Dynamic load on anchoring structures(AS)within deep roadways can result in cumulative damage and failure.This study develops an experimental device designed to test AS under triaxial loads.The device enables the inves...Dynamic load on anchoring structures(AS)within deep roadways can result in cumulative damage and failure.This study develops an experimental device designed to test AS under triaxial loads.The device enables the investigation of the mechanical response,failure mode,instability assessment criteria,and anchorage effect of AS subjected to combined cyclic dynamic-static triaxial stress paths.The results show that the peak bearing strength is positively correlated with the anchoring matrix strength,anchorage length,and edgewise compressive strength.The bearing capacity decreases significantly when the anchorage direction is severely inclined.The free face failure modes are typically transverse cracking,concave fracturing,V-shaped slipping and detachment,and spallation detachment.Besides,when the anchoring matrix strength and the anchorage length decrease while the edgewise compressive strength,loading rate,and anchorage inclination angle increase,the failure intensity rises.Instability is determined by a negative tangent modulus of the displacement-strength curve or the continued deformation increase against the general downward trend.Under cyclic loads,the driving force that breaks the rock mass along the normal vector and the rigidity of the AS are the two factors that determine roadway stability.Finally,a control measure for surrounding rock stability is proposed to reduce the internal driving force via a pressure relief method and improve the rigidity of the AS by full-length anchorage and grouting modification.展开更多
Understanding the hydrological processes of forest ecosystems in Tibetan Plateau is crucial for protecting water resources and the environment, especially considering that evapotranspiration is the most dominant hydro...Understanding the hydrological processes of forest ecosystems in Tibetan Plateau is crucial for protecting water resources and the environment, especially considering that evapotranspiration is the most dominant hydrologic process in most forest systems. SHAW, as a physically based, hydrological model, provides a useful tool for understanding and analyzing evapotranspiration processes. Using the measured data of a faber fir forest ecosystem in eastern Tibetan Plateau, this paper assessed the model performance in simulating evapotranspiration and variability and transferability of the model parameters. Comparison of the simulated results by SHAW to the measured data showed that SHAW performed satisfactorily. Based on analyzing the simulated results by the calibrated and validated SHAW, some ET characteristics of faber fir forest ecosys-tem in the eastern Tibetan Plateau were found: 1) Daily plant transpiration is low, and daily ET mainly comes from surface evaporation including canopy, litter and soil evaporation. Peak ET rate was approxi-mately 4mm/day, occurring around late July. 2) Solar radiation is the most important factor accounting for daily ET variation, while air temperature is the secondary, wind speed and air relative humidity are minor and soil water storage is the least important among all the related factors. 3) The ratio of annual ET to pre-cipitation for the faber fir forest ecosystem in eastern Tibetan Plateau is low (18%) compared with the other forest ecosystems owing to high-elevation, high atmospheric humidity and low annual temperature.展开更多
Elucidating the factors that determine the effects of temporal and spatial variation of nutrients is important for analyzing the characteristics of an ecosystem. The goal of this paper was to estimate how values obtai...Elucidating the factors that determine the effects of temporal and spatial variation of nutrients is important for analyzing the characteristics of an ecosystem. The goal of this paper was to estimate how values obtained using a particular sampling approach correlated with the actual data for an entire plot. The mesh partition method was employed to divide an integrated observing field (IOF) located at the Haibei National Field Research Station of an alpine grassland ecosystem, China, into 25 subplots. Five of the 25 subplots were randomly selected for soil sampling and to determine the source of variations in soil nutrient content from 2001 to 2012. The results showed that, contributions of temporal and spatial variation in available nitrogen in the 0 - 10 cm soil layer accounted for 47.3% and 52.7%, respectively. The contribution of spatial variance was higher than that of temporal variance especially in the surface soil layers. The available soil nitrogen content in the alpine meadow was not obviously affected by fluctuations in rainfall and temperature. Increasing the number of samples could reduce calculation errors in measuring available soil nitrogen content, while collecting a reasonable number of samples can save time and labor.展开更多
