Quantifying global soil carbon losses in response to warming.

The majority of the Earth's terrestrial carbon is stored in the soil. If anthropogenic warming stimulates the loss of this carbon to the atmosphere, it could drive further planetary warming. Despite evidence that warming enhances carbon fluxes to and from the soil, the net global balance between these responses remains uncertain. Here we present a comprehensive analysis of warming-induced changes in soil carbon stocks by assembling data from 49 field experiments located across North America, Europe and Asia. We find that the effects of warming are contingent on the size of the initial soil carbon stock, with considerable losses occurring in high-latitude areas. By extrapolating this empirical relationship to the global scale, we provide estimates of soil carbon sensitivity to warming that may help to constrain Earth system model projections. Our empirical relationship suggests that global soil carbon stocks in the upper soil horizons will fall by 30 ± 30 petagrams of carbon to 203 ± 161 petagrams of carbon under one degree of warming, depending on the rate at which the effects of warming are realized. Under the conservative assumption that the response of soil carbon to warming occurs within a year, a business-as-usual climate scenario would drive the loss of 55 ± 50 petagrams of carbon from the upper soil horizons by 2050. This value is around 12-17 per cent of the expected anthropogenic emissions over this period. Despite the considerable uncertainty in our estimates, the direction of the global soil carbon response is consistent across all scenarios. This provides strong empirical support for the idea that rising temperatures will stimulate the net loss of soil carbon to the atmosphere, driving a positive land carbon-climate feedback that could accelerate climate change.

Topsoil porosity prediction across habitats at large scales using environmental variables.

Soil porosity and its reciprocal bulk density are important environmental state variables that enable modelers to represent hydraulic function and carbon storage. Biotic effects and their 'dynamic' influence on such state variables remain largely unknown for larger scales and may result in important, yet poorly quantified environmental feedbacks. Existing representation of hydraulic function is often invariant to environmental change and may be poor in some systems, particularly non-arable soils. Here we assess predictors of total porosity across two comprehensive national topsoil (0-15 cm) data sets, covering the full range of soil organic matter (SOM) and habitats (n = 1385 & n = 2570), using generalized additive mixed models and machine learning. Novel aspects of this work include the testing of metrics on aggregate size and livestock density alongside a range of different particle size distribution metrics. We demonstrate that porosity trends in Great Britain are dominated by biotic metrics, soil carbon and land use. Incorporating these variables into porosity prediction improves performance, paving the way for new dynamic calculation of porosity using surrogate measures with remote sensing, which may help improve prediction in data sparse regions of the world. Moreover, dynamic calculation of porosity could support representation of feedbacks in environmental and Earth System Models. Representing the hydrological feedbacks from changes in structural porosity also requires data and models at appropriate spatial scales to capture conditions leading to near-saturated soil conditions. Classification. Environmental Sciences.

Internal friction of hydrated soda-lime-silicate glasses.

The internal friction of hydrated soda-lime-silica glasses with total water content (C(W)) up to 1.9 wt. % was studied by dynamic mechanical analysis (DMA) using temperature-frequency sweeps from 723 K to 273 K and from 1 s(-1) to 50 s(-1). Total water content and concentrations of H2O molecules (C(H2O)) and OH groups (C(OH)) in the DMA specimens were determined by infrared spectroscopy. For low water contents (C(W) ≈ C(OH) < 0.25 wt. %) two discrete internal friction peaks below the glass transition (α relaxation) were assigned to the low-temperature motion of alkali ions (γ relaxation) and cooperative movements of dissimilar mobile species under participation of OH at higher temperature (ß(OH) relaxation). For large water contents (C(W) > 1 wt. %), where significant amounts of molecular water are evident (C(H2O) > 0.15 wt. %), however, internal friction spectra change unexpectedly: the ß(OH) peak heights saturate and a low temperature shoulder appears on the ß-relaxation peak. This emerging relaxation mode (ß(H2O) relaxation) was assigned to the motions of H2O molecules. ß(H2O) relaxation was found to be faster than ß(OH) but slower than γ relaxation. Activation energy of the different relaxation modes increased in the order γ < ß(H2O) < ß(OH) < α.

Analytical modelling of soil porosity and bulk density across the soil organic matter and land-use continuum.

