Abiotic Sources Research Articles

Biological Control of Dense-Thorned Bitter Apple,Solanum sisymbriifoliumLam. (Solanaceae), in South Africa

Solanum sisymbriifolium Lam. is a weed of disturbed areas in South Africa, particularly in the high-elevation summer rainfall areas of the country. Despite the introduction of the South American leaf-feeding tortoise beetle, Gratiana spadicea (Klug) (Coleoptera: Chrysomelidae: Cassidinae) in 1994, the weed has continued to spread. Although established in a number of regions, beetle populations appear to persist in relatively low numbers, inflicting minimal damage to the weed. Consequently, a number of variables have been investigated in order to explain this lack of efficacy, and in some cases, failure to establish. Gratiana spadicea populations in South Africa are under considerable stress both from abiotic and biotic sources. Population-limiting factors such as disturbance of overwintering sites, climatic incompatibility, and high rates of pupal parasitism translate into low numbers of the agent at the start of each growing season. Small early-season populations which are slow to build-up, coupled with asynchronous development of S. sisymbriifolium, limit the beetles' effectiveness and pre-empt any impact on the weeds' reproductive output. Consequently, G. spadicea alone is unlikely to control S. sisymbriifolium infestations in South Africa. The flower-feeding weevil Anthonomus sisymbrii Hustache (Coleoptera: Curculionidae: Anthonominae), may therefore warrant study as it could have the potential, if released, to curtail fruit production and further spread of S. sisymbriifolium.

Fish as major carbonate mud producers and missing components of the tropical carbonate factory

Carbonate mud is a major constituent of recent marine carbonate sediments and of ancient limestones, which contain unique records of changes in ocean chemistry and climate shifts in the geological past. However, the origin of carbonate mud is controversial and often problematic to resolve. Here we show that tropical marine fish produce and excrete various forms of precipitated (nonskeletal) calcium carbonate from their guts ("low" and "high" Mg-calcite and aragonite), but that very fine-grained (mostly < 2 μm) high Mg-calcite crystallites (i.e., > 4 mole % MgCO(3)) are their dominant excretory product. Crystallites from fish are morphologically diverse and species-specific, but all are unique relative to previously known biogenic and abiotic sources of carbonate within open marine systems. Using site specific fish biomass and carbonate excretion rate data we estimate that fish produce ∼6.1 × 10(6) kg CaCO(3)/year across the Bahamian archipelago, all as mud-grade (the < 63 μm fraction) carbonate and thus as a potential sediment constituent. Estimated contributions from fish to total carbonate mud production average ∼14% overall, and exceed 70% in specific habitats. Critically, we also document the widespread presence of these distinctive fish-derived carbonates in the finest sediment fractions from all habitat types in the Bahamas, demonstrating that these carbonates have direct relevance to contemporary carbonate sediment budgets. Fish thus represent a hitherto unrecognized but significant source of fine-grained carbonate sediment, the discovery of which has direct application to the conceptual ideas of how marine carbonate factories function both today and in the past.

Heterospecific Vocal Interactions in a Frog from the Southern Temperate Forest, Batrachyla taeniata

AbstractAnimals using sound communication employ different strategies to overcome interferences from biotic and abiotic sources. However, interactions among acoustically active species have been studied to a very limited extent. The evoked vocal responses of 20 male frogs Batrachyla taeniata from the temperate austral forest in Chile were tested with conspecific calls and with the calls of two sympatric species: B. antartandica and B. leptopus, broadcast at amplitudes of 73, 79, 85, 91 and 97 dB peak SPL. The subjects responded actively to the conspecific call, but only responded weakly to the call of B. leptopus at the highest intensity. The preferential responses to conspecific calls could contribute to the typical segregation in monospecific choruses observed in areas where these frogs breed in sympatry.

