[Change of arbuscular mycorrhizal fungi community in response to elevational gradients on the Tibetan Plateau, China].

The community structure of arbuscular mycorrhizal fungi (AMF) and mycorrhizal infection in the main herbaceous plants were studied along the elevational gradients on the Tibetan Plateau, and AMF community was characterized based on spore morphology. Community of AMF at lower elevations (2200-3400 m) in southeast Tibetan Plateau included 11 genera, covering 31 species, whereas AMF at intermediate elevations (3400-3900 m) in central Tibet included 11 genera, covering 20 species, and that at higher elevations (4300-5300 m) in northern Tibet included 6 genera, covering 14 species. With the increase of elevation, both spore density (r = 0.978, P <0.01) and species abundance (r = 0.462, P > 0.05) tended to increase. The proportion of dominant species and endemic species increased substantially, while the Shannon index (r = -0.945, P < 0.01) decreased significantly. There was no significant difference in Sorensen index (0.526-0.592) among different altitudes. Mycorrhizal infection at intermediate elevations was significantly higher than that at lower elevations or higher elevations, while the latter two did not differ significantly. Within an altitude range, elevation had significant influence on AMF community and mycorrhizal infection, and the effect differed among the three elevational sites. The results demonstrated that AMF community on the Tibetan Plateau tends to be habitat specific. The water and thermal environment as well as soil environment are the driving forces for shaping AMF community assemblages.

[Influence of soil factors on species diversity of arbuscular mycorrhizal (AM) fungi in Stipa steppe of Tibet Plateau].

This study was based on the isolation and identification of arbuscular mycorrhizal (AM) fungi collected from the alpine Stipa steppe of north Tibet, and focused on the influence of soil texture, pH, organic matter, and available P on the spore density, isolation frequency, relative abundance, importance value, species diversity, and species evenness of the AM fungi. In the rhizosphere soil of the steppe, a total of 15 species AM fungi were isolated and identified, including 9 species of Glomus, 6 species of Acaulospora, and 1 species of Scutellospora. Among them, Glomus and Acaulospora were the dominant genera, and Glomus claroideum and Acaulospora laevis were the dominant species. In the soils with different texture, the spore density, isolation frequency, relative abundance, and importance value of the AM fungi all showed a trend of Glomus > Acaulospora > Scutellospora. Soil pH value had no significant effects on the species composition of AM fungi. However, the isolation frequency, relative abundance, and importance value of Glomus and Acaulospora showed an increasing trend with increasing soil pH, while Scutellospora showed the contrary trend. In the soils with different organic matter content, the spore density of AM fungi all showed a trend of Glomus > Acaulospora > Scutellospora, while the distribution of AM fungi had no definite pattern. The species richness and spore density of AM fungi were less affected by the soil available P content, but the species diversity and evenness showed an increasing trend with the increasing content of soil available P.

[Ecological distribution of arbuscular mycorrhizal fungi in alpine grasslands of Tibet Plateau].

Seventy soil samples with the roots of 37 dominant or common plant species on the grasslands in south and north Tibet Plateau were collected to study the ecological distribution of arbuscular mycorrhizal (AM) fungi in the investigation area. A total of 35 AM fungi species belonging to 5 genera were isolated, among which, 18 species belonged to Glomus, 9 species belonged to Acaulospora, 6 species belonged to Scutellospora, 1 species belonged to Entrophospora, and 1 species belonged to Paraglomus. There were 23 AM fungi species belonging to 4 genera isolated from south Tibet, and 22 species belonging to 4 genera from north Tibet. The Shannon diversity index of AM fungi in south and north Tibet Plateau was 2.31 and 2.75, respectively, and the spore density and species richness were significantly higher in north Tibet than in south Tibet. In different ecological zones, lesser AM fungi common species were found, species distribution was more site-specific, and different dominant species were observed. In alpine grassland, mountain meadow, and alpine meadow, the Shannon index of AM fungi was 1.91, 1.83, and 1.80, respectively; while in severely degraded temperate grassland, this index was only 1.64. The highest species richness of AM fungi occurred at the altitude of 4000-4600 m, but the highest Shannon index and species evenness occurred at the altitude of 4600-5220 m, with the values being 2.42 and 0.79, respectively. At all altitudes, Glomus was the dominant genus, and its relative abundance was higher when the altitude was below 4000 m. Acaulospora was mainly observed at the altitudes higher than 4000 m, Scutellospora was mainly distributed at the altitude 3500-5220 m, Paraglomus mainly occurred in the north alpine meadow with an altitude of 4000-5220 m and occasionally in the alpine steppe, whereas Entrophospora was only found in the south temperate grassland with an altitude of 3500-3700 m.

[Spatial-temporal variation of soil organic carbon and its relations to soil physical properties in degraded alpine grasslands].

