Research progress and prospect of grassland degradation based on bibliometrics analysis during 1970–2020

To understand the research trends and areas of focus on the grassland degradation(GD),a bibliometric study based on the Science Citation Index-Expanded(SCI-E)was performed.This study presented a comprehensive overview of the field based on the annual papers,research areas,temporal trends in keywords,marked journals,institutions,and authors.In the SCI-E database,GD publications first appeared in1970.Thus,we chose the study period between 1970 and 2020.The results showed that the annual number of publications increased in exponential model,with an especially rapid increase after 2009.Dong S.K.,Wang S.P.,and Liu S.L.were the most competitive authors based on their large numbers of papers and citations.A keyword analysis indicated that“grazing,alpine grassland,soil carbon and nitrogen,plant diversity,vegetation restoration”was the most popular study area.The institution with the greatest research publications and most citations was the Chinese Academy of Sciences.Journal of Arid Environments was one of the most popular journals for researchers to publish their research and had greater influence in the field with larger citations than other journals.Environmental science and ecology,soil science,plant science,biodiversity protection,geoscience,and water resources were the most popular Web of Science research areas.The keywords knowledge map mainly divides into four clusters,which are“vegetation”,“soil carbon”,“climate change”,and“grazing”.The ten clusters of the author’s co-occurrence analysis showed that the research areas of GD mainly concentrate on alpine grassland of Qinghai Tibetan Plateau and temperate steppe of Inner Mongolia.Especially under global climate change and the increasing human activities,they were continually increasing close attention to the present.The research methods are mainly in the combination of micro and macro view,such as high-throughput sequencing of the microbial community,remote sensing,quantitative analysis of models,etc.The current international research frontiers are alpine meadow degradation and the assessment of ecosystem service in degraded grassland.To distinguish human activities and climate change to the GD rate is also a new research hotspot in recent years.As the first bibliometrics paper in GD,this paper presents an attempt to better understanding of the progress on GD research.

Housing Sulfur in Polymer Composite Frameworks for Li–S Batteries

Extensive efforts have been devoted to the design of micro-, nano-, and/or molecular structures of sulfur hosts to address the challenges of lithium–sulfur(Li–S) batteries, yet comparatively little research has been carried out on the binders in Li–S batteries. Herein, we systematically review the polymer composite frameworks that confine the sulfur within the sulfur electrode, taking the roles of sulfur hosts and functions of binders into consideration. In particular, we investigate the binding mechanism between the binder and sulfur host(such as mechanical interlocking and interfacial interactions), the chemical interactions between the polymer binder and sulfur(such as covalent bonding, electrostatic bonding, etc.), as well as the beneficial functions that polymer binders can impart on Li–S cathodes, such as conductive binders, electrolyte intake, adhesion strength etc. This work could provide a more comprehensive strategy in designing sulfur electrodes for long-life, large-capacity and high-rate Li–S battery.

Soil seed banks along elevational gradients in tropical, subtropical and subalpine forests in Yunnan Province, southwest China

Soil seed banks are a vital part of ecosystems and influence community dynamics and regeneration.Although soil seed banks in different habitats have been reported, how soil seed banks vary with elevational gradients in different climatic zones is still unknown. This paper investigates seed density,species composition and nonconstituent species of forest soil seed banks in Yunnan Province, southwest China. Similarity between the soil seed bank and standing vegetation was also examined. We collected soil samples from sites spanning 12 elevations in tropical rain forests, subtropical evergreen broadleaved forests and subalpine coniferous forests, and transported them to a glasshouse for germination trials for species identification. The soil seed banks of tropical and subtropical forests had much higher seed densities and species richness than those of subalpine forests. Seeds of woody species dominated the soil seed banks of tropical and subtropical forests, while herbs dominated those of subalpine forests.The nonconstituent species in the soil seed banks were all herbs and were most abundant in tropical forests, followed by subtropical forests but were completely absent from subalpine forests.