Distribution Analysis of Hydrogenases in Surface Waters of Marine and Freshwater Environments

BackgroundSurface waters of aquatic environments have been shown to both evolve and consume hydrogen and the ocean is estimated to be the principal natural source. In some marine habitats, H2 evolution and uptake are clearly due to biological activity, while contributions of abiotic sources must be considered in others. Until now the only known biological process involved in H2 metabolism in marine environments is nitrogen fixation.Principal FindingsWe analyzed marine and freshwater environments for the presence and distribution of genes of all known hydrogenases, the enzymes involved in biological hydrogen turnover. The total genomes and the available marine metagenome datasets were searched for hydrogenase sequences. Furthermore, we isolated DNA from samples from the North Atlantic, Mediterranean Sea, North Sea, Baltic Sea, and two fresh water lakes and amplified and sequenced part of the gene encoding the bidirectional NAD(P)-linked hydrogenase. In 21% of all marine heterotrophic bacterial genomes from surface waters, one or several hydrogenase genes were found, with the membrane-bound H2 uptake hydrogenase being the most widespread. A clear bias of hydrogenases to environments with terrestrial influence was found. This is exemplified by the cyanobacterial bidirectional NAD(P)-linked hydrogenase that was found in freshwater and coastal areas but not in the open ocean.SignificanceThis study shows that hydrogenases are surprisingly abundant in marine environments. Due to its ecological distribution the primary function of the bidirectional NAD(P)-linked hydrogenase seems to be fermentative hydrogen evolution. Moreover, our data suggests that marine surface waters could be an interesting source of oxygen-resistant uptake hydrogenases. The respective genes occur in coastal as well as open ocean habitats and we presume that they are used as additional energy scavenging devices in otherwise nutrient limited environments. The membrane-bound H2-evolving hydrogenases might be useful as marker for bacteria living inside of marine snow particles.

Emissions of volatile organic compounds during the decomposition of plant litter

Volatile organic compounds (VOCs) are emitted during plant litter decomposition, and such VOCs can have wide‐ranging impacts on atmospheric chemistry, terrestrial biogeochemistry, and soil ecology. However, we currently have a limited understanding of the relative importance of biotic versus abiotic sources of these VOCs and whether distinct types of litter emit different types and quantities of VOCs during decomposition. We analyzed VOCs emitted by microbes or by abiotic mechanisms during the decomposition of litter from 12 plant species in a laboratory experiment using proton transfer reaction mass spectrometry (PTR‐MS). Net emissions from litter with active microbial populations (non‐sterile litters) were between 0 and 11 times higher than emissions from sterile controls over a 20‐d incubation period, suggesting that abiotic sources of VOCs are generally less important than biotic sources. In all cases, the sterile and non‐sterile litter treatments emitted different types of VOCs, with methanol being the dominant VOC emitted from litters during microbial decomposition, accounting for 78 to 99% of the net emissions. We also found that the types of VOCs released during biotic decomposition differed in a predictable manner among litter types with VOC profiles also changing as decomposition progressed over time. These results show the importance of incorporating both the biotic decomposition of litter and the species‐dependent differences in terrestrial vegetation into global VOC emission models.

The influence of geological, geochemical, and biogenic habitat heterogeneity on seep biodiversity

AbstractCold seeps are among the most heterogeneous of all continental margin habitats. Abiotic sources of heterogeneity in these systems include local variability in fluid flow, geochemistry, and substrate type, which give rise to different sets of microbial communities, microbial symbiont‐bearing foundation species, and associated heterotrophic species. Biogenic habitats created by microbial mats and the symbiotic species including vesicomyid clams, bathymodiolin mussels, and siboglinid tubeworms add an additional layer of complexity to seep habitats. These forms of habitat heterogeneity result in a variety of macrofaunal and meiofaunal communities that respond to changes in structural complexity, habitat geochemistry, nutrient sources, and interspecific interactions in different ways and at different scales. These responses are predicted by a set of theoretical metacommunity models, the most appropriate of which for seep systems appears to be the ‘species sorting’ concept, an extension of niche theory. This concept is demonstrated through predictable patterns of community assembly, succession, and beta‐level diversity. These processes are described using a newly developed analytical technique examining the change in the slope of the species accumulation curve with the number of habitats examined. The diversity response to heterogeneity has a consistent form, but quantitatively changes at different seep sites around the world as the types of habitats present and the size‐classes of fauna analyzed change. The increase in beta diversity across seep habitat types demonstrates that cold seeps and associated biogenic habitats are significant sources of heterogeneity on continental margins globally.

