Total Uptake Rate Research Articles

Increased hepatic glucose production with lower oxidative metabolism in the growth-restricted fetus.

Fetal growth restriction (FGR) is accompanied by early activation of hepatic glucose production (HGP), a hallmark of type 2 diabetes (T2D). Here, we used fetal hepatic catheterization to directly measure HGP and substrate flux in a sheep FGR model. We hypothesized that FGR fetuses would have increased hepatic lactate and amino acid uptake to support increased HGP. Indeed, FGR fetuses compared with normal (CON) fetuses had increased HGP and activation of gluconeogenic genes. Unexpectedly, hepatic pyruvate output was increased, while hepatic lactate and gluconeogenic amino acid uptake rates were decreased in FGR liver. Hepatic oxygen consumption and total substrate uptake rates were lower. In FGR liver tissue, metabolite abundance, 13C-metabolite labeling, enzymatic activity, and gene expression supported decreased pyruvate oxidation and increased lactate production. Isolated hepatocytes from FGR fetuses had greater intrinsic capacity for lactate-fueled glucose production. FGR livers also had lower energy (ATP) and redox state (NADH/NAD+ ratio). Thus, reduced hepatic oxidative metabolism may make carbons available for increased HGP, but also produces nutrient and energetic stress in FGR liver. Intrinsic programming of these pathways regulating HGP in the FGR fetus may underlie increased HGP and T2D risk postnatally.

Nitrogen acquisition strategy shifts with tree age depending on root functional traits and soil properties in Larix principis-rupprechtii plantations.

Variation in plant nitrogen uptake rate and substrate preference is complicated due to the combined influence of abiotic and biotic factors. For the same species of tree across different ages, the interactions between root structural traits, nitrogen uptake rate, and soil environment have not been fully characterized, a situation that constrains our understanding of underground resource strategies employed by trees at different ages. In the present study, we examined the nitrogen uptake rate, mycorrhiza, morphology, architecture, and chemistry of the roots of Larix principis-rupprechtii in a chronosequence (aged 18, 27, 37, 46, and 57 years) in the Saihanba Mechanical Forest Farm in Northern China. L. principis-rupprechtii preferred to absorb ammonium, followed in order by glycine and nitrate. The ammonium uptake rate of L. principis-rupprechtii significantly decreased (aged 18-37 years) and then increased (aged 46-57 years) with tree age. The glycine, nitrate, and total nitrogen uptake rates decreased with tree age. The root resource acquisition strategy appeared to shift from an acquisitive strategy to a conservative strategy associated with increasing tree age. Along the root-mycorrhizal collaboration gradient, the younger L. principis-rupprechtii relied more on their own root morphology and physiology to acquire resources, adopting a "do it yourself" strategy comprising increasing the specific root length, the specific root area, and the N uptake rate (nitrate and glycine). Conversely, older trees depended more on mycorrhizal partners to acquire nitrogen resources, an "outsourcing" strategy. The results contribute to our understanding of underground resource-use strategies of plants and the nitrogen cycle in forest ecosystems according to stand age.

Inter-seasonal variation in nitrogen uptake rates of the eutrophic Cochin estuary and adjacent coastal Arabian Sea

The study assessed the Cochin estuary and adjacent coastal Arabian Sea for their seasonal variation in nitrate (NO3−) and ammonium (NH4+) uptake rates by total and nano + picoplankton using the 15N tracer technique. The results suggested that the NO3− and NH4+ uptake rates in the Cochin estuary are higher than those in the adjacent coastal Arabian Sea. NO3− and NH4+ uptake rates in the nearshore stations in the off Cochin station were high, indicating the influence of the eutrophic estuary. NO3− and NH4+ uptake rates conducted in off Mangalore transect were significantly lower than those of the off Cochin as it does not have an exchange with eutrophic systems. The nano + picoplankton's contribution to the total DIN uptake rates in the Cochin estuary was 77–98 %, indicating the relevance of nano + pico phytoplankton in the N cycling of the region.

