Nutrient loading accelerates breakdown of refractory dissolved organic carbon in seagrass ecosystem waters.

Nutrient loading is a major driver of seagrass ecosystem decline and also threatens the capacity for seagrass ecosystems to act as 'blue carbon' sinks. Dissolved organic carbon (DOC) represents a crucial component of carbon storage in seagrass ecosystems, with refractory DOC (RDOC) playing a key role in long-term (millennial time scale) carbon stocks. The processes governing RDOC are heavily influenced by microbial activity.

Seasonal and spatial variability of dissolved organic nitrogen concentration and composition in Daya Bay, China.

Dissolved organic nitrogen (DON) has recently been recognized as an important nitrogen source for marine phytoplankton. However, the composition, sources, and biogeochemical cycling of DON in coastal ecosystems remain poorly understood. This study investigates the spatial distribution and seasonal variability of DON in Daya Bay, a subtropical semi-enclosed bay in the northern South China Sea.

Nutrient-loaded seagrass litter experiences accelerated recalcitrant organic matter decay.

High coastal nutrient loading can cause changes in seagrass chemistry traits that may lead to variability in seagrass litter decomposition processes. Such changes in decomposition have the potential to alter the carbon (C) sequestration capacity within seagrass meadows ('blue carbon'). However, the external and internal factors that drive the variability in decomposition rates of the different organic matter (OM) types of seagrass are poorly understood, especially recalcitrant OM (i.

The metabolic network response and tolerance mechanism of Thalassia hemprichii under high sulfide based on widely targeted metabolome and transcriptome.

Costal eutrophication leads to increased sulfide levels in sediments, which has been identified as a major cause of the global decline in seagrass beds. The seagrass Thalassia hemprichii, a dominant tropical species in the Indo-Pacific, is facing a potential threat from sulfide, which can be easily reduced from sulfate in porewater under the influence of global climate change and eutrophication. However, its metabolic response and tolerance mechanisms to high sulfide remain unclear.

Regime shift in a coastal pelagic ecosystem with increasing human-induced nutrient inputs over decades.

Human-induced nutrient inputs to global coastal waters are leading to increasing nutrients and escalating eutrophication. However, how aquatic ecosystem functioning responds to these changes remains insufficiently studied. Here we report the long-term changes in the nutrient regime and planktonic ecosystem functioning in the Daya Bay, a typical subtropical semi-enclosed bay experiencing rapid economic and social development for several decades.

Seagrass decline weakens sediment organic carbon stability.

Seagrass meadows are globally recognized as critical natural carbon sinks, commonly known as 'blue carbon'. However, seagrass decline attributed to escalating human activities and climate change, significantly influences their carbon sequestration capacity. A key aspect in comprehending the impact of seagrass decline on carbon sequestration is understanding how degradation affects the stored blue carbon, primarily consisting of sediment organic carbon (SOC).

Hydrodynamics and dissolved organic matter components shaped the fate of dissolved heavy metals in an intensely anthropogenically disturbed estuary.

Anthropogenic activities and natural erosion caused abundant influx of heavy metals (HMs) and organic matter (OM) into estuaries characterized by the dynamic environments governed by tidal action and river flow. Similarities and differences in the fate of HM and OM as well as the influences of OM on HMs remain incomplete in estuaries with seasonal human activity and hydrodynamic force. To address this gap, dissolved HMs (dHMs) and fluorescence dissolved OM (FDOM) were investigated in the Pearl River Estuary, a highly seasonally anthropogenic and dynamic estuary.

In-situ construction of InO/InS-CdInS Z-scheme heterojunction nanotubes for enhanced photocatalytic hydrogen production.

Semiconductor photocatalysis was considered as an ideal solution to energy shortages. Herein, a novel ternary InO/InS-CdInS (IOSC) nanotube (NTs) photocatalyst was successfully constructed via in situ growth of InS and CdInS nanosheets onto InO skeleton. It was used for the efficient and stable photo-production of hydrogen from water splitting.

Estuarine hydrodynamic processes driving the molecular changes of terrestrial dissolved organic nitrogen: From mixing to biological modification.

Estuaries receive substantial amounts of terrestrial dissolved organic nitrogen (tDON), which will be transported from the freshwater to the oceanic terminus through vigorous exchange processes. However, the intricate migration and transformation dynamics of tDON during this transportation, particularly at a molecular level, remain constrained. To address this knowledge gap, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) was used for the analysis of DON molecular composition in the Pearl River Estuary (PRE), a river-dominated estuarine system influenced by intensified anthropogenic activities in southern China.

Identification of anthropogenic source of Pb and Cd within two tropical seagrass species in South China: Insight from Pb and Cd isotopes.

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.

Plant growth and development of tropical seagrass determined rhizodeposition and its related microbial community.

In the recent study, we investigated the seasonal variations in root exudation and microbial community structure in the rhizosphere of seagrass Enhalus acoroides in the South China Sea. We found that the quantity and quality of root exudates varied seasonally, with higher exudation rates and more bioavailable dissolved organic matter (DOM) during the seedling and vegetative stages in spring and summer. Using Illumina NovaSeq sequencing, we analyzed bacterial and fungal communities and discovered that microbial diversity and composition were influenced by root exudate characteristics s and seagrass biomass, which were strongly dependent on seagrass growth stages.

Temporal and spatial variations of air-sea CO fluxes and their key influence factors in seagrass meadows of Hainan Island, South China Sea.

