Plankton Community Respiration and ETS Activity Under Variable CO2 and Nutrient Fertilization During a Mesocosm Study in the Subtropical North Atlantic

The enzymatic electron transport system (ETS) assay is frequently used as a proxy of respiratory activity in planktonic communities. It is thought to estimate the maximum overall activity of the enzymes associated with the respiratory ETS systems in both eukaryotic and prokaryotic organisms. Thus, in order to derive actual respiration rates (R) from ETS it is necessary to determine empirical R/ETS conversion algorithms. In this study we explore the temporal development of R and ETS activity in natural plankton communities (from bacteria to large phytoplankton) enclosed in mesocosms, treated with different CO2 concentrations. The experiment lasted 30 days, during which abrupt changes in community structure and biomass occurred through a sharp transition from oligotrophy (phase I) to highly eutrophic conditions (phase II) after nutrient-induced fertilization (day 18). R and ETS did not show any response to CO2 under oligotrophic conditions, but R increased significantly more in the two high CO2 mesocosms after fertilization, coinciding with a sharp rise in large phytoplankton (mostly diatoms). R and ETS were significantly correlated only during the eutrophic phase. The R/ETS ranged more than threefold in magnitude during the experiment, with phase-averaged values significantly higher under oligotrophic conditions (0.7-1.1) than after nutrient fertilization (0.5-0.7). We did not find any significant relationship between R/ETS and community structure or biomass, although R correlated significantly with total biomass after fertilization in the four mesocosms. Multiple stepwise regression models show that large phytoplankton explains most of the variance in R during phases I (86%) and II (53%) and of ETS (86%) during phase II, while picophytoplankton contributes up to 73% to explain the variance in the ETS model during phase I. Our results suggest that R/ETS may be too variable in the ocean as to apply constant values to different communities living under contrasting environmental conditions. Controlled experiments with natural communities, like the present one, would help to constrain the range of variability of the R/ETS ratio, and to understand the factors driving it

Reference intervals for bone turnover markers in Spanish premenopausal women

BACKGROUND: The aims of this study were to establish robust reference intervals and to investigate the factors influencing bone turnover markers (BTMs) in healthy premenopausal Spanish women. METHODS: A total of 184 women (35-45 years) from 13 centers in Catalonia were analyzed. Blood and second void urine samples were collected between 8 a.m. and 10 a.m. after an overnight fast. Serum procollagen type I amino-terminal propeptide (PINP) and serum cross-linked C-terminal telopeptide of type I collagen (CTX-I) were measured by two automated assays (Roche and IDS), bone alkaline phosphatase (bone ALP) by ELISA, osteocalcin (OC) by IRMA and urinary NTX-I by ELISA. PTH and 25-hydroxyvitamin D (25OHD) levels were measured. All participants completed a questionnaire on lifestyle factors. RESULTS: Reference intervals were: PINP: 22.7-63.1 and 21.8-65.5 μg/L, bone ALP: 6.0-13.6 μg/L, OC: 8.0-23.0 μg/L, CTX-I: 137-484 and 109-544 ng/L and NTX-I: 19.6-68.9 nM/mM. Oral contraceptive pills (OCPs) influenced PINP (p=0.007), and low body mass index (BMI) was associated with higher BTMs except for bone ALP. Women under 40 had higher median values of most BTMs. CTX-I was influenced by calcium intake (p=0.010) and PTH (p=0.007). 25OHD levels did not influence BTMs. Concordance between the two automated assays for PINP and particularly CTX-I was poor. CONCLUSIONS: Robust reference intervals for BTMs in a Southern European country are provided. The effects of OCPs and BMI on their levels are significant, whilst serum 25OHD levels did not influence BTMs. Age, calcium intake, BMI and PTH influenced CTX-I. The two automated assays for measuring PINP and CTX-I are not interchangeable

Factors controlling plankton community production, export flux, and particulate matter stoichiometry in the coastal upwelling system off Peru

