Land use alters arbuscular mycorrhizal fungal communities and their potential role in carbon sequestration on the Tibetan Plateau.

Loss of belowground biodiversity by land-use change can have a great impact on ecosystem functions, yet appropriate investigations remain rare in high-elevation Tibetan ecosystems. We compared arbuscular mycorrhizal (AM) fungal communities in arable soils with those in native forest and grassland in southeast Tibet and investigated their potential contribution to carbon sequestration. The AM fungi were abundant and diverse. AM fungal diversity was significantly higher in grassland than in forest or arable land. Significant differences in AM fungal community composition were found among different land use types. The relative abundance of operational taxonomic units (OTUs) in forest and grassland were positively related to glomalin-related soil protein (GRSP), soil organic carbon, macroaggregates, and the unprotected and physically protected carbon, while the AM fungal community in arable soils was dominated by a few OTUs which were positively linked to soil pH. Changes in GRSP content were closely related to water-stable macroaggregates and carbon storage in grassland and forest soils but not in arable soil. Given the inevitable trend toward agricultural management this study emphasizes the need to implement effective agricultural practices that can enhance AM fungal activity to maintain soil quality and carbon sequestration for the sustainable development of this fragile ecosystem.

Temperature-mediated local adaptation alters the symbiotic function in arbuscular mycorrhiza.

Variation in the symbiotic function of arbuscular mycorrhizal fungi (AM fungi) has been demonstrated among distinct biotic and abiotic interactions. However, there is little knowledge on how local temperature conditions influence the functional divergence of AM symbionts in alpine ecosystems. Here, we conduct a reciprocal inoculation experiment to explore the three-way interactions among plants, AM fungal inoculum and temperature at sites of contrasting elevation. Evidence of local adaptation of plant growth was found only under low temperature conditions, with no consistent local versus foreign effect found in AM fungal performance. The origin of either the plant or the inoculum relative to the temperature was important in explaining symbiotic function. Specifically, when inoculum and temperature were sympatric but allopatric to the plant, poor adaptation by the plant to the novel environment was clearly found under both temperature conditions. Further analysis found that the symbiotic function was inversely related to fungal diversity under high temperature conditions. These results suggest that local adaptation represents a powerful factor in the establishment of novel combinations of plant, inoculum and temperature, and confirms the importance of taking into account both biotic and abiotic interactions in the prediction of the response of symbionts to global environmental change.

Responses of arbuscular mycorrhizal symbionts to contrasting environments: field evidence along a Tibetan elevation gradient.

Plant adaptation to alpine ecosystems is not fully explained by plant physiological and morphological traits. Arbuscular mycorrhizal (AM) associations may be involved in mediating plant performance in response to environmental differences. Little is known, however, as to whether or not a close relationship exists between plant performance and arbuscular mycorrhizal fungus status across environmental gradients. We conducted a field investigation of the performance of six plant species and their associated AM fungi along higher and lower elevation gradients on Mount Segrila in Tibet. In most of our species, we observed higher shoot and inflorescence biomass production and a lower root-to-shoot ratio in the populations at those sites where the species was dominant (intermediate elevation sites) than in populations sampled at the limits of the distribution. The elevation pattern of root colonization differed with plant species on both gradients, and the extraradical hypha development of most species showed a unimodal pattern as did plant growth. The relationship between plant and fungus traits shows that AM fungus development generally matched host plant performance on the lower elevation gradient but not on the higher elevation gradient. This study provides evidence that plant distribution and productivity were significantly related to root and soil colonization by AM fungi, especially under less physically stressful conditions.

The key factor limiting plant growth in cold and humid alpine areas also plays a dominant role in plant carbon isotope discrimination.

Many environmental factors affect carbon isotope discrimination in plants, yet the predominant factor influencing this process is generally assumed to be the key growth-limiting factor. However, to our knowledge this hypothesis has not been confirmed. We therefore determined the carbon isotope composition (δ(13)C) of plants growing in two cold and humid mountain regions where temperature is considered to be the key growth-limiting factor. Mean annual temperature (MAT) showed a significant impact on variation in carbon isotope discrimination value (Δ) irrespective of study area or plant functional type with either partial correlation or regression analysis, but the correlation between Δ and soil water content (SWC) was usually not significant. In multiple stepwise regression analysis, MAT was either the first or the only variable selected into the prediction model of Δ against MAT and SWC, indicating that the effect of temperature on carbon isotope discrimination was predominant. The results therefore provide evidence that the key growth-limiting factor is also crucial for plant carbon isotope discrimination. Changes in leaf morphology, water viscosity and carboxylation efficiency with temperature may be responsible for the observed positive correlation between Δ and temperature.

