Phlebotomine sandfly responses to carbon dioxide and human odour in the field

Responses of Lutzomyia sandflies (Diptera: Psychodidae: Phlebotominae) to carbon dioxide (CO2) and human odour were investigated by field experiments in Parana State, southern Brazil. Catches of two predominant species: Lu. intermedia (Antunes & Coutinho) and Lu. whitmani Lutz & Neiva, were compared between traps baited with a human adult or with CO2 emitted at the human-equivalent rate. When the baits were only 40 cm apart, no difference of attractiveness was detected. When baits were separated by 20 m, however, significantly fewer sandflies (44% Lu. intermedia, 46% Lu. whitmani) were trapped with CO2 compared with human bait. This is the first field evidence that anthropophilic sandflies are attracted by human kairomones in addition to CO2. For both species [Lutzomyia intermedia and Lu. whitmani] [corrected], the proportion of human attractiveness attributable to CO2 was significantly more [corrected] for males than females; for Lu. intermedia males human bait was no more attractive than CO2 alone. Gender differences in sandfly olfactory sensitivity are likely to be associated with behavioural differences on the host, where females feed on blood and males find mates. With traps 20 m apart, both Lutzomyia spp. showed roughly linear increased responses (log-log scale) to 0.08-0.55% CO2 equivalent to 0.5-4 humans. This would explain why host size is generally proportional to attractiveness, as observed for other species of phlebotomine sandflies.     

The effects of water hardness upon the uptake, accumulation and excretion of zinc in the brown trout, Salmo trutta L.

The effects of water hardness (9 and 220 mgl⁻¹ as CaCO₃) upon zinc exchange in brown trout exposed to 0.77 μmol Zn 1⁻¹ have been investigated using artificial soft water (<49.9 μmol Ca ^l-1, <40.1 μmol Mg 1⁻¹) and mains hard water (1671.7 μmol Ca 1⁻¹, 493.6 μmol Mg 1⁻¹) of known composition. Both hard and soft water-adapted fish exhibited a bimodal pattern of net zinc influx. Net zinc influxes during both fast and slow uptake phases were significantly greater ( P <0.001) in soft (82.9 and 6.2 μmol Zn 100 g⁻¹ h⁻¹) than in hard water (46.3 and 2.4 μmol Zn 100 g h⁻¹). Zinc efflux (- 0.2 μmol Zn 100 g⁻¹ h⁻¹) was enhanced only in hard water during the slow net influx phase.
Brown trout exposed to zinc in hard water and placed in metal-free media exhibited a greater net efflux (- 25.6 μmol Zn 100 g⁻¹ h⁻¹) of the metal than did fish in soft water (-4.2 μmol Zn 100 g⁻¹ h⁻¹) treated in the same manner. Tissue ⁶⁵Zn activities reflected both the differences in uptake and excretion rates of the metal between hard and soft water fish. During zinc exposure (0.77 μmol Zn 1⁻¹) high water hardness reduced tissue burdens of the metal by reducing net branchial influx, and enhancing efflux of the metal in hard water fish.     

Temperature acclimation in a biochemical model of photosynthesis: a reanalysis of data from 36 species

The Farquhar et al. model of C(3) photosynthesis is frequently used to study the effect of global changes on the biosphere. Its two main parameters representing photosynthetic capacity, V(cmax) and J(max), have been observed to acclimate to plant growth temperature for single species, but a general formulation has never been derived. Here, we present a reanalysis of data from 36 plant species to quantify the temperature dependence of V(cmax) and J(max) with a focus on plant growth temperature, i.e. the plants' average ambient temperature during the preceding month. The temperature dependence of V(cmax) and J(max) within each data set was described very well by a modified Arrhenius function that accounts for a decrease of V(cmax) and J(max) at high temperatures. Three parameters were optimized: base rate, activation energy and entropy term. An effect of plant growth temperature on base rate and activation energy could not be observed, but it significantly affected the entropy term. This caused the optimum temperature of V(cmax) and J(max) to increase by 0.44 degrees C and 0.33 degrees C per 1 degrees C increase of growth temperature. While the base rate of V(cmax) and J(max) seemed not to be affected, the ratio J(max) : V(cmax) at 25 degrees C significantly decreased with increasing growth temperature. This moderate temperature acclimation is sufficient to double-modelled photosynthesis at 40 degrees C, if plants are grown at 25 degrees C instead of 17 degrees C.     

