Inter‐regional comparison of land‐use effects on stream metabolism

1. Rates of whole‐system metabolism (production and respiration) are fundamental indicators of ecosystem structure and function. Although first‐order, proximal controls are well understood, assessments of the interactions between proximal controls and distal controls, such as land use and geographic region, are lacking. Thus, the influence of land use on stream metabolism across geographic regions is unknown. Further, there is limited understanding of how land use may alter variability in ecosystem metabolism across regions. 2. Stream metabolism was measured in nine streams in each of eight regions (n = 72) across the United States and Puerto Rico. In each region, three streams were selected from a range of three land uses: agriculturally influenced, urban‐influenced, and reference streams. Stream metabolism was estimated from diel changes in dissolved oxygen concentrations in each stream reach with correction for reaeration and groundwater input. 3. Gross primary production (GPP) was highest in regions with little riparian vegetation (sagebrush steppe in Wyoming, desert shrub in Arizona/New Mexico) and lowest in forested regions (North Carolina, Oregon). In contrast, ecosystem respiration (ER) varied both within and among regions. Reference streams had significantly lower rates of GPP than urban or agriculturally influenced streams. 4. GPP was positively correlated with photosynthetically active radiation and autotrophic biomass. Multiple regression models compared using Akaike’s information criterion (AIC) indicated GPP increased with water column ammonium and the fraction of the catchment in urban and reference land‐use categories. Multiple regression models also identified velocity, temperature, nitrate, ammonium, dissolved organic carbon, GPP, coarse benthic organic matter, fine benthic organic matter and the fraction of all land‐use categories in the catchment as regulators of ER. 5. Structural equation modelling indicated significant distal as well as proximal control pathways including a direct effect of land‐use on GPP as well as SRP, DIN, and PAR effects on GPP; GPP effects on autotrophic biomass, organic matter, and ER; and organic matter effects on ER. 6. Overall, consideration of the data separated by land‐use categories showed reduced inter‐regional variability in rates of metabolism, indicating that the influence of agricultural and urban land use can obscure regional differences in stream metabolism.     

Effect of CO2 on uninfected Sf‐9 cell growth and metabolism

A problem in the mass production of recombinant proteins and biopesticides using insect cell culture is CO₂ accumulation. This research investigated the effect of elevated CO₂ concentration on insect cell growth and metabolism. Spodoptera frugiperda Sf‐9 insect cells were grown at 20% air saturation, 27^°C, and a pH of 6.2. The cells were exposed to a constant CO₂ concentration by purging the medium with CO₂ and the headspace with air. The population doubling time (PDT) of Sf‐9 cells increased with increasing CO₂ concentration. Specifically, the PDT for 0‐37, 73, 147, 183, and 220 mm Hg CO₂ concentrations were 23.2 ± 6.7, 32.4 ± 7.2, 38.1 ± 13.3, 42.9 ± 5.4, and 69.3 ± 35.9 h (n = 3 or 4, 95% confidence level), respectively. The viability of cells in all experiments was above 90%, i.e., while increased CO₂ concentrations inhibited cell growth, it did not affect cell viability. The osmolality for all bioreactor experiments was observed to be 300–360 mOsm/kg, a range that is known to have a negligible effect on insect cell culture. Elevated CO₂ concentration did not significantly alter the cell specific glucose consumption rate (2.5–3.2 × 10^?17 mol/cell s), but slightly increased the specific lactate production rate from ?3.0 × 10^?19 to 10.2 × 10^?19 mol/cell s. Oxidative stress did not contribute to CO₂ inhibition in uninfected Sf‐9 cells as no significant increase in the levels of lipid hydroperoxide and protein carbonyl concentrations was discovered at elevated CO₂ concentration. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:465–469, 2016     

Effects of Experience on Short‐ and Long‐term Foraging Performance in Bumblebees

Honeybees in natural settings show a gradual increase in foraging performance similar to the general pattern of lifetime performance seen in a wide variety of animals including humans. To quantify the factors contributing to such gradual increase in foraging success, we studied bumblebees foraging on pepper plants inside a greenhouse. This allowed us to combine the global measure of the net rate of food delivery to the hive with a detailed examination of bees’ performance at flowers over time. Although bees exhibited short‐term improvements in foraging ability during their first few foraging trips, we did not observe the predicted long‐term increase in performance over days. Our results suggest that a variety of flower‐handling tasks, flower choice and movements between plants can be learned quickly under the simple greenhouse settings. The long‐term increase in performance under natural settings may be caused by factors including spatial orientation and locating the best plant species, flower patches and individual plants over a large area.     

