Elliptically polarized high-order harmonic generation in nitrogen molecules with cross-linearly polarized two-color laser fields

Circularly and elliptically polarized high-order harmonics have unique advantages when used in studying the chiral and magnetic features of matter.Here,we studied the polarization properties of high-order harmonics generated from alignment nitrogen molecules driven by cross-linearly polarized two-color laser fields.Through adjusting various laser parameters and targets,such as the relative phase,the crossing angle,the intensity ratio of the driving fields,and the molecular alignment angle,we obtained highly elliptically polarized high-order harmonics with the same helicity in a wide spectral range.This provides a possible effective way to generate elliptically polarized attosecond pulses.Finally,we showed the probability of controlling the spectral range of elliptically polarized harmonics.

Phase separation of GRP7 facilitated by FERONIAmediated phosphorylation inhibits mRNA translation to modulate plant temperature resilience

Changes in ambient temperature profoundly affect plant growth and performance.Therefore,the molecu-larbasis of plant acclimation to temperature fluctuation is of great interest.In this study,we discovered that GLYCINE-RICH RNA-BINDING PROTEIN 7(GRP7)contributes to cold and heat tolerance in Arabidopsis thaliana.We found that exposure to a warm temperature rapidly induces GRP7 condensates in planta,which can be reversed by transfer to a lower temperature.Cell biology and biochemical assays revealed that GRP7 undergoes liquid-liquid phase separation(LLPS)in vivo and in vitro.LLPS of GRP7 in the cyto-plasm contributes to the formation of stress granules that recruit RNA,along with the translation machinery component eukaryotic initiation factor 4E1(elF4E1)and the mRNA chaperones COLD SHOCK PROTEIN 1(CSP1)and CSP3,to inhibit translation.Moreover,natural variations in GRP7 affecting the residue phos-phorylated by the receptorkinase FERONIA alter its capacity to undergo LLPS and correlate with the adap-tation of some Arabidopsis accessions to a widertemperature range.Taken together,ourfindings illustrate the role of translational control mediated by GRP7 LLPS to confer plants with temperature resilience.

Similarity on neural stem cells and brain tumor stem cells in transgenic brain tumor mouse models

Although it is believed that glioma is derived from brain tumor stem cells, the source and molecular signal pathways of these cells are still unclear. In this study, we used stable doxycycline-inducible transgenic mouse brain tumor models （c-myc/SV40Tag＋/Tet-on＋） to explore the malignant trans- formation potential of neural stem cells by observing the differences of neural stem cells and brain tumor stem cells in the tumor models. Results showed that chromosome instability occurred in brain tumor stem cells. The numbers of cytolysosomes and autophagosomes in brain tumor stem cells and induced neural stem cells were lower and the proliferative activity was obviously stronger than that in normal neural stem cells. Normal neural stem cells could differentiate into glial fibrillary acidic protein-positive and microtubule associated protein-2-positive cells, which were also negative for nestin. However, glial fibrillary acidic protein/nestin, microtubule associated protein-2/nestin, and glial fibrillary acidic protein/microtubule associated protein-2 double-positive cells were found in induced neural stem cells and brain tumor stem cells. Results indicate that induced neural stem cells are similar to brain tumor stem cells, and are possibly the source of brain tumor stem cells.

Manipulating Nonsequential Double Ionization of Argon Atoms via Orthogonal Two-Color Field

Using a three-dimensional classical ensemble model,we investigate the dependence of relative frequency and relative initial phase for nonsequential double ionization(NSDI)of atoms driven by orthogonal two-color(OTC)fields.Our findings reveal that the NSDI probability is clearly dependent on the relative initial phase of OTC fields at different relative frequencies.The inversion analysis results indicate that adjusting the relative frequency of OTC fields helps control returning probability and flight time of the first electron.Furthermore,manipulating the relative frequency at the same relative initial phases can vary the revisit time of the recolliding electron,leading that the emission direction of Ar^(2+)ions is explicitly dependent on the relative frequency.

