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Seagrass beds are susceptible to deterioration and heavy metals represent a crucial impact factor. The accumulation of heavy metal in two tropical seagrass species were studied in South China in this study and multiple methods were used to identify the heavy metal sources. E. acoroides (Enhalus acoroides) and T. hemperichii (Thalassia hemperichii) belong to the genus of Enhalus and Thalassia in the Hydrocharitaceae family, respectively. Heavy metal concentrations in the two seagrasses followed the order of Cr > Zn > Cu > Ni > As > Pb > Co > Cd based on the whole plant, and their bioconcentration factors were 31.8 ± 29.3 (Cr), 5.7 ± 1.3 (Zn), 7.0 ± 3.8 (Cu), 3.0 ± 1.9 (Ni), 1.2 ± 0.3 (As), 1.7 ± 0.9 (Pb), 9.1 ± 11.1 (Co) and 2.8 ± 0.6 (Cd), indicating the intense enrichment in Co and Cr within the two seagrasses. The two seagrasses were prone to accumulate all the listed heavy metals (except for As in E. acoroides), especially Co (BCFs of 1124) and Cr (BCFs of 2689) in the aboveground parts, and the belowground parts of both seagrasses also accumulated most metals (BCFs of 27) excluding Co and Pb. The Pb isotopic ratios (mean 208Pb/204Pb, 207Pb/204Pb and 206Pb/204Pb values of 38.2054, 15.5000 and 18.3240, respectively) and Cd isotopic compositions (δ114/110Cd values ranging from –0.09‰ to 0.58‰) within seagrasses indicated the anthropogenic sources of Pb and Cd including coal combustion, traffic emissions and agricultural activities. This study described the absorption characteristics of E. acoroides and T. hemperichii to some heavy metals, and further demonstrated the successful utilization of Pb and Cd isotopes as discerning markers to trace anthropogenic origins of heavy metals (mainly Pb and Cd) in seagrasses. Pb and Cd isotopes can mutually verify and be helpful to understand more information in pollution sources and improve the reliability of conclusion deduced from concentrations or a single isotope.

Coastal nutrient loading has been linked to a decline in the capacity of seagrass ecosystems to sequester carbon (‘blue carbon’); however, the mechanisms are unclear. Here we investigated how nutrient loading can affect the contribution that seagrass plant material makes to blue carbon stocks by investigating plant quality-decomposition dynamics. Specifically, we used a combination of laboratory and field experiments to account for various changes in biogeochemical cycling from seagrass meadows, ranging from changes in leaf quality to CO2 fluxes. It was found that nutrient loading increased the ‘labile’ content of seagrass (i.e. increased levels of leaf nitrogen, phosphorus and soluble organic carbon (amino acid and soluble sugar content), and at the same time decreased levels of ‘recalcitrant’ carbon (i.e. materials that are harder for microbes to break down, such hemicellulose, cellulose and lignin contents). Nutrient-enriched leaves decomposed ∼ 18 % faster than non-enriched leaves (i.e. greater biomass loss from nutrient-affected seagrass), resulting in ∼ 80 % more CO2 emissions from nutrient-enriched seagrass. We also found that seagrass that naturally contained high levels of labile carbon at the start of the experiment were affected to a greater degree (i.e. higher CO2 emissions) by nutrients addition than seagrass that had high proportions of recalcitrant carbon to begin with. Overall, these findings suggest that nutrient loading can weaken the capacity of seagrass ecosystems to act as blue carbon sinks through its effect on seagrass leaf decomposability.