Short‐term lime pretreatment of poplar wood

Short‐term lime pretreatment uses lime and high‐pressure oxygen to significantly increase the digestibility of poplar wood. When the treated poplar wood was enzymatically hydrolyzed, glucan and xylan were converted to glucose and xylose, respectively. To calculate product yields from raw biomass, these sugars were expressed as equivalent glucan and xylan. To recommend pretreatment conditions, the single criterion was the maximum overall glucan and xylan yields using a cellulase loading of 15 FPU/g glucan in raw biomass. On this basis, the recommended conditions for short‐term lime pretreatment of poplar wood follow: (1) 2 h, 140°C, 21.7 bar absolute and (2) 2 h, 160°C, and 14.8 bar absolute. In these two cases, the reactivity was nearly identical, thus the selected condition depends on the economic trade off between pressure and temperature. Considering glucose and xylose and their oligomers produced during 72 h of enzymatic hydrolysis, the overall yields attained under these recommended conditions follow: (1) 95.5 g glucan/100 g of glucan in raw biomass and 73.1 g xylan/100 g xylan in raw biomass and (2) 94.2 g glucan/100 g glucan in raw biomass and 73.2 g xylan/100 g xylan in raw biomass. The yields improved by increasing the enzyme loading. An optimal enzyme cocktail was identified as 67% cellulase, 12% β‐glucosidase, and 24% xylanase (mass of protein basis) with cellulase activity of 15 FPU/g glucan in raw biomass and total enzyme loading of 51 mg protein/g glucan in raw biomass. Ball milling the lime‐treated poplar wood allowed for 100% conversion of glucan in 120 h with a cellulase loading of only 10 FPU/g glucan in raw biomass. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009     

A method to estimate net community metabolism from profiles of dissolved O2 and N2

A method to estimate net community metabolism (NCM) in natural waters using vertical profiles of water temperature, salinity, dissolved O₂, gas tension, and calculated dissolved N₂ is presented. The method utilizes the disparate biological activity of dissolved O₂ and N₂ to estimate metabolism at different depths in the water column. For well-mixed surface waters, N₂ saturation levels are assumed to be the result of a quasi steady state balance of net warming or cooling and air–water gas exchange. Dissolved O₂ levels are assumed to maintain a similar balance, subject to net biological activity, and NCM is then calculated based on the difference between N₂ and O₂ saturation levels and the estimated timescale required to equilibrate the layer with the atmosphere. For deeper stratified layers of water that warmed after layer formation in isolation from the atmosphere, the temperature at formation is calculated using the measured N₂ concentration and an assumed N₂ saturation level of 100% at formation. By assuming that initial N₂ and O₂ saturation levels were equal, the initial O₂ concentration is calculated based on solubility relationships. NCM of the deeper waters is then estimated based on this information and knowledge of the general seasonal heating cycle of the waters. Daily mean water temperature and dissolved gas levels are used in the calculations. The method was assessed using profile measurements collected at Long Pond, Plymouth, Massachusetts, USA, on 23 August 2002. Oxygen was supersaturated relative to N₂ by approximately 4% in the 0–6 m deep epilimnion, and undersaturated relative to N₂ by approximately 7% in the stratified water at 9 m depth. The estimated 4-day average NCM for the epilimnion was 140 ± 70 mgC m⁻²day⁻¹. For waters at 9 m depth, the temperature at formation was calculated to be 6.58 °C, and the estimated 100-day average NCM was −2.5 ± 0.6 mgC m⁻³ day⁻¹. An independent estimate of −4.6 ± 0.9 mgC m⁻³ day⁻¹ was derived from the measured O₂ decline at 9 m depth over the same period of 2003.     

