Thinning is an effective management step for sustainable forest development,yet less attention is paid to the restoration of soil microbiota after thinning.In this study,both abundant and rare soil microbial communiti...Thinning is an effective management step for sustainable forest development,yet less attention is paid to the restoration of soil microbiota after thinning.In this study,both abundant and rare soil microbial communities(i.e.,bacterial,fungal),were evaluated under various thinning treatments in a mixed stand of Cunninghamia lanceolata and Sassafras tzumu using Mi Seq sequencing.Thinning did not significantly change either abundant or rare bacterial and fungal community composition,but affected their alpha diversity.The Shannon–Wiener indexes of rare fungal taxa under medium thinning were significantly lower than in the light thinning(P<0.05 level).Xanthobacteraceae dominated the abundant bacterial taxa,and Saitozyma and Mortierlla the abundant fungal taxa.The most common rare bacterial taxa varied;there was no prevalent rare fungal taxa under different thinnings.In addition,soil available nitrogen,total phosphorus,and p H had significant effects on rare bacterial taxa.Nutrients,especially available phosphorus,but not nitrogen,affected abundant and rare soil fungi.The results indicate that soil properties rather than plant factors affect abundant and rare microbial communities in soils of mixed stands.Thinning,through mediating soil properties,influences both abundant and rare bacterial and fungal communities in the mixed C.lanceolata and S.tzumu stand.展开更多
On an agrosilvopastoral farm in central Italy where Maremmana cattle graze in Turkey oak forests,we evaluated the impact of different livestock densities on stand structure,tree diversity and natural regeneration in f...On an agrosilvopastoral farm in central Italy where Maremmana cattle graze in Turkey oak forests,we evaluated the impact of different livestock densities on stand structure,tree diversity and natural regeneration in four types of grazed areas based on the grazing regime adopted:calf-grazed,high-intensity-grazed,low-intensity-grazed,ungrazed control.For each area,we set up three permanent circular plots(radius of 15 m)to survey the structural and dasometric characteristics of the overstorey,understorey,and regeneration layer.The results showed that grazing negatively affected the complexity of the forest structure and its potential to regenerate and maintain a high level of biodiversity.The differences in stand structure observed between the grazing areas were closely related to livestock density.The most sensitive components of the system were the understorey and the regeneration layers.Contrarily,the current grazing management did not affect the dominant tree structure or its composition.Our findings identified medium-term monitoring and regeneration management as the two significant aspects to consider when assessing sustainable livestock.New forests can be established by excluding graz-ing for about 20–25 years.展开更多
Based on the investigation data of 12 Haloxylon ammodendron plots in the south edge of Gurbantunggut Desert, Fuzzy distribution was introduced into the study of Haloxylon ammodendron base diameter structure fitting ac...Based on the investigation data of 12 Haloxylon ammodendron plots in the south edge of Gurbantunggut Desert, Fuzzy distribution was introduced into the study of Haloxylon ammodendron base diameter structure fitting according to the consistency between the characteristics of Fuzzy distribution function and the distribution series of cumulative percentage of stand base diameter, and the fitting precision and effect of Fuzzy distribution function were discussed. The root mean square error RMSE and determination coefficient R<sup>2</sup> values showed that Fuzzy-Γ<sub>1</sub>, Fuzzy-Γ<sub>2</sub>, Fuzzy-Γ<sub>3</sub>, Fuzzy-Γ<sub>4</sub> had good fitting performance, among which Fuzzy-Γ<sub>1</sub> had relatively high fitting precision, and its parameters were closely related to stand age and density, Fuzzy-Γ<sub>2</sub> distribution function was the second, and Fuzzy-Γ<sub>4</sub> distribution function had the worst fitting effect. By introducing a parameter c from the similarity of four distribution function formulas, a generalized Fuzzy distribution function Fuzzy-Γ<sub>5</sub> is obtained. This function shows the highest fitting accuracy. Most of the values of parameter c are near 1 or 2, which shows that the diameter distribution is mainly approximate to Fuzzy-Γ<sub>1</sub> and Fuzzy-Γ<sub>2</sub>.展开更多
Food safety problems caused by excessive nitrite addition have been frequently reported and the detection of nitrite in food is particularly important. The standing time during the pretreatment of primary sample has a...Food safety problems caused by excessive nitrite addition have been frequently reported and the detection of nitrite in food is particularly important. The standing time during the pretreatment of primary sample has a great influence on the concentration of nitrite tested by spectrophotometric method. In this context, three kinds of food samples are prepared, including canned mustard, canned fish and home-made pickled water. A series of standing times are placed during the sample pretreatments and the corresponding nitrite contents in these samples are detected by spectrophotometric method based on N-ethylenediamine dihydrochloride. This study aims to find out a reasonable standing time during the pretreatment of food sample, providing influence factor for precise detection of nitrite.展开更多
In this paper, we study the existence of standing waves for the nonlinear Schrödinger equation with combined power-type nonlinearities and a partial harmonic potential. In the L<sup>2</sup>-supercriti...In this paper, we study the existence of standing waves for the nonlinear Schrödinger equation with combined power-type nonlinearities and a partial harmonic potential. In the L<sup>2</sup>-supercritical case, we obtain the existence and stability of standing waves. Our results are complements to the results of Carles and Il’yasov’s artical, where orbital stability of standing waves have been studied for the 2D Schrödinger equation with combined nonlinearities and harmonic potential.展开更多