Abstract Background Nanoparticle-based photothermal therapy (PTT) is capable of inducing immunogenic cell death (ICD) and eradicating local tumor via hyperthermia. However, it can hardly prevent tumor recurrence and metastasis owing to inadequate immune activation. Results To this end, manganese-coordinated polyphenol carbon dots (MP-CDs) were synthesized by hydrothermal carbonization and metal–polyphenol coordination. This prepared MP-CDs had ultra-small particle size of 5 nm, excellent optical performance, good dispersibility in water and favorable biocompatibility. Under 808 nm near-infrared laser irradiation, the MP-CDs with high photothermal conversion efficiency could kill tumor cells and induce the release of damage-associated molecular patterns (DAMPs) from tumor cells. Notably, the MP-CDs can promote the maturation and antigen presentation ability of dendritic cells (DCs) via manganese-mediated immune activation. Conclusion The present work offers a versatile strategy to integrate functional metal into CDs via metal–polyphenol coordination for photothermal/immune therapy.

Identifying the trophic role of primary producers is the basis of assessing seagrass bed functions but remains difficult due to the underdetermined analysis method. Here, we analyzed the multiple isotopes (δ13C, δ15N, and δ34S values) and fatty acid markers of food sources and macrobenthos in a tropical seagrass bed in summer and winter, and tried to combine these indicators to resolve the limitation of δ13C and δ15N values analysis. We found that the δ13C and δ15N values of epiphytes were like that of seagrass and macroalgae, while the δ34S values of epiphytes and macroalgae were significantly different, and the dominant unsaturated Fatty acid markers of seagrass (18:2n6c and 18:3n3) and epiphytes (16:1n7) were obviously different. These results suggest that the combination of multiple isotopes and Fatty acid markers can effectively distinguish the complex food source. In addition, we also found that multiple isotopes were more suitable to identify the food sources of polychaetes and snails with simple diets, fatty acids were more suitable to identify the food sources of crustaceans with complex diets, but their combination is essential in identifying the diets of macrobenthos since the wide range of isotopic values for omnivores crustaceans and the Fatty acid markers transformation during snails and polychaetes assimilation might mislead us when only isotopes or Fatty acid markers were used. Our findings suggest that in tropical seagrass beds, using multiple isotopes and fatty acid markers together can help reduce the uncertainty caused by single markers variation and thus strengthen the separation of food sources and the diets of different consumer species.

Abstract Background Sediment is crucial for the unique marine angiosperm seagrass growth and successful restoration. Sediment modification induced by eutrophication also exacerbates seagrass decline and reduces plantation and transplantation survival rates. However, we lack information regarding the influence of sediment on seagrass photosynthesis and the metabolics, especially regarding the key secondary metabolic flavone. Meanwhile, sulfation of flavonoids in seagrass may mitigate sulfide intrusion, but limited evidence is available. Results We cultured the seagrass Thalassia hemprichii under controlled laboratory conditions in three sediment types by combining different ratios of in-situ eutrophic sediment and coarse beach sand. We examined the effects of beach sand mixed with natural eutrophic sediments on seagrass using photobiology, metabolomics and isotope labelling approaches. Seagrasses grown in eutrophic sediments mixed with beach sand exhibited significantly higher photosynthetic activity, with a larger relative maximum electron transport rate and minimum saturating irradiance. Simultaneously, considerably greater belowground amino acid and flavonoid concentrations were observed to counteract anoxic stress in eutrophic sediments without mixed beach sand. This led to more positive belowground stable sulfur isotope ratios in eutrophic sediments with a lower Eh. Conclusions These results indicated that coarse beach sand indirectly enhanced photosynthesis in T. hemprichii by reducing sulfide intrusion with lower amino acid and flavonoid concentrations. This could explain why T. hemprichii often grows better on coarse sand substrates. Therefore, it is imperative to consider adding beach sand to sediments to improve the environmental conditions for seagrass and restore seagrass in eutrophic ecosystems.