Physiological girdling of pine trees via phloem chilling: proof of concept

Quantifying below-ground carbon (C) allocation is particularly difficult as methods usually disturb the root-mycorrhizal-soil continuum. We reduced C allocation below ground of loblolly pine trees by: (1) physically girdling trees and (2) physiologically girdling pine trees by chilling the phloem. Chilling reduced cambium temperatures by approximately 18 degrees C. Both methods rapidly reduced soil CO2 efflux, and after approximately 10 days decreased net photosynthesis (P(n)), the latter indicating feedback inhibition. Chilling decreased soil-soluble C, indicating that decreased soil CO2 efflux may have been mediated by a decrease in root C exudation that was rapidly respired by microbes. These effects were only observed in late summer/early autumn when above-ground growth was minimal, and not in the spring when above-ground growth was rapid. All of the effects were rapidly reversed when chilling was ceased. In fertilized plots, both chilling and physical girdling methods reduced soil CO2 efflux by approximately 8%. Physical girdling reduced soil CO2 efflux by 26% in non-fertilized plots. This work demonstrates that phloem chilling provides a non-destructive alternative to reducing the movement of recent photosynthate below the point of chilling to estimate C allocation below ground on large trees.     

Near edge X-ray absorption fine structure spectroscopy (NEXAFS) of pigment-protein complexes: peridinin-chlorophyll a protein (PCP) of Amphidinium carterae

Peridinin-chlorophyll a protein (PCP) is a unique water soluble antenna complex that employs the carotenoid peridinin as the main light-harvesting pigment. In the present study the near edge X-ray absorption fine structure (NEXAFS) spectrum of PCP was recorded at the carbon K-edge. Additionally, the NEXAFS spectra of the constituent pigments, chlorophyll a and peridinin, were measured. The energies of the lowest unoccupied molecular levels of these pigments appearing in the carbon NEXAFS spectrum were resolved. Individual contributions of the pigments and the protein to the measured NEXAFS spectrum of PCP were determined using a “building block” approach combining NEXAFS spectra of the pigments and the amino acids constituting the PCP apoprotein. The results suggest that absorption changes of the pigments in the carbon near K-edge region can be resolved following excitation using a suitable visible pump laser pulse. Consequently, it may be possible to study excitation energy transfer processes involving “optically dark” states of carotenoids in pigment-protein complexes by soft X-ray probe optical pump double resonance spectroscopy (XODR).     

Microbial carbon monoxide consumption in salt marsh sediments

We have examined sediments from a fringing salt marsh in Maine to further understand marine CO metabolism, about which relatively little is known. Intact cores from the marsh emitted CO during dark oxic incubations, but emission rates were significantly higher during anoxic incubations, which provided evidence for simultaneous production and aerobic consumption in surface sediments. CO emission rates were also elevated when cores were exposed to light, which indicated that photochemical reactions play a role in CO production. A kinetic analysis of marsh surface sediments yielded an apparent K(m) of about 82 ppm, which exceeded values reported for well-aerated soils that consume atmospheric CO (65nM). Surface (0-0.2 cm depth interval) sediment slurries incubated under oxic conditions rapidly consumed CO, and methyl fluoride did not inhibit uptake, which indicated that neither ammonia nor methane oxidizers contributed to the observed activity. In contrast, aerobic CO uptake was inhibited by additions of readily available organic substrates (pyruvate, glucose and glycine), but not by cellulose. CO was also consumed by surface and sub-surface sediment slurries incubated under anaerobic conditions, but rates were less than during aerobic incubations. Molybdate and nitrate or nitrite, but not 2-bromoethanesulfonic acid, partially inhibited anaerobic uptake. These results suggest that sulfidogens and acetogens, but not dissimilatory nitrate reducers or methanogens, actively consume CO. Sediment-free plant roots also oxidized CO aerobically; rates for Spartina patens and Limonium carolinianum roots were significantly higher than rates for Spartina alterniflora roots. Thus plants may also impact CO cycling in estuarine environments.     

