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The composition of plant communities everywhere now likely comprises alien as well as native species, and those aliens that become invasive have wide-ranging impacts on the structure and function of recipient ecosystems. These impacts include perturbations to soil carbon (C) cycling, but the direction and magnitude of impacts are species and climate dependent, making it difficult to generalize whether a specific invader will promote losses or gains in soil C stocks. Generalizations of a specific invader??s impacts are necessary; however, because the range of an invader can encompass thousands of square kilometers, meaning their effects can have broad, regional consequences. To quantify broad-scale and context-dependent impacts of a specific invader, multi-site investigations that capture and measure local and regional environmental heterogeneity are necessary. Using this approach, we show that a widespread grass invader of forest understories is associated with declines in soil C during infilling (spreading within the invaded range). Across the 36 study sites, total soil C stocks declined (P?=?0.113) by approximately 12% (estimated mean?±?SD, uninvaded: 2,429?±?512.9 vs. invaded: 2,140?±?520.7?g?C?m?2). The decline in total soil C is driven by a significant (P?=?0.047) reduction in the native-derived, mineral-associated soil C fraction. This fraction, whose mass and slow turnover makes it an important C store, is approximately 15% lower in invaded (estimated mean?±?SD: 1,560?±?400.4?g?C?m?2) than uninvaded plots (1,826?±?398.1?g?C?m?2). Notably, declines in this C fraction are only apparent at 21 of the sites, reflecting how environmental heterogeneity in other variables (specifically pH, soil moisture, and clay content) are important to quantify to determine invader impacts across a region. The 26% decline in microbial biomass with invasion (P?=?0.011; estimated mean?±?SD, uninvaded: 10.05?±?1.79 vs. invaded: 7.40?±?1.80?g?C?m?2) is also dependent on site characteristics (pH), and reductions are greater where the invader occurs at higher densities. Reductions in microbial biomass and soil C with invasion suggest that grass invasion will alter soil C cycling and decrease forest-C stores across the study region, although invader effects at a specific-site will be dependent on environmental context. 相似文献
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Although ecological risk assessment (ERA) and environmental monitoring would seem to be potentially complimentary activities, they have been disjunct in practice. This is because of differences in goals and products. Environmental monitoring determines status and trends in indicators to determine whether the environment is improving. ERA estimates effects of stressors on endpoint attributes to support decision making. Indicators are, by definition, indicative of some unmeasured condition. Assessment endpoints are valued properties of the environment that are susceptible to stressors of concern. Indicators are justified by the logic of the monitoring program, which may be self-referential. Assessment endpoints are justified by their potential susceptibility and by environmental policies and public values. Indicators are often expressed in terms of indices or scores that obscure the actual condition of the environment. Because assessment endpoints must be clear to decision makers and the public, they require real units of actual environmental properties. Monitoring programs are peripherally concerned about causal relationships, while risk assessment is devoted to elucidating causal relationships. As a result, risk assessments may use the results of monitoring studies, but only after disaggregating the indicators to their components and choosing those that are appropriate. Monitoring programs could be more useful if they used a risk-based approach to address important problems rather than simply tracking indicators. 相似文献
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Phylogenetic analyses inferred from rbcL sequences indicates that specimens of Caloglossa (Harvey) G. Martens collected from Vermilion Bay, Louisiana and Galveston, Texas, reported as C. leprieurii (Montagne) G. Martens (1869) constitutes a separate taxon. Studies are presently being conducted to compare this northwestern Gulf of Mexico taxon with material of C. intermedia Kamiya et West in Kamiya et al. (2000, J. Phycol. 36:411-420) from the Western Atlantic coast and with C. apomeiotica West et Zuccarello in West et al. (1994, Bot. Mar. 37:381–390) from Baja California, Mexico. 相似文献
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Identification of Listeria monocytogenes Genes Expressed in Response to Growth at Low Temperature 总被引:4,自引:0,他引:4
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Siqing Liu James E. Graham Lance Bigelow Philip D. Morse II Brian J. Wilkinson 《Applied microbiology》2002,68(4):1697-1705
Listeria monocytogenes is a food-borne bacterial pathogen that is able to grow at refrigeration temperatures. To investigate microbial gene expression associated with cold acclimation, we used a differential cDNA cloning procedure known as selective capture of transcribed sequences (SCOTS) to identify bacterial RNAs that were expressed at elevated levels in bacteria grown at 10°C compared to those grown at 37°C. A total of 24 different cDNA clones corresponding to open reading frames in the L. monocytogenes strain EGD-e genome were obtained by SCOTS. These included cDNAs for L. monocytogenes genes involved in previously described cold-adaptive responses (flaA and flp), regulatory adaptive responses (rpoN, lhkA, yycJ, bglG, adaB, and psr), general microbial stress responses (groEL, clpP, clpB, flp, and trxB), amino acid metabolism (hisJ, trpG, cysS, and aroA), cell surface alterations (fbp, psr, and flaA), and degradative metabolism (eutB, celD, and mleA). Four additional cDNAs were obtained corresponding to genes potentially unique to L. monocytogenes and showing no significant similarity to any other previously described genes. Northern blot analyses confirmed increased steady-state levels of RNA for all members of a subset of genes examined during growth at a low temperature. These results indicated that L. monocytogenes acclimation to growth at 10°C likely involves amino acid starvation, oxidative stress, aberrant protein synthesis, cell surface remodeling, alterations in degradative metabolism, and induction of global regulatory responses. 相似文献
106.
