Surface pollen distribution patterns in Beibu Gulf and corresponding sediment dynamics environment

The Beibu Gulf is a semi-enclosed gulf in the northwest of the South China Sea.We palynologically analyzed 306 surface sediment samples from the eastern Beibu Gulf to improve bioclimatic interpretation of fossil pollen records there.Surface pollen assemblages could be classified into five pollen regions based on the distributions of total,arboreal,herbaceous and fern pollen concentrations.Four high-concentration and three low-concentration subregions could be distinguished within these regions.The distribution patterns of surface pollen assemblages were consistent with those of grain sizes of surface sediments.Sediments from regions with high pollen concentrations were very fine and fine silts (>7.0,<0.008 mm),whereas those with low pollen concentrations were fine sand (<3.5,>0.088 mm).Sedimentary heterogeneity of surface pollen assemblages was closely related to pollen source,transportation and sedimentation controlled by ocean currents,tides and waves,and oceanic bottom topography.Fern spores exhibited higher percentages along the east margins of the region,while arboreal types like Pinus increased in concentration towards the center.Herbaceous pollen appeared in high percentages around seacoasts near their source areas.Dacrydium and mangrove pollen were distributed near their source regions at low percentages.We discuss the sediment dynamic environments in the eastern Beibu Gulf based on surface pollen distributions.The estuary region is an important access to the sea basin and a depositional site for terrestrial pollen grains.Coastal regions can accumulate pollen due to the back-and-forth movements of tides there.Although ocean currents on a gulf scale tend to spread pollen grains,the interaction of multiple currents could lead to pollen accumulation and deposition.Low surface pollen concentrations in the northeast shallow-water regions of the eastern Beibu Gulf could be attributed to repeated washing and sediment floatation caused by severe wave activities during the summer.Strong tides in Qiongzhou Strait frequently wash the seabed and disadvantage pollen deposition,leading to low surface pollen concentrations there.     

Genetic diversity, geographic differentiation and evolutionary relationship among ecotypes of Glycine max and G. soja in China

The knowledge of origin and evolution of cultivated soybeans is one of the basic issues in both biology and agronomy of the crop. In order to investigate the nuclear and cytoplasmic genetic diversity, geographic differentiation and genetic relationship among geographic ecotypes of cultivated （Glycine max） and wild （G. soja） soybeans, the allelic profiles at 60 nuclear simple-sequence repeat （nuSSR） loci and 11 chloroplastic SSR （cpSSR） loci evenly distributed on whole genome of 393 landraces and 196 wild accessions from nation-wide growing areas in China were analyzed. （i） The genetic diversity of the wild soybean was obviously larger than that of the cultivated soybean, with their nuSSR and cpSSR alleles as 1067 vs. 980 and 57 vs 44, respectively. Of the 980 nuclear alleles detected in the cultivated soybean, 377 new ones （38.5%） emerged, while of the 44 chloroplastic alleles in the cultivated soybean, seven new ones （15.9%） emerged after domestication. （ii） Among the cultivated geographic ecotypes, those from southern China, including South-Central China, Southwest China and South China possessed relatively great genetic diversity than those from northern China, while among the wild geographic ecotypes, the Middle and Lower Changjiang Valleys wild ecotype showed the highest genetic diversity. （iii） The analysis of molecular variance, association analysis between geographic grouping and molecular marker clustering and analysis of specific-present alleles of ecotypes demonstrated that the geographic differentiation of both cultivated and wild soybeans associated with their genetic differentiation, or in other words, had their relevant genetic bases. （iv） The cluster analysis of all accessions clearly showed that the wild accessions from Middle and Lower Changjiang Valleys and South-Central ＆ Southwest China had relatively small genetic distances with all cultivated accessions. The UPGMA dendrogram among geographic ecotypes further showed that the genetic distances between all cultivated ecotypes and the Middle and Lower Changjiang Valleys wild ecotype were smaller than those with other wild ones, including their local wild counterparts. Therefore, it is inferred that the wild ancestors in southern China, especially those from Middle and Lower Changjiang Valleys might be the common ancestor of all the cultivated soybeans.