Ordered nanoripples on the niobium-doped SrTiO_3 surfaces were fabricated through focused ion beam bombardment. The surface morphology of the SrTiO_3 nanoripples was characterized using in situ focused ion beam/scanni...Ordered nanoripples on the niobium-doped SrTiO_3 surfaces were fabricated through focused ion beam bombardment. The surface morphology of the SrTiO_3 nanoripples was characterized using in situ focused ion beam/scanning electron microscopy. The well-aligned SrTiO_3 nanostructures were obtained under optimized ion irradiation conditions. The characteristic wavelength was measured as about 210 nm for different ion beam currents. The relationship between the ion irradiation time and current and SrTiO_3 surface morphology was analyzed. The presented method will be an effective supplement for fabrication of SrTiO_3 nanostructures that can be used for ferroelectric and electronic applications.展开更多
Plants require a number of essential elements in different proportions for ensuring their growth and development.The elemental concentrations in leaves reflect the functions and adaptations of plants under specific en...Plants require a number of essential elements in different proportions for ensuring their growth and development.The elemental concentrations in leaves reflect the functions and adaptations of plants under specific environmental conditions.However,less is known about how the spectrum of leaf elements associated with resource acquisition,photosynthesis and growth regulates forest biomass along broad elevational gradients.We examined the influence of leaf element distribution and diversity on forest biomass by analyzing ten elements(C,N,P,K,Ca,Mg,Zn,Fe,Cu,and Mn)in tree communities situated every 100 meters along an extensive elevation gradient,ranging from the tropical forest(80 meters above sea level)to the alpine treeline(4200 meters above sea level)in the Kangchenjunga Landscape in eastern Nepal Himalayas.We calculated communityweighted averages(reflecting dominant traits governing biomass,i.e.,mass-ratio effect)and functional divergence(reflecting increased trait variety,i.e.,complementarity effect)for leaf elements in a total of 1,859 trees representing 116 species.An increasing mass-ratio effect and decreasing complementarity in leaf elements enhance forest biomass accumulation.A combination of elements together with elevation explains biomass(52.2%of the variance)better than individual elemental trait diversity(0.05%to 21%of the variance).Elevation modulates trait diversity among plant species in biomass accumulation.Complementarity promotes biomass at lower elevations,but reduces biomass at higher elevations,demonstrating an interaction between elevation and complementarity.The interaction between elevation and mass-ratio effect produces heterogeneous effects on biomass along the elevation gradient.Our research indicates that biomass accumulation can be disproportionately affected by elevation due to interactions among trait diversities across vegetation zones.While higher trait variation enhances the adaptation of species to environmental changes,it reduces biomass accumulation,especially at higher elevations.展开更多
Backgrounds:Grazing prohibition and reduced grazing intensity,as two important“vegetation close-to-nature recovery”methods,have been suggested as economical and effective technologies for enhancing forage production...Backgrounds:Grazing prohibition and reduced grazing intensity,as two important“vegetation close-to-nature recovery”methods,have been suggested as economical and effective technologies for enhancing forage production.However,numerous studies have found that the yield of forage could be increased by removing or reducing grazing in a short time in some steady stage of alpine Kobresia meadows,but not in others.To reveal the mechanism behind this phenomenon,we proposed a series of experiments.Methods:We monitored the plant and soil characteristics in the key steady stages of Kobresia meadows under reduced and prohibited grazing conditions in the same geographic and climatic environments in the northeastern Qinghai-Tibet Plateau for 6 years.We estimated the relationships between the plant community and soil nutrients and obtained the following results.Results:All measured variables were positively correlated with each other.The plant community structure had higher path coefficients to aboveground biomass,soil organic matter,total nitrogen,and nitrate nitrogen than to other factors.The plant community structure played an important role in response to grazing intensity.Different plant functional groups(PFGs)had different responses to grazing intensity,which led to plant community re-establishment or re-organization under different grazing intensities.Poaceae and Kobresia were more sensitive to grazing intensity than other PFGs,and the ratio of Kobresia biomass(including Kobresia humilis and Kobresia pygmaea)to the total biomass of Poaceae and Kobresia could be used as an indicator of regime shifts within plant communities.With Kobresia pygmaea as the dominant species,the prohibition of grazing was not an efficient approach to increase the yield in the steady stages because this treatment needed more time to recover aboveground biomass.If Poaceae is the dominant PFG,grazing should only be prohibited for 3 years in the steady stages because the aboveground biomass will decrease if grazing is prohibited for more than 3 years.Conclusions:Therefore,the different steady stages of alpine meadows require different recovery methods to increase recovery efficiency and speed.展开更多
