Variable nutrient stoichiometry (carbon:nitrogen:phosphorus) across trophic levels determines community and ecosystem properties in an oligotrophic mangrove system.

Our study investigated the carbon:nitrogen:phosphorus (C:N:P) stoichiometry of mangrove island of the Mesoamerican Barrier Reef (Twin Cays, Belize). The C:N:P of abiotic and biotic components of this oligotrophic ecosystem was measured and served to build networks of nutrient flows for three distinct mangrove forest zones (tall seaward fringing forest, inland dwarf forests and a transitional zone). Between forest zones, the stoichiometry of primary producers, heterotrophs and abiotic components did not change significantly, but there was a significant difference in C:N:P, and C, N, and P biomass, between the functional groups mangrove trees, other primary producers, heterotrophs, and abiotic components. C:N:P decreased with increasing trophic level. Nutrient recycling in the food webs was highest for P, and high transfer efficiencies between trophic levels of P and N also indicated an overall shortage of these nutrients when compared to C. Heterotrophs were sometimes, but not always, limited by the same nutrient as the primary producers. Mangrove trees and the primary tree consumers were P limited, whereas the invertebrates consuming leaf litter and detritus were N limited. Most compartments were limited by P or N (not by C), and the relative depletion rate of food sources was fastest for P. P transfers thus constituted a bottleneck of nutrient transfer on Twin Cays. This is the first comprehensive ecosystem study of nutrient transfers in a mangrove ecosystem, illustrating some mechanisms (e.g. recycling rates, transfer efficiencies) which oligotrophic systems use in order to build up biomass and food webs spanning various trophic levels.

Shifts in δ15 N signature following the onset of exogenous feeding in rainbow trout Oncorhynchus mykiss: importance of combining length and age data.

The δ(15) N isotopic change of recently emerged rainbow trout Oncorhynchus mykiss due to diet shift from yolk sac to exogenous feeding was evaluated in a field study. The fit of a general model including both fish length and age in days as co-variables indicates that the specific δ(15) N of individual fish at any given time along the ontogeny is determined by its growth trajectory. The results suggest that estimations based on fish size alone could bias data interpretation and maternal origin determinations in partially migratory salmonids.

Isotopic tracking of change in diet and habitat use in african elephants.

The carbon, nitrogen, and strontium isotope compositions of elephants in Amboseli Park, Kenya, were measured to examine changes in diet and habitat use since the 1960s. Carbon isotope ratios, which reflect the photosynthetic pathway of food plants, record a shift in diet from trees and shrubs to grass. Strontium isotope ratios, which reflect the geologic age of bedrock, document the concentration of elephants within the park. The high isotopic variability produced by behavioral and ecological shifts, if it is representative of other East African elephant populations, may complicate the use of isotopes as indicators of the source region of ivory.

Photosynthetic Fractionation of the Stable Isotopes of Oxygen and Carbon.

Isotope discrimination during photosynthetic exchange of O2 and CO2 was measured using enzyme, thylakoid, and whole cell preparations. Evolved oxygen from isolated spinach thylakoids was isotopically identical (within analytical error) to its source water. Similar results were obtained with Anacystis nidulans Richter and Phaeodactylum tricornutum Bohlin cultures purged with helium. For consumptive reactions, discrimination ([delta], where 1 + [delta]/1000 equals the isotope effect, k16/k18 or k12/k13) was determined by analysis of residual substrate (O2 or CO2). The [delta] for the Mehler reaction, mediated by ferredoxin or methylviologen, was 15.3[per mille (thousand) sign]. Oxygen isotope discrimination during oxygenation of ribulose-1,5-bisphosphate (RuBP) catalyzed by RuBP carboxylase/oxygenase (Rubisco) was 21.3[per mille (thousand) sign] and independent of enzyme source, unlike carbon isotope discrimination: 30.3[per mille (thousand) sign] for spinach enzyme and 19.6 to 23[per mille (thousand) sign] for Rhodospirillum rubrum and A. nidulans enzymes, depending on reaction conditions. The [delta] for O2 consumption catalyzed by glycolate oxidase was 22.7[per mille (thousand) sign]. The expected overall [delta] for photorespiration is about 21.7[per mille (thousand) sign]. Consistent with this, when Asparagus sprengeri Regel mesophyll cells approached the compensation point within a sealed vessel, the [delta]18O of dissolved O2 came to a steady-state value of about 21.5[per mille (thousand) sign] relative to the source water. The results provide improved estimates of discrimination factors in several reactions prominent in the global O cycle and indicate that photorespiration plays a significant part in determining the isotopic composition of atmospheric oxygen.

Pigment production and isotopic fractionations in continuous culture: okenone producing purple sulfur bacteria Part II.

