Inorganic Nitrogen Concentrations Research Articles

Simultaneous methane mitigation and nitrogen removal by denitrifying anaerobic methane oxidation in lake sediments

Methane (CH4) is a potent greenhouse gas, with lake ecosystems significantly contributing to its global emissions. Denitrifying anaerobic methane oxidation (DAMO) process, mediated by NC10 bacteria and ANME-2d archaea, links global carbon and nitrogen cycles. However, their potential roles in mitigating methane emissions and removing nitrogen from lake ecosystems remain unclear. This study explored the spatial variations in activities of nitrite- and nitrate-DAMO and their functional microbes in Changdanghu Lake sediments (Jiangsu Province, China). The results showed that although the average abundance of ANME-2d archaea (5.0 × 106 copies g−1) was significantly higher than that of NC10 bacteria (2.1 × 106 copies g−1), the average potential rates of nitrite-DAMO (4.59 nmol 13CO2 g−1 d−1) and nitrate-DAMO (5.01 nmol 13CO2 g−1 d−1) showed no significant difference across all sampling sites. It is estimated that nitrite- and nitrate-DAMO consumed approximately 6.46 and 7.05 mg CH4 m−2 d−1, respectively, which accordingly achieved 15.07–24.95 mg m−2 d−1 nitrogen removal from the studied lake sediments. Statistical analyses found that nitrite- and nitrate-DAMO activities were both significantly related to sediment nitrate contents and ANME-2d archaeal abundance. In addition, NC10 bacterial and ANME-2d archaeal community compositions showed significant correlations with sediment organic carbon content and water depth. Overall, this study underscores the dual roles of nitrite- and nitrate-DAMO processes in CH4 mitigation and nitrogen elimination and their key environmental impact factors (sediment organic carbon and inorganic nitrogen contents, and water depth) in shallow lake, enhancing the understanding of carbon and nitrogen cycles in freshwater aquatic ecosystems.

Snow depth has greater influence on moss biocrusts' soil multifunctionality than the number of freeze-thaw cycles

Continued global warming and changes in precipitation patterns, especially regarding snow depth and freeze-thaw cycles (FTCs), have significantly affected the hydrothermal environment in winter at mid- and high-latitudes. In this study, we assessed the effects of changes in snow depth and FTCs, on the biogeochemical cycling of biological soil crusts. We collected moss crust soil samples from a temperate desert in northwest China, and measured the changes in the amount of snow (65 % snow removal, ambient snow, and 65 % snow increase) and FTCs (FT0, FT5, and FT15) under an artificial environment simulation, to determine the nutrient content and enzyme activities related to soil carbon, nitrogen, and phosphorus cycles. In terms of how snowfall and FTCs affect soil multifunctionality (SMF) of desert moss crusts, the research findings demonstrated that snow depth, FTCs, and their interplay have a significant influence on the carbon, nitrogen, phosphorus contents, enzyme activities, and SMF of moss crusts. Compared to snow removal, an increase in snow depth corresponded to a significant increase in the soil water content, and an improvement in soil carbon and nitrogen cycling and SMF. The number of FTCs increased, which led to enhancements in soil phosphorus cycling, soil total phosphorus, and available phosphorus content, together with a reduction in inorganic nitrogen content and the activities of certain enzymes involved in carbon and nitrogen cycling. The structural equation model indicated that snow depth had the greatest effect (total effect of 0.165) on SMF in moss crusts compared to FTCs (total effect of 0.048). Therefore, it is necessary to consider snow depth when examining the effects of climate change on nutrient cycling in the biological soil crusts of temperate deserts.

