Background and aims In Australia's Mediterranean hyperdiverse vegetation, species that produce cluster roots to mobilise poorly-available nutrients (e.g. Banksia spp.) are an important functional and ...structural component. Cluster roots are only active during the wet season, indicating a strong dependence on suitable surface soil moisture conditions. Winter rainfall in this region is declining due to global climate change, with a delayed commencement of rains and a decline in precipitation. It is unknown how lower soil moisture levels will affect the root dynamics of these globally-significant plant communities. Methods We determined the root dynamics and root lifespan with minirhizotrons with or without irrigation to simulate reduced rainfall scenarios. Results We found a major effect of irrigation on the early production (0.24 m m−2 d−1 increase), occurrence (97% increase) of cluster roots and only slight effects on lifespan (∼10 days less) of all root types. With irrigation, the resultant greater soil moisture levels increased the deployment of cluster roots. Apart from cluster roots, the dynamics of other roots did not decline at lower soil moisture levels, suggesting that this system shows some resilience to decreased rainfall. Conclusions Future research should focus on assessing if climate-altered cluster-root activity may be promoting compositional shifts in plant communities with additional restraining effects on root trait diversity.
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BFBNIB, DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NMLJ, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
► Snow damage following fire is a self-thinning agent in dense pine stands. ► Thinning and fertilization place valuable dominant trees at risk of snow damage. ► Crown shape and asymmetry were only ...important predictors after thinning and fertilization. ► Models predicted smaller trees were more susceptible to damage in the unthinned stands. ► Thinning and fertilization promoted damage to larger but slender trees with asymmetrical crowns.
Several heavy wet snowfalls occurred during 2007–2009 across a broad-scale thinning and fertilization experiment to bring overstocked juvenile lodgepole pine (
Pinus contorta var.
latifolia) in the foothills of Alberta, Canada into an intensive management regime. We examined the bending and breakage of trees in relation to thinning and fertilization and used a multimodel information-theoretic approach to model stand and tree level predictors of snow damage. Fertilized stands suffered the greatest amount of snow damage, and this was most noteworthy when stands were also thinned; here 22% (17% broken stems) of trees were damaged compared to 8% (4% broken stems) in the thinned and unfertilized stands. At the stand level, needle weight and crown cover were reliable predictors of snow damage. At the tree level, separate models were developed for each combination of thinning and fertilization. All models used total tree volume; usually the smaller trees in the stands were more susceptible to damage but in the thinned and fertilized stands larger but slender trees with large asymmetrical crowns tended to be damaged. Also, trees with lower total stem volume were more susceptible to damage. Only in the thinned and fertilized stands were variables related to crown shape and asymmetry important predictors of snow damage. We conclude that snow damage is an important agent for self-thinning in unthinned stands and fertilization tends to exacerbate damage because of increase in foliage size. In areas with regular occurrence of heavy snow, we do not recommend fertilization at the same time as thinning, as the larger and more economically important trees in the stand are at risk.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Since the signature of the ITER treaty in 2006, a new research programme targeting the emergence of a new generation of neutral beam (NB) system for the future fusion reactor (DEMO Tokamak) has been ...underway between several laboratories in Europe. The specifications required to operate a NB system on DEMO are very demanding: the system has to provide plasma heating, current drive and plasma control at a very high level of power (up to 150 MW) and energy (1 or 2 MeV), including high performances in term of wall-plug efficiency (η > 60%), high availability and reliability. To this aim, a novel NB concept based on the photodetachment of the energetic negative ion beam is under study. The keystone of this new concept is the achievement of a photoneutralizer where a high power photon flux (~3 MW) generated within a Fabry-Perot cavity will overlap, cross and partially photodetach the intense negative ion beam accelerated at high energy (1 or 2 MeV). The aspect ratio of the beam-line (source, accelerator, etc) is specifically designed to maximize the overlap of the photon beam with the ion beam. It is shown that such a photoneutralized based NB system would have the capability to provide several tens of MW of D0 per beam line with a wall-plug efficiency higher than 60%. A feasibility study of the concept has been launched between different laboratories to address the different physics aspects, i.e. negative ion source, plasma modelling, ion accelerator simulation, photoneutralization and high voltage holding under vacuum. The paper describes the present status of the project and the main achievements of the developments in laboratories.
