Survey of Heterodera glycines population abundance and virulence phenotypes during 2021-2022 in Heilongjiang Province.

Soybean cyst nematode (SCN), Heterodera glycines, poses a significant threat to global soybean production. Heilongjiang, the largest soybean-producing province in China, contributes over 40% to the country's total yield. This province has much longer history of SCN infestation. To assess the current situation in Heilongjiang, we conducted a survey to determine the SCN population density and virulence phenotypes during 2021-2022 and compared the data with a previous study in 2015. A total of 377 soil samples from 48 counties representing eleven major soybean-planting regions were collected. The prevalence of SCN increased from 55.4% in 2015 to 59% in the current survey. The population densities ranged from 80 to 26,700 eggs and juveniles per 100 cm3 of soil. Virulence phenotypes were evaluated for 60 representative SCN populations using the HG type test, revealing nine different HG types. The most common virulence phenotypes were HG types 7 and 0, accounting for 56.7% and 20% of all SCN populations, respectively. The prevalence of populations with a reproductive index (FI) greater than 10% on PI548316 increased from 64.5% in 2015 to 71.7%. However, the FI on the commonly used resistance sources PI 548402 (Peking) and PI 437654 remained low at 3.3%. These findings highlight the increasing prevalence and changing virulence phenotypes of SCN in Heilongjiang. They also emphasize the importance of rotating soybean varieties with different resistance sources and urgently identifying new sources of resistance to combat SCN.

Biocontrol efficacy of Bacillus velezensis strain YS-AT-DS1 against the root-knot nematode Meloidogyne incognita in tomato plants.

Root-knot nematodes (RKNs; Meloidogyne spp.), one of the most economically important plant-parasitic nematodes (PPNs), cause severe yield and quality losses in agriculture annually. The application of biological control agents is an environmentally safe and effective approach to control RKNs. Here, we report the genomic characteristics of a Bacillus velezensis strain YS-AT-DS1 (Bv-DS1) isolated from the tidal soil, revealing that it has a 4.73 Mb circular chromosome with an average GC-content of 46.43%, 3,977 genes, 86 tRNAs, and 27 rRNAs, and contains secondary metabolite clusters for producing antimicrobial compounds. In vitro assays indicated that Bv-DS1 has not only antagonistic activities against fungal pathogens, but also shows nematicidal activity, with a mortality rate of 71.62% mortality rates in second-stage juvenile (J2s) Meloidogyne incognita. We then focused on the biocontrol efficiency of Bv-DS1 against M. incognita in pot assays. Preinoculation with Bv-DS1 enhanced tomato growth, and significantly reduced the infection rate of J2s, and the number of galls and egg masses on tomato roots. The underlying mechanism in Bv-DS1-induced resistance to M. incognita was further investigated through split-root experiments, and analysing the expression of the genes related to jasmonic acid (JA), salicylic acid (SA), and the tonoplast intrinsic protein (TIP). The results indicated that Bv-DS1 could not activate host systemic-induced resistance (ISR) in the split-root system of tomatoes. Additionally, the expression of JA- (LOX D and MC) and SA- (PAL2 and PR) responsive genes did not change in Bv-DS1-pretreated plants at 3 and 14 days after nematode inoculation. The presented data showed that JA-and SA-dependent pathways were not required for the biocontrol action of the Bv-DS1 against RKN. The TIP genes, responsible for transport of water and small substrates in plants, have previously been shown to negatively regulate the parasitism of PPNs. Surprisingly, Bv-DS1 compromised the downregulation of TIP1.1 and TIP1.3 by M. incognita. Together, our data suggest that Bv-DS1 exhibits a dual effect on plant growth promotion and protection against RKN, possibly related to the regulation of water and solute transport via TIPs. Thus, the Bv-DS1 strain could be used as a biocontrol agent for RKN control in sustainable agriculture.

First Report of Aphelenchoides besseyi Causing White Tip Disease of Rice in Heilongjiang Province of China.