The thin layer of soil at the earth's surface supports life, storing water and nutrients for plant uptake. These processes occur in the soil pore space, often half the soil volume, but our understanding of how this volume responds to environmental change is poor. Convention, has been to predict soil porosity, or its reciprocal bulk density (BD), from soil texture using pedotransfer functions (PTFs). A texture based approach, invariant to environmental change, prevents feedback from land use or climate change to soil porosity. Moreover, PTFs are often limited to mineral soils with < 20% soil organic matter (SOM) content. Here, we develop an analytical model to predict soil porosity, or BD, as a function of SOM. We test it on two comprehensive, methodologically consistent, temperate national-scale topsoil data sets (0-15 cm) (Wales, n = 1385; Great Britain, n = 2570). The purpose of the approach is to generate an analytical function suitable for predicting soil porosity change with SOM content, while providing insight into the main grain-scale factors determining the porosity emergence. The newly developed function covering the entire SOM gradient allows for impacts of land use, management or climate change to feedback on soil porosity or bulk density through decadal dynamic changes in SOM.

Orientation of spindle axis and distribution of plasma membrane proteins during cell division in polarized MDCKII cells.

MDCKII cells differentiate into a simple columnar epithelium when grown on a permeable support; the monolayer is polarized for transport and secretion. Individual cells within the monolayer continue to divide at a low rate without disturbing the function of the epithelium as a barrier to solutes. This presents an interesting model for the study of mitosis in a differentiated epithelium which we have investigated by confocal immunofluorescence microscopy. We monitored the distribution of microtubules, centrioles, nucleus, tight junctions, and plasma membrane proteins that are specifically targeted to the apical and basolateral domains. The stable interphase microtubule cytoskeleton was rapidly disassembled at prophase onset and reassembled at cytokinesis. As the interphase microtubules disassembled at prophase, the centrioles moved from their interphase position at the apical membrane to the nucleus and acquired the ability to organize microtubule asters. Orientation of the spindle parallel to the plane of the monolayer occurred between late prophase and metaphase and persisted through cytokinesis. The cleavage furrow formed asymmetrically perpendicular to the plane of the monolayer initiating at the basolateral side and proceeding to the apical domain. The interphase microtubule network reformed after the centrioles migrated from the spindle poles to resume their interphase apical position. Tight junctions (ZO-1), which separate the apical from the basolateral domains, remained assembled throughout all phases of mitosis. E-cadherin and a 58-kD antigen maintained their basolateral plasma membrane distributions, and a 114-kD antigen remained polarized to the apical domain. These proteins were useful for monitoring the changes in shape of the mitotic cells relative to neighboring cells, especially during telophase when the cell shape changes dramatically. We discuss the changes in centriole position during the cell cycle, mechanisms of spindle orientation, and how the maintenance of polarized plasma membrane domains through mitosis may facilitate the rapid reformation of the polarized interphase cytoplasm.

Microtubule polymer assembly and transport during axonal elongation.

As axons elongate, tubulin, which is synthesized in the cell body, must be transported and assembled into new structures in the axon. The mechanism of transport and the location of assembly are presently unknown. We report here on the use of tubulin tagged with a photoactivatable fluorescent group to investigate these issues. Photoactivatable tubulin, microinjected into frog embryos at the two-cell stage, is incorporated into microtubules in neurons obtained from explants of the neural tube. When activated by light, a fluorescent mark is made on the microtubules in the axon, and transport and turnover can be visualized directly. We find that microtubules are generated in or near the cell body and continually transported distally as a coherent phase of polymer during axon elongation. This vectorial polymer movement was observed at all levels on the axon, even in the absence of axonal elongation. Measurements of the rate of polymer translocation at various places in the axon suggest that new polymer is formed by intercalary assembly along the axon and assembly at the growth cone in addition to transport of polymer from the cell body. Finally, polymer movement near the growth cone appeared to respond in a characteristic manner to growth cone behavior, while polymer proximally in the axon moved more consistently. These results suggest that microtubule translocation is the principal means of tubulin transport and that translocation plays an important role in generating new axon structure at the growth cone.

Rab11 regulates recycling through the pericentriolar recycling endosome.

Small GTPases of the rab family are crucial elements of the machinery that controls membrane traffic. In the present study, we examined the distribution and function of rab11. Rab11 was shown by confocal immunofluorescence microscopy and EM to colocalize with internalized transferrin in the pericentriolar recycling compartment of CHO and BHK cells. Expression of rab11 mutants that are preferentially in the GTP- or GDP-bound state caused opposite effects on the distribution of transferrin-containing elements; rab11-GTP expression caused accumulation of labeled elements in the perinuclear area of the cell, whereas rab11-GDP caused a dispersion of the transferrin labeling. Functional studies showed that the early steps of uptake and recycling for transferrin were not affected by overexpression of rab11 proteins. However, recycling from the later recycling endosome was inhibited in cells overexpressing the rab11-GDP mutant. Rab5, which regulates early endocytic trafficking, acted before rab11 in the transferrin-recycling pathway as expression of rab5-GTP prevented transport to the rab11-positive recycling endosome. These results suggest a novel role for rab11 in controlling traffic through the recycling endosome.

Rab6 coordinates a novel Golgi to ER retrograde transport pathway in live cells.

