Modeled subalpine plant community response to climate change and atmospheric nitrogen deposition in Rocky Mountain National Park, USA.

To evaluate potential long-term effects of climate change and atmospheric nitrogen (N) deposition on subalpine ecosystems, the coupled biogeochemical and vegetation community competition model ForSAFE-Veg was applied to a site at the Loch Vale watershed of Rocky Mountain National Park, Colorado. Changes in climate and N deposition since 1900 resulted in pronounced changes in simulated plant species cover as compared with ambient and estimated future community composition. The estimated critical load (CL) of N deposition to protect against an average future (2010-2100) change in biodiversity of 10% was between 1.9 and 3.5 kg N ha(-1) yr(-1). Results suggest that the CL has been exceeded and vegetation at the study site has already undergone a change of more than 10% as a result of N deposition. Future increases in air temperature are forecast to cause further changes in plant community composition, exacerbating changes in response to N deposition alone.

Nitrogen preferences and plant-soil feedbacks as influenced by neighbors in the alpine tundra.

Plant resource partitioning of chemical forms of nitrogen (N) may be an important factor promoting species coexistence in N-limited ecosystems. Since the microbial community regulates N-form transformations, plant partitioning of N may be related to plant-soil feedbacks. We conducted a (15)N tracer addition experiment to study the ability of two alpine plant species, Acomastylis rossii and Deschampsia caespitosa, to partition organic and inorganic forms of N. The species are codominant and associated with strong plant-soil feedbacks that affect N cycling. We manipulated interspecific interactions by removing Acomastylis or Deschampsia from areas where the species were codominant to test if N uptake patterns varied in the presence of the other species. We found that Deschampsia acquired organic and inorganic N more rapidly than Acomastylis, regardless of neighbor treatment. Plant N uptake-specifically ammonium uptake-increased with plant density and the presence of an interspecific neighbor. Interestingly, this change in N uptake was not in the expected direction to reduce niche overlap and instead suggested facilitation of ammonium use. To test if N acquisition patterns were consistent with plant-soil feedbacks, we also compared microbial rhizosphere extracellular enzyme activity in patches dominated by one or the other species and in areas where they grew together. The presence of both species was generally associated with increased rhizosphere extracellular enzyme activity (five of ten enzymes) and a trend towards increased foliar N concentrations. Taken together, these results suggest that feedbacks through the microbial community, either in response to increased plant density or specific plant neighbors, could facilitate coexistence. However, coexistence is promoted via enhanced resource uptake rather than reduced niche overlap. The importance of resource partitioning to reduce the intensity of competitive interactions might vary across systems, particularly as a function of plant-soil feedbacks.

De/remineralization from sodium fluoride dentifrices.

PURPOSE: To test the demineralization/remineralization effects of sodium fluoride dentifrices using an in situ single-section crown model system. MATERIALS AND METHODS: A fluoride dose response was evaluated using 0, 1100 and 2800 ppm F-, along with the effects of an enhanced fluoride delivery system (polyampholyte-NaF). The single-section crown model was employed with supervised toothbrushing twice a day. At the end of each 1-month study leg, sections were removed and replaced with new sections for the next leg. Both before and after the double-blind, crossover portion of the study, sections were evaluated by polarized light microscopy and microradiography. The change in mineral content of the enamel and root lesions was analyzed by ANOVA with a Waller-Duncan K-Ratio Test post hoc. RESULTS: The placebo dentifrice group showed a loss of mineral and was statistically different from all groups. The fluoride dentifrices showed increasing amounts of enamel mineral gain, with increasing fluoride concentration. The polyampholyte-NaF delivery system with 1100 ppm F- was equivalent to the 2800 ppm F- dentifrice. Root lesions gave similar rank-order results although all treatments showed demineralization or mineral loss.

Shoot growth dynamics and photosynthetic response to increased nitrogen availability in the alpine willow Salix glauca.

