bluuebunny/crossref_metadata_2025_split huggingface dataset:
Greenhouse gas dynamics in boreal, littoral sediments under raised CO2 and nitrogen supply
Authors: Liikanen Anu , Ratilainen Eeva , Saarnio Sanna , Alm Jukka , Martikainen Pertti J. , Silvola Jouko 
Published: March 2003

SUMMARY 1. The effects of increasing CO2 and nitrogen loading and of a change in water table and temperature on littoral CH4, N2O and CO2 fluxes were studied in a glasshouse experiment with intact sediment cores including vegetation (mainly sedges), taken from a boreal eutrophic lake in Finland. Sediments with the water table held at a level of 0 or at −15 cm were incubated in an atmosphere of 360 or 720 p.p.m. CO2 for 18 weeks. The experiment included fertilisation with NO3– and NH4+ (to a total 3 g N m−2).2. Changes in the water table and temperature strongly regulated sediment CH4 and cCO2 fluxes (community CO2 release), but did not affect N2O emissions. Increase in the water table increased CH4 emissions but reduced cCO2 release, while increase in temperature increased emissions of both CO2 and CH4.3. The raised CO2 increased carbon turnover in the sediments, such that cCO2 release was increased by 16–26%. However, CH4 fluxes were not significantly affected by raised CO2, although CH4 production potential (at 22 °C) of the sediments incubated at high CO2 was increased. In the boreal region, littoral CH4 production is more likely to be limited by temperature than by the availability of carbon. Raised CO2 did not affect N2O production by denitrification, indicating that this process was not carbon limited.4. A low availability of NO3– did severely limit N2O production. The NO3– addition caused up to a 100‐fold increase in the fluxes of N2O. The NH4+ addition did not increase N2O fluxes, indicating low nitrification capacity in the sediments.
Resource availability and population size in cactophilicDrosophila
Authors: Breitmeyer C. M. , Markow T. A. 
Published: March 2003

1.Four species ofDrosophila, Drosophila nigrospiracula(Patterson & Wheeler 1942), Drosophila mettleri(Heed 1977), Drosophila pachea(Patterson & Wheeler 1942),andDrosophila mojavensis(Patterson & Crow 1940),are endemic to the Sonoran Desert of North America and breed in different species of necrotic columnar cacti. Differences in resource availability have been suggested to explain the interspecific variability in fly population biology, but resource availability for these species has not been quantitatively assessed thoroughly in either spatial or temporal terms. The resource availability was quantified quarterly at three sites for 3 years and population sizes for eachDrosophilaspecies were estimated.2.Spatial and temporal availability of resources differed significantly among species of host cacti, with organpipe cactus (Stenocereus thurberi) being the least abundant and senita (Lophocereus schottii) the most abundant spatially.3.Drosophilaspecies differed significantly in population size. The largest population sizes were found forD. nigrospiraculaandD. mojavensisand smallest forD. pachea. Populations ofD. mettleriwere intermediate to these.4.Population size was greatest for fly species utilizing host species having the largest and longest lasting necroses.5.Resource availability does not explain the reduction of fly populations in the summer. Necroses were most abundant when flies were absent.
Implications of shoot structure on the rate of photosynthesis at different levels in a coniferous canopy using a model incorporating grouping and penumbra
Authors: Stenberg P. 
Published: March 2003

1. The connection between high leaf area index (LAI) and photosynthetic production with two attributes of coniferous canopy structure: small leaf size and grouping of needles on shoots, was analysed using a simulation model. 2. The small size of conifer needles gives rise to penumbras, which even out the distribution of direct sunlight on the leaf area and thereby act to increase the rate of canopy photosynthesis per unit of LAI. 3. Grouping, by producing a non‐uniform distribution of leaf area, causes a decrease in total canopy light interception at any given LAI, but improves the photosynthetic light capture by shoots in the lower canopy. 4. Application of the model on a case study showed that: (a) grouping had a negative effect on the rate of photosynthesis in the upper canopy, but deeper down in the canopy the situation was reversed; (b) in the lower canopy, photosynthetic rates were up to 10 times higher as a result from the combined effect of grouping and penumbra; (c) grouping did not improve the rate of canopy photosynthesis per unit of LAI, however, it can have a positive effect on the total photosynthetic production by allowing a higher productive LAI to be maintained; (d) penumbra, on the other hand, increased the rate of canopy photosynthesis by as much as 40% for moderate values of the LAI.
Experimental testing of dynamic energy budget models
Authors: Noonburg E. G. , Nisbet R. M. , Mccauley E. , Gurney W. S. C. , Murdoch W. W. , DE Roos A. M. 
Published: March 2003