High CO2 partial pressure effects on dark and light CO2 fixation and metabolism in Vicia faba leaves

Stomatal opening on Vicia faba can be induced by high CO₂ partial pressures (10.2%) in dark as well as in light. Stomatal aperture was measured in both cases with a hydrogen porometer. The distribution of ¹⁴C among early products of photosynthesis was studied. Comparisons are made with carboxylations occurring when stomata were open in the dark with CO₂-free air and in light with 0.034% CO₂. Results showed that in high CO₂ partial pressure in light, less radioactivity was incorporated in Calvin cycle intermediates and more in sucrose. carboxylations and photorespiration seemed to be inhibited. In the dark in both CO₂ conditions, ¹⁴C incorporation was found in malate and aspartate but also in serine and glycerate in high CO₂ conditions. In light these changes in metabolic pathways may be related with the deleterious effects recorded on leaves after long-term expositions to high partial pressure of CO₂.Abbreviations DHAP dihydroxyacetone phosphate - PEP phosphonenolpyruvate - PEPCK phosphonenolpyruvatecarboxykinase - PGA 3-phosphoglyceric acid - RUBPc ribulose 1,5-bisphosphate carboxylase     

Conditions leading to high CO2 (>5 kPa) in waterlogged-flooded soils and possible effects on root growth and metabolism

AIMS: Soil waterlogging impedes gas exchange with the atmosphere, resulting in low P(O2) and often high P(CO2). Conditions conducive to development of high P(CO2) (5-70 kPa) during soil waterlogging and flooding are discussed. The scant information on responses of roots to high P(CO2) in terms of growth and metabolism is reviewed. SCOPE: P(CO2) at 15-70 kPa has been reported for flooded paddy-field soils; however, even 15 kPa P(CO2) may not always be reached, e.g. when soil pH is above 7. Increases of P(CO2) in soils following waterlogging will develop much more slowly than decreases in P(O2); in soil from rice paddies in pots without plants, maxima in P(CO2) were reached after 2-3 weeks. There are no reliable data on P(CO2) in roots when in waterlogged or flooded soils. In rhizomes and internodes, P(CO2) sometimes reached 10 kPa, inferring even higher partial pressures in the roots, as a CO2 diffusion gradient will exist from the roots to the rhizomes and shoots. Preliminary modelling predicts that when P(CO2) is higher in a soil than in roots, P(CO2) in the roots would remain well below the P(CO2) in the soil, particularly when there is ventilation via a well-developed gas-space continuum from the roots to the atmosphere. The few available results on the effects of P(CO2) at > 5 kPa on growth have nearly all involved sudden increases to 10-100 kPa P(CO2); consequently, the results cannot be extrapolated with certainty to the much more gradual increases of P(CO2) in waterlogged soils. Nevertheless, rice in an anaerobic nutrient solution was tolerant to 50 kPa CO2 being suddenly imposed. By contrast, P(CO2) at 25 kPa retarded germination of some maize genotypes by 50%. With regard to metabolism, assuming that the usual pH of the cytoplasm of 7.5 was maintained, every increase of 10 kPa CO2 would result in an increase of 75-90 mM HCO3(-) in the cytoplasm. pH maintenance would depend on the biochemical and biophysical pH stats (i.e. regulatory systems). Furthermore, there are indications that metabolism is adversely affected when HCO3(-) in the cytoplasm rises above 50 mM, or even lower; succinic dehydrogenase and cytochrome oxidase are inhibited by HCO3(-) as low as 10 mM. Such effects could be mitigated by a decrease in the set point for the pH of the cytoplasm, thus lowering levels of HCO3(-) at the prevailing P(CO2) in the roots. CONCLUSIONS: Measurements are needed on P(CO2) in a range of soil types and in roots of diverse species, during waterlogging and flooding. Species well adapted to high P(CO2) in the root zone, such as rice and other wetland plants, thrive even when P(CO2) is well over 10 kPa; mechanisms of adaptation, or acclimatization, by these species need exploration.     

Temporal and spatial variation in ecosystem metabolism and food web carbon transfer in a wet‐dry tropical river