By using grid sampling method, the spatial-temporal variation of soil organic carbon (SOC) and its relations to soil physical properties in degraded alpine grasslands in North Tibet were studied. The SOC content and its density both in surface (0-10 cm) and in subsurface (10-20 cm) layers decreased in order of slightly degraded grassland > normal grassland > moderately degraded grasslands > seriously degraded grasslands, and the differences of SOC content and its density between the two layers showed the same variation trend. An opposite trend was observed in the annual variation rates of SOC content and its density in different grasslands, and the variation was larger in surface than in subsurface layer. The annual accumulation rate of SOC in 0-10 cm layer in not degraded and slightly degraded grasslands was 0.018 and 0.003 g x kg(-1), being 6.0 and 2.0 times of that in 10-20 cm layer, while the annual loss rate of SOC in 0-10 cm layer in moderately and seriously degraded grasslands was 0.150 and 0.231 g x kg(-1), being 2.3 and 2.2 times of that in 10-20 cm layer, respectively. The total annual loss of SOC in moderately and seriously degraded grasslands was 3.8 times of the total annual accumulation of SOC in not degraded and slightly degraded grasslands. The degraded alpine grasslands in North Tibet had an average annual SOC loss of 7.87 x 10(7) t C x a(-1), and a greater potential to further loss in the future. The SOC content was significantly positively correlated with the contents of 5.0-1.0 mm, 1.0-0.5 mm, and 0.5-0.25 mm soil aggregates, soil bulk density, and soil moisture content.

Alcohol consumption and metabolic syndrome among Shanghai adults: a randomized multistage stratified cluster sampling investigation.

AIM: To examine the relations of alcohol consumption to the prevalence of metabolic syndrome in Shanghai adults. METHODS: We performed a cross-sectional analysis of data from the randomized multistage stratified cluster sampling of Shanghai adults, who were evaluated for alcohol consumption and each component of metabolic syndrome, using the adapted U.S. National Cholesterol Education Program criteria. Current alcohol consumption was defined as more than once of alcohol drinking per month. RESULTS: The study population consisted of 3953 participants (1524 men) with a mean age of 54.3 +/- 12.1 years. Among them, 448 subjects (11.3%) were current alcohol drinkers, including 405 males and 43 females. After adjustment for age and sex, the prevalence of current alcohol drinking and metabolic syndrome in the general population of Shanghai was 13.0% and 15.3%, respectively. Compared with nondrinkers, the prevalence of hypertriglyceridemia and hypertension was higher while the prevalence of abdominal obesity, low serum high-density-lipoprotein cholesterol (HDL-C) and diabetes mellitus was lower in subjects who consumed alcohol twice or more per month, with a trend toward reducing the prevalence of metabolic syndrome. Among the current alcohol drinkers, systolic blood pressure, HDL-C, fasting plasma glucose, and prevalence of hypertriglyceridemia tended to increase with increased alcohol consumption. However, low-density-lipoprotein cholesterol concentration, prevalence of abdominal obesity, low serum HDL-C and metabolic syndrome showed the tendency to decrease. Moreover, these statistically significant differences were independent of gender and age. CONCLUSION: Current alcohol consumption is associated with a lower prevalence of metabolic syndrome irrespective of alcohol intake (g/d), and has a favorable influence on HDL-C, waist circumference, and possible diabetes mellitus. However, alcohol intake increases the likelihood of hypertension, hypertriglyceridemia and hyperglycemia. The clinical significance of these findings needs further investigation.

[Characterization of soil biological properties on degraded alpine grasslands].

The study of degraded alpine grasslands in northern Tibet showed that compared with normal alpine grassland, slightly degraded alpine grassland had higher amounts of soil bacteria, fungi and actinomyces, higher activities of cellulase, urease and alkali phosphatase, and higher contents of microbial biomass C and N and organic matter in its 2-10 cm soil layer, while these parameters were much lower on moderately or severely degraded alpine grassland. There was a positive correlation between soil microbial biomass C/N (B(C)/B(N)) and soil total C/N (T(C)/T(N)), with coefficient value (r) being 0.9088 (P < or = 0.01, n = 4). The ratios of soil B(C)/T(C) and B(N)/T(N) had an increasing trend on slightly and moderately degraded grasslands, but decreased obviously on severely degraded alpine grassland. Soil microbial biomass had a significant positive correlation with soil enzyme activity, and these two parameters were both positively correlated with the amounts of soil bacteria and fungi, but negatively correlated with that of soil actinomyces. In 2-10 cm soil layer, microbial biomass and enzyme activities were significantly positively correlated with organic matter content, and the ratios of humus C/organic C and humic acid C/humus C in 2-10 cm and 11-20 cm soil layers increased significantly with increasing degradation of grassland.