Performance of novel VUV-sensitive Silicon Photo-Multipliers for nEXO

Liquid xenon time projection chambers are promising detectors to search for neutrinoless double beta decay (0$\nu \beta \beta$), due to their response uniformity, monolithic sensitive volume, scalability to large target masses, and suitability for extremely low background operations. The nEXO collaboration has designed a tonne-scale time projection chamber that aims to search for 0$\nu \beta \beta$ of \ce{^{136}Xe} with projected half-life sensitivity of $1.35\times 10^{28}$~yr. To reach this sensitivity, the design goal for nEXO is $\leq$1\% energy resolution at the decay $Q$-value ($2458.07\pm 0.31$~keV). Reaching this resolution requires the efficient collection of both the ionization and scintillation produced in the detector. The nEXO design employs Silicon Photo-Multipliers (SiPMs) to detect the vacuum ultra-violet, 175 nm scintillation light of liquid xenon. This paper reports on the characterization of the newest vacuum ultra-violet sensitive Fondazione Bruno Kessler VUVHD3 SiPMs specifically designed for nEXO, as well as new measurements on new test samples of previously characterised Hamamatsu VUV4 Multi Pixel Photon Counters (MPPCs). Various SiPM and MPPC parameters, such as dark noise, gain, direct crosstalk, correlated avalanches and photon detection efficiency were measured as a function of the applied over voltage and wavelength at liquid xenon temperature (163~K). The results from this study are used to provide updated estimates of the achievable energy resolution at the decay $Q$-value for the nEXO design

Treating eutrophic water for nutrient reduction using an aquatic macrophyte (Ipomoea aquatica Forsskal) in a deep flow technique system

Wetlands can be used in a cost-effective manner to treat nutrient-rich water for release to freshwater ecosystems. Eutrophic water was treated with the freshwater macrophyte, Ipomoea aquatica Forsskal (swamp cabbage), in a horizontal-flow, Deep Flow Technique (DFT) system. Plants were also exposed to a Hoagland and Arnon [Hoagland, D.R., Arnon, D., l938. The water culture method for growing plants without soil. Calif. Agr. Expt. Sta. Circ., 347] solution using the same exposure system. After a 48-h exposure to the plant, chemical oxygen demand (COD), biochemical oxygen demand (BOD5), total suspended solids (TSS) and chlorophyll a (Chla) in the effluent were reduced by 84.5, 88.5, 91.1, and 68.8%, respectively, and the removal of nutrients (total nitrogen and total phosphorus) varied between 41.5 and 75.5%. Vitamin C and NO3-N concentrations in plants grown in the eutrophic water were significantly different from those grown in a standard nutrient solution. Chlorophyll a, chlorophyll a/b and shoot to root dry weight ratio were not significantly different between the different waters. The concentrations of cadmium, copper, lead and zinc were lower than the permissible levels set by the FAO and WHO for human consumption. The results of this study indicate that cultivating edible, aquatic macrophytes with nutrient-rich, eutrophic water in a DFT system can be an effective, low-cost phytoremediation technology to treat water with undesirable levels of nitrogen and/or phosphorus.

Differential response of root morphology to potassium deficient stress among rice genotypes varying in potassium efficiency*

Disparity in the root morphology of six rice (Oryza sativa L.) genotypes varying in potassium (K) efficiency was studied with three K levels: 5 mg/L (low), 10 mg/L (moderate) and 40 mg/L (adequate) in hydroponic culture. Morphological parameters included root length, surface area, volume and count of lateral roots, as well as fine (diameter<0.2 mm) and thick (diameter>0.2 mm) roots. The results indicate that the root growth of all genotypes was reduced under low K, but moderate K deficiency increased the root length of the efficient genotypes. At deficient and moderate K levels, all the efficient rice genotypes developed more fine roots (diameter<0.2 mm) than the inefficient ones. Both fine root count and root surface area were found to be the best parameters to portray K stress in rice. In accordance with the root morphology, higher K concentrations were noted in shoots of the efficient genotypes when grown at moderate and deficient K levels, indicating that root morphology parameters are involved in root uptake for K and in the translocation of K up to shoots. K deficiency affected not only the root morphology, but also the root ultra-structure. The roots of high-efficient genotypes had stronger tolerance to K deficient stress for root membrane damage, and could maintain the developed root architecture to adapt to the low K growth medium

Response of ATP sulfurylase and serine acetyltransferase towards cadmium in hyperaccumulator Sedum alfredii Hance*