Aphelenchoides besseyi is considered one of the most damaging plant parasitic nematodes to rice and can cause white tip disease. It was first discovered in Kyushu, Japan in 1915 and introduced into China from Japan in the 1940s. The disease is mainly found in rice-planting areas in South China (Zhu et al. 2016; Wang et al. 2017; Xu et al. 2019), causing yield losses of 30%-50% in irrigated rice (Wang et al. 2014). In summer 2021, rice plants displaying distortion and discoloration on new leaves, white tips on flag leaves, erect and shorter panicles, and fewer or less filled spikelets were observed in the rice field in Acheng district, Harbin city, Heilongjiang Province, China (13°32'33″S, 58°48'51″W). Plant samples with the typical symptoms of 'white tip' in the flag leaves were collected and transported to the laboratory for further pathogen identification. Nematodes were extracted from the leaves and panicles of diseased plants using Baermann funnel method, and the population density of nematode was an average of 57 individuals per sample (total 28 diseased samples). The main morphological characteristics of females (n = 20) and males (n = 15) were individually determined using a microscope (LEICA, DM2500). Female body was slender, and straight to ventrally curved when heat-relaxed, with a rounded cephalic region, the lateral field with four incisures, the excretory pore close to the anterior edge of the nerve ring, a narrow post-vulval sac and less than 1/3 the distance from the vulva to the anus, and a conoid tail with star-shaped mucro. Female measurements: body length = 724.6 (593.3 to 867.5) µm, stylet = 11.7 (10.9 to 12.5) µm, tail length = 39.4 (35.8 to 44.4) µm, a = 45.2 (38.6 to 51.0), b = 10.1 (9.4 to 10.7), c = 18.47 (14.7 to 21.4), and V = 71.1 (65.0 to 79.6). The body of male usually showed in a 'J' shape when relaxed, spicule length between 17.1 and 19.4 µm, and a conoid tail, with terminal mucro bearing two to four pointed processes. Male measurements: body length = 546.3 (521.7 to 587.6) µm, stylet = 11.9 (10.7 to 12.6) µm, tail length = 32.54 (29.53 to 34.35) µm, a = 37.7 (35.7 to 40.4), b = 8.7 (8.5 to 9.1), c = 17.8 (15.8 to19.4). The key morphological characteristics were coincident with the description of A. besseyi by Christie (1942), Ou et al. (2014) and Chen et al. (2020). DNA was extracted from six fresh nematodes, and the partial 18S-rRNA was amplified with a pair of primers 1813F/2646R (5'-CTGCGTGAGAGGTGAAAT-3'; 5'-GCTACCTTGTTACGACTTTT-3') (Holterman et al. 2006). PCR products of expected size were purified and sequenced. The newly obtained sequence (accession no. ON629604) was submitted to GenBank and displayed more than 99.5% identity with that of A. besseyi isolates (KT943536, KT454963, JQ957877). Additionally, the isolated nematodes were further confirmed using the species-specific primers Abess_11F/Abess_11R (5'-GTATTCAATCCCGCGACACT-3'; 5'-CATCCTGTTCGGGCATAGTT-3'), and the PCR amplification generated a 570 bp fragment which was specific to the 28S rDNA region of A. besseyi reported previously (Noronha et al. 2020). The pathogenicity test was confirmed in a pot assay. Approximately 2000 mixed-stage A. besseyi (juveniles, males and females) were obtained from the field-diseased rice plants, and ten-day-old rice seedlings (Japonica rice variety, Keyou 1) (n = 5) were inoculated with 400 nematodes per seedling and maintained in a greenhouse. During early growth stages (fifty days after inoculation), some young leaves of infected plants showed the chlorotic tips. Ninety days after inoculation, similar field symptoms (white tip on leaves) were observed on the aerial tissues of the inoculated plants, and an average of 237 A. besseyi were re-isolated from each plant. To the best of our knowledge, this is the first report of A. besseyi on rice plant in Heilongjiang Province of Northeast China. This finding indicates that A. besseyi could become a severe threat to rice production in Heilongjiang Province and contributes to the further inspection and prevention of white tip disease in rice-growing areas of Heilongjiang Province.

Land use alters diazotroph community structure by regulating bacterivores in Mollisols in Northeast China.

