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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 K obresia pygmaea C. B. Clarke and C arex pseudofoetida Kük. in alpine K obresia 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. [ABSTRACT FROM AUTHOR]

Knowledge about the distribution pattern and function of soil microbial communities is essential for understanding their vital role in ecosystem functioning. However, little is known about the elevational patterns of microbial communities at high altitudes on the Tibetan Plateau, a region that is very sensitive to global change. We investigated the microbial community composition and functional patterns along an elevational gradient (3100-4600 m above sea level) on Mount Segrila using phospholipid fatty acids (PLFAs) and community level physiological profiles (CLPP). Soil microbes were abundant even at higher altitudes and ranged from 1.52 to 3.53 μmol per g organic carbon (OC) by total PLFAs. Soil microbial biomass (expressed as Total PLFAs) declined at higher elevations, and the highest abundance was observed at the low-elevation site. Fungal to bacterial ratio decreased with increasing elevation. While no consistent elevational pattern was observed for PLFA profiles, richness and diversity of carbon source utilization by the microbial community decreased significantly at higher altitudes. Soil microbes at higher altitudes had the potential to metabolize relatively more recalcitrant carbon components while microbes at lower altitudes tended to utilize labile carbon sources. The results were in line with the chemical composition of soil organic matter. Increasing O-alkyl C and decreasing alkyl C content indicate slow decomposition at higher elevations. Variations in structure and activity of microbial community were mainly attributable to MAT, pH, and litter C:N. Our results indicate that pH is a major factor affecting microbial communities, and the impact of soil pH is closely correlated with temperature and vegetation changes along the elevational gradient. As future climate warming may lead to temperature increases and an upward migration of vegetation, our results provide fundamental knowledge of soil microbial communities in the Tibetan alpine region and may help to predict responses of the belowground community to global climate change. [ABSTRACT FROM AUTHOR]