1. Dynamic energy budget (DEB) models describing the allocation of assimilate to the competing processes of growth, reproduction and maintenance in individual organisms have been applied to a variety of species with some success. There are two contrasting model formulations based on dynamic allocation rules that have been widely used (net production and net assimilation formulations). However, the predictions of these two classes of DEB models are not easily distinguished on the basis of simple growth and fecundity data. 2. It is shown that different assumptions incorporated in the rules determining allocation to growth and reproduction in two classes of commonly applied DEB models predict qualitatively distinct patterns for an easily measured variable, cumulative reproduction by the time an individual reaches an arbitrary size. 3. A comparison with experimental data from Daphnia pulex reveals that, in their simplest form, neither model predicts the observed qualitative pattern of reproduction, despite the fact that both formulations capture basic growth features. 4. An examination of more elaborate versions of the two models, in which the allocation rules are modified to account for brief periods of starvation experienced in the laboratory cultures, reveals that a version of the net production model can predict the qualitative pattern seen for cumulative eggs as a function of mass in D. pulex. The analysis leads to new predictions which can be easily tested with further laboratory experiments.
The phenology of gender in homogamous flowers: temporal change in the residual sex function of flowers of Oil‐seed Rape (Brassica napus)
Authors: Bell S. A. , Cresswell J. E. 
Published: March 2003

1. We investigated the phenology of the male and female sexual functions in flowers of Oil‐seed Rape (Brassica napus) that were exposed to pollinators in an experimental garden. The female ‘residual sex function’ (RSF) of flowers was measured by hand‐pollinating with genetically marked pollen in order to determine the proportion of ovules that remained available for fertilization by incoming pollen. Male RSF was measured by estimating the proportion of pollen grains that remained in dehiscing anthers. 2. Following flower opening, an average flower’s male and female sexual functions each required for completion c. 13 h of exposure to pollinators. One hour after opening, c. 50% of a flower’s ovules were unavailable to incoming pollen whereas only c. 10% of pollen was removed. Therefore, a flower’s sexual function was predominantly female for the first hour and predominantly male thereafter. 3. We found a fairly close correspondence between the proportion of the stigma covered with pollen and the depletion of female RSF. 4. On average, floral senescence occurred after c. 14·5 h of exposure to pollinators. Our observations are fairly consistent with a simple, economic model of optimal senescence time because the flowers remained open for approximately the same length of time as was necessary for the completion of their sexual functions. 5. A flower’s senescence was hastened when pollen was removed from the anthers, but not when pollen was deposited on the stigma. 6. When flowers were either left undisturbed or hand‐pollinated, senescence occurred after c. 24 h. Pollen removal caused senescence after c. 13 h, which also approximated the longevity of flowers in the experimental garden. Apparently, pollen removal governed floral longevity under field conditions.
The use of variance in enzyme activity as an indicator of long‐term exposure to toxicant‐stressed environments inCulex pipiensmosquitoes
Authors: Callaghan A. , Parker P. J. A. N. , Holloway G. J. 
Published: March 2003