Dune soil nitrogen leaching for Chinese-yam cultivation: Impact of microbe-decomposable slow-release fertilizer

Chinese yam production is thriving in Aomori Prefecture, a cold and snowy region in Japan. Recently, there has been an increasing risk of nitrogen leaching in Chinese-yam fields, which consist of sandy soil, due to localized torrential rain. The relationships between the type of fertilizer used for Chinese-yam cultivation, the amount of nitrogen (N) leaching, and the timing of leaching remain unknown. Therefore, this study aimed to fill this knowledge gap by investigating the effects of different fertilizers (fast-acting and/or slow-release fertilizer) and irrigation practices (conventional and/or excessive irrigation) in order to mitigate the detrimental impact of nitrogen leaching on groundwater quality. An enhanced mathematical model and the spatiotemporal dynamics of inorganic nitrogen concentration in soil pore water were evaluated the negative impact of nitrogen leaching on the groundwater environment was evaluated. The results showed that the combined use of slow-release fertilizers could significantly reduce nitrate-nitrogen concentration in soil-water, especially during the harvest season. This study demonstrated that cultivating Chinese yam with a fertilizer application system that includes the use of slow-release fertilizer can diminish the negative impact of nitrogen leaching on the groundwater environment, contributing to our understanding of sustainable agricultural practices in regions facing similar environmental challenges. Therefore, our findings represent an important advancement providing new approaches to maintaining productivity while mitigating the adverse impacts on groundwater environments, as well as offering guidelines for agricultural practices in regions facing similar environmental challenges.

Nutrient concentration, loads and retention in a semiarid micro-estuary: The relative contribution of baseflow and flood events

Estuaries are a significant source of nutrients to the marine environment. The magnitude of this source is a function of nutrients load reaching the estuary and removal (attenuation) within estuaries. Most estuarine research is conducted in large estuaries, which do not reflect the processes in small estuaries in urban and semi-arid regions where flood water is a substantial portion of the annual discharge and the estuarine baseflow is often low and dominated by wastewater. To improve the understanding of nutrient attenuation and load into the Mediterranean, we conducted high-resolution nutrient sampling in the eutrophic Alexander micro-estuary as a test case. We sampled once per month during baseflows (years 2014–2019) and hourly during floods (years 2016–2018). The concentrations of inorganic nutrients (phosphorous (P) and nitrogen (N)) were extremely high during baseflows. Dissolved ammonium and particulate P were the only nutrients that were in the estuary (by 55 % and 30 %, respectively). Floods were rare, occurring ~4 % of the time, but contributed 62 % of the annual water discharge of the Alexander micro-estuary (14.7 ± 3.8 106 m3 y−1). The concentration of all dissolved nutrients decreased during floods but was higher than expected (DIN 584 ± 50 μmol L−1, phosphate 21 ± 2 μmol L−1), accounting for 42 % and 55 % of the overall annual DIN (123.5 ± 44.9-ton yr−1) and P (6.7 ± 1.9 ton yr−1) loads to sea, respectively. The N:P ratios were 16 and 34 during baseflow and flood events, respectively. Previously, nutrient loads were calculated by multiplying baseflow-measured concentrations by the total water volume of baseflow and floods. Our calculations, based on high-resolution sampling, revealed lower annual loads of P and N to the sea that were 56 % and 89 % of previous estimates, which is a considerable difference in an oligotrophic system such as the eastern Mediterranean.

Effect of electrode in UASB-MFC reactor for nitrogen removal under anammox condition and its microbial community profile

Nitrogen removal through anammox is well-known for its low cost and less CO2 emissions, in this process ammonium converted into nitrogen gas with the help of anammox. It is hypothesized that the presence of electrodes in upflow anaerobic sludge blanket-microbial fuel cell (UASB-MFC) might increase nitrogen removal. In order to check this, two experimental setup were used to remove ammonium with electrode (UASB-MFC) and without electrode (UASB), under anammox condition. Different parameters were analyzed including nitrate, nitrite, total nitrogen and voltage. After 164 days, the NH4+ concentration in effluent was 3.20 mg/L and 4.23 mg/L, total inorganic nitrogen was 11.9 mg/L and 8.45 mg/L in UASB and UASB-MFC effluent respectively. Bacterial growth rate was calculated through biokinetic modelling, indicating anammox growth rate 0.00294 g VSS/m3.d in UASB-MFC with maximum voltage production of 774 mV. Metagenomic study was performed through 16 S rRNA genome sequencing showed, Firmicutes phylum was high in both reactors, while Planctomycetes, abundance 2.8% showing anammox growth achievement only in UASB-MFC. Lower concentration of nitrate, nitrite and total inorganic nitrogen were found in the UASB-MFC effluent which suggested the higher conversion of ammonium into nitrogen gas. It is concluded that the presence of an electrode oxidizes more nitrogen; hence total nitrogen was removed much more than in the absence of an electrode.

