Increased dependence on nitrogen-fixation of a native legume in competition with an invasive plant

Suppression of roots and/or their symbiotic microorganisms,such as mycorrhizal fungi and rhizobia,is an effective way for alien plants to outcompete native plants.However,little is known about how invasive and native plants interact with the quantity and activity of nutrient-acquisition agents.Here a pot experiment was conducted with monoculture and mixed plantings of an invasive plant,Xanthium strumarium,and a common native legume,Glycine max.We measured traits related to root and nodule quantity and activity and mycorrhizal colonization.Compared to the monoculture,fine root quantity(biomass,surface area)and activity(root nitrogen(N)concentration,acid phosphatase activity)of G.max decreased in mixed plantings;nodule quantity(biomass)decreased by 45%,while nodule activity in Nfixing via rhizobium increased by 106%;mycorrhizal colonization was unaffected.Contribution of N fixation to leaf N content in G.max increased in the mixed plantings,and this increase was attributed to a decrease in the rhizosphere soil N of G.max in the mixed plantings.Increased root quantity and activity,along with a higher mycorrhizal association was observed in X.strumarium in the mixed compared to monoculture.Together,the invasive plant did not directly scavenge N from nodule-fixed N,but rather depleted the rhizosphere soil N of the legume,thereby stimulating the activity of N-fixation and increasing the dependence of the native legume on this N source.The quantity-activity framework holds promise for future studies on how native legumes respond to alien plant invasions.

Unexpected Diversity in Ecosystem Nutrient Responses to Experimental Drought in Temperate Grasslands

The responses of ecosystem nitrogen (N) and phosphorus (P) to drought are an important component of globalchange studies. However, previous studies were more often based on site-specific experiments, introducing a significantuncertainty to synthesis and site comparisons. We investigated the responses of vegetation and soil nutrientsto drought using a network experiment of temperate grasslands in Northern China. Drought treatment (66%reduction in growing season precipitation) was imposed by erecting rainout shelters, respectively, at the driest,intermediate, and wettest sites. We found that vegetation nutrient concentrations increased but soil nutrient concentrationsdecreased along the aridity gradient. Differential responses were observed under experimentaldrought among the three grassland sites. Specifically, the experimental drought did not change vegetation andsoil nutrient status at the driest site, while strongly reduced vegetation but increased soil nutrient concentrationsat the site with intermediate precipitation. On the contrary, experimental drought increased vegetation N concentrationsbut did not change vegetation P and soil nutrient concentrations at the wettest site. In general, the differentialeffects of drought on ecosystem nutrients were observed between manipulative and observationalexperiments as well as between sites. Our research findings suggest that conducting large-scale, consistent, andcontrolled network experiments is essential to accurately evaluate the effects of global climate change on terrestrialecosystem bio-geochemistry.

Advances in machine learning-and artificial intelligence-assisted material design of steels

With the rapid development of artificial intelligence technology and increasing material data,machine learning-and artificial intelligence-assisted design of high-performance steel materials is becoming a mainstream paradigm in materials science.Machine learning methods,based on an interdisciplinary discipline between computer science,statistics and material science,are good at discovering correlations between numerous data points.Compared with the traditional physical modeling method in material science,the main advantage of machine learning is that it overcomes the complex physical mechanisms of the material itself and provides a new perspective for the research and development of novel materials.This review starts with data preprocessing and the introduction of different machine learning models,including algorithm selection and model evaluation.Then,some successful cases of applying machine learning methods in the field of steel research are reviewed based on the main theme of optimizing composition,structure,processing,and performance.The application of machine learning methods to the performance-oriented inverse design of material composition and detection of steel defects is also reviewed.Finally,the applicability and limitations of machine learning in the material field are summarized,and future directions and prospects are discussed.