1.The identification of easy to use and cheap biomarkers is important as a means of determining whether animals are developing under stressful environmental conditions. Previous studies have indicated that the variance about the mean esterase activity in toxic environments increases in the absence of a significant shift in the mean value, suggesting that variance levels may have potential as a biomarker of toxicant‐stressed or otherwise stressful environments.2.Several field and laboratory populations of the mosquito,Culex pipiens, were examined for esterase activities using a colorimetric assay and levels of polymorphism using polyacrylamide gel electrophoresis. Some of these populations had been exposed to environmental toxicants (organophosphorus (OP) insecticides).3.The OP‐stressed field population had lower levels of polymorphism as indicated by fewer electromorphs than the populations that had not been exposed to OPs. However, the mean level of esterase activity was higher in the OP‐stressed populations.4.Despite having lower genetic variation, the OP‐stressed populations showed much higher levels of variation about the mean enzyme activity, at least two orders of magnitude higher, than the unstressed populations. Knowledge of the genetics of OP resistance in these populations confirmed that the increase in variance was not due to the general switching on of genes in response to stress.5.One field population that had been exposed to heavy metal pollution had similar levels of esterase activity and variation about the mean as the unstressed populations, suggesting that variation only increases in characters directly affected by the environmental pollutant.6.The probable factors causing the increase in variance and the potential of this type of variation as a biomarker of stressful environments are discussed.
The photosynthetic drought physiology of a diverse group of southern hemisphere conifer species is correlated with minimum seasonal rainfall
Authors: Brodribb T. , Hill R. S. 
Published: March 2003

1. The instantaneous and integrated leaf gas exchange of 13 species of southern hemisphere conifers grown under identical glasshouse conditions were examined to determine whether there was any correlation between the characteristics of water use at the leaf level and environmental water availability. 2. In the conifer species examined, the minimum ratio of internal to ambient CO2 measured in leaves during artificially imposed drought [(ci/ca)min] was strongly correlated with the minimum rainfall observed within the natural range of each species. This suggests that the distributions of these species are constrained by the drought tolerance of their photosynthetic apparatus. 3. A good correlation was found between the ratio of internal to ambient CO2 measured in leaves under optimal conditions (ci/ca)max and leaf δ13C (and hence inferred ∫[ci/ca]). Neither of these, however, correlated with the environmental parameters considered most likely to be limiting species distribution, i.e. precipitation and altitude. 4. These data suggest that decreasing water availability may have been the major factor responsible for the restriction and extinction of conifers in the southern hemisphere.
Seed size and shape are not related to persistence in soil in Australia in the same way as in Britain
Authors: Leishman M. R. , Westoby M. 
Published: March 2003

1. Previous studies have shown that among British species, seeds that persist in the soil tend to be small and compact compared with non‐persistent seeds. We tested whether or not this pattern is repeated among 101 Australian species, from a range of habitats. 2. Seed mass was plotted against variance of seed dimensions, across all species. Species with persistent seeds were found across the whole range of seed mass (0·217–648·9 mg) and variance (0·0000–0·2497), providing no evidence for a critical mass or variance which separated persistent from transient seeds. 3. We tested whether or not divergence within individual clades between persistent and transient seeds was associated with increased seed mass or seed dimension variance, using phylogenetically independent contrasts (PICs). There was no consistent tendency found. 4. Thus for Australian species, persistent seeds were not smaller or more compact than transient seeds when compared across all species or when compared using PICs. Presumably the natural history of burial and disturbance operates differently in British and Australian habitats.
Climate change andCognettia sphagnetorum: effects on carbon dynamics in organic soils
Authors: Briones M. J. I. , Ineson P. , Poskitt J. 
Published: March 2003

1.A microcosm experiment was performed to test the impacts ofCognettia sphagnetorumon carbon leaching in a cambic stagnohumic gley soil.2.Leaching of dissolved organic carbon (DOC) was significantly enhanced byC.sphagnetorum,with the greatest effect being found in the upper, 0–6 cm, soil layers. The ratio of DOC to dissolved organic nitrogen (DON) in the leachate decreased in faunated systems, indicating that the enchytraeids were mobilizing carbon from organic matter with a low C to N ratio.3.The vertical distribution of the enchytraeids had an effect on the production of DOC, and this vertical distribution is affected strongly by climate. It is proposed that increases in DOC found in a field soil‐warming experiment with the same soil are largely a result of changes in the vertical distribution of these organisms.
Which components of diet quality affect retention time of digesta in seabirds?
Authors: Hilton G. M. , Houston D. C. , Furness R. W. 
Published: March 2003

