Abstract A steady-state, 1D semi-analytical model for prompt redeposition based on the separation between redeposition caused by the electric field in the sheath and redeposition related to ...gyromotion is here described. The model allows for the estimation of not only the fraction of promptly redeposited flux but also the energy and angular distribution of the non-promptly redeposited population, along with their average charge state. Thus, the temperature and mean parallel-to-B velocity of the non-promptly redeposited flux are also available. The semi-analytical model was validated against equivalent Monte Carlo simulations across a broad range of input parameters. In this paper the eroded material under exam was tungsten (W) for which the code demonstrated consistent agreement with respect to numerical results, within its defined validity limits. The model can theoretically provide a solution for any material, temperature and electron density profile in the sheath, monotonic potential drop profile, and sputtered particles energy and angular distribution at the wall. As such, this code emerges as a potential tool for addressing the boundary redeposition phenomenon in fluid impurity transport simulations.
•A large custom cryogen-free cryostat has been designed and built in order to operate the CUORE detector.•The CUORE cryostat has a 1 m3 experimental volume and is able to host a tonne-scale ...bolometric detector.•The CUORE cryostat guarantees a low noise and low radioactivity environment, needed to search for 0nbb.•The CUORE detector has been cooled down to 8.3 mK and steadily operated at 15 mK, proving the success of the cryostat.
The CUORE experiment is the world’s largest bolometric experiment. The detector consists of an array of 988 TeO2 crystals, for a total mass of 742 kg. CUORE is presently taking data at the Laboratori Nazionali del Gran Sasso, Italy, searching for the neutrinoless double beta decay of 130Te. A large custom cryogen-free cryostat allows reaching and maintaining a base temperature of ∼10 mK, required for the optimal operation of the detector. This apparatus has been designed in order to achieve a low noise environment, with minimal contribution to the radioactive background for the experiment. In this paper, we present an overview of the CUORE cryostat, together with a description of all its sub-systems, focusing on the solutions identified to satisfy the stringent requirements. We briefly illustrate the various phases of the cryostat commissioning and highlight the relevant steps and milestones achieved each time. Finally, we describe the successful cooldown of CUORE.
While the positive relationship between plant biodiversity and ecosystem functioning (BEF) is well established, the extent to which this is mediated via belowground microbial processes is poorly ...understood. Growing evidence suggests that plant community structure influences soil microbial diversity, which in turn promotes functions desired for sustainable agriculture. Here, we outline the ‘plant-directed’ and soil microbe-mediated mechanisms expected to promote positive BEF. We identify how this knowledge can be utilized in plant diversification schemes to maximize ecosystem functioning in agroecosystems, which are typically species poor and sensitive to biotic and abiotic stressors. In the face of resource overexploitation and global change, bridging the gaps between biodiversity science and agricultural practices is crucial to meet food security in the Anthropocene.
Modern agriculture is characterized by monocultures, which rely on external inputs and contribute to greenhouse gas emissions and biodiversity loss.Biodiversity drives ecosystem functions through multiple mechanisms.The importance of plant–soil feedbacks mediated by soil microbial communities in biodiversity–ecosystem functioning (BEF) relationships for agricultural practices is increasingly recognized.BEF research can guide the development of agricultural diversification practices that rely not only on species diversity but on mechanisms stemming from composition and functional traits to enhance both above- and belowground ecosystem functions.We identify how plant diversity may enhance carbon retention in soils via effects on soil microorganisms.Diversification in agriculture requires a fundamental ecological understanding of underlying mechanisms to alleviate trade-offs between desired ecosystem functions and crop yields.
Aboveground fungal pathogens can substantially reduce biomass production in grasslands. However, we lack a mechanistic understanding of the drivers of fungal pathogen infection and impact. Using a ...grassland global change and biodiversity experiment we show that the trade‐off between plant growth and defense is the main determinant of infection incidence. In contrast, nitrogen addition only indirectly increased incidence via shifting plant communities towards faster growing species. Plant diversity did not decrease incidence, likely because spillover of generalist pathogens or dominance of susceptible plants counteracted negative diversity effects. A fungicide treatment increased plant biomass production and high levels of infection incidence were associated with reduced biomass. However, pathogen impact was context dependent and infection incidence reduced biomass more strongly in diverse communities. Our results show that a growth‐defense trade‐off is the key driver of pathogen incidence, but pathogen impact is determined by several mechanisms and may depend on pathogen community composition.
