic yield results (0.59–0.72) indicate that the culture was minimally stressed in all tested conditions. This paper compares these results to findings of published, steady-state experiments conducted under similar carbon dioxide environments. The findings presented here imply that a sufficient volume of C. vulgaris, with nutrient supplementation or biomass harvesting, could support the respiratory requirements of a long duration human mission with a dynamic cabin environment and these data can be used in future dynamic models.

Extended photoperiods after flowering increase the rate of dry matter production and nitrogen assimilation in mid maturing soybean cultivars

• Extended photoperiods after flowering prolonged reproductive growth. • Vegetative and reproductive biomass increased under extended photoperiods. • Crop growth rate increased, and duration of the growth period was lengthened. • Nitrogen assimilation increased with no change in tissue nitrogen concentration. In soybeans, exposure to non-inductive photoperiods ( i.e ., long or extended days) after flowering triggers a number of responses, including slower development of reproductive structures, enhanced vegetative growth and increased production of flowers. The larger number of flowers under extended photoperiods results in an increase of the number of fruits, which eventually may translate into greater grain yield. The main goal of this work was to assess whether C and N assimilation rates increase in soybeans subjected to long days after flowering. Soybean cultivars NS4619 and NS5019 were planted in the field during the normal planting season in 2016−17 and 2018−19. At flowering, two treatments were imposed: natural (Nat) or extended photoperiods (Ext) in which daylength was prolonged by 4 h with low intensity illumination from light-emitting diode lamps delivering less than 10 μmol m −2 s −1 of photosynthetically active radiation at the top of the canopy. Extended photoperiods prolonged reproductive growth, thereby delaying crop maturity. Growth of the main stem and branches was promoted by Ext, with plants showing greater number of nodes and main stem + branches dry weight at maturity. The number of pods and seeds increased by 69–87 % and 31–76 %, respectively, in Ext, and pod and seed dry weight increased significantly in 2016−17. Averaged over the whole reproductive period, crop growth rate increased under Ext in 2016−17 and 2018−2019. Ext promoted post-flowering vegetative growth more than growth of seeds, therefore harvest index was lower under Ext. The growth increase under Ext was larger if the biomass of abscised leaf blades and petioles was taken into account. Consistently with increased biomass under Ext, nitrogen accumulation by the crop was higher under extended photoperiods, with no dilution effect of N due to increased dry mass. About half of the N in plant tissues derived from biological nitrogen fixation, irrespective of photoperiodic condition, which implied that both, nitrogen fixation and uptake of soil nitrogen increased under long photoperiods. In brief, both the amounts of C and N assimilated by the crop were higher under Ext. Understanding the molecular, biochemical and physiological basis of post-flowering photoperiodic effects might offer clues to increase the yield potential of soybeans.

Technology for increasing the bioavailability of feed using quorum sensing inhibitors

The article presents the results of studies on increasing the bioavailability of feed, when using oak bark extract (OBE) and quorum sensing inhibitors (QSI) in the diet of cattle, in particular, the effect on volatile fatty acids, pH, ammonia and the content of nitrogen metabolites. The use of OBE and QSI was accompanied by an increase in the concentration of VFAs by 1.17 and 5.56 % (P≤0.05) three hours after feeding. The studies revealed an increase in the concentration of ammonia in the cicatricial content when adding ECD and IR by up to 2.88 and 8.80 % (P≤0.001) 3 hours after feeding, respectively. The same tendency is observed at a 6-hour exposure, the ammonia level increases by 6.08 % (P≤0.01) and 11.08 % (P≤0.001). The effect of oak bark extract on the bioavailability of the forage substrate in the rumen was accompanied by an increase in the total nitrogen content by 2.10% (P≤0.05), and in the group using quorum inhibitors, by 4.41% (P≤0.01). 6 hours after feeding, the content of non-protein nitrogen decreased by 4.56 and 7.45 % (P≤0.01) in the OBE and QSI groups; this indicates a significant rate of nitrogen assimilation by the scar microbiota which converts it into protein.