Supercritical carbon dioxide and hydrogen peroxide cause mild changes in spore structures associated with high killing rate of Bacillus anthracis

The present work examines chemical and structural response in B. anthracis spores killed by a mixture of supercritical carbon dioxide (SCCO₂) and hydrogen peroxide (H₂O₂). Deactivation of 6-log of B. anthracis spores by SCCO₂ + H₂O₂ was demonstrated, but changes in structure were observed in only a small portion of spores. Results from phase contrast microscopy proved that this treatment is mild and does not trigger germination-like changes. TEM imaging revealed mild damage in a portion of spores while the majority remained intact. Dipicolinic acid (DPA) analysis showed that < 10% of the DPA was released from the spore core into the external milieu, further demonstrating only modest damage to the spores. Confocal fluorescent microscopy, assessing uptake of DNA-binding dyes, directly demonstrated compromise of the permeability barrier. However, the magnitude of uptake was small compared to spores that had been autoclaved. This work suggests that SCCO₂ + H₂O₂ is quite mild compared to other sterilization methods, which has major implications in its application. These results provide some insight on the possible interactions between spores and the SCCO₂ + H₂O₂ sterilization process.     

Does Phaeocystis spp. contribute significantly to vertical export of organic carbon?

Phaeocystis spp. cell and colony mass fluxes and their contribution to the vertical particulate organic carbon (POC) export from a wide range of stations were quantified by short-term sediment traps. The compilation of available data, ranging from polar to sub-arctic and boreal regions, revealed that Phaeocystis colonial and single cells frequently are observed in shallow sediment traps at 30–50 m depth (average of 7 ± 11% of POC export). A strong vertical export decline between 40 m and 100 m diminished the contribution of Phaeocystis spp. cell carbon to vertical export of POC to only 3 ± 2% at 100 m depth, with two exceptions (deeper mixed stations). Estimates of potential corresponding mucus contribution increased the average Phaeocystis spp. contribution to <5% of POC export. The vertical flux attenuation efficiency is higher for Phaeocystis spp. than for diatoms. The overall contribution of Phaeocystis spp. to vertical carbon export based on direct investigations of vertical organic carbon export is small.     

Soil carbon saturation: concept,evidence and evaluation

Current estimates of soil C storage potential are based on models or factors that assume linearity between C input levels and C stocks at steady-state, implying that SOC stocks could increase without limit as C input levels increase. However, some soils show little or no increase in steady-state SOC stock with increasing C input levels suggesting that SOC can become saturated with respect to C input. We used long-term field experiment data to assess alternative hypotheses of soil carbon storage by three simple models: a linear model (no saturation), a one-pool whole-soil C saturation model, and a two-pool mixed model with C saturation of a single C pool, but not the whole soil. The one-pool C saturation model best fit the combined data from 14 sites, four individual sites were best-fit with the linear model, and no sites were best fit by the mixed model. These results indicate that existing agricultural field experiments generally have too small a range in C input levels to show saturation behavior, and verify the accepted linear relationship between soil C and C input used to model SOM dynamics. However, all sites combined and the site with the widest range in C input levels were best fit with the C-saturation model. Nevertheless, the same site produced distinct effective stabilization capacity curves rather than an absolute C saturation level. We conclude that the saturation of soil C does occur and therefore the greatest efficiency in soil C sequestration will be in soils further from C saturation.