We visualized a fluorescent-protein (FP) fusion to Rab6, a Golgi-associated GTPase, in conjunction with fluorescent secretory pathway markers. FP-Rab6 defined highly dynamic transport carriers (TCs) translocating from the Golgi to the cell periphery. FP-Rab6 TCs specifically accumulated a retrograde cargo, the wild-type Shiga toxin B-fragment (STB), during STB transport from the Golgi to the endoplasmic reticulum (ER). FP-Rab6 TCs associated intimately with the ER, and STB entered the ER via specialized peripheral regions that accumulated FP-Rab6. Microinjection of antibodies that block coatomer protein I (COPI) function inhibited trafficking of a KDEL-receptor FP-fusion, but not FP-Rab6. Additionally, markers of COPI-dependent recycling were excluded from FP-Rab6/STB TCs. Overexpression of Rab6:GDP (T27N mutant) using T7 vaccinia inhibited toxicity of Shiga holotoxin, but did not alter STB transport to the Golgi or Golgi morphology. Taken together, our results indicate Rab6 regulates a novel Golgi to ER transport pathway.

Movement of nuclei along microtubules in Xenopus egg extracts.

Microtubules are implicated in the movement and positioning of nuclei in many cell types. Nuclei can be moved by forces acting on microtubules nucleated at the spindle pole body, as in fungi [1], or microtubules nucleated at the centrosome, as during migration of the male (sperm) pronucleus towards the centre of the zygote after fertilization [2] [3] [4]. The dramatic movements of the female pronucleus towards the male pronucleus potentially involve another mechanism: movement along the microtubules of the sperm aster towards their slower growing, attached or 'minus' ends [3] [5]. Here, we have reconstituted this last type of nuclear movement in vitro. Synthetic nuclei assembled in cytoplasmic extracts made from interphase Xenopus eggs move along microtubules towards their minus ends. We provide strong experimental evidence that cytoplasmic dynein is the motor for nuclear movement in this in vitro system, and discuss our results in terms of current knowledge of motility of the endoplasmic reticulum.

The core of the mammalian centriole contains gamma-tubulin.

BACKGROUND: The microtubule network, upon which transport occurs in higher cells, is formed by the polymerization of alpha and beta tubulin. The third major tubulin isoform, gamma tubulin, is believed to serve a role in organizing this network by nucleating microtubule growth on microtubule-organizing centers, such as the centrosome. Research in vitro has shown that gamma tubulin must be restored to stripped centrioles to regenerate the centrosomal functions of duplication and microtubule nucleation. RESULTS: We have re-examined the localization of gamma tubulin in isolated and in situ mammalian centrosomes using a novel immunocytochemical technique that preserves antigenicity and morphology while allowing increased accessibility. As expected, alpha tubulin was localized in cytoplasmic and centriolar barrel microtubules and in the associated pericentriolar material. Foci of gamma tubulin were observed at the periphery of the organized pericentriolar material, as reported previously, often near the termini of microtubules. A further and major location of gamma tubulin was a structure within the proximal end of the centriolar barrel. The distributions were complementary, in that alpha tubulin was excluded from the core of the centriole, and gamma tubulin was excluded from the microtubule barrel. CONCLUSIONS: We have shown that gamma tubulin is localized both in the pericentriolar material and in the core of the mammalian centriole. This result suggests that gamma tubulin has a role in the centriolar duplication process, perhaps as a template for growth of the centriolar microtubules, in addition to its established role in the nucleation of astral microtubules.

Visual perception dominance of fallers among community-dwelling older adults.

The authors postulated that older adult fallers show a greater tendency than older adult nonfallers to rely more on visual information sources in maintaining upright posture than on kinesthetic and vestibular cues. This paper presents descriptive statistics on 199 older adults living independently in the community. Their visual perception of the vertical and horizontal was analyzed with respect to age, sex, health status, and severity of injury as a result of a fall. The finding of significant impairments for fallers in visual perceptual abilities confirmed a trend previously established by one of the authors (Tobis). When the visual field entailed only misleading or ambiguous cues in the form of a tilted frame, fallers again showed a larger error than nonfallers in establishing the vertical and horizontal. The authors feel that this relatively greater dependence on visual sources may develop in response to impairment of feedback on posture and gait from the kinesthetic and vestibular systems as a result of age and chronic health problems. Errors in visual perception of the vertical and horizontal intercorrelated with age, sex, and a large number of medical problems. However, visual variables were more important in predicting faller status than physical characteristics.

Specific efficacy expectations mediate exercise compliance in patients with COPD.