Altitudinal distribution patterns of AM fungal assemblages in a Tibetan alpine grassland.

A better understanding of biogeography of Glomeromycota is essential for the conservation of arbuscular mycorrhizal (AM) fungal species and the ecosystem services that they provide worldwide. We examined the spatial dynamics of AM fungi along two slopes (4149 m a.s.l. to the summit at 5033 m a.s.l.) of Mount Mila on the Tibetan Plateau. Our hypothesis was that AM fungal communities at higher elevation would show distinct assemblages with lower diversity in conditions of increasing environmental harshness. A total of 52 operational taxonomic units (OTUs) spanning all four orders were detected and some OTUs were habitat specific. Nearly 30% of the OTUs were new phylotypes, including two family-like clades. Distinct communities of AM fungi were found at the higher elevation, demonstrating potential niche differentiation along the elevation gradient. Elevation patterns of taxon richness/diversity differed between the two transects, decreasing with increasing elevation on the eastern slope and being unimodal (or lacking a pattern) on the western slope. Taken together, our findings provide evidence of a significant spatial structure of AM fungi across the elevation gradient, with the distribution patterns of these fungi regulated simultaneously by the plant communities, soil properties and climatic conditions in this plateau montane ecosystem.

Contribution of arbuscular mycorrhizal fungi of sedges to soil aggregation along an altitudinal alpine grassland gradient on the Tibetan Plateau.

The diversity of arbuscular mycorrhizal fungi (AMF) in sedges on the Tibetan Plateau remains largely unexplored, and their contribution to soil aggregation can be important in understanding the ecological function of AMF in alpine ecosystems. Roots of Kobresia pygmaea C.B. Clarke and Carex pseudofoetida Kük. in alpine Kobresia pastures along an elevational transect (4149-5033 m) on Mount Mila were analysed for AMF diversity. A structural equation model was built to explore the contribution of biotic factors to soil aggregation. Sedges harboured abundant AMF communities covering seven families and some operational taxonomic units are habitat specific. The two plant species hosted similar AMF communities at most altitudes. The relative abundance of the two sedges contributed largely to soil macroaggregates, followed by extraradical mycorrhizal hyphae (EMH) and total glomalin-related soil protein (T-GRSP). The influence of plant richness was mainly due to its indirect influence on T-GRSP and EMH. There was a strong positive correlation between GRSP and soil total carbon and nitrogen. Our results indicate that mycorrhization might not be a major trait leading to niche differentiation of the two co-occurring sedge species. However, AMF contribute to soil aggregation and thus may have the potential to greatly influence C and N cycling in alpine grasslands.

[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.

Molecular diversity of arbuscular mycorrhizal fungi associated with two co-occurring perennial plant species on a Tibetan altitudinal gradient.

Plant communities on Mount Segrila on the Tibetan Plateau show distinct changes at different altitudes, but little information is available on belowground communities of arbuscular mycorrhizal fungi (AMF). Root samples of two co-occurring species, Pennisetum centrasiaticum and Kobresia sp., growing in open grasslands at eight altitudes (3,446-4,556 m) were analyzed for diversity of AMF by PCR, cloning, and sequencing. Dominant plants were well colonized by AMF even at higher altitudes where spore density in rhizospheres decreased dramatically. A total of 29 operational taxonomic units (OTUs) of AMF were detected, and some novel sequence types were found. Acaulosporaceae and Glomeraceae were the dominant families. There was no significant difference in OTU richness along elevational gradients in Kobresia sp., but OTU richness in P. centrasiaticum was higher at intermediate elevations. Elevation, host plant species, and soil variables (pH, soil organic matter, and available P and N) were found to have significant effects on the overall AMF community across all elevations. Fungal community composition differed significantly between the two plant species at each elevation, and the similarity was generally higher at the intermediate elevations. No significant difference in compositional similarity was observed for Kobresia sp. with increasing elevation, but the dissimilarity increased significantly for P. centrasiaticum. These results suggest that host identity is an important determinant for the structure of the AMF communities along the elevational gradients in high altitude environments.