Changes in land use can generate environmental pressures that influence soil biodiversity, and numerous studies have examined the influences of land use on the soil microbial communities. However, little is known about the effects of land use on ecological interactions of soil microbes and their predators. Diazotrophs are key soil microbes that play important functional roles in fixing atmospheric nitrogen. In this study, we investigated the co-association of diazotroph community members and patterns of diazotroph and bacterivore networks under different long-term land uses including cropland, grassland, and bare land. Diazotroph community was characterized by high-throughput sequencing. The results indicated that land use type influenced the dominant genera of diazotrophs and shaped the occurrence of specific indicator diazotroph taxa. Co-existing pattern analysis of diazotrophs and bacterivores indicated that grassland converted from cropland increased the complexity of diazotroph and bacterivore network structure. The number of nodes for diazotrophs and bacterivores was higher in grassland than in cropland and bare land. Random forest analysis revealed that six bacterivore genera Cephalobus, Protorhabditis, Acrobeloides, Mesorhabditis, Anaplectus, and Monhystera had significant effects on diazotrophs. Bacterivores were found to have predominantly negative effects in bare land. Different bacterivores had differing effects with respect to driving changes in diazotroph community structure. Structural equation model showed that land use could control diazotroph community composition by altering soil properties and regulating abundance of bacterivores. These findings accordingly enhance our current understanding of mechanisms underlying the influence of land use patterns on diazotrophs from the perspective of soil food webs.

First Report of Trichotylenchus changlingensis infecting Maize in Shaanxi, China.

Maize (Zea mays L.) is one of the most important crops worldwide. In September 2020, five maize plants and soil samples were received from a farmer. The samples were collected from a maize field in Fugu County (N 39.02805, E 111.06723), Shaanxi Province, China. These maize plants had the symptoms of stunting or thinning. Soil nematodes were extracted from soils with modified Baermann funnel method for 48 h (Barker 1985). Trichotylenchus sp. were detected with populations ranging from 12 to 45 (in five soil samples) nematodes per 100 gram of fresh soil. Maize were planted in pots with soil samples containing Trichotylenchus sp. to propagate this plant-parasitic nematode at 20-28 °C in a greenhouse. After plants had grown for 60 days, active Trichotylenchus sp. were observed and picked under an anatomical lens (SZX16, Olympus, Tokyo, Japan) for an inoculation experiment. Freshly germinated maize (Limin 33) seeds were planted into paper pots with a sterilized mixture of soil and sand (4:1). Four plants were inoculated with approximately 2800 mixed-stage nematodes. The maize plants were allowed to grow under room conditions (15-20 °C) for two weeks and transferred to plastic pots (12 cm diameter × 10 cm deep) with the same soil mixture. After 30 days, all inoculated plants displayed the disease symptoms such as hypoplasia of fibrous roots and a hole at the base of the maize stem, but the Trichotylenchus sp. was not detected in maize roots and stems. The control plants did not exhibit any disease symptoms. The nematodes from the inoculated pots were identified by both morphological and molecular methods. The bodies of female and male were usually C-shaped when killed by hot water. The stylet was well developed with basal knobs. The posterior part of esophagus basal bulb did not overlap dorsally with the intestine. The female had a subcylindrical tail, but the male had a conical tail. The spicule of male was ventrally curved. The gubernaculum was well developed. Morphometric data based on females and males were presented as means (range). For female (n= 20): L = 1142.7 (1002.3 to 1313.4) µm, St = 26.5 (23.9 to 29.4) µm, a = 32.8 (27.4 to 38.7), b = 6.8 (6.0 to 7.9), c = 16.3 (14.9 to 19.4), c' = 2.7 (2.3 to 3.1), v = 51.3 (30.3 to 54.8), T = 70.1 (59.0 to 78.9) µm. For male (n= 20): L = 1093.3 (960.6 to 1183.7) µm, St = 24.3 (22.1 to 26.1) µm, a = 34.9 (31.1 to 39.1), b = 6.5 (5.6 to 7.4), c = 15.1 (13.6 to 16.7), c' = 3.6 (2.9 to 4.3), T = 72.5 (63.8 to 81.1) µm, SL = 28.8 (22.2 to 32.5) µm, GL = 11.5 (7.2 to 16.1) µm. The characteristics were coincident with the description of Trichotylenchus changlingensis (Guo et a., 2015). Genomic DNA was extracted from 10 nematodes, and PCR amplifications of the D2/D3 region of 28S rRNA were performed using universal primers D2A/D3B (Castillo et al. 2003), and that of the internal transcribed spacer (ITS)-rRNA region were amplified using universal primers TW81/AB28 (Amiri et al. 2002). A 780 bp amplicon of the 28S rRNA (GenBank accession no. OM276857.1) had 90.6% (Query Cover = 95%) identity with that of Tylenchorhynchus mediterraneus (KJ461557.1). Three ITS-rRNA region sequences (GenBank accession nos. OM294652.1, OM294653.1 and OM294654.1) were obtained, and the comparison revealed that sequences OM294652.1 and OM294653.1 had 98.90% (Query Cover = 100%) identity with the ITS-rRNA region sequence of T. changlingensis isolate (MH545694.1) from China, and OM294654.1 showed a 99.09 % (Query Cover = 99%) similarity to T. changlingensis sequence (MH545693.1). The morphological and molecular characterizations confirmed that the observed nematode was T. changlingensis, which is distributed in Heilongjiang, Jilin, Liaoning, Hebei, Gansu provinces and Inner Mongolia of China (Guo et al. 2020). To our knowledge, this is the first report of T. changlingensis infecting maize and causing disease in Shaanxi Province.

