No abstract

The bacterial communities played important roles in the high productivity mangrove ecosystem. In this study, we investigated the vertical distributions of rhizosphere bacteria from three mangrove species (Bruguiera gymnorrhiza, Kandelia candel and Aegiceras corniculatum) in Beilun Estuary, China using high throughput DNA pyrosequencing of the 16S rRNA gene. Phylogenetic analysis showed that bacterial communities from mangrove rhizosphere sediments were dominated by Proteobacteria (mostly Deltaproteobacteria and Gammaproteobacteria), followed by Chloroflexi, Bacteroidetes, Planctomycetes and Acidobacteria. However, the ANOVA analysis on Shannon and Chao1 indices indicated that bacterial communities among sediments of the three mangrove species varied more strongly than the sampling depths. In addition, the PCA result demonstrated that the bacterial communities could be separated into three groups according to the mangrove species. Moreover, the dominated orders Rhodospirillales, GCA004 and envOPS12 were significantly different among sediments of the three mangrove species. The results of this study provided valuable information about the distribution feature of rhizosphere bacteria from Chinese mangrove plants and shed insights into biogeochemical transformations driven by bacteria in rhizosphere sediments.

The distribution, species, biomass, productivity of main seagrasses and their suffered main threats are introduced and discussed in this paper based on the field surveys in the offshore areas of Guangdong, Guangxi and Hainan provinces. The seagrass beds distributed mainly in Liusha Bay, Donghai Island and Hailing Island of Guangdong Province; Hepu and Pearl Bay of Guangxi Zhuang Autonomous Region; Li'an Bay, Xincun Bay, Longwan Bay and Sanya Bay of Hainan Province and so on. The total area of seagrass beds in the coastal sea of South China is about 2400 ha. There are about 8 species, such as Halophila ovalis, Halodule uninervis, Halophila beccarii, Zostera japonica, Enhalus acoroides, Thalassia hemperichii, Ruppia martime and Cymodocea rotundata. These seagrasses have high biomass and productivity. However, they are subjected to some threats resulting from artificial and natural factors, especially anthropogenic causes, such as culture of shrimps and fishes, shellfish collection, fishing by means of poisons, electric power and explosives as well as trawling, artificial pollution, dredging channels, and typhoons natural disaster.Keywords: seagrass, distribution, ecological character, threats, South China.The seagrass is the only epigeal angiosperms, which fructifies and germinates under the seawater. There are about 50 species of seagrass belonging to 12 genera in the world, and more than 20 species in South China Sea 1) . Seagrasses distribute widely in the coastal areas of temperate zone and tropical zone, and they are frequently and seriously disturbed by natural and artificial factors. The seagrasses prefer living in inshore lagoons, estuaries and bays with slow current. Mangrove, coral reef and seagrass bed are the three typical marine ecosystems in tropical and semi-tropical zones. The seagrass bed is one of the most productive marine ecosystems in the biosphere [1] . Seagrasses are very important in the marine ecological environment, such as improving shallow seawater quality, being the direct food resource of many creatures, providing important habitat and concealment for many creatures, and a natural barrier resisting against wave and tide and thus protecting the coast. The roots of seagrasses are able to utilize abundant nutrients in the sediments, which generally cannot be utilized by other primary producers in this ecosystem. Seagrasses are productive and form a large carbon storehouse. The carbonaceous nutrients are usually foods for vegetarian such as sea turtle, birds and marine mammal in tropical zone. Oddment food chain is usually regarded as the main energy flowing pathway of seagrasses.One of the hot points for seagrass researches is to take carbon as research objective and to study its flowing process in the ecosystem of the food net in the seagrass beds [2][3][4] . The stable isotope method instead of traditional analytical method, namely analysis of the internal substances in the alimentary canals, is used to study nutrient classes and the flowing of substances and energy in the ecos...

No abstract

Simulated rainfall experiments were conducted to investigate the effect of Astragalus adsurgens roots and canopy on water erosion yield, erosion processes and soil resistance to erosion. Experiments were conducted on grass, root and bare slopes, with sandy soil from a water–wind crisscrossed erosion region of the Loess Plateau, China. A. adsurgens coverage on grass slopes was approximately 40%. There were three rainfall intensities of 30, 60 and 90 mm h–1 and four slope gradients of 3, 6, 9 and 12°. A. adsurgens had a significant effect on soil erosion control; soil loss was reduced by ~70% on slopes with the grass compared with bare slopes. The grass roots reduced soil loss more than its canopy, particularly in high‐intensity rainfall, which reduced soil loss by 82%. The presence of the grass and its roots changed the soil erosion process, reducing soil erodibility (Kr) and increasing the critical shear stress (τc). The soil erosion rate on the bare slope increased steadily over time; on the grass and root slopes, its rate initially increased, then decreased and then finally stabilized. Kr on the grass and root slopes was reduced by 96% and 89%, respectively, compared with the bare slope, while the corresponding τc increased by 92% and 195% respectively. These results provide insights into the mechanisms of grass on soil and water conservation and may help to improve vegetation construction in water–wind crisscrossed erosion regions of the Loess Plateau. Copyright © 2016 John Wiley & Sons, Ltd.

No abstract

No abstract

No abstract