We studied the responses of the activities of adenosine-triphosphate (ATP) sulfurylase (ATPS) and serine acetyltransferase (SAT) to cadmium (Cd) levels and treatment time in hyperaccumulating ecotype (HE) Sedum alfredii Hance, as compared with its non-hyperaccumulating ecotype (NHE). The results show that plant growth was inhibited in NHE but promoted in HE when exposed to high Cd level. Cd concentrations in leaves and shoots rapidly increased in HE rather than in NHE, and they became much higher in HE than in NHE along with increasing treatment time and Cd supply levels. ATPS activity was higher in HE than in NHE in all Cd treatments, and increased with increasing Cd supply levels in both HE and NHE when exposed to Cd treatment within 8 h. However, a marked difference of ATPS activity between HE and NHE was found with Cd treatment for 168 h, where ATPS activity increased in HE but decreased in NHE. Similarly, SAT activity was higher in HE than in NHE at all Cd treatments, but was more sensitive in NHE than in HE. Both ATPS and SAT activities in NHE leaves tended to decrease with increasing treatment time after 8 h at all Cd levels. The results reveal the different responses in sulfur assimilation enzymes and Cd accumulation between HE and NHE. With increasing Cd stress, the activities of sulfur assimilation enzymes (ATPS and SAT) were induced in HE, which may contribute to Cd accumulation in the hyperaccumulator Sedum alfredii Hance

Differential generation of hydrogen peroxide upon exposure to zinc and cadmium in the hyperaccumulating plant specie (Sedum alfredii Hance)*

Sedum alfredii Hance has been identified as zinc (Zn) and cadmium (Cd) co-hyperaccumulator. In this paper the relationships of Zn or Cd hyperaccumulation to the generation and the role of H2O2 in Sedum alfredii H. were examined. The results show that Zn and Cd contents in the shoots of Sedum alfredii H. treated with 1000 μmol/L Zn2+ and/or 200 μmol/L Cd2+ increased linearly within 15 d. Contents of total S, glutathione (GSH) and H2O2 in shoots also increased within 15 d, and then decreased. Total S and GSH contents in shoots were higher under Cd2+ treatment than under Zn2+ treatment. However, reverse trends of H2O2 content in shoots were obtained, in which much higher H2O2 content was observed in Zn2+-treated shoots than in Cd2+-treated shoots. Similarly, the microscopic imaging of H2O2 accumulation in leaves using H2O2 probe technique showed that much higher H2O2 accumulation was observed in the Zn2+-treated leaf than in the Cd2+-treated one. These results suggest that there are different responses in the generation of H2O2 upon exposure to Zn2+ and Cd2+ for the hyperaccumulator Sedum alfredii H. And this is the first report that the generation of H2O2 may play an important role in Zn hyperaccumulation in the leaves. Our results also imply that GSH may play an important role in the detoxification of dissociated Zn/Cd and the generation of H2O2