Novel sequential flow baffled microalgal-bacterial photobioreactor for enhancing nitrogen assimilation into microalgal biomass whilst bioremediating nutrient-rich wastewater simultaneously

A novel sequential flow baffled microalgal-bacterial (SFB-AlgalBac) photobioreactor was designed to cater for the synergistic interactions between microalgal and bacterial consortia to enhance nitrogen assimilation into microalgal biomass from nutrient-rich wastewater medium. The performance of the SFB-AlgalBac photobioreactor was found to be optimum at the influent flow rate of 5.0 L/d, equivalent to 20 days of hydraulic retention time (HRT). The highest microalgal nitrogen assimilation rate (0.0271 /d) and biomass productivity (1350 mg/d) were recorded amidst this flow rate. Further increase to the 10.0 L/d flow rate reduced the photobioreactor performance, as evidenced by a reduction in microalgal biomass productivity (>10%). The microalgal biomass per unit of nitrogen assimilated values were attained at 16.69 mg/mg for the 5.0 L/d flow rate as opposed to 7.73 mg/mg for the 10.0 L/d flow rate, despite both having comparable specific growth rates. Also, the prior influent treatment by activated sludge was found to exude extracellular polymeric substances which significantly improved the microalgal biomass settleability up to 37%. The employment of SFB-AlgalBac photobioreactor is anticipated could exploit the low-cost nitrogen sources from nutrient-rich wastewaters via bioconversion into valuable microalgal biomass while fulfilling the requirements of sustainable wastewater treatment technologies.

The Contribution of Small Phytoplankton Communities to the Total Dissolved Inorganic Nitrogen Assimilation Rates in the East/Japan Sea: An Experimental Evaluation

As a part of Korean-Russian joint expeditions in the East/Japan Sea during 2012 and 2015, a set of total and small (<2 μm) phytoplankton NO3− and NH4+ uptake rate estimations were carried out. The study aimed to assess the spatio-temporal variations in dissolved inorganic nitrogen (DIN) assimilation by the total and small phytoplankton. The results show that the total NO3− uptake rates during 2012 varied between 0.001 and 0.150 μmol NL−1h−1 (mean ± SD = 0.034 ± 0.033) and that the total NH4+ uptake rates ranged between 0.002 and 0.707 μmol NL−1h−1 (mean ± SD = 0.200 ± 0.158). The total uptake rates during 2015 were ranged from 0.003 to 0.530 (mean ± S.D. = 0.117 ± 0.120 μmol NL−1h−1) for NO3− and from 0.008 to 1.17 (mean ± S.D. = 0.199 ± 0.266 NL−1h−1) for NH4+. The small phytoplankton NO3− and NH4+ uptake rates during 2015 ranged between 0.001 and 0.164 (mean ± S.D. = 0.033 ± 0.036) μmol NL−1h−1 and 0.010–0.304 (mean ± S.D. = 0.101 ± 0.073) μmol NL−1h−1, respectively. Small phytoplankton’s contribution to the total depth-integrated NO3− and NH4+ uptake rates ranged from 10.24 to 59.36% and from 30.21 to 68.55%, respectively. The significant negative relationship observed between the depth-integrated total NO3− and NH4+ uptake rates and small phytoplankton contributions indicates a possible decline in the DIN assimilation rates under small phytoplankton dominance. The results from the present study highlight the possibility of a reduction in the total DIN assimilation process in the East/Japan Sea when small phytoplankton dominate under strong thermal stratification due to sea surface warming. The present study’s findings agree with the model projections, which suggested a decline in primary production in the global warming scenario.

Can luminescent solar concentrators increase microalgal growth on anaerobically digested food effluent?

Increasing microalgal biomass productivity and enhancing nutrient removal rates are critical when growing microalgae in wastewater. In most cases, the effluents such as anaerobically digested food effluent (ADFE) are very turbid. Using such effluents as a medium for an algal culture would leave the culture with high turbidity resulting in photo-limitation of the algal culture. Light-diffusing systems can be used to overcome the light limitation in microalgal cultures. In this study, red luminescent solar concentrators were used to shift the sunlight into the desired wavelength and deliver it into the depth of cultures of an outdoor microalgal consortium cultivated in ADFE in paddlewheel-driven raceway ponds. Biomass productivity and specific growth rate of cultures grown using red luminescent solar concentrators (LSCs) were 61% and 59% higher than those in control cultures. The nitrogen assimilation rate of biomass under red LSCs was 1.8-fold higher than that in the control. Further, the lipid content of the cultures under red LSCs (490 mg lipid g−1 biomass) was 30% higher than that of the control. The results of this study showed that using red LSCs can improve microalga growth on ADFE when paddlewheel raceway ponds are used.