Abstract Background Phototherapy-triggered immunogenic cell death (ICD) rarely elicits a robust antitumour immune response, partially due to low antigen exposure and inefficient antigen presentation. To address these issues, we developed novel methylene blue-loaded ovalbumin/polypyrrole nanoparticles (MB@OVA/PPY NPs) via oxidative polymerization and π–π stacking interactions. Results The as-prepared MB@OVA/PPY NPs with outstanding photothermal conversion efficiency (38%) and photodynamic properties were readily internalized into the cytoplasm and accumulated in the lysosomes and mitochondria. Upon 808 nm and 660 nm laser irradiation, the MB@OVA/PPY NPs not only ablated tumour cells by inducing local hyperthermia but also damaged residual tumour cells by generating a large amount of reactive oxygen species (ROS), finally triggering the release of many damage-associated molecular patterns (DAMPs). Moreover, the MB@OVA/PPY NPs synergized with DAMPs to promote the maturation and improve the antigen presentation ability of DCs in vitro and in vivo. Conclusions This work reported a PPY NPs-based nanoplatform to encapsulate the therepeutic proteins and absorb the functional molecules for combination therapy of tumours. The results demonstrated that the prepared MB@OVA/PPY NPs could be used as effective nanotherapeutic agents to eliminate solid tumours and trigger a powerful antitumour immune response.

Plant-herbivore interaction, susceptible to nutrient enrichment, is fundamental for maintaining a healthy and stable ecosystem. Hence, identifying nutrient thresholds may enable better management and monitoring of ecosystems. However, little information is available for the nutrient threshold for the susceptibility of seagrass, the only marine angiosperm, to herbivory. In present study, we investigated how nitrate enrichment altered the traits of dominant tropical seagrass Thalassia hemprichii at the physiological level (nutritional quality, chemical deterrents, and structural characteristics), changing its susceptibility to the herbivory of Cerithidea rhizophorarum. A set of multiple-choice feeding assays were conducted using nitrate-enriched seagrass pre-cultivated in the lab for 60 days. The present study found that the effect of nitrate enrichment on seagrass susceptibility to herbivory was non-linear, with a threshold effect. Low nitrate enrichment chemically and structurally defended seagrass, subsequently reducing herbivory, while continuously increasing nutrient enrichment crossing the threshold enhanced seagrass susceptibility to herbivory. Meanwhile, seagrass leaf total phenol and free fatty acid contents were the two dominant factors determining the herbivory preference of C. rhizophorarum. Overall, since anthropogenic nitrogen enrichment is increasing in intensity and frequency, our findings are significant for conservation and emphasize the importance of coastal eutrophication control.

Bacterial pathogen removal function in seagrass meadows is gaining attention worldwide, with enhancing particle sedimentation as the main potential mechanism. Unfortunately, seagrass meadows are declining to patchiness and fragmentation due to anthropogenic activities and global climate change. However, the effects of seagrass decline on bacterial pathogen removal potential are poorly understood, limiting our ability to understand coastal-living humans and marine organisms that suffered pressure from diseases and other health-related effects in response to seagrass decline. Here we investigated abundance of putative bacterial pathogens (including Vibrio spp., Salmonella spp., Staphylococcus spp., and Enterococcus spp.) in trapped particles under different canopy structures of Enhalus acoroides patches in South China Sea. The abundance of Vibrio spp., Salmonella spp., and Staphylococcus spp. trapped particles, respectively, was observed much greater in seagrass patches with high density and height than other patches, and significantly positive correlations with seagrass density and height were observed. This was mainly ascribed to seagrass patches of high density and height being able to trap more particles. Surprisingly, however, the Enterococcus spp. abundance showed negative correlations with density and area. Enterococcus spp. is generally inhibited in well-oxygenated environments, of which the microenvironment of dissolved oxygen might be mediated by seagrass density and area. Overall, this research suggests that the potential of removal of putative bacterial pathogen was inhibited in fragmented seagrass meadow; therefore, coastal-living humans and marine organisms might suffer from an increasing risk of diseases due to the decline of seagrass meadows.

