Do pyrene and Kandelia obovata improve removal of BDE-209 in mangrove soils?

Combined pollution caused by polybrominated diphenyl ethers (PBDEs) and polycyclic aromatic hydrocarbons (PAHs) in mangrove wetlands is serious, with their remediation to be been paid more and more attention. However, little is known about the combined impact of PAHs and mangrove species on removal of PBDEs in contaminated soils. In this study, BDE-209 and pyrene were selected and a 9 months experiment was conducted to explore how BDE-209 removal in contaminated soil varied with pyrene addition and Kandelia obovata planting, and to clarify corresponding microbial responses. Results showed that BDE-209 removals in soil induced by pyrene addition or K. obovata planting were significant and stable after 6 months, with the lowest levels of BDE-209 in combined pyrene addition with K. obovata planting. Unexpected, root uptake of BDE-209 in K. obovata was limited for BDE-209 removal in soil, which was verified by lower total amount of BDE-209 bioaccumulated in K. obovata's root. In soil without K. obovata planting, BDE-209 removal caused by pyrene addition coexisted with changed bacterial abundance at phylum Planctomycetes and Chloroflexi, class Planctomycetacia, and genus Blastopirellula. K. obovata-induced removal of BDE-209 in soil may be related to bacterial enrichment in phylum Proteobacteria, class Gammaproteobacteria and genus Ilumatobacter, Gaiella. Thus, in BDE-209 contaminated soil, microbial community responses induced by pyrene addition and K. obovata planting were different at phylum, class and genus levels. This is the first study demonstrating that pyrene addition and K. obovata planting could improve BDE-209 removal, and differently affected the corresponding responses of microbial communities.

Spatial variation and ecological risk assessment of heavy metals in mangrove sediments across China.

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.

Effects of mangrove plant species on accumulation of heavy metals in sediment in a heavily polluted mangrove swamp in Pearl River Estuary, China.

The present study compared accumulation of heavy metals in a mangrove swamp dominated by Kandelia obovata with that by Sonneratia apetala in Pearl River Estuary, China. The results showed that the concentrations of heavy metals at all sediment depths in the S. apetala site were significantly higher than that in K. obovata. The geo-accumulation index and potential ecological risk index also showed that S. apetala sediment had a higher contamination of heavy metals, especially Cd. S. apetala significantly altered the biogeochemical cycles of Cd, lead (Pb), nickel (Ni) and chromium (Cr). In S. apetala sediment, TOC played an important role in sequestering heavy metals as reflected by its positive correlations with Zn and Pb. This study demonstrated the importance of plant species in altering soil quality and heavy metal accumulation, and S. apetala is more efficiently working as a pollution barrier than K. obovata.

Effects of conversion of mangroves into gei wai ponds on accumulation, speciation and risk of heavy metals in intertidal sediments.

Mangroves are often converted into gei wai ponds for aquaculture, but how such conversion affects the accumulation and behavior of heavy metals in sediments is not clear. The present study aims to quantify the concentration and speciation of heavy metals in sediments in different habitats, including gei wai pond, mangrove marsh dominated by Avicennia marina and bare mudflat, in a mangrove nature reserve in South China. The results showed that gei wai pond acidified the sediment and reduced its electronic conductivity and total organic carbon (TOC) when compared to A. marina marsh and mudflat. The concentrations of Cd, Cu, Zn and Pb at all sediment depths in gei wai pond were lower than the other habitats, indicating gei wai pond reduced the fertility and the ability to retain heavy metals in sediment. Gei wai pond sediment also had a lower heavy metal pollution problem according to multiple evaluation methods, including potential ecological risk coefficient, potential ecological risk index, geo-accumulation index, mean PEL quotients, pollution load index, mean ERM quotients and total toxic unit. Heavy metal speciation analysis showed that gei wai pond increased the transfer of the immobilized fraction of Cd and Cr to the mobilized one. According to the acid-volatile sulfide (AVS) and simultaneously extracted metals (SEM) analysis, the conversion of mangroves into gei wai pond reduced values of ([SEM] - [AVS])/foc, and the role of TOC in alleviating heavy metal toxicity in sediment. This study demonstrated the conversion of mangrove marsh into gei wai pond not only reduced the ecological purification capacity on heavy metal contamination, but also enhanced the transfer of heavy metals from gei wai pond sediment to nearby habitats.

