Resolving colocalization of bacteria and metal(loid)s on plant root surfaces by combining fluorescence in situ hybridization (FISH) with multiple-energy micro-focused X-ray fluorescence (ME μXRF)

Metal(loid)-contamination of the environment due to anthropogenic activities is a global problem. Understanding the fate of contaminants requires elucidation of biotic and abiotic factors that influence metal(loid) speciation from molecular to field scales. Improved methods are needed to assess micro-scale processes, such as those occurring at biogeochemical interfaces between plant tissues, microbial cells, and metal(loid)s. Here we present an advanced method that combines fluorescence in situ hybridization (FISH) with synchrotron-based multiple-energy micro-focused X-ray fluorescence microprobe imaging (ME pXRF) to examine colocalization of bacteria and metal(loid)s on root surfaces of plants used to phytostabilize metalliferous mine tailings. Bacteria were visualized on a small root section using SytoBC nucleic acid stain and FISH probes targeting the domain Bacteria and a specific group (Alphaproteobacteria, Gammaproteobacteria, or Actinobacteria). The same root region was then analyzed for elemental distribution and metal(loid) speciation of As and Fe using ME pXRF. The FISH and ME pXRF images were aligned using Image.' software to correlate microbiological and geochemical results. Results from quantitative analysis of colocalization show a significantly higher fraction of As colocalized with Fe-oxide plaques on the root surfaces (fraction of overlap 0.49 +/- 0.19) than to bacteria (0.072 +/- 0.052) (p < 0.05). Of the bacteria that colocalized with metal(loid)s, Actinobacteria, known for their metal tolerance, had a higher correlation with both As and Fe than Alphaproteobacteria or Gammaproteobacteria. This method demonstrates how coupling these micro-techniques can expand our understanding of micro-scale interactions between roots, metal(loid)s and microbes, information that should lead to improved mechanistic models of metal(loid) speciation and fate. (C) 2016 Elsevier B.V. All rights reserved.National Institute of Environmental Health Sciences (NIEHS) Superfund Research Program (SRP) [P42 ES04940, R01 ES1709]; National Science Foundation Graduate Research Fellowhip Program (NSF GRFP) [DGE-1143953]; U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences [DE-AC02-765F00515]12 month embargo; published online: 29 September 2016This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Bacterial Rhizoplane Colonization Patterns of Buchloe dactyloides Growing in Metalliferous Mine Tailings Reflect Plant Status and Biogeochemical Conditions

Plant establishment during phytostabilization of legacy mine tailings in semiarid regions is challenging due to low pH, low organic carbon, low nutrients, and high toxic metal(loid) concentrations. Plant-associated bacterial communities are particularly important under these harsh conditions because of their beneficial services to plants. We hypothesize that bacterial colonization profiles on rhizoplane surfaces reflect deterministic processes that are governed by plant health and the root environment. The aim of this study was to identify associations between bacterial colonization patterns on buffalo grass (Buchloe dactyloides) rhizoplanes and both plant status (leaf chlorophyll and plant cover) and substrate biogeochemistry (pH, electrical conductivity, total organic carbon, total nitrogen, and rhizosphere microbial community). Buffalo grass plants from mesocosm- and field-scale phytostabilization trials conducted with tailings from the Iron King Mine and Humboldt Smelter Superfund Site in Dewey-Humboldt, Arizona, were analyzed. These tailings are extremely acidic and have arsenic and lead concentrations of 2-4 g kg-1 substrate. Bacterial communities on rhizoplanes and in rhizosphere-associated substrate were characterized using fluorescence in situ hybridization and 16S rRNA gene amplicon sequencing, respectively. The results indicated that the metabolic status of rhizoplane bacterial colonizers is significantly related to plant health. Principal component analysis revealed that root-surface Alphaproteobacteria relative abundance was associated most strongly with substrate pH and Gammaproteobacteria relative abundance associated strongly with substrate pH and plant cover. These factors also affected the phylogenetic profiles of the associated rhizosphere communities. In summary, rhizoplane bacterial colonization patterns are plant specific and influenced by plant status and rhizosphere biogeochemical conditions.National Institute of Environmental and Health Sciences (NIEHS) Superfund Research Program (SRP) [P42 ES004940, R01 ES01709]; National Science Foundation Graduate Research Fellowhip Program (NSF GRFP) [DGE-1143953]12 month embargo; published online: 2 June 2017This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Magnetization of coupled spin clusters in Ladder Geometry

In this paper, we construct a class of spin-1/2 antiferromagnetic (AFM) two-chain ladder models consisting of blocks of n-spin tetrahedral clusters alternating with two-spin rungs. For n=4 and 6 and in extended parameter regimes, the exact ground state of the ladder is shown to be a product of the ground states of the rungs and the n-spin blocks, in both zero and finite magnetic fields. In the latter case, magnetization/site (m) versus magenetic field (h) plot exhibits well-defined magnetization plateaus.Comment: 9 pages, latex, 6 figures, To be published in Phys. Rev.

