Cyanobacteria occur worldwide but play an important role in the formation and primary activity of biological soil crusts (BSCs) in arid and semi-arid ecosystems. The cyanobacterial diversity in BSCs ...of the northwest Negev desert of Israel was surveyed at three fixed sampling stations situated along a precipitation gradient in the years 2010 to 2012. The three stations also are characterized by marked differences in soil features such as soil carbon, nitrogen, or electrical conductivity. The cyanobacterial biodiversity was analyzed by sequencing inserts of clone libraries harboring partial 16S rRNA gene sequences obtained with cyanobacteria-specific primers. Filamentous, non-diazotrophic strains (subsection III), particularly Microcoleuslike, dominated the cyanobacterial community (30 % proportion) in all years. Specific cyanobacterial groups showed increased (e.g., Chroococcidiopsis, Leptolyngbya, and Nostoc strains) or decreased (e.g., unicellular strains belonging to the subsection I and Scytonema strains) abundances with declining water availability at the most arid, southern station, whereas many cyanobacterial strains were frequently found in the soils of all three stations. The cyanobacterial diversity at the three sampling stations appears dependent on the available precipitation, whereas the differences in soil chemistry were of lower importance.
Biological soil crusts (BSCs) fulfil numerous ecological functions in arid and semiarid areas. Cyanobacteria are important BSC organisms, which are responsible for carbon fixation, N2 fixation and ...binding of soil via extracellular polysaccharides. The cyanobacterial populations were characterised in different sampling plots established in three experimental stations along a rainfall gradient within NW Negev Desert, Israel. Cyanobacterial crust thickness and osmolyte accumulation therein decreased in plots with lower moisture. The cyanobacterial population structure also changed in different plots. We observed an increase of subsection III cyanobacteria such as Microcoleus spp. and Leptolyngbya spp. and a decreasing proportion of strains belonging to subsections I and IV in drier areas on the rainfall gradient. This population shift was also observed in the sampling plots, which were situated at various relief positions within the sand dune experimental sites. We also characterised the cyanobacterial populations within mechanically disturbed plots. After 4 years, they reached between 80% and 50% of the control populations in the northernmost and southern stations, respectively. Our results suggest that the cyanobacterial population is sensitive not only to macroscale factors but may also be subject to local climate variations and that 4 years was insufficient for complete recovery of the cyanobacterial population.
Under continuous human disturbance, regeneration is the basis for biodiversity persistence and ecosystem service provision. In tropical dry forests, edaphic ecosystem engineering by biological soil ...crusts (biocrusts) could impact regeneration by influencing erosion control and soil water and nutrient fluxes, which impact landscape hydrology, geomorphology, and ecosystem functioning. This study investigated the effect of cyanobacteria-dominated biocrusts on water infiltration and aggregate stability in a human-modified landscape of the Caatinga dry forest (NE Brazil), a system characterized by high levels of forest degradation and increasing aridity. By trapping dust and swelling of cyanobacterial filaments, biocrusts can seal soil surfaces and slow down infiltration, which potentially induces erosion. To quantify hydraulic properties and erosion control, we used minidisc-infiltrometry, raindrop-simulation, and wet sieving at two sites with contrasting disturbance levels: an active cashew plantation and an abandoned field experiencing forest regeneration, both characterized by sandy soils. Under disturbance, biocrusts had a stronger negative impact on infiltration (reduction by 42% vs. 37% during regeneration), although biocrusts under regenerating conditions had the lowest absolute sorptivity (0.042 ± 0.02 cm s
) and unsaturated hydraulic conductivity (0.0015 ± 0.0008 cm s
), with a doubled water repellency. Biocrusts provided high soil aggregate stability although stability increased considerably with progression of biocrust succession (raindrop simulation disturbed: 0.19 ± 0.22 J vs. regenerating: 0.54 ± 0.22 J). The formation of stable aggregates by early successional biocrusts on sandy soils suggests protection of dry forest soils even on the worst land use/soil degradation scenario with a high soil erosion risk. Our results confirm that biocrusts covering bare interspaces between vascular plants in human-modified landscapes play an important role in surface water availability and erosion control. Biocrusts have the potential to reduce land degradation, but their associated ecosystem services like erosion protection, can be impaired by disturbance. Considering an average biocrust coverage of 8.1% of the Caatinga landscapes, further research should aim to quantify the contribution of biocrusts to forest recovery to fully understand the role they play in the functioning of this poorly explored ecosystem.
Biocrusts are biological communities that occupy the soil surface, accumulate organic matter and mineral particles and hence strongly affect the properties of the soils they cover. Moreover, by ...affecting water repellency, biocrusts may cause a preferential infiltration of rainwater, with a high impact on the formation of local water pathways, especially for sand dunes. The aim of this study is to shed light on the connections between water repellency and pH, carbonate and organic matter content in two dune ecosystems with different biocrust types. For this, we used contact angle measurements, gas volumetric carbonate determination and organic matter characterization via FT-IR and TOF-SIMS. In both ecosystems, moss-dominated biocrusts showed higher water repellency and higher amounts of organic matter compared to algal or cyanobacterial biocrusts. Surprisingly, the biocrusts of the two dune systems did not show differences in organic matter composition or organic coatings of the mineral grains. Biocrusts on the more acidic dunes showed a significantly higher level of water repellency as compared to higher carbonate containing dunes. We conclude that the driving factor for the increase in water repellency between cyanobacterial and moss-dominated biocrusts within one study site is the content of organic matter. However, when comparing the different study sites, we found that higher amounts of carbonate reduced biocrust water repellency.