Dissolved organic carbon (DOC) pool in seawater plays an important role in long-term carbon sequestration in seagrass meadows. Microbial activities (microbial communities and their extracellular enzymes) are the key determining factors of DOC decomposition and sequestration potential, and are affected by nutrient enrichment. However, there is little information on the response of microbial communities and carbon-degrading extracellular enzymes to nutrient loading within seagrass meadows, limiting our understanding of the driving mechanism of DOC decomposition under nutrient enrichment. Here, microbial communities (including bacteria and fungi) and representative extracellular enzyme activity (EEA) in three seagrass meadows with different nutrients levels were investigated across four seasons. Water temperature was the driving factor influencing the seasonal dynamics of EEAs. In addition, the hydrolysis rates of chitinase, β-glucosidase, and α-glucosidase were significantly higher at a high nutrient loading seagrass meadow than at a low nutrient loading meadow. Furthermore, higher relative abundance of bacterial groups, such as Actinobacteria, Bacteroidetes, Cellvibrionale, and Verrucomicrobia were in according with enhanced EEAs, suggesting that these K-strategists were likely involved in enzyme production and the subsequent remineralization of organic matter in seagrass meadows. In contrast with the bacterial community, fungal communities were not sensitive to nutrient concentrations, and there was no strong association between the given fungal groups and EEA. This may be attributed to the low taxonomic resolution of marine planktonic fungi or the minor role of fungi in EEA production. Overall, these results suggested that nutrient loading enhanced EEA levels, modified bacterial rather than fungal communities, and consequently accelerated DOC remineralization, thereby reducing DOC contribution potential of seagrass ecosystems to long term carbon sequestration.

Seagrass ecosystems rank among the most effective blue carbon sinks in climate change mitigation and greenhouse gas removal. Nutrient pollution has emerged as a leading threat to seagrass decline and has diminished the carbon sequestration potential in recent decades. Changes in the nutrient regime can also impact the organic carbon compositions (labile and refractory organic carbon compositions) of seagrass tissues, with important implications for determining the quantity and quality of carbon sequestration. However, there is still little information about the impact of nutrient loading on seagrass plant refractory organic carbon composition (ROC), which hinders our ability to reveal the driving mechanisms of anthropogenic factors that decrease seagrass organic carbon sequestration capability. Here, a multidisciplinary approach was employed to investigate the organic carbon variations of Halophila beccarii at five seagrass meadows with contrasting nutrient loading levels. The results showed that H. beccarii plant nitrogen (N) content ranged from 2.21% to 5.65%, which well reflected the external nutrient loading levels. High nutrient loading elevated labile organic carbon content, like free amino acids and soluble sugars. Nevertheless, ROC content (cellulose-associated organic matter) decreased with increasing nutrient loading, which presented a significant negative linear correlation with plant N content. These results provide evidence that eutrophic conditions enhance H. beccarii plant quality (high N and labile organic carbon) and consequently decrease plant ROC sequestration potential. This suggests that reducing nitrogen input to seagrass meadows would aid in increasing seagrass carbon storage.

Abstract Background Therapeutic tumor vaccine (TTV) that induces tumor-specific immunity has enormous potentials in tumor treatment, but high heterogeneity and poor immunogenicity of tumor seriously impair its clinical efficacy. Herein, a novel NIR responsive tumor vaccine in situ (HA-PDA@IQ/DOX HG) was prepared by integrating hyaluronic acid functionalized polydopamine nanoparticles (HA-PDA NPs) with immune adjuvants (Imiquimod, IQ) and doxorubicin (DOX) into thermal-sensitive hydrogel. Results HA-PDA@IQ NPs with high photothermal conversion efficiency (41.2%) and T 1-relaxation efficiency were using HA as stabilizer by the one-pot oxidative polymerization. Then, HA-PDA@IQ loaded DOX via π-π stacking and mixed with thermal-sensitive hydrogel to form the HA-PDA@IQ/DOX HG. The hydrogel-confined delivery mode endowed HA-PDA@IQ/DOX NPs with multiple photothermal ablation performance once injection upon NIR irradiation due to the prolonged retention in tumor site. More importantly, this mode enabled HA-PDA@IQ/DOX NPs to promote the DC maturation, memory T cells in lymphatic node as well as cytotoxic T lymphocytes in spleen. Conclusion Taken together, the HA-PDA@IQ/DOX HG could be served as a theranostic tumor vaccine for complete photothermal ablation to trigger robust antitumor immune responses.