Microbial carbon fixation and its influencing factors in saline lake water

Microbial carbon fixation in saline lakes constitutes an important part of the global lacustrine carbon budget. However, the microbial inorganic carbon uptake rates in saline lake water and its influencing factors are still not fully understood. Here, we studied in situ microbial carbon uptake rates under light-dependent and dark conditions in the saline water of Qinghai Lake using a carbon isotopic labeling (14C-bicarbonate) technique, followed by geochemical and microbial analyses. The results showed that the light-dependent inorganic carbon uptake rates were 135.17–293.02 μg C L−1 h−1 during the summer cruise, while dark inorganic carbon uptake rates ranged from 4.27 to 14.10 μg C L−1 h−1. Photoautotrophic prokaryotes and algae (e.g. Oxyphotobacteria, Chlorophyta, Cryptophyta and Ochrophyta) may be the major contributors to light-dependent carbon fixation processes. Microbial inorganic carbon uptake rates were mainly influenced by the level of nutrients (e.g., ammonium, dissolved inorganic carbon, dissolved organic carbon, total nitrogen), with dissolved inorganic carbon content being predominant. Environmental and microbial factors jointly regulate the total, light-dependent and dark inorganic carbon uptake rates in the studied saline lake water. In summary, microbial light-dependent and dark carbon fixation processes are active and contribute significantly to carbon sequestration in saline lake water. Therefore, more attention should be given to microbial carbon fixation and its response to climate and environmental changes of the lake carbon cycle in the context of climate change.

Size-differential photosynthetic traits of phytoplankton in the Chukchi Sea

Understanding size-differential productivity characteristics of phytoplankton is important to evaluating climate-driven environmental changes in marine ecosystems. In this study, we derived the relative contribution of small phytoplankton (Psmall; <5 μm) to the total primary production (TPP) and characterized their photosynthetic traits in comparison to large phytoplankton (Plarge) based on field-measured observations in the Chukchi Sea, 2012. The overall chlorophyll-a (51.8 ± 23.1%) and TPP contributions (52.3 ± 29.8%) of Psmall observed in this study were closely related to freshwater contents. In regards to nitrogen uptake, Psmall contributed 39.0% (S.D. = ± 28.4%) and 73.4% (S.D. = ± 50.1%) to the total nitrate uptake rate (TNP) and the total ammonium uptake rate (TAP), respectively, which is consistent with previous findings. Particulate and assimilated carbon/nitrogen (C/N) ratios were significantly (p < 0.01 and 0.05, respectively) lower in Psmall compared to Plarge, indicating their different natural capacities during growths. A significantly negative relationship was observed between the Psmall contribution and the TPP in the Chukchi Sea. These results imply that the more Psmall contribution in marine ecosystems could lead the less C sequestration from euphotic depths to deep ocean. In comparison to other regions, a more rapid decreasing TPP in the Chukchi Sea with increasing Psmall contribution is distinctively noticeable, which suggest that the Chukchi Sea ecosystem could be more vulnerable to an expected increase in Psmall contribution.

Abdominal aortic aneurysm screening in an academic family practice: Short-term impact of guideline changes.

To investigate abdominal aortic aneurysm (AAA) screening rates in the 6 months before and after the introduction of updated Canadian Task Force on Preventive Health Care (CTFPHC) guidelines to determine effects on practice patterns, as well as to determine whether certain patient characteristics impact AAA screening rates. Retrospective chart review. Academic family health centre in London, Ont. Male patients between the ages of 65 and 80. Screening rates for AAA before and after the guideline update were compared using the normal approximation of the binomial distribution. Analysis of demographic characteristic effects on screening rates was completed with the Fisher exact test. Number of visits to the clinic with a primary care provider within the study period and imaging type were collected. Of the 266 patients included in the study, 160 patients were eligible for screening at the start of the study period, 6 months before publication of the CTFPHC AAA guideline. Individuals eligible for screening visited the clinic an average (SD) of 2.44 (1.82) times in the 6 months before and 2.66 (1.99) times in the 6 months after. Overall, 69 individuals had AAA screening completed and 9 had a discussion of AAA screening without any imaging, for a total uptake rate of 88.5% for those who had screening recommended. The overall imaging rate was 48.9%. There was no statistically significant difference in screening rates between the time periods (P=.337) among those eligible for screening. For demographic characteristics for risk stratification, 7 individuals had a documented family history, of whom 5 had imaging of their abdominal aorta performed, plus 1 additional individual who had screening recommended but not completed. This was not statistically significant relative to the total population (P=.0598). Positive smoking status (active or ex-smoker) was more common, with 135 individuals having a relevant smoking history. Approximately half of these current and former smokers (68 individuals [50.4%]) had any sort of abdominal aortic imaging performed or recommended, which was not statistically significantly different compared with non-smokers (62 of 126 imaging performed or recommended, 49.2%; P=.9016). Screening practices did not change appreciably with the introduction of the CTFPHC AAA screening guidelines. Further research is needed to improve AAA screening rates. It is worth exploring electronic medical record-based reminders, nursing staff involvement in screening, screening programs via public health, and point-of-care ultrasound screening in a primary care setting.