Contamination of polybrominated diphenyl ethers (PBDEs) in urban mangroves of Southern China.

Mangroves are threatened due to urban development and human activities in coastal regions. Four urban mangroves in Shenzhen (rapidly developing city of China) were selected according to urban functional zoning, namely, Shajing mangrove (SJM) and Xixiang mangrove (XXM) featured with industry district, Futian mangrove (FTM) and Baguang mangrove (BGM) featured with central business district and ecological preserve. Eight BDE congeners (BDE-28, -47, -99, -100, -153, -154, -183, and -209) in mangrove sediments and leaves were determined. The highest level of BDE-209 in SJM was proximate to areas of point-source discharges of Dongbao River in Pearl River Estuary, China. Total organic carbon (TOC) was influential in BDE-209 accumulations in SJM, XXM, and FTM. Multiple variate analysis implied that PBDEs in SJM, XXM and FTM mainly composed of penta-, octa-, and deca-BDEs, with surface runoff to be the main contamination sources; while BGM was contaminated by penta- and octa-BDEs. Ecological risk of BDE-209 was high in SJM, with medium/negligible risk in the other urban mangroves. The transfers of BDE-209 from sediment to leaf were weak (BGM and FTM), improved (XXM), and restricted (SJM), respectively. This is the first reports of spatial distribution and bioaccumulation of PBDEs in urban mangroves featured with different urban functional zonings. More attention is required to reduce emission of PBDEs into the environment and manage PBDEs contamination in urban mangroves.

Occurrence and contamination of heavy metals in urban mangroves: A case study in Shenzhen, China.

Urban mangroves are affected by surrounding anthropogenic activities. Heavy metals in urban mangroves lack systematic evaluation, and their relationships with surrounding anthropogenic activities have not been explored with quantified data. In this study, urban mangroves with different urban functional zonings were selected in Shenzhen, South China, including: Shajing mangrove (SJM) and Xixiang mangrove (XXM) featured with industry district, Futian mangrove (FTM) and Baguang mangrove (BGM) featured with central business district and ecological preserve, respectively. The distribution, ecological risk, and pollution sources of heavy metals were determined. Heavy metals' relationships with surrounding functional zonings were also explored. The levels of Cu, Zn, Pb, Ni and Cr in SJM were significantly higher than the other mangrove stands, which may be related to its proximity to point-source discharges of Maozhou River in Pearl River Estuary, China. Potential ecological risk index, pollution load index, mean PEL quotient, mean effect range median quotient, and total toxic unit showed the highest ecological risk in SJM, followed by XXM, FTM, and BGM. With the order of BGM - FTM - XXM - SJM, Zn, Ni, and Cr presented dominantly in the labile fraction, demonstrating increased anthropogenic impacts. Heavy metals in FTM and BGM were mainly from anthropogenic and lithogenic originations, with only anthropogenic origination of heavy metals to be detected in SJM and XXM. Heavy metal pollution was highest in SJM featured with industry district, and metal products industry in surrounding district should attract special attention due to its affinity for heavy metal accumulation in urban mangroves.

Does ammonium nitrogen affect accumulation, subcellular distribution and chemical forms of cadmium in Kandelia obovata?