Spectral Fingerprints of Habitability

The emerging field of extrasolar planet search has shown an extraordinary ability to combine research by astrophysics, chemistry, biology and geophysics into a new and exciting interdisciplinary approach to understand our place in the universe. Are there other worlds like ours? How can we characterize those planets and assess if they are habitable? After a decade rich in giant exoplanet detections, observation techniques have now reached the ability to find planets of less than 10 M_Earth (so called Super-Earths) that may potentially be habitable. The detection and characterization of Earth-like planet is approaching rapidly with dedicated space observatories already in operation (Corot) or in development phase (Kepler, James Webb Space Telescope, Extremely Large Telescope (ELT), Darwin/TPF). Space missions like CoRoT (CNES, Rouan et al. 1998) and Kepler (NASA, Borucki et al. 1997) will give us statistics on the number, size, period and orbital distance of planets, extending to terrestrial planets on the lower mass range end as a first step, while missions like Darwin/TPF are designed to characterize their atmospheres. In this chapter we discuss how we can read a planet's spectral fingerprint and characterize if it is potentially habitable. We discuss the first steps to detect a habitable planet and set biomarker detection in context in Section 1. In Section 2 we focus on biomarkers, their signatures at different wavelengths, abiotic sources and cryptic photosynthesis – using Earth as our primary example – the only habitable planet we know of so far. Section 3 concentrates on planets around different stars, and Section 4 summarizes the chapter.

Mercury in 16 demersal sharks from southeast Australia: Biotic and abiotic sources of variation and consumer health implications

Total mercury (THg) and monomethylmercury (MMHg) concentrations were determined in the tissues of demersal shark (Order Squaliformes and the Families: Scyliorhinidae, Hexanchidae) and chimaera species (Families: Chimaeridae and Rhinochimaeridae) from continental shelf and slope waters off southeast Australia, including embryos, juveniles and adults. The distribution of THg in various tissues (muscle, liver, kidney and skin), examined in ten species, shows higher levels in the muscle tissue (1.49 ± 0.47 mg kg −1, ww), which accounted for between 59% and 82% of the total body burden of mercury and in the kidney (0.93 ± 0.14 mg kg −1, ww) and liver (0.61 ± 0.25 mg kg −1, ww) with lower levels observed in the skin (0.12 ± 0.06 mg kg −1, ww). Additional THg determinations were performed in the muscle tissue of five other species allowing geographical and inter-specific comparisons. Speciation analysis demonstrated that more than 90% mercury was bound in muscle tissue as MMHg with higher percentages (>95%) observed in sharks species occupying deeper environments. Species differences were observed. Highest THg levels in the muscle tissue (up to 6.64 mg kg −1 wet weight, ww) were recorded in Proscymnodon plunketi and Centrophorus zeehaani (mean values; 4.47 ± 1.20 and 3.52 ± 0.07 mg kg −1, ww, respectively). Consistent with the ongoing paradigm on mercury bioaccumulation, we systematically observed THg concentrations increasing with animal size from the embryos to the larger sharks. Embryos of Etmopterus baxteri and Centroselachus crepidater had average levels 0.28 and 0.06 mg kg −1 (ww), while adult specimens reached 3.3 and 2.3 mg kg −1 (ww), respectively. THg concentrations in Australian sharks were compared with the same genus collected in other world regions. Levels were closer to data reported for East Atlantic than for the epicontinental Mediterranean margins. At a smaller geographical scale, the habitat effect on mercury concentration in sharks seems less clear. Squalid sharks occupying shelf waters showed higher mean mercury levels relative to their size (body weight, bw) than mid-slope species (0.4–6.7 mg kg −1 bw and 0.3–2.2 mg kg −1 bw, respectively). However, local regional differences (East and South Tasmania vs. Victoria) in Hg levels were not detected for the majority of taxa examined. All species, with the exception of Figaro boardmani showed values greater than 0.5 mg kg −1 (ww) and all but four were above many international regulatory thresholds (1.0 mg kg −1, ww).

Cadmium and phosphorus cycling in the water column of the South China Sea: The roles of biotic and abiotic particles

