Phosphorus limitation of primary productivity in the eastern Mediterranean Sea

Although NO3- is generally considered to limit primary productivity in most of the world’s oceans, previous studies have suggested the Mediterranean Sea may be an exception. In this study of the southeastern Mediterranean, we found that all the PO43- was removed from the upper water column during the winter phytoplankton bloom in the core and boundary of a warm-core eddy, while measurable (0.3-0.6 µM) NO3- remained. The N:P (NO3-: PO43-) ratio in the core and boundary of the Cyprus eddy was 27.4 and the slope of the linear portion of the N vs. P scattergram with 25.5 with a positive intercept of 0.5 µM on the NO3- axis. A similar N:P ratio (28-29), slope (21-23), and intercept (0.9-1.1) was found for the water column across much of the southern Levantine basin. These data, taken together with the results of incubation experiments, lead us to conclude that the southeastern Mediterranean is strongly P limited. The degree of P limitation increases from west to east across the entire basin. We suggest that removal of PO43 by adsorbtion on Fe- rich dust particles may be an important process controlling the concentration of P in the water column

Transporters involved in uptake of di- and tricarboxylates in Bacillus subtilis

Di- and tricarboxylates found as intermediates in the tricarboxylic acid cycle can be utilized by many bacteria and serve as carbon and energy source under aerobic and anaerobic conditions. A prerequisite for metabolism is that the carboxylates are transported into the cells across the cytoplasmic membrane. Bacillus subtilis is able to metabolize many di- and tricarboxylates and in this overview the available data on all known and putative di- and tricarboxylate transporters in B. subtilis is summarized. The B. subtilis transporters, that are of the secondary type, are discussed in the context of the protein families to which they belong. Available data on biochemical characterization, regulation of gene expression and the physiological function is summarized. It is concluded that in B. subtilis multiple transporters are present for tricarboxylic acid cycle intermediates.</p

Silica cycling in the ultra-oligotrophic eastern Mediterranean Sea

Although silica is a key plant nutrient, there have been few studies aimed at understanding the Si cycle in the eastern Mediterranean Sea (EMS). Here we use a combination of new measurements and literature values to explain the silicic acid distribution across the basin and to calculate a silica budget to identify the key controlling processes. The surface water concentration of ∼1 μM, which is unchanging seasonally across the basin, was due to the inflow of western Mediterranean Sea (WMS) water at the Straits of Sicily. It does not change seasonally because there is only a sparse population of diatoms due to the low nutrient (N and P) supply to the photic zone in the EMS. The concentration of silicic acid in the deep water of the western Ionian Sea (6.3 μM) close to the S Adriatic are an of formation was due to the preformed silicic acid (3 μM) plus biogenic silica (BSi) from the dissolution of diatoms from the winter phytoplankton bloom (3.2 μM). The increase of 4.4 μM across the deep water of the EMS was due to silicic acid formed from in situ diagenetic weathering of aluminosilicate minerals fluxing out of the sediment. The major inputs to the EMS are silicic acid and BSi inflowing from the western Mediterranean (121 × 109 mol Si yr−1 silicic acid and 16 × 109 mol Si yr−1 BSi), silicic acid fluxing from the sediment (54 × 109 mol Si yr−1) and riverine (27 × 109 mol Si yr−1) and subterranean groundwater (9.7 × 109 mol Si yr−1) inputs, with only a minor direct input from dissolution of dust in the water column (1 × 109 mol Si yr−1). This budget shows the importance of rapidly dissolving BSi and in situ weathering of aluminosilicate minerals as sources of silica to balance the net export of silicic acid at the Straits of Sicily. Future measurements to improve the accuracy of this preliminary budget have been identified

Haptic feedback in a teleoperated box &amp; blocks task

Haptic feedback is a desired feature in teleoperation as it can improve dexterous manipulation. Direct force feedback to the operator’s hand and fingers requires complex hardware and therefore substituting force by for instance vibration is a relevant topic. In this experiment, we tested performance on a Box &amp; Blocks task in a teleoperation set-up with no feedback, direct force feedback and substituted vibration feedback. Objective performance was the same in all conditions as was the learning effect over three sessions, but participants had a clear preference for haptic feedback over no haptic feedback. The preferred type of feedback (force or vibration or both) varied over participants. In general, this study showed that haptic feedback is preferred in teleoperation, the Box &amp; Blocks task seems not sensitive enough for our (and most) current teleoperation set-up(s), and vibration feedback as substitute for direct force feedback works well and can be used intuitively.</p

