Transformation of Carbon Tetrachloride and Chloroform by Trichloroethene Respiring Anaerobic Mixed Cultures and Supernatant

Carbon tetrachloride (CT) and chloroform (CF) were transformed in batch reactor experiments conducted with anaerobic dechlorinating cultures and supernatant (ADC+S) harvested from continuous flow reactors. The Evanite (EV-5L) and Victoria/Stanford (VS-5L) cultures capable of respiring trichloroethene (TCE), 1,2-cis-dichloroethene (cDCE), and vinyl chloride (VC) to ethene (ETH) were grown in continuous flow reactors receiving an influent feed of saturated TCE (10 mM; 60 mEq) and formate (45 mM; 90 mEq) but no CT or CF. In all experiments, cells and supernatant were harvested from the chemostats and inoculated into batch reactors. Transformation of various concentrations of CT (0.86, 2.6, or 8.6 μM), CF (2.1 or 21.1 μM), dichloromethane (DCM; 23.1 μM), and TCE (50 μM) was examined. CT transformation was complete and exhibited pseudo-first order kinetics with CF as the primary measured transformation product in all treatments. Lesser amounts of DCM and carbon disulfide (CS₂) were measured leading to an overall mass balance of 20-40% of the original mass as CT accounted for. An analytical first order solution was developed to model CT degradation and product formation under multiple conditions. Cells poisoned with 50 mM sodium azide (NaN₃) catalyzed rapid and complete CT transformation suggesting a greater importance of redox active cofactors than live cells in the abiotic and cometabolic transformation. DCM and CS₂ however were not produced in the poisoned treatments. TCE and CT simultaneous transformation occurred with an approximately two-fold increase in the CT degradation rate while maintaining complete TCE respiration to ETH. During the initial round of TCE respiration, the rate limiting step was VC to ETH, which was impacted by the presence of CT and CF. A subsequent addition of 50 μM TCE showed a substantial decline in the rates of reductive dechlorination owing to the inhibitory effects of long term exposure to CF. The results clearly demonstrate that transformation can be promoted by anaerobic dechlorinating cultures and supernatant not previously acclimated to CT and CF. However, abiotic reactions account for much of the observed transformation. The role of CF inhibition on H₂ utilization by the culture was also explored. Sodium formate was provided as a rapid release substrate, providing H₂ as an electron donor. H₂ partial pressures were tracked throughout the course of the kinetic experiments. The rapid transformation of CT to CF made it not possible to determine if CT inhibited H₂ use by the anaerobic dechlorinating cultures. However, the rapid buildup and subsequent slow transformation of CF was found to reversibly inhibit H₂ consumption for homoacetogenesis. It was found that an aqueous CF concentration above 0.4 μM or 0.6 μM inhibited H₂ consumption by the EV-5L and VS-5L cultures, respectively. This result differed for the VS-5L culture when metabolizing TCE in the presence of CT and CF. The VS-5L culture consumed H₂ at CF concentrations as high as 1.3 μM. The culture may have been partially inhibited at CF concentrations greater than 0.6 μM, which is shown by slower consumption of H₂ than controls that did not contain CF. The results demonstrate that CF reversibly inhibits the consumption of H₂ by the anaerobic dechlorinating cultures, and that more research is required to determine if it is through a chemical inhibition or toxicity

Early Successional Microhabitats Allow the Persistence of Endangered Plants in Coastal Sand Dunes

Many species are adapted to disturbance and occur within dynamic, mosaic landscapes that contain early and late successional microhabitats. Human modification of disturbance regimes alters the availability of microhabitats and may affect the viability of species in these ecosystems. Because restoring historical disturbance regimes is typically expensive and requires action at large spatial scales, such restoration projects must be justified by linking the persistence of species with successional microhabitats. Coastal sand dune ecosystems worldwide are characterized by their endemic biodiversity and frequent disturbance. Dune-stabilizing invasive plants alter successional dynamics and may threaten species in these ecosystems. We examined the distribution and population dynamics of two federally endangered plant species, the annual Layia carnosa and the perennial Lupinus tidestromii, within a dune ecosystem in northern California, USA. We parameterized a matrix population model for L. tidestromii and examined the magnitude by which the successional stage of the habitat (early or late) influenced population dynamics. Both species had higher frequencies and L. tidestromii had higher frequency of seedlings in early successional habitats. Lupinus tidestromii plants in early successional microhabitats had higher projected rates of population growth than those associated with stabilized, late successional habitats, due primarily to higher rates of recruitment in early successional microhabitats. These results support the idea that restoration of disturbance is critical in historically dynamic landscapes. Our results suggest that large-scale restorations are necessary to allow persistence of the endemic plant species that characterize these ecosystems

