Contrasting fine-scale genetic structure of two sympatric clonal plants in an alpine swampy meadow featured by tussocks.

Tussocks are unique vegetation structures in wetlands. Many tussock species mainly reproduce by clonal growth, resulting in genetically identical offspring distributed in various spatial patterns. These fine-scale patterns could influence mating patterns and thus the long-term evolution of wetland plants. Here, we contribute the first genetic and clonal structures of two key species in alpine wetlands on the Qinghai-Tibet Plateau, Kobresia tibetica and Blysmus sinocompressus, using > 5000 SNPs identified by 2b-RAD sequencing. The tussock-building species, K. tibetica, has a phalanx (clumping) growth form, but different genets could co-occur within the tussocks, indicating that it is not proper to treat a tussock as one genetic individual. Phalanx growth does not necessarily lead to increased inbreeding in K. tibetica. B. sinocompressus has a guerilla (spreading) growth form, with the largest detected clone size being 18.32 m, but genets at the local scale tend to be inbred offspring. Our results highlight that the combination of clone expansion and seedling recruitment facilitates the contemporary advantage of B. sinocompressus, but its evolutionary potential is limited by the input genetic load of the original genets. The tussocks of K. tibetica are more diverse and a valuable genetic legacy of former well-developed wet meadows, and they are worthy of conservation attention.

[Spatial characteristics of grain size of surface sediments in mangrove wetlands in Gaoqiao of Zhanjiang, Guangdong province of South China].

Mangrove wetland is an important type of coastal wetlands, and also, an important sediment trap. Sediment is an essential medium for mangrove recruitment and development, which records the environmental history of mangrove wetlands and can be used for the analysis of material sources and the inference of the materials depositing process, being essential to the ecological restoration and conservation of mangrove. In this paper, surface sediment samples were collected along a hydrodynamic gradient in Gaoqiao, Zhanjiang Mangrove National Nature Reserve in 2011. The characteristics of the surface sediments were analyzed based on grain size analysis, and the prediction surfaces were generated by the geo-statistical methods with ArcGIS 9.2 software. A correlation analysis was also conducted on the sediment organic matter content and the mangrove community structure. In the study area, clay and silt dominated the sediment texture, and the mean content of sand, silt, and clay was (27.8 +/- 15.4)%, (40.3 +/- 15.4)%, and (32.1 +/- 11.4)%, respectively. The spatial gradient of the sediment characteristics was expressed in apparent interpolation raster. With increasing distance from the seawall, the sediment sand content increased, clay content decreased, and silt content was relatively stable at a certain level. There was a positive correlation between the contents of sediment organic matter and silt, and a negative correlation between the contents of sediment organic matter and sand. Much more sediment organic matter was located at the high tide area with weak tide energy. There existed apparent discrepancies in the characteristics of the surface sediments in different biotopes. The sediment characteristics had definite correlations with the community structure of mangroves, reflecting the complicated correlations between the hydrodynamic conditions and the mangroves.