Eastern boundary upwelling systems (EBUS) are among the most productive marine ecosystems on Earth. The production of organic material is fueled by upwelling of nutrient-rich deep waters and high incident light at the sea surface. However, biotic and abiotic factors can modify surface production and related biogeochemical processes. Determining these factors is important because EBUS are considered hotspots of climate change, and reliable predictions of their future functioning requires understanding of the mechanisms driving the biogeochemical cycles therein. In this field experiment, we used in situ mesocosms as tools to improve our mechanistic understanding of processes controlling organic matter cycling in the coastal Peruvian upwelling system. Eight mesocosms, each with a volume of ∼55 m3, were deployed for 50 d ∼6 km off Callao (12∘ S) during austral summer 2017, coinciding with a coastal El Niño phase. After mesocosm deployment, we collected subsurface waters at two different locations in the regional oxygen minimum zone (OMZ) and injected these into four mesocosms (mixing ratio ≈1.5 : 1 mesocosm: OMZ water). The focus of this paper is on temporal developments of organic matter production, export, and stoichiometry in the individual mesocosms. The mesocosm phytoplankton communities were initially dominated by diatoms but shifted towards a pronounced dominance of the mixotrophic dinoflagellate (Akashiwo sanguinea) when inorganic nitrogen was exhausted in surface layers. The community shift coincided with a short-term increase in production during the A. sanguinea bloom, which left a pronounced imprint on organic matter C : N : P stoichiometry. However, C, N, and P export fluxes did not increase because A. sanguinea persisted in the water column and did not sink out during the experiment. Accordingly, export fluxes during the study were decoupled from surface production and sustained by the remaining plankton community. Overall, biogeochemical pools and fluxes were surprisingly constant for most of the experiment. We explain this constancy by light limitation through self-shading by phytoplankton and by inorganic nitrogen limitation which constrained phytoplankton growth. Thus, gain and loss processes remained balanced and there were few opportunities for blooms, which represents an event where the system becomes unbalanced. Overall, our mesocosm study revealed some key links between ecological and biogeochemical processes for one of the most economically important regions in the oceans

Organic matter and gel particles of Maria S. Merian cruise MSM85

The discrete biogeochemical measurements from RV Maria S. Merian MSM85 sampled for dissolved organic matter, microbial cell abundances and gel particles. The parameters include POC/PON, DOC/TDN, microbial cell abundances, gel particle concentrations like TEP and CSP. The samples were aquired within 5-2700 m of the Greenland Sea between 61 N to 77 N and 40 W to 4 W. The data was collected on board MSM85 from 27th July 2018-11th August 2019. The water collection occured using a CTD and laboratory methods varied by parameter. POC/PON was analysed using CHNS-O Elemental Analyser, DOC/TDN was analysed using TOC-VCSH, cell abundance (phytoplankton, bacteria, viral) was analysed using flow cytometery, gel particles were analysed colorimetrically using a spectrophotometer. The purpose of data collection was to understand spatial variability of organic mater and associated dynamics of the microbial loop

Dissolved organic matter offsets the detrimental effects of climate change in the nitrogen‐fixing cyanobacterium Crocosphaera

Abstract Diazotrophs provide a significant reactive nitrogen source in the ocean. Increased warming and stratification may decrease nutrient availability in the future, forcing microbial communities toward using dissolved organic matter (DOM). Not depending on reactive nitrogen availability, diazotrophs may be “winners” in a nutrient‐depleted ocean. However, their ability to exploit DOM may influence this success. We exposed cultures of the widespread Crocosphaera to low (26°C, pH 8.1), moderate (28°C, pH 8.0), and extreme (30°C, pH 7.9) climate change scenarios, under control or DOM‐amended conditions. Growth was suboptimal in the low and extreme treatments and favored in the moderate treatment. DOM was preferred as a carbon source regardless of the treatment and promoted N2 fixation in extreme conditions. This was reflected in the increased expression of photosynthesis genes to obtain energy. DOM provides Crocosphaera with a key ecological advantage, possibly dictating diazotroph‐derived nitrogen inputs in the future ocean

Contrasting Roles of DOP as a Source of Phosphorus and Energy for Marine Diazotrophs

International audienceThe oceanic dissolved organic phosphorus (DOP) pool is mainly composed of P-esters and, to a lesser extent, equally abundant phosphonate and P-anhydride molecules. In phosphate-limited ocean regions, diazotrophs are thought to rely on DOP compounds as an alternative source of phosphorus (P). While both P-esters and phosphonates effectively promote dinitrogen (N 2 ) fixation, the role of P-anhydrides for diazotrophs is unknown. Here we explore the effect of P-anhydrides on N 2 fixation at two stations with contrasting biogeochemical conditions: one located in the Tonga trench volcanic arc region (“volcano,” with low phosphate and high iron concentrations), and the other in the South Pacific Gyre (“gyre,” with moderate phosphate and low iron). We incubated surface seawater with AMP (P-ester), ATP (P-ester and P-anhydride), or 3polyP (P-anhydride) and determined cell-specific N 2 fixation rates, nifH gene abundance, and transcription in Crocosphaera and Trichodesmium . Trichodesmium did not respond to any DOP compounds added, suggesting that they were not P-limited at the volcano station and were outcompeted by the low iron conditions at the gyre station. Conversely, Crocosphaera were numerous at both stations and their specific N 2 fixation rates were stimulated by AMP at the volcano station and slightly by 3polyP at both stations. Heterotrophic bacteria responded to ATP and 3polyP additions similarly at both stations, despite the contrasting phosphate and iron availability. The use of 3polyP by Crocosphaera and heterotrophic bacteria at both low and moderate phosphate concentrations suggests that this compound, in addition to being a source of P, can be used to acquire energy for which both groups compete. P-anhydrides may thus leverage energy restrictions to diazotrophs in the future stratified and nutrient-impoverished ocean

