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481.
Relative growth rate (RGR) is currently the most commonly used method for measuring and comparing species' intrinsic growth potential. Comparative studies have, for example, revealed that small-seeded species have higher RGR, leading to the common belief that small-seeded species possess physiological adaptations for rapid growth that would allow them to outgrow large-seeded species, given sufficient time. We show that, because RGR declines as individual plants grow, it is heavily biased by initial size and does not measure the size-corrected growth potential that determines the outcome of competition in the long-term. We develop a daily growth model that includes a simple mechanistic representation of aboveground and belowground growth and its dependency on plant size and environmental factors. Intrinsic growth potential is encapsulated by the size-independent growth coefficient, G. We parameterized the model using repeated-harvest data from 1724 plants of nine species growing in contrasting nutrient and temperature regimes. Using information-theoretic criteria, we found evidence for interspecific differences in only three of nine model parameters: G, aboveground allocation, and frost damage. With other parameters shared between species, the model accurately reproduced above- and belowground biomass trajectories for all nine species in each set of environmental conditions. In contrast to conventional wisdom, the relationship between G and seed size was positive, despite a strong negative correlation between seed size and average RGR, meaning that large-seeded rather than small-seeded species have higher size-corrected growth potential. Further, we found a significant positive correlation between G and frost damage that, according to simulations, causes rank reversals in final biomass under daily temperature changes of +/- 5 degrees C. We recommend the wider use of this new kind of plant growth analysis as a better way of understanding underlying differences in species' physiology; but we recognize that RGR is still a useful metric if considering the potential rate of population increase in empty habitats. 相似文献
482.
Nitrous Oxide Concentrations in the Soil of a Mown Grassland: Comparison of Model Results with Soil Profile Measurements 总被引:1,自引:0,他引:1
Nitrous oxide (N2O) concentrations in the soilprofile of a fertilized grassland on the Swiss plateauwere measured at irregular intervals during one year.Air samples were taken from air-permeable tubesinstalled at depths between 2 and 100 cm belowthe surface. Highest concentrations in thetopsoil were observed following precipitationafter fertilization. In the subsoil,concentrations were highest when the soil watercontent fell below about 92% after a wet periodand mineral nitrogen was available from priorfertilization. N2O concentrations in thetopsoil were simulated with the process-basedgrassland ecosystem model PaSim 2.5 (PastureSimulation Model) and compared with measured soilN2O concentrations. The model simulated wellthe concentration peaks after fertilizeradditions and the concentrations in winter. Butthe simulated baseline concentrations during thegrowing season were overestimated. Possiblecauses for this discrepancy are discussed andsuggestions are made to improve the model. 相似文献
483.
The species Thecoscyphus zibrowii Werner, 1984 has an exceptional life cycle, which lacks a medusa stage but develops an extraordinary structure (egg sac)
for reproduction. Investigation of the life cycle, as well as anatomical and histological studies of the different developmental
stages of T. zibrowii were performed to provide evidence for a possible homology of the egg sac with the medusa stage and to determine whether
the reduced metagenesis of T. zibrowii is derived from strobilation. The egg sac showed several characteristics, which were compared to those of coronate medusae.
The ectodermis of the egg sac had a plate-like appearance and was completely ciliated as is typical for coronate medusae.
The number and the location of the gonads were similar to those of coronate medusae. The cnidocysts were significantly larger
in the egg sac than in the polyp. A size difference of cnidocysts in the medusa and the polyp stage is known for several Coronatae.
Characteristics of egg sac formation were compared to characteristics of strobilation. The formation of the early operculum
was similar in T. zibrowii and N. eumedusoides. The constriction of egg sac and strobila occurred in the same mode and the gastric cavities of two egg sacs stayed in contact
in a similar fashion to the gastric cavities of the strobila discs. The developmental zones of cnidoblasts of the egg sac
and polyp were separated during the formation of the egg sac which showed a similar developmental gradient to a strobila.
The existence of all of these consistent characteristics makes it very likely that the egg sac structure was homologous to
a medusa. The species T. zibrowii would therefore be derived from a metagenetic ancestor. This species has reduced the medusa generation to the greatest extent
within the Nausithoidae and has demonstrated thus far the endpoint of a regressive evolution of the medusa generation. 相似文献
484.
A study was performed comparing ambient air monitoring (AM) and biological monitoring (BM) in order to evaluate the reliability of passive sampling (PS) in occupational medicine. Five groups of persons (total number = 188) exposed to tetrachloroethene, isopropanol, toluene, xylene and styrene at the workplace were examined. AM was performed over several hours using one or two brands of passive samplers (Monitor 3500 and/or ORSA 5). BM includes the determination of the solvent and specific metabolites resp. in blood or urine samples taken at the end of workshift. On the basis of our results we recommend that PS can supply relevant data for the estimation of external exposure to several solvents like chlorinated‐ and aromatic‐hydrocarbons. 相似文献
485.