Plants subjected to increases in the supply of resource(s) limiting growth may allocate more of those resources to existing leaves, increasing photosynthetic capacity, and/or to production of more leaves, increasing whole-plant photosynthesis. The responses of three populations of the alpine willow, Salix glauca, growing along an alpine topographic sequence representing a gradient in soil moisture and organic matter, and thus potential N supply, to N amendments, were measured over two growing seasons, to elucidate patterns of leaf versus shoot photosynthetic responses. Leaf-(foliar N, photosynthesis rates, photosynthetic N-use efficiency) and shoot-(leaf area per shoot, number of leaves per shoot, stem weight, N resorption efficiency) level measurements were made to examine the spatial and temporal variation in these potential responses to increased N availability. The predominant response of the willows to N fertilization was at the shoot-level, by production of greater leaf area per shoot. Greater leaf area occurred due to production of larger leaves in both years of the experiment and to production of more leaves during the second year of fertilization treatment. Significant leaflevel photosynthetic response occurred only during the first year of treatment, and only in the dry meadow population. Variation in photosynthesis rates was related more to variation in stomatal conductance than to foliar N concentration. Stomatal conductance in turn was significantly related to N fertilization. Differences among the populations in photosynthesis, foliar N, leaf production, and responses to N fertilization indicate N availability may be lowest in the dry meadow population, and highest in the ridge population. This result is contrary to the hypothesis that a gradient of plant available N corresponds with a snowpack/topographic gradient.

Demineralization and remineralization evaluation techniques--added considerations.

Methods used for the analysis of tooth de- and remineralization include techniques with various degrees of sophistication and quantitative capabilities, ranging from direct measures of mineral gain/loss (e.g., microradiography) to indirect measures (e.g., iodide permeability) of changes in tooth mineral properties. In all instances, the capabilities of methods for accurate determination of changes in tooth mineral properties are affected by procedures used in the preparation of specimens for analysis, the magnitude of change taking place in the test (vs. the detection limits of the techniques), and protocols for specimen analysis. In specific instances, such as in the case of dentin, unique specimen-handling and analysis procedures must be used to prevent artifacts. The choice of techniques for the assessment of de- and remineralization depends strongly upon study protocols and laboratory capabilities; however, 'quantitative' measures of mineral gain and loss are possible only if direct chemical or radiographic techniques are used. Either radiographic, cross-sectioned microhardness or polarized light can be used for the determination of lesion depth. Porosity, light-scattering, and surface microhardness are indirect techniques which complement direct measures of mineral gain and loss. Whatever methods are used in the analysis of de- and remineralization, researchers must take care to differentiate accurately among the quantitative capabilities of techniques used in analysis.

Delayed Onset of Isoprene Emission in Developing Velvet Bean (Mucuna sp.) Leaves.

Isoprene (2-methyl-1,3-butadiene) is one of the major volatile hydrocarbons emitted by plants, but its biosynthetic pathway and role in plant metabolism are unknown. Mucuna sp. (velvet bean) is an isoprene emitter, and leaf isoprene emission rate increased as much as 125-fold as leaves developed, and declined in older leaves. Net CO(2) assimilation and stomatal conductance, under different growth and environmental conditions, increased 3 to 5 days prior to an increase in isoprene emission rate, indicating that photosynthetic competence develops before significant isoprene emission occurs.

Short-term changes in leaf carbon isotope discrimination in salt- and water-stressed c(4) grasses.

Online carbon isotope discrimination (Delta) and leaf gas exchange measurements were made with control and salt-stressed Zea mays and Andropogon glomeratus, two NADP-ME type C(4) grasses. Linear relationships between Delta and p(i)/p(a) (the ratio of intercellular to atmospheric CO(2) partial pressure) were found for control plants which agreed well with theoretical models describing carbon isotope discrimination in C(4) plants. These data provided estimates of phi, the proportion of CO(2) fixed by phosphoenolpyruvate carboxylase which leaks out of the bundle sheath and the component of fractionation due to diffusion in air. Salt-stressed plants had wider variation in Delta for the same or less range in p(i)/p(a). Additional work indicated Delta changed independently of p(i)/p(a) in both water- and salt-stressed plants, suggesting a possible diurnal change in phi as plant water status changed linked to a decrease in the activity of the C(3) photosynthetic pathway relative to C(4) pathway activity. The possible effect of stress-induced changes in phi on organic matter delta(13) C of C(4) plants is apt to be most apparent in chronically stressed environments.

19F MAS-NMR and solution chemical characterization of the reactions of fluoride with hydroxyapatite and powdered enamel.

Solution chemical and 19F magic angle spinning-nuclear magnetic resonance (MAS-NMR) methods have been utilized to study the effects of fluoride dose, fluoridating pH, and mineral surface area on the dynamics of fluoride reactivity with hydroxyapatite and powdered human dental enamel in vitro. Both solution chemical fluoride uptake and NMR measurements demonstrated that the reaction products of ionic fluoride with apatite include mixtures of FAP, FHAP, and CaF2, with increased amounts of CaF2 promoted by increased F concentration or decreased pH. NMR analysis showed FAP or FHAP as a reaction product of fluoride uptake under all conditions, regardless of whether CaF2 was formed, unambiguously demonstrating fluorite as an additive rather than substitute form of F reactivity. pH stat measurements demonstrated the release of OH- during F reactivity with apatites corresponding to ion exchange formation of FAP/FHAP or dissolution/reprecipitation formation of CaF2. Phosphate release into solution accompanied fluoride uptake under all conditions, including regions where ion exchange predominated. Whereas powdered dental enamel demonstrated fluoride uptake behavior similar to that of synthetic apatite, the resulting reaction products differed as analyzed by 19F MAS-NMR.