Background:Due to the effects of climate change and overgrazing in recent decades,alternative stable states in the alpine Kobresia meadow degradation process have coexisted in the same geographical and climatic enviro...Background:Due to the effects of climate change and overgrazing in recent decades,alternative stable states in the alpine Kobresia meadow degradation process have coexisted in the same geographical and climatic environment,with variations occurring among microsites.Methods:We used a space-for-time substitution approach to explore the synergies of microsite variation according to its numerical characteristics and the proportion of each stable state at various stages of succession in alpine Kobresia meadows on the Qinghai-Tibetan Plateau.Results:(1)The highest average aboveground biomass in summer was 196.2±20.3 gm^(-2),with significantly higher levels of biomass in≤3.65 sheep unit ha^(-1) than in other levels of grazing intensity,while the parameters showed no significant differences among grazing intensity levels in>3.65 sheep unit ha^(-1).(2)The importance of plant functional groups,aboveground biomass,and niche breadth of Poaceae and Cyperaceae significantly decreased as the grazing intensity increased.(3)The effects of≥0°C accumulated temperature,total precipitation,altitude,longitude,and latitude cumulatively contributed less than 20%of the variation in the distribution of functional group characteristics across microsites.Conclusions:(1)Overgrazing decreases primary production in alpine Kobresia meadows,but ecosystem responses regulate plant community structure and botanical components so as to partially counteract grazing disturbance.(2)Overgrazing changed the proportion of microsites,which in turn led to regime shift in the plant community and subsequent synergies between the microsites of plant communities and their stable states.展开更多
Assessment of soil health requires complexevaluation of properties and functions responsible for abroad range of ecosystem services. Numerous soil qualityindices (SQI) have been suggested for the evaluation ofspecific...Assessment of soil health requires complexevaluation of properties and functions responsible for abroad range of ecosystem services. Numerous soil qualityindices (SQI) have been suggested for the evaluation ofspecific groups of soil functions, but comparison of variousSQI is impossible because they are based on a combinationof specific soil properties. To avoid this problem, wesuggest an SQI-area approach based on the comparison ofthe areas on a radar diagram of a combination of chemical,biological and physical properties. The new approach isindependent of the SQI principle and allows rapid andsimple comparison of parameter groups and soils. Anotherapproach analyzing the resistance and sensitivity ofproperties to degradation is suggested for a detailedevaluation of soil health. The resistance and sensitivityof soil properties are determined through comparison withthe decrease of soil organic carbon (SOC) as a universalparameter responsible for many functions. The SQI-areaand resistance/sensitivity approaches were tested based on quences after the ab and on ment of agricultural soils. Both the SQI-area and the resistance/sensitivity approaches areuseful for basic and applied research, and for decisionmakersto evaluate land-use practices and measure thedegree of soil degradation.展开更多
Reclamation of degraded grasslands as managed grasslands has been increasingly accelerated in recent years in China. Land use change affects soil nitrogen(N) dynamics and nitrous oxide(N2O) emissions. However, it ...Reclamation of degraded grasslands as managed grasslands has been increasingly accelerated in recent years in China. Land use change affects soil nitrogen(N) dynamics and nitrous oxide(N2O) emissions. However, it remains unclear how large-scale grassland reclamation will impact the grassland ecosystem as a whole. Here, we investigated the effects of the conversion from native to managed grasslands on soil N dynamics and N2O emissions by field experiments in Hulunber in northern China. Soil(0-10 cm), nitrate(NO3-),ammonium(NH4+), and microbial N were measured in plots in a temperate steppe(Leymus chinensis grassland) and two managed grasslands(Medicago sativa and Bromus inermis grasslands) in 2011 and 2012. The results showed conversion of L. chinensis grassland to M.sativa or B. inermis grasslands decreased concentrations of NO3--N, but did not change NH4-N . Soil microbial N was slightly decreased by the conversion of L. chinensis grassland to M.sativa, but increased by the conversion to B. inermis. The conversion of L. chinensis grassland to M. sativa(i.e., a legume grass) increased N2O emissions by 26.2%, while the conversion to the B. inermis(i.e., a non-legume grass) reduced N2O emissions by 33.1%. The conversion from native to managed grasslands caused large created variations in soil NO3-+-N and NH4-N concentrations. Net N mineralization rates did not change significantly in growing season or vegetation type, but to net nitrification rate. These results provide evidence on how reclamation may impact the grassland ecosystem in terms of N dynamics and N2O emissions.展开更多