Nanoporous SiO_x coated amorphous silicon anode material with robust mechanical behavior for high-performance rechargeable Li-ion batteries

Silicon is a promising anode material for rechargeable Li-ion battery (LIB) due to its high energy density and relatively low operating voltage. However, silicon based electrodes suffer from rapid capacity degradation during electrochemical cycling. The capacity decay is predominantly caused by (i) cracking due to large volume variations during lithium insertion/extraction and (ii) surface degradation due to excessive solid electrolyte interface (SEI) formation. In this work, we demonstrate that coating of a-Si thin film with a Li-active, nanoporous SiOx layer can result in exceptional electrochemical performance in Li-ion battery. The SiOx layer provides improved cracking resistance to the thin film and prevent the active material loss due to excessive SEI formation, benefiting the electrode cycling stability. Half-cell experiments using this anode material show an initial reversible capacity of 2173 mAh g^-1 with an excellent coulombic efficiency of 90.9%. Furthermore, the electrode shows remarkable capacity retention of ~97% after 100 cycles at C/2 charging rate. The proposed anode architecture is free from Liinactive binders and conductive additives and provides mechanical stability during the charge/discharge process.

α-Fe_2O_3 nanoplates with superior electrochemical performance for lithium-ion batteries

On account of the high theoretical capacity, high corrosion resistance, environmental benignity, abundant availability and low cost, the research on a-Fe_2O_3 has been gradually fastened on as promising anodes materials toward lithium-ion batteries(LIBs). A high-performance anode for LIBs based on α-Fe_2O_3 nanoplates have been selectively prepared. The α-Fe_2O_3 nanoplates can be synthesized with iron ionbased ionic liquid as iron source and template. The α-Fe_2O_3 nanoplates as the anode of LIBs can display high capacity of around1950 mAh g^(-1) at 0.5 A g^(-1) which have exceeded the theoretical capacity of α-Fe_2O_3. On account of unique nanoplate structures and gum arabic as binder, the α-Fe_2O_3 nanoplates also exhibit high rate capability and excellent cycling performance.

Oil-Price Forecasting Based on Various Univariate Time-Series Models

Time-series-based forecasting is essential to determine how past events affect future events. This paper compares the performance accuracy of different time-series models for oil prices. Three types of univariate models are discussed: the exponential smoothing (ES), Holt-Winters (HW) and autoregressive intergrade moving average (ARIMA) models. To determine the best model, six different strategies were applied as selection criteria to quantify these models’ prediction accuracies. This comparison should help policy makers and industry marketing strategists select the best forecasting method in oil market. The three models were compared by applying them to the time series of regular oil prices for West Texas Intermediate (WTI) crude. The comparison indicated that the HW model performed better than the ES model for a prediction with a confidence interval of 95%. However, the ARIMA (2, 1, 2) model yielded the best results, leading us to conclude that this sophisticated and robust model outperformed other simple yet flexible models in oil market.

Changing the Paradigm

A simple but useful method of analysis of hyperbolic processes is presented and its application is illustrated by using the growth of human population in Africa, the economic growth in Western Europe and the examination of the fundamental postulates of the Unified Growth Theory. It is shown how this method can revolutionize the interpretation of the historical economic growth and the growth of human population and how it can help to understand the current growth. Examples used to illustrate the application of this method show that, contrary to the accepted interpretations, the Industrial Revolution and the accompanying unprecedented technological development had no impact on the economic growth even in Western Europe and that Galor’s Unified Growth Theory fails the scientific test.

Environmental and spatial contributions to seedling and adult tree assembly across tropical,subtropical and subalpine elevational gradients

Aims Quantifying the relative importance of the mechanisms that drive community assembly in forests is a crucial issue in community ecol-ogy.The present study aims to understand the ways in which niche-based and spatially based processes influence community assembly in areas in different climatic conditions and how these processes change during the transition from seedling to adult.Methods In this study,we investigated how taxonomic and phylogenetic beta diversity in seedling and adult stages of forest trees change across three elevational transects in tropical,subtropical and subalpine for-ests in Southwest China,and the relationships of these changes to the environment and inter-site distances.We quantified the relative contribution of environmental conditions and spatial distribution to taxonomic and phylogenetic beta diversity of both seedling and adult life stages along each elevational transect.We also quantified the taxonomic and phylogenetic similarity between seedlings and adult trees along elevations.Important Findings Taxonomic and phylogenetic beta diversity of both seedlings and adult trees increased with an increase in both environmental distance and spatial distance in all three transects.On both taxonomic and phylo-genetic levels,the effects of environmental filtering and spatial dispos-ition varied between life stages and among forest types.Phylogenetic similarity between seedlings and adult trees increased with elevation,although the taxonomic similarity did not show clear elevational pat-terns.Our results suggest that the relative contribution of niche-based and space-based processes to taxonomic and phylogenetic assem-blages varies across major plant life stages and among forest types.Our findings also highlight the importance of ontogenetic stages for fully understanding community assembly of long-lived tree species.

