Rhizosphere activity and atmospheric methane concentrations drive variations of methane fluxes in a temperate forest soil

Aerated soils represent an important sink for atmospheric methane (CH⁠4), due to the effect of methanotrophic bacteria, thus mitigating current atmospheric CH⁠4 increases. Whilst rates of CH⁠4 oxidation have been linked to types of vegetation cover, there has been no systematic investigation of the interaction between plants and soil in relation to the strength of the soil CH⁠4 sink. We used quasi-continuous automated chamber measurements of soil CH⁠4 and CO⁠2 flux from soil collar treatments that selectively include root and ectomycorrhizal (ECM) mycelium to investigate the role of rhizosphere activity as well as the effects of other environmental drivers on CH⁠4 uptake in a temperate coniferous forest soil. We also assessed the potential impact of measurement bias from sporadic chamber measurements in altering estimates of soil CO⁠2 efflux and CH⁠4 uptake. Results show a clear effect of the presence of live roots and ECM mycelium on soil CO⁠2 efflux and CH⁠4 uptake. The presence of ECM hyphae alone (without plant roots) showed intermediate fluxes of both CO⁠2 and CH⁠4 relative to soils that either contained roots and ECM mycelium, or soil lacking root- and ECM mycelium. Regression analysis confirmed a significant influence of soil moisture as well as temperature on flux dynamics of both CH⁠4 and CO⁠2 flux. We further found a surprising increase in soil CH⁠4 uptake during the night, and discuss diurnal fluctuations in atmospheric CH⁠4 (with higher concentrations during stable atmospheric conditions at night) as a potential driver of CH⁠4 oxidation rates. Using the high temporal resolution of our data set, we show that low-frequency sampling results in systematic bias of up-scaled flux estimates, resulting in under-estimates of up to 20% at our study site, due to fluctuations in flux dynamics on diurnal as well as longer time scales

Evaluation of the ECOSSE model to predict heterotrophic soil respiration by direct measurements

Acknowledgements This work contributes to the ELUM (Ecosystem Land Use Modelling & Soil Carbon GHG Flux Trial) project, which was commissioned and funded by the Energy Technologies Institute (ETI), and to Carbo-BioCrop (http://www.carbobiocrop.ac.uk; a NERC funded project; NE/H010742/1), UKERC Phase II and III (NERC; NE/H013237/1), MAGLUE (http://www.maglue.ac.uk; an EPSRC funded project; EP/M013200/1) and as part of the Seventh Framework For Research Programme of the EU, within the EUROCHAR project (N 265179) and EXPEER within WU FP7-Infrastructures. We acknowledge the use of the E-OBS dataset from the EU-FP6 project ENSEMBLES (http://ensembles-eu.metoffice.com) and the data providers in the ECA&D project (http://www.ecad.eu). We thank two anonymous reviewers and Dr William van Dijk for their valuable suggestions.Peer reviewedPostprin

Anomalous Self-Energy Effects of the B_1g Phonon in Y_{1-x}(Pr,Ca)_xBa_2Cu_3O_7 Films

In Raman spectra of cuprate superconductors the gap shows up both directly, via a redistribution of the electronic background, the so-called "2Delta peaks", and indirectly, e.g. via the renormalization of phononic excitations. We use a model that allows us to study the redistribution and the related phonon self-energy effects simultaneously. We apply this model to the B_1g phonon of Y_{1-x}(Pr,Ca)_xBa_2Cu_3O_7 films, where Pr or Ca substitution enables us to investigate under- and overdoped samples. While various self-energy effects can be explained by the strength and energy of the 2\Delta peaks, anomalies remain. We discuss possible origins of these anomalies.Comment: 6 pages including 4 figure

Bomb-¹⁴C analysis of ecosystem respiration reveals that peatland vegetation facilitates release of old carbon

The largest terrestrial-to-atmosphere carbon flux is respired CO<sub>2</sub>. However, the partitioning of soil and plant sources, understanding of contributory mechanisms, and their response to climate change are uncertain. A plant removal experiment was established within a peatland located in the UK uplands to quantify respiration derived from recently fixed plant carbon and that derived from decomposition of soil organic matter, using natural abundance <sup>13</sup>C and bomb-<sup>14</sup>C as tracers. Soil and plant respiration sources were found respectively to contribute ~ 36% and between 41-54% of the total ecosystem CO<sub>2</sub> flux. Respired CO<sub>2</sub> produced in the clipped (‘soil’) plots had a mean age of ~ 15 years since fixation from the atmosphere, whereas the <sup>14</sup>C content of ecosystem CO<sub>2</sub> was statistically indistinguishable from the contemporary atmosphere. Results of carbon mass balance modelling showed that, in addition to respiration from bulk soil and plant respired CO<sub>2</sub>, a third, much older source of CO<sub>2</sub> existed. This source, which we suggest is CO<sub>2</sub> derived from the catotelm constituted between ~ 10 and 23% of total ecosystem respiration and had a mean radiocarbon age of between several hundred to ~ 2000 years before present (BP). These findings show that plant-mediated transport of CO<sub>2</sub> produced in the catotelm may form a considerable component of peatland ecosystem respiration. The implication of this discovery is that current assumptions in terrestrial carbon models need to be re-evaluated to consider the climate sensitivity of this third source of peatland CO<sub>2</sub>

