Element cycling in the dominant plant community in the Alpine tundra zone of Changbai Mountains, China

Element cycling in the dominant plant communities including Rh. aureum, Rh. redowskianum and Vaccinium uliginosum in the Alpine tundra zone of Changbai Mountains in northeast China was studied. The results indicate that the amount of elements from litter decomposition was less than that of the plant uptake from soil, but that from plant uptake was higher than that in soil with mineralization process released. On the other hand, in the open system including precipitation input and soil leaching output, because of great number of elements from precipitation into the open system, the element cycling(except N, P) in the Alpine tundra ecosystem was in a dynamic balance. In this study, it was also found that different organ of plants had significant difference in accumulating elements. Ca, Mg, P and N were accumulated more obviously in leaves, while Fe was in roots. The degree of concentration of elements in different tissues of the same organ of the plants also was different, a higher concentration of Ca, Mg, P and N in mesophyll than in nerve but Fe was in a reversed order. The phenomenon indicates (1) a variety of biochemical functions of different elements, (2) the elements in mesophyll were with a shorter turnover period than those in nerve or fibre, but higher utilization rate for plant. Therefore, this study implies the significance of keeping element dynamic balance in the alpine tundra ecosystem of Changbai Mountains.

Characteristics,classification and ordination of riparian plant communities in the Three-Gorges areas

Sixteen different vegetation types of grassland and shrubland were selected to study the component and diversity of plant species of riparian plant communities along main channel in the Three-Gorges areas. Species richness (s), Simpson index (D), and Shannon-Weiner index (H) were used to study the biodiversity and the hierarchical classification was carried out by the methods of TWINSPAN and DCA ordination. The results showed that the components of flora were complex and dominated by the temperate type in the riparian plant communities. Species diversity was not different between the communities, but Shannon-Weiner indexes of different layers in some grassland were significantly different. TWINSPAN and DCA indicated that riparian plant communities distributed along the gradient of moisture.

Geomorphic predictors of riparian vegetation in small mountain watersheds

Aims Hydrogeomorphic processes operating at watershed,process zone and site scales influence the distribution of riparian vegeta-tion.However,most studies examining the relationships between hydrogeomorphic processes and riparian vegetation are conducted at site scales.We quantified the relative importance of watershed,process zone and site geomorphic characteristics for predicting riparian plant community types and plant species abundances in four small mountain watersheds in central Nevada,u.Methods We mapped riparian vegetation types and identified process zones(based on dominant geomorphic process and valley fill material)within the watersheds.We sampled sites in each combination of veg-etation type and process zone(n=184 sites)and collected data on watershed scale factors,valley and stream geomorphic characteristics and on plant cover of each geomorphic surface.Plant community types were defined by cluster and indicator species analyses of plant cover data,and related to geomorphic variables using ordination analysis(nonmetric multidimensional scaling).linear mixed effects models were used to predict abundances of indicator species.Important Findings Variables describing position in the watershed(elevation,contrib-uting area)that are related to gradients of temperature,moisture and stream discharge were of primary importance in predicting plant community types.Variables describing local geomorphic setting(valley width,stream gradient,channel sediments,geomor-phic surface height)were of secondary importance,but accurately described the geomorphic setting of indicator species.The process zone classification did not include position in the watershed or channel characteristics and only predicted plant community types with unique geomorphic settings.In small mountain watersheds,predicting riparian vegetation distribution requires explicit consid-eration of scale and geomorphic context within and among water-sheds in addition to site variables.