In this study, a stand-off and collinear double pulse laser-induced breakdown spectroscopy (DP LIBS) system was designed, and the magnesium alloy samples at a distance of 2.5 m away from the LIBS system were measure...In this study, a stand-off and collinear double pulse laser-induced breakdown spectroscopy (DP LIBS) system was designed, and the magnesium alloy samples at a distance of 2.5 m away from the LIBS system were measured. The effect of inter-pulse delay on spectra was studied, and the signal enhancement was observed compared to the single pulse LIBS (SP LIBS). The morphology of the ablated crater on the sample indicated a higher efficiency of surface pretreatment in DP LIBS. The calibration curves of Ytterbium (Y) and Zirconium (Zr) were investigated. The square of the correlation coefficient of the calibration curve of element Y reached up to 0.9998.展开更多
A century and a half ago,in the European part of Russia(Moscow),forest scientists established the first long-term observations of forests,many of which are under observation to the present day.In the twentieth century...A century and a half ago,in the European part of Russia(Moscow),forest scientists established the first long-term observations of forests,many of which are under observation to the present day.In the twentieth century,climate changes and,due to industrial development,forest areas were under air pollution.Based on observations from 157 sites,this study shows that the growth and density of Scots pine(Pinus sylvestris L.)have decreased by the end of the twentieth century.The environment has changed,and the growth and development of plantations has slowed.Pine yields(-34%stand volume)and their life expectancy(on average 50 years)have decreased.These changes are critical for forestry and for the management of forests in urban centers.Due to the decline in growth,ecosystem functions by urban forests has decreased.In order to increase the sustainability of urban forests and the provision of ecosystem services,it is preferable to create multi-species stands with a complex structure.展开更多
Fine roots play key roles in belowground C cycling in terrestrial ecosystems.Based on their distinct functions,fi ne roots are either absorptive fi ne roots(AFRs)or transport fi ne roots(TFRs).However,the function-bas...Fine roots play key roles in belowground C cycling in terrestrial ecosystems.Based on their distinct functions,fi ne roots are either absorptive fi ne roots(AFRs)or transport fi ne roots(TFRs).However,the function-based fi ne root dynamics of trees and their responses to forest stand properties remain unclear.Here,we studied the dynamics of AFRs and TFRs and their responses to stand conditions and root density in a subtropical montane mixed forest based on a 2-a root window experiment.Mean(±SE)annual production,mortality,and turnover rate of AFRs were 7.87±0.17 m m^(−2)a^(−1),8.13±0.20 m m^(−2)a^(−1)and 2.96±0.24 a^(−1),respectively,compared with 7.09±0.17 m m^(−2)a^(−1),4.59±0.17 m m^(−2)a^(−1),and 2.01±0.22 a^(−1),respectively,for TFRs.The production and mortality of fi ne roots were signifi cantly higher in high root-density sites than in low-root density sites,whereas the turnover of fi ne roots was faster in the low root-density sites.Furthermore,root density had a larger positive eff ect than other environmental factors on TFR production but had no obvious impact on AFR production.Tree species diversity had an apparent positive eff ect on AFR production and was the crucial driver of AFR production,probably due to a complementary eff ect,but had no evident impact on TFR.Both tree density and tree species diversity were positively correlated with the mortality of AFRs and negatively related to the turnover of TFRs,suggesting that higher root density caused stronger competition for rooting space and that plants tend to reduce maintenance costs by decreasing TFR turnover.These fi ndings illustrated the importance of root functional groups in understanding root dynamics and their responses to changes in environmental conditions.展开更多
Twenty-seven specimens were tested to investigate the uniaxial compression behaviour of an innovative standing support for underground space applications.The innovative standing support consisted of an external fibre ...Twenty-seven specimens were tested to investigate the uniaxial compression behaviour of an innovative standing support for underground space applications.The innovative standing support consisted of an external fibre reinforced polymer(FRP)jacket and the infill column made of cementitious grout,tailings and coal wash rejects.Effects of the FRP layers number and water to the cementitious grout(w/g)ratio were evaluated.Test results indicated that lower w/g ratios produced stronger infill columns.With FRP confinement,the standing support demonstrated strain-hardening loading characteristics with a significant improvement in both strength and ductility.The highest strength and strain of the specimens achieved was 58.4 MPa and 11.8%respectively.Compared with the unconfined specimens,the confinement with four FRP layers increased the specimen strength and associated strain up to 3.6 and 27.0 times respectively.A correlation between the compressive strength of the infill material and the ultrasonic pulse velocity was also investigated.Furthermore,a simple design-oriented model was proposed to predict the peak strength and the corresponding strain of the innovative standing support.展开更多
The streamer that is driven by the specific pulse DC discharge parameters can stably form a three-dimensional helical plasma channel in a long dielectric tube in the low-temperature plasma experiment,in cases when the...The streamer that is driven by the specific pulse DC discharge parameters can stably form a three-dimensional helical plasma channel in a long dielectric tube in the low-temperature plasma experiment,in cases when there were neither external background magnetic field or other factors that destroyed the poloidal symmetry of the tube.The formation mechanism and chirality of helical streamers are discussed according to the surface electromagnetic standing wave theory.The shape of the helical streamers and the characteristics of helical branches are quantitatively analyzed to further expand the application of plasma and streamer theory in the helix problem and chiral catalytic synthesis.展开更多