1. The nature of the diet can affect the gut retention time of food consumed by an animal, and a theoretical framework has been developed to explain this in terms of optimal digestion rates. However, diets may differ in a number of different attributes, all of which may separately affect the optimal length of time that they are retained in the gut. 2. Here an attempt is made to elucidate which of these features are important in determining gut retention time of different fish species when fed to nine north Atlantic seabird species, and discuss the different potential optimization criteria for retention time in seabirds. 3. Retention times of Lesser Sandeel (Ammodytes marinus Raitt.) were shortest, and this species was also rapidly broken down in vitro. Sprat (Sprattus sprattus (L.)) took longer to be broken down in vitro than Whiting (Merlangius merlangus (L.)), and also had a high energy and lipid content, which might be expected to result in slow digestion; yet retention times of the two species were similar. 4. Meal size also had an important effect on gut retention times, large meals being retained for longer in the gut than small meals, apparently because of an upper limit on the peak excretion rate. 5. Diet and meal‐size related characteristics are important factors influencing prey profitability, prey selection and foraging patterns in seabirds.
Symbiotic N2 fixation in a high Alpine grassland: effects of four growing seasons of elevated CO2
Authors: Arnone Iii J. A. 
Published: March 2003

1. Increasing carbon dioxide concentration (E: 680 μl CO2 litre–1vs ambient, A: 355 μl CO2 litre–1) around late‐successional Alpine sedge communities of the Swiss Central Alps (2450 m) for four growing seasons (1992–1995) had no detectable effect on symbiotic N2 fixation in Trifolium alpinum—the sole N2‐fixing plant species in these communities (74 ± 30 mg N m–2 year–1, A and E plots pooled). 2. This result is based on data collected in the fourth growing season showing that elevated CO2 had no effect on Trifolium above‐ground biomass (4·4 ± 1·7 g m–2, A and E plots pooled, n = 24) or N content per unit land area (124 ± 51 mg N m–2, A and E pooled), or on the percentage of N Trifolium derived from the atmosphere through symbiotic N2 fixation (%Ndfa: 61·0 ± 4·1 across A and E plots) estimated using the 15N dilution method. 3. Thus, it appears that N inputs to this ecosystem via symbiotic N2 fixation will not be dramatically affected in the foreseeable future even as atmospheric CO2 continues to rise.
Maternal body volume constrains water uptake by lizard eggs in utero
Authors: Qualls C. P. , Andrews R. M. 
Published: March 2003

1. Flexible shelled eggs of squamate reptiles normally take up substantial amounts of water, and swell accordingly, during development. However, most water uptake occurs after oviposition, beginning immediately or soon after oviposition, and water uptake is severely restricted in eggs that are retained in utero past the normal time of oviposition. 2. These observations suggest that some aspect of retention in the oviductal environment limits the amount of water eggs can absorb prior to oviposition. 3. This paper presents evidence, from two species of Sceloporus lizard, supporting the hypothesis that limited space within the mother’s body cavity physically constrains the ability of eggs to expand, and thereby their ability to absorb water. When adjusted for maternal body size, the water content of a female’s clutch of eggs is negatively correlated with the dry mass of her clutch (the space available in the body cavity is finite, and thus a greater dry mass content leaves less volume for water). 4. If such a constraint on water uptake is widespread, it can have important implications for our understanding of the evolution of viviparity, the costs of reproduction, and the determinants of reproductive output in squamate reptiles.
Allocation of nitrogen and carbon in leaves of Metrosideros polymorpha regulates carboxylation capacity and δ13C along an altitudinal gradient
Authors: Cordell S. , Goldstein G. , Meinzer F. C. , Handley L. L. 
Published: March 2003

