Understanding the factors that drive variation in species distribution is a central theme of ecological research. Although several studies focused on alpine vegetation, few efforts have been made to identify the envir...Understanding the factors that drive variation in species distribution is a central theme of ecological research. Although several studies focused on alpine vegetation, few efforts have been made to identify the environmental factors that are responsible for the variations in species composition and richness of alpine shrublands using numerical methods. In the present study, we investigated vegetation and associated environmental variables from 45 sample plots in the middle Qilian Mountains of the northwestern China to classify different community types and to elucidate the species- environment relationships. We also estimated the relative contributions of topography and site conditions to spatial distribution patterns of the shrub communities using the variation partitioning. The results showed that four shrub community types were identified and striking differences in fioristic composition were found among them. Species composition greatly depended on elevation, slope, shrub cover, soil pH and organic carbon. The important determinants of species richness were soil bulk density and slope. No significant differences in species richness were detected among the community types. Topography and site conditions had almost equal effects on compositional variation. Nonetheless,a large amount of the variation in species composition remained unexplained.展开更多
The epidemiology of Salmonella involves food, especially meat and dairy products. These have a high salmonella outbreak in the summer. The majority of Salmonella enteritis in young children occurs in the form of scatt...The epidemiology of Salmonella involves food, especially meat and dairy products. These have a high salmonella outbreak in the summer. The majority of Salmonella enteritis in young children occurs in the form of scattered cases. At least 25% of summer gastroenteritis in young children is caused by Salmonella. In Western Europe, S. typhimurium accounts for nearly 70% of isolates. The objective of this study was to investigate the Salmonella contaminating meat and dairy products as well as define the percentages of contamination by Salmonella from 2004 to 2006, by the Department of Hygiene of Tunis. For this study, we collected samples in various motherboard solutions, and conducted a pre-nonselective enrichment in selective enrichment in isolation and identification and ultimately biochemical confirmation. One hundred and sixty two samples, 125 samples of meat products including 68 samples of red meat （beef and sheep, beef, offal and Merguez） and 57 samples of poultry （chicken and turkey）, 37 samples of milk products which included 32 samples of cheese and five samples milk, were analysed microbiologically from 2004 to 2006, in the Health Service in Tunis. These analyses include the detection and enumeration of Salmonella. From 2004 to 2006, the rate of infections by the Salmonella, meat and dairy products were： 55.9% for red meat, 71.9% for poultry, 68.8% for cheeses, 40% for milk. The meat of poultry is contaminated with Salmonella that the cheeses, which are more than red meats, which are also more contaminated than milk. This might be due to a lack of hygiene throughout the circuit processing （slaughter, transport, processing, etc.）. The increased risk of contamination of milk products by Salmonella is proportional to the manipulation done on these products. The latter must be handled by pasteurization and sterilization.展开更多
Aims Litter is frequently buried in the soil in alpine grasslands due to grassland degradation,serious rodent infestation and frequent strong winds.However,the effects of various litter positions on litter decompositi...Aims Litter is frequently buried in the soil in alpine grasslands due to grassland degradation,serious rodent infestation and frequent strong winds.However,the effects of various litter positions on litter decomposition rates and nutrient dynamics under nitrogen(N)enrichment in such areas remain unknown.Methods A field experiment was performed in the alpine grasslands of northwest China to investigate the influence of litter position(surface,buried in the soil and standing)and N enrichment on litter decomposition,using data from two dominant grass species(Festuca ovina and Leymus tianschanicus)in control and N-enriched plots.Important Findings Litter decomposition rates were much faster in buried litter and slower in standing litter than in surface litter.N enrichment significantly affected litter quality and then influenced decomposition.But no significant differences in litter mass remaining were observed between control and N-enriched soil burial.These results indicated that N enrichment significantly affected litter decomposition by changes in litter quality.In addition,all litter exhibited net carbon(C)and phosphorus(P)release regardless of treatments.Litter exhibited net N accumulation for litter from the control plots but showed N release for litter from N enrichment plots.These suggested that litter decomposition can be limited by N and N enrichment influenced N cycling of litter.Current study presented direct evidence that soil buried litter exhibited faster mass loss and C release,and that soil burial can be a candidate explanation why litter decomposes faster than expected in dryland.展开更多