The concentrations of cadmium, phosphorus, and aluminum in size-fractionated phytoplankton, zooplankton, and sinking particles are determined using ICPMS to evaluate the roles of biotic and abiotic particles on the cycling and ratios of Cd and P in the water column. Plankton were collected with a filtration apparatus equipped with 10-, 60-, and 150-μm aperture plankton nets on two occasions (2002 and 2006), and sinking particles were sampled by moored sediment traps deployed at depths of 120, 600, and 3500 m from 2004 to 2005. In contrast to what our previous study revealed, i.e., that most of the other bioactive trace metals in plankton were strongly correlated with abiotic Al and adsorbed on phytoplankton [Ho, T.Y., Wen, L.S., You, C.F., Lee, D.C., 2007. The trace metal composition of size-fractionated plankton in the South China Sea: biotic versus abiotic sources. Limnol Oceanogr 52, 1776–88.], Cd/P ratios, ranging from 0.12 to 0.34 mmol/mol P, did not vary with Al and exhibited fairly consistent values among different sizes of plankton, showing that Cd was mostly incorporated on an intracellular basis. In terms of the sinking particles, fluxes in Cd and P as well as in Cd/P ratios were strongly influenced by both biotic and abiotic particles. Overall, the Cd/P ratios in the sinking particles ranged from 0.03 to 1.2 mmol/mol, with the highest value observed in traps at 120 m during the productive season. The lowest value was observed in deep water during high flux periods for lithogenic particles. At surface depth, flux and Cd/P ratios were elevated during the most productive season in the region. The elevated ratios in the traps at 120 m were most likely related to preferential uptake of Cd for the dominant species (coccolithophores) during the productive period. Relatively, Cd/P ratios sharply decreased with increasing Al flux in deep water and ratios were much lower than the expected Cd/P ratios obtained from the relative portion of lithogenic and biogenic particles, indicating that the adsorption of soluble P into lithogenic particles was significant in the deep water during high lithogenic particle flux periods. Using averaged annual fluxes and standing stock in the water column, the residence time of biogenic Cd and P are 0.10 and 0.20, 250 and 100, and 9100 and 5000 years respectively in the top 120 m, 600 m, and water column as a whole, also showing preferential removal for Cd in the euphotic zone but relatively higher removal rates for P in the deep water. Our study suggests that the shift in microalgal community structure along with input of lithogenic minerals are both potentially important factors in influencing Cd/P ratios in oceanic water on a geological time scale.

Natural Abiotic Formation of Trihalomethanes in Soil: Results from Laboratory Studies and Field Samples

Trihalomethanes (THM), especially trichloromethane, play an important role in photochemical processes of the lower atmosphere, but the current knowledge of the known sources and sinks of trichloromethane is still incomplete. The trichloromethane flux through the environment is estimated at approximately 660 kt year(-1) and 90% of the emissions are of natural origin. Next to offshore seawater contributing approximately 360 kt year(-1) unknown soil processes are the most prominent source (approximately 220 kt year(-1)). This paper describes a new abiotic source of trichloromethane from the terrestrial environment induced by the oxidation of organic matter by iron(III) and hydrogen peroxide in the presence of chloride. Different organic-rich soils and a series of organic substances regarded as monomeric constituents of humus were investigated for their release of trichloromethene. The influence of iron(III), hydrogen peroxide, halide, and pH on its formation was assayed. The optimal reaction turn over for the representative compound catechol was 58.4 ng of CHCl3 from 1.8 mg of carbon applying chloride and 1.55 microg of CHBr3 from 1.8 mg of carbon applying bromide; resorcin and hydroquinone displayed similar numbers. Results presented in this paper pinpoint 1,2,4,5-tetrahydroxybenzene as playing a key role as intermediate in the formation pathway of the trihalomethanes. The highest THM yields were obtained when applying the oxidized form of 1,2,4,5-tetrahydroxybenzene as THM precursor. These findings are consistent with the well-known degradation pathway starting from resorcin-like dihydroxylated compounds proceeding via further hydroxylation and after halogenation finally ending up in trihalomethanes. In conclusion, Fenton-like reaction conditions (iron(III) and hydrogen peroxide), elevated halide content and an extended reaction time can be seen as the most important parameters required for an optimal THM formation.

Interactions between physical and biotic factors influence CO 2 flux in Antarctic dry valley soils