降水格局改变及氮沉降对北方典型草原土壤线虫多样性的影响

在全球气候变化的影响下,干旱和半干旱地区的降水格局呈现出降雨强度增加、降雨频率减少但降雨总量不变的趋势。大气氮沉降作为另一个全球气候变化的重要因子,沉降速率逐年加剧,显著影响生态功能及过程。线虫是陆地生态系统中最主要的土壤生物,参与多种地下生态过程。线虫群落的多样性尤其是功能、系统发育多样性如何对降水格局的改变做出响应,以及氮沉降如何调节这些响应,目前仍不清楚。本研究利用中国科学院植物研究所多伦恢复生态学试验研究站长期模拟降水格局改变及氮沉降添加试验平台,开展了5个降雨强度(2 mm、5 mm、10 mm、20 mm、40 mm)处理和氮添加(10 g N·m^(-2)·yr^(-1))对土壤线虫分类、功能和系统发育多样性的影响研究。结果表明,降水强度较强但频率较低可以提高线虫的分类α多样性、功能α多样性、系统发育α多样性;同时降低了分类β多样性和系统发育β多样性。然而,氮添加降低了中高强度降水处理下线虫的分类α多样性、功能α多样性、系统发育α多样性,同时提高了分类β多样性、功能β多样性和系统发育β多样性。土壤含水量和土壤微生物量碳含量是影响线虫功能及系统发育多样性的主要因素。本研究结果表明,由于全球气候变化,未来几十年降雨强度的增加可能有利于干旱和半干旱生态系统中的土壤线虫功能多样性和系统发育多样性。然而,在氮沉降严重的地区,这种正效应可能会被氮沉降导致的土壤环境的恶化所抵消。

Effect of grassland degradation on soil quality and soil biotic community in a semi-arid temperate steppe

Grasslands provide a number of ecosystem services for human society.Degradation of grasslands results in the loss of biodiversity and leads to the deterioration of ecosystem functions.In order to accurately assess the influence of grassland degradation on belowground ecosystems,we conducted experiments on a temperate steppe with different levels of degradation and investigated the influence of degradation on soil quality and soil biotic communities.Our results showed that grassland degradation significantly decreased soil quality,with lower values of soil quality index(SQI)observed in the degraded grassland than the meadow steppe and the grassland from the forest-steppe ecotone.Changes in the SQI along the grassland degradation gradient were positively correlated with soil carbon stock and the aboveground biomass,and negatively correlated with the root shoot ratio.Nematode trophic diversity and the ratio of fungal to bacterial PLFA were lower in the degraded grassland than the grassland from the forest-steppe ecotone.The dissimilarities in soil microbial and nematode community composition increased with the changes in soil quality index.Our results indicate that soil quality index based on the minimum data sets could effectively assess the influence of grassland degradation on soil biodiversity and ecosystem function.In order to effectively restore degraded grasslands,the key contributors to the soil quality,such as soil carbon,should be taken on priority basis for revitalizing the soil biodiversity and ecosystem function.

Database and primer selections affect nematode community composition under different vegetations of Changbai Mountain

High-throughput sequencing technology is increasingly used in the study of nematode biodiversity.However,the annotation difference of commonly used primers and reference databases on nematode community is still unclear.We compared two pairs of primers(3NDf/C_1132rmod,NF1F/18Sr2bR)and three databases(NT_V20200604,SILVA138/18s Eukaryota and PR2_v4.5 databases)on the determination of nematode community from four different vegetation types in Changbai Mountain,including mixed broadleaf-conifer forest,dark coniferous forest,betula ermanii Cham and alpine tundra.Our results showed that the selection of different primers and databases influenced the annotation of nematode taxa,but the diversity of nematode community showed consistent pattern among different vegetation types.Our findings emphasize that it is necessary to select appropriate primer and database according to the target taxonomic level.The difference in primers will affect the result of nematode taxa at different classification levels,so sequencing analysis cannot be used for comparison with studies using different primers.In terms of annotation effect in this study,3NDf/C_1132rmod primers with NT_v20200604 database could provide more information than other combinations at the genus or species levels.