Picocyanobacterial Contribution to the Total Primary Production in the Northwestern Pacific Ocean

Picocyanobacteria (Prochlorococcus and Synechococcus) play an important role in primary production and biogeochemical cycles in the subtropical and tropical Pacific Ocean, but little biological information on them is currently available in the North Pacific Ocean (NPO). The present study aimed to determine the picocyanobacterial contributions to the total primary production in the regions in the NPO using a combination of a dual stable isotope method and metabolic inhibitor. In terms of cell abundance, Prochlorococcus were mostly dominant (95.7 ± 1.4%) in the tropical Pacific region (hereafter, TP), whereas Synechococcus accounted for 50.8%–93.5% in the subtropical and temperate Pacific region (hereafter, SP). Regionally, the averages of primary production and picocyanobacterial contributions were 11.66 mg C m−2·h−1 and 45.2% (±4.8%) in the TP and 22.83 mg C m−2·h−1 and 70.2% in the SP, respectively. In comparison to the carbon, the average total nitrogen uptake rates and picocyanobacterial contributions were 10.11 mg N m−2·h−1 and 90.2% (±5.3%) in the TP and 4.12 mg N m−2·h−1 and 63.5%, respectively. These results indicate that picocyanobacteria is responsible for a large portion of the total primary production in the region, with higher contribution to nitrogen uptake rate than carbon. A long-term monitoring on the picocyanobacterial variability and contributions to primary production should be implemented under the global warming scenario with increasing ecological roles of picocyanobacteria.

CO2 uptake model of limestone-powder-blended concrete due to carbonation

In this study, a model for evaluating the CO2 uptake rate of plain concrete and limestone-powder-blended concrete in both the service and recycling phases was proposed. First, a blended cement hydration model was proposed to evaluate the content of carbonatable substances, porosity and carbon dioxide diffusivity. In the service phase, a one-dimensional carbonation model was proposed to evaluate the carbonation depth. In the recycling stage, an unreacted core model was proposed to evaluate the carbonation process of spherical recycled concrete. Secondly, considering the concrete materials, structural elements and environmental exposure, a CO2 uptake model at the service stage and recycling stage was proposed. The total CO2 uptake rate is the sum of the CO2 uptake rates in the service stage and the recycling stage. The analysis results showed (1) as the limestone replacement rate increased from 0% to 20% (water–binder ratio is 0.3), the CO2 uptake rate in the service phase increased from 3.12% to 3.84%, and the total CO2 uptake rate increased from 22.82% to 26.11%. (2) Given a certain concrete mixture, as the surface area to volume ratio of structural units increased, or the amount of recycled concrete decreased, the CO2 uptake rate increased, but the total CO2 uptake rate did not change. (3) Given a certain limestone powder replacement ratio, as the water/binder ratio increased, the total CO2 uptake ratio increased. The contributions of this study are 1) propose an integrated hydration-carbonation-CO2 uptake model for limestone blended concrete, 2) clarify the differences of carbonation equations between service stage and recycling stage, and 3) determine the effects of concrete mixtures, structural element sizes and types, life cycle stages, and recycled concrete sizes on CO2 uptake.

Characteristics of Different Size Phytoplankton for Primary Production and Biochemical Compositions in the Western East/Japan Sea.