Biotic carbon feedbacks in a materially-closed soil-vegetation-atmosphere system

The magnitude and direction of the coupled feedbacks between the biotic and abiotic components of the terrestrial carbon cycle is a major source of uncertainty in coupled climate–carbon-cycle models1, 2, 3. Materially closed, energetically open biological systems continuously and simultaneously allow the two-way feedback loop between the biotic and abiotic components to take place4, 5, 6, 7, but so far have not been used to their full potential in ecological research, owing to the challenge of achieving sustainable model systems6, 7. We show that using materially closed soil–vegetation–atmosphere systems with pro rata carbon amounts for the main terrestrial carbon pools enables the establishment of conditions that balance plant carbon assimilation, and autotrophic and heterotrophic respiration fluxes over periods suitable to investigate short-term biotic carbon feedbacks. Using this approach, we tested an alternative way of assessing the impact of increased CO2 and temperature on biotic carbon feedbacks. The results show that without nutrient and water limitations, the short-term biotic responses could potentially buffer a temperature increase of 2.3 °C without significant positive feedbacks to atmospheric CO2. We argue that such closed-system research represents an important test-bed platform for model validation and parameterization of plant and soil biotic responses to environmental changes

Effect of moisture on leaf litter decomposition and its contribution to soil respiration in a temperate forest

The degree to which increased soil respiration rates following wetting is caused by plant (autotrophic) versus microbial (heterotrophic) processes, is still largely uninvestigated. Incubation studies suggest microbial processes play a role but it remains unclear whether there is a stimulation of the microbial population as a whole or an increase in the importance of specific substrates that become available with wetting of the soil. We took advantage of an ongoing manipulation of leaf litter <sup>14</sup>C contents at the Oak Ridge Reservation, Oak Ridge, Tennessee, to (1) determine the degree to which an increase in soil respiration rates that accompanied wetting of litter and soil, following a short period of drought, could be explained by heterotrophic contributions; and (2) investigate the potential causes of increased heterotrophic respiration in incubated litter and 0–5 cm mineral soil. The contribution of leaf litter decomposition increased from 6 ± 3 mg C m<sup>−2</sup> hr<sup>−1</sup> during a transient drought, to 63 ± 18 mg C m<sup>−2</sup> hr<sup>−1</sup> immediately after water addition, corresponding to an increase in the contribution to soil respiration from 5 ± 2% to 37 ± 8%. The increased relative contribution was sufficient to explain all of the observed increase in soil respiration for this one wetting event in the late growing season. Temperature (13°C versus 25°C) and moisture (dry versus field capacity) conditions did not change the relative contributions of different decomposition substrates in incubations, suggesting that more slowly cycling C has at least the same sensitivity to decomposition as faster cycling organic C at the temperature and moisture conditions studied

Practices of caring for nursing students : a clinical learning environment

Abstract: Objective: The purpose of this study was to explore, describe and illuminate nursing students’ best encounters of caring in the clinical learning environment. Caring for nursing students was emphasized and recommendations provided to enhance caring for nursing students within their clinical learning environment. Methods: Qualitative data was collected by the researcher using semi-structured individual interviews and an Appreciative Inquiry (AI) methodology. Ten second year nursing students undertaking the bridging course leading to registration as general nurses in terms of Regulation 683 of the South African Nursing Council (SANC) were purposively sampled from 3 private hospitals within the Western Cape. Data was analysed using Giorgi’s method. Results: The main theme included the best and ‘least best’ caring practices embedded in the centrality of the heart. The subthemes comprised of the nursing students’ experiences of caring literacy and caring illiteracy. The second theme included the creation of best caring practices within a conducive clinical learning environment. Within this theme, the subthemes comprised of the caring attributes required in reflecting best caring practices, as well the creation of a clinical learning environment to optimise caring. Conclusions: The significance and necessity of caring for the nursing student were clearly illustrated and confirmed by participants. Caring was equated to the heart as the core to the nursing students’ being. Recommendations for nursing education, management, practice and research were therefore specifically formulated to enhance caring towards nursing students

The influence of soil communities on the temperature sensitivity of soil respiration

Soil respiration represents a major carbon flux between terrestrial ecosystems and the atmosphere, and is expected to accelerate under climate warming. Despite its importance in climate change forecasts, however, our understanding of the effects of temperature on soil respiration (RS) is incomplete. Using a metabolic ecology approach we link soil biota metabolism, community composition and heterotrophic activity, to predict RS rates across five biomes. We find that accounting for the ecological mechanisms underpinning decomposition processes predicts climatological RS variations observed in an independent dataset (n = 312). The importance of community composition is evident because without it RS is substantially underestimated. With increasing temperature, we predict a latitudinal increase in RS temperature sensitivity, with Q10 values ranging between 2.33 ±0.01 in tropical forests to 2.72 ±0.03 in tundra. This global trend has been widely observed, but has not previously been linked to soil communities

THEORETICAL MODEL VALIDATION OF MUSCLE FORCES DURING EXTREME MOVEMENTS

Introduction: The validation of the involved muscular forces for a computer model of the human body, which allows simulation of internal forces in patients, was achieved by inverse-dynamic analysis. Methods: Beginning with an extreme vertical jump, joint moments were extracted from high-speed film data and eventually subdivided into muscular forces. The muscle groups responsible for movements were determined by electromyography. A squat jump with both legs and maximum strength was filmed in the sagittal plane with a frequency of 200 Hz. Moments in the hip, knee and ankle joints were determined from the film data. Using surface electrodes of a Neuraxon Myosoft 2008 system and an amplifier system from Multichannel Systems, the muscle groups responsible for movements were electromyographically determined. The muscle insertions and muscle paths were extracted from MRI pictures of patients. Results: With this information joint moments can be subdivided into single muscle forces. Depending on the jump demands, the muscle groups responsible for movements can be divided and analyzed in six extensor groups. Conclusion: Inverse-dynamic muscle force analysis is a basis which can be expanded for the validation of complex movements under extreme internal loads in patients