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731.
We designed a new gas exchange system that concurrently measures foliar H2O, O3, and CO2 flux (HOC flux system) while delivering known O3 concentrations. Stomatal responses of three species were tested: snapbean, and seedlings of California black oak (deciduous broadleaf) and blue oak (evergreen broadleaf). Acute O3 exposure (120-250 ppb over an hour) was applied under moderate light and low vapor pressure deficits during near steady state conditions. The rate of stomatal closure was measured when the whole plant was placed in the dark. An adjacent leaf on each plant was also concurrently measured in an O3-free cuvette. Under some conditions, direct measurements and calculated foliar O3 flux were within the same order of magnitude; however, endogenously low gs or O3 exposure-induced depression of gs resulted in an overestimation of calculated O3 fluxes compared with measured O3 fluxes. Sluggish stomata in response to light extinction with concurrent O3 exposure, and incomplete stomatal closure likewise underestimated measured O3 flux. 相似文献
732.
Alonso R Bermejo V Sanz J Valls B Elvira S Gimeno BS 《Environmental pollution (Barking, Essex : 1987)》2007,146(3):692-698
Intra-genus and intra-specific variation and the influence of nitrogen enrichment on net assimilation and stomatal conductance of some annual Trifolium species of Mediterranean dehesa grasslands were assessed under experimental conditions. Also gas exchange rates were compared between some Leguminosae and Poaceae species growing in the field in a dehesa ecosystem in central Spain. The results showed that the previously reported different O3 sensitivity of some Trifolium species growing in pots does not seem to be related to different maximum g(s) values. In addition, no clear differences on gas exchange rates could be attributed to Leguminosae and Poaceae families growing in the field, with intra-genus variation being more important than differences found between families. Further studies are needed to increase the database for developing a flux-based approach for setting O3 critical levels for semi-natural Mediterranean species. 相似文献
733.
Linking ground-water age and chemistry data along flow paths: implications for trends and transformations of nitrate and pesticides 总被引:2,自引:1,他引:1
Tesoriero AJ Saad DA Burow KR Frick EA Puckett LJ Barbash JE 《Journal of contaminant hydrology》2007,94(1-2):139-155
Tracer-based ground-water ages, along with the concentrations of pesticides, nitrogen species, and other redox-active constituents, were used to evaluate the trends and transformations of agricultural chemicals along flow paths in diverse hydrogeologic settings. A range of conditions affecting the transformation of nitrate and pesticides (e.g., thickness of unsaturated zone, redox conditions) was examined at study sites in Georgia, North Carolina, Wisconsin, and California. Deethylatrazine (DEA), a transformation product of atrazine, was typically present at concentrations higher than those of atrazine at study sites with thick unsaturated zones but not at sites with thin unsaturated zones. Furthermore, the fraction of atrazine plus DEA that was present as DEA did not increase as a function of ground-water age. These findings suggest that atrazine degradation occurs primarily in the unsaturated zone with little or no degradation in the saturated zone. Similar observations were also made for metolachlor and alachlor. The fraction of the initial nitrate concentration found as excess N2 (N2 derived from denitrification) increased with ground-water age only at the North Carolina site, where oxic conditions were generally limited to the top 5 m of saturated thickness. Historical trends in fluxes to ground water were evaluated by relating the times of recharge of ground-water samples, estimated using chlorofluorocarbon concentrations, with concentrations of the parent compound at the time of recharge, estimated by summing the molar concentrations of the parent compound and its transformation products in the age-dated sample. Using this approach, nitrate concentrations were estimated to have increased markedly from 1960 to the present at all study sites. Trends in concentrations of atrazine, metolachlor, alachlor, and their degradates were related to the timing of introduction and use of these compounds. Degradates, and to a lesser extent parent compounds, were detected in ground water dating back to the time these compounds were introduced. 相似文献
734.