Karen A. Bjorndal Barbara A. Schroeder Allen M. Foley Blair E. Witherington Michael Bresette David Clark Richard M. Herren Michael D. Arendt Jeffrey R. Schmid Anne B. Meylan Peter A. Meylan Jane A. Provancha Kristen M. Hart Margaret M. Lamont Raymond R. Carthy Alan B. Bolten 《Marine Biology》2013,160(10):2711-2721
In response to a call from the US National Research Council for research programs to combine their data to improve sea turtle population assessments, we analyzed somatic growth data for Northwest Atlantic (NWA) loggerhead sea turtles (Caretta caretta) from 10 research programs. We assessed growth dynamics over wide ranges of geography (9–33°N latitude), time (1978–2012), and body size (35.4–103.3 cm carapace length). Generalized additive models revealed significant spatial and temporal variation in growth rates and a significant decline in growth rates with increasing body size. Growth was more rapid in waters south of the USA (<24°N) than in USA waters. Growth dynamics in southern waters in the NWA need more study because sample size was small. Within USA waters, the significant spatial effect in growth rates of immature loggerheads did not exhibit a consistent latitudinal trend. Growth rates declined significantly from 1997 through 2007 and then leveled off or increased. During this same interval, annual nest counts in Florida declined by 43 % (Witherington et al. in Ecol Appl 19:30–54, 2009) before rebounding. Whether these simultaneous declines reflect responses in productivity to a common environmental change should be explored to determine whether somatic growth rates can help interpret population trends based on annual counts of nests or nesting females. Because of the significant spatial and temporal variation in growth rates, population models of NWA loggerheads should avoid employing growth data from restricted spatial or temporal coverage to calculate demographic metrics such as age at sexual maturity. 相似文献
486.
487.
Oettl D Sturm PJ Pretterhofer G Bacher M Rodler J Almbauer RA 《Journal of the Air & Waste Management Association (1995)》2003,53(10):1233-1240
Transit traffic through the Austrian Alps is of major concern in government policy. Pollutant burdens resulting from such traffic are discussed widely in Austrian politics and have already led to measures to restrict traffic on transit routes. In the course of an environmental assessment study, comprehensive measurements were performed. These included air quality observations using passive samplers, a differential optical absorption spectroscopy system, a mobile and a fixed air quality monitoring station, and meteorological observations. As was evident from several previous studies, dispersion modeling in such areas of complex terrain and, moreover, with frequent calm wind conditions, is difficult to handle. Further, in the case presented here, different pollutant sources had to be treated simultaneously (e.g., road networks, exhaust chimneys from road tunnels, and road tunnel portals). No appropriate system for modeling all these factors has so far appeared in the literature. A prognostic wind field model coupled with a Lagrangian dispersion model is thus presented here and is designed to treat all these factors. A comparison of the modeling system with results from passive samplers and from a fixed air quality monitoring station proved the ability of the model to provide reasonable figures for concentration distributions along the A10. 相似文献
488.
489.
By chance, we had the opportunity to make serial sonographic observations of the extrusion of meconium in a case of meconium peritonitis. Inflammation leads to exudative processes and production of fluid (ascites) in the fetal abdomen. Sonography at that stage of the disease may lead to a misdiagnosis such as ‘fetal ascites’ or ‘non-immune hydrops’. After bowel perforation and extrusion of meconium, the latter appears as a solitary mass inside fetal ascites or as disseminated echogenic masses distributed subdiaphragmatically or perihepatically. Within a couple of days, in most cases the echogenicity of the masses increases. Calcifications lead to distinct shadowing. These calcifications are often the only visible signs of a previous meconium peritonitis. Serial sonograms are essential for the management of pregnancies with meconium peritonitis. If the amount of fetal ascites does not increase and no signs of cardiovascular stagnation appear, no invasive intrauterine diagnostic and therapeutic steps are required. In none out of the nine cases was a cause found. 相似文献
490.
Gerhard Bringmann 《Die Naturwissenschaften》1979,66(1):22-27
The formation of tetrahydro-isoquinoline alkaloids in human and animal metabolisms subsequent to alcohol consumption is reported. The spectrum of identified products ranges from simple structures such as salsolinol to the complicated skeleton of protoberberines. These substances, hitherto found exclusively in plants, interfere with the biosynthesis, biodegradation and neurotransmission of the structurally closely related biogenic amines from which they are formed, and thus affect the vegetative nervous system. 相似文献