Phosphorus (P) sorption by red soil is strong due to its acidic pH and high content of metal oxides. Biochar addition may increase the availability of red soil P by altering P sorption characteristics. This study examined the influences of doping ratios of the biochar, phosphate concentration, solution pH, and biochar-derived dissolved black carbon (DBC) on P sorption in red soil. The specific sorption mechanisms were explored using 3D fluorescence spectroscopy, infrared spectroscopy, and zeta potential analysis. The results show that the bioavailable P content in the biochar-amended red soil increased to 1.92 mg kg−1, which is an increase of 255% compared with the original red soil. With the increase in the doping ratio of biochar, the maximum sorption amount of P initially decreased and then increased. Moreover, the pH value and the content of the dissolved organic carbon (DOC) of the red soil were effectively elevated by biochar addition. The increase in the DOC content is likely caused by the DBC released from biochar. As the soil pH value increased, the amount of P sorption was reduced due to electrostatic repulsion. P sorption by the red soil decreased with the increasing DBC concentration. The humic acid-like substances in DBC can compete with phosphate for soil sorption sites, leading to a decrease in P absorption. This study demonstrates that the addition of biochar affects P sorption of the red soil mainly by changing its physicochemical properties or by releasing DBC to occupy the sorption sites.

Abstract Although research on plant rhizosphere is extensive, studies focusing on rhizoplane, rhizosphere, and outer rhizosphere of seagrass remain rare. Here, we present a detailed characterization across root‐associated microbiomes of the seagrass Enhalus acoroides at two locations (Xincun Bay and Li'an Harbor in Hainan, South China) with different sediment properties. The metabolic activity and composition of microbial communities within the rhizoplane (R), rhizosphere (SR), and outer rhizosphere (OR) compartments were compared using the Biolog‐Eco method and high‐throughput sequencing, respectively. These results showed R sediment had the highest metabolic ability in utilizing carbon substrates, followed by SR and OR in both locations, which indicated higher or more diverse carbon resources in sediment in proximity to the roots. With respect to bacterial diversity, our study showed that the OR region supported the highest biodiversity (α indices), followed by SR and R communities, which revealed the strongest selective effect of rhizoplane niche. With respect to community composition, three root‐associated communities at Xincun Bay were characterized by a decreasing trend in relative abundance of Sulfurovum and Sulfurimonas (sulfide oxidizers belonging to Episilonproteobacteria) from R to OR, which revealed their better adaption to lower oxygen concentrations and lower available carbon conditions. Vibrio and Photobacterium assigned to Gammaproteobacteria were highly enriched in rhizoplane compared with SR and OR at Li'an Harbor, which may play an important role in nutrient cycling around the seagrass roots. On the other hand, the gradient of bacterial community structure and metabolic capability created by seagrass roots was more obvious at Li'an Harbor than that at Xincun Bay, which may be related to sediment grain size.