Seagrass ecosystems have received a great deal of attention for contributing to uptake of atmospheric CO, and thereby helping to mitigate global climate change ('blue carbon'). Carbon budgets for seagrass ecosystems are developed by estimating air-sea CO fluxes. Data for air-sea CO flux for tropical seagrass ecosystems are lacking, which is problematic for constraining global seagrass carbon budgets.

The distinct phases of fresh-seawater mixing intricately regulate the nitrogen transformation processes in a high run-off estuary: Insight from multi-isotopes and microbial function analysis.

Excessive anthropogenic nitrogen inputs lead to the accumulation of nitrogen, and significantly impact the nitrogen transformation processes in estuaries. However, the governing of nitrogen during its transport from terrestrial to estuary under the influence of diverse human activities and hydrodynamic environments, particularly in the fresh-seawater mixing zone, remains insufficient researched and lack of basis. To address this gap, we employed multi-isotopes, including δN-NO, δO-NO, δN-NH, and δN-PN, as well as microbial function analysis, to investigate the nitrogen transformation processes in the Pearl River Estuary (PRE), a highly anthropogenic and terrestrial estuary.

Seasonal dynamics of bacterial community and co-occurrence with eukaryotic phytoplankton in the Pearl River Estuary.

In this study, we investigated the taxonomic composition of the bacteria and phytoplankton communities in the Pearl River Estuary (PRE) through Illumina sequencing of the V3-V4 region of the 16 S rRNA gene. Furthermore, their relationships as well as recorded environmental variables were explored by co-occurrence networks. Bacterial community composition was different in two size fractions, as well as along the salinity gradient across two seasons.

Effects of herbivore on seagrass, epiphyte and sediment carbon sequestration in tropical seagrass bed.

Herbivores strongly affect the ecological structure and functioning in seagrass bed ecosystems, but may exhibit density-dependent effects on primary producers and carbon sequestration. This study examined the effects of herbivorous snail (Cerithidea rhizophorarum) density on snail intraspecific competition and diet, dominant seagrass (Thalassia hemprichii) and epiphyte growth metrics, and sediment organic carbon (SOC). The growth rates of the herbivorous snail under low density (421 ind m) and mid density (842 ind m) were almost two times of those at extremely high density (1684 ind m), indicating strong intraspecific competition at high density.

Saltwater intrusion regulates the distribution and partitioning of heavy metals in water in a dynamic estuary, South China.

The mixing processes of fresh-salt water in estuarine and coastal regions have a substantial impact on the characteristics of heavy metals. A study was conducted in the Pearl River Estuary (PRE), located in South China, to examine the distribution and partitioning of heavy metals and the factors that influence their presence. Results showed that the hydrodynamic force, caused by the landward intrusion of the salt wedge, was the major contributor to the aggregation of heavy metals in the northern and western PRE.

Response of tropical seagrass palatability based on nutritional quality, chemical deterrents and physical defence to ammonium stress and its subsequent effect on herbivory.

Seagrass-herbivore interactions play a principal role in regulating the structure and function of coastal food webs, which were affected by nutrient enrichment. Seawater nutrient enrichment might change seagrass palatability by altering seagrass physical and chemical traits, consequently modulating herbivory patterns, but this remains elusive. In this study, the dominant tropical seagrass Thalassia hemprichii was cultured in different ammonium concentrations to examine the response of seagrass nutritional quality, deterrent secondary metabolites, and leaf toughness, as well as the subsequent effect of the changed physical (e.

Eutrophication reduced the release of dissolved organic carbon from tropical seagrass roots through exudation and decomposition.

Seagrass bed ecosystem is one of the most effective carbon capture and storage systems on earth. Seagrass roots are the key link of carbon flow between leaf-root-sediment, and the release of dissolved organic carbon (DOC) from seagrass roots through exudation and decomposition are vital sources to the sediment organic carbon (SOC) in the seagrass beds. Unfortunately, human-induced eutrophication may change the release process of DOC from seagrass roots, thereby affecting the sediment carbon storage capacity.

Calcium and phosphorus co-doped carbon dots enhance osteogenic differentiation for calvarial defect repair.

Calvarial bone defect remains a clinical challenge due to the lack of efficient osteo-inductive agent. Herein, a novel calcium and phosphorus codoped carbon dot (Ca/P-CD) for bone regeneration was synthesized using phosphoethanolamine and calcium gluconate as precursors. The resultant Ca/P-CDs exhibited ultra-small size, stable excitation dependent emission spectra and favorable dispersibility in water.

Fabrication of methylene blue-loaded ovalbumin/polypyrrole nanoparticles for enhanced phototherapy-triggered antitumour immune activation.

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.

Sand supplementation favors tropical seagrass Thalassia hemprichii in eutrophic bay: implications for seagrass restoration and management.

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.

Characteristics of nutrients and heavy metals and potential influence of their benthic fluxes in the Pearl River Estuary, South China.

Nutrient and heavy metal concentrations in porewater/overlying water and their benthic fluxes were investigated to study their accumulation and transport at the sediment-water interface and the influences of sediment in the Pearl River Estuary, China. Results revealed that distribution of nutrients and metals reflected the effects of terrestrial inputs and some physicochemical processes. Benthic fluxes also suggested that nutrients and heavy metals Pb, Zn and Cd diffused from sediment to overlying water, but not for As, Co, Cr, Fe, Mn and Ni.