Development of soil microbial communities is driven by local abiotic and biotic conditions, yet our current understanding of their ecology is limited to studies in modified or young and relatively ...fertile ecosystems. In nutrient-impoverished soils, microbial communities may be predominantly structured by availability of key elements such as phosphorus (P) or nitrogen, regardless of the taxa (bacteria, archaea or fungi). Here, we determined if shifts in bacterial communities and biomass occurred along a long-term soil chronosequence in south-western Australia, and whether such shifts were related to changes in soil nutrient availability along the retrogressive phase of this chronosequence. We quantified shifts in the biomass and abundance of major soil microbial groups using phospholipid fatty acids and quantitative polymerase chain reaction. We found that declining soil P availability limited microbial growth and community structure. Common cations, notably magnesium, showed strong relationships with the abundance of most bacterial and archaeal taxa. In the oldest most severely impoverished soils, the fungal to bacteria ratio was higher than in the young soils, indicating fungi are better adapted to such environments. Finally, archaeal copy numbers decreased more strongly than bacterial copy numbers with increasing nutrient-impoverishment of soils. The study enhances our understanding of the ecology of soil bacteria, archaea, and fungi during ecosystem development and retrogression.
•Declining soil phosphorus (P) availability appeared to limit microbial growth and abundance.•Common cations, particularly magnesium, appeared important for the abundance of most bacterial and archaeal taxa.•Our data suggest that fungi are likely better adapted to severely nutrient-impoverished soils than bacteria are.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Premise of the study: Seed banks are important for the natural regeneration of many forest species. Most of the seed bank of serotinous lodgepole pine is found in the canopy, but after an outbreak of ...mountain pine beetle (MPB), a considerable forestfloor seed bank develops through the falling of canopy cones. After large-scale mortality of pine stands from MPB, however, the viability of seeds in both the canopy and the forest-floor cone bank is uncertain. Methods: We sampled cones in five stands 3 yr after MPB (3y-MPB); five stands 6 yr after MPB (6y-MPB); and 10 stands 9 yr after MPB (9y-MPB), in central British Columbia, Canada. Seeds were extracted and viability tested using germination techniques. Key results: Forest-floor cones had seed with high germination capacity (GC): 82% for embedded (partly buried) closed cones vs. 45% for buried partly open cones. For canopy cones, GC steeply declined about 15 yr after cone maturation and by 25 yr, GC was 50%, compared with 98% in the first year. In the 3y-and 6y-MPB stands, seeds from cones that were 7 to 9 yr old had similar GC on dead and living trees; however, seeds from the dead trees had lower vigor than seeds from living trees. Conclusions: We demonstrate for the first time that a serotinous pine can form a viable soil seed bank by cone burial, which may facilitate natural regeneration if a secondary disturbance occurs. Seeds contained in 15-yr-old cones showed a steep decline in viability, which could limit regeneration if there is a long delay before a secondary disturbance.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NMLJ, NUK, OILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
We conducted greenhouse experiments using Douglas-fir (Pseudotsuga menziesii var. glauca) seedlings where chemical methods (fungicides) were used to prevent ectomycorrhizal colonization of single ...seedlings or physical methods (mesh barriers) were used to prevent formation of mycorrhizal connections between neighboring seedlings. These methods were chosen for their ease of application in the field. We applied the fungicides, Topas® (nonspecific) and Senator® (ascomycete specific), separately and in combination at different concentrations and application frequencies to seedlings grown in unsterilized forest soils. Additionally, we assessed the ability of hyphae to penetrate mesh barriers of various pore sizes (0.2, 1, 20, and 500 μm) to form mycorrhizas on roots of neighboring seedlings. Ectomycorrhizal colonization was reduced by approximately 55% with the application of Topas® at 0.5 g l-¹. Meshes with pore sizes of 0.2 and 1 μm were effective in preventing the formation of mycorrhizas via hyphal growth across the mesh barriers. Hence, meshes in this range of pore sizes could also be used to prevent the formation of common mycorrhizal networks in the field. Depending on the ecological question of interest, Topas® or the employment of mesh with pore sizes <1 μm are suitable for restricting mycorrhization in the field.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Aims
Plant–soil feedback (PSF) is an important mechanism controlling plant growth, vegetation dynamics, and longer-term and larger-scale patterns of plant community diversity. We know that feedback ...between plants and soil biota depends on several external factors, such as nutrient and water availability, and interactions with neighbouring plants. We argue that in the ‘real world’, PSF are not working in isolation but instead proceed within a complex context of multiple interacting factors. Fire is one of those complex external factors which could greatly alter PSF by re-setting or re-directing plant-soil biota interactions.
Methods
We reviewed key literature on the effects of fire on soil biota and soil physicochemical properties with soil depth, to generate predictions on the complex effects of fire on PSF.