Soil carbon dioxide (CO 2) flux is an integrative measure of ecosystem functioning representing both biotic and physical controls over carbon (C) balance. In the McMurdo Dry Valleys of Antarctica, soil CO 2 fluxes (approximately −0.1–0.15 μmol m −2 s −1) are generally low, and negative fluxes (uptake of CO 2) are sometimes observed. A combination of biological respiration and physical mechanisms, driven by temperature and mediated by soil moisture and mineralogy, determine CO 2 flux and, therefore, soil organic C balance. The physical factors important to CO 2 flux are being altered with climate variability in many ecosystems including arid forms such as the Antarctic terrestrial ecosystems, making it critical to understand how climate factors interact with biotic drivers to control soil CO 2 fluxes and C balances. We measured soil CO 2 flux in experimental field manipulations, microcosm incubations and across natural environmental gradients of soil moisture to estimate biotic soil respiration and abiotic sources of CO 2 flux in soils over a range of physical and biotic conditions. We determined that temperature fluctuations were the most important factor influencing diel variation in CO 2 flux. Variation within these diel CO 2 cycles was explained by differences in soil moisture. Increased temperature (as opposed to temperature fluctuations) had little or no effect on CO 2 flux if moisture was not also increased. We conclude that CO 2 flux in dry valley soils is driven primarily by physical factors such as soil temperature and moisture, indicating that future climate change may alter the dry valley soil C cycle. Negative CO 2 fluxes in arid soils have recently been identified as potential net C sinks. We demonstrate the potential for arid polar soils to take up CO 2, driven largely by abiotic factors associated with climate change. The low levels of CO 2 absorption into soils we observed may not constitute a significant sink of atmospheric CO 2, but will influence the interpretation of CO 2 flux for the dry valley soil C cycle and possibly other arid environments where biotic controls over C cycling are secondary to physical drivers.

Differential defoliation of Eucalyptus grandis arises from indiscriminant oviposition and differential larval survival

Abstract1 The influence of six open‐pollinated families (OPFs) of Eucalyptus grandis on both the growth and development of larvae and the oviposition preference of a paropsine chrysomelid (Paropsis atomaria) was investigated. The OPFs had previously been identified as differing in their susceptibility to defoliation by P. atomaria in forestry progeny trials.2 Oviposition preference for resistant and susceptible foliage was tested using binary choice tests. These tests did not demonstrate any significant preference for either resistant or susceptible open‐pollinated material indicating that adult host preference for susceptible trees was not a likely cause of differential defoliation.3 Quantification and analysis of growth and development parameters for all larval stages of P. atomaria showed that feeding on genetic material identified as resistant resulted in a significant reduction of relative growth rate of first instar larvae and an alteration to normal feeding behaviour. There was also a trend towards increased larval mortality on resistant E. grandis.4 We argue that although the magnitude of these effects was minor, interactions with additional biotic and abiotic sources of mortality in the field have the potential, when magnified over successive generations, to result in significant variation in defoliation of host genotypes in the field.

Bird hearing and communication in natural environments.

A soundscape, taken from human work, generally refers to the complex of sounds that are integral to and formed by a particular natural environment. Some of this sound is from abiotic sources (e.g., wind, streams, various anthropogenic sources, etc.) while some of this sound may come from conspecifics or other animals. In nature, all sound reaching an animal’s ears, whether from biotic or abiotic sources, is shaped by this natural environment. Noise, sound distortion, and frequency‐dependent attenuation can increase detection thresholds and interfere with discrimination, recognition, and localization of sound sources. Signals degraded by travel through the environment and/or affected by masking can in turn adversely affect critical behaviors such as mate attraction, territorial defense, parent‐offspring communication, predator avoidance, and prey detection. Using laboratory psychophysical data from several species of birds, some interactions among these factors and the implications for communication in a noisy environment are described. Species differences in auditory sensitivity and the characteristics of the environment are major factors in predicting whether a given soundscape limits communication between birds or interferes with detection of other biologically important sounds. [Work supported by NIH grant to R.J.D.]

Proteome Analysis of Potato under Salt Stress

Because salt stress is a major abiotic source of stress on potato crops, the molecular mechanism of the response of potato plants to salt stress was examined. On exposure to salt, the salt-sensitive cultivar Concord showed a greater reduction in shoot and root length than did the salt-tolerant cultivar Kennebec. For both cultivars, the reduction in the length of shoots was more severe than that of the roots. Salt exposure increased the content of free proline and total soluble sugars in shoots of Kennebec; these remained unchanged in Concord. Proteins extracted from shoots of both cultivars exposed to 90 mM NaCl were separated by two-dimensional polyacrylamide gel electrophoresis: 322 and 305 proteins were detected in shoots of Kennebec and Concord, respectively. Of these, 47 proteins were differentially expressed under NaCl treatment in shoot of both cultivars. Among the differentially expressed proteins, photosynthesis- and protein-synthesis-related proteins were drastically down-regulated, whereas osmotine-like proteins, TSI-1 protein, heat-shock proteins, protein inhibitors, calreticulin, and five novel proteins were markedly up-regulated. These results suggest that up-regulation of defense-associated proteins may confer relative salt tolerance to potato plants.