Transcriptome analysis in switchgrass discloses ecotype difference in photosynthetic efficiency

Citation: Serba, D. D., Uppalapati, S. R., Krom, N., Mukherjee, S., Tang, Y. H., Mysore, K. S., & Saha, M. C. (2016). Transcriptome analysis in switchgrass discloses ecotype difference in photosynthetic efficiency. Bmc Genomics, 17, 14. doi:10.1186/s12864-016-3377-8Background: Switchgrass, a warm-season perennial grass studied as a potential dedicated biofuel feedstock, is classified into two main taxa - lowland and upland ecotypes - that differ in morphology and habitat of adaptation. But there is limited information on their inherent molecular variations. Results: Transcriptome analysis by RNA-sequencing (RNA-Seq) was conducted for lowland and upland ecotypes to document their gene expression variations. Mapping of transcriptome to the reference genome (Panicum virgatum v1. 1) revealed that the lowland and upland ecotypes differ substantially in sets of genes transcribed as well as levels of expression. Differential gene expression analysis exhibited that transcripts related to photosynthesis efficiency and development and photosystem reaction center subunits were upregulated in lowlands compared to upland genotype. On the other hand, catalase isozymes, helix-loop-helix, late embryogenesis abundant group I, photosulfokinases, and S-adenosyl methionine synthase gene transcripts were upregulated in the upland compared to the lowlands. At >= 100x coverage and >= 5% minor allele frequency, a total of 25,894 and 16,979 single nucleotide polymorphism (SNP) markers were discovered for VS16 (upland ecotype) and K5 (lowland ecotype) against the reference genome. The allele combination of the SNPs revealed that the transition mutations are more prevalent than the transversion mutations. Conclusions: The gene ontology (GO) analysis of the transcriptome indicated lowland ecotype had significantly higher representation for cellular components associated with photosynthesis machinery controlling carbon fixation. In addition, using the transcriptome data, SNP markers were detected, which were distributed throughout the genome. The differentially expressed genes and SNP markers detected in this study would be useful resources for traits mapping and gene transfer across ecotypes in switchgrass breeding for increased biomass yield for biofuel conversion

Potentially bioavailable iron delivery by iceberg-hosted sediments and atmospheric dust to the polar oceans

Iceberg-hosted sediments and atmospheric dust transport potentially bioavailable iron to the Arctic and Southern oceans as ferrihydrite. Ferrihydrite is nanoparticulate and more soluble, as well as potentially more bioavailable, than other iron (oxyhydr)oxide minerals (lepidocrocite, goethite, and hematite). A suite of more than 50 iceberghosted sediments contain a mean content of 0.076 wt% Fe as ferrihydrite, which produces iceberg-hosted Fe fluxes ranging from 0.7 to 5.5 and 3.2 to 25 Gmoles yr 1 to the Arctic and Southern oceans respectively. Atmospheric dust (with little or no combustion products) contains a mean ferrihydrite Fe content of 0.038 wt% (corresponding to a fractional solubility of 1 %) and delivers much smaller Fe fluxes (0.02–0.07 Gmoles yr 1 to the Arctic Ocean and 0.0– 0.02 Gmoles yr 1 to the Southern Ocean). New dust flux data show that most atmospheric dust is delivered to sea ice where exposure to melting/re-freezing cycles may enhance fractional solubility, and thus fluxes, by a factor of approximately 2.5. Improved estimates for these particulate sources require additional data for the iceberg losses during fjord transit, the sediment content of icebergs, and samples of atmospheric dust delivered to the polar regions

Iron from coal combustion particles dissolves much faster than mineral dust under simulated atmospheric acidic conditions