Response of Soil Nematode Community Structure and Function to Monocultures of Pumpkin and Melon.

It is well known that crop monoculture can induce negative effects on soil ecosystems and crop productivity. However, little is known about how vegetable monoculture affects the soil nematode community structure and its relationship with vegetable yields. In this study, the composition, abundance, metabolic footprint, and ecological indices of soil nematodes are investigated in monocultures of pumpkin and melon. The relationships between nematode community structure and yields of pumpkin and melon were analyzed by linear regression. Both monoculture soils of pumpkin and melon suppressed the relative abundance of bacterivores but increased the relative abundance of plant parasites. Pumpkin monoculture soils decreased soil nematode diversity but increased the maturity index of plant parasites. Monoculture soils of pumpkin and melon decreased the metabolic footprint of lower- and higher-level trophic groups of the soil food web, respectively. Pumpkin and melon monoculture soils increased the food web indices channel index (CI) but decreased the enrichment index (EI) and the structure index (SI). The monoculture soils of pumpkin and melon led to a more fungal-dominated decomposition pathway and degraded soil food web conditions. The abundance of bacterivores and food web indices EI and SI were positively correlated with soil nutrients and pH, while the abundance of plant parasites and CI were negatively correlated with soil nutrients and pH. Paratylenchus was negatively correlated with pumpkin and melon yields and could be the potential plant parasites threatening pumpkin and melon productions. Redundancy analysis showed that monocultures of pumpkin and melon altered the soil nematode community via soil properties; total N, total P, alkeline-N, and pH were the main driving factors.

First Detection of Ditylenchus destructor Parasitizing Maize in Northeast China.

Maize is one of the most important crops in the world. Heilongjiang province has the largest maize area in China. Plant-parasitic nematodes are important agricultural pests, which cause huge economic losses every year and have attracted global attention. Potato rot nematode Ditylenchus destructor is a plant-parasitic nematode with a wide range of hosts and strong survival ability in different environments, which brings risks to agricultural production. In 2020, D. destructor was detected in seven maize fields in Heilongjiang province. Morphological identification and molecular approach were used to characterize the isolated D. destructor. The observed morphological and morphometric characteristics were highly similar and consistent with the existing description. The DNA sequencing on the D2/D3 region of the ribosomal DNA 28S and the phylogenetic analysis showed that D. destructor population obtained from maize and other isolates infesting carrot, sweet potato, and potato were in subclade I supported by a 96% bootstrap value. Additionally, the phylogenetic analysis of the ITS rRNA gene sequence further indicated that this D. destructor population from maize clustered in a clade I group and belonged to ITS rRNA haplotype C. An inoculation experiment revealed that D. destructor was pathogenic on the maize seedlings in pots and caused the disease symptoms in the stem base of maize seedlings. This is the first report of D. destructor causing stem rot of maize in Heilongjiang province, and contributes additional information on disease control and safe production of maize in the region.

FMRFamide-Like Peptide 22 Influences the Head Movement, Host Finding, and Infection of Heterodera glycines.