The distribution and enrichment patterns of selenium(Se) in the E-?1 strata in the Yangtze Gorges area of South China were obtained. The geochemical characteristics of the significantly and non-significantly enriched ...The distribution and enrichment patterns of selenium(Se) in the E-?1 strata in the Yangtze Gorges area of South China were obtained. The geochemical characteristics of the significantly and non-significantly enriched strata of Se were analyzed.The observed enrichment factor(EF, relative to the upper continental crust) and concentration coefficient(CC, relative to the similar lithology in Eastern China) both suggest that Se is the most enriched/concentrated(SeEF=26.97, SeCC=48.04) among the analyzed23 trace elements the E-?1 strata. The normalized enrichment factor(EF′, EF after Al or Th normalized) shows Se is secondly enriched(SeEF′=218.73), which is slightly lower than cadmium(CdEF′=288.46) but significantly higher than the third enriched trace element arsenic(AsEF′=97.49). Se concentrations in the E-?1 strata vary from <10.5 to 30.08 ppm with an arithmetic mean value of 1.35 ppm. Compared to the Nantuo Formation, Se increased 11.78 times in the whole E-?1 strata and the average EF values are displayed as Shuijingtuo(92.58)>Yanjiahe(54.45)>Doushantuo(24.72)>Dengying(2.48)>Shipai(1.95)>lower Tianheban(1.24)Formations. Se concentrations in the E-?1 strata are best displayed on natural logarithm normal quantile-quantile(Q-Q) plots and shown as a positive-skewed distribution pattern. The Se significantly enriched(EF>10) strata sequences mainly include the lower and upper Doushantuo member II(DST-II), top DST-III, DST-IV, the basal and upper Yanjiahe Formation, and lower and upper Shuijingtuo Formation. Geochemical characteristics indicate that Se concentrations in the significantly enriched strata were generally influenced by terrigenous detrital as well as the combined action of single or multiple factors, such as hydrotherm,volcanic debris and deep source. Moreover, pyrite and organic matter promoted the enrichment of Se in the upper DST-II, DST-IV,upper Shuijingtuo Formation and lower DST-II, upper Shuijingtuo Formation, respectively. The Se concentrations in the not significantly enriched strata(except for DST-I, middle Shuijingtuo Formation, Shipai Formation and lower Tianheban Formation)were also influenced by terrigenous detrital, but other enrichment activities(e.g., hydrothermal, volcanic debris, and deep source)were generally insignificant.展开更多
基金supported by the National Natural Science Foundation of China (Grant No. 91025002)
文摘Understanding the factors that drive variation in species distribution is a central theme of ecological research. Although several studies focused on alpine vegetation, few efforts have been made to identify the environmental factors that are responsible for the variations in species composition and richness of alpine shrublands using numerical methods. In the present study, we investigated vegetation and associated environmental variables from 45 sample plots in the middle Qilian Mountains of the northwestern China to classify different community types and to elucidate the species- environment relationships. We also estimated the relative contributions of topography and site conditions to spatial distribution patterns of the shrub communities using the variation partitioning. The results showed that four shrub community types were identified and striking differences in fioristic composition were found among them. Species composition greatly depended on elevation, slope, shrub cover, soil pH and organic carbon. The important determinants of species richness were soil bulk density and slope. No significant differences in species richness were detected among the community types. Topography and site conditions had almost equal effects on compositional variation. Nonetheless,a large amount of the variation in species composition remained unexplained.
文摘The epidemiology of Salmonella involves food, especially meat and dairy products. These have a high salmonella outbreak in the summer. The majority of Salmonella enteritis in young children occurs in the form of scattered cases. At least 25% of summer gastroenteritis in young children is caused by Salmonella. In Western Europe, S. typhimurium accounts for nearly 70% of isolates. The objective of this study was to investigate the Salmonella contaminating meat and dairy products as well as define the percentages of contamination by Salmonella from 2004 to 2006, by the Department of Hygiene of Tunis. For this study, we collected samples in various motherboard solutions, and conducted a pre-nonselective enrichment in selective enrichment in isolation and identification and ultimately biochemical confirmation. One hundred and sixty two samples, 125 samples of meat products including 68 samples of red meat （beef and sheep, beef, offal and Merguez） and 57 samples of poultry （chicken and turkey）, 37 samples of milk products which included 32 samples of cheese and five samples milk, were analysed microbiologically from 2004 to 2006, in the Health Service in Tunis. These analyses include the detection and enumeration of Salmonella. From 2004 to 2006, the rate of infections by the Salmonella, meat and dairy products were： 55.9% for red meat, 71.9% for poultry, 68.8% for cheeses, 40% for milk. The meat of poultry is contaminated with Salmonella that the cheeses, which are more than red meats, which are also more contaminated than milk. This might be due to a lack of hygiene throughout the circuit processing （slaughter, transport, processing, etc.）. The increased risk of contamination of milk products by Salmonella is proportional to the manipulation done on these products. The latter must be handled by pasteurization and sterilization.