Heavy metals and nutrients are commonly found in mangrove sediments, but the effect of nutrients on heavy metals in mangrove plants is not clear. A study quantifying the effects of ammonium nitrogen (NH4+-N) on the accumulation, subcellular distribution and chemical forms of cadmium (Cd) in Kandelia obovata seedlings were conducted. The experiment consisted of four levels of NH4+-N (0, 10, 50 and 100 mg L-1) in each of which consisted of four Cd levels (0, 1, 5 and 10 mg L-1). The results showed that NH4+-N magnified the Cd toxicity due to reduced plant biomass, especially with 10 mg L-1 Cd and 100 mg L-1 NH4+-N supply. NH4+-N, especially at 100 mg L-1, enhanced the concentration and accumulation of Cd in root but its role on Cd translocation from root to stem and leaf was limited, probably due to low translocation factor. At subcellular level, Cd mainly accumulated in root cell wall but its fractionation depended on Cd levels. Under the stress of 1 and 5 mg L-1 Cd, 50 mg L-1 NH4+-N supply improved transfer of Cd from root cell wall into cell, and increased pectate and protein integrated forms of intracellular Cd to alleviate Cd toxicity. Under the stress of 10 mg L-1 Cd, NH4+-N supply promoted the deposition of Cd on root cell wall to restrain its transfer to root cell, which was verified by the reduced levels of pectate and protein integrated forms of Cd in root cell. Thus, NH4+-N supply improved immobilization of Cd in roots and alleviated Cd toxicity through integration with pectate and protein as well as cell wall combinations in root of K. obovata.

Assessing the effect of extra nitrogen on Kandelia obovata growth under cadmium stress using high-resolution thermal infrared remote sensing and the three-temperature model.

Mangrove forests provide many ecological services and are among the most productive intertidal ecosystems on earth. Currently, these forests frequently face significant heavy metal pollution as well as eutrophication. The present study assessed the response of Kandelia obovata Sheue, H.Y. Liu & J. Yong to combined NH4+-N addition and Cd stress based on a three-temperature (3T) model using high-resolution thermal infrared remote sensing. The results show that leaf surface temperature (Tc) and the plant transpiration transfer coefficient (hat) became larger with increasing NH4+-N concentrations in the same Cd treatment, especially under high NH4+-N (50 and 100 mg·L-1) and Cd stress. The thermal bioindicators, growth responses and photosynthetic parameters changed in a consistent fashion, indicating that combined high NH4+-N addition and Cd stress led to stomatal closure, reduced the cooling effect of transpiration, and increased Tc and hat values. Furthermore, appropriate NH4+-N supply reduced stomatal conductance (gs) and the transpiration rate (Tr), which were increased by Cd stress, and then maintained Tc and hat at normal levels. The normalised hat helped to reduce the influence of environmental variation during the diagnosis of mangrove plant health. This indicated that the 3T model with high-resolution thermal infrared remote sensing provides an effective technique for determining the health status of mangrove plants under stress.

Performance and bacterial community structure of a 10-years old constructed mangrove wetland.

Constructed mangrove wetland has been used for wastewater treatment but its long-term performance has not been reported. One-year monitoring of a 10-years old horizontal subsurface-flow constructed mangrove wetland consisting of three belts, two with mangrove plants and one without, revealed that the system maintained high and stable removal percentages of organic matter and nutrients, and planted belts performed better than unplanted control. Substrates in belts planted with Aegiceras corniculatum or Kandelia obovata had higher abundance of ammonifiers, nitrifiers and denitrifiers but lower total heterotrophic bacteria than unplanted substrate. Denaturing gradient gel electrophoresis showed that microbial diversity in planted substrate was significantly lower than that in unplanted one. The bacteria in substrates, irrespective to belts, were phylogenetically related to Proteobacteria (most dominant), Acidobacteria, Firmicutes, Nitrospirae, Gemmatimonadetes, Chloroflexi and Cyanobacteria. The steady performance of this 10-year old constructed mangrove wetland was affected by the abundance and diversity of bacterial community in substrate.

Impact of habitat management on waterbirds in a degraded coastal wetland.

The loss of coastal wetlands in Hong Kong Mai Po Nature Reserve adversely affected wetland-depended species. To mitigate this impact, gei wai ponds were reconstructed according to a set of biodiversity management zones (BMZs). This study, based on Canonical Correspondence Analysis (CCA), investigated if waterbird distribution was related to BMZ characteristics. Based on habitat characteristics, ponds in the same BMZ generally clumped in the same quadrant or within a short distance on CCA scatter plots, indicating that a BMZ zone produced common habitat traits. Ponds in a close distance on the plot had similar bird abundance or community structure. Significant correlations were noted between the abundance of cormorants and tall tree, and between waders and bare ground areas within study ponds. This study indicated that the control of key habitat factors was important for the success of reconstruction of gei wais and management of waterbirds in Mai Po.