The FMRFamide-like peptides (FLPs) represent the largest family of nematode neuropeptides and are involved in multiple parasitic activities. The immunoreactivity to FMRFamide within the nervous system of Heterodera glycines, the most economically damaging parasite of soybean [Glycine max L. (Merr)], has been reported in previous research. However, the family of genes encoding FLPs of H. glycines were not identified and functionally characterized. In this study, an FLP encoding gene Hg-flp-22 was cloned from H. glycines, and its functional characterization was uncovered by using in vitro RNA interference and application of synthetic peptides. Bioinformatics analysis showed that flp-22 is widely expressed in multiple nematode species, where they encode the highly conserved KWMRFamide motifs. Quantitative real-time (qRT)-PCR results revealed that Hg-flp-22 was highly expressed in the infective second-stage juveniles (J2s) and adult males. Silencing of Hg-flp-22 resulted in the reduced movement of J2s to the host root and reduced penetration ability, as well as a reduction in their subsequent number of females. Behavior and infection assays demonstrated that application of synthetic peptides Hg-FLP-22b (TPQGKWMRFa) and Hg-FLP-22c (KMAIEGGKWVRFa) significantly increased the head movement frequency and host invasion abilities in H. glycines but not in Meloidogyne incognita. In addition, the number of H. glycines females on the host roots was found to be significantly higher in Hg-FLP-22b treated nematodes than the ddH2O-treated control J2s. These results presented in this study elucidated that Hg-flp-22 plays a role in regulating locomotion and infection of H. glycines. This suggests the potential of FLP signaling as putative control targets for H. glycines in soybean production.

Modulated structure determination and ion transport mechanism of oxide-ion conductor CeNbO4+δ.

CeNbO4+δ, a family of oxygen hyperstoichiometry materials with varying oxygen content (CeNbO4, CeNbO4.08, CeNbO4.25, CeNbO4.33) that shows mixed electronic and oxide ionic conduction, has been known for four decades. However, the oxide ionic transport mechanism has remained unclear due to the unknown atomic structures of CeNbO4.08 and CeNbO4.33. Here, we report the complex (3 + 1)D incommensurately modulated structure of CeNbO4.08, and the supercell structure of CeNbO4.33 from single nanocrystals by using a three-dimensional electron diffraction technique. Two oxide ion migration events are identified in CeNbO4.08 and CeNbO4.25 by molecular dynamics simulations, which was a synergic-cooperation knock-on mechanism involving continuous breaking and reformation of Nb2O9 units. However, the excess oxygen in CeNbO4.33 hardly migrates because of the high concentration and the ordered distribution of the excess oxide ions. The relationship between the structure and oxide ion migration for the whole series of CeNbO4+δ compounds elucidated here provides a direction for the performance optimization of these compounds.

Calcium inhibitor inhibits high glucose­induced hypertrophy of H9C2 cells.

The aim of the present study was to explore whether the hypertrophy of H9C2 cardiomyocytes was induced by high glucose, to investigate whether the calcium channel inhibitor (Norvasc) could inhibit this process and to clarify the possible signaling pathways. The morphology of H9C2 cells was observed under an optical microscope, and the cell surface area was measured by Image Pro Plus 6.1 software. Furthermore, fluorescence spectrophotometry was used to detect intracellular calcium concentration ([Ca2+]i). ELISA was performed to detect calcineurin (CaN) activity; reverse transcription­quantitative PCR and western blotting were performed to detect the mRNA and protein expression levels of CaN Aß subunit (CnAß), nuclear factor of activated T cells 3 (NFAT3) and ß type myosin heavy chain (ß­MHC). Cell size was increased with the increase in glucose concentration of culture medium at 48 and 72 h, respectively, and decreased with the addition of Norvasc compared with those without Norvasc (P<0.05). There was no significant difference in cell size with the addition of Norvasc compared with cells cultured with 5 mM glucose (P>0.05). The average [Ca2+]i activity of single cells in the 48­ and 72­h culture groups treated with 50 mM glucose was significantly higher than cells treated with 5 mM glucose (P<0.05); and the fluorescent value of average [Ca2+]i activity of single cells was lower, following the addition of Norvasc than that without Norvasc (P<0.05). CaN activity in the 48­ and 72­h culture group treated with 50 mM glucose was markedly higher than that treated with 5 mM glucose, and the activity of CaN notably decreased with the addition of Norvasc compared with those without Norvasc. The mRNA and protein expression levels of CnAß, NFAT3 and ß­MHC in the 48­ and 72­h culture groups treated with 50 mM glucose were all significantly higher than those treated with 5 mM glucose (P<0.05). The mRNA and protein expression of CnAß, NFAT3 and ß­MHC cultured with 50 mM glucose were significantly decreased following the addition of Norvasc (P<0.05). Thus, the calcium channel inhibitor Norvasc may inhibit high glucose­induced hypertrophy of H9C2 cardiomyocytes by inhibiting the Ca2+­CaN­NFAT3 signaling pathway.

The Heterodera glycines effector Hg16B09 is required for nematode parasitism and suppresses plant defense response.