1. High light availability and stable base flow during the dry season promote primary production in perennial rivers of the wet–dry tropics, in contrast to production during the wet season which is often limited by turbidity and scouring. The Mitchell River of northern Queensland (Australia) was studied to understand controls on aquatic production and respiration in the dry season in relation to spatial and temporal gradients of light and temperature. 2. At three sites along the river, whole‐ecosystem gross primary production (GPP) and respiration (ER) were measured from diel changes of dissolved oxygen using the open‐channel single station method. Using stable carbon and nitrogen isotope analysis, aquatic consumers and their potential basal food resources were also assessed to determine food web relationships at the beginning and end of the dry season. 3. Nutrient limitation of aquatic net primary production was implied from the oligotrophic conditions and high algal C:N ratios. Rates of GPP were comparable with other tropical and temperate rivers and were regulated by light availability. 4. Respiration rates were high and similar to other tropical and subtropical rivers. Up to 52% of temporal variation of ER was explained by temperature, while P/R was lowest at the downstream site. 5. Benthic algae were the major carbon source for primary and secondary benthic consumers (insects) in the dry season but not for higher consumers (fish and crustaceans). Despite high rates of ER, which were probably supported by decaying terrestrial C3 plant material, this carbon source was not identified as contributing to animal consumer biomass. 6. While benthic algal production in the dry season sustained benthic invertebrates, the importance of external subsidies of carbon along the river, probably from the floodplain, was emphasised for fish and large invertebrates, which evidently were feeding on carbon sources not present in channel waterholes during the dry season.     

Mass-spectrometric determination of O2 and CO2 gas exchange in illuminated higher-plant cells

In order to estimate photosynthetic and respiratory rates in illuminated photoautotrophic cells of carnation (Dianthus caryophyllus L.), simultaneous measurements of CO₂ and O₂ gas exchange were performed using ¹⁸O₂, ¹³CO₂ and a mass-spectrometry technique. This method allowed the determination, and thus the comparison, of unidirectional fluxes of O₂ and CO₂. In optimum photosynthetic conditions (i.e. in the presence of high light and a saturating level of CO₂), the rate of CO₂ influx represented 75±5% of the rate of gross O₂ evolution. After a dark-to-light transition, the rate of CO₂ efflux was inhibited by 50% whereas the O₂-uptake rate was little affected. The effect of a recycling of respiratory CO₂ through photosynthesis on the exchange of CO₂ gas was investigated using a mathematical model. The confliction of the experimental data with the simulated gas-exchange rates strongly supported the view that CO₂ recycling was a minor event in these cells and could not be responsible for the observed inhibition of CO₂ efflux. On the basis of this assumption it was concluded that illumination of carnation cells resulted in a decrease of substrate decarboxylations, and that CO₂ efflux and O₂ uptake were not as tightly coupled in the light as in the dark. Furthermore, it could be calculated from the rate of gross photosynthesis that the chloroplastic electron-transport chain produced enough ATP in the light to account for the measured CO₂-uptake rate without involving cyclic transfer of electrons around PS I or mitochondrial supplementation.Abbreviations Chl chlorophyll - K_d permeability coefficient The authors thank Drs A. Vermeglio and P. Thibault, Dépt. de Biologie, CEN-Cadarache, St. Paul Lez Durance, France, for helpful discussions.     

Assessing the effects of nitrogen deposition and climate on carbon isotope discrimination and intrinsic water‐use efficiency of angiosperm and conifer trees under rising CO2 conditions

The objective of this study is to globally assess the effects of atmospheric nitrogen deposition and climate, associated with rising levels of atmospheric CO₂, on the variability of carbon isotope discrimination (Δ¹³C), and intrinsic water‐use efficiency (iWUE) of angiosperm and conifer tree species. Eighty‐nine long‐term isotope tree‐ring chronologies, representing 23 conifer and 13 angiosperm species for 53 sites worldwide, were extracted from the literature, and used to obtain long‐term time series of Δ¹³C and iWUE. Δ¹³C and iWUE were related to the increasing concentration of atmospheric CO₂ over the industrial period (1850–2000) and to the variation of simulated atmospheric nitrogen deposition and climatic variables over the period 1950–2000. We applied generalized additive models and linear mixed‐effects models to predict the effects of climatic variables and nitrogen deposition on Δ¹³C and iWUE. Results showed a declining Δ¹³C trend in the angiosperm and conifer species over the industrial period and a 16.1% increase of iWUE between 1850 and 2000, with no evidence that the increased rate was reduced at higher ambient CO₂ values. The temporal variation in Δ¹³C supported the hypothesis of an active plant mechanism that maintains a constant ratio between intercellular and ambient CO₂ concentrations. We defined linear mixed‐effects models that were effective to describe the variation of Δ¹³C and iWUE as a function of a set of environmental predictors, alternatively including annual rate (N_rate) and long‐term cumulative (N_cum) nitrogen deposition. No single climatic or atmospheric variable had a clearly predominant effect, however, Δ¹³C and iWUE showed complex dependent interactions between different covariates. A significant association of N_rate with iWUE and Δ¹³C was observed in conifers and in the angiosperms, and N_cum was the only independent term with a significant positive association with iWUE, although a multi‐factorial control was evident in conifers.     