Characterization of the Hamamatsu R11780 12 in. photomultiplier tube Brack, J.; Delgado, B.; Dhooghe, J. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
06/2013, Letnik:
712, Številka:
C
Journal Article
Recenzirano
Odprti dostop
Future large water Cherenkov and scintillator detectors have been proposed for measurements of long baseline neutrino oscillations, proton decay, supernova and solar neutrinos. To ensure ...cost-effectiveness and optimize scientific reach, one of the critical requirements for such detectors are large-area, high performance photomultiplier tubes (PMTs). One candidate for such a device is the Hamamatsu R11780, a 12 in. PMT that is available in both standard and high quantum efficiency versions. Measurements of the single photoelectron response characteristics, relative efficiencies of the standard and high quantum efficiency versions, a preliminary measurement of the absolute quantum efficiency of the standard quantum efficiency version, and a two-dimensional scan of the relative efficiency across the photocathode surface are presented in this paper. All single photoelectron investigations were made using a Cherenkov light source at room temperature at a gain of 1×107. These results show that the R11780 PMT is an excellent candidate for such large optical detectors.
Summary
Desert biological soil crusts (BSCs) are formed by adhesion of soil particles to polysaccharides excreted by filamentous cyanobacteria, the pioneers and main producers in this habitat. ...Biological soil crust destruction is a central factor leading to land degradation and desertification. We study the effect of BSC structure on cyanobacterial activity. Micro‐scale structural analysis using X‐ray microtomography revealed a vesiculated layer 1.5–2.5 mm beneath the surface in close proximity to the cyanobacterial location. Light profiles showed attenuation with depth of 1%–5% of surface light within 1 mm but also revealed the presence of ‘light pockets’, coinciding with the vesiculated layer, where the irradiance was 10‐fold higher than adjacent crust parts at the same depth. Maximal photosynthetic activity, examined by O2 concentration profiles, was observed 1 mm beneath the surface and another peak in association with the ‘light pockets’. Thus, photosynthetic activity may not be visible to currently used remote sensing techniques, suggesting that BSCs' contribution to terrestrial productivity is underestimated. Exposure to irradiance higher than 10% full sunlight diminished chlorophyll fluorescence, whereas O2 evolution and CO2 uptake rose, indicating that fluorescence did not reflect cyanobacterial photosynthetic activity. Our data also indicate that although resistant to high illumination, the BSC‐inhabiting cyanobacteria function as ‘low‐light adapted’ organisms.
One of the most prominent changes in the rhizospheric soil structure is associated with the formation of a strongly bound soil layer in the surroundings of the root, which is named rhizosheath. In ...this study, we investigated how root hair elongation, a ubiquitous root morphological trait, affect the stability of rhizosheath aggregates. Using
13
CO
2
pulse labeling, we tracked the fate of root-derived
13
C inputted into the rhizosheath of two
Zea mays
L. genotypes with contrasting root hair elongation: a mutant with root hair defective elongation (
rth3
) and a corresponding wild type (WT). In addition, we also investigated the differences between two
13
CO
2
labeling approaches (single vs. multiple pulse labeling) in the distribution of
13
C in the rhizosheath aggregates. We were able to demonstrate that the rhizosheath aggregate stability and the resulting aggregate size distribution follows the same mechanisms irrespective of the root hair elongation. This result reinforces the assumption that other soil properties are more decisive for the soil structure formation in the rhizosheath in comparison to root hair elongation. The majority of recently deposited root-derived C (57%) was found in the macroaggregates. Increasing the number of pulses (multiple pulse labeling approach) resulted in a higher
13
C enrichment of the rhizosheath aggregates fractions in comparison to the application of a single pulse. While both labeling approaches resulted in a similar distribution of
13
C in the rhizosheath aggregates, the higher enrichment given by multiple pulse labeling allowed the separation of significant differences between the genotypes in plant C allocation in the rhizosheath.
Developing a new waterborne logistics service based on a possibly higher number of transshipment points, smaller barges, and different transshipment techniques as a competitive alternative to ...existing road-borne transportation services requires an intelligent design of the network. The identification of such (not fully known) potential decentralized transshipment points poses a challenge which, however, is hardly covered in research literature. Mostly, the underlying network with the possible nodes and arcs are already known when starting to develop a new transportation service. It is of high relevance because the economic viability of a logistics concept can be influenced by adding or dropping the number of transshipment points.The present paper presents the use case from the West German canal system where all points of interest have been recorded in a database. With the help of the collected data, various examinations and comparisons can be conducted before eventually selecting a subset of relevant points of interest and examine different scenarios. The presented methodology acts as a blueprint and can be extended to further types of points of interest and other geographical areas.
The advance of efficient hydrogen-air combustion systems has increasingly become of interest in the framework of the development of fuel cell systems, especially for the automotive sector. Therefore, ...compact modulating systems are required, with the additional demand of low emissions, to be integrated in a fuel cell system. A modulating combustion system based on combustion within inert porous media and an integrated heat exchanger has been developed and investigated. The system is able to handle premixed combustion of lean H
2/air mixtures at a surface load range of 1075 kW/m
2–2150 kW/m
2, and a global equivalence ratio of
ϕ
=
0.5
. The special hydrogen-air mixing concept eliminates the risk of flame flashback and enables operation with very low NO
x emissions.
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