Soybean cyst nematode (Heterodera glycines Ichinohe) is a sedentary root endoparasite that causes serious yield losses on soybean (Glycine max) worldwide. H. glycines secrets effector proteins into host cells to facilitate the success of parasitism. Nowadays, a large number of candidate effectors were identified from the genome sequence of H. glycines. However, the precise functions of these effectors in the nematode-host plant interaction are unknown. Here, an effector gene of dorsal gland protein Hg16B09 from H. glycines was cloned and functionally characterized through generating the transgenic soybean hairy roots. In situ hybridization assay and qRT-PCR analysis indicated Hg16B09 is exclusively expressed in the dorsal esophageal cells and up-regulated in the parasitic-stage juveniles. The constitutive expression of Hg16B09 in soybean hairy roots caused an enhanced susceptibility to H. glycines. In contrast, in planta silencing of Hg16B09 exhibited that nematode reproduction in hairy roots was decreased compared to the empty vector control. In addition, Hg16B09 also suppressed the expression of soybean defense-related genes induced by the pathogen-associated molecular pattern flg22. These data indicate that the effector Hg16B09 might aid H. glycines parasitism through suppressing plant basal defenses in the early parasitic stages.

Discovery of Layered Indium Hydroxide via a Hydroperoxyl Anion Coordinated Precursor at Room Temperature.

All reported layered metal hydroxides have brucite-like metal-hydroxyl host layers, and the discovery of other types of layered metal hydroxides could significantly extend the layered metal hydroxide families, which is meaningful in both theory and applications. Here, through hydroperoxyl anion coordinated In3+ cations as a precursor, a new layered indium hydroxide was synthesized, where only a three-dimensional cubic phase had existed before. The layer of the product exhibits an unusual structure where In(OH)6 octahedra share edges and vertexes with each other to form layers, which is completely different from the common edge-sharing brucite-like metal-hydroxyl layers. By investigating the formation mechanism, the new layered structure is found to be formed by changing the traditional crystallization path through the hydroperoxyl anion coordinated intermediates. Many other new phases could also be discovered by following the same intrinsic principle.

Highly Stable K2SiF6:Mn4+@K2SiF6 Composite Phosphor with Narrow Red Emission for White LEDs.

Poor water resistance and nongreen synthesis remain great challenges for commercial narrow red-emitting phosphor A2MF6:Mn4+ (A = alkali metal ion; M = Si, Ge, Ti) for solid-state lighting and display. We develop here a simple and green growth route to synthesize homogeneous red-emitting composite phosphor K2SiF6:Mn4+@K2SiF6 (KSFM@KSF) with excellent water resistance and high efficiency without the usage of toxic and volatile hydrogen fluoride solution. After immersing into water for 6 h, the as-obtained water-resistant products maintain 76% of the original emission intensity, whereas the emission intensity of non-water-resistant ones steeply drops down to 11%. A remarkable result is that after having kept at 85% humidity and at 85 °C for 504 h (21 days), the emission intensity of the as-obtained water-resistant products is at 80-90%, from its initial value, which is 2-3 times higher than 30-40% for the non-water-resistant products. The surface deactivation-enabled growth mechanism for these phosphors was proposed and investigated in detail. We found that nontoxic H3PO4/H2O2 aqueous solution promotes the releasing and decomposition of the surface [MnF6]2- ions and the transformation of the KSFM surface to KSF, which finally contributes to the homogeneous KSFM@KSF composite structure. This composite structure strategy was also successfully used to treat KSFM phosphor prepared by other methods. We believe that the results obtained in the present paper will open the pathway for the large-scale environmentally friendly synthesis of the excellent antimoisture narrow red-emitting A2MF6:Mn4+ phosphor to be used for white light-emitting diode applications.

Redefinition of Crystal Structure and Bi3+ Yellow Luminescence with Strong Near-Ultraviolet Excitation in La3BWO9:Bi3+ Phosphor for White Light-Emitting Diodes.