Lance J. Miller Moby Solangi Stan A. Kuczaj II 《Ethology : formerly Zeitschrift fur Tierpsychologie》2010,116(12):1127-1137
Many of the threats to bottlenose dolphins are anthropogenic factors including overfishing, high‐speed boats, chemical runoff, and noise pollution. Having a thorough understanding of the behavior and behavioral patterns of these animals can help with conservation plans to protect this species. This study examined the behavioral states and behavioral events of Atlantic bottlenose dolphins (Tursiops truncatus) in the Mississippi Sound. The behavioral states exhibited by dolphins within the Sound were found to vary by both season and time of day. Dolphins socialized more during the spring and spent more time feeding in the fall. Feeding was highest early in the morning and decreased throughout the day, while socializing occurred at low levels in the morning and increased in the early afternoon. Two distinct forms of social behavior and multiple feeding strategies were exhibited by dolphins within the Sound. Results suggest that certain percussive behavioral events may be used to communicate motivation during transitional behavioral states. These results demonstrate the need for a more complete understanding of dolphin behavior that will facilitate the conservation of this species. 相似文献
107.
Katherina Walz Devon Cohen Paul M. Neilsen Joseph Foster II. Francesco Brancati Korcan Demir Richard Fisher Michelle Moffat Nienke E. Verbeek Kathrine Bjørgo Adriana Lo Castro Paolo Curatolo Giuseppe Novelli Clemer Abad Cao Lei Lily Zhang Oscar Diaz-Horta Juan I. Young David F. Callen Mustafa Tekin 《Human genetics》2015,134(2):181-190
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John F. Brooks II Mattias C. Gyllborg Acadia A. Kocher Laura E. H. Markey Mark J. Mandel 《Journal of bacteriology》2015,197(6):1065-1074
Bacterial strain variation exists in natural populations of bacteria and can be generated experimentally through directed or random mutation. The advent of rapid and cost-efficient whole-genome sequencing has facilitated strain-level genotyping. Even with modern tools, however, it often remains a challenge to map specific traits to individual genetic loci, especially for traits that cannot be selected under culture conditions (e.g., colonization level or pathogenicity). Using a combination of classical and modern approaches, we analyzed strain-level variation in Vibrio fischeri and identified the basis by which some strains lack the ability to utilize glycerol as a carbon source. We proceeded to reconstruct the lineage of the commonly used V. fischeri laboratory strains. Compared to the wild-type ES114 strain, we identify in ES114-L a 9.9-kb deletion with endpoints in tadB2 and glpF; restoration of the missing portion of glpF restores the wild-type phenotype. The widely used strains ESR1, JRM100, and JRM200 contain the same deletion, and ES114-L is likely a previously unrecognized intermediate strain in the construction of many ES114 derivatives. ES114-L does not exhibit a defect in competitive squid colonization but ESR1 does, demonstrating that glycerol utilization is not required for early squid colonization. Our genetic mapping approach capitalizes on the recently discovered chitin-based transformation pathway, which is conserved in the Vibrionaceae; therefore, the specific approach used is likely to be useful for mapping genetic traits in other Vibrio species. 相似文献