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41.
The mutualism-parasitism continuum in ectomycorrhizas: a quantitative assessment using meta-analysis 总被引:4,自引:0,他引:4
Context dependency is deemed to position the outcomes of species interactions along a continuum of mutualism to parasitism. Thus, it is imperative to understand which factors determine where a particular interspecific interaction falls along the continuum. Over the past 20 years research on the ectomycorrhizal symbiosis has resulted in sufficient independent studies to now generalize about the factors and mechanisms that affect host response to ectomycorrhizas. Using meta-analysis we quantitatively evaluated the role of biotic (partner identity and colonization levels of ectomycorrhizal fungi) and abiotic (phosphorus levels) factors in determining host biomass, height, and shoot:root responses to ectomycorrhizal associations. On average, seedlings across multiple host genera increased in total biomass when inoculated with ectomycorrhizal fungi regardless of the identity of the fungal associate; host genera differed in the magnitude of response for both total biomass and shoot:root ratio. Association with different fungal genera modified only host allocation of biomass to shoots and roots. Neither level of colonization on inoculated seedlings nor the level of contamination on control seedlings relative to colonization levels by target fungi on inoculated seedlings was important in explaining variation in effect sizes for any growth response. None of our proposed factors (identity of partners, colonization level, magnitude of contamination, or duration of association) explained variation in effect sizes for shoot height, although in general seedlings were taller when inoculated with ectomycorrhizal fungi. Phosphorus additions did not influence effect sizes. Although the general trend across studies was for a positive response of hosts to ectomycorrhizal inoculation, publication bias and methodological issues effectively reduce and distort the spectrum on which we evaluate host responses to ectomycorrhizal inoculation. Our results indicate that the variation in ectomycorrhizal fungi perceived by the host may be of a discrete (presence/absence of ectomycorrhizal fungi) rather than continuous nature (variation in identity or abundance of ectomycorrhizal fungi). 相似文献
42.
43.
OBJECTIVES: To determine whether the substantial short-term declines in drivers' use of hand-held phones achieved in the District of Columbia (DC) were sustained 1 year after a ban. METHODS: Drivers' daytime hand-held cell phone use was observed in DC and nearby areas of Virginia and Maryland, states without bans. Observations were conducted several months before the ban, shortly after, and 1 year later. The number of vehicles observed in all three surveys combined was 51,945 in DC, 36,796 in Maryland, and 43,033 in Virginia. RESULTS: The rate of talking on hand-held phones declined significantly from 6.1 percent before the law to 3.5 percent shortly after; when measured 1 year later, use was 4.0 percent, still significantly lower than baseline. Based on increases in rates of talking on hand-held phones in Maryland and Virginia, longer-term phone use in DC was estimated to be 53 percent lower than would have been expected without the ban. Declines in DC were identified for drivers of vehicles registered in all three jurisdictions. CONCLUSIONS: In DC, there was an initial decline of about 50 percent in drivers talking on hand-held cell phones following a ban, and this decline was sustained about 1 year later. After a similar ban in New York, there was an initial decline in phone use comparable with the initial decline in DC, but the decline a year after the New York ban took full effect was only about 21 percent and not statistically significant. The potential difference in sustained effectiveness for the DC ban may reflect tougher enforcement in DC. Even if full compliance with hand-held phone bans can be achieved, the risks from drivers' use of hands-free phones will remain. 相似文献
44.