Prevalence and diversity of avian influenza viruses in environmental reservoirs

Little is known about the ecology and evolution of avian influenza in the natural environment, despite how these affect the potential for transmission. Most work has focused on characterizing viruses isolated from hosts such as waterfowl, and there have also been several instances of isolation and detection from abiotic sources such as water and ice. We used RT-PCR to amplify and characterize the influenza virus sequences present in sediments of ponds that are used heavily by waterfowl. The detection rate of influenza virus was high (>50%). Characterization of the viruses present by sequencing part of the haemagglutinin (HA) gene showed that there is a diverse collection of viruses in these sediments. We sequenced 117 partial HA gene clones from 11 samples and detected four different HA subtypes (H3, H8, H11 and H12), with approximately 65% of clone sequences being unique. This culture-independent approach was also able to detect a virus subtype that was not found by sampling of birds in the same geographical region in the same year. Viruses were detected readily in the winter when the ponds were frozen, indicating that these sediments could be a year-to-year reservoir of viruses to infect birds using the ponds, although we have not shown that these viruses are viable. We demonstrate that this approach is a feasible and valuable way to assess the prevalence and diversity of viruses present in the environment, and can be a valuable complement to more difficult viral culturing in attempting to understand the ecology of influenza viruses.

The trace metal composition of size‐fractionated plankton in the South China Sea: Biotic versus abiotic sources

We report the elemental composition (P, Si, Al, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) in the size‐fractionated plankton and suspended particulate matter (SPM) in the surface waters of the South China Sea. The sizefractionated plankton were effectively and gently separated by gravity through a novel trace‐metal‐clean filtration device, equipped with 150‐, 60‐, and 10‐µm aperture nets in sequence to concentrate the plankton. P‐normalized metal quotas in the largest fraction, mostly composed of copepods, were close to or slightly lower than the average metal quotas obtained from previous field studies. However, the total metal quotas in the two smaller fractions were 8‐ to 40‐fold higher than the largest one, and they increased with decreasing sizes. The striking correlation between some essential metals and chlorophyll (Chl) in the SPM at the offshore site indicates that the majority of the metals were associated with algae. Nevertheless, the P‐normalized metal quotas also showed positive correlations with abiogenic Al and Mn, indicating that most of the metals associated with phytoplankton were from extracellular inorganic particles. Preliminary evidence suggests that the extracellular metals were originally derived from anthropogenic aerosols, which contain abundant dissolvable trace metals. The metal quotas of the zooplankton assemblages have a fairly consistent value as compared to observations from other regions, but algae larger than 10 mm carry overwhelming amounts of extracellular metals even in offshore areas. The stoichiometry concept for trace‐metal composition in marine plankton assemblages is unrealistic in the field.

Search for methane on Mars: Observations, interpretation and future work

The detection of methane on Mars has been reported by three different teams in 2004. Two of them used ground-based high-resolution spectroscopy in the near infrared range. The third one used the Planetary Fourier Spectrometer aboard Mars Express. Among the data sets, two of them reported a mean CH 4 mixing ratio of 10 ppb. However, these are marginal detections, which should be considered as tentative. The third (ground-based) data set, unpublished so far, seems to show evidence for strong localized sources of CH 4, corresponding to mixing ratios as high as 250 ppb in some cases. However, the high values reported in 2003 were not confirmed by subsequent observations performed by the PFS instrument in 2004. In the absence of a refereed publication, it is difficult to judge if the high values are indeed correct. Assuming that they are, the lack of their confirmation by the PFS could have several explanations, including, among others, localized transient vents, or time variations in the methane destruction rate. A biogenic source was first suggested for the martian methane. However, later studies showed that an abiotic source such as hydrogeology can be just as effective. Further dedicated observations are obviously needed to firm up the detection and distribution of methane on Mars.