Land use change affects the balance of organic carbon(C)reserves and the global C cycle.Microbial residues are essential constituents of stable soil organic C(SOC).However,it remains unclear how microbial residue chan...Land use change affects the balance of organic carbon(C)reserves and the global C cycle.Microbial residues are essential constituents of stable soil organic C(SOC).However,it remains unclear how microbial residue changes over time following afforestation.In this study,16-,23-,52-,and 62-year-old Mongolian pine stands and 16-year-old cropland were studied in the Horqin Sandy Land,China.We analyzed changes in SOC,amino sugar content,and microbial parameters to assess how microbial communities influence soil C transformation and preservation.The results showed that SOC storage increased with stand age in the early stage of afforestation but remained unchanged at about 1.27-1.29 kg/m2 after 52 a.Moreover,there were consistent increases in amino sugars and microbial residues with increasing stand age.As stand age increased from 16 to 62 a,soil pH decreased from 6.84 to 5.71,and the concentration of total amino sugars increased from 178.53 to 509.99 mg/kg.A significant negative correlation between soil pH and the concentration of specific and total amino sugars was observed,indicating that the effects of soil acidification promote amino sugar stabilization during afforestation.In contrast to the Mongolian pine plantation of the same age,the cropland accumulated more SOC and microbial residues because of fertilizer application.Across Mongolian pine plantation with different ages,there was no significant change in calculated contribution of bacterial or fungal residues to SOC,suggesting that fungi were consistently the dominant contributors to SOC with increasing time.Our results indicate that afforestation in the Horqin Sandy Land promotes efficient microbial growth and residue accumulation in SOC stocks and has a consistent positive impact on SOC persistence.展开更多
Volume is an important attribute used in many forest management decisions.Data from 83 fixed-area plots located in central New Brunswick,Canada,are used to examine how different measures of stand-level diameter and he...Volume is an important attribute used in many forest management decisions.Data from 83 fixed-area plots located in central New Brunswick,Canada,are used to examine how different measures of stand-level diameter and height influence volume prediction using a stand-level variant of Honer's(1967)volume equation.When density was included in the models(Volume=f(Diameter,Height,Density))choice of diameter measure was more important than choice of height measure.When density was not included(Volume=f(Diameter,Height)),the opposite was true.For models with density included,moment-based estimators of stand diameter and height performed better than all other measures.For models without density,largest tree estimators of stand diameter and height performed better than other measures.The overall best equation used quadratic mean diameter,Lorey's height,and density(root mean square error=5.26 m^3·ha^(-1);1.9%relative error).The best equation without density used mean diameter of the largest trees needed to calculate a stand density index of 400 and the mean height of the tallest 400 trees per ha(root mean square error=32.08 m^(3)·ha^(-1);11.8%relative error).The results of this study have some important implications for height subsampling and LiDAR-derived forest inventory analyses.展开更多
如何在逆境中坚持不懈,将失败转化为通往成功的阶梯?让我们一起到文章中寻找答案!Life is like a big picture, and every part of it stands for a choice, a hard time,or a win. Making your own way isn't just about getting w...如何在逆境中坚持不懈,将失败转化为通往成功的阶梯?让我们一起到文章中寻找答案!Life is like a big picture, and every part of it stands for a choice, a hard time,or a win. Making your own way isn't just about getting where you want to go;it's about keeping on trying, even when things get tough.展开更多
Good crop stand establishment and root system development are essential for optimum grain yield of dryland wheat (Triti-cum aestivumL.). At present, little is known about the effect of tilage and straw mulch on the ...Good crop stand establishment and root system development are essential for optimum grain yield of dryland wheat (Triti-cum aestivumL.). At present, little is known about the effect of tilage and straw mulch on the root system of wheat under dryland areas in southwestern China. The aim of this study was to evaluate the effect of three tilage treatments (no-til, NT; rotary til, RT; conventional til, CT) and two crop residue management practices (straw mulch, ML; non-straw mulch, NML) on stand establishment, root growth and grain yield of wheat. NT resulted in lower soil cover thickness for the wheat seed, higher number of uncovered seeds, lower percentage of seedling-less ridges and lower tiler density compared to RT and CT; ML resulted in higher tiler density compared to NML. Straw mulching resulted in more soil water content and root length density (RLD) at most of the growth stages and soil depths. The maximum RLD, root surface area density and root dry matter density were obtained under NT. In the topmost 10 cm soil layer, higher RLD values were found under NT than those under RT and CT. There were no signiifcant differences in the yield or yield components of wheat among the tilage treatments in 2011–2012, but NT resulted in a signiifcant higher yield compared to RT and CT in 2012–2013. Grain yield was signiifcantly higher in ML compared to in NML. A strong relationship was observed between the water-use efifciency and the grain yield. Both NT and ML proved beneifcial for wheat in term of maintaining higher tiler density, better soil water status and root growth, leading to a higher grain yield and enhanced water-use efifciency, especialy in a low rainfal year.展开更多