Does energetic cost for leaf construction in Sonneratia change after introduce to another mangrove wetland and differ from native mangrove plants in South China?

Exotic species invasions are serious ecological problems. Leaf construction cost (CC) and growth traits of two Sonneratia (Sonneratia caseolaris and S. apetala) and four native species (Bruguiera gymnorrhiza, Kandelia obovata, Aegiceras corniculatum and Avicennia marina) in Hainan and Shenzhen mangrove wetlands were compared to evaluate invasive potentials of Sonneratia after introduced to Shenzhen, their new habitat. There were no significant differences in CC and growth traits between two wetlands, suggesting Sonneratia did not lose any advantage in the new habitat and were competitive in both wetlands. CC per unit mass (CCM), CC per unit area (CCA) and caloric values of Sonneratia were significantly lower than those of native mangrove species while specific leaf area (SLA) was just the opposite. CCM of S. caseolaris and S. apetala were 6.1% and 11.9% lower than those of natives, respectively. These findings indicated the invasive potential of Sonneratia in Shenzhen after their introduction.

Are Photosynthetic Characteristics and Energetic Cost Important Invasive Traits for Alien Sonneratia Species in South China?

A higher photosynthesis and lower energetic cost are recognized as important characteristics for invasive species, but whether these traits are also important for the ability of alien mangrove species to become invasive has seldom been reported. A microcosm study was conducted to compare the photosynthetic characteristics, energetic cost indices and other growth traits between two alien species (Sonneratia apetala and S. caseolaris) and four native mangrove species over four seasons in a subtropical mangrove nature reserve in Shenzhen, South China. The aim of the study was to evaluate the invasive potential of Sonneratia based on these physiological responses. The annual average net photosynthetic rate (Pn), stomatal conductance (Gs) and total carbon assimilation per unit leaf area (Atotal) of the two alien Sonneratia species were significantly higher than the values of the native mangroves. In contrast, the opposite results were obtained for the leaf construction cost (CC) per unit dry mass (CCM) and CC per unit area (CCA) values. The higher Atotal and lower CC values resulted in a 72% higher photosynthetic energy-use efficiency (PEUE) for Sonneratia compared to native mangroves, leading to a higher relative growth rate (RGR) of the biomass and height of Sonneratia with the respective values being 51% and 119% higher than those of the native species. Higher photosynthetic indices for Sonneratia compared to native species were found in all seasons except winter, whereas lower CC values were found in all four seasons. The present findings reveal that alien Sonneratia species may adapt well and become invasive in subtropical mangrove wetlands in Shenzhen due to their higher photosynthetic characteristics coupled with lower costs in energy use, leading to a higher PEUE. The comparison of these physiological responses between S. apetala and S. caseolaris reveal that the former species is more invasive than the latter one, thus requiring more attention in future.

Mudskipper genomes provide insights into the terrestrial adaptation of amphibious fishes.

Mudskippers are amphibious fishes that have developed morphological and physiological adaptations to match their unique lifestyles. Here we perform whole-genome sequencing of four representative mudskippers to elucidate the molecular mechanisms underlying these adaptations. We discover an expansion of innate immune system genes in the mudskippers that may provide defence against terrestrial pathogens. Several genes of the ammonia excretion pathway in the gills have experienced positive selection, suggesting their important roles in mudskippers' tolerance to environmental ammonia. Some vision-related genes are differentially lost or mutated, illustrating genomic changes associated with aerial vision. Transcriptomic analyses of mudskippers exposed to air highlight regulatory pathways that are up- or down-regulated in response to hypoxia. The present study provides a valuable resource for understanding the molecular mechanisms underlying water-to-land transition of vertebrates.

Long-term differences in annual litter production between alien (Sonneratia apetala) and native (Kandelia obovata) mangrove species in Futian, Shenzhen, China.

