Zhao-Yu Jiang

Metal (Pb, Zn and Cu) uptake and tolerance by mangroves in relation to root anatomy and lignification/suberization

Metal pollution has been widely reported in mangrove wetlands; however, the mechanisms involved in metal detoxification by mangroves are still poorly understood. This study aimed to investigate the possible function of root anatomy and lignification/suberization on metal uptake and tolerance in seedlings of six species of mangroves. The results revealed that the three rhizophoraceous species (Bruguiera gymnorrhiza (L.) Poir, Kandelia obovata Sheue, Liu & Yong and Rhizophora stylosa Griff) consistently exhibited higher metal tolerances than the three pioneer species (Aegiceras corniculatum (Linn.) Blanco, Acanthus ilicifolius L. and Avicennia marina (Forsk.) Viern.). Moreover, metal-tolerant species often exhibited a thick exodermis with high lignification and suberization. The tolerance indices of the mangroves were found to be positively correlated with the amounts of lignin and suberin deposition within the exodermal cell walls. The observed metal uptake by the excised roots further illustrated that a lignified/suberized exodermis directly delayed the entry of metals into the roots, and thereby contributed to a higher tolerance to heavy metals. In summary, the present study proposes a barrier property of the lignified/suberized exodermis in dealing with the stresses of heavy metals, such that the mangroves which possessed more extensive lignification/suberization within the exodermis appeared to exhibit higher metal tolerance.

Differences in root aeration, iron plaque formation and waterlogging tolerance in six mangroves along a continues tidal gradient

Mangrove is a special coastal forest along tropical and subtropical intertidal shores. However, how mangroves adapt to tidal flooding and the mechanisms involved in mangrove zonation are still poorly understood. In this study, a pot trial with different tide treatments was conducted to investigate the differences in root anatomy, porosity, radial oxygen loss, iron plaque formation and waterlogging tolerance among six mangroves along a continuous tidal gradient. The index of waterlogging tolerance illustrated that Sonneratia apetala possessed the highest index, followed by Aeguceras corniculatum/Kandelia, Rhizophora stylosa, Heritiera littorlis and Thespesia populnea. Waterlogging tolerances of the mangroves were found to be positively correlated with their root porosity, radial oxygen loss and iron plaque formation. Waterlogging-sensitive species such as landward semi-mangroves exhibited small root porosity and ROL, while waterlogging-tolerant species such as seaward pioneer and rhizophoraceous mangroves exhibited extensive porosity, ROL and iron plaque formation. Nevertheless, grater root porosity and iron plaque formation were detected in permanent waterlogged plants when compared to drained plants. In conclusion, The present study proposes a structural adaptive strategy to tidal flooding in mangroves, such that the mangroves with higher root porosity, ROL and iron plaque appeared to exhibit higher waterlogging tolerance and adaptability in anaerobic foreshores.

Influence of environmental changes on phytoplankton pattern in Daya Bay, South China Sea

In this study, we analyzed the environmental (physical and chemical) and biological (phytoplankton) data obtained from the Daya Bay, South China Sea, during 4 cruises, carried out in January, April, August and October, 2001. The main objective of this study was to identify the key environmental factors affecting phytoplankton structure in the bay. The results suggest that environmental factors like temperature and nutrients ratios have great influence on phytoplankton succession. Environmental factors are affected by the combination of human activities and nature processes. The limiting factor transited from N limiting in winter to P limiting in spring. Hydrodynamic processes (mixing in winter and stratification in summer) seem to be another main driving force for phytoplankton growth. The diatoms were the dominant group during most of the year and the dominant species were Chaetoceros affinis, Chaetoceros lorenzianus, and Nitzschia pungens all the year round.

Genetic Diversity of Bacterial Communities and Gene Transfer Agents in Northern South China Sea

Pyrosequencing of the 16S ribosomal RNA gene (rDNA) amplicons was performed to investigate the unique distribution of bacterial communities in northern South China Sea (nSCS) and evaluate community structure and spatial differences of bacterial diversity. Cyanobacteria, Proteobacteria, Actinobacteria, and Bacteroidetes constitute the majority of bacteria. The taxonomic description of bacterial communities revealed that more Chroococcales, SAR11 clade, Acidimicrobiales, Rhodobacterales, and Flavobacteriales are present in the nSCS waters than other bacterial groups. Rhodobacterales were less abundant in tropical water (nSCS) than in temperate and cold waters. Furthermore, the diversity of Rhodobacterales based on the gene transfer agent (GTA) major capsid gene (g5) was investigated. Four g5 gene clone libraries were constructed from samples representing different regions and yielded diverse sequences. Fourteen g5 clusters could be identified among 197 nSCS clones. These clusters were also related to known g5 sequences derived from genome-sequenced Rhodobacterales. The composition of g5 sequences in surface water varied with the g5 sequences in the sampling sites; this result indicated that the Rhodobacterales population could be highly diverse in nSCS. Phylogenetic tree analysis result indicated distinguishable diversity patterns among tropical (nSCS), temperate, and cold waters, thereby supporting the niche adaptation of specific Rhodobacterales members in unique environments.

Spatial structure of eukaryotic ultraplankton community in the northern South China Sea

Spatial distribution, diversity and composition of eukaryotic ultraplankton community of the northern South China Sea (nSCS) surface water and the relationship with the in situ water environment were investigated by the method of polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE). A total of 18 DGGE intensive bands were detected and the sequence analysis of these DGGE bands revealed that Alveolata was the dominant eukaryotic ultraplankton group of surface water in the nSCS (50%). Other species belonged to Bicoecea, Bolidophyceae, Polycystinea and Chlorophyta, which accounted for less proportion of eukaryotic ultraplankton in the study area. Unweighted pair group method with arithmetic averages clustering of the sampling stations indicated that all stations were classified mainly based on geographical proximity. Redundancy analysis (RDA) was employed to further investigate the relationships between DGGE band pattern and the environmental variables. Based on the RDA analysis, temperature, salinity, phosphorus and silicate were the important factors to shape the eukaryotic ultraplankton community composition in the nSCS.