The current phytoplankton community structure is expected to change, with small phytoplankton becoming dominant under ongoing warming conditions. To understand and evaluate the ecological roles of small phytoplankton in terms of food quantity and quality, the carbon uptake rates and intracellular biochemical compositions (i.e., carbohydrates, CHO; proteins, PRT; and lipids, LIP) of phytoplankton of different sizes were analyzed and compared in two different regions of the western East/Japan Sea (EJS): the Ulleung Basin (UB) and northwestern East/Japan Sea (NES). The average carbon uptake rate by the whole phytoplankton community in the UB (79.0 ± 12.2 mg C m–2 h–1) was approximately two times higher than that in the NES (40.7 ± 2.2 mg C m–2 h–1), although the average chlorophyll a (chl a) concentration was similar between the UB (31.0 ± 8.4 mg chl a m–2) and NES (28.4 ± 7.9 mg chl a m–2). The main reasons for the large difference in the carbon uptake rates are believed to be water temperature, which affects metabolic activity and growth rate, and the difference in euphotic depths. The contributions of small phytoplankton to the total carbon uptake rate were not significantly different between the regions studied. However, the rate of decrease in the total carbon uptake with increasing contributions from small phytoplankton was substantially higher in the UB than in the NES. This result suggests that compared to other regions in the EJS, the primary production in the UB could decrease rapidly under ongoing climate change. The calorific contents calculated based on biochemical compositions were similar between the small (1.01 ± 0.33 Kcal m–3) and large (1.14 ± 0.36 Kcal m–3) phytoplankton in the UB, whereas the biochemical contents were higher in the large phytoplankton (1.88 ± 0.54 Kcal m–3) than in the small phytoplankton (1.06 ± 0.18 Kcal m–3) in the NES. The calorific values per unit of chl a were higher for the large phytoplankton than for the small phytoplankton in both regions, which suggests that large phytoplankton could provide a more energy efficient food source to organisms in higher trophic levels in the western EJS.

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 (&lt;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.

In Situ Rates of Carbon and Nitrogen Uptake by Phytoplankton and the Contribution of Picophytoplankton in Kongsfjorden, Svalbard

Rapid climate warming and the associated melting of glaciers in high-latitude open fjord systems can have a significant impact on biogeochemical cycles. In this study, the uptake rates of carbon and nitrogen (nitrate and ammonium) of total phytoplankton and picophytoplankton (&lt;2 μm) were measured in Kongsfjorden in early May 2017 using the dual stable isotope technique. The daily uptake rates of total carbon and nitrogen ranged from 0.3 to 1.1 g C m−2 day−1, with a mean of 0.7 ± 0.3 g C m−2 day−1, and 0.13 to 0.17 g N m−2 day−1, with a mean of 0.16 ± 0.02 g N m−2 day−1. Microphytoplankton (20–200 μm) accounted for 68.1% of the total chlorophyll a (chl-a) concentration, while picophytoplankton (&lt;2 μm) accounted for 19.6% of the total chl-a, with a high contribution to the carbon uptake rate (42.9%) due to its higher particulate organic carbon-to-chl-a ratio. The contributions of picophytoplankton to the total nitrogen uptake rates were 47.1 ± 10.6% for nitrate and 74.0 ± 16.7% for ammonium. Our results indicated that picophytoplankton preferred regenerated nitrogen, such as ammonium, for growth and pointed to the importance of the role played by picophytoplankton in the local carbon uptake rate during the early springtime in 2017. Although the phytoplankton community, in terms of biovolume, in all samples was dominated by diatoms and Phaeocystis sp., a higher proportion of nano- and picophytoplankton chl-a (mean ± SD = 71.3 ± 16.4%) was observed in the relatively cold and turbid surface water in the inner fjord. Phytoplankton production (carbon uptake) decreased towards the inner fjord, while nitrogen uptake increased. The contrast in carbon and nitrogen uptake is likely caused by the gradient in glacial meltwater which affects both the light regime and nutrient availability. Therefore, global warming-enhanced glacier melting might support lower primary production (carbon fixation) with higher degrees of regeneration processes in fjord systems.

The effect of temperature on Antarctic lichen cytochrome and alternative respiratory pathway rates

Respiration is a crucial process that provides all living organisms with energy and metabolites for growth and cellular maintenance. The processes that control respiration in lichens remain poorly understood. We investigated the effects of short-term temperature changes on the respiration rate, as well as the relative contributions of the cytochrome and alternative pathways of thalli from four green-algal lichen species collected from their natural habitats in Antarctica. Lichen respiration was sensitive to short-term temperature increases over a range of 5–35 °C. The total O2 uptake rate was increased by fourfold, and the mean respiratory coefficient (Q10) decreased from 2.5 to 1.3 as the temperature increased. An increase in temperature from 5 to 15 °C had a positive effect on cytochrome respiration coupled with energy production. Temperatures above 15 °C stimulated the activation of the alternative (energy-dissipating) respiratory pathway. Hyperthermia led to increased O2 consumption that was not associated with mitochondrial oxidases. The effects of increased temperature on the respiration rates were more pronounced in the bipolar lichens Umbilicaria decussata and Usnea sphacelata than in the Usnea aurantiaco-atra species with a narrower geographical distribution.