This paper presents the design and fabrication of an etched implant junction termination extension(JTE)for high-voltage 4H-SiC PiN diodes. Unlike the conventional JTE structure, the proposed structure utilizes multi...This paper presents the design and fabrication of an etched implant junction termination extension(JTE)for high-voltage 4H-SiC PiN diodes. Unlike the conventional JTE structure, the proposed structure utilizes multiple etching steps to achieve the optimum JTE concentration range. The simulation results show that the etched implant JTE method can improve the blocking voltage of SiC PiN diodes and also provides broad process latitude for parameter variations, such as implantation dose and activation annealing condition. The fabricated SiC PiN diodes with the etched implant JTE exhibit a highest blocking voltage of 4.5 kV and the forward on-state voltage of 4.6 V at room temperature. These results are of interest for understanding the etched implant method in the fabrication of high-voltage power devices.展开更多
基金This paper is financially supported by the National Natural Science Foundation of China(Grant Nos.52074263 and 52034007)the Postgraduate Research and Practice Innovation Program of Jiangsu Province(Grant No.KYCX21_2332).
文摘Dynamic load on anchoring structures(AS)within deep roadways can result in cumulative damage and failure.This study develops an experimental device designed to test AS under triaxial loads.The device enables the investigation of the mechanical response,failure mode,instability assessment criteria,and anchorage effect of AS subjected to combined cyclic dynamic-static triaxial stress paths.The results show that the peak bearing strength is positively correlated with the anchoring matrix strength,anchorage length,and edgewise compressive strength.The bearing capacity decreases significantly when the anchorage direction is severely inclined.The free face failure modes are typically transverse cracking,concave fracturing,V-shaped slipping and detachment,and spallation detachment.Besides,when the anchoring matrix strength and the anchorage length decrease while the edgewise compressive strength,loading rate,and anchorage inclination angle increase,the failure intensity rises.Instability is determined by a negative tangent modulus of the displacement-strength curve or the continued deformation increase against the general downward trend.Under cyclic loads,the driving force that breaks the rock mass along the normal vector and the rigidity of the AS are the two factors that determine roadway stability.Finally,a control measure for surrounding rock stability is proposed to reduce the internal driving force via a pressure relief method and improve the rigidity of the AS by full-length anchorage and grouting modification.
文摘Understanding the hydrological processes of forest ecosystems in Tibetan Plateau is crucial for protecting water resources and the environment, especially considering that evapotranspiration is the most dominant hydrologic process in most forest systems. SHAW, as a physically based, hydrological model, provides a useful tool for understanding and analyzing evapotranspiration processes. Using the measured data of a faber fir forest ecosystem in eastern Tibetan Plateau, this paper assessed the model performance in simulating evapotranspiration and variability and transferability of the model parameters. Comparison of the simulated results by SHAW to the measured data showed that SHAW performed satisfactorily. Based on analyzing the simulated results by the calibrated and validated SHAW, some ET characteristics of faber fir forest ecosys-tem in the eastern Tibetan Plateau were found: 1) Daily plant transpiration is low, and daily ET mainly comes from surface evaporation including canopy, litter and soil evaporation. Peak ET rate was approxi-mately 4mm/day, occurring around late July. 2) Solar radiation is the most important factor accounting for daily ET variation, while air temperature is the secondary, wind speed and air relative humidity are minor and soil water storage is the least important among all the related factors. 3) The ratio of annual ET to pre-cipitation for the faber fir forest ecosystem in eastern Tibetan Plateau is low (18%) compared with the other forest ecosystems owing to high-elevation, high atmospheric humidity and low annual temperature.