Inhibitory effects of Pseudomonas sp. W112 on cadmium accumulation in wheat grains: Reduced the bioavailability in soil and enhanced the interception by plant organs

Microorganisms play an important role in heavy metal bioremediation and soil fertility. The effects of soil inoculation with Pseudomonas sp. W112 on Cd accumulation in wheat were investigated by analyzing the transport, subcellular distribution and speciation of Cd in the soil and plants. Pseudomonas sp. W112 application significantly decreased Cd content in the roots, internode and grains by 10.2%, 29.5% and 33.0%, respectively, and decreased Cd transfer from the basal nodes to internodes by 63.5%. Treatment with strain W112 decreased the inorganic and water-soluble Cd content in the roots and increased the proportion of residual Cd in both the roots and basal nodes. At the subcellular level, the Cd content in the root cell wall and basal node cytosol increased by 19.6% and 61.8%, respectively, indicating that strain W112 improved the ability of the root cell wall and basal node cytosol to fix Cd. In the rhizosphere soil, strain W112 effectively colonized and significantly decreased the exchangeable Cd, carbonate-bound Cd and iron-manganese oxide-bound Cd content by 43.5%, 27.3% and 17.6%, respectively, while it increased the proportion of residual Cd by up to 65.2%. Moreover, a 3.1% and 23.5% increase in the pH and inorganic nitrogen content in the rhizosphere soil, respectively, was recorded. Similarly, soil bacterial community sequencing revealed that inoculating with strain W112 increased the abundance of Pseudomonas, Thauera and Azoarcus, which are associated with inorganic nitrogen metabolism, and decreased that of Acidobacteria, which is indicative of soil alkalinization. Hence, root application of Pseudomonas sp. W112 improved soil nitrogen availability and inhibited Cd accumulation in the wheat grains in a two-stage process: by reducing the Cd availability in the rhizosphere soil and by improving Cd interception and fixation in the wheat roots and basal nodes. Pseudomonas sp. W112 may be a suitable bioremediation agent for restoring Cd-contaminated wheat fields.

Uncovering the role of oxygen on organic carbon cycling: insights from a continuous culture study with a facultative anaerobic bacterioplankton species (Shewanella baltica)

Deoxygenation is tied to organic carbon (Corg) supply and utilization in marine systems. Under oxygen-depletion, bacteria maintain Corg respiration using alternative electron acceptors such as nitrate. Since anaerobic respiration’s energy yield is lower, Corg remineralization may be reduced and its residence time increased. We investigated the influence of oxygen and alternative electron acceptors’ availability on Corg cycling by heterotrophic bacteria during a continuous culture experiment with Shewanella baltica, a facultative anaerobic γ-Proteobacteria in the Baltic Sea. We tested six different oxygen levels, from suboxic (<5 µmol L-1) to fully oxic conditions, using a brackish (salinity=14 g L-1) media supplied with high (HighN) or low (LowN) inorganic nitrogen concentrations relative to glucose as labile Corg source. Our results show that suboxia limited DOC (glucose) uptake and cell growth only under LowN, while higher availability of alternative electron acceptors seemingly compensated oxygen limitation under HighN. N-loss was observed under suboxia in both nitrogen treatments. Under HighN, N-loss was highest and a C:N loss ratio of ~2.0 indicated that Corg was remineralized via denitrification. Under LowN, the C:N loss ratio under suboxia was higher (~5.5), suggesting the dominance of other anaerobic respiration pathways, such as dissimilatory nitrate reduction to ammonium (DNRA). Bacterial growth efficiency was independent of oxygen concentration but higher under LowN (34 ± 3.0%) than HighN (26 ± 1.6%). Oxygen concentration also affected dissolved organic matter (DOM) cycling. Under oxic conditions, the release of dissolved combined carbohydrates was enhanced, and the amino acid-based degradation index (DI) pointed to more diagenetically altered DOM. Our results suggest bacterial Corg uptake in low-oxygen systems dominated by S. baltica can be limited by oxygen but compensated by high nitrate availability. Hence, suboxia diminishes Corg remineralisation only when alternative electron acceptors are lacking. Under high nitrate:Corg supply, denitrification leads to a higher N:C loss ratio, potentially counteracting eutrophication in the long run. Low nitrate:Corg supply may favour other anaerobic respiration pathways like DNRA, which sustains labile nitrogen in the system, potentially intensifying the cycle of eutrophication. Going forward, it will be crucial to establish the validity of our findings for S. baltica in natural systems with diverse organic substrates and microbial consortia.