1.
Metrosideros polymorpha (O’hia), the dominant tree species in Hawaiian forest ecosystems, grows from sea level to treeline (2500 m). Consistent changes in its morphology and anatomy occur along this altitudinal/temperature gradient. Patterns of variation in photosynthetic gas exchange, leaf nitrogen content, nitrogen‐use efficiency, δ13C, and morphological and anatomical characteristics were determined across the elevational gradient. In addition, on‐line carbon isotope discrimination studies of high and low elevation M. polymorpha were performed. 2. Observed trends with increasing altitude were: (1) progressively higher carboxylation efficiency, leaf N content on an area basis, leaf mass per unit area (LMA), less negative foliar δ13C and (2) progressively smaller leaf size. Net CO2 assimilation (A) expressed on an area basis, leaf dry mass and N content per leaf remained relatively constant along the gradient. 3. Foliar δ13C became less negative with increasing elevation (– 30‰ at low elevation to – 24‰ at high elevation) and was strongly correlated with foliar N and LMA. Foliar δ13C was also correlated with variations in the ratio of intercellular to ambient partial pressure of CO2 (pi/pa), as determined by field gas‐exchange studies. 4. Results from on‐line fractionation experiments suggested that the relatively large internal resistance to CO2 diffusion did not differ between high and low elevation populations, despite differences in LMA. Less negative values of δ13C at high elevations and corresponding lower values of pi/pa were associated with increased carboxylation efficiency and N content on a unit leaf area basis. 5. Two major homeostatic responses in M. polymorpha plants along elevational/temperature gradients were observed: (1) maintenance of similar photosynthetic rates per unit leaf surface area despite suboptimal conditions for CO2 assimilation at high elevation and (2) similar N content per leaf despite lower soil N availability at high elevations. These homeostatic mechanisms allow M. polymorpha to maintain a relatively high level of growth‐related activities at high elevation, despite limiting environmental conditions.
Selfing rates in natural populations of Echium vulgare: a combined empirical and model approach
Authors: Rademaker M. C. J. , De Jong T. J. , Van Der Meijden E. 
Published: March 2003

1. We quantified geitonogamous selfing in Echium vulgare, a self‐compatible, bumble‐bee pollinated plant. A maximum estimate of selfing was determined using a paternity analysis with RAPDs. In the first experiment, bumble‐bees visited a sequence of virgin flowers. The percentage selfing increased rapidly from 12% in the first flower visited, up to 50% in the 15th flower visited in the sequence. In the second experiment, when bees visited plants in a natural population, the average selfing of plants increased with the number of open flowers from 0% to maximally 33%. 2. The results obtained in both experiments are consistently lower than predicted by our model on pollen dynamics (Rademaker, de Jong & Klinkhamer 1997). We modified the model on pollen dynamics to link it more to the field situation with observations on flower stage, flower opening and bumble‐bee preference, so that the bumble‐bees encounter a variable number of pollen grains per flower. We also adjusted the parameters. If less pollen adheres to the bee (25% instead of 50%) after removal from the anthers, or if bees arrive at a plant with more pollen grains (6000 instead of 4448), the predictions of the model in regard to selfing could be improved but were still high compared with the observed selfing rates measured with RAPDs. 3. We suggest that the model is consistent with pollen dynamics in the field. However, post‐pollination processes like selective abortion could play a role in E. vulgare.
Changing fitness consequences of hsp70 copy number in transgenic Drosophila larvae undergoing natural thermal stress
Authors: Roberts S. P. , Feder M. E. 
Published: March 2003

Abstract1. Transgenic manipulation of the gene copy number of hsp70, which encodes the major inducible heat‐shock protein of Drosophila melanogaster (Hsp70), affects both Hsp70 levels and inducible thermotolerance in the laboratory; here parallel effects in transgenic Drosophila larvae undergoing natural or simulated natural thermal stress are demonstrated.2. Necrotic fruit was infested with larvae of either of two transgenic strains, one transformed with 12 extra copies of the hsp70 gene (extra‐copy strain) and a sister strain possessing only the wild‐type number (10) of hsp70 genes (excision strain), and then allowed to heat to variable extents.3. As the intensity of thermal stress increased, the consequences of extra hsp70 copies reversed. After no or moderate thermal stress, excision larvae survived better than did extra copy larvae. By contrast, extra copy larvae tolerated intense hyperthermia better than did excision larvae.4. These results establish that the Hsp70‐mediated enhancement of stress tolerance, previously demonstrated only for artificial stress regimes in the laboratory, extends to natural stress regimes.5. Mortality due to overexpression of Hsp70, however, also increases under mild natural stress regimes, buttressing the ecological relevance of a hypothesized evolutionary trade‐off of the benefits and adverse consequences of Hsp70 expression.