文摘Elucidating the factors that determine the effects of temporal and spatial variation of nutrients is important for analyzing the characteristics of an ecosystem. The goal of this paper was to estimate how values obtained using a particular sampling approach correlated with the actual data for an entire plot. The mesh partition method was employed to divide an integrated observing field (IOF) located at the Haibei National Field Research Station of an alpine grassland ecosystem, China, into 25 subplots. Five of the 25 subplots were randomly selected for soil sampling and to determine the source of variations in soil nutrient content from 2001 to 2012. The results showed that, contributions of temporal and spatial variation in available nitrogen in the 0 - 10 cm soil layer accounted for 47.3% and 52.7%, respectively. The contribution of spatial variance was higher than that of temporal variance especially in the surface soil layers. The available soil nitrogen content in the alpine meadow was not obviously affected by fluctuations in rainfall and temperature. Increasing the number of samples could reduce calculation errors in measuring available soil nitrogen content, while collecting a reasonable number of samples can save time and labor.
基金the financial support from the Arkansas Institute for Nanoscience and Engineering at University of Arkansasthe International Centre of Artificial Materials(iCAM)at University of Electronic Science and Technology of China
文摘Ordered nanoripples on the niobium-doped SrTiO_3 surfaces were fabricated through focused ion beam bombardment. The surface morphology of the SrTiO_3 nanoripples was characterized using in situ focused ion beam/scanning electron microscopy. The well-aligned SrTiO_3 nanostructures were obtained under optimized ion irradiation conditions. The characteristic wavelength was measured as about 210 nm for different ion beam currents. The relationship between the ion irradiation time and current and SrTiO_3 surface morphology was analyzed. The presented method will be an effective supplement for fabrication of SrTiO_3 nanostructures that can be used for ferroelectric and electronic applications.
基金supported by the National Natural Science Foundation of China(Grant No.42030508)the Second Tibetan Plateau Scientific Expedition and Research Program(Grant No.2019QZKK0301)+3 种基金supported by CAS-TWAS President’s Fellowship Program for International Ph.D.studentssupported by Spanish Government(Grant Nos.PID2019-110521GB-I00 and TED2021-132627B-I00)the Catalan Government(Grant No.SGR 2017-1005)and the Fundación“Ramón Areces”(Grant No.CIVP20A6621)supported by the Spanish Government(Grant No.RTI2018-096884-B-C31)。
文摘Plants require a number of essential elements in different proportions for ensuring their growth and development.The elemental concentrations in leaves reflect the functions and adaptations of plants under specific environmental conditions.However,less is known about how the spectrum of leaf elements associated with resource acquisition,photosynthesis and growth regulates forest biomass along broad elevational gradients.We examined the influence of leaf element distribution and diversity on forest biomass by analyzing ten elements(C,N,P,K,Ca,Mg,Zn,Fe,Cu,and Mn)in tree communities situated every 100 meters along an extensive elevation gradient,ranging from the tropical forest(80 meters above sea level)to the alpine treeline(4200 meters above sea level)in the Kangchenjunga Landscape in eastern Nepal Himalayas.We calculated communityweighted averages(reflecting dominant traits governing biomass,i.e.,mass-ratio effect)and functional divergence(reflecting increased trait variety,i.e.,complementarity effect)for leaf elements in a total of 1,859 trees representing 116 species.An increasing mass-ratio effect and decreasing complementarity in leaf elements enhance forest biomass accumulation.A combination of elements together with elevation explains biomass(52.2%of the variance)better than individual elemental trait diversity(0.05%to 21%of the variance).Elevation modulates trait diversity among plant species in biomass accumulation.Complementarity promotes biomass at lower elevations,but reduces biomass at higher elevations,demonstrating an interaction between elevation and complementarity.The interaction between elevation and mass-ratio effect produces heterogeneous effects on biomass along the elevation gradient.Our research indicates that biomass accumulation can be disproportionately affected by elevation due to interactions among trait diversities across vegetation zones.While higher trait variation enhances the adaptation of species to environmental changes,it reduces biomass accumulation,especially at higher elevations.