Annual litter production in alien (Sonneratia apetala) and native (Kandelia obovata) mangrove forests in Shenzhen, China were compared from 1999 to 2010. S. apetala had significantly higher litter production than K. obovata, with mean annual total litter of 18.1 t ha(-1) yr(-1) and 15.2 t ha(-1) yr(-1), respectively. The higher litter production in S. apetala forest indicates higher productivity and consequently more nutrient supply to the estuarine ecosystems but may be more invasive due to positive plant-soil feedbacks and nutrient availability to this alien species. Two peaks were recorded in S. apetala (May and October), while only one peak was observed in K. obovata, in early spring (March and April). Leaf and reproductive materials were the main contributors to litter production (>80%) in both forests. These results suggest that the ecological function of S. apetala and its invasive potential can be better understood based on a long-term litter fall analysis.

Contamination of polycyclic aromatic hydrocarbons (PAHs) in surface sediments and plants of mangrove swamps in Shenzhen, China.

The concentrations of 16 individual and total polycyclic aromatic hydrocarbons (∑PAHs) in sediments, roots and leaves of three mangrove swamps in Shenzhen, China, namely Futian, Baguang and Waterlands, were determined. The mean concentration of ∑PAHs in Futian (4480 ng g(-1)) was significantly higher than that in Baguang (1262 ng g(-1)) and Waterlands (2711 ng g(-1)). Among the 16 PAHs, the concentration of naphthalene was the highest. Based on the ratios of phenanthrene/anthracene and fluoranthene/pyrene, PAHs in Futian and Waterlands came from petrogenic and pyrolytic sources, while Baguang was mainly from pyrolytic. More PAHs were accumulated in leaves, as reflected by its higher mean concentration of ∑PAHs (3697 ng g(-1)) and bioconcentration factor of PAHs (BCF) (>1.5) than that in roots. The BCF values in plants collected from Futian were significantly higher than that from Waterlands. These results indicated that more attention should be paid to the PAH contamination in Futian.

AFLP genome scan to detect genetic structure and candidate loci under selection for local adaptation of the invasive weed Mikania micrantha.

Why some species become successful invaders is an important issue in invasive biology. However, limited genomic resources make it very difficult for identifying candidate genes involved in invasiveness. Mikania micrantha H.B.K. (Asteraceae), one of the world's most invasive weeds, has adapted rapidly in response to novel environments since its introduction to southern China. In its genome, we expect to find outlier loci under selection for local adaptation, critical to dissecting the molecular mechanisms of invasiveness. An explorative amplified fragment length polymorphism (AFLP) genome scan was used to detect candidate loci under selection in 28 M. micrantha populations across its entire introduced range in southern China. We also estimated population genetic parameters, bottleneck signatures, and linkage disequilibrium. In binary characters, such as presence or absence of AFLP bands, if all four character combinations are present, it is referred to as a character incompatibility. Since character incompatibility is deemed to be rare in populations with extensive asexual reproduction, a character incompatibility analysis was also performed in order to infer the predominant mating system in the introduced M. micrantha populations. Out of 483 AFLP loci examined using stringent significance criteria, 14 highly credible outlier loci were identified by Dfdist and Bayescan. Moreover, remarkable genetic variation, multiple introductions, substantial bottlenecks and character compatibility were found to occur in M. micrantha. Thus local adaptation at the genome level indeed exists in M. micrantha, and may represent a major evolutionary mechanism of successful invasion. Interactions between genetic diversity, multiple introductions, and reproductive modes contribute to increase the capacity of adaptive evolution.

Differences in leaf construction cost between alien and native mangrove species in Futian, Shenzhen, China: implications for invasiveness of alien species.

Construction cost (CC) is a quantifiable measure of energy demand for biomass production, and low CC is hypothesized to give an alien plant growth advantages and increase its potential to be an invader. Comparison of leaf CC and growth traits between alien and native mangroves in Shenzhen Futian Nature Reserve showed CC per unit mass (CC(mass)), carbon concentration and gross and ash-free caloric values of alien mangroves were significantly lower than those of native species, while the height and chest circumference were just the opposite. Alien species Sonneratia apetala had the lowest CC(mass) while Sonneratia caseolaris had the lowest CC(area), and were 8.99% and 32.17% lower than those of native species, respectively. Conversely, specific leaf area (SLA) of these two Sonneratia species was significantly higher than native species. Lower CC and higher SLA make the two Sonneratia species grow and spread faster than other mangroves and enhance their invasive potential.