Recent research progress on the phase-field model of microstructural evolution during metal solidification

Solidification structure is a key aspect for understanding the mechanical performance of metal alloys,wherein composition and casting parameters considerably influence solidification and determine the unique microstructure of the alloys.By following the principle of free energy minimization,the phase-field method eliminates the need for tracking the solid/liquid phase interface and has greatly accelerated the research and development efforts geared toward optimizing metal solidification microstructures.The recent progress in the application of phasefield simulation to investigate the effect of alloy composition and casting process parameters on the solidification structure of metals is summarized in this review.The effects of several typical elements and process parameters,including carbon,boron,silicon,cooling rate,pulling speed,scanning speed,anisotropy,and gravity,on the solidification structure are discussed.The present work also addresses the future prospects of phase-field simulation and aims to facilitate the widespread applications of phase-field approaches in the simulation of microstructures during solidification.

Tribological properties of high-entropy alloys:A review

Tribology,which is the study of friction,wear,and lubrication,largely deals with the service performance of structural materials.For example,newly emerging high-entropy alloys(HEAs),which exhibit excellent hardness,anti-oxidation,anti-softening ability,and other prop-erties,enrich the wear-resistance alloy family.To demonstrate the tribological behavior of HEAs systematically,this review first describes the basic tribological characteristics of single-,dual-,and multi-phase HEAs and HEA composites at room temperature.Then,it summarizes the strategies that improve the tribological property of HEAs.This review also discusses the tribological performance at elevated temperatures and provides a brief perspective on the future development of HEAs for tribological applications.

Polymer-/Ceramic-based Dielectric Composites for Energy Storage and Conversion

Dielectric composites boost the family of energy storage and conversion materials as they can take full advantage of both the matrix and filler.This review aims at summarizing the recent progress in developing highperformance polymer-and ceramic-based dielectric composites,and emphases are placed on capacitive energy storage and harvesting,solid-state cooling,temperature stability,electromechanical energy interconversion,and high-power applications.Emerging fabrication techniques of dielectric composites such as 3D printing,electrospinning,and cold sintering are addressed,following by highlighted challenges and future research opportunities.The advantages and limitations of the typical theoretical calculation methods,such as finite-element,phase-field model,and machine learning methods,for designing high-performance dielectric composites are discussed.This review is concluded by providing a brief perspective on the future development of composite dielectrics toward energy and electronic devices.

室温电致水结冰:相图中“遗漏”的一个高密度冰相

水可以根据温度(T)和压力(P)等外部条件冻结成不同的冰形态。分子动力学模拟显示,室温时,在高压和高电场强度的条件下,液态水可以自发形成一种高密度(1.27g/cm^3)的新型铁电冰晶体—“冰x相”。同时,基于爱因斯坦分子自由能计算方法,结果表明:在水相图上的一个高压低温区,冰x相是最稳定的结构。

氮添加对内蒙古草原植物地上和地下碳氮磷化学计量学特征的影响

氮沉降对生态系统功能和过程具有显著影响。已有研究表明氮添加会影响植物叶片C:N:P化学计量特征。然而,氮添加对植物根系C:N:P化学计量特征影响的研究罕有报道。本论文的主要目的是对比氮添加对草原植物群落地上和地下C:N:P化学计量特征的影响。我们在内蒙古锡林郭勒草原开展了一个7年的氮添加实验,该实验包括6个处理,分别是对照:control;N1:0.4 mol·m-2 N;N2:0.8 mol·m^(-2) N;N3:1.6 mol·m^(-2) N;N4:2.8 mol·m^(-2) N;N5:4 mol·m^(-2) N,每个处理6次重复。我们测量并分析了植物地上、地下生物量和C:N:P化学计量特征。研究结果表明,氮添加会导致植物群落地上部分碳浓度降低,氮浓度和磷浓度升高,C:N和C:P比值降低,N:P升高,而且地上碳、氮、磷库均因施氮而增加。然而,氮添加对0-10,10-30,30-50和50-100 cm 4个土层的地下部分碳、氮、磷浓度、比例、库和化学计量特征没有显著影响。综上所述,氮添加会显著改变植物群落地上部分C:N:P化学计量特征,进而影响草地生态系统的功能和过程,但对地下C:N:P化学计量特征几乎没有影响。