Canadian boreal mixedwood forests are extensive,with large potential for carbon sequestration and storage;thus,knowledge of their carbon stocks at different stand ages is needed to adapt forest management practices to...Canadian boreal mixedwood forests are extensive,with large potential for carbon sequestration and storage;thus,knowledge of their carbon stocks at different stand ages is needed to adapt forest management practices to help meet climate-change mitigation goals.Carbon stocks were quantified at three Ontario boreal mixedwood sites.A harvested stand,a juvenile stand replanted with spruce seedlings and a mature stand had total carbon stocks(±SE)of 133±13 at age 2,130±13 at age 25,and 207±15 Mg C ha^-1 at age 81 years.At the clear-cut site,stocks were reduced by about 40%or 90 Mg C ha^-1 at harvest.Vegetation held 27,34 and 62%of stocks,while detritus held 34,29 and 13%of stocks at age 2,25 and 81,respectively.Mineral soil carbon stocks averaged 51 Mg C ha^-1,and held 38,37 and 25%of stocks.Aboveground net primary productivity(±SE)in the harvested and juvenile stand was 2.1±0.2 and 3.7±0.3 Mg C ha^-1 per annum(p.a.),compared to 2.6±2.5 Mg C ha^-1 p.a.in the mature stand.The mature canopies studied had typical boreal mixedwood composition and mean carbon densities of 208 Mg C ha^-1,which is above average for managed Canadian boreal forest ecosystems.A comparison of published results from Canadian boreal forest ecosystems showed that carbon stocks in mixedwood stands are typically higher than coniferous stands at all ages,which was also true for stocks in vegetation and detritus.Also,aboveground net primary productivity was typically found to be higher in mixedwood than in coniferous boreal forest stands over a range of ages.Measurements from this study,together with those published from the other boreal forest stands demonstrate the potential for enhanced carbon sequestration through modified forest management practices to take advantage of Canadian boreal mixedwood stand characteristics.展开更多
Understanding stand structure and height-diameter relationship of trees provides very useful information to establish appropriate countermeasures for sustainable management of endangered forests. Populus euphratica, a...Understanding stand structure and height-diameter relationship of trees provides very useful information to establish appropriate countermeasures for sustainable management of endangered forests. Populus euphratica, a dominant tree species along the Tarim River watershed, plays an irreplaceable role in the sustainable development of regional ecology, economy and society. However, as the result of climate changes and human activities, the natural riparian ecosystems within the whole river basin were degraded enormously, particularly in the lower reaches of the river where about 320 km of the riparian forests were either highly degraded or dead. In this study, we presented one of the main criteria for the assessment of vitality of P. euphrafica forests by estimating the defoliation level, and analyzed forest structure and determined the height-diameter (height means the height of a tree and diameter means the diameter at breast height (DBH) of a tree) relationship of trees in different vitality classes (i.e. healthy, good, medium, senesced, dying, dead and fallen). Trees classified as healthy and good ac- counted for approximately 40% of all sample trees, while slightly and highly degraded trees took up nearly 60% of total sample trees. The values of TH (tree height) and DBH ranged from 0-19 m and 0-125 cm, respectively. Trees more than 15 m in TH and 60 cm in DBH appeared sporadically. Trees in different vitality classes had different distribution patterns. Healthy trees were mainly composed more of relatively younger trees than of degraded tress. The height-diameter relationships differed greatly among tress in different vitality classes, with the coefficients ranging from 0.1653 to 0.6942. Correlation coefficients of TH and DBH in healthy and good trees were higher than those in trees of other vitality classes. The correlation between TH and DBH decreased with the decline of tree vitality. Our results suggested that it might be able to differentiate degraded P. euphratica trees from healthy trees by determining the height-diameter correlation coefficient, and the coefficient would be a new parameter for detecting degradation and assessing sustainable management of floodplain forests in arid regions. In addition, tree vitality should be taken into account to make an accurate height-diameter model for tree height prediction.展开更多
Pulsed power technology,whereas the electrical energy stored in a relative long period is released in much shorter timescale,is an efficient method to create high energy density physics(HEDP)conditions in laboratory.A...Pulsed power technology,whereas the electrical energy stored in a relative long period is released in much shorter timescale,is an efficient method to create high energy density physics(HEDP)conditions in laboratory.Around the beginning of this century,China Academy of Engineering Physics(CAEP)began to build some experimental facilities for HEDP investigations,among which the Primary Test Stand(PTS),a multi-module pulsed power facility with a nominal current of 10 MA and a current rising time~90 ns,is an important achievement on the roadmap of the electro-magnetically driven inertial confinement fusion(ICF)researches.PTS is the first pulsed power facility beyond 10 TW in China.Therefore,all the technologies have to be demonstrated,and all the engineering issues have to be overcome.In this article,the research outline,key technologies and the preliminary HEDP experiments are reviewed.Prospects on HEDP research on PTS and pulsed power development for the next step are also discussed.展开更多
基金the Sino-German Cooperation Forestry Major Scientific Research Project(zdczhz2021ky09)the National Natural Science Foundation of China(31971487 and 42277245).