The growth strategy of a plant community is the main determinat of fungal infection incidence of that community. However, the consequences of infection are context dependent which is likely linked to the specific composition of the fungal community.
Plant functional traits can provide a mechanistic understanding of community responses to global change and of community effects on ecosystem functions. Nitrogen enrichment typically shifts trait ...composition by promoting the dominance of acquisitive plants (high specific leaf area SLA and low leaf dry matter content LDMC), translating into high biomass production. Changes in mean trait values can be due to shifts in species identity, relative abundances and/or intraspecific trait values. However, we do not know the relative importance of these shifts in determining trait responses to environmental changes, or trait effects on ecosystem functioning, such as biomass production.
We quantified the relative importance of species composition, abundance and intraspecific shifts in driving variation in SLA and LDMC, and how these shifts affected above‐ and below‐ground biomass. We measured traits in a grassland experiment manipulating nitrogen fertilisation, plant species richness, foliar fungal pathogen removal and sown functional composition (slow vs. fast species). We fitted structural equation models to test the importance of abundance and intraspecific shifts in determining (a) responses of functional composition to treatments and (b) effects on above‐ and below‐ground biomass.
We found that species intraspecific shifts were as important as abundance shifts in determining the overall change in functional composition (community weighted mean trait values), and even had large effects compared to substantial initial variation in sown trait composition. Intraspecific trait shifts resulted in convergence towards intermediate SLA in diverse communities; although convergence was reduced by nitrogen addition and enhanced by pathogen removal. In contrast, large intraspecific shifts in LDMC were not influenced by the treatments. However, despite large responses, intraspecific trait shifts had no effect on above‐ or below‐ground biomass. Only interspecific trait variation affected functioning: below‐ground biomass was reduced by SLA and increased by LDMC, while above‐ground biomass was increased by SLA.
Synthesis. Our results add to a growing body of literature showing large intraspecific trait variation and emphasise the importance of using field collected data to determine community functional composition. However, they also show that intraspecific variation does not necessarily affect ecosystem functioning and therefore response–effect trait relationships may differ between versus within species.
Résumé
Les traits fonctionnels des plantes aident à comprendre les mécanismes qui régissent les réponses des communautés aux changements globaux, ainsi que les effets de ces communautés sur les fonctions écosystémiques. L'enrichissement en azote modifie généralement la composition des traits en favorisant la dominance des plantes acquisitives (surface foliaire spécifique SLA élevée et faible teneur en matière sèche foliaire LDMC), ce qui se traduit par une production élevée de biomasse. Les changements des valeurs moyennes des traits peuvent être dus à l'identité des espèces, aux abondances relatives et/ou aux valeurs des traits intraspécifiques. Cependant, nous ne connaissons pas l'importance relative de ces variations dans la réponse des traits aux changements environnementaux, ni dans les effets des traits sur les fonctions écosystémiques, comme la production de biomasse.
Nous avons quantifié l'importance relative de la composition des espèces, de l'abondance et des changements intraspécifiques dans la variation de la SLA et de la LDMC, et testé comment ces changements affectent la biomasse aérienne et souterraine. Nous avons mesuré ces traits dans une prairie où nous avons mené une expérience manipulant la fertilisation azotée, le nombre d’espèces de plantes, l'élimination des pathogènes foliaires fongiques et la composition fonctionnelle des plantes (espèces lentes vs rapides). À l’aide de modèles d'équations structurelles, nous avons testé l'importance de l'abondance et des changements intraspécifiques dans la détermination 1) des réponses de la composition fonctionnelle aux traitements et 2) des effets sur la biomasse aérienne et souterraine.