Okenone is a carotenoid pigment unique to certain members of Chromatiaceae, the dominant family of purple sulfur bacteria (PSB) found in euxinic photic zones. Diagenetic alteration of okenone produces okenane, the only recognized molecular fossil unique to PSB. The in vivo concentrations of okenone and bacteriochlorophyll a (Bchl a) on a per cell basis were monitored and quantified as a function of light intensity in continuous cultures of the purple sulfur bacterium Marichromatium purpuratum (Mpurp1591). We show that okenone-producing PSB have constant bacteriochlorophyll to carotenoid ratios in light-harvesting antenna complexes. The in vivo concentrations of Bchl a, 0.151 ± 0.012 fmol cell(-1), and okenone, 0.103 ± 0.012 fmol cell(-1), were not dependent on average light intensity (10-225 Lux) at both steady and non-steady states. This observation revealed that in autotrophic continuous cultures of Mpurp1591, there was a constant ratio for okenone to Bchl a of 1:1.5. Okenone was therefore constitutively produced in planktonic cultures of PSB, regardless of light intensity. This confirms the legitimacy of okenone as a signature for autotrophic planktonic PSB and by extrapolation water column euxinia. We measured the δ(13)C, δ(15)N, and δ(34)S bulk biomass values from cells collected daily and determined the isotopic fractionations of Mpurp1591. There was no statistical relationship in the bulk isotope measurements or stable isotope fractionations to light intensity or cell density under steady and non-steady-state conditions. The carbon isotope fractionation between okenone and Bchl a with respect to overall bulk biomass ((13)ε pigment - biomass) was 2.2 ± 0.4‰ and -4.1 ± 0.9‰, respectively. The carbon isotopic fractionation (13ε pigment-CO2) for the production of pigments in PSB is more variable than previously thought with our reported values for okenone at -15.5 ± 1.2‰ and -21.8 ± 1.7‰ for Bchl a.

Ecologically and geologically relevant isotope signatures of C, N, and S: okenone producing purple sulfur bacteria Part I.

Purple sulfur bacteria (PSB) are known to couple the carbon, nitrogen, and sulfur cycling in euxinic environments. This is the first study with multiple strains and species of okenone-producing PSB to examine the carbon (C), nitrogen (N), and sulfur (S) metabolisms and isotopic signatures in controlled laboratory conditions, investigating what isotopic fractionations might be recorded in modern environments and the geologic record. PSB play an integral role in the ecology of euxinic environments and produce the unique molecular fossil okenane, derived from the diagenetic alteration of the carotenoid pigment okenone. Cultures of Marichromatium purpuratum 1591 (Mpurp1591) were observed to have carbon isotope fractionations ((13)ε biomass - CO2), via RuBisCO, ranging from -16.1 to -23.2‰ during exponential and stationary phases of growth. Cultures of Thiocapsa marina 5653 (Tmar5653) and Mpurp1591 had a nitrogen isotope fractionation ((15)ε biomass - NH 4) of -15‰, via glutamate dehydrogenase, measured and recorded for the first time in PSB. The δ(34) SVCDT values and amount of stored elemental sulfur for Mpurp1591 cells grown autotrophically and photoheterotrophically were dependent upon their carbon metabolic pathways. We show that PSB may contribute to the isotopic enrichments observed in modern and ancient anoxic basins. In a photoheterotrophic culture of Mpurp1591 that switched to autotrophy once the organic substrate was consumed, there were bulk biomass δ(13)C values that span a broader range than recorded across the Late Devonian, Permian-Triassic, Triassic-Jurassic, and OAE2 mass extinction boundaries. This finding stresses the complexities in interpreting and assigning δ(13)C values to bulk organic matter preserved in the geologic record.

Rorschach-based indices of visual imagery reactivity.

A method using a specially developed Rorschach-based procedure was applied in conjunction with a visual imagery technique in evaluating protocols of 40 outpatient subjects. The subjects were divided into Reactor and Nonreactor groups, according to how productive in clinically significant material their responses were in the imagery condition contrasted to a conventional administration of the Rorschach. A scoring method correctly classified 35 of the 40 subjects as being Reactors or Nonreactors. In addition to previously demonstrated utility as a research tool, the method may be used in clinical situations.

Effects of instructions for visual imagery on Rorschach responses.

The Rorschach was administered to two groups of 12 subjects under two conditions. The first group was classified as imagery Reactors based upon their prior responsivity to imagery instructions during therapy. The second group was labelled Nonreactors using the same clinical criteria. The condition administered first utilized the standard Rorschach; in the second, subjects were asked to produce sequences of visual imagery using Rorschach cards as stimuli. Both groups received both Rorschach administrations. Responses were scored without knowledge of the two classifications of subjects. Instructions for imagery appeared to have a disinhibiting effect and led to significant changes in several major Rorschach scoring categories and in a specially derived index of the amount of clinically relevant conflictual and affective material manifested. There were a number of significant differences between Reactors and Nonreactors in Rorschach response levels under the imagery condition, among other changes. Reactors yielded significantly more complex and clinically revealing material under imagery than did Nonreactors. The findings were considered to be particularly useful for diagnostic and therapeutic decisions with certain types of patients. The results also suggest the possibility of differences in personality structure between imagery Reactors and Nonreactors which warrant further investigation.