高通量测序技术在线虫多样性研究中的应用

土壤线虫多样性是土壤生态学研究的热点之一,然而对土壤线虫群落组成及多样性的研究通常受到分类学和方法学的限制。当前,分子生物学技术的快速发展丰富了我们对土壤线虫多样性的认识,但也存在一定的局限性。本文综述了常用分子生物学技术如变性梯度凝胶电泳(denaturing gradient gel electrophoresis,DGGE)、末端限制性片段长度多态性分析(terminal restriction fragment length polymorphism,T-RFLP)、实时荧光定量PCR(quantitative real-time PCR,qPCR)和高通量测序(high-throughput sequencing,HTS)技术近年来在线虫多样性研究中的应用,重点从土壤线虫DNA提取方法、引物和数据库的选择、高通量测序技术和形态学鉴定结果的比较等方面阐述了高通量测序技术在线虫多样性研究中的优势与不足,并提出选择合适的线虫DNA提取方法结合特定引物和数据库进行注释分析,仍是今后使用高通量测序技术开展线虫多样性研究的重点。当研究目标是土壤线虫多样性时,优先推荐富集线虫悬液提取DNA的方法,因此,研究人员应根据具体目标选择最优组合开展实验研究。

揭开“植物细胞感知胞外酸碱性”之谜

细胞外pH(简称胞外pH)是调控生长和免疫的重要因素.细菌、真菌、哺乳动物细胞感知胞外pH的机制已被揭示[1].早在20世纪90年代,科学家们就提出假设:植物细胞也具有感知胞外pH的能力[2].但该机制至今未被阐明.近期,南方科技大学郭红卫课题组与清华大学-德国马克斯普朗克研究所-科隆大学柴继杰课题组合作,以模式植物拟南芥的根尖分生组织(root apical meristem, RAM)为模型,发现了基于细胞表面“配体-受体复合物”的胞外pH感应机制.此机制不仅调节了RAM的生长、发育过程,也参与了根部细胞的免疫反应[3].

Mowing did not mitigate the negative effects of nitrogen deposition on soil nematode community in a temperate steppe

Soil nematodes are the most numerous components of the soil fauna in terrestrial ecosystems.The occurrence and abundance of nematode trophic groups determine the structure and function of soil food webs.However,little is known about how nitrogen deposition and land-use practice(e.g.mowing)affect soil nematode communities.We investigated the main and interactive effects of nitrogen addition and mowing on soil nematode diversity and biomass carbon in nematode trophic groups in a temperate steppe in northern China.Nitrogen addition and mowing significantly decreased the abundance of soil nematodes and trophic diversity but had no effects on nematode richness and the Shannon-Wiener diversity.Nitrogen addition influenced soil nematode communities through decreasing soil pH.Mowing influenced soil nematode communities through decreasing soil moisture.Nitrogen addition enhanced the bacterial energy channel but mowing promoted fungal energy channel in the soil micro-food web.Our study emphasizes that ecosystem function supported by soil organisms can be greatly influenced by nitrogen deposition,and mowing cannot mitigate the negative effects of nitrogen deposition on soil food webs.

Predictions of high-pressure structural, electronic and thermodynamic properties of α-Si_3N_4

The plane-wave pseudo-potential method within the framework of first-principles technique is used to investigate the fundamental structural properties of Si3N4. The calculated ground-state parameters agree quite well with the experimental data. Our calculation reveals that α-Si3N4 can retain its stability to at least 45 GPa when compressed below 300 K. No phase transition can be seen in the pressure range of 0-45 GPa and the temperature range of 0-300 K. Actually, the α→β transition occurs at 1600 K and 7.98 GPa. Many thermodynamic properties, such as bulk modulus, heat capacity, thermal expansion, Gr/ineisen parameter and Debye temperature of a-Si3N4 were determined at various temperatures and pressures. Significant differ- ences in these properties were observed at high temperature and high pressure. The calculated results are in good agreement with the available experimental data and previous theoretical values. Therefore, our results may provide useful information for theoretical and experimental investigations of the N-based hard materials like α-Si3N4.