Early Successional Microhabitats Allow the Persistence of Endangered Plants in Coastal Sand Dunes

<div><p>Many species are adapted to disturbance and occur within dynamic, mosaic landscapes that contain early and late successional microhabitats. Human modification of disturbance regimes alters the availability of microhabitats and may affect the viability of species in these ecosystems. Because restoring historical disturbance regimes is typically expensive and requires action at large spatial scales, such restoration projects must be justified by linking the persistence of species with successional microhabitats. Coastal sand dune ecosystems worldwide are characterized by their endemic biodiversity and frequent disturbance. Dune-stabilizing invasive plants alter successional dynamics and may threaten species in these ecosystems. We examined the distribution and population dynamics of two federally endangered plant species, the annual <i>Layia carnosa</i> and the perennial <i>Lupinus tidestromii</i>, within a dune ecosystem in northern California, USA. We parameterized a matrix population model for <i>L</i>. <i>tidestromii</i> and examined the magnitude by which the successional stage of the habitat (early or late) influenced population dynamics. Both species had higher frequencies and <i>L</i>. <i>tidestromii</i> had higher frequency of seedlings in early successional habitats. <i>Lupinus tidestromii</i> plants in early successional microhabitats had higher projected rates of population growth than those associated with stabilized, late successional habitats, due primarily to higher rates of recruitment in early successional microhabitats. These results support the idea that restoration of disturbance is critical in historically dynamic landscapes. Our results suggest that large-scale restorations are necessary to allow persistence of the endemic plant species that characterize these ecosystems.</p></div

Population growth rate of <i>Lupinus tidestromii</i> in different successional microhabitats.

<p>Deterministic matrix model projections of population growth rate (λ) for <i>Lupinus tidestromii</i> at Abbotts Lagoon are higher in early microhabitats in 2010 and 2011. We present observed values and 95% confidence intervals from 1,000 bootstrap estimates.</p

Stage structure of <i>Lupinus tidestromii</i> in three successional microhabitats at Abbotts Lagoon.

<p>Stacked bars indicate the proportion of <i>Lupinus tidestromii</i> individuals in each of three stage classes (seedling, non-reproductive, and reproductive) found in each of three successional microhabitats at Abbotts Lagoon. Individuals were pooled across plots within each of the three habitat types. Within 145 vegetation plots, there were 198 plants in 22 early plots, 382 plants in 98 mid plots, and 31 plants in 25 late plots; in total, 109 seedlings, 64 non-reproductive plants, and 438 adult plants were found.</p

Life table response experiment for <i>Lupinus tidestromii</i> populations in early versus late successional microhabitats at Abbotts Lagoon.

<p>Results are shown separately for year 2010–2011 and 2011–2012. Key to abbreviations: SB2, seeds in the seed bank that will germinate in two years; SB1, seeds in the seed bank that will germinate in one year; SL, seedling; NR, non-reproductive; REP, reproductive.</p><p>Life table response experiment for <i>Lupinus tidestromii</i> populations in early versus late successional microhabitats at Abbotts Lagoon.</p

Average transition matrices (with 95% bootstrapped confidence intervals and sample sizes for growth, survival, and regression transitions) for <i>Lupinus tidestromii</i> in early and late successional microhabitat at Abbotts Lagoon.

<p>Key to abbreviations: SB2, seeds in the seed bank that will germinate in two years; SB1, seeds in the seed bank that will germinate in one year; SL, seedling; NR, non-reproductive; REP, reproductive.</p><p>Average transition matrices (with 95% bootstrapped confidence intervals and sample sizes for growth, survival, and regression transitions) for <i>Lupinus tidestromii</i> in early and late successional microhabitat at Abbotts Lagoon.</p

Vegetation community composition of successional microhabitats at Abbotts Lagoon.

<p>Non-metric multidimensional scaling ordination plots of community composition in two-dimensional space. Each point represents the composition of herbaceous plants in a site in multidimensional space, and the distance between any two points represents the difference between those two sites according to a modified Raup-Crick metric. Sites that are closer together are more similar in community composition. Open triangles represent the early successional sites, gray circles represent mid successional sites and gray squares represent late successional sites. Lines represent the minimum convex hulls around the data.</p