[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.

[Field inoculation effect of AM fungi on Tibet plateau Stipa bungeana grassland].

A field experiment was conducted on the Tibet plateau Stipa bungeana grassland to investigate the effects of arbuscular mycorrhizal fungi (AMF) inoculation on S. bungeana growth and its phosphorus uptake, and on soil microbial communities under unsterilized condition. The results showed that AMF inoculation increased the AMF spore density, infection rate and infection intensity in rhizosphere soil significantly, but had less effect on arbuscule richness. The infection rate of AMF increased with its increasing spore density, and the plant dry weight and P uptake of S. bungeana increased significantly with AMF infection rate. Similar results were observed in S. bungeana root dry weight and its P content. AMF inoculation increased the acid and alkaline phosphatase activities and bacterial biomass in rhizosphere soil, but had less effect on fungal and actinomyces communities. The infection effect of AMF varied with inoculation treatments, being in the sequence of Glomus mosseae + G. intraradices + Scutellospora calospora > G. mosseae + G. aggregatum > Glomus sp. > G. mosseae > G. mosseae + G. etunicatum + G. intraradices + S. erythropa > G. geosporum.

[Effects of environmental factors on AM fungi around steppe plant roots in Tibet Plateau].

The study on the representative steppe plant species in Tibet Plateau showed that the density of AM fungi spores in host plant rhizosphere did not correlate with the infection rate of AM fungi. The big changes in air temperature and rainfall at different altitudes played an important role in determining the growth and infection of AM fungi specific to steppe plants, and steppe type and soil texture also had obvious effects on AM fungi's growth and infection. Within a certain range, the spore density increased significantly with increasing soil pH (r = 0.5319, n = 20), but showed a declining trend with the improvement of soil organic matter (r = - 0.1973, n = 20). In contrast, the infection rates of AM fungi to host plants were to some extent negatively and positively correlated with soil pH and soil organic matter, respectively. Phosphorus (P) enrichment in soil environment led to the inhibition of the reproduction and infection of AM fungi. The suitable soil pH, OM and Olsen P contents for the growth and reproduction of AM fungi ranged from 8.0-8.7, 3.8-4.8 g.kg(-l) and 7.8-10.1 mg.kg(-1), respectively. Moderate and serious degradation of steppe (especially the serious degradation) had negative or detrimental impacts on the reproduction and infection of AM fungi. Reasonable grazing was helpful to the conservation of critical species of AM fungi. AM fungi also showed a relatively high infection rate on the roots of sedge species such as Carex praecpara, Kobresia humilis and Cyperus compressus.

[Microbial characteristics of straw-amended degraded soils in central Tibet and its effect on soil fertility].

This paper studied the dynamics of microbial communities in degraded soils of central Tibet under straw amendment and its effect on soil fertility. The results showed that straw amendment, and soil covering with spring highland barley (Hordeum vulgare var. nudum) straw in particular, could supply a beneficial soil environment for the relatively balanced growth of soil microbes, e.g., reduced water evaporation, appropriate temperature, and increased content of organic matter and nutrients. All the results demonstrated the possibility of straw amendment in recovering soil fertility and in reconstructing of soil structure in a relatively short period.

[Effects of forms and application rate of nitrogen fertilizer on yield and qualities of tobacco in southeast Tibet].

Field experiments in southeast Tibet were conducted to study the effect of nitrogenous fertilizer supply and its forms on tobacco. The result indicated that the yield, production value, and the contents of nicotine, potassium oxide and total nitrogen of the cured leaves were positively correlated to the amount of N application, and significantly and negatively correlated to the percentage of superior-medium class leaves of tobacco and contents of deoxidize sugar. The highest yield and best quality of tobacco were obtained by applying 75 kg N per hectare. Inorganic nitrogenous fertilizer could significantly improve the yield and quality of tobacco, compared with organic nitrogenous fertilizer. Although there was no significant difference among ammonium N, nitrate N and nitrate-ammonium N application, the effects of ammonium N, nitrate N, and nitrate-ammoniun N application were significantly higher than that of urea application. The effect of ammoniun N application on tobacco yield and quality was better than that of nitrate N application, and the important reason was the great difference in the process of absorption and assimilation of ammoniun N and nitrate N.