Hygrothermal impact of adhesive-applied rooftop photovoltaic system

Adhesive mounting of photovoltaic (PV) modules on residential roofs can significantly reduce the installed cost. The potential for undesirable moisture buildup under the module, however, may reduce shingle life and degrade the underlying roof elements. High moisture levels in roof elements may also adversely affect the energy performance of the building. This study investigates whether an adhesively mounted PV system causes a preferential moisture buildup under the module on an asphalt shingle roof. Lightweight PV modules were adhesively mounted on half of the roof of an instrumented test hut located in Boston, MA. Moisture pin sensors, installed in various locations of the roof deck, determined the moisture content (MC) of the wood in the roof assembly. The MC is found to follow a seasonal pattern: lower values (7-11 %) during the summer and higher values (11-15 %) during the winter. MC measurements during the winter and summer seasons showed no adverse impact of the adhesive-mounted rooftop PVs on the hygrothermal behavior of the underlying roof deck element over the 1-year measurement period

Root Metabolic Responses to Drought Drive Plant-Microbe Interactions in the Rhizosphere

t the interface of plant-soil-microbe interactions lies the rhizosphere, a narrow zone surrounding roots rich in metabolic activity and nutrient cycling. As climate warming and its accompanying water scarcity increases in both frequency and duration, it is unknown how plant-mediated processes such as root exudation will alter and influence soil organic matter composition in the rhizosphere. Here we integrated 16S rRNA gene amplicon sequencing for microbial community analysis, high-resolution organic matter measurements for meta-metabolome characterization, and position-specific 13C-pyruvate labeling to track carbon allocation pathways to fully characterize how microbes and species-specific plant roots influence rhizosphere soil organic carbon turnover. In situ metabolic and microbial rhizosphere profiles of three plant species, Piper auritum, Hibiscus rosa sinensis, and Clitoria fairchildiana revealed drastically different drought-response mechanisms, enhancing our understanding of niche rhizosphere dynamics. Overall, drought conditions intensified the exclusion of phylogenetically distant microbes, sufficiently conserved microbial functional traits, and decreased microbial heterogeneity across roots of all plant species. Yet, individual host rhizosphere profiles responded differently; P. auritum decreased root exudation into the rhizosphere indicating a decreased dependence on surrounding microbes. Meanwhile, H. rosa sinensis and C. fairchildiana responded aptly to water stress through modulating their exudate metabolic composition and, therefore, rhizosphere microbial communities. Our results revealed how plant species-specific microbial interactions systematically progressed with the root metabolome; as roots responded to drought, their associated microbial communities adapted, potentially supplementing drought tolerance strategies for plant roots. These findings have significant implications for maintaining plant health during drought stress and improving plant performance for climate change mitigation in both natural systems and agriculture

Residential solar systems as an appliance - Plug and Play PV

The DOE SunShot-funded Plug and Play PV project seeks to dramatically reduce the soft costs of US residential solar by simplying the installation and commissioning processes. Adhesive mounting of lightweight (frame-less, glass-less) modules is one technology being studied. Temperature concerns due to the small gap between the shingled roof and the adhered module are examined in field testing in Albuquerque, NM. Compared to a conventional module, a 3% yield loss was measured after one year of data collection. The temperature of shingles underneath the adhered modules are lower than those for exposed shingles indicating that the modules cool the roof during sunlight hours. Modeling of the attic thermal profile demonstrates an average drop in the attic air temperature of 1°C in hot climates

Thermal impact of adhesive-mounted rooftop PV on underlying roof shingles

Adhesive mounting of residential rooftop photovoltaics (PV) is an alternative to traditional rack mounting that reduces installation costs. Adhesive mounting is fast, simple and reduces the need for skilled labor. In our novel design that further reduces the installation costs, a lightweight (glassless and frameless) PV module is directly adhered to a shingled roof using an adhesive tape, creating a <5 mm air gap between the PV back-panel and the roof shingle surface. Although the gap is sufficient for moisture and rainwater transport under the PV panel, potential heat buildup under the module may adversely impact the long-term durability of the shingles. Heat buildup may also increase the heat flux through the roof, resulting in an overall increase in building cooling loads. This study investigates the thermal behavior of the roof under an adhered PV system. Two identical test huts with dark shingle-covered roofs were located in the hot, desert climate of Albuquerque, NM. Adhesively-mounted lightweight PV modules were installed on the south-facing roof of one of the test huts (PV hut), with the other one serving as a reference hut. During the summer season, the asphalt roof shingles under the PV modules experienced a 13 °C reduction in daytime peak temperature compared with the exposed shingles. No evidence of heat buildup under the PV module was observed. It was also found that the temperature of shingles underneath the adhesive was up to 6 °C higher than for shingles underneath the gap space at the daily peak time. Thin but ventilated air gap between the PV back-panel and the roof shingles helped remove the heat, while the adhesive pads (patches) served as thermal bridges between the PV module and the roof. Daily peak heat flow through the attic ceiling was almost 49% lower in the PV hut compared to the reference hut. These results show no evidence of an adverse thermal impact of the adhesive-mounted PV system on the roofing materials, while demonstrating a potential for a notable reduction in space conditioning energy requirements

Mechanical load testing of solar panels - beyond certification testing

Mechanical load tests are a commonly-performed stress test where pressure is applied to the front and back sides of solar panels. In this paper we review the motivation for load tests and the different ways of performing them. We then discuss emerging durability concerns and ways in which the load tests can be modified and/or enhanced by combining them with other characterization methods. In particular, we present data from a new tool where the loads are applied by using vacuum and air pressure from the rear side of the panels, thus leaving the front side available for EL and IV characterization with the panels in the bent state. Tightly closed cracks in the cells can be temporarily opened by such a test, thus enabling a prediction of panel degradation in the field were these cracks to open up over time. Based on this predictive crack opening test, we introduce the concept of using a quick load test on each panel in the factory as a quality control tool and potentially as a type of burn-in test to initiate cracks that would certainly form early on during a panel's field life. We examine the stresses seen by the cells under panel load through Finite Element Modeling and demonstrate the importance of constraining the panel motion during testing as it will be constrained when mounted in the field