Mineral dust is the largest source of aerosol iron (Fe) to the offshore global ocean, but acidic processing of coal fly ash (CFA) in the atmosphere could be an important source of soluble aerosol Fe. Here, we determined the Fe speciation and dissolution kinetics of CFA from Aberthaw (United Kingdom), Krakow (Poland), and Shandong (China) in solutions which simulate atmospheric acidic processing. In CFA PM10 fractions, 8 %–21.5 % of the total Fe was found to be hematite and goethite (dithionite-extracted Fe), and 2 %–6.5 % was found to be amorphous Fe (ascorbate-extracted Fe), while magnetite (oxalate-extracted Fe) varied from 3 %–22 %. The remaining 50 %–87 % of Fe was associated with other Fe-bearing phases, possibly aluminosilicates. High concentrations of ammonium sulfate ((NH4)2SO4), often found in wet aerosols, increased Fe solubility of CFA up to 7 times at low pH (2–3). The oxalate effect on the Fe dissolution rates at pH 2 varied considerably, depending on the samples, from no impact for Shandong ash to doubled dissolution for Krakow ash. However, this enhancement was suppressed in the presence of high concentrations of (NH4)2SO4. Dissolution of highly reactive (amorphous) Fe was insufficient to explain the high Fe solubility at low pH in CFA, and the modelled dissolution kinetics suggest that other Fe-bearing phases such as magnetite may also dissolve relatively rapidly under acidic conditions. Overall, Fe in CFA dissolved up to 7 times faster than in a Saharan dust precursor sample at pH 2. Based on these laboratory data, we developed a new scheme for the proton- and oxalate-promoted Fe dissolution of CFA, which was implemented into the global atmospheric chemical transport model IMPACT (Integrated Massively Parallel Atmospheric Chemical Transport). The revised model showed a better agreement with observations of Fe solubility in aerosol particles over the Bay of Bengal, due to the initial rapid release of Fe and the suppression of the oxalate-promoted dissolution at low pH. The improved model enabled us to predict sensitivity to a more dynamic range of pH changes, particularly between anthropogenic combustion and biomass burning aerosols

The potential impact of Saharan dust and polluted aerosols on microbial populations in the East Mediterranean Sea, an overview of a mesocosm experimental approach.

Recent estimates of nutrient budgets for the Eastern Mediterranean Sea (EMS) indicate that atmospheric aerosols play a significant role as suppliers of macro- and micro- nutrients to its Low Nutrient Low Chlorophyll water. Here we present the first mesocosm experimental study that examines the overall response of the oligotrophic EMS surface mixed layer (Cretan Sea, May 2012) to two different types of natural aerosol additions, “pure” Saharan dust (SD, 1.6 mg l-1) and mixed aerosols (A - polluted and desert origin, 1 mg l-1). We describe the rationale, the experimental set-up, the chemical characteristics of the ambient water and aerosols and the relative maximal biological impacts that resulted from the added aerosols. The two treatments, run in triplicates (3 m3 each), were compared to control-unamended runs. Leaching of approximately 2.1-2.8 and 2.2-3.7 nmol PO4 and 20-26 and 53-55 nmol NOx was measured per each milligram of SD and A, respectively, representing an addition of approximately 30% of the ambient phosphate concentrations. The nitrate/phosphate ratios added in the A treatment were twice than those added in the SD treatment. Both types of dry aerosols triggered a positive change (25-600% normalized per 1 mg l-1 addition) in most of the rate and state variables that were measured: bacterial abundance (BA), bacterial production (BP), Synechococcus (Syn) abundance, chlorophyll-a (chl-a), primary production (PP) and dinitrogen fixation (N2-fix), with relative changes among them following the sequence BP>PP≈N2-fix>chl-a≈BA≈Syn. Our results show that the ‘polluted’ aerosols triggered a relatively larger biological change compared to the SD amendments (per a similar amount of mass addition), especially regarding BP and PP. We speculate that despite the co-limitation of P and N in the EMS, the additional N released by the A treatment may have triggered the relatively larger response in most of the rate and state variables as compared to SD. An implication of our study is that a warmer atmosphere in the future may increase dust emissions and influence the intensity and length of the already well stratified water column in the EMS and hence the impact of the aerosols as a significant external source of new nutrients