snow sample Raw sequence reads

Fresh snow sampling A total of 48 snow sampling sites, 44 fresh snow samples from major cities in China, and three in North America and one in Europe, were collected (across a 13,000-km transect belt) in the Northern Hemisphere (23°05′N-66°05′N). Of these, 22 national-scale sampling sites were taken from China in 2016–2017, and 22 sites were further collected in 2018–2019 to verify the previous results. At the same time, in order to better reveal the occurrence, distribution, and inherent underlying mechanism, we also collected four samples from Munich, Washington, New Jersey, and Edmonton, where the level of local air pollution is lower than that of China. These sample sites have different energy structures, population, socio-economic development levels, and air pollution levels. For each location, five replicate samples were taken at each sampling site (100 × 100 m; all four corners and the central point) and measured separately. Details of sampling sites are presented in the Supplementary Table S1. Sampling dates were determined from forecasts for snowfall. Fresh snow samples were taken from the beginning until the end of one snow event. When the snow began to land, it was collected on the ground on top of a plastic sheet; the collected samples were stored in a portable freezer and immediately sent to the laboratory. In the laboratory, the snow samples were melted and mixed at 4 °C, and divided into two portions for DNA extraction and chemical analyses. To ensure a sufficient sample size, from each point, we collected at least 30 L of snow (about 4–8 L snow can melt into 1 L of snow water). The extracted DNA was stored at −80 °C until analysis. Air quality index (AQI) The AQI is used by Chinese government agency to communicate to the public how polluted the air currently is or how polluted it will, most likely, become. There are six pollutant monitoring items in the AQI: sulfur dioxide (SO2), nitrogen dioxide (NO2), inhalable particles (PM10), PM2.5, carbon monoxide (CO2), and ozone (O3). Public health risks increase with increasing AQI levels, and different countries have their own air quality indices, corresponding to different national air quality standards. The computation of the AQI requires an air pollutant concentration over a specified averaging period; it can be calculated either per hour or per 24 h. An individual score (Individual Air Quality Index) is assigned to each pollutant, and the final AQI is the highest of these six scores (for detailed information, see the Supplementary Table S2). Backward trajectory analysis The 2-day (48 h) backward trajectories were calculated every hour at a height of 100 m above the ground level, ending at each snow sampling day, using the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT, NOAA) 4.9 model [26]. The trajectories were then grouped into five clusters using the algorithm of cluster analysis. The clustering of trajectories is based on the total spatial variance method [27], which minimizes the inter-cluster differences among trajectories while maximizing the outer-cluster differences; it has been widely used in previous studies [22, 28]. Sample chemical analysis Concentrations of NH4+, NO3−, and NO2− were measured using continuous flow analyzers (Germany, SEAL, AA3), while Cl− and SO42− were determined using ion chromatography (USA, Diana, ICS-1000). The Na+, K+, Ca2+, and Mg2+ cations were measured using a full-spectrum direct-reading plasma emission spectrometer (USA, Leeman, Prodigy). Specific-surface area and concentration of particulate matter were measured by a Laser Particle Size Meter (Supplementary Table S3). Socio-economic parameters were collected and calculated from governmental statistical yearbooks, bulletins, and reports (Supplementary Table S1). DNA extraction and HT-qPCR The water from the melted snow (0.5–2 L, depending on the pollution level) was filtered through a 0.22-μm-pore-size filter (diameter, 45 mm; Millipore, New Bedford, MA), which was then used for DNA extraction, using the FastDNA Spin Kit for Soil (MP Biomedicals) according to the manufacturer’s protocol. The DNA quality analysis was performed using a NanoDrop2000 UV-visible spectrophotometer (Thermo Fisher Scientific Inc., Wilmington, DE, USA) and 1% (w/v) agarose gel electrophoresis, and the OD260/OD280 ratio of the DNA was between 1.8 and 2.0. The extracted DNA was quantified using the QuantiFluor dsDNA kit (Promega) in a 96-well microplate reader (SpectraMax M5, Molecular Devices), diluted to 50 ng μL−1 using sterile water, and stored at −80 °C for further analysis. A total of 296 primer sets were selected to investigate genes present in the atmospheric snow DNA. These primer sets targeted resistance genes for all major classes of antibiotics (285 primer sets), transposase genes (8 primer sets), one universal class I integron-integrase gene (intI), and one clinical class 1 integron-integrase gene (cintI), and the 16S rRNA gene. The HT-qPCR was performed using the Wafergen Smart Chip Real-time PCR system at the Key Lab of Urban Environment and Health, Institute of Urban Environment, Chinese Academy of Sciences. For each primer set, a non-template negative control was included. The PCR cycle consisted of 10 min at 95 °C, followed by 40 cycles of denaturation at 95 °C for 30 s and annealing at 60 °C for 30 s. Melting curve analyses were automatically generated by the Wafergen software. All quantitative PCRs were carried out in technical triplicates. Wells with efficiencies beyond the range of 1.7–2.3 or an R2 under 0.99 were discarded. Only data for samples with at least three repeated sampling replicates, which generated amplification products, were regarded as positive and used for further data analysis. The relative copy numbers of ARGs generated by the HT-qPCR were transformed into absolute copy numbers by normalization, using the absolute 16S rRNA gene copy number. The standard curve method of quantification by the Roche 480 system was used to determine the absolute 16S rRNA copy numbers at the same Key Lab facility. Each qPCR reaction mixture (20 μL) contained 10 μL 2× Light Cycle 480 SYBR Green I Master (Roche Applied Sciences), 1 μg μL–1 bovine serum albumin, 1 μM of each primer, 1 ng μL–1 template DNA, and 6 μL nuclease-free PCR-grade water. The thermal cycle consisted of a 10 min of initial enzyme activation at 95 °C, followed by 40 cycles of denaturation at 95 °C for 30 s, annealing at 60 °C for 30 s and extension at 72 °C for 15 s. A plasmid control containing a cloned and sequenced 16S rRNA gene fragment (1.39 × 1010 copies per liter) was used to generate eight-point calibration curves from tenfold dilutions for standard calculation. All qPCRs were performed in technical triplicates with negative controls. Bacterial 16S rRNA gene sequencing The V4–V5 region of the 16S rRNA gene was amplified, purified, quantified, pooled-, and multiplex-sequenced on an Illumina Miseq platform at Novogene to characterize bacterial communities. Each of the 50-μL PCR reaction mixtures contained 25 μL TaKaRa ExTaq, 0.5 μL bovine serum albumin, 1 μL of each primer, 1 μL DNA as template, and 21.5 μL nuclease-free PCR-grade water. The thermal cycle consisted of 3 min of initial enzyme activation at 94 °C, followed by 30 cycles of denaturation at 94 °C for 30 s, annealing at 58 °C for 1 min, and extension at 72 °C for 1 min, with a final extension step at 72 °C for 5 min. Raw, paired-end reads were merged to clean sequences after filtering the adapter sequences and removing low-quality reads, ambiguous nucleotides, and barcodes. Raw sequences were demultiplexed and quality-filtered using QIIME [29] and Mothur [30]