Testing interactive effects of global environmental changes on soil nitrogen cycling

Responses of soil nitrogen (N) cycling to simultaneous and potentially interacting global environmental changes are uncertain. Here, we investigated the combined effects of elevated CO2, warming, increased precipitation and enhanced N supply on soil N cycling in an annual grassland ecosystem as part of the Jasper Ridge Global Change Experiment (CA, USA). This field experiment included four treatments-CO2, temperature, precipitation, nitrogen-with two levels per treatment (ambient and elevated), and all their factorial combinations replicated six times. We collected soil samples after 7 and 8 years of treatments, and measured gross rates of N mineralization, N immobilization and nitrification, along with potential rates of ammonia oxidation, nitrite oxidation and denitrification. We also determined the main drivers of these microbial activities (soil ammonium and nitrate concentrations, soil moisture, soil temperature, soil pH, and soil CO2 efflux, as an indicator of soil heterotrophic activity). We found that gross N mineralization responded to the interactive effects of the CO2, precipitation and N treatments: N addition increased gross N mineralization when CO2 and precipitation were either both at ambient or both at elevated levels. However, we found limited evidence for interactions among elevated CO2, warming, increased precipitation, and enhanced N supply on the other N cycling processes examined: statistically significant interactions, when found, tended not to persist across multiple dates. Soil N cycling responded mainly to single-factor effects: long-term N addition increased gross N immobilization, potential ammonia oxidation and potential denitrification, while increased precipitation depressed potential nitrite oxidation and increased potential ammonia oxidation and potential denitrification. In contrast, elevated CO2 and modest warming did not significantly affect any of these microbial N transformations. These findings suggest that global change effects on soil N cycling are primarily additive, and therefore generally predictable from single factor studies

Responses of soil nitrite-oxidizers to global environmental changes

Background/Question/Methods
There is increasing evidence that global change can alter the structure of plant
communities with large impacts on the functioning of terrestrial ecosystems. However, little is known about the impact of global change on soil microbial communities. In particular, the response of soil nitrite-oxidizers microorganisms that mediate the second step of nitrification, a key process of the nitrogen cycle, has never been investigated.
Here, we examined the effects of four main global environmental changes on the activity, the abundance and the diversity of soil nitrite-oxidizers in an annual grassland ecosystem as part of the Jasper Ridge Global Change Experiment (CA, USA). This experiment includes four treatments - CO2, temperature, precipitation and nitrogen - with two levels per treatment (ambient and elevated, with elevated treatment based on prediction for the end of the century), and all of their factorial combinations. We measured potential nitrite oxidation, the abundance of soil Nitrobacter- and Nitrospiralike nitrite-oxidizers (using quantitative PCR targeting nxrA and 16S rRNA gene, respectively) and the diversity of soil Nitrobacter-like nitrite-oxidizers (using cloning sequencing targeting the nxrA gene) in each treatment combination at the end of the 7th and 8th growing seasons under treatments. Furthermore, we analyzed to what extent changes in the activity of the soil nitrite-oxidizers result from changes in their abundance or diversity.

Results/Conclusions
Simulated global environmental changes significantly altered the activity, as well as the abundance and the diversity of soil nitrite-oxidizers. Potential nitrite oxidation decreased with increased precipitation and increased with elevated CO2 when combined with added nitrogen or precipitation. The abundance of soil Nitrobacter-like nitrite-oxidizers also decreased with increased precipitation and increased with elevated levels of CO2 and nitrogen. In contrast, the abundance of soil Nitrospira-like nitrite-oxidizers increased with enhanced precipitation and decreased with elevated levels of CO2 and temperature. Finally, the structure of the soil Nitrobacter-like nitrite-oxidizers was significantly altered by the treatments. Consistent with results reported by Attard et al. (2010) for agroecosystems, we found that changes in potential rates of nitrite oxidation in response to treatments were partly explained by changes in the abundance of soil Nitrobacter-like nitrite-oxidizers, but not by changes in the abundance of soil Nitrospiralike nitrite-oxidizers, suggesting that Nitrobacter-like nitrite-oxidizers were the main functional players of the soil nitrite-oxidizing microbial community.
Our study provides evidence that global change could alter the abundance and diversity of soil nitrite-oxidizers, with potential impacts for soil nitrogen cycling.

*The audio track for talks in this symposium may be obtained at the following web address:*

*https://sites.google.com/site/esa2010symposium13audiocontent/esa2010-symposium13-audio-content

Global Change Could Amplify Fire Effects on Soil Greenhouse Gas Emissions

Background: Little is known about the combined impacts of global environmental changes and ecological disturbances on ecosystem functioning, even though such combined impacts might play critical roles in shaping ecosystem processes that can in turn feed back to climate change, such as soil emissions of greenhouse gases.[br/] Methodology/Principal Findings: We took advantage of an accidental, low-severity wildfire that burned part of a long-term global change experiment to investigate the interactive effects of a fire disturbance and increases in CO(2) concentration, precipitation and nitrogen supply on soil nitrous oxide (N(2)O) emissions in a grassland ecosystem. We examined the responses of soil N(2)O emissions, as well as the responses of the two main microbial processes contributing to soil N(2)O production - nitrification and denitrification - and of their main drivers. We show that the fire disturbance greatly increased soil N(2)O emissions over a three-year period, and that elevated CO(2) and enhanced nitrogen supply amplified fire effects on soil N(2)O emissions: emissions increased by a factor of two with fire alone and by a factor of six under the combined influence of fire, elevated CO(2) and nitrogen. We also provide evidence that this response was caused by increased microbial denitrification, resulting from increased soil moisture and soil carbon and nitrogen availability in the burned and fertilized plots. [br/] Conclusions/Significance: Our results indicate that the combined effects of fire and global environmental changes can exceed their effects in isolation, thereby creating unexpected feedbacks to soil greenhouse gas emissions. These findings highlight the need to further explore the impacts of ecological disturbances on ecosystem functioning in the context of global change if we wish to be able to model future soil greenhouse gas emissions with greater confidence