Nous avons constaté que les changements intraspécifiques des espèces étaient aussi importants que les changements en abondance pour déterminer la composition fonctionnelle (valeurs moyennes pondérées des traits de la communauté), et qu'ils avaient même des effets importants par rapport à une grande variation initiale en composition des traits. Les changements intraspécifiques ont entraîné une convergence vers une SLA intermédiaire dans les communautés riches en espèces, et cette convergence a été réduite par l'ajout d'azote et renforcée par l’application de fongicide. Ces traitements n'ont pas eu d'incidence sur les variations intraspécifiques de la LDMC. Cependant, malgré des réponses importantes, les variations intraspécifiques n'ont eu aucun effet sur la biomasse aérienne ou souterraine. Seule la variation interspécifique a eu un effet: la biomasse souterraine a diminué avec la SLA et a augmenté avec la LDMC, tandis que la biomasse aérienne a augmenté avec la SLA.
Nos résultats s'ajoutent à un nombre croissant de publications montrant une grande variation intraspécifique des traits des espèces, et soulignent l'importance d'utiliser des données collectées sur le terrain pour déterminer la composition fonctionnelle des communautés. Cependant, ils montrent également que la variation intraspécifique n'affecte pas nécessairement le fonctionnement de l'écosystème et que, par conséquent, les relations réponse‐effet des traits peuvent différer entre les espèces et au sein d'une même espèce.
Our results add to a growing body of literature showing large intraspecific trait variation and emphasise the importance of using field collected data to determine community functional composition. However, they also show that intraspecific variation does not necessarily affect ecosystem functioning and therefore response–effect trait relationships may differ between versus within species.
Biodiversity effects on ecosystem functioning can be partitioned into complementarity effects, driven by many species, and selection effects, driven by few. Selection effects occur through ...interspecific abundance shifts (dominance) and intraspecific shifts in functioning. Complementarity and selection effects are often calculated for biomass, but very rarely for secondary productivity, that is, energy transfer to higher trophic levels. We calculated diversity effects for three functions: aboveground biomass, insect herbivory and pathogen infection, the latter two as proxies for energy transfer to higher trophic levels, in a grassland experiment (PaNDiv) manipulating species richness, functional composition, nitrogen enrichment, and fungicide treatment. Complementarity effects were, on average, positive and selection effects negative for biomass production and pathogen infection and multiple species contributed to diversity effects in mixtures. Diversity effects were, on average, less pronounced for herbivory. Diversity effects for the three functions were not correlated, because different species drove the different effects. Benefits (and costs) from growing in diverse communities, be it reduced herbivore or pathogen damage or increased productivity either due to abundance increases or increased productivity per area were distributed across different plant species, leading to highly variable contributions of single species to effects of diversity on different functions. These results show that different underlying ecological mechanisms can result in similar overall diversity effects across functions.
Effects of plant diversity on grassland productivity, or overyielding, are found to be robust to nutrient enrichment. However, the impact of cumulative nitrogen (N) addition (total N added over time) ...on overyielding and its drivers are underexplored. Synthesizing data from 15 multi-year grassland biodiversity experiments with N addition, we found that N addition decreases complementarity effects and increases selection effects proportionately, resulting in no overall change in overyielding regardless of N addition rate. However, we observed a convex relationship between overyielding and cumulative N addition, driven by a shift from complementarity to selection effects. This shift suggests diminishing positive interactions and an increasing contribution of a few dominant species with increasing N accumulation. Recognizing the importance of cumulative N addition is vital for understanding its impacts on grassland overyielding, contributing essential insights for biodiversity conservation and ecosystem resilience in the face of increasing N deposition.
An experiment was performed in the DIII-D lower divertor to validate numerical SOL tungsten (W) impurity erosion and redeposition simulations against experimental data. The net and gross erosion of W ...were calculated as a function of the voltage (or bias) applied to the exposed material. Five samples were inserted into the DIII-D lower divertor using the Divertor Material Evaluation System (DiMES) manipulator and exposed to constant L-mode attached plasma conditions. Each sample was partially coated with W. During plasma shots, samples were biased with respect to the machine vessel ground, ranging from −60 V to 25 V. The ERO2.0 code was used to numerically simulate the experiment aiming to compare the numerical results with experimental measures. A good agreement is found between estimated and measured tungsten erosion at least for negative biases.
•The surface electric potential of an exposed material affects its erosion rate.•W targets were inserted in the lower divertor of DIII-D and exposed to plasma.•Net and gross erosion were experimentally measured with RBS and UV spectrometer.•Measurements were compared with numerical results obtained with ERO2.0.
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