青藏高原高寒草地土壤微生物群落及影响因子

青藏高原是我国生态安全的重要屏障,但目前青藏高原上大尺度上的微生物地理学研究还很缺乏.因此,采用高通量测序技术,在跨越2121 km的尺度上针对高寒草地不同生态系统类型研究了土壤原核生物(细菌和古菌)微生物量、多样性和群落组成的分布格局,及与气候、植物和土壤因子的关系.在高寒草甸、高寒草原、高寒灌丛和高寒荒漠中,高寒荒漠具有最低的微生物多样性,而高寒草甸具有最高的微生物量碳.高寒草地土壤微生物的多样性与大气温度而非降水显著相关,说明其在高寒条件下可能受温度而非水分控制.微生物多样性随耦合了水、热要素的干旱指数的增加而降低,解释量比单一要素更高.此外,植物功能群多样性与微生物多样性有显著的正相关关系,解释量比植物物种多样性更高.结构方程模型显示,干旱指数和年均温通过影响植物功能群多样性和地上生物量而改变土壤表层的碳氮比,从而直接或间接影响到微生物多样性.与多样性不同,土壤微生物量碳与可溶性有机碳、氨态氮、速效磷及碳氮比等土壤营养指标和植物地上生物量具有显著的相关性.这些结果意味着微生物多样性和微生物量可能有着不同的控制因子;随着未来青藏高原的'暖湿化',干旱指数的降低可能提高土壤微生物的多样性.

Microporous bamboo biochar for lithium-sulfur batteries

Being simple, inexpensive, scalable and environmentally friendly, microporous biomass biochars have been attracting enthusiastic attention for application in lithium-sulfur （Li-S） batteries. Herein, porous bamboo biochar is activated via a KOH/annealing process that creates a microporous structure, boosts surface area and enhances electronic conductivity. The treated sample is used to encapsulate sulfur to prepare a microporous bamboo carbon-sulfur （BC-S） nanocomposite for use as the cathode for Li-S batteries for the first time. The BC-S nanocomposite with 50 wt.% sulfur content delivers a high initial capacity of 1,295 mA-h/g at a low discharge rate of 160 mA/g and high capacity retention of 550 mA-h/g after 150 cycles at a high discharge rate of 800 mA/g with excellent coulombic efficiency （995%）. This suggests that the BC-S nanocomposite could be a promising cathode material for Li-S batteries.

High-performance aqueous symmetric sodium-ion battery using NASICON-structured Na2VTi（PO4）3

A high-safety and low-cost route is important in the development of sodium-ion batteries, especially for large-scale stationary battery systems. An aqueous sodium-ion battery is demonstrated using a single NASICON-structured Na2VTi（PO4）3 material with the redox couples of V4＋/V3＋ and Ti4＋/Ti3＋ working on the cathode and anode, respectively. The symmetric full cell fabricated based on the bi-functional electrode material exhibits a well-defined voltage plateau at ~ 1.2 V and an impressive cycling stability with capacity retention of 70% exceeding 1,000 cycles at 10C （1C = 62 mA.g-1）. This study provides a feasible strategy for obtaining high-safety and low-cost rechargeable batteries using a single active material in aqueous media.