文摘Thinning is an effective management step for sustainable forest development,yet less attention is paid to the restoration of soil microbiota after thinning.In this study,both abundant and rare soil microbial communities(i.e.,bacterial,fungal),were evaluated under various thinning treatments in a mixed stand of Cunninghamia lanceolata and Sassafras tzumu using Mi Seq sequencing.Thinning did not significantly change either abundant or rare bacterial and fungal community composition,but affected their alpha diversity.The Shannon–Wiener indexes of rare fungal taxa under medium thinning were significantly lower than in the light thinning(P<0.05 level).Xanthobacteraceae dominated the abundant bacterial taxa,and Saitozyma and Mortierlla the abundant fungal taxa.The most common rare bacterial taxa varied;there was no prevalent rare fungal taxa under different thinnings.In addition,soil available nitrogen,total phosphorus,and p H had significant effects on rare bacterial taxa.Nutrients,especially available phosphorus,but not nitrogen,affected abundant and rare soil fungi.The results indicate that soil properties rather than plant factors affect abundant and rare microbial communities in soils of mixed stands.Thinning,through mediating soil properties,influences both abundant and rare bacterial and fungal communities in the mixed C.lanceolata and S.tzumu stand.
基金This research is related to the project GO NEWTON“Agroforestry Network in Tuscany”,financed by the Tuscany Region through the Measure 16.2 of Rural Development Plan 2014-2020 to promote agroforestry systems by spreading knowledge to farmers and promoting innovation in the Tuscan territory.
文摘On an agrosilvopastoral farm in central Italy where Maremmana cattle graze in Turkey oak forests,we evaluated the impact of different livestock densities on stand structure,tree diversity and natural regeneration in four types of grazed areas based on the grazing regime adopted:calf-grazed,high-intensity-grazed,low-intensity-grazed,ungrazed control.For each area,we set up three permanent circular plots(radius of 15 m)to survey the structural and dasometric characteristics of the overstorey,understorey,and regeneration layer.The results showed that grazing negatively affected the complexity of the forest structure and its potential to regenerate and maintain a high level of biodiversity.The differences in stand structure observed between the grazing areas were closely related to livestock density.The most sensitive components of the system were the understorey and the regeneration layers.Contrarily,the current grazing management did not affect the dominant tree structure or its composition.Our findings identified medium-term monitoring and regeneration management as the two significant aspects to consider when assessing sustainable livestock.New forests can be established by excluding graz-ing for about 20–25 years.
文摘Based on the investigation data of 12 Haloxylon ammodendron plots in the south edge of Gurbantunggut Desert, Fuzzy distribution was introduced into the study of Haloxylon ammodendron base diameter structure fitting according to the consistency between the characteristics of Fuzzy distribution function and the distribution series of cumulative percentage of stand base diameter, and the fitting precision and effect of Fuzzy distribution function were discussed. The root mean square error RMSE and determination coefficient R<sup>2</sup> values showed that Fuzzy-Γ<sub>1</sub>, Fuzzy-Γ<sub>2</sub>, Fuzzy-Γ<sub>3</sub>, Fuzzy-Γ<sub>4</sub> had good fitting performance, among which Fuzzy-Γ<sub>1</sub> had relatively high fitting precision, and its parameters were closely related to stand age and density, Fuzzy-Γ<sub>2</sub> distribution function was the second, and Fuzzy-Γ<sub>4</sub> distribution function had the worst fitting effect. By introducing a parameter c from the similarity of four distribution function formulas, a generalized Fuzzy distribution function Fuzzy-Γ<sub>5</sub> is obtained. This function shows the highest fitting accuracy. Most of the values of parameter c are near 1 or 2, which shows that the diameter distribution is mainly approximate to Fuzzy-Γ<sub>1</sub> and Fuzzy-Γ<sub>2</sub>.
文摘Food safety problems caused by excessive nitrite addition have been frequently reported and the detection of nitrite in food is particularly important. The standing time during the pretreatment of primary sample has a great influence on the concentration of nitrite tested by spectrophotometric method. In this context, three kinds of food samples are prepared, including canned mustard, canned fish and home-made pickled water. A series of standing times are placed during the sample pretreatments and the corresponding nitrite contents in these samples are detected by spectrophotometric method based on N-ethylenediamine dihydrochloride. This study aims to find out a reasonable standing time during the pretreatment of food sample, providing influence factor for precise detection of nitrite.
