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Background and Aims: Fenced enclosures have become an important method for re-establishing degraded grassland on the Tibetan plateau, and examination of soil seed banks may provide useful insights to understanding the effects and mechanisms of fencing enclosure on the restoration. Methods: An investigation was conducted into the effects of enclosure for 3 years on the soil seed banks of degraded natural and sown grasslands at eight study sites. Species composition, soil seed bank density and the relationships with above-ground vegetation were analysed based on 4800 soil core samples and counting of seeds extracted from soil samples. Results: After 3 years of fencing enclosure, soil seed banks differed between the different communities across the study sites. Species numbers and seed density in soil seed banks decreased from natural grassland to sown grassland, with most seeds occurring in the upper 5 cm soil layer. In these alpine grasslands, relatively few species produced high numbers of seeds, although their occurrence across the eight study sites was variable. Total vegetation cover increased with enclosure due to the colonization capacity of the vegetation rather than soil seed banks. Conclusions: This study provided evidence that soil seed banks do not play an important role in the restoration of degraded alpine grassland when using fencing enclosures. Further studies conducted over longer periods are needed to address this subject. [ABSTRACT FROM AUTHOR]

Seed rain is a crucial element in vegetation regeneration, but has been rarely studied in high altitude regions, particularly degraded Kobresia meadow. Weed infestation is a distinctive feature of pasture degradation in Kobresia meadows on the Tibetan plateau, the ecological mechanism of which is closely related with vegetation's seed rain. In this paper we assess the effect of vegetation degradation on seed rain and consider its implication for restoration of degraded Kobresia meadows in the headwater area of Yellow river, through analysis of seed species composition, number of seeds landing per m of soil surface, and their relationship with above ground vegetation. Vegetation degradation had an impact on the species composition and numbers of seeds in seed rain and their relationship with above-ground vegetation. Within the un-degraded meadow, which provided a closed vegetation cover, 35 % of the seed rain was of sedge and gramineae species. However, within the degraded meadows, as the extent of degradation increased, so the total number of seeds m increased, with those derived from sedge and gramineae species forming a declining proportion of the total. Degradation of Kobresia meadow on the Tibetan plateau is exacerbated by the seed input of weed species (such as Oxytropis ochrocephala, Carum carvi, Aconitum pendulum, Pedicularis kansuensis in this study). Therefore, a major priority for the restoration of such degraded meadows should be the elimination of these weeds from the above ground vegetation by human intervention. [ABSTRACT FROM AUTHOR]

Nitraria tangutorum Bor., having edible berries, is valued for reputed health benefits in Qinghai-Tibet plateau. The phytochemical research on the fruit juice of N. tangutorum led to the isolation of twenty-six compounds including five new compounds, tangutorids A–D ( 1 , 2 , 3a , and 3b ), and (3 E ,5 E )-7- O -β-glucosyl-4-(2-methoxy-2-oxoethyl)hepta-3,5-dienoic acid ( 15 ). The structures of these compounds were elucidated through comprehensive spectroscopic analyses. Tangutorids A–F were the first examples of glucose-derived β-carbolines from natural products. The biogenetic pathways of 1 – 8 were proposed to involve Pictet–Spengler reactions and described starting from the co-isolated tryptophan ( 10 ) and corresponding aldehydes. All isolates were evaluated for their antioxidant and α -glucosidase inhibitory activities. Compounds 21 , 22 , and 24 showed antioxidant activity with SC 50 values ranging from 12.2 ± 1.9 to 30.4 ± 2.7 μg/mL, and compound 1 showed strong α -glucosidase inhibitory effect with IC 50 value of 63.3 ± 4.6 μg/mL. [ABSTRACT FROM AUTHOR]