Van Campenhout K Bervoets L Blust R 《Environmental pollution (Barking, Essex : 1987)》2007,145(3):905-914
The impact of several factors on the assimilation efficiency (AE) of Cd and Zn from food in the common carp (Cyprinus carpio) was studied. Tested prey species were midge larvae (Chironomus riparius), zebra mussels (Dreissena polymorpha) and oligochaetes (Tubifex tubifex). The Cd load of the larvae did not affect the Cd AE in the carp. The Zn AE however, was negatively related to the Zn load of the prey. Food quantity and starvation of the carp did not significantly affect the Cd AE. For Zn, a significant decrease in AE was found when carp were fed ad libitum. Decreasing the temperature from 25 degrees C to 15 degrees C did not influence the Cd AE, while for Zn a significant decrease of the AE was measured. Carp assimilated Cd from both zebra mussels and oligochaetes with a significantly lower efficiency in comparison to the midge larvae, although Zn AEs was prey independent. 相似文献
735.
Effect of temperature on statolith growth of the European squid Loligo vulgaris during early life 总被引:1,自引:0,他引:1
R. Villanueva 《Marine Biology》2000,136(3):449-460
Over the past decade, statolith interpretation has resulted in a major advance in our knowledge of squid population-dynamics,
but the way in which environmental conditions affect the statolith increment-deposition ratio remains virtually unknown. The
object of the present study was to determine the effect of temperature on this process, using tetracycline marks to validate
statolith growth in Loligo vulgaris Lamarck, 1798 under rearing conditions equivalent to severe winter (11 °C) and summer (19 °C) temperature regimes. Tetracycline
marking was performed every 10 d (at 10, 20, 30, 40, 50 and 60 d of age). The newly hatched squid paralarvae were slightly
smaller in summer than those hatched in winter. Survival rates were similar in both cultures, but growth rates (wet mass)
of summer squids were double those in winter. At hatching, statoliths were already longer in the summer squids, and growth
rates were 2% d−1 as opposed to 0.9% d−1 for winter statoliths. For the dorsal dome area of the statolith, where more increment counts were made, statolith growth
was of 3.25 μm d−1 in summer, and daily increment deposition was confirmed in 87% of the statoliths. The slow growth of statoliths at winter
temperatures yielded a mean growth of 1.1 μm d−1– insufficient to discern the increments using light microscopy. Subsequent SEM observation enabled only 21% of the winter
statoliths to be read; these also indicated a deposition rate of one increment d−1. Since the life span of L. vulgaris is ≃1 yr, squids will experience at least one winter during their life cycle, and this might be visible on the statolith.
Received: 28 June 1999 / Accepted: 20 December 1999 相似文献
736.
An experimental study on recolonization and succession of marine macrobenthos in defaunated sediment 总被引:3,自引:0,他引:3
Hypoxia/anoxia in coastal waters is a world wide problem which often results in mass mortality and defaunation of benthos.
In this study, field experiments were carried out to examine recolonization and succession of macrobenthic infauna in defaunated
sediments, and the time required for recovery from complete defaunation to a stable community. Trays (33 cm length × 25.5 cm
width × 11 cm depth) of defaunated sediment were exposed at the subtidal of a pristine site in subtropical Hong Kong. Temporal
changes of macrobenthic communities in defaunated sediment were analyzed by univariate and multivariate statistics, and compared
with those in undisturbed natural sediment at the same site. Initial colonization of macrobenthos occurred rapidly. A total
of 42 species was found, with an average of 258 animals per tray and 24 species per tray recorded in the first month. Abundance
showed a small peak (496 animals per tray) after 3 months, reached a sharp peak (1154 animals per tray) after 6 months, and
declined thereafter. Species number increased gradually, reached a maximum (68 species per tray) after 9 months, and then
decreased. Recolonization was predominantly contributed by larval settlement rather than adult migration. Temporal changes
in abundance, species number and diversity of the macrobenthic community in defaunated sediment resemble the spatial changes
along a decreasing pollution gradient previously defined by other authors. Results of this experiment suggest that newly available
sediment may allow more species to colonize (or coexist) than sediment pre-occupied by an established community. This is probably
due to less interspecific competition in the former habitat. No significant difference in abundance or species richness was
observed between defaunated and natural sediments after 15 months, suggesting that a stable community had been achieved, although
minor variations in species composition were still discernible between defaunated and natural sediments.