Featured Collection Introduction: Connectivity of Streams and Wetlands to Downstream Waters
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Laurie C. Alexander Ken M. Fritz Kate A. Schofield Bradley C. Autrey Julie E. DeMeester Heather E. Golden David C. Goodrich William G. Kepner Hadas R. Kiperwas Charles R. Lane Stephen D. LeDuc Scott G. Leibowitz Michael G. McManus Amina I. Pollard Caroline E. Ridley Melanie K. Vanderhoof Parker J. Wigington Jr. 《Journal of the American Water Resources Association》2018,54(2):287-297
Connectivity is a fundamental but highly dynamic property of watersheds. Variability in the types and degrees of aquatic ecosystem connectivity presents challenges for researchers and managers seeking to accurately quantify its effects on critical hydrologic, biogeochemical, and biological processes. However, protecting natural gradients of connectivity is key to protecting the range of ecosystem services that aquatic ecosystems provide. In this featured collection, we review the available evidence on connections and functions by which streams and wetlands affect the integrity of downstream waters such as large rivers, lakes, reservoirs, and estuaries. The reviews in this collection focus on the types of waters whose protections under the U.S. Clean Water Act have been called into question by U.S. Supreme Court cases. We synthesize 40+ years of research on longitudinal, lateral, and vertical fluxes of energy, material, and biota between aquatic ecosystems included within the Act's frame of reference. Many questions about the roles of streams and wetlands in sustaining downstream water integrity can be answered from currently available literature, and emerging research is rapidly closing data gaps with exciting new insights into aquatic connectivity and function at local, watershed, and regional scales. Synthesis of foundational and emerging research is needed to support science‐based efforts to provide safe, reliable sources of fresh water for present and future generations. 相似文献
45.
Future atmospheric CO2 levels will most likely have complex consequences for marine organisms, particulary photosynthetic calcifying organisms.
Corallina officinalis L. is an erect calcifying macroalga found in the inter- and subtidal regions of temperate rocky coastlines and provides important
substrate and refugia for marine meiofauna. The main goal of the current study was to determine the physiological responses
of C. officinalis to increased CO2 concentrations expected to occur within the next century and beyond. Our results show that growth and production of inorganic
material decreased under high CO2 levels, while carbonic anhydrase activity was stimulated and negatively correlated to algal inorganic content. Photosynthetic
efficiency based on oxygen evolution was also negatively affected by increased CO2. The results of this study indicate that C. officinalis may become less competitive under future CO2 levels, which could result in structural changes in future temperate intertidal communities. 相似文献
46.
Laurie Sorenson Gerald R. Allen Mark V. Erdmann Chang-Feng Dai Shang-Yin Vanson Liu 《Marine Biology》2014,161(11):2495-2507
Pleistocene eustatic changes in sea level are often invoked to explain genetic divergence among marine organisms. However, molecular phylogenies have revealed relatively few examples of speciation events dating to the Pleistocene. We present a species-level hypothesis of the timing of evolution for the Pomacentrus coelestis species complex (Pomacentridae), based on the nuclear S7 intron and the mitochondrial Cytb gene, and reconstruct ancestral range distributions across the timetree. Ancestral range reconstruction suggests the complex originated in the Coral Triangle and East Indian Ocean, with subsequent range expansion outward from this region. We suggest that land barriers to dispersal (e.g., Indo-Pacific barrier) may be responsible for the divergence between Indian (P. alleni, P. similis, P. caeruleopunctatus, and P. caeruleus) and Pacific (P. micronesicus, P. auriventris, and P. coelestis) species groups, and subsequent isolation by Pleistocene sea-level fluctuations in certain areas of the Coral Triangle (glacial refugia) may play an important role in the diversification of this species complex. Additionally, our analyses show cryptic lineages within P. micronesicus and highlight the need for comprehensive sampling within and among species to reveal recent speciation events. 相似文献
47.
Scott Elliott Gerald E. Streit Jeffrey S. Gaffney James E. Bossert Michael Brown Jon Reisner Laurie A. McNair 《Environmental science and pollution research international》1999,6(2):103-105
The nerve agent sarin has recently been deployed by terrorists in a major city. The molecule is volatile and made its way
to many victims by passing as vapor through a highly reactive medium. Here we estimate rates and pathways for the removal
of gas phase sarin from a generalized urban atmosphere. Only information from the open scientific literature is used. By structure
reactivity comparisons with the organophosphorus pesticides, hydroxyl radical hydrogen abstraction may occur in as little
as one hour. Decomposition of side chains after hydroxyl attack leads to organic oxygenates which preserve the phosphonofluoridate
and so toxicity. The aqueous aerosol surface is contacted in minutes and offers access to a range of dissolved nucleophiles.