文摘In this paper, we study the existence of standing waves for the nonlinear Schrödinger equation with combined power-type nonlinearities and a partial harmonic potential. In the L<sup>2</sup>-supercritical case, we obtain the existence and stability of standing waves. Our results are complements to the results of Carles and Il’yasov’s artical, where orbital stability of standing waves have been studied for the 2D Schrödinger equation with combined nonlinearities and harmonic potential.
基金supported by National Natural Science Foundation of China(No.61473279)the National High-Tech Research and Development Program of China(863 Program)(No.2012AA040608)Equipment Development Programs of the Chinese Academy of Sciences(No.YZ201247)
文摘In this study, a stand-off and collinear double pulse laser-induced breakdown spectroscopy (DP LIBS) system was designed, and the magnesium alloy samples at a distance of 2.5 m away from the LIBS system were measured. The effect of inter-pulse delay on spectra was studied, and the signal enhancement was observed compared to the single pulse LIBS (SP LIBS). The morphology of the ablated crater on the sample indicated a higher efficiency of surface pretreatment in DP LIBS. The calibration curves of Ytterbium (Y) and Zirconium (Zr) were investigated. The square of the correlation coefficient of the calibration curve of element Y reached up to 0.9998.
基金supported by the Russian State Agrarian University–Moscow Timiryazev Agricultural Academy。
文摘A century and a half ago,in the European part of Russia(Moscow),forest scientists established the first long-term observations of forests,many of which are under observation to the present day.In the twentieth century,climate changes and,due to industrial development,forest areas were under air pollution.Based on observations from 157 sites,this study shows that the growth and density of Scots pine(Pinus sylvestris L.)have decreased by the end of the twentieth century.The environment has changed,and the growth and development of plantations has slowed.Pine yields(-34%stand volume)and their life expectancy(on average 50 years)have decreased.These changes are critical for forestry and for the management of forests in urban centers.Due to the decline in growth,ecosystem functions by urban forests has decreased.In order to increase the sustainability of urban forests and the provision of ecosystem services,it is preferable to create multi-species stands with a complex structure.
基金supported by the National Natural Science Foundation of China(Grant No.3217159931870465).
文摘Fine roots play key roles in belowground C cycling in terrestrial ecosystems.Based on their distinct functions,fi ne roots are either absorptive fi ne roots(AFRs)or transport fi ne roots(TFRs).However,the function-based fi ne root dynamics of trees and their responses to forest stand properties remain unclear.Here,we studied the dynamics of AFRs and TFRs and their responses to stand conditions and root density in a subtropical montane mixed forest based on a 2-a root window experiment.Mean(±SE)annual production,mortality,and turnover rate of AFRs were 7.87±0.17 m m^(−2)a^(−1),8.13±0.20 m m^(−2)a^(−1)and 2.96±0.24 a^(−1),respectively,compared with 7.09±0.17 m m^(−2)a^(−1),4.59±0.17 m m^(−2)a^(−1),and 2.01±0.22 a^(−1),respectively,for TFRs.The production and mortality of fi ne roots were signifi cantly higher in high root-density sites than in low-root density sites,whereas the turnover of fi ne roots was faster in the low root-density sites.Furthermore,root density had a larger positive eff ect than other environmental factors on TFR production but had no obvious impact on AFR production.Tree species diversity had an apparent positive eff ect on AFR production and was the crucial driver of AFR production,probably due to a complementary eff ect,but had no evident impact on TFR.Both tree density and tree species diversity were positively correlated with the mortality of AFRs and negatively related to the turnover of TFRs,suggesting that higher root density caused stronger competition for rooting space and that plants tend to reduce maintenance costs by decreasing TFR turnover.These fi ndings illustrated the importance of root functional groups in understanding root dynamics and their responses to changes in environmental conditions.
文摘Twenty-seven specimens were tested to investigate the uniaxial compression behaviour of an innovative standing support for underground space applications.The innovative standing support consisted of an external fibre reinforced polymer(FRP)jacket and the infill column made of cementitious grout,tailings and coal wash rejects.Effects of the FRP layers number and water to the cementitious grout(w/g)ratio were evaluated.Test results indicated that lower w/g ratios produced stronger infill columns.With FRP confinement,the standing support demonstrated strain-hardening loading characteristics with a significant improvement in both strength and ductility.The highest strength and strain of the specimens achieved was 58.4 MPa and 11.8%respectively.Compared with the unconfined specimens,the confinement with four FRP layers increased the specimen strength and associated strain up to 3.6 and 27.0 times respectively.A correlation between the compressive strength of the infill material and the ultrasonic pulse velocity was also investigated.Furthermore,a simple design-oriented model was proposed to predict the peak strength and the corresponding strain of the innovative standing support.
基金This work was supported by National Natural Science Foundation of China(Nos.12005061,12065019)the Natural Science Foundation of Jiangxi Province(No.20202 BABL214036).