极端干旱与食草昆虫对草原群落的交互作用受干旱模式的影响

极端干旱和食草昆虫可以共同影响植物群落,并且它们的交互作用可能受到干旱模式的影响。然而,目前尚缺乏相关的观测证据。本研究以半干旱草原为研究对象,通过控制实验探讨了不同极端干旱模式与食草昆虫的交互作用对植物群落的影响。实验设置了3种干旱处理,分别为对照(自然降雨量)、慢性干旱(生长季5–8月减少66%降雨量)和急性干旱(6–7月完全无降雨)。在各小区设置了两种食草昆虫处理,分别是有食草昆虫和无食草昆虫。结果表明,食草昆虫和极端干旱及二者的交互作用对物种丰富度无显著影响。食草昆虫缓解了慢性干旱对总盖度的负面影响,而这种缓解作用在急性干旱下较低。食草昆虫对慢性干旱带来的负面效应具有更强的缓解作用,这主要是因为食草昆虫导致慢性干旱下适口性较高的杂类草(具有较低叶片碳含量、叶片干物质含量,以及较低叶片淀粉、钙、镁、锰含量)的大幅降低,进而降低了禾草的负面效应。上述结果表明,干旱和食草昆虫的交互作用受干旱模式的影响。通过调节植物的适口性来控制食草昆虫的采食行为,可以减轻极端干旱对草原生态系统的影响。

内蒙古草原优势物种光合速率对极端干旱的响应

评估极端干旱对优势植物物种光合速率(Pn)的影响对于我们理解极端干旱影响生态系统功能的机制至关重要。极端干旱可能由降雨量减少或降雨频率减少造成。这两种不同模式的极端干旱可能造成不同的影响。此外,不同草原类型可能对这两种极端干旱模式表现出不同的敏感性。然而,目前尚不清楚这两种极端干旱模式对草原优势植物物种Pn的影响有何差异,以及在不同草原类型这两种不同模式的极端干旱的效应是否改变。为此,我们于2014年在内蒙古草原两个不同类型的草原(荒漠草原vs.典型草原)站点各进行了一项多年的极端干旱(CHR:将生长季期间每次降雨事件的降雨量减少66%vs.INT:完全排除生长季内一段较短时间的降水)模拟实验。于2017年的7月和8月,我们在这两个草原站点各测量了两种优势物种的Pn。结果发现,CHR和INT均显著降低了优势物种的Pn。无论草原类型如何,INT对Pn造成的负面影响都更大。在荒漠草原,极端干旱对Pn的负面影响普遍大于典型草原,尤其是对于CHR处理下的羊草(Leymus chinensis)。这些结果表明,与降雨量减少相比,降雨频率减少所引起的极端干旱对Pn的负面影响更大。草地类型可能会改变极端干旱模式效应的程度,但不会改变其方向。这些发现强调了应对未来极端干旱的草原生态系统管理应考虑极端干旱模式和草地类型的影响。

Enhanced plastic deformation capacity in hexagonal-close-packed medium entropy alloys via facilitating cross slip

Alloys with a hexagonal close-packed(HCP)lattice often suffer from intrinsic brittleness due to their in-sufficient number of slip systems,which limits their practical uses.In this paper,nevertheless,we show that remarkably tensile ductility in HCP Hf-Zr-Ti medium entropy alloys(MEAs)was achieved,particu-larly in the MEAs with a higher content of Hf.Both first-principles calculation and experimental analyses reveal that addition of Hf increases basal I2 stacking fault energy and decreases prismatic stacking fault energy in these HCP MEAs,which promotes the source of pyramidal dislocations due to the facilitated cross slips of basal dislocations and eventually give rise to the observed large tensile ductility.Our current findings not only shed new insights into understanding deformation of HCP alloys,but also provide a basis for controlling alloying effects for developing novel HCP complex alloys with optimized properties.

Effects of trace elements on mechanical properties of the TiZrHfNb high-entropy alloy

Refractory high-entropy alloys have great potential to be utilized as high-temperature materials,and the repeatability and reproducibility of their mechanical properties are critical for practical applications.In this work,nevertheless,we found that the mechanical properties of the TiZrHfNb HEA greatly varied with the content of impurities in the samples even using high-purity raw materials.Specifically,the oxygen impurity is mainly responsible for the increment of the yield stress due to the strong interstitial hardening effect,whilst the ductility deterioration closely associates with the content of metalloid elements B,C,and Si.Our analysis reveals that the metalloid elements not only tend to segregate at grain boundaries but also enhance the aggregation of Zr and Ti.Such co-segregation induced the formation of strong(Zr,Ti)-metalloid bonds,resulting in grain boundary embrittlement and brittle fracture.Our current work demonstrates that the impurity contents in refractory HEAs need to be strictly controlled during production in order to improve their stability of mechanical performance.