Characterization and function of particulate organic matter: Evidence from lakes undergoing ecological restoration

Particulate organic matter (POM) plays a crucial role in the organic composition of lakes; however, its characteristics remain poorly understood. This study aimed to characterize the structure and composition of POM in Lake Baiyangdian using many kinds of techniques and investigate the effects of different extracted forms of POM on water quality. The suspended particulate matter in the lake had complex compositions, with its components primarily derived from aquatic plants and their detritus. The organic matter content of the suspended particulate matter was relatively high (organic carbon content 27.29–145.94 g/kg) for the sum of three extractable states (water-extracted organic matter [WEOM], humic acid, and fulvic acid) and one stable bound state (humin). Spatial distribution analysis revealed that the POM content in the water increased from west to east, which was consistent with the water flow pattern influenced by the Baiyangdian water diversion project. Fluorescence spectroscopy analysis of the WEOM showed three prominent peaks with excitation/emission wavelengths similar to those of dissolved organic matter peaks. These peaks were potentially initial products of POM conversion into dissolved organic matter. Furthermore, the intensity of the WEOM fluorescence peak (total fluorescence peak intensity) was negatively correlated with the inorganic nitrogen concentration in water (p < 0.01), while the intensity of the HA fluorescence peak showed a positive correlation with the inorganic nitrogen concentration (p < 0.01). This suggested that exogenous organic matter inputs led to the diffusion of alkaline dissolved nitrogen from sediment into water, while degradation processes of aquatic plant debris contributed to the decrease in inorganic nitrogen concentrations in the water column. These findings enhance our understanding of POM characteristics in shallow lakes and the role of POM in shallow lake ecosystems.

Characteristics of soil nitrogen and phosphorus fractions and microbial traits with increasing stand age in two-layered Cunninghumia lanceolata + Phoebe bournei plantations.

Soil nitrogen and phosphorus are two key elements limiting tree growth in subtropical areas. Understanding the regulation of soil microorganisms on nitrogen and phosphorus nutrition is beneficial to reveal maintenance mechanism of soil fertility in plantations. We analyzed the characteristics of soil nitrogen and phosphorus fractions, soil microbial community composition and function, and their relationship across three stands of two-layered Cunninghumia lanceolata + Phoebe bournei with different ages (4, 7 and 11 a) and the pure C. lanceolata plantation. The results showed that the contents of most soil phosphorus fractions increased with increasing two-layered stand age. The increase in active phosphorus fractions with increasing stand age was dominated by the inorganic phosphorus (9.9%-159.0%), while the stable phosphorus was dominated by the organic phosphorus (7.1%-328.4%). The content of soil inorganic and organic nitrogen also increased with increasing two-layered stand age, with NH4+-N and acid hydrolyzed ammonium N contents showing the strongest enhancement, by 152.9% and 80.2%, respectively. With the increase of stand age, the composition and functional groups of bacterial and fungal communities were significantly different, and the relative abundance of some dominant microbial genera (such as Acidothermus, Saitozyma and Mortierella) increased. The relative abundance of phosphorus solubilization and mineralization function genes, nitrogen nitrification function and aerobic ammonia oxidation function genes tended to increase. The functional taxa of fungi explained 48.9% variation of different phosphorus fractions. The conversion of pure plantations to two-layered mixed plantation affected soil phosphorus fractions transformation via changing the functional groups of saprophytes (litter saprophytes and soil saprophytes). Changes in fungal community composition explained 45.0% variation of different nitrogen fractions. Some key genera (e.g., Saitozyma and Mortierella) play a key role in promoting soil nitrogen transformation and accumulation. Therefore, the conversion of pure C. lanceolata plantation to two-layered C. lanceolata + P. bournei plantation was conducive to improving soil nitrogen and phosphorus availability. Bacteria and fungi played important roles in the transformation process of soil nitrogen and phosphorus forms, with greater contribution of soil fungi.