Received: 24 May 1999 / Accepted: 20 October 1999 相似文献
737.
Phylogenetic analyses of the left domain of the mitochondrial DNA control-region sequence have been used to examine the relationships
among species of the genus Merluccius (Rafinesque, 1810), and to compare these with hypotheses based on morphological, meristic and allozyme characters. Analysis
of aligned sequences revealed that transition bias was much lower than in mammalian mtDNA, and that nucleotide composition
of control-region sequences was biased toward A and T. We have roughly calibrated a molecular clock for the genus, based on
the rise of the Isthmus of Panamá, which is believed to have created a barrier to dispersal between marine species of the
Atlantic and Pacific Oceans. Our mtDNA-based phylogeny was highly congruent with allozyme-based phylogenies, but poorly so
with a previously described phylogeny based on morphology. Specifically, our phylogeny resolved two well-supported principal
clades, one of American (west Atlantic and east Pacific) species and the other of Euro–African (east Atlantic) species. This
suggests an evolutionary history during which the ancestral lineage of Merluccius was divided between two geographic regions, with subsequent dispersal and vicariant events resulting in the evolution and
distribution of extant taxa. However, the relationships between some taxa within the American clade could not be resolved.
We suggest that this is consistent with an hypothesis of a rapid origin and radiation of these taxa.
Received: 12 December 1998 / Accepted: 15 October 1999 相似文献
738.
The benthic response to a plume front was studied in two areas of the northern Adriatic (Mediterranean Sea) differently influenced
by the Po River freshwater input. Sediment samples were collected in June 1996 and February 1997 from 12 stations. The adopted
sampling strategy was able to identify the front line in real time by satellite images and to locate sampling stations along
an inner–outer plume gradient in order to cover the benthic area beneath the river plume, where enhanced biological production
was expected, and open-sea sediments not directly influenced by freshwater inputs. Meiofaunal parameters were compared to
the physical conditions and to phytodetritus inputs, organic matter accumulation and bacterial secondary production. The sediments
of the Adriatic Sea were characterised by high concentrations of phytopigments (0.6 to 13.9 μg g−1 for chlorophyll a and 1.2 to 17.7 μg g−1 for phaeopigments) and biopolymeric organic carbon (0.15 to 3.02 mg g−1). The plume system extended for a large sector of the northern Adriatic. In the northern area, a large and highly dynamic
plume area was coupled with a sediment organic matter concentration significantly higher than in open-sea sediments. In the
southern sector, where the plume area and the front line did not change markedly during the year, plume–benthic coupling was
evident only in the sediments beneath the front, and corresponded to phaeopigment accumulation. Bacterial parameters and secondary
production were high and significantly higher in the frontal area than at open-sea stations. Meiofauna density (1342 to 8541
ind. 10 cm−2) did not change either by season or between areas and was significantly correlated with phaeopigments and bacterial secondary
production. Meiofauna displayed different responses to plume inputs in the two sampling areas. In the northern sector, meiofauna
density was coupled with organic matter distribution and displayed highest values beneath the plume. In the southern sector,
the densities of copepods, turbellarians and kinorhynchs displayed highest values under the front in summer, and the same
applied to total meiofauna density in winter. Juvenile decapods and copepod nauplii significantly increased their densities
in sediments beneath the front. Data presented in the present study suggest that plume inputs and frontal systems, enhancing
phytodetritus accumulation and benthic bacterial response, might influence density, composition and distribution of meiofaunal
assemblages. As river plumes are highly variable systems affecting the trophic characteristics of the sediments underneath,
their dynamics should be considered when analysing mesoscale spatial changes of meiofaunal assemblages.