Primary production and nitrogen assimilation rates from bay to offshore waters in the oyashio-kuroshio-Tsugaru Warm Current interfrontal region of the northwestern north Pacific Ocean

We examined primary production (PP) and the assimilation rates of nitrate (ρNO3-), ammonium (ρNH4+) and dinitrogen (ρN2) using 13C and 15N tracer techniques along bay to offshore transects in the Oyashio-Kuroshio-Tsugaru Warm Current interfrontal region in the northwestern North Pacific Ocean, during five research cruises covering a full seasonal cycle. Surface inorganic N was depleted in the bays and the offshore region from summer to fall, but the higher particulate organic carbon (POC)/particulate nitrogen (PN) ratio and higher maximum N assimilation rate observed kinetics experiments in the bays suggest that N limitation was stronger in bays than offshore. PP (295–19,200 nmol C L−1 d−1), ρNO3- (9.45–650 nmol N L−1 d−1) and ρNH4+ (11.6–494 nmol N L−1 d−1) in the surface waters were generally low in summer and high in spring. Different from the cases of ρNO3- and ρNH4+, ρN2 was high (up to 12 nmol N L−1 d−1) in mid-summer, especially in offshore regions, and moderate or low (≤2.26 nmol N L−1 d−1) during other seasons. N2 fixation largely contributed to total new production (up to 29%) in mid-summer. The mean f-ratio, estimated as the ratio of (ρNO3- + ρN2) to (ρNO3- + ρN2 + ρNH4+) at two offshore stations varied within the range of 0.29–0.83 (mean 0.54 ± 0.20). Comparison of the PP and total N assimilation (ρNO3- + ρN2 + ρNH4+) indicated that the ratio of C to N assimilation rates (max. 95) far exceeded the Redfield ratio (6.6). This finding suggests that other sources of N (e.g., dissolved organic nitrogen) contributed significantly to total N assimilation; if this is correct, the estimated f-ratio may be too high. Alternatively, the fC-ratio was estimated from the ratio of (ρNO3- + ρN2) to PP by assuming the Redfieldian assimilation ratio, and it ranged from 0.06 to 1.10 (mean 0.45 ± 0.31). Despite uncertainties in both the f- and fC-ratio estimation, our data provide evidence that a large fraction of PP is potentially available for export to deep waters and to higher trophic levels in the interfrontal region of the western North Pacific.

Resting Stages of Skeletonema marinoi Assimilate Nitrogen From the Ambient Environment Under Dark, Anoxic Conditions.

The planktonic marine diatom Skeletonema marinoi forms resting stages, which can survive for decades buried in aphotic, anoxic sediments and resume growth when re-exposed to light, oxygen, and nutrients. The mechanisms by which they maintain cell viability during dormancy are poorly known. Here, we investigated cell-specific nitrogen (N) and carbon (C) assimilation and survival rate in resting stages of three S.marinoi strains. Resting stages were incubated with stable isotopes of dissolved inorganic N (DIN), in the form of 15 N-ammonium (NH4+ ) or -nitrate (NO3- ) and dissolved inorganic C (DIC) as 13 C-bicarbonate (HCO3- ) under dark and anoxic conditions for 2months. Particulate C and N concentration remained close to the Redfield ratio (6.6) during the experiment, indicating viable diatoms. However, survival varied between <0.1% and 47.6% among the three different S. marinoi strains, and overall survival was higher when NO3- was available. One strain did not survive in the NH4+ treatment. Using secondary ion mass spectrometry (SIMS), we quantified assimilation of labeled DIC and DIN from the ambient environment within the resting stages. Dark fixation of DIC was insignificant across all strains. Significant assimilation of 15 N-NO3- and 15 N-NH4+ occurred in all S.marinoi strains at rates that would double the nitrogenous biomass over 77-380years depending on strain and treatment. Hence, resting stages of S.marinoi assimilate N from the ambient environment at slow rates during darkness and anoxia. This activity may explain their well-documented long survival and swift resumption of vegetative growth after dormancy in dark and anoxic sediments.