Substitution displaces the fluoride leaving group, giving safe phosphoric acid analogs. Because of uncertainties in the electron
distribution and in aqueous decay mechanisms, the time constants must be viewed as lower limits. 相似文献
48.
Ian C. Laurie 《Journal of Environmental Planning and Management》1983,26(2):89-98
The United Kingdom offers some of the finest designed parks and garden landscapes in the world and, whilst there is a wide range of skills and a wealth of literature on the subject, there is little evidence of official effort to systematically record historic sites. This, it is argued, is a factor in the continuing decline of many examples. This paper records an attempt at a comprehensive examination of one county — Cheshire — begun in 1970. The method is described and the results discussed in some detail. Some suggestions are put forward for improvements to official incentives for site owners. 相似文献
49.
Thullner M Mauclaire L Schroth MH Kinzelbach W Zeyer J 《Journal of contaminant hydrology》2002,58(3-4):169-189
Bacterial growth and its interaction with water flow was investigated in a two-dimensional flow field in a saturated porous medium. A flow cell (56 x 44 x 1 cm) was filled with glass beads and operated under a continuous flow of a mineral medium containing nitrate as electron acceptor. A glucose solution was injected through an injection port, simulating a point source contamination. Visible light transmission was used to observe the distribution of the growing biomass and water flow during the experiment. At the end of the experiment (on day 31), porous medium samples were destructively collected and analyzed for abundance of total and active bacterial cells, bacterial cell volume and concentration of polysaccharides and proteins. Microbial growth was observed in two stripes along the length of the flow cell, starting at the glucose injection port, where highest biomass concentrations were obtained. The spatial distribution of biomass indicated that microbial activity was limited by transverse mixing between glucose and nitrate media, as only in the mixing zone between the media high biological activities were achieved. The ability of the biomass to change the flow pattern in the flow cell was observed, indicating that the biomass was locally reducing the hydraulic conductivity of the porous medium. This bioclogging effect became evident when the injection of the glucose solution was turned off and water flow still bypassed the area around the glucose injection port, preserving the flow pattern as it was during the injection of the glucose solution. As flow bypass was possible in this system, the average hydraulic properties of the flow cell were not affected by the produced biomass. Even in the vicinity of the injection port, the total volume of the bacterial cells remained below 0.01% of the pore space and was unlikely to be responsible for the bioclogging. However, the bacteria produced large amounts of extracellular polymeric substances (EPS), which likely caused the observed bioclogging effects. 相似文献
50.
Burton GA Greenberg MS Rowland CD Irvine CA Lavoie DR Brooker JA Moore L Raymer DF McWilliam RA 《Environmental pollution (Barking, Essex : 1987)》2005,134(1):133-144
An in situ toxicity and bioaccumulation assessment approach is described to assess stressor exposure and effects in surface waters (low and high flow), the sediment-water interface, surficial sediments and pore waters (including groundwater upwellings). This approach can be used for exposing species, representing major functional and taxonomic groups. Pimephales promelas, Daphnia magna, Ceriodaphnia dubia, Hyalella azteca, Hyalella sp., Chironomus tentans, Lumbriculus variegatus, Hydra attenuatta, Hexagenia sp. and Baetis tibialis were successfully used to measure effects on survival, growth, feeding, and/or uptake. Stressors identified included chemical toxicants, suspended solids, photo-induced toxicity, indigenous predators, and flow. Responses varied between laboratory and in situ exposures in many cases and were attributed to differing exposure dynamics and sample-processing artifacts. These in situ exposure approaches provide unique assessment information that is complementary to traditional laboratory-based toxicity and bioaccumulation testing and reduce the uncertainties of extrapolating from the laboratory to field responses. 相似文献