Social learning theory has generated two different approaches for the assessment of expectancies. Bandura argues that expectancies are specific and do not generalize. Therefore, he prefers measures of specific efficacy expectations. Others endorse the role of generalized expectancies measured by locus of control scales. The present study examines specific versus generalized expectancies as mediators of changes in exercise behavior among 60 older adult patients with Chronic Obstructive Pulmonary Disease. The patients were given a prescription to increase exercise and randomly assigned to experimental groups or control groups. All groups received attention but only experimental groups received training to increase their exercise. After 3 months, groups given specific training for compliance with walking significantly increased their activity in comparison to the control group receiving only attention. These changes were mediated by changes in perceived efficacy for walking, with efficacy expectations for other behaviors changing as a function of their similarity to walking. A generalized health locus of control expectancy measure was less clearly associated with behavior change. The results are interpreted as supporting Bandura's version of social theory.

Attempts to prevent falls and injury: a prospective community study.

At 16 senior centers, we studied the effectiveness of exercise and cognitive-behavioral programs, compared with a discussion control program, in reducing falls and injuries among 230 older adults. After 1 year of the programs, we observed no significant difference in time to first fall. Even though a relatively high percentage (38.6%) suffered at least one fall, only 7.8% of these community-residing elderly required medical attention. Secondary outcome measures such as strength, balance, fear of falling, and perceived health did not significantly change.

Accuracy of self-monitoring of blood glucose: impact on diabetes management decisions during pregnancy.

PURPOSE: This study tested the hypothesis that the accuracy of self-monitoring of blood glucose (SMBG) values of patients with diabetes during pregnancy deviates substantially from reference values. METHODS: The patients' glucose values were measured on 6 different SMBG meters; reference values were from the HemoCue B Glucose Analyzer. Over a 5-year period, 1973 comparisons between SMBG values and reference values were recorded during clinic visits and used for this study. Data were analyzed for percent of values that varied more than +/- 10.5% and +/- 15.5% from the reference value. Out-of-range data at each variance level were analyzed to determine the impact on medical management if decisions were based solely on SMBG values. RESULTS: One third of SMBG readings deviated significantly, which could adversely affect treatment for half of these patients if diabetes management was based on SMBG values. At the 10.5% deviation level, 34% of SMBG meter readings were out of range; 54% of these would have implied erroneous treatment. At the 15.5% deviation level, 18% were out of range; 63% of these would have implied erroneous management. CONCLUSIONS: The accuracy of home meters should be verified at regular intervals, and SMBG values should not be the sole criterion for diabetes management during pregnancy.

Adjusting for recall bias with the proportional hazards model.

In studying falling frequency in the elderly, we observed that having subjects keep a diary led to a larger number of falls reported than had been noted in a previous study in the same population. The previous study asked subjects to report any falls in the previous three months. We considered two related explanations for the observation of lower incidence reports with a 3-month recall survey. First, there may have been under-reporting of falls due to recall bias. Second, the less severe falls (which did not result in injuries) may not be reported. We suggest that the proportional hazards model may be used to adjust studies in which recall is used to determine incidence and time to falls.

Intergenerational relations: pre-med students at senior centers.

Misconceptions about aging and a negative bias against caring for older adults entail unfortunate consequences for society. This study explored the potential of frequent personal contact in reducing misconceptions and improving personal attitude towards older adults. Thirty students, predominantly Asian, with English as their second language, attended senior centers three times per week for 11 months, on the average. They assisted in teaching health promotion classes for the prevention of falls, conducted health assessments by interview, and collected physiological data. At the senior centers, a sample of 70 older adult Americans participated in the health promotion classes and in this evaluation of intergenerational relations. Students completed anonymously two questionnaires; one was objective, testing misconceptions about aging; the other was subjective, rating their reactions to elders at senior centers. Older adults completed, also anonymously, a subjective questionnaire on their reactions to students at their centers. Results on students' misconceptions about aging were similar to those among students at Duke University who did not experience frequent personal contact with well elderly. According to the Facts on Aging Quiz, the overall attitude among students at senior centers was more biased in the negative direction than among Duke students, especially among students who had just joined the project. However, in the subjective questionnaires, students at senior centers expressed feeling at ease at the centers and they disagreed with statements of impatience and frustration. Older adults at the centers had a positive attitude toward the students and most thought that students were sympathetic.

Midtrimester amniocentesis. Subjective maternal responses.

Studies, through questionnaire and interview, of couples who elect or decline midtrimester amniocentesis demonstrate that both groups cope well with new decisions surrounding this procedure. The pregnancy monitored by genetic amniocentesis does not appear to receive special status as viewed by the parents, nor is the developing fetus placed in a special category during the pregnancy.

Movement of nuclei.

This unit describes the first assay that reconstructs the movement of the female pronucleus in the newly fertilized frog egg. Nuclei are assembled in frog egg extracts and translocated along microtubules using the microtubule motor dynein.