基金supported by the Second Tibetan Plateau Scientific Expedition and Research Program(2019QZKK0304-02)Joint Chinese Academy of Sciences(CAS)-Max Planck Society(MPG)Research Project(HZXM20225001MI)+3 种基金the Strategic Priority Research Program A of Chinese Academy of Sciences(XDA20050104)the National Natural Science Foundation of China(42041005)CAS Light of West China Programthe Fundamental Research Funds for the Central Universities。
基金the Natural Science Foundation of Qinghai Province(2020-ZJ-720)Joint research project of Three River Resource National Park funded by Chinese Academy of Sciences and Qinghai Provincial People's Government(LHZX-2020-08).
基金The Natural Science Foundation of Qinghai Province for providing funding for“Research on health assessment and sustainable development in alpine Kobresia meadows in Qinghai Province”,Grant/Award Number:2020-ZJ-720。
文摘Backgrounds:Grazing prohibition and reduced grazing intensity,as two important“vegetation close-to-nature recovery”methods,have been suggested as economical and effective technologies for enhancing forage production.However,numerous studies have found that the yield of forage could be increased by removing or reducing grazing in a short time in some steady stage of alpine Kobresia meadows,but not in others.To reveal the mechanism behind this phenomenon,we proposed a series of experiments.Methods:We monitored the plant and soil characteristics in the key steady stages of Kobresia meadows under reduced and prohibited grazing conditions in the same geographic and climatic environments in the northeastern Qinghai-Tibet Plateau for 6 years.We estimated the relationships between the plant community and soil nutrients and obtained the following results.Results:All measured variables were positively correlated with each other.The plant community structure had higher path coefficients to aboveground biomass,soil organic matter,total nitrogen,and nitrate nitrogen than to other factors.The plant community structure played an important role in response to grazing intensity.Different plant functional groups(PFGs)had different responses to grazing intensity,which led to plant community re-establishment or re-organization under different grazing intensities.Poaceae and Kobresia were more sensitive to grazing intensity than other PFGs,and the ratio of Kobresia biomass(including Kobresia humilis and Kobresia pygmaea)to the total biomass of Poaceae and Kobresia could be used as an indicator of regime shifts within plant communities.With Kobresia pygmaea as the dominant species,the prohibition of grazing was not an efficient approach to increase the yield in the steady stages because this treatment needed more time to recover aboveground biomass.If Poaceae is the dominant PFG,grazing should only be prohibited for 3 years in the steady stages because the aboveground biomass will decrease if grazing is prohibited for more than 3 years.Conclusions:Therefore,the different steady stages of alpine meadows require different recovery methods to increase recovery efficiency and speed.
基金National Natural Science Foundation of China,Grant/Award Number:U20A2006Youth Project of Qinghai Province,Grant/Award Number:2023-ZJ-967Q Abstract。
文摘Background:Due to the effects of climate change and overgrazing in recent decades,alternative stable states in the alpine Kobresia meadow degradation process have coexisted in the same geographical and climatic environment,with variations occurring among microsites.Methods:We used a space-for-time substitution approach to explore the synergies of microsite variation according to its numerical characteristics and the proportion of each stable state at various stages of succession in alpine Kobresia meadows on the Qinghai-Tibetan Plateau.Results:(1)The highest average aboveground biomass in summer was 196.2±20.3 gm^(-2),with significantly higher levels of biomass in≤3.65 sheep unit ha^(-1) than in other levels of grazing intensity,while the parameters showed no significant differences among grazing intensity levels in>3.65 sheep unit ha^(-1).(2)The importance of plant functional groups,aboveground biomass,and niche breadth of Poaceae and Cyperaceae significantly decreased as the grazing intensity increased.(3)The effects of≥0°C accumulated temperature,total precipitation,altitude,longitude,and latitude cumulatively contributed less than 20%of the variation in the distribution of functional group characteristics across microsites.Conclusions:(1)Overgrazing decreases primary production in alpine Kobresia meadows,but ecosystem responses regulate plant community structure and botanical components so as to partially counteract grazing disturbance.(2)Overgrazing changed the proportion of microsites,which in turn led to regime shift in the plant community and subsequent synergies between the microsites of plant communities and their stable states.