Bi3+-activated photonic materials have received increased interest recently because they can be excited effectively with near-ultraviolet (NUV) but not visible light, thereby avoiding the reabsorption among phosphors, which cannot be solved intrinsically by traditional rare earth (e.g., Eu2+, Ce3+) phosphors. Such unique property suggests their potential application in NUV chip-based WLEDs. However, few Bi3+ phosphors exhibit strong excitation peak in NUV, though the excitation tail of some can extend to NUV. Herein, we report a novel yellow-emitting La3BWO9:Bi3+ (LBW:Bi3+) phosphor with strong NUV excitation. The photoluminescence (PL) spectroscopy analysis indicates that there are two Bi3+ luminescent centers in LBW:Bi3+ phosphor, which is clearly in contradiction with the established hexagonal structure of La3BWO9 with P63 space group because only one La site in this structure can accommodate Bi3+ ions. Combining the luminescent properties of Bi3+ with Rietveld refinement, La3BWO9 was redefined as a trigonal structure with the lower space group of P3 in which there are two independent crystallographic La sites. In addition, the rationalization of P3 space group was further confirmed by the finding of the reflection (0001) according to the extinction rule. Therefore, the PL behavior of Bi3+ can act as a complementary tool to determinate the real crystal structure especially when it is hard to distinguish by conventional X-ray diffraction techniques.

Synthesis and crystal structure of Sr3Bi2O6 and structural change in the strontium-bismuth-oxide system.

The crystal structures and their changing trend in the strontium-bismuth-oxide system are critical for the studies of the related systems and their applications. The crystal structure of Sr3Bi2O6 was obtained for the first time in the space group of R3[combining macron] with a huge unit cell of a = b = 25.1146(19) Å and c = 18.3685(16) Å and all bismuth ions are Bi3+ forming [BiO3] trigonal pyramids. Sr3Bi2O6 is a key compound for the structural change trend in the SrO-Bi2O3 binary oxide system at 1000 °C. With a decrease in the bismuth content, its valence state changes from +3 to +5 and Bi-O polyhedra changes from connected to isolated before Bi(v) appearance. In the system, the boundary of the solid solution ß-phase (Sr1-xBixO1+0.5x) at 900 °C was also determined accurately as 0.770 ≤ x ≤ 0.862, experimentally.

Response of Soil Fungal Community Structure to Long-Term Continuous Soybean Cropping.

Long-term continuous soybean cropping can lead to the aggravation of soil fungal disease. However, the manner in which the fungal community and functional groups of fungi are affected by continuous soybean cropping remains unclear. We investigated the fungal abundance, composition and diversity during soybean rotation (RS), 2-year (SS) and long-term (CS) continuous soybean cropping systems using quantitative real-time PCR and high-throughput sequencing. The results showed that the fungal abundance was significantly higher in CS than in SS and RS. CS altered the fungal composition. Compared with RS, SS had an increase of 29 and a decrease of 12 genera in fungal relative abundance, and CS increased 38 and decreased 17 genera. The Shannon index was significantly higher in CS and SS than in RS. The result of principal coordinate analysis (PCoA) showed that CS and SS grouped together and were clearly separated from RS on the PCoA1. A total of 32 features accounted for the differences in fungal composition across RS, SS, and CS. The relative abundance of 10 potentially pathogenic and 10 potentially beneficial fungi changed, and most of their relative abundances dramatically increased in SS and CS compared with RS. Our study indicated that CS results in selective stress on pathogenic and beneficial fungi and causes the development of the fungal community structure that is antagonistic to plant health.

A crystalline AlPO4-5 intermediate: designed synthesis, structure, and phase transformation.

AlPO4-5 is the most extensively studied material in exploring the crystallization mechanism of aluminophosphate molecular sieves, and it can be synthesized using 4-dimethylaminopyridine (DMAP) as an organic structure-directing agent (OSDA). Achieving the AlPO4-5 intermediate in the crystalline form would be of great importance and significance for this purpose. In this study, we proposed a concept that by carefully regulating the synthesis conditions, crystalline alumimophosphate intermediates could be rationally prepared. A crystalline AlPO4-5 intermediate, (C7H11N2)2(H3O)(Al3P4O16)·(H2O)2.5 (1), was, therefore, synthesized by significantly increasing the amounts of orthophosphoric acid and DMAP. The intermediate 1 consists of alternating organic DMAP and inorganic [Al3P4O16]3- layers with abundant hydrogen bonds and can transform to the AlPO4-5 framework upon heating in air or through a steam-assisted conversion (SAC) method. To unravel the role of DMAP in the transformation, pure AlPO4-5 (2) was also synthesized by altering the synthesis conditions. The supramolecular assembly templating (SAT) effects of DMAP in 1 and 2 were verified via fluorescence spectra. Thus, the π-π stacking interactions between the DMAP molecules and the abundant hydrogen bonds between the adjacent layers are considered to be important for the phase transformation of 1. This crystalline intermediate would promote the understanding of the crystallization mechanism in the system of aluminophosphate molecular sieves.