[Correlation analysis on the damage of Mikania micrantha to plant communities in Neilingdind Island of Guandong Province, China].

The analysis showed that 58 species of trees, short-trees and shrubs in Neilingding Island of Guangdong Province were damaged by M. micrantha, of which, woody trees accounted for 67%. Short-trees and sunny shrubs were damaged most seriously, followed by the communities with low canopy density consisted of only 2 dominant species, and those with high canopy density consisted of 5 or 6 dominant species. The coverage of M. micrantha mainly related to the vertical structure of plant communities. The taller the community height and the more the synusia, the lesser was the coverage of M. micrantha. The damaging ratio mainly related to species diversity and community density. The higher the species diversity and community density, the lower the damaging ratio was. The damaging degree mainly related to the coverage of other liana. The more the coverage of other liana, the higher was the damaging degree of M. micrantha.

[Energy situation of Sonneratia apetala-S. caseloris forest in Futian of Shenzhen].

Based on the measurement of biomass and productivity, the caloric value of different fractions of two species in S. apetala-S. caseloris forest, and their standing crop of energy and net energy production were determined. There were some differences in caloric values among the fractions of S. apetala and S. caseloris, and the caloric value of leaf was the highest, while that of the fine-roots was the lowest. The caloric values of various fractions of S. apetala were much higher than those of S. caseloris. The standing crop of energy in S. apetala-S. caseloris forest was 84,744.72 kJ.m-2. The standing crop of energy accumulated in S. apetala population was 54,693.26 kJ.m-2, accounting for 64.54% of the total, and that of S. caseloris population was 30,051.46 kJ.m-2, accounting for 35.46%. The energy return value of litters was 24,549.54 kJ.m-2.yr-1, that of S. apetala population was 17,233.99 kJ.m-2.yr-1(accounting for 70.16%), and that of S. caseloris population was 7,325.55 kJ.m-2.yr-1(29.84%). The net energy production was 50,391.4 kJ.m-2.yr-1 for S. apetala-S. caseloris forest in 1999, in which the net energy production of S. apetala population was 31,778 kJ.m-2.yr-1.

[Accumulation and cycle of heavy metal in Sonneratia apetala and S. caseolaris Mangrove Community at Futian of Shenzhen, China].

The absorption, accumulation, distribution and cycle of Cu, Pb, Zn, Cr and Ni in S. apetala and S. caseolaris Mangrove Community at Futian Mangrove Nature Reserve of Shenzhen were studied. The results showed that the Cu, Pb, Zn, Cr and Ni contents in forest soil were increased from bottom to surface layer, and the storage of the five heavy metals in the surface layer(depth 0-30 cm) was Zn > Pb > Ni > Cr > Cu. The concentration ability was S. caseolaris > S. apetala > K. candel. The existing accumulation of Cu, Pb, Zn, Cr and Ni in the community were respectively 23,019.61 micrograms/m2, 23,429.65 micrograms/m2, 117,870.41 micrograms/m2, 6835.79 micrograms/m2, 12,995.08 micrograms/m2. The annual absorption were 6592.20 micrograms/m2, 2664.77 micrograms/m2, 24,123.56 micrograms/m2, 853.25 micrograms/m2, 1990.86 micrograms/m2, respectively. The annual return were 3179.50 micrograms/m2, 1300.64 micrograms/m2, 8401.31 micrograms/m2, 398.99 micrograms/m2, 646.20 micrograms/m2, respectively. The annual net retention accumulation of Cu, Pb, Zn, Cr and Ni in the community were 3413.07 micrograms/m2, 1364.13 micrograms/m2, 15,722.25 micrograms/m2, 454.25 micrograms/m2, 1344.66 micrograms/m2. The turn over period of Cu, Pb, Zn, Cr and Ni were 8, 19, 15, 18 and 21 years.