基金We are most grateful for the state assignment AAAA-A18-118013190177-9the Russian Foundation for Basic Research(18-04-00773 and 19-29-05260).
文摘Assessment of soil health requires complexevaluation of properties and functions responsible for abroad range of ecosystem services. Numerous soil qualityindices (SQI) have been suggested for the evaluation ofspecific groups of soil functions, but comparison of variousSQI is impossible because they are based on a combinationof specific soil properties. To avoid this problem, wesuggest an SQI-area approach based on the comparison ofthe areas on a radar diagram of a combination of chemical,biological and physical properties. The new approach isindependent of the SQI principle and allows rapid andsimple comparison of parameter groups and soils. Anotherapproach analyzing the resistance and sensitivity ofproperties to degradation is suggested for a detailedevaluation of soil health. The resistance and sensitivityof soil properties are determined through comparison withthe decrease of soil organic carbon (SOC) as a universalparameter responsible for many functions. The SQI-areaand resistance/sensitivity approaches were tested based on quences after the ab and on ment of agricultural soils. Both the SQI-area and the resistance/sensitivity approaches areuseful for basic and applied research, and for decisionmakersto evaluate land-use practices and measure thedegree of soil degradation.
基金supported by The National Basic Research Program (973) of China (No. 2015CB150800)the National Key Research and Development Program of China (No. 2016YFC0500603)+1 种基金the China Agriculture Research System “China agriculture research system” (No. CARS-35)the National Nonprofit Institute Research Grant of CAAS (No. 647-53)
文摘Reclamation of degraded grasslands as managed grasslands has been increasingly accelerated in recent years in China. Land use change affects soil nitrogen(N) dynamics and nitrous oxide(N2O) emissions. However, it remains unclear how large-scale grassland reclamation will impact the grassland ecosystem as a whole. Here, we investigated the effects of the conversion from native to managed grasslands on soil N dynamics and N2O emissions by field experiments in Hulunber in northern China. Soil(0-10 cm), nitrate(NO3-),ammonium(NH4+), and microbial N were measured in plots in a temperate steppe(Leymus chinensis grassland) and two managed grasslands(Medicago sativa and Bromus inermis grasslands) in 2011 and 2012. The results showed conversion of L. chinensis grassland to M.sativa or B. inermis grasslands decreased concentrations of NO3--N, but did not change NH4-N . Soil microbial N was slightly decreased by the conversion of L. chinensis grassland to M.sativa, but increased by the conversion to B. inermis. The conversion of L. chinensis grassland to M. sativa(i.e., a legume grass) increased N2O emissions by 26.2%, while the conversion to the B. inermis(i.e., a non-legume grass) reduced N2O emissions by 33.1%. The conversion from native to managed grasslands caused large created variations in soil NO3-+-N and NH4-N concentrations. Net N mineralization rates did not change significantly in growing season or vegetation type, but to net nitrification rate. These results provide evidence on how reclamation may impact the grassland ecosystem in terms of N dynamics and N2O emissions.
基金Project supported by the Science and Technology Development Foundation of China Academy of Engineering Physics(No.2014A05011)the Special Foundation of President of China Academy of Engineering Physics(No.2014-1-100)
文摘This paper presents the design and fabrication of an etched implant junction termination extension(JTE)for high-voltage 4H-SiC PiN diodes. Unlike the conventional JTE structure, the proposed structure utilizes multiple etching steps to achieve the optimum JTE concentration range. The simulation results show that the etched implant JTE method can improve the blocking voltage of SiC PiN diodes and also provides broad process latitude for parameter variations, such as implantation dose and activation annealing condition. The fabricated SiC PiN diodes with the etched implant JTE exhibit a highest blocking voltage of 4.5 kV and the forward on-state voltage of 4.6 V at room temperature. These results are of interest for understanding the etched implant method in the fabrication of high-voltage power devices.