Contrasting Roles of DOP as a Source of Phosphorus and Energy for Marine Diazotrophs

The oceanic dissolved organic phosphorus (DOP) pool is mainly composed of P-esters and, to a lesser extent, equally abundant phosphonate and P-anhydride molecules. In phosphate-limited ocean regions, diazotrophs are thought to rely on DOP compounds as an alternative source of phosphorus (P). While both P-esters and phosphonates effectively promote dinitrogen (N2) fixation, the role of P-anhydrides for diazotrophs is unknown. Here we explore the effect of P-anhydrides on N2 fixation at two stations with contrasting biogeochemical conditions: one located in the Tonga trench volcanic arc region (“volcano,” with low phosphate and high iron concentrations), and the other in the South Pacific Gyre (“gyre,” with moderate phosphate and low iron). We incubated surface seawater with AMP (P-ester), ATP (P-ester and P-anhydride), or 3polyP (P-anhydride) and determined cell-specific N2 fixation rates, nifH gene abundance, and transcription in Crocosphaera and Trichodesmium. Trichodesmium did not respond to any DOP compounds added, suggesting that they were not P-limited at the volcano station and were outcompeted by the low iron conditions at the gyre station. Conversely, Crocosphaera were numerous at both stations and their specific N2 fixation rates were stimulated by AMP at the volcano station and slightly by 3polyP at both stations. Heterotrophic bacteria responded to ATP and 3polyP additions similarly at both stations, despite the contrasting phosphate and iron availability. The use of 3polyP by Crocosphaera and heterotrophic bacteria at both low and moderate phosphate concentrations suggests that this compound, in addition to being a source of P, can be used to acquire energy for which both groups compete. P-anhydrides may thus leverage energy restrictions to diazotrophs in the future stratified and nutrient-impoverished ocean

Reference intervals for bone turnover markers in Spanish premenopausal women

BACKGROUND: The aims of this study were to establish robust reference intervals and to investigate the factors influencing bone turnover markers (BTMs) in healthy premenopausal Spanish women. METHODS: A total of 184 women (35-45 years) from 13 centers in Catalonia were analyzed. Blood and second void urine samples were collected between 8 a.m. and 10 a.m. after an overnight fast. Serum procollagen type I amino-terminal propeptide (PINP) and serum cross-linked C-terminal telopeptide of type I collagen (CTX-I) were measured by two automated assays (Roche and IDS), bone alkaline phosphatase (bone ALP) by ELISA, osteocalcin (OC) by IRMA and urinary NTX-I by ELISA. PTH and 25-hydroxyvitamin D (25OHD) levels were measured. All participants completed a questionnaire on lifestyle factors. RESULTS: Reference intervals were: PINP: 22.7-63.1 and 21.8-65.5 μg/L, bone ALP: 6.0-13.6 μg/L, OC: 8.0-23.0 μg/L, CTX-I: 137-484 and 109-544 ng/L and NTX-I: 19.6-68.9 nM/mM. Oral contraceptive pills (OCPs) influenced PINP (p=0.007), and low body mass index (BMI) was associated with higher BTMs except for bone ALP. Women under 40 had higher median values of most BTMs. CTX-I was influenced by calcium intake (p=0.010) and PTH (p=0.007). 25OHD levels did not influence BTMs. Concordance between the two automated assays for PINP and particularly CTX-I was poor. CONCLUSIONS: Robust reference intervals for BTMs in a Southern European country are provided. The effects of OCPs and BMI on their levels are significant, whilst serum 25OHD levels did not influence BTMs. Age, calcium intake, BMI and PTH influenced CTX-I. The two automated assays for measuring PINP and CTX-I are not interchangeable