Hydrogenation of nanostructured semiconductors for energy conversion and storage

Nanostructured semiconductors have been researched intensively for energy conversion and storage applications in recent decades.Despite of tremendous findings and achievements,the performance of the devices resulted from the nanomaterials in terms of energy conversion efficiency and storage capacity needs further improvement to become economically viable for subsequent commercialization.Hydrogenation is a simple,efficient,and cost-effective way for tailoring the electronic and morphological properties of the nanostructured materials.This work reviews a series of hydrogenated nanostructured materials was produced by the hydrogenation of a wide range of nanomaterials.These materials with improved inherent conductivity and changed characteristic lattice structure possess much enhanced performance for energy conversion application,e.g.,photoelectrocatalytic production of hydrogen,and energy storage applications,e.g.,lithium-ion batteries and supercapacitors.The hydrogenation mechanisms as well as resultant properties responsible for the efficiency improvement are explored in details.This work provides guidance for researchers to use the hydrogenation technology to design functional materials.

Root-order-associated variations in fine-root decomposition and their effects on soil in a subtropical evergreen forest

Background:Despite the importance of root decomposition in predicting ecosystem responses to future climate change,the effects of branch order on root decomposition and the feedback to soil still remains poorly understood.Here we separated root samples taken from two tree species(Castanopsis fargesii and Schima superba in subtropical forests along the coastal area in eastern China)into four-order classes(1st–2nd order,3rd order,4th order,and 5th order)and conducted a 540-day litterbag incubation experiment in laboratory to examine root mass loss,nutrient release,and the influence on soil during decomposition.Results:C.fargesii roots of 1st–2nd and 3rd order decayed more slowly than those of 4th and 5th order,but this pattern was not significant for S.superba.Of all the measured root traits,the decomposition rates correlated best with root C/N ratio,diameter and specific root length(SRL)based on the structural equation modeling.Both tree species and root order exhibited significantly effects on root initial traits.Overall,C.fargesii roots decay faster than S.superba,and this appears to be associated with root initial C quality and N concentration.In addition,root order positively affected root decomposition rates mainly through root diameter and SRL.However,no significant difference was found in C and N content between soils below the litterbag with different-order roots.Conclusions:Our findings suggest the effects of branch order on root decomposition are dependent on tree species.Moreover,root morphological properties might also be the controlling factor in root decay besides root chemistry fractions.Overall,the integrative effects should be considered to improve our understanding of the fate of fine-root litter and their contribution to soil C and N pool.

Interactive antimicrobial and toxicity profiles of Pittosporum angustifolium Lodd. extracts with conventional antimicrobials

Objective: Pittosporum angustifolium Lodd. is used to treat a variety of pathogenic diseases and inflamma-tion by Australian aborigines. Practitioners of complementary medicine frequently use herbal medicines concurrently with conventional antibiotics. There is a need to evaluate their effects in combination. Methods: The bacterial growth inhibitory activity of P. angustifolium leaf extracts was assessed against a panel of pathogenic triggers of some autoimmune diseases by standard disc diffusion and liquid dilution minimum inhibitory concentration (MIC) methods. Combinational effects between the extracts and con-ventional antimicrobials were classified using the sum of the fractional inhibitory concentration. Synergistic interactions were further assessed across a range of ratios by isobologram analysis. The tox-icity of the individual samples and combinations was evaluated by Anemia lethality and 3-(4,5-dimethyl thiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium) human dermal fibroblast cell viability assays. Results: P. angustifolium leaf extracts strongly inhibited the growth of several bacterial triggers of autoim-mune diseases. The methanolic, aqueous and ethyl acetate extracts were pwrticularly good inhibitors of Proteus mirabilis and Klebsiella pneumonia growth (MIC=26 and 57 ng/mL respectively). Some combinations of the extracts and conventional antibiotics signiflcantlv potentiated the combined inhibitory activity compared to the individual components. Of the 250 combinations studied, approximately 0.02% showed synergistic interactions, 49.6% were additive, 46.8% showed indifferent interactions and antago-nism occurred in only 0.02% of the combinations. Interestingly, all of the synergistic and antagonistic combinations contained tetracycline as their antibiotic component. Conclusion: P. angustifolium leaf extracts inhibit the growth of pathogenic triggers of some autoimmune diseases. Some extracts also potentiated the activity of conventional antibiotics, without significantly affecting the toxicity of the combination.