An active electrode for biopotential recording from small localized bio-sources

BACKGROUND: Laser bio-stimulation is a well-established procedure in Medical Acupuncture. Nevertheless there is still a confusion as to whether it works or the effect is just placebo. Although a plethora of scientific papers published, showing positive clinical results, there is still a lack of objective scientific proofs about the bio-stimulation effect of lasers used in Acupuncture. The objective of this work was to design and build a body surface electrode and an amplifier for biopotential recording from acupuncture points, considered here as small localized bio-sources (SLB). The design is aimed for studying SLB potentials provoked by laser stimulus, in search for objective proofs of the bio-stimulation effect of lasers used in Medical Acupuncture. METHODS: The active electrode presented features a new adjustable anchoring system and fractionation of the biopotential amplifier between the electrode and the cabinet's location. The new adjustable electrode anchoring system is designed to reduce the electrode-skin contact impedance, its variation and motion artifacts. That is achieved by increasing the electrode-skin tension and decreasing its relative movement. Additionally the sensing element provides local constant skin stretching thus eliminating the contribution of the skin potential artifact. The electrode is attached to the skin by a double-sided adhesive pad, where the sensing element is a stainless steel, 4 mm in diameter. The fractionation of the biopotential amplifier is done by incorporating the amplifier's front-end op-amps at the electrodes, thus avoiding the use of extra buffers. The biopotential amplifier features two selectable modes of operation: semi-AC-mode with a -3 dB bandwidth of 0.32–1000 Hz and AC-mode with a bandwidth of 0.16–1000 Hz. RESULTS: The average measured DC electrode-skin contact impedance of the proposed electrode was 450 kΩ, with electrode tension of 0.3 kg/cm(2 )on an unprepared skin of the inner forearm. The peak-to-peak noise voltage measured at the amplifier output, with input terminals connected to common, was 10 mV(p-p), or 2 μV(p-p )referred to the input. The common-mode rejection ratio of the amplifier was 96 dB at 50 Hz, measured with imbalanced electrodes' impedances. The prototype was also tested practically and sample records were obtained after a low intensity SLB laser stimulation. All measurements showed almost a complete absence of 50 Hz interference, although no electrolyte gel or skin preparation was applied. CONCLUSION: The results showed that the new active electrode presented significantly reduced the electrode-skin impedance, its variation and motion artifact influences. This allowed SLB signals with relatively high quality to be recorded without skin preparation. The design offers low noise and major reduction in parts, size and power consumption. The active electrode specifications were found to be better or at least comparable to those of other existing designs

Long-term effect of multiple global environmental changes on the retention and distribution of nitrogen in a grassland ecosystem

Long-term effect of multiple global environmental changes on the retention and distribution of nitrogen in a grassland ecosystem. Annual Meeting British Ecological Society and Société Française d'Ecologi

Elevated CO2 mediates the short-term drought recovery of ecosystem function in low-diversity grassland systems

Ecosystems are expected to experience simultaneous environmental changes. This study examines the interactive effects of atmospheric CO2 and plant community composition on grassland ecosystem functioning after a severe drought. Monocultures of the grass Dactylis glomerata were compared to a four-species grassland community under ambient and elevated CO2, with or without drought. Greenhouse gas fluxes, C and N pools in plants and soil were measured over a 55-day, post-rewetting period for all mesocosms. Experimental drought reduced aboveground biomass production, but increased soil inorganic N and dissolved organic C (DOC) across CO2 and community composition treatments. Following rewetting, droughted mesocosms had lower ecosystem respiration and higher N2O emissions. After 55 days, negative drought effects persisted on above- and belowground C stocks and root N stocks. Elevated CO2 reduced the magnitude of drought effects on ecosystem respiration, N2O fluxes and plant C:N ratios but increased drought-induced changes to soil DOC. The four-species mixture buffered ecosystem respiration from drought effects, but showed higher drought-induced increases in soil inorganic N shortly after rewetting. Elevated CO2 mitigates the effects of extreme drought on multiple grassland functions. In contrast, grassland composition appears to have mainly additive effects with drought and elevated CO2 in our simple sown systems

Objectifs et décisions cliniques modernes en odontologie reconstructrice

Ce rapport de cas illustre le traitement d'un cas d'usure d'origine intrinsèque ainsi que son approche décisionnelle, clinique et technique qui se veulent modernes : 1. L'élaboration du projet morpho-fonctionnel puis sa validation clinique par le patient et l'équipe soignante, avant toute intervention, son influence bénéfique tout au long du traitement. 2. La préservation tissulaire et principes adhésifs utilisés, les vitrocéramiques renforcées et mordançables. 3. Un choix d'outils, de techniques et de procédures toujours, simples, efficaces et fiables. 4. L'importance de qualité de la communication avec le laboratoire. In fine, cette approche moderne permet la fusion entre équilibre neuro-musculo-articulaire (fonction et économie d'énergie) et équilibre du sourire, au sein du visage (esthétique et économie tissulaire)