Site Occupancies, Luminescence, and Thermometric Properties of LiY9(SiO4)6O2:Ce3+ Phosphors.

In this work, we report the tunable emission properties of Ce3+ in an apatite-type LiY9(SiO4)6O2 compound via adjusting the doping concentration or temperature. The occupancies of Ce3+ ions at two different sites (Wyckoff 6h and 4f sites) in LiY9(SiO4)6O2 have been determined by Rietveld refinements. Two kinds of Ce3+ f-d transitions have been studied in detail and then assigned to certain sites. The effects of temperature and doping concentration on Ce3+ luminescence properties have been systematically investigated. It is found that the Ce3+ ions prefer occupying Wyckoff 6h sites and the energy transfer between Ce3+ at two sites becomes more efficient with an increase in doping concentration. In addition, the charge-transfer vibronic exciton (CTVE) induced by the existence of free oxygen ion plays an important role in the thermal quenching of Ce3+ at 6h sites. Because of the tunable emissions from cyan to blue with increasing temperature, the phosphors LiY9(SiO4)6O2:Ce3+ are endowed with possible thermometric applications.

Site-Dependent Luminescence and Thermal Stability of Eu(2+) Doped Fluorophosphate toward White LEDs for Plant Growth.

Eu(2+) activated fluorophosphate Ba3GdNa(PO4)3F (BGNPF) with blue and red double-color emitting samples were prepared via a solid-state method in a reductive atmosphere. Their crystal structure and cationic sites were identified in light of X-ray diffraction pattern Rietveld refinement. Three different Ba(2+) sites, coordinated by six O atoms referred to as Ba1, two F and five O atoms as Ba2, and two F and six O atoms as Ba3, were partially substituted by Eu(2+). Photoluminescence emission (PL) and excitation (PLE) spectra of phosphor BGNPF:Eu(2+) along with the lifetimes were characterized at the liquid helium temperature (LHT), which further confirm the existence of three Eu(2+) emitting centers resulting in 436, 480, and 640 nm emission from the 5d → 4f transitions of Eu(2+) in three different Ba(2+) crystallographic sites. These emissions overlap with the absorption spectra of carotenoids and chlorophylls from plants, which could directly promote the photosynthesis. Temperature-dependent PL spectra were used to investigate the thermal stability of phosphor, which indicates that the PL intensity of BGNPF:0.9% Eu(2+) with optimal composition at 150 °C still keeps 60% of its PL intensity at room temperature, in which blue emission has higher thermal-stability than the red emission. Furthermore, the approaching white LED devices have also been manufactured with a 365 nm n-UV LED chip and present phosphor, which make operators more comfortable than that of the plant growth purple emitting LEDs system composed of blue and red light. Results indicate that this phosphor is an attractive dual-responsive candidate phosphor in the application n-UV light-excited white LEDs for plant growth.

Nonstoichiometric control of tunnel-filling order, thermal expansion, and dielectric relaxation in tetragonal tungsten Bronzes Ba0.5-xTaO3-x.

Ordering of interpolated Ba(2+) chains and alternate Ta-O rows (TaO)(3+) in the pentagonal tunnels of tetragonal tungsten bronzes (TTB) is controlled by the nonstoichiometry in the highly nonstoichiometric Ba0.5-xTaO3-x system. In Ba0.22TaO2.72, the filling of Ba(2+) and (TaO)(3+) groups is partially ordered along the ab-plane of the simple TTB structure, resulting in a √2-type TTB superstructure (Pbmm), while in Ba0.175TaO2.675, the pentagonal tunnel filling is completely ordered along the b-axis of the simple TTB structure, leading to a triple TTB superstructure (P21212). Both superstructures show completely empty square tunnels favoring Ba(2+) conduction and feature unusual accommodation of Ta(5+) cations in the small triangular tunnels. In contrast with stoichiometric Ba6GaTa9O30, which shows linear thermal expansion of the cell parameters and monotonic decrease of permittivity with temperature within 100-800 K, these TTB superstructures and slightly nonstoichiometric simple TTB Ba0.4TaO2.9 display abnormally broad and frequency-dependent extrinsic dielectric relaxations in 10(3)-10(5) Hz above room temperature, a linear deviation of the c-axis thermal expansion around 600 K, and high dielectric permittivity ∼60-95 at 1 MHz at room temperature.