文摘The streamer that is driven by the specific pulse DC discharge parameters can stably form a three-dimensional helical plasma channel in a long dielectric tube in the low-temperature plasma experiment,in cases when there were neither external background magnetic field or other factors that destroyed the poloidal symmetry of the tube.The formation mechanism and chirality of helical streamers are discussed according to the surface electromagnetic standing wave theory.The shape of the helical streamers and the characteristics of helical branches are quantitatively analyzed to further expand the application of plasma and streamer theory in the helix problem and chiral catalytic synthesis.
基金funded by the Fundamental Research Funds of Chinese Academy of Forestry(CAF)(CAFYBB2020QD002-2).
文摘Land use change affects the balance of organic carbon(C)reserves and the global C cycle.Microbial residues are essential constituents of stable soil organic C(SOC).However,it remains unclear how microbial residue changes over time following afforestation.In this study,16-,23-,52-,and 62-year-old Mongolian pine stands and 16-year-old cropland were studied in the Horqin Sandy Land,China.We analyzed changes in SOC,amino sugar content,and microbial parameters to assess how microbial communities influence soil C transformation and preservation.The results showed that SOC storage increased with stand age in the early stage of afforestation but remained unchanged at about 1.27-1.29 kg/m2 after 52 a.Moreover,there were consistent increases in amino sugars and microbial residues with increasing stand age.As stand age increased from 16 to 62 a,soil pH decreased from 6.84 to 5.71,and the concentration of total amino sugars increased from 178.53 to 509.99 mg/kg.A significant negative correlation between soil pH and the concentration of specific and total amino sugars was observed,indicating that the effects of soil acidification promote amino sugar stabilization during afforestation.In contrast to the Mongolian pine plantation of the same age,the cropland accumulated more SOC and microbial residues because of fertilizer application.Across Mongolian pine plantation with different ages,there was no significant change in calculated contribution of bacterial or fungal residues to SOC,suggesting that fungi were consistently the dominant contributors to SOC with increasing time.Our results indicate that afforestation in the Horqin Sandy Land promotes efficient microbial growth and residue accumulation in SOC stocks and has a consistent positive impact on SOC persistence.
基金the Natural Sciences and Engineering Research Council of Canada(Discovery Grant RGPIN-2023-05879)the New Brunswick Innovation Foundation(Emerging Projects Grant EP-0000000033)。
文摘Volume is an important attribute used in many forest management decisions.Data from 83 fixed-area plots located in central New Brunswick,Canada,are used to examine how different measures of stand-level diameter and height influence volume prediction using a stand-level variant of Honer's(1967)volume equation.When density was included in the models(Volume=f(Diameter,Height,Density))choice of diameter measure was more important than choice of height measure.When density was not included(Volume=f(Diameter,Height)),the opposite was true.For models with density included,moment-based estimators of stand diameter and height performed better than all other measures.For models without density,largest tree estimators of stand diameter and height performed better than other measures.The overall best equation used quadratic mean diameter,Lorey's height,and density(root mean square error=5.26 m^3·ha^(-1);1.9%relative error).The best equation without density used mean diameter of the largest trees needed to calculate a stand density index of 400 and the mean height of the tallest 400 trees per ha(root mean square error=32.08 m^(3)·ha^(-1);11.8%relative error).The results of this study have some important implications for height subsampling and LiDAR-derived forest inventory analyses.
文摘如何在逆境中坚持不懈,将失败转化为通往成功的阶梯?让我们一起到文章中寻找答案!Life is like a big picture, and every part of it stands for a choice, a hard time,or a win. Making your own way isn't just about getting where you want to go;it's about keeping on trying, even when things get tough.
基金supported by the China Agriculture Research System(CARS-3)the Public Welfare Industry(Agriculture)Scientific Research of China(200903010-06)
文摘Good crop stand establishment and root system development are essential for optimum grain yield of dryland wheat (Triti-cum aestivumL.). At present, little is known about the effect of tilage and straw mulch on the root system of wheat under dryland areas in southwestern China. The aim of this study was to evaluate the effect of three tilage treatments (no-til, NT; rotary til, RT; conventional til, CT) and two crop residue management practices (straw mulch, ML; non-straw mulch, NML) on stand establishment, root growth and grain yield of wheat. NT resulted in lower soil cover thickness for the wheat seed, higher number of uncovered seeds, lower percentage of seedling-less ridges and lower tiler density compared to RT and CT; ML resulted in higher tiler density compared to NML. Straw mulching resulted in more soil water content and root length density (RLD) at most of the growth stages and soil depths. The maximum RLD, root surface area density and root dry matter density were obtained under NT. In the topmost 10 cm soil layer, higher RLD values were found under NT than those under RT and CT. There were no signiifcant differences in the yield or yield components of wheat among the tilage treatments in 2011–2012, but NT resulted in a signiifcant higher yield compared to RT and CT in 2012–2013. Grain yield was signiifcantly higher in ML compared to in NML. A strong relationship was observed between the water-use efifciency and the grain yield. Both NT and ML proved beneifcial for wheat in term of maintaining higher tiler density, better soil water status and root growth, leading to a higher grain yield and enhanced water-use efifciency, especialy in a low rainfal year.