Short-term changes in carbon-isotope discrimination identify transitions between C3 and C4 carboxylation during Crassulacean acid metabolism

Short-term measurements of instantaneous carbon-isotope discrimination have been determined from mass-spectrometric analyses of CO₂ collected online during gas exchange for the epiphytic bromeliad Tillandsia utriculata L. Using this technique, the isotopic signature of CO₂ exchange for each phase of Crassulacean acid metabolism (CAM) has been characterised. During night-time fixation of CO₂ (Phase I), discrimination () ranged from 4.4 to 6.6, equivalent to an effective carbon-isotope ratio (¹³C) of –12.3 to –14.5 versus Pee Dee Belemnite (PDB). These values reflected the gross photosynthetic balance between net CO₂ uptake and refixation of respiratory CO₂, characteristic of CAM in the Bromeliaceae. When for the relative proportion of external (p _a ) and internal (p _i) CO₂ is taken into account, calculated p _i/p _a decreased during the later part of the dark period from 0.68 to 0.48. Measurements of during Phase II, early in the light period, showed the transition between C₄ and C₃ pathways, with carboxylation being increasingly dominated by ribulose bisphosphate carboxylase (Rubisco) as increased from 10.5 to 21.2 During decarboxylation in the light period (Phase III), CO₂ leaked out of the leaf and the inherent discrimination of Rubisco was expressed. The value of calculated from on-line measurements (64.4) showed that the CO₂ lost was considerably enriched in ¹³C, and this was confirmed by direct analysis of the CO₂ diffusing out into a CO₂-free atmosphere ( ¹³C = + 51.6 versus PDB). Instantaneous discrimination was characteristic of the C₃ pathway during Phase IV (late in the light period), but a reduction in showed an increasing contribution from phosphoenolpyruvate carboxylase. The results from this non-invasive technique confirm the observations that double carboxylation involving both phosphoenolpyruvate carboxylase and Rubisco occurs during the transient phases of CAM (II and IV) in the light period.Abbreviations and Symbols CAM Crassulacean acid metabolism - H⁺ (dawn-dusk) variation in titratable acidity - ¹³C carbonisotope ratio of plant organic material, relative to Pee Dee Belemnite (vs. PDB) - discrimination against ¹³CO₂, - p _i, p _a internal, external partial pressures of CO₂ - Rubisco ribulose1,5-bisphosphate carboxylase - PAR photosynthetically active radiation - PEPCase phosphoenolpyruvate carboxylase We are grateful for financial support in respect of research grants (GR3/5360, GR3/6419) and a studentship awarded by the Natural Environment Research Council, UK.     

Short‐term costs related to male and female structures in alpine Parnassia palustris

The aim of this study was to investigate the potential costs related to male and female structures in a small, hermaphroditic alpine plant species, Parnassia palustris L. We studied in the field the effect of experimental manipulation of seed set (female structures) as well as anthers and staminodes (male structures) on next year's survival, flowering, seed set and growth. We found no statistically significant differences between the treatments in survival, number of flowers and fruits, fruit/flower ratio, seed number or mean mass per seed the following year. Furthermore, there was no statistically significant difference in growth response between the treatments. These observations indicate both that the manipulations of the flowers the previous year had no effect on growth and that the competition between growth and sexual reproduction was negligible. Our results may reflect small investments in reproduction, abundance of soil resources and/or that all resources saved by the plant one year are not necessarily invested in reproduction or growth next year.     

Short‐term side effects of 0.2% alcohol‐free chlorhexidine mouthrinse in geriatric patients: a randomized,double‐blind,placebo‐controlled study

doi: 10.1111/j.1741‐2358.2012.00671.x Short‐term side effects of 0.2% alcohol‐free chlorhexidine mouthrinse in geriatric patients: a randomized, double‐blind, placebo‐controlled study Objective: To determine the effects of a 0.2% alcohol‐free chlorhexidine mouthwash applied twice a day during 30 days in patients over 65 years of age. Materials and methods: A randomized, double‐blind, placebo‐controlled study was made of 70 denture wearers over 65 years of age. The study subjects were randomly assigned to one of the two groups (chlorhexidine or placebo). The patients were instructed to complete a first whitening phase with a duration of 1 week, followed by a 30‐day treatment period. The following data were collected: Silness and Löe plaque index, gingival index, the number of colony‐forming units of Candida albicans at the start and end of treatment and the possible adverse effects of chlorhexidine. Results: Significant differences were observed in the evolution of the Silness and Löe plaque index and gingival index in the two groups, as well as in the number of colony‐forming units of C. albicans between the start and end of treatment. Conclusions: These results suggest that the clinical benefits of antiplaque, antigingivitis mouthrinses in both study groups.     