Effect of salinity on leaf gas exchange in two populations of a c(4) nonhalophyte.

Gas exchange measurements were made on plants from two natural populations differing in salt tolerance of Andropogon glomeratus, a C(4) nonhalophyte, to examine the effect of salinity on components responsible for differences in photosynthetic capacity. Net CO(2) uptake and stomatal conductance decreased with increasing salinity in both populations, but to a greater extent in the inland (nontolerant) population. The intercellular CO(2) concentrations increased with increasing salinity in the inland population, but decreased in the marsh (tolerant) population. Water use efficiency decreased as salinity increased in the inland population, and remained unchanged in the marsh population. Carboxylation efficiency decreased and CO(2) compensation points increased with increasing salinity in both populations, but to a lesser extent in the marsh population. Carboxylation efficiencies were higher with 2% relative to 21% atmospheric O(2) in salt stressed plants, suggesting that a decrease in the carboxylation:oxygenation ratio of ribulose 1,5-bisphosphate carboxylase/oxygenase was partly responsible for the decrease in photosynthetic capacity. Populational differences in photosynthetic capacity were the result of greater salinity-induced changes in carboxylation efficiency in the inland population, and not due to differences in the stomatal limitation to CO(2) diffusion.

Randomized clinical trial of cyclophosphamide, 5-FU, and prednisone with or without tamoxifen in postmenopausal women with advanced breast cancer.

The purpose of this study was to determine if tamoxifen added to the efficacy of a CFP (cyclophosphamide, 5-FU, and prednisone) regimen. One hundred thirty-one postmenopausal women with advanced breast cancer without prior chemotherapy exposure were randomized to receive CFP alone or combined with tamoxifen; six were disqualified because of ineligibility. Objective responses were seen in 68% of the eligible patients receiving CFP and in 61% of those receiving CFP plus tamoxifen. Median times to progression were 287 days for CFP and 158 days for CFP plus tamoxifen (two-sided log-rank test of equality of progression distributions, P = 0.07). Median survival times were 544 days for CFP and 394 days for CFP plus tamoxifen (two-sided log-rank test of equality of survival distributions, P = 0.14). The addition of tamoxifen to CFP was not associated with longer time to progression or survival in any Cox covariate model. On the basis of our data, it can be concluded that the addition of tamoxifen to CFP does not substantially improve either the time to disease progression or survival in women with metastatic breast cancer.

Normal mode analysis of lumiflavin and interpretation of resonance Raman spectra of flavoproteins.

The normal modes of lumiflavin (10-methyliso-alloxazine) are analyzed with a valence force field constructed with bond length-stretching force constant correlations and bending and interaction force constants transferred from small ring molecules. Observed resonance Raman (RR) bands of flavin are assigned to calculate modes on the basis of frequency and isotope shift matching. The normal mode patterns confirm previous inferences, based on selective effective of chemical substitutions, of localization to certain regions of the molecule. These results are used to interpret the observed variability of the prominent RR bands among different flavoproteins on the basis of protein-isoalloxazine interactions.

Quality control of small-volume sterile products.

A method for bacterial surveillance of small-volume sterile products in hospitals was developed and tested. The criteria for the method of quality control were to: (1) assure detection of contamination associated with touch, which could occur during the filling process; (2) be economically feasible; (3) be simple and easy to implement; and (4) be versatile in adapting to small-volume sterile packages with and without needles. Ten percent of each lot of prepackaged unit dose syringes is tested by filtration through a sterile micropore filter. The filter unit is incubated after fluid thioglycollate medium has been added. If turbidity or color change is found, further testing with blood agar and gram staining is performed to identify the organism. The effectiveness of the method was tested by adding E. coli to one lot within each of several lots tested of six products. The inoculated samples were stored under refrigeration for three days before testing. With one exception, the E. coli was detected in the samples. Growth did not occur in any of the noninoculated units. The apparent false negative result was believed to be caused by the bacteriostatic agent killing the organism during the three-day storage period.