Fine regulation of the starch liquefaction process and its application in the production of citric acid

Citric acid (CA), generally fermented from the starchy material, has attracted intense attention because of its wide applications in many aspects. However, the traditional starchy-liquefaction process based on the dextrose equivalent value and iodine-testing method is inappropriate as it hinders the subsequent CA fermentations. Here, a novel method of evaluating the starch liquefaction in the CA production process was established. Firstly, dextrin samples with the molecular weight (Mw) narrow distribution were prepared by alcohol fractional precipitation. Glucoamylase (GM) from the culture of CA-producing strain Aspergillus niger was purified. Then, the structure-activity relationship between the dextrin and GM was analyzed. Results demonstrated that the Mw of liquefied components aggregated in the range of 1.4–1.9 kDa could improve the efficiency of simultaneous saccharification and fermentation process. CA production rate and total sugar uptake rate were evidently improved with residual total sugar decreasing by 10.8% and fermentation efficiency enhanced by 21.1% in 9 h shorter fermentation time. All these results confirmed that fine regulation of the starch liquefaction based on the Mw characteristics was feasible and effective to improve the CA fermentation. Our proposed strategy could also be useful for other fermentations and sugar industry involving the starchy material.

The impact of temperature on the metabolism of volatile fatty acids by polyphosphate accumulating organisms (PAOs)

This study investigated the effects of different carbon sources on enriched Accumulibacter PAO cultures at high temperature (30 °C) and compared the carbon transformation with low temperature (20 °C) cases reported in literature, revealing several key metabolic differences. While PAOs seemed to prefer propionate anaerobically as compared to other VFAs at high temperature, high aerobic glycogen replenishment was realized with propionate as the anaerobic carbon source, a trait not previously observed at low temperatures. Therefore, it was found that propionate is not correlated with high P removal by Accumulibacter PAO at high temperatures. A combined substrate of acetate, propionate and perhaps butyrate seemed to be a better carbon source combination, since the total VFA uptake rate increased by up to 46%, and this increased the aerobic P-removal efficiency by up to 38.4% and reduced the glycogen recovery by more than 63% compared to the use of only propionate as substrate. This study improves our understanding of how to stimulate successful EBPR operation in warm climates by augmenting the P removal performance of PAOs.

Mass screening for colorectal cancer in a population of two million older adults in Guangzhou, China

Screening is an effective measure to prevent and control colorectal cancer (CRC). A mass CRC screening programme was conducted in Guangzhou from 2015 to 2017. Public media and reminders from a mobile short message service were used to invite residents aged between 50 and 74 years. A high-risk factor questionnaire (HRFQ) and biennial faecal immunochemical testing (FIT) were chosen as the primary screening methods, and individuals with a positive test result were referred to a defined hospital for an assessment colonoscopy. During the 3 years, 350,581 residents of the total eligible population of 2,283,214 attended the free first stage of screening. In all, 91.0% of the participants finished the HRFQs and FITs. The total uptake rate was 15.4%, which increased with age, female sex, and rural location. There was 15.9% positivity in the first stage of screening, including 8.5% positive HRFQs, 6.2% positive FITs and 1.2% positive HRFQs and FITs. In total, 10,600 individuals with positive HRFQs/FITs completed an assessment colonoscopy. The total uptake rate of colonoscopies was 18.9%, which decreased with age and female sex. Three hundred fifty-one CRCs and 980 advanced adenomas (AAs) were diagnosed with positive predictive values (PPV) of 3.3% and 9.2%, respectively. The PPVs of CRCs in the exclusively FIT-positive population were 4.9%, which was 10 times greater than in the exclusively HRFQ-positive population (0.5%). The PPVs of CRCs and AAs increased with age and male sex. The detection ratio of localized CRCs (including stage I and stage II) increased 68.1% due to screening. Although the compliance rate was low, the PPVs for CRCs and AAs were high. More effective mobilization of the programme’s needs and subsidies for colonoscopies should be taken into account to increase compliance.