Seagrass meadows provide important habitats and rich organic carbon sources for consumers at different trophic levels but are threatened by accelerating eutrophication in coastal waters. Nevertheless, at present, carbon transfer processes throughout the food web and trophic pathways in eutrophic seagrass meadows are still poorly known. To resolve this issue, carbon sources of different trophic communities in a eutrophic tropical seagrass meadow [Xincun (XC) bay, South China Sea] under eutrophication were examined in summer and winter using dual stable isotopes. The δ13C value of omnivores and carnivores overlapped more with that of herbivores and planktivores/filter feeders, which mainly overlapped with that of epiphytes in summer and macroalgae in winter. Meanwhile, epiphytes and macroalgae exhibited high biomass and corresponding highest contribution to herbivores, omnivores, and carnivores in summer and winter, respectively. These results suggest that the grazing food chain was the main trophic pathway in this eutrophic seagrass meadow, and that the transfer of carbon flow in the grazing food chain was mainly dominated by the proliferating epiphytes or macroalgae carbon. In contrast, the contribution of seagrass to detritivores in both seasons was higher than that of other food sources. Our findings suggest that in eutrophic tropical seagrass meadows, the proliferation of epiphytes or macroalgae induced by high nutrient loading, as well as their seasonal changes, has a greater impact on the transfer of carbon in the grazing food chain than that in the detritus food chain, and the seagrass fueled the food web mainly through the detritus food chain.

Eutrophication, dredging, agricultural and urban runoffs, and epiphyte overgrowth could reduce light availability for seagrass. This may affect “blue carbon” stocks in seagrass beds. However, little research is available on the effect of light intensities on carbon sequestration capacity in seagrass beds, especially small-bodied seagrasses. The dominant seagrass Halophila beccarii, a vulnerable species on the IUCN Red List, was cultured in different light intensities to examine the response of vegetation and sediment carbon in seagrass beds. The results showed that low light significantly reduced leaf length and above-ground biomass, while carbon content in both above-ground and below-ground tissues were not affected. Low light reduced both the above-ground biomass carbon and the total biomass carbon. Interestingly, while under saturating light conditions, the subsurface and surface carbon content was similar, under low light conditions, subsurface sediment carbon was significantly lower than the surface content. The reduction of subsurface sediment carbon might be caused by less release flux of dissolved organic carbon from roots in low light. Taken together, these results indicate that reduced light intensities, to which these meadows are exposed to, will reduce carbon sequestration capacity in seagrass beds. Measures should be taken to eliminate the input of nutrients on seagrass meadows and dredging activities to maintain the “blue carbon” storage service by enhancing light penetration into seagrass.

Abstract Food sources and food web structure in seagrass meadows are important determinants of ecosystem functions and services. However, there is little information on the effect of eutrophication on food source contributions and food web structure in seagrass meadows. Here we used stable isotopes of carbon and nitrogen (δ13C and δ15N) to investigate how do different levels of nutrient enrichment affect the diets of consumers and food web structure within tropical seagrass meadows. We found that the diet contributions of macroalgae (mean 24% ± 12% for fish, 21% ± 5% for invertebrates), particulate organic matter (mean 19% ± 12% for fish, 18% ± 8% for invertebrates), and sediment organic matter (mean 24% ± 13% for fish, 21% ± 8% for invertebrates) to fish and invertebrates were all higher in seagrass meadows with higher nutrient concentrations, while seagrass and epiphytes contributed more to consumers in seagrass meadows with lower nutrient concentrations. Meanwhile, higher nutrient concentrations decreased the trophic position (mean 2.6 ± 0.5 in high‐nutrient level, 3.4 ± 0.6 in low‐nutrients level) of consumers and food chain length (2.5 in high‐nutrient level, 2.9 in low‐nutrients level). Higher nutrient concentrations reduced the contribution of seagrass carbon to consumers through the grazing food chain, but enhanced the flow of macroalgal carbon to consumers through the grazing food chain. Overall, eutrophication modified the food web structure of seagrass meadows. We recommend that measures be taken to decrease nutrient input into seagrass ecosystems to maintain its important functions and services.