New sensor technologies in quality evaluation of Chinese materia medica:2010–2015

New sensor technologies play an important role in quality evaluation of Chinese materia medica(CMM) and include near-infrared spectroscopy,chemical imaging,electronic nose and electronic tongue.This review on quality evaluation of CMM and the application of the new sensors in this assessment is based on studies from 2010 to 2015,with prospects and opportunities for future research.

Short-range ordering and its effects on mechanical properties of high-entropy alloys

In this letter,we briefly summarize experimental and theoretical findings of fo rmation and characterization of short-range orderings(SROs)as well as their effects on the defo rmation behavior of high-entropy alloys(HEAs).We show that existence of SROs is a common yet key structural feature of HEAs,and tuning the degree of SROs is an effective way for optimizing mechanical properties of HEAs.In additional,the challenges concerning about formation mechanism and characterization of SROs in HEAs are discussed,and future research activities in this regard are also proposed.

Oxidation behavior of Mo-Si-B alloys at medium-to-high temperatures

Continuous exploration of high-temperature structural materials is being driven by the needs of gasturbine engines capable of withstanding the high-temperature environment.Relatively low melting points of currently applied superalloys restrain the further improvement of service tempe ratures.With higher melting tempe ratures above 2000℃,Mo-Si-B alloys are regarded as a new generation of ultrahightemperature structural materials.However,oxidation is a concern for the industrial application of Mo-Si-B alloys.Therefore,an in-depth understanding of the oxidation mechanisms may contribute to solving this issue,whereas relevant reviews about their recent advances are lacking.In the current work,a comprehensively systematic review about the oxidation behaviors of Mo-Si-B alloys is described for this purpose.

New idea to promote the clinical applications of stem cells or their extracellular vesicles in central nervous system disorders:Combining with intranasal delivery

The clinical translation of stem cells and their extracellular vesicles(EVs)-based therapy for central nervous system(CNS) diseases is booming. Nevertheless, the insufficient CNS delivery and retention together with the invasiveness of current administration routes prevent stem cells or EVs from fully exerting their clinical therapeutic potential. Intranasal(IN) delivery is a possible strategy to solve problems as IN route could circumvent the brain-blood barrier non-invasively and fit repeated dosage regimens. Herein, we gave an overview of studies and clinical trials involved with IN route and discussed the possibility of employing IN delivery to solve problems in stem cells or EVs-based therapy. We reviewed relevant researches that combining stem cells or EVs-based therapy with IN administration and analyzed benefits brought by IN route. Finally, we proposed possible suggestions to facilitate the development of IN delivery of stem cells or EVs.

Herbivores alleviate the negative effects of extreme drought on plant community by enhancing dominant species

Aims Both extreme drought and insect herbivores can suppress plant growth in grassland communities.However,most studies have examined extreme drought and insects in isolation,and there is reason to believe that insects might alter the ability of grasslands to withstand drought.Unfortunately,few studies have tested the interactive effects of extreme drought and insect herbivores in grassland communities.Methods Here,we tested the drought–herbivore interactions using a manipulative experiment that factorially crossed extreme drought with the exclusion of insect herbivores in a temperate semiarid grassland in Inner Mongolia.Important Findings Our results demonstrated that both extreme drought and insect herbivores separately decreased total plant cover.When combined,insect herbivores reduced the impact of drought on total cover by increasing the relative abundance of drought-resistant dominant species.Our results highlight that the negative effect of extreme drought on total plant cover could be alleviated by maintaining robust insect herbivore communities.

Tradeoff between productivity and stability across above-and below-ground communities

Because of the aggravated agricultural fertilization and combustion of fossil fuels,the nitrogen(N)deposition rate has increased from the pre-industrial levels of about 0.1–0.3 to as high as 10 g N m^(-2)year^(-1)in some developed countries,and it is predicted to increase similarly over the next 50 years in many developing countries(Galloway et al.,2004).