Carbon isotope composition of biochemical fractions isolated from leaves of Bryophyllum daigremontianum berger,a plant with crassulacean acid metabolism: Some physiological aspects related to CO2 dark fixation

Isotope analysis of the biochemical fractions isolated quantitatively from young and mature leaves of Bryophyllum daigremontianum Berger have been carried out before and after a dark period of accumulation of organic acids. The mature leaf is enriched in ¹³C compared to the young leaf. The ¹³C values of the different leaf constituents vary between the ¹³C values of C₄ plants (-11) and those of C₃ plants (-27). During the dark period, the two types of leaves store organic acids with ¹³C values of -15 and lose insoluble sugars, including starch with a ¹³C value of -12. Furthermore, young leaves store phosphorylated compounds with ¹³C values of -11 and lose weakly polymerised sugars with ¹³C values of -18. These results led to the formulation of a hypothesis of the origin of the two substrates of -carboxylation: phosphoenolpyruvate arises from the glycolytic breakdown of the insoluble sugars rich in ¹³C, and the major portion of the CO₂ is the result of the complete breakdown (respiration) of the soluble sugars rich in ¹²C. The existence of two independent sugar pools leads to the assumption that there are two separate glycolytic pathways. The ¹³C enrichment of the stored products of the young leaves in the day seems to be the result of a weak discrimination for ¹³C by ribulose diphosphate carboxylase, which reassimilates to a great extent the CO₂ released from malate accumulated in the night.Abbreviations CAM crassulacean acid metabolism - C₃ metabolism metabolism with primary carbon fixed by the Calvin and Benson pathway - C₄ metabolism metabolism with primary carbon fixed by the Hatch and Slack pathway - ¹³C() (R_sample-R_PDB) 10³/R_PDB where PDB=Pee Dee belemnite (belemite from the Pee Dee formation South Carolina) and R=¹³C/¹²C - NAD-MDH(EC1.1.1.37) NAD-malate dehydrogenase - NADP-ME (EC1.1.1.40) NADP-malic enzyme - PEP phosphoenolpyruvate - PEPC (EC4.1.1.31) PEP carboxylase - PGA phosphoglyceric acid - Py.di-PK(EC2.7.9.1) pyruvate, Pi-dikinase - RuDP ribulose diphosphate - RuDPC (EC4.1.1.39) RuDP carboxylase     

Short‐ and long‐term consequences of early developmental conditions: a case study on wild and domesticated zebra finches

Divergent selection pressures among populations can result not only in significant differentiation in morphology, physiology and behaviour, but also in how these traits are related to each other, thereby driving the processes of local adaptation and speciation. In the Australian zebra finch, we investigated whether domesticated stock, bred in captivity over tens of generations, differ in their response to a life‐history manipulation, compared to birds taken directly from the wild. In a ‘common aviary’ experiment, we thereto experimentally manipulated the environmental conditions experienced by nestlings early in life by means of a brood size manipulation, and subsequently assessed its short‐ and long‐term consequences on growth, ornamentation, immune function and reproduction. As expected, we found that early environmental conditions had a marked effect on both short‐ and long‐term morphological and life‐history traits in all birds. However, although there were pronounced differences between wild and domesticated birds with respect to the absolute expression of many of these traits, which are indicative of the different selection pressures wild and domesticated birds were exposed to in the recent past, manipulated rearing conditions affected morphology and ornamentation of wild and domesticated finches in a very similar way. This suggests that despite significant differentiation between wild and domesticated birds, selection has not altered the relationships among traits. Thus, life‐history strategies and investment trade‐offs may be relatively stable and not easily altered by selection. This is a reassuring finding in the light of the widespread use of domesticated birds in studies of life‐history evolution and sexual selection, and suggests that adaptive explanations may be legitimate when referring to captive bird studies.     