Estimating microplastic-bound intake of hydrophobic organic chemicals by fish using measured desorption rates to artificial gut fluid

One of the most important concerns about marine microplastics is their role in delivery of chemical contaminants to biota. The contribution of microplastic ingestion to the overall uptake of five hydrophobic organic chemicals (HOCs) [α-, β-, and γ-hexachlorocyclohexanes (HCHs), pentachlorobenzene (PeCB), and hexachlorobenzene (HeCB)] by fish is evaluated in this study. Partition coefficients of all five HOCs between surfactant micelles and simulated intestinal fluid (SIF), as well as between protein and SIF, were experimentally determined. Desorption of model HOCs from a polyethylene film into an artificial gut solution was measured to estimate the fraction of HOCs that can be absorbed from microplastics during their gut retention time. Monte-Carlo simulation (n = 100,000) showed that the uptake via microplastic ingestion will be negligible for HCHs as compared to uptake via other exposure routes, water ventilation and food ingestion. On the other hand, microplastic ingestion might increase the total uptake rate of PeCB and HeCB due to their accelerated desorption from microplastics into the artificial gut solution under the model scenario, assuming an extremely high intake of microplastics. However, the steady-state bioaccumulation factor was predicted to decrease with increasing ingestion of microplastics, showing a dilution effect by microplastic ingestion. Results indicate that HOCs that are close to be at phase equilibrium between microplastics and environmental media are not likely to be further accumulated via ingestion of microplastics; this is true even for cases, where ingestion of microplastics contributes significantly to the total uptake of HOCs. Therefore, future studies need to focus on hydrophobic plastic additives that may exist in microplastics at a concentration higher than their equilibrium concentration with water.

Mineral iron utilization by natural and cultured Trichodesmium and associated bacteria

AbstractThe high iron (Fe) demands of Trichodesmium, a keystone nitrogen‐fixing cyanobacterium, are often met by dust deposition at the ocean surface. Following up on our findings of unique dust capturing and processing by Trichodesmium, we explored the ability of natural Trichodesmium colonies from the Gulf of Aqaba and Fe‐limited laboratory culture (IMS101) to obtain Fe from the mineral ferrihydrite and compete with their epibiotic bacteria for this Fe source. To study this complex system, we carefully optimized a radiotracer method ensuring complete removal of external ferrihydrite and efficient separation of bacteria from the colonies. Trichodesmium‐only uptake rates of natural colonies were 5–50 times faster than those of laboratory culture, suggesting that natural colonies acquire ferrihydrite at a greater efficiency. In some days, total uptake rates of natural colonies exceeded dissolved Fe release from ferrihydrite, indicating that the colonies enhance the mineral dissolution rate. Furthermore, uptake rates of bacteria associated with natural colonies were faster than those of bacteria associated with the culture, implying that the bacteria benefit from the Trichodesmium‐enhanced mineral dissolution. At the cellular level, surface area normalized uptake rates of bacteria always exceeded those of cultured Trichodesmium, but in natural populations, the dominance shifted between Trichodesmium and bacteria on different days. At the community level, when accounting for the total bacteria and Trichodesmium cells, Trichodesmium dominated Fe uptake in both cultured and natural colonies. Overall, our findings suggest that natural Trichodesmium colonies are exceptionally adapted for accessing mineral Fe and maintaining a sustainable relationship with their associated bacteria.

Recent Primary Production and Small Phytoplankton Contribution in the Yellow Sea during the Summer in 2016