Seagrasses inhabiting the intertidal zone experience periodically repeated cycles of air exposure and rehydration. However, little is known about the photoprotective mechanisms in photosystem (PS)II and PSI, as well as changes in carbon utilization upon air exposure. The photoprotective processes upon air exposure in Halophila beccarii Asch., an endangered seagrass species, were examined using the Dual-PAM-100 and non-invasive micro-test technology. The results showed that air exposure enhanced non-photochemical quenching (NPQ) in both PSII and PSI, with a maximum increase in NPQ and Y(ND) (which represents the fraction of overall P700 that is oxidized in a given state) of 23 and 57%, respectively, resulting in intensive thermal energy dissipation of excess optical energy. Moreover, cyclic electron transport driven by PSI (CEF) was upregulated, reflected by a 50 and 22% increase in CEF and maximum electron transport rate in PSI to compensate for the abolished linear electron transport with significant decreases in pmfLEF (the proton motive force [pmf]) attributable solely to proton translocation by linear electron flow [LEF]). Additionally, H+ fluxes in mesophyll cells decreased steadily with increased air exposure time, exhibiting a maximum decrease of six-fold, indicating air exposure modified carbon utilization by decreasing the proton pump influxes. These findings indicate that efficient heat dissipation and CEF confer daily air exposure tolerance to the intertidal seagrass H. beccarii and provide new insights into the photoprotective mechanisms of intertidal seagrasses. This study also helps explain the extensive distribution of H. beccarii in intertidal zones.

Rapid urbanization leads to an accelerating decline of seagrass beds. The status of seagrass beds along the entire coastline of a rapidly urbanizing area, Guangdong Province, was examined to document the change in seagrass beds and to explore the determinants of seagrasses characteristics and their plasticity. Thirteen seagrass beds were newly discovered with a total area as 679.04 ha, whereas eleven known seagrass beds have decreased from 972.55 ha to 858.67 ha with seven of them having disappeared in recent decade primarily due to exacerbated construction of artificial shorelines and beach dams, increased nutrient inputs from fish caging and shrimp pond culture, oyster culture, mangrove planting and shellfish collection. The leaf nitrogen content of Halophila ovalis, which dominated the largest beds, increased from (2.09 ± 0.24)% in 2011 to (3.39 ± 0.18)% in 2017, indicating enhanced eutrophication. The optimum seawater dissolved inorganic nitrogen and dissolved inorganic phosphorus levels for Halophila beccarii were 40 μmol/L and 2.5 μmol/L, respectively. The standing stock and plant dimensions of H. beccarii were positively correlated with sediment mud content. Longer, wider leaves, and greater aboveground and belowground biomass were observed at lower salinities, indicating that H. beccarii prefers hyposaline habitats. High shoot density could induce intraspecific competition followed by self-thinning in H. beccarii, leading to reduced leaf area, aboveground and belowground biomass, and root length. Thus, long-term monitoring of seagrass beds along the rapidly urbanizing coastline of Guangdong Province is needed to unravel the mechanisms of decline and to develop effective management strategies.

Seagrass beds provide nursery habitats for marine species. Seagrass leaves, in particular, are used as spawning grounds and as a food source for fish and invertebrates, but direct evidence of spawning in seagrass leaves is rare. It is also very challenging to identify eggs through morphological analysis, since the eggs of many marine species appear similar. To accurately identify the eggs on the leaves of the dominant seagrass species in the South China Sea, and evaluate seasonal contribution of seagrass leaves as a food source, DNA barcoding and stable isotope technique were conducted. Interestingly, Monetaria annulus was found to spawn on the leaf sheath of Thalassia hemprichii in Li’an gang, Hainan Island. This choice of oviposition site might increase embryo survival compared to the other parts of the seagrass leaves. Meanwhile, the eggs of Stethojulis trilineata were deposited on the entire leaf of Halophila ovalis in Liusha Bay, Guangdong Province. The small fingernail-shaped leaves of H. ovalis might be beneficial for S. trilineata to lay eggs as they are closer to the sediment surface than other seagrass leaves. Based on the stable carbon and nitrogen isotope analyses, the primary food source of M. annulus in summer and in winter were particulate organic matter and seagrass, respectively. The results suggest that seagrass leaves are not only important for fish and invertebrates as a spawning site, but also as a food source. The findings of the present study may support the urgent requirement of the conservation of seagrass beds for sustaining the productivity of marine fisheries.

