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The spatial variations of nine heavy metals in the surface sediments of six Avicennia marina mangrove wetlands across China were investigated. These were Yunxiao, Futian (FT), Zhanjiang, Fangchenggang (FCG), Dongfang (DF), and Dongzhaigang (DZG). Results showed that environmental factors, such as organic matter and sediment grain size, affected heavy metal distribution. The high heavy metal levels in mangrove sediments may be due to their large retention capacity. The dominant heavy metals were Zn, Cr, Pb, Cu, and Cd. Pollution was highest at FT and lowest at FCG. The principal component analysis indicated that Zn, Cd, Cu, Ni, Cr, and Pb were mainly derived from anthropogenic activities. Ecological risk assessments showed that FT was the most polluted area with considerable ecological risk, whereas pollution levels were lowest at FCG, DF, and DZG. This study provides the first integrated analysis of heavy metal pollution of sediments across China. • First report on heavy metal pollution in mangroves sediments across China • Metal pollution risk: Futian > Yunxiao, Zhanjiang > Dongfang, Dongzhaigang, Fangchenggang • Heavy metals in mangrove sediments were dominated by Zn, Cr, Pb, Cu, and Cd. • Principal component analysis suggests human activity affects Zn, Cd, Cu, Ni, Cr, and Pb in Futian. [ABSTRACT FROM AUTHOR]

The halophytic Avicennia marina (Forsk.) is one of the pioneer mangroves along the south coast of China. It is an appropriate material for understanding molecular mechanisms of heavy metal tolerance in mangrove plants. A forward and a reverse cDNA library was constructed by PCR-based suppressive subtractive hybridization (SSH) to isolate these tolerance-associated genes from A. marina leaves. A total of 99 ESTs obtained from the forward and reverse libraries showed significant differential expressions. Twenty-nine genes selected by SSH were studied by real-time PCR in order to analyze their expression level. Most of these genes' expression increased in leaves under Cd stress, which suggests that these genes contribute to the heavy metal tolerance in A. marina . The diversity of these genes indicated that heavy metal stress resulted in a complex response in mangrove plants. This could prove a useful approach for further exploring the molecular mechanisms behind such heavy metal tolerance. [ABSTRACT FROM AUTHOR]

Avicennia marinais a typical mangrove species of subtropical coastlines of China. However, little is known about the retention of nutrients by this species in oligotrophic, coastal environments. In this study, seasonal changes in nitrogen (N) and phosphorus (P) concentrations, N:P ratio and total phenolic concentration inA. marinaleaves during senescence were studied.Avicennia marinaleaves had high N and P concentrations but the seasonal pattern of N concentration was different from that of P concentration. TheA. marinaforest was N-limited as the N:P ratio of mature leaves was less than 14. Nitrogen resorption efficiency was higher than P resorption efficiency, and the concentrations of N and P in senescent leaves indicated that N resorption was mostly complete whereas P resorption was incomplete.Avicennia marinaleaves contained low tannin concentrations, particularly condensed tannins, as the leaf extracts did not react with acid butanol. Total phenolic concentrations were not correlated with N concentrations in mature and senescent leaves ofA. marina. These findings suggest that the high N resorption efficiency and low nutrient losses play an important role in nutrient conservation strategies forA. marinaforests, whereas low tannin concentations have limited effects on nutrient cycling. [ABSTRACT FROM PUBLISHER]

Introduced mangroves are widely used to restore mangrove ecosystems in South China. Results of potential impacts on indicative benthic macroinvertebrates are divergent. We explored the community structure of benthic macroinvertebrates in the mangrove ecosystem of northern Beibu Gulf, China across four habitats: native Avicennia marina mangrove, introduced Laguncularia racemosa mangrove, native-introduced mixed mangrove, and unvegetated intertidal flat. Based on the Hill number, community structure was estimated from the dimensions of estimated species richness, diversity, evenness, and species composition similarity. Benthic macroinvertebrates in the unvegetated flat significantly differed from the other three assemblages in mangroves; introduced L. racemosa mangrove had relatively distinct benthic macroinvertebrate assemblage from the native A. marina and the mixed mangroves, with lower species richness and similarity but higher diversity and evenness. Considering the lack of unanimous conclusion of potential impact on benthic macroinvertebrates under complex species interactions, native mangroves should be of top priority in ecosystem restoration. • Community structure of benthic macroinvertebrates among distinct habitats is shown. • The Hill number based estimates for taxonomic diversity are presented. • Introduced mangroves had lower species richness, but higher diversity and evenness. • Unvegetated flat had lower species richness, diversity, evenness, and similarity. • Native mangroves should be used under unknown species interactions in communities. [ABSTRACT FROM AUTHOR]