Effect of changes in water content on photosynthesis,transpiration and discrimination against 13CO2 and C18O16O in Pleurozium and Sphagnum

Photosynthetic gas exchange characteristics of two common boreal forest mosses, Sphagnum (section acutifolia) and Pleurozium schreberi, were measured continuously during the time required for the moss to dry out from full hydration. Similar patterns of change in CO₂ assimilation with variation in water content occurred for both species. The maximum rates of CO₂ assimilation for Sphagnum (approx. 7 mol m^–2 s^–1) occurred at a water content of approximately 7 (fresh weight/dry weight) while for Pleurozium the maximum rate (approx. 2 mol m^–2 s^–1) occurred at a water content of approximately 6 (fresh weight/dry weight). Above and below these water contents CO₂ assimilation declined. In both species total conductance to water vapour (expressed as a percentage of the maximum rates) remained nearly constant at a water content above 9 (fresh weight/dry weight), but below this level declined in a strong linear manner. Short-term, on-line ¹³CO₂ and C¹⁸O¹⁶O discrimination varied substantially with changes in moss water content and associated changes in the ratio of chloroplast CO₂ to ambient CO₂ partial pressure. At full hydration (maximum water content) both Sphagnum and Pleurozium had similar values of ¹³CO₂ discrimination (approx. 15). Discrimination against ¹³CO₂ increased continuously with reductions in water content to a maximum of 27 in Sphagnum and 22 in Pleurozium. In a similar manner C¹⁸C¹⁶O discrimination increased from approximately 30 at full hydration in both species to a maximum of 150 in Sphagnum and 90 in Pleurozium, at low water content. The observed changes in C¹⁸O¹⁶O were strongly correlated to predictions of a mechanistic model of discrimination processes. Field measurements of moss water content suggested that photosynthetic gas exchange by moss in the understory of a black spruce forest was regularly limited by low water content.     

Fungal community composition and metabolism under elevated CO2 and O3

Atmospheric CO₂ and O₃ concentrations are increasing due to human activity and both trace gases have the potential to alter C cycling in forest ecosystems. Because soil microorganisms depend on plant litter as a source of energy for metabolism, changes in the amount or the biochemistry of plant litter produced under elevated CO₂ and O₃ could alter microbial community function and composition. Previously, we have observed that elevated CO₂ increased the microbial metabolism of cellulose and chitin, whereas elevated O₃ dampened this response. We hypothesized that this change in metabolism under CO₂ and O₃ enrichment would be accompanied by a concomitant change in fungal community composition. We tested our hypothesis at the free-air CO₂ and O₃ enrichment (FACE) experiment at Rhinelander, Wisconsin, in which Populus tremuloides, Betula papyrifera, and Acer saccharum were grown under factorial CO₂ and O₃ treatments. We employed extracellular enzyme analysis to assay microbial metabolism, phospholipid fatty acid (PLFA) analysis to determine changes in microbial community composition, and polymerase chain reaction–denaturing gradient gel electrophoresis (PCR–DGGE) to analyze the fungal community composition. The activities of 1,4-β-glucosidase (+37%) and 1,4,-β-N-acetylglucosaminidase (+84%) were significantly increased under elevated CO₂, whereas 1,4-β-glucosidase activity (−25%) was significantly suppressed by elevated O₃. There was no significant main effect of elevated CO₂ or O₃ on fungal relative abundance, as measured by PLFA. We identified 39 fungal taxonomic units from soil using DGGE, and found that O₃ enrichment significantly altered fungal community composition. We conclude that fungal metabolism is altered under elevated CO₂ and O₃, and that there was a concomitant change in fungal community composition under elevated O₃. Thus, changes in plant inputs to soil under elevated CO₂ and O₃ can propagate through the microbial food web to alter the cycling of C in soil.     

O2 uptake through water during early life of Heteropneustes fossilis (Bloch)

The O₂ uptake through water has been measured in case of Heteropneustes fossilis during development and growth and its relationship to body size established. A higher rate of O₂ uptake during the early phase of ontogenesis is related to intense growth of the respiratory surface area and increasing metabolic demand of the fish.The logarithmic plot of data for O₂ uptake in relation to body size shows a statistically significant two-component curve; one related to the fish when it is a fully aquatic breather and the other when it changes to bimodal gas exchange. The onset of the air breathing habit brings about a 40% drop in O₂ uptake through water, which is made good through the newly developed air breathing organ.