Rhizosphere bacterial community structures and their determining drivers have been studied in a variety of marine and freshwater ecosystems for a range of plant species. However, there is still limited information about the influence of habitat on microbial communities in seagrass beds. This study aimed to determine which factors (habitat and plant species) have crucial roles on the rhizospheric bacteria associated with two tropical seagrass species (Thalassia hemprichii and Enhalus acoroides) that are dominant at Xincun Bay and Tanmen Harbor in Hainan Island, South China. Using Illumina HiSeq sequencing, we observed substantial differences in the bacterial richness, diversity, and relative abundances of taxa between the two habitats, which were characterized differently in sediment type and nutrient status. Rhizospheric bacteria from sandy sediment at the eutrophic Xincun Bay were dominated by Desulfobacteraceae and Helicobacteraceae, which are primarily involved in sulfate cycling, whereas rhizosphere microbes from the reef flat at oligotrophic Tanmen Harbor were dominated by Vibrionaceae and Woeseiaceae, which may play important roles in nitrogen and carbon fixing. Additionally, we speculated that host-specific effects of these two seagrass species may be covered under nutrient-rich conditions and in mixed community patches, emphasizing the importance of the nutrient status of the sediment and vegetation composition of the patches. In addition, our study confirmed that Proteobacteria was more adapted to the rhizosphere environment than to low-carbon conditions that occurred in bulk sediment, which was primarily dominated by well-known fermentative bacteria in the phylum Firmicutes.

In automated manufacturing systems, resource failures are often inevitable. They reduce the number of available resources and may cause some processing routes of parts to halt and sometimes the whole system to shutdown. This article focuses on the robust deadlock control problem in automated manufacturing systems with multiple resource failures. To obtain such a robust controller, we first put forward a new concept of blocked states of automated manufacturing systems. From such a state, the production of some part types through one of their routes is blocked as caused by resource failures, and only after some failed resources are repaired, these parts can resume their normal processing. Then, these blocked states are characterized in terms of emptied siphons caused by resource failures. In order to prevent the system from deadlocks and blocked states, a robust controller is proposed by the following two steps. First, for siphons without unreliable resources, optimal deadlock control places are added. Then for siphons which contain unreliable resources, new control places are devised to ensure that they could be marked even when resource failures happen. It is proved that the proposed controller can guarantee that all types of parts can be processed repeatedly as long as one unit of unreliable resources can still work. This means that the proposed controller is of greatest robustness, that is, it can tolerate a maximum number of resource failures. Some examples are provided to illustrate the proposed method and show the advantage over the previous ones.

This paper presents a novel approach for semantic segmentation of building roofs in dense urban environments with a Deep Convolution Neural Network (DCNN) using Chinese Very High Resolution (VHR) satellite (i.e., GF2) imagery. To provide an operational end-to-end approach for accurately mapping build roofs with feature extraction and image segmentation, a fully convolutional DCNN with both convolutional and deconvolutional layers is designed to perform building roof segmentation. We selected typical cities with dense and diverse urban environments in different metropolitan regions of China as study areas, and sample images were collected over cities. High performance GPU-mounted workstations are employed to perform the model training and optimization. With the building roof samples collected over different cities, the predictive model with convolution layers is developed for building roof segmentation. The validation shows that the overall accuracy (OA) and the mean Intersection Over Union (mIOU) of DCNN-based semantic segmentation results are 94.67% and 0.85, respectively, and the CRF-refined segmentation results achieved OA of 94.69% and mIOU of 0.83. The results suggest that the proposed approach is a promising solution for building roof mapping with VHR images over large areas in dense urban environments with different building patterns. With the operational acquisition of GF2 VHR imagery, it is expected to develop an automated pipeline of operational built-up area monitoring, and the timely update of building roof map could be applied in urban management and assessment of human settlement-related sustainable development goals over large areas.