Results
We highlight that fire has strong potential to directly and indirectly affect the strength of PSF. To what extent this influences longer-term plant community trajectories depends on the interactions between fire characteristics and ecosystem type. Here, we conceptualized these effects of fire on soil properties and biota, and then discuss the main pathways through which fire should alter PSF.
Conclusions
We think that PSF processes should be nullified under and after fire. Average neutral PSF responses are expected to be more common in the short-term or within the timeframe required for major soil microbial players to regain their pre-fire abundances and diversity. We conclude by providing directions for future research and possible methods to study fire effects on PSF both in the field and under controlled conditions.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Mycorrhizal fungi enhance plant phosphorus (P) acquisition via their extraradical hyphae (ERH) that scavenge nutrients outside root depletion zones. While soil P availability declines during ...ecosystem retrogression, how ERH biomass and scavenging vary during ecosystem retrogression remains unknown; it is expected to increase if plants allocate more carbon (C) to mycorrhizal fungi as P availability declines. We measured fungal and bacterial biomass using in-growth cores and lipid biomarkers along a 2-million-year dune chronosequence in an Australian biodiversity hotspot showing a ∼60-fold decline in total soil P concentration with increasing soil age. We compared the levels of key fungal biomarkers (ergosterol, NLFA 16:1ω5, and PLFA 18:2ω6,9) between closed, mesh, and open cores during five months (four sampling dates including the wet winter months), thus allowing us to also determine the dynamics of mycorrhizal fungal scavenging. We found strikingly low and declining biomass of ERH with declining P availability, with minimal long-distance scavenging by ERH. Biomass of ERH was highest in the younger (c. 1 ka) soils that were comparatively rich in P and other nutrients. By contrast, the oldest, most P-impoverished soils had the lowest biomass of ERH, despite high mycorrhizal root colonisation, and high abundance and diversity of potential plant hosts. We show that extremely low P availability constrains ERH biomass. Such low mycorrhizal fungal biomass highlights the need for a more ‘mycocentric’ view of plant–mycorrhizal relationships in old, severely P-impoverished ecosystems.
•Low soil phosphorus (P) availability appears to limit biomass of soil biota.•Mycorrhizal scavenging is driven by nutrient availability and soil age.•A ‘mycocentric’ view of plant–soil relationships in P-impoverished ecosystems is needed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Abstract
During lightning strikes to aircraft, there is a displacement of the impacted area on the aircraft’s surface and the dynamic of the arc root is a key to understanding and predicting the ...damage produced on the aircraft skin. This work aims at studying experimentally this dynamic with a new method of producing sweeping arcs based on a stationary arc and an electromagnetic launcher propelling aeronautical test samples. The experiments are also achieved with a wind tunnel that blows the arc on the test sample for comparison. After a description of the previous experiments of arc root displacement and a distinction between the cathodic and anodic emission processes, this paper characterizes the arc root physical properties with direct visualization through high-speed cameras and electric measurements for different initial conditions. The results are separated by the arc root polarity and discussed to give an insight into the influence of the experimental conditions on the interaction between the electric arc root and the test sample during swept-stroke. It is shown that for a cathodic arc root, the nature of the displacement—continuous or jumping—highly depends on the current level and the speed of the relative motion between the electric arc and the test sample. For an anodic arc roots, the variations of these parameters provoke jumping modes of displacement with different characteristics.
The importance of mycorrhizal network (MN)-mediated colonization under field conditions between trees and seedlings was investigated. We also determined the combined influences of inoculum source and ...distance from trees on the ectomycorrhizal (EM) community of seedlings. On six sites, we established trenched plots around 24 residual
Pseudotsuga menziesii var.
glauca trees and then planted seedlings at four distances (0.5, 1.0, 2.5, and 5.0
m) from the tree into four mesh treatments that served to restrict inoculum access (i.e., planted into mesh bags with 0.5, 35, 250
μm pores or directly into soil). Ectomycorrhizal communities were identified after two growing seasons using morphological and molecular techniques. Mesh treatments had no effect on seedling mycorrhizal colonization, richness, or diversity, suggesting that MN-mediated colonization, was not an essential mechanism by which EM communities were perpetuated to seedlings. Instead, wind-borne and soil inoculum played an important role in seedling colonization. The potential for MNs to form in these forests was not dismissed, however, because trees and seedlings shared 83
% of the abundant EM. Seedlings furthest from trees had a simpler EM community composition and reduced EM richness and diversity compared to seedlings in closer proximity.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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