Mangrove forests are distributed in the intertidal zones of tropical and subtropical regions, and have been severely damaged by anthropogenic activities, climate change, and stochastic events. Although much progress has been made in the conservation and restoration of mangroves in China, studies of the genetic diversity of mangroves are lacking, especially for isolated populations, yet such studies are essential for guiding conservation and restoration efforts. Here, we evaluated the genetic diversity, spatial genetic structure, and mating system of two mangrove species, Rhizophora apiculata and Avicennia marina, in a heavily disturbed area in Tielu Harbor, Sanya City, Hainan Island, China, using 18 nuclear microsatellite markers. We found that the genetic diversity of R. apiculata, which is classified as 'Vulnerable' in the China Red List categories, was high and similar compared with the genetic diversity estimates of other populations reported in previous studies. In contrast, the genetic diversity of A. marina, which is classified as a species of 'Least Concern', was low compared with the genetic diversity estimates of other populations. We then evaluated the presence of genetic bottlenecks, spatial genetic structure, and the mating system to determine the effects that habitat destruction has had on these two species. Our findings indicate that distinct conservation and restoration approaches are needed for these two species. Generally, our results provide valuable information that will aid the development of conservation and restoration strategies for the mangroves of Tielu Harbor. [ABSTRACT FROM AUTHOR]

Two new metabolites, named no. 2106 A (1) and cyclo-(N-MeVal-N-MeAla) (2), have been produced by the endophytic fungus no. 2106 isolated from the seeds of the mangrove Avicennia marina in Hong Kong. The structures were elucidated by 2D NMR, HR-MS, and X-ray diffraction analyses. [ABSTRACT FROM AUTHOR]

Many previous studies demonstrate that carbon stable isotope composition (usually expressed as isotopic ratio, δ13C) can reflect the integrated response of physiological processes to environment, but little is known of the variation in δ13C of mangrove plants as affected by salinity, especially in response to long term saline environment. The variation in δ13C of three dominant mangroves growing in long-term saline environments in the field was assessed. Mature leaves of Avicennia marina (Forsk) Vierh., Kandelia candel (L.) Duce., and Aegiceras corniculatum Blanco. were collected at seven sample sites covering seven salinity levels (14.07%-19.83%) at a natural mangrove wetland located in southeast China. The δ13C values varied from -31.46% to -27.33‰ with increasing salinity, reflecting the typical C3 pathway of CO2 fixation. The δ13C was positively related to salinity in K candel and A. marina, and the reverse was observed in A. corniculatum, even though the correlations were not statistically significant for A. corniculatum and A. marina. The mean δ13C at high salinity was, in descending order, K candel > A. marina > A. corniculcitum. It is concluded that responses of δ13C to salinity is species-dependent and assessment of carbon isotopic composition is helpful for evaluating the salt tolerance of mangrove species, but it should be used with caution when comparing the salt tolerance between different species, particularly when they have the different patterns of δ13C in response to salinity. [ABSTRACT FROM AUTHOR]

Many previous studies demonstrate that carbon stable isotope composition (usually expressed as isotopic ratio, δ13C) can reflect the integrated response of physiological processes to environment, but little is known of the variation in δ13C of mangrove plants as affected by salinity, especially in response to long term saline environment. The variation in δ13C of three dominant mangroves growing in long-term saline environments in the field was assessed. Mature leaves of Avicennia marina (Forsk) Vierh., Kandelia candel (L.) Duce., and Aegiceras corniculatum Blanco. were collected at seven sample sites covering seven salinity levels (14.07%-19.83%) at a natural mangrove wetland located in southeast China. The δ13C values varied from -31.46% to -27.33% with increasing salinity, reflecting the typical C3 pathway of CO2 fixation. The δ13C was positively related to salinity in K. candel and A. marina, and the reverse was observed in A. corniculatum, even though the correlations were not statistically significant for A. corniculatum and A. marina. The mean δ13C at high salinity was, in descending order, K. candel > A. marina > A. corniculatum. It is concluded that responses of δ13C to salinity is species-dependent and assessment of carbon isotopic composition is helpful for evaluating the salt tolerance of mangrove species, but it should be used with caution when comparing the salt tolerance between different species, particularly when they have the different patterns of δ13C in response to salinity. [ABSTRACT FROM AUTHOR]