基金This work was supported financially by the Strategic Priority Research Program of the Chinese Academy of Sciences(XDA20050103)Natural Science Foundation of Xinjiang Uygur Autonomous Region(2019D01C066)+1 种基金Tianshan Cedar Project of Xinjiang Uygur Autonomous Region(2020XS26)the National Natural Science Foundation of China(41425007,41673079)。
文摘Aims Litter is frequently buried in the soil in alpine grasslands due to grassland degradation,serious rodent infestation and frequent strong winds.However,the effects of various litter positions on litter decomposition rates and nutrient dynamics under nitrogen(N)enrichment in such areas remain unknown.Methods A field experiment was performed in the alpine grasslands of northwest China to investigate the influence of litter position(surface,buried in the soil and standing)and N enrichment on litter decomposition,using data from two dominant grass species(Festuca ovina and Leymus tianschanicus)in control and N-enriched plots.Important Findings Litter decomposition rates were much faster in buried litter and slower in standing litter than in surface litter.N enrichment significantly affected litter quality and then influenced decomposition.But no significant differences in litter mass remaining were observed between control and N-enriched soil burial.These results indicated that N enrichment significantly affected litter decomposition by changes in litter quality.In addition,all litter exhibited net carbon(C)and phosphorus(P)release regardless of treatments.Litter exhibited net N accumulation for litter from the control plots but showed N release for litter from N enrichment plots.These suggested that litter decomposition can be limited by N and N enrichment influenced N cycling of litter.Current study presented direct evidence that soil buried litter exhibited faster mass loss and C release,and that soil burial can be a candidate explanation why litter decomposes faster than expected in dryland.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41172310 & 41472322)the National Basic Research Program of China (Grant No. 2014CB238906)
文摘The distribution and enrichment patterns of selenium(Se) in the E-?1 strata in the Yangtze Gorges area of South China were obtained. The geochemical characteristics of the significantly and non-significantly enriched strata of Se were analyzed.The observed enrichment factor(EF, relative to the upper continental crust) and concentration coefficient(CC, relative to the similar lithology in Eastern China) both suggest that Se is the most enriched/concentrated(SeEF=26.97, SeCC=48.04) among the analyzed23 trace elements the E-?1 strata. The normalized enrichment factor(EF′, EF after Al or Th normalized) shows Se is secondly enriched(SeEF′=218.73), which is slightly lower than cadmium(CdEF′=288.46) but significantly higher than the third enriched trace element arsenic(AsEF′=97.49). Se concentrations in the E-?1 strata vary from <10.5 to 30.08 ppm with an arithmetic mean value of 1.35 ppm. Compared to the Nantuo Formation, Se increased 11.78 times in the whole E-?1 strata and the average EF values are displayed as Shuijingtuo(92.58)>Yanjiahe(54.45)>Doushantuo(24.72)>Dengying(2.48)>Shipai(1.95)>lower Tianheban(1.24)Formations. Se concentrations in the E-?1 strata are best displayed on natural logarithm normal quantile-quantile(Q-Q) plots and shown as a positive-skewed distribution pattern. The Se significantly enriched(EF>10) strata sequences mainly include the lower and upper Doushantuo member II(DST-II), top DST-III, DST-IV, the basal and upper Yanjiahe Formation, and lower and upper Shuijingtuo Formation. Geochemical characteristics indicate that Se concentrations in the significantly enriched strata were generally influenced by terrigenous detrital as well as the combined action of single or multiple factors, such as hydrotherm,volcanic debris and deep source. Moreover, pyrite and organic matter promoted the enrichment of Se in the upper DST-II, DST-IV,upper Shuijingtuo Formation and lower DST-II, upper Shuijingtuo Formation, respectively. The Se concentrations in the not significantly enriched strata(except for DST-I, middle Shuijingtuo Formation, Shipai Formation and lower Tianheban Formation)were also influenced by terrigenous detrital, but other enrichment activities(e.g., hydrothermal, volcanic debris, and deep source)were generally insignificant.