Clinical applications of Rorschach-based visual imagery reactivity.

A diverse set of findings from recent research suggests the value of visual imagery techniques in clinical practice.

Free visual imagery sequences in reactors and nonreactors.

The technique of Free Visual Imagery Sequences was used with 32 outpatients, M age of 33.9, to determine the differences between Visual Imagery Reactors and Nonreactors as defined in previous studies. Reactors showed significantly more responses associated with Affect/Conflict material, frequently including bizarre and distorted images. The Affect/Conflict responses occurred earlier and had longer duration spans in Reactors. Neutral content was more prevalent in Nonreactors. An interpretive approach involving a regulatory processing system is proposed. Free Visual Imagery Sequences appears to be a simple and efficient clinical technique which can contribute data useful in determining the extent to which imagery techniques could be employed in certain forms of psychotherapy.

Effect of instructions given to reactors and nonreactors to produce visual imagery sequences following an imagined pleasant scene.

15 Visual Imagery Reactors and 15 Nonreactors were instructed to produce Visual Imagery Sequences using as a point of departure a pleasant scene imagined by themselves. Despite these instructions, Reactors developed significantly less pleasant scene materials, more High and Low Affect/Conflict, less Neutral Content, and briefer sequences preceding all Affect/Conflict. Four Reactors and no Nonreactors expressed difficulty in visualizing pleasant scenes. Reactors made more interruptions when attempting to continue imagery of the pleasant scene. Several additional scores occurred almost exclusively within a subgroup of Reactors. These results are consistent with previous studies using different test stimuli and are congruent with previously advanced theoretical formulations.

A simple method for evaluation of Rorschach Imagery Reactivity.

A general scoring system, previously developed for the analysis of pictorial associations within the paradigm of Visual Imagery Sequences, was applied in the evaluation of visual associations to memory images of Rorschach inkblots (Imagery condition) in a comparison with standard Rorschach responses (Conventional condition). The participants, 80 consecutively selected psychiatric outpatients, were divided into Clinical Reactor and Nonreactor groups, according to how productive they were of psychodynamically revealing material during insight-oriented therapy using imagery. For this simple scoring method (which does not include the customary Rorschach scores), conclusions concerning Imagery Reactivity in the Rorschach agreed with those of previous studies using a scoring system more unique to the Rorschach. The inferences drawn from statistical analysis by groups and conditions also contribute additional refinements to the understanding of the subtle interplay between defensiveness and sensitivity to imagery in determining the patterns of scorable components within the response complex. This general scoring method correctly identified 95.6% of Imagery Reactors and 100% of Imagery Nonreactors, an improvement over the 87% efficiency of the previously described, Rorschach-based method for assessing Imagery Reactivity in the Rorschach.

The provenances of asteroids, and their contributions to the volatile inventories of the terrestrial planets.

Determining the source(s) of hydrogen, carbon, and nitrogen accreted by Earth is important for understanding the origins of water and life and for constraining dynamical processes that operated during planet formation. Chondritic meteorites are asteroidal fragments that retain records of the first few million years of solar system history. The deuterium/hydrogen (D/H) values of water in carbonaceous chondrites are distinct from those in comets and Saturn's moon Enceladus, implying that they formed in a different region of the solar system, contrary to predictions of recent dynamical models. The D/H values of water in carbonaceous chondrites also argue against an influx of water ice from the outer solar system, which has been invoked to explain the nonsolar oxygen isotopic composition of the inner solar system. The bulk hydrogen and nitrogen isotopic compositions of CI chondrites suggest that they were the principal source of Earth's volatiles.

A reduced organic carbon component in martian basalts.

The source and nature of carbon on Mars have been a subject of intense speculation. We report the results of confocal Raman imaging spectroscopy on 11 martian meteorites, spanning about 4.2 billion years of martian history. Ten of the meteorites contain abiotic macromolecular carbon (MMC) phases detected in association with small oxide grains included within high-temperature minerals. Polycyclic aromatic hydrocarbons were detected along with MMC phases in Dar al Gani 476. The association of organic carbon within magmatic minerals indicates that martian magmas favored precipitation of reduced carbon species during crystallization. The ubiquitous distribution of abiotic organic carbon in martian igneous rocks is important for understanding the martian carbon cycle and has implications for future missions to detect possible past martian life.