Dune-scale distribution pattern of herbaceous plants and their relationship with environmental factors in a saline-alkali desert in Central Asia.

Sand dunes are the main landforms in modern deserts worldwide. As an important type of desert vegetation, herbaceous plants have long been acknowledged for their important ecological functions. We focus on the dune-scale distribution pattern of herbaceous plants and their relationship with the environment. During the early summer of 2010, the herbaceous plant density, coverage, aboveground biomass and eighteen environmental factors were surveyed from 214 plots (5m×5m) across two linear sand dunes (220m×110m) located in the Gurbantunggut Desert, China, a typical saline-alkali desert in Central Asia. Data were analyzed using univariate, ordination, and geostatistical techniques. Three vegetation variables represent a significant clumped distribution (P<0.01) across the entire study site. Obvious differences were observed among different slope positions/transects, with the lowest values observed at the summit. Geostatistics indicated that all of the variables showed a moderate spatial dependence and obvious zonal distribution along the sand dunes. The ranges (lag distance) of density (32.2m) and coverage (33.5m) were close to the average width (31.4m) of the transects. The biomass range (74.1m) was almost equal to the average width (75m) of the sand dunes. Pearson's correlation analysis and nonmetric multidimensional scaling analysis consistently demonstrated that the distributions of herbs on sand dunes were dominantly influenced by sand dune topography (slope position, convexity, and relative height), soil nutrients (total nitrogen and phosphorus) and deep-rooted shrubbery (Ephedra distachya). Compared to large, mobile and steep sand dunes, low, fixed and gentle sand dunes contribute to herbaceous plant abundance and distribution as well as the stability maintenance of the whole desert ecosystem.

[Analysis of volatile compounds of fresh tea leaves from yaoluoping nature preserve by SDE-GC-MS].

OBJECTIVE: To study the volatile compounds of fresh tea leaves from Yaoluoping Nature Preserve, and to provide scientific basis for the quality and medicinal value of tea from high mountainous area. METHODS: The volatile compounds were extracted from fresh tea leaves by simultaneous distillation and extraction, and analyzed by gas chromatography-mass spectrum (GC-MS). RESULTS: 41 volatile compounds were identified from two tea cultivars, Shifoxiang and Shifocui. Shifoxiang had 32 kinds of volatile compounds and Shifocui had 38 kinds of volatile compounds. The main volatile components of Shifoxiang and Shifocui were green leaf volatiles. The kind and relative content of terpenes of Shifocui were more than that of Shifoxiang. Also the kind and relative content of ketones of Shifocui were more than that of Shifoxiang. There was one kind of heterocyclic compound of Shifocui. CONCLUSION: The main volatile components of Shifoxiang and Shifocui had an important role for the formation of unique aroma of high mountain ous tea. The composition and proportion of volatile components between Shifoxiang and Shifocui had certain differences. Some trace components may be associated with defense in the process of tea plant growth. The functional components from the volatile components had good medicinal value, worthy of further research.