Application of the Mars Organic Analyzer to Nucleobase and Amine Biomarker Detection

The Mars Organic Analyzer (MOA), a portable microfabricated capillary electrophoresis instrument being developed for planetary exploration, is used to analyze a wide variety of fluorescamine-labeled amine-containing biomarker compounds, including amino acids, mono and diaminoalkanes, amino sugars, nucleobases, and nucleobase degradation products. The nucleobases cytosine and adenine, which contain an exocyclic primary amine, were effectively labeled, separated, and detected at concentrations <500 nM. To test the general applicability of the MOA for biomarker detection, amino acids and mono- and diamines were extracted from bacterial cells using both hydrolysis and sublimation followed by analysis. The extrapolated limit of detection provided by the valine biomarker was approximately 4 x 10(3) cells per sample. Products of an NH(4)CN polymerization that simulate a prebiotic synthesis were also successfully isolated via sublimation and analyzed. Adenine and alanine/serine were detected with no additional sample cleanup at 120 +/- 13 microM and 4.1 +/- 1 microM, respectively, corresponding to a reaction yield of 0.04% and 0.0003%, respectively. This study demonstrates that the MOA provides sensitive detection and analysis of low levels of a wide variety of amine-containing organic compounds from both biological and abiotic sources.

Effluxed CO 2- 13C from sterilized and unsterilized treatments of a calcareous soil

Soil inorganic carbon (C) represents a substantial C pool in arid ecosystems, yet little data exist on the contribution of this pool to ecosystem C fluxes. A closed jar incubation study was carried out to test the hypothesis that CO 2- 13C production and response to sterilization would differ in a calcareous (Mojave Desert) soil and a non-calcareous (Oklahoma Prairie) soil due to contributions of carbonate-derived CO 2. In addition to non-sterilized controls, soils were subjected to sterilization treatments (unbuffered HgCl 2 addition for Oklahoma soil and unbuffered HgCl 2 addition, buffered HgCl 2 addition, and autoclaving for Mojave Desert soil) to decrease biotic respiration and more readily measure abiotic CO 2 flux. Temperature and moisture treatments were also included with sterilization treatments in a factorial design. The rate of CO 2 production in both soils was significantly decreased (36–87%) by sterilization, but sterilization treatments differed in effectiveness. Sterilization had no significant effect on effluxed CO 2- 13C values in the non-calcareous Oklahoma Prairie soil and autoclaved Mojave Desert soil as compared to their respective non-sterilized controls. However, sterilization significantly altered CO 2- 13C values in Mojave Desert soil HgCl 2 sterilization treatments (both buffered and non-buffered). Plots of 1/CO 2 versus CO 2-δ 13C (similar to Keeling plots) indicated that the source CO 2-δ 13C value of the Oklahoma Prairie soil treatments was similar to the δ 13C value of soil organic matter [(SOM); −17.76‰ VPDB] whereas the source for the (acidic) unbuffered-HgCl 2 sterilized Mojave Desert soil was similar to the δ 13C value of carbonates (−0.93‰ VPDB). The source CO 2-δ 13C value of non-sterilized and autoclaved (−18.4‰ VPDB) Mojave Desert soil treatments was intermediate between SOM (−21.43‰ VPDB) and carbonates and indicates up to 13% of total C efflux may be from abiotic sources in calcareous soils.

Abiotic Source of Reactive Organic Halogens in the Sub-Arctic Atmosphere?

Recent theoretical studies indicate that reactive organic iodocarbons such as CH2I2 would be extremely effective agents for tropospheric Arctic ozone depletion and that iodine compounds added to a Br2/BrCl mixture have a significantly greater ozone (and mercury) depletion effect than additional Br2 and BrCl molecules. Here we report the first observations of CH2I2, CH2IBr, and CH2ICl in Arctic air, as well as other reactive halocarbons including CHBr3, during spring at Kuujjuarapik, Hudson Bay. The organoiodine compounds were present atthe highest levels yet reported in air. The occurrence of the halocarbons was associated with northwesterly winds from the frozen bay, and, in the case of CHBr3, was anticorrelated with ozone and total gaseous mercury (TGM), suggesting a link between inorganic and organic halogens. The absence of local leads coupled with the extremely short atmospheric lifetime of CH2I2 indicates that production occurred in the surface of the sea-ice/overlying snowpack over the bay. We propose an abiotic mechanism for the production of polyhalogenated iodo- and bromocarbons, via reaction of HOI and/or HOBr with organic material on the quasi-liquid layer above sea-ice/snowpack, and report laboratory data to support this mechanism. CH2I2, CH2IBr, and other organic iodine compounds may therefore be a ubiquitous component of air above sea ice where they will increase the efficiency of bromine-initiated ozone and mercury depletion.