基金provided by the Canadian Forest Service,with in-kind support from the Ontario Ministry of Natural Resources and Forestry
文摘Canadian boreal mixedwood forests are extensive,with large potential for carbon sequestration and storage;thus,knowledge of their carbon stocks at different stand ages is needed to adapt forest management practices to help meet climate-change mitigation goals.Carbon stocks were quantified at three Ontario boreal mixedwood sites.A harvested stand,a juvenile stand replanted with spruce seedlings and a mature stand had total carbon stocks(±SE)of 133±13 at age 2,130±13 at age 25,and 207±15 Mg C ha^-1 at age 81 years.At the clear-cut site,stocks were reduced by about 40%or 90 Mg C ha^-1 at harvest.Vegetation held 27,34 and 62%of stocks,while detritus held 34,29 and 13%of stocks at age 2,25 and 81,respectively.Mineral soil carbon stocks averaged 51 Mg C ha^-1,and held 38,37 and 25%of stocks.Aboveground net primary productivity(±SE)in the harvested and juvenile stand was 2.1±0.2 and 3.7±0.3 Mg C ha^-1 per annum(p.a.),compared to 2.6±2.5 Mg C ha^-1 p.a.in the mature stand.The mature canopies studied had typical boreal mixedwood composition and mean carbon densities of 208 Mg C ha^-1,which is above average for managed Canadian boreal forest ecosystems.A comparison of published results from Canadian boreal forest ecosystems showed that carbon stocks in mixedwood stands are typically higher than coniferous stands at all ages,which was also true for stocks in vegetation and detritus.Also,aboveground net primary productivity was typically found to be higher in mixedwood than in coniferous boreal forest stands over a range of ages.Measurements from this study,together with those published from the other boreal forest stands demonstrate the potential for enhanced carbon sequestration through modified forest management practices to take advantage of Canadian boreal mixedwood stand characteristics.
基金supported by International Science & Technology Cooperation Program of China (2010DFA92720-12)the National Natural Science Foundation of China (31360200)+1 种基金the German Volkswagen Foundation Eco CAR Project (Az88497)the German Federal Ministry of Education and Research (BMBF) within the framework of the Su Ma Ri O Project (01LL0918D)
文摘Understanding stand structure and height-diameter relationship of trees provides very useful information to establish appropriate countermeasures for sustainable management of endangered forests. Populus euphratica, a dominant tree species along the Tarim River watershed, plays an irreplaceable role in the sustainable development of regional ecology, economy and society. However, as the result of climate changes and human activities, the natural riparian ecosystems within the whole river basin were degraded enormously, particularly in the lower reaches of the river where about 320 km of the riparian forests were either highly degraded or dead. In this study, we presented one of the main criteria for the assessment of vitality of P. euphrafica forests by estimating the defoliation level, and analyzed forest structure and determined the height-diameter (height means the height of a tree and diameter means the diameter at breast height (DBH) of a tree) relationship of trees in different vitality classes (i.e. healthy, good, medium, senesced, dying, dead and fallen). Trees classified as healthy and good ac- counted for approximately 40% of all sample trees, while slightly and highly degraded trees took up nearly 60% of total sample trees. The values of TH (tree height) and DBH ranged from 0-19 m and 0-125 cm, respectively. Trees more than 15 m in TH and 60 cm in DBH appeared sporadically. Trees in different vitality classes had different distribution patterns. Healthy trees were mainly composed more of relatively younger trees than of degraded tress. The height-diameter relationships differed greatly among tress in different vitality classes, with the coefficients ranging from 0.1653 to 0.6942. Correlation coefficients of TH and DBH in healthy and good trees were higher than those in trees of other vitality classes. The correlation between TH and DBH decreased with the decline of tree vitality. Our results suggested that it might be able to differentiate degraded P. euphratica trees from healthy trees by determining the height-diameter correlation coefficient, and the coefficient would be a new parameter for detecting degradation and assessing sustainable management of floodplain forests in arid regions. In addition, tree vitality should be taken into account to make an accurate height-diameter model for tree height prediction.
文摘Pulsed power technology,whereas the electrical energy stored in a relative long period is released in much shorter timescale,is an efficient method to create high energy density physics(HEDP)conditions in laboratory.Around the beginning of this century,China Academy of Engineering Physics(CAEP)began to build some experimental facilities for HEDP investigations,among which the Primary Test Stand(PTS),a multi-module pulsed power facility with a nominal current of 10 MA and a current rising time~90 ns,is an important achievement on the roadmap of the electro-magnetically driven inertial confinement fusion(ICF)researches.PTS is the first pulsed power facility beyond 10 TW in China.Therefore,all the technologies have to be demonstrated,and all the engineering issues have to be overcome.In this article,the research outline,key technologies and the preliminary HEDP experiments are reviewed.Prospects on HEDP research on PTS and pulsed power development for the next step are also discussed.