Received: 30 November 1999 / Accepted: 24 May 2000 相似文献
739.
Western sandpiper (Calidris mauri) predation was examined by concurrent experiments and direct observations of foraging behaviour on high intertidal mudflats
of the Fraser River estuary, British Columbia. Western sandpipers foraged by either “pecking” on the surface (64% of observational
time) or probing into sediment (29%). The first experiment (probe-mark method) consisted of collecting small-volume cores
(21.2 cm3) of probed (experimental) and non-probed (control) sediment on the tidal flat, following a 22.5-min feeding period. The second
experiment (exclosure method) involved deploying exclosures immediately prior to the feeding period and subsequent collection
of cores from inside (control) and outside (experimental) the exclosures. Sediment cores were analysed for both macrofaunal
and meiofaunal size fractions. Comparisons between macro- and meiofaunal invertebrate densities in experimental and control
sediments revealed significant differences, attributed to shorebird predation, for both experiments. The probe-mark experiment
detected the removal of large infaunal polychaetes (∼ 20 mm), while the exclosure experiment showed depletion of epifaunal
harpacticoid copepods (0.063–0.5 mm). Predation on macrofaunal cumaceans was detected in both experiments. Invertebrates selected
by western sandpipers neither fell within traditional infaunal size classifications (macro- vs. meiofauna; 500 μm delineation)
nor corresponded to the highest densities of taxa. Rather, inference from experimental results and observations is that western
sandpipers forage in two modes, by: (1) surface gleaning of epibenthic copepods and cumaceans in the macro- and meiofaunal
size ranges and (2) selective probing for larger infauna, such as polychaetes. These findings were facilitated by the combination
of methodologies employed.
Received: 29 December 1999 / Accepted: 11 September 2000 相似文献
740.
The pathway for the flow of salt-marsh grass production into marsh food-webs is still not well defined. We compared the abilities
of three marsh macroinvertebrates [salt marsh periwinkles, Littoraria irrorata (Say) (=Littorina irrorata), salt-marsh coffee-bean snails, Melampus bidentatus (Say); and a talitrid amphipod, Uhlorchestia spartinophila Bounsfield and Heard] to access standing-dead leaves of smooth cordgrass (Spartina alterniflora Loisel). The invertebrates were incubated with naturally-decaying leaves, and the rates of removal of organic matter and
living fungal biomass (ergosterol) were measured. The impact of invertebrate activity upon fungal growth rates was measured
as rates of fungal-membrane synthesis (incorporation of radioacetate into ergosterol). The removal rates of organic leaf biomass
per mg individual biomass were highest for amphipods (700 μg mg−1 d−1) and lowest for periwinkles (90 μg mg−1 d−1), but the relatively large biomass of the snails made their removal rates per individual greater than those of amphipods.
Net removal of ergosterol by all three invertebrates was >50% for yellow-brown (early-decay) leaf blades. For fully-brown
(advanced-decay) blades, >50% removal of ergosterol was found only for periwinkles; exposure to coffee-bean snails and amphipods
resulted in a net ergosterol reduction of ≤20%. The lower net reduction of living fungal biomass by coffee-bean snails and
amphipods may have been due to fungal-growth stimulation (2.3-fold stimulation in coffee-bean snails and 1.5-fold stimulation
in amphipods). Grazing by periwinkles did not stimulate fungal growth, possibly because of its high intensity. Grazing by
these three salt-marsh shredders may affect marsh-grass shoot-decay in different ways. Periwinkles may abbreviate the period
of fungal production, and incorporate the decaying material relatively quickly into snail biomass and fecal-pellet rain to
the sediments. Coffee-bean snails and amphipods may enhance and prolong fungal production, along with the formation of fecal-pellet
rain. All three invertebrates fed preferentially on leaf blades rather than leaf sheaths, and feeding rates of gastropods
were higher during the night than during the day.
Received: 25 November 1998 / Accepted: 4 November 1999 相似文献