The high nutrient concentration associated with the mixing dynamics of two warm and cold water masses supports high primary production in the Yellow Sea. Although various environmental changes have been reported, no recent information on small phytoplankton contribution to the total primary production as an important indicator for marine ecosystem changes is currently available in the Yellow Sea. The major objective of this study is to determine the small (< 2 μm) phytoplankton contribution to the total primary production in the Yellow Sea during August, 2016. In this study, we found relatively lower chlorophyll a concentrations in the water column than those previously reported in the central waters of the Yellow Sea. Moreover, the overall contribution of small phytoplankton (53.1%) to the total chlorophyll a concentration was considerably higher in this study than that (10.7%) observed previously. Based on the N/P ratio (67.6 ± 36.6) observed in this study, which is significantly higher than the Redfield ratio (16), we believe that phytoplankton experienced P-limiting conditions during the study period. The average daily carbon uptake rate of total phytoplankton in this study was 291.1 mg C m-2 d-1 (± 165.0 mg C m-2 d-1) and the rate of small phytoplankton was 205.7 mg C m-2 d-1 (± 116.0 mg C m-2 d-1) which is 71.9% (± 8.8%) of the total daily carbon uptake rate. This contribution of small phytoplankton observed in this study appears to be higher than that reported previously. Our recent measured primary production is approximately 50% lower than the previous values decades ago. The higher contributions of small phytoplankton to the total chlorophyll a concentration and primary production might be caused by P-limited conditions and this resulted in lower chlorophyll a concentration and total primary production in this study compared to previous studies.

Small phytoplankton contribution to the standing stocks and the total primary production in the Amundsen Sea

Abstract. Small phytoplankton are anticipated to be more important in a recently warming and freshening ocean condition. However, little information on the contribution of small phytoplankton to overall phytoplankton production is currently available in the Amundsen Sea. To determine the contributions of small phytoplankton to total biomass and primary production, carbon and nitrogen uptake rates of total and small phytoplankton were obtained from 12 productivity stations in the Amundsen Sea. The daily carbon uptake rates of total phytoplankton averaged in this study were 0.42 g C m−2 d−1 (SD = ± 0.30 g C m−2 d−1) and 0.84 g C m−2 d−1 (SD = ± 0.18 g C m−2 d−1) for non-polynya and polynya regions, respectively, whereas the daily total nitrogen (nitrate and ammonium) uptake rates were 0.12 g N m−2 d−1 (SD = ± 0.09 g N m−2 d−1) and 0.21 g N m−2 d−1 (SD = ± 0.11 g N m−2 d−1), respectively, for non-polynya and polynya regions, all of which were within the ranges reported previously. Small phytoplankton contributed 26.9 and 27.7 % to the total carbon and nitrogen uptake rates of phytoplankton in this study, respectively, which were relatively higher than the chlorophyll a contribution (19.4 %) of small phytoplankton. For a comparison of different regions, the contributions for chlorophyll a concentration and primary production of small phytoplankton averaged from all the non-polynya stations were 42.4 and 50.8 %, which were significantly higher than those (7.9 and 14.9 %, respectively) in the polynya region. A strong negative correlation (r2 = 0. 790, p&lt;0. 05) was found between the contributions of small phytoplankton and the total daily primary production of phytoplankton in this study. This finding implies that daily primary production decreases as small phytoplankton contribution increases, which is mainly due to the lower carbon uptake rate of small phytoplankton than large phytoplankton.

Differential Responses of Water Uptake Pathways and Expression of Two Aquaporin Genes to Water-Deficit in Rice Seedlings of Two Genotypes

Water-deficit (WD) is a major abiotic stress constraining crop productivity worldwide. Zhenshan 97 is a drought-susceptible rice genotype, while IRAT109 is a drought-resistant one. However, the physiological basis of the difference remains unclear. These two genotypes had similar total water uptake rates under both WD and well-watered (WW) conditions, and their water uptake rates under WD were significantly decreased compared with those under WW. However, the water uptake rate via the cell-to-cell pathway was significantly increased in Zhenshan 97 but decreased in IRAT109 under WD, whereas the opposite trends were observed through the apoplastic pathway. These results indicated that the stress responses and relative contributions of these two water uptake pathways were associated with rice genotype under WD. The expression levels of OsPIP2;4 and OsPIP2;5 genes were significantly higher in roots of Zhenshan 97 than in IRAT109 under the two conditions. OsPIP2;4 expression in roots was significantly up-regulated under WD, while OsPIP2;5 expression showed no significant change. These results suggest that the expression levels of OsPIP2;4 and OsPIP2;5 in rice are dependent on genotype and water availability. Compared with Zhenshan 97, IRAT109 had a higher root dry weight, water uptake rate and xylem sap flow rate, and lower leaf water potential and root porosity under WD, which might be responsible for the drought resistance in IRAT109.