Optimizing irrigation and nitrogen management improves soil soluble nitrogen pools and reduces nitrate residues in a drip-fertigated apple orchard on the Loess Plateau

Appropriate water and nitrogen fertilizer management is crucial for achieving sustainable development in the apple industry. However, the soil nitrogen supply capacity and residual nitrate characteristics under drip fertigation remain poorly understood. Therefore, this study aims to (1) investigate the coupling effects of irrigation and nitrogen levels on the concentrations and distribution characteristics of soil soluble nitrogen fractions and residual soil nitrate; (2) explore the relationships between Christiansen uniformity coefficient (CU) of soil nitrate and apple yield, water productivity (WPc) and nitrogen use efficiency (nitrogen agronomic efficiency, AEn). The field experiment was conducted in a drip-fertigated apple orchard starting in 2017, which included two irrigation levels, 85% (W1) and 100% (W2) of field capacity (FC), and four nitrogen rates, 0 (N1), 120 (N2), 240 (N3) and 360 (N4) kg ha–1. The results showed that nitrogen inputs significantly increased soil soluble inorganic nitrogen and soluble organic nitrogen (SON) contents. However, the SON content significantly decreased when 360 kg N ha–1 was applied, particularly at W1. The maximum nitrate accumulation in the 0–3 m soil layer at N4 reached 2540.97 kg ha–1 in 2021, but the maximum value decreased to 1251.62 kg ha–1 in 2022 due to extreme rainfall. The average CU of residual nitrate across irrigation levels in the 0–3 m soil layer was highest at N3, with values of 0.68 and 0.57 in 2021 and 2022, respectively. High irrigation level increased the diffusion distances of nitrate both vertically and horizontally, resulting in a significant effect on CU. Apple yield and WPc first increased and then decreased with increasing nitrogen rates, while AEn consistently decreased, but they were all greater with a higher CU. The recommended combination of irrigation and nitrogen application was 85% FC and 240 kg N ha–1, which can achieve the dual goals of enhancing soil nitrogen supply capacity and minimizing environmental risks while improving orchard productivity.

Synergistic regulation of hydrogen sulfide and nitric oxide on biochemical components, exopolysaccharides, and nitrogen metabolism in nickel stressed rice field cyanobacteria.

The present study examined the regulatory mechanism of hydrogen sulfide (H2S) and nitric oxide (NO) in nickel (Ni) stressed cyanobacteria viz., Nostoc muscorum and Anabaena sp. by analyzing growth, photosynthetic pigments, biochemical components (protein and carbohydrate), exopolysaccharides (EPS), inorganic nitrogen content, and activity of enzymes comprised in nitrogen metabolism and Ni accumulation. The 1µM Ni substantially diminished growth by 18% and 22% in N. muscorum and Anabaena sp. respectively, along with declining the pigment contents (Chl a/Car ratio and phycobiliproteins), and biochemical components. It also exerted negative impacts on inorganic uptake of nitrate and nitrite contents; nitrate reductase and nitrite reductase; and ammonium assimilating enzymes (glutamine synthetase, glutamate synthase, and glutamate dehydrogenase exhibited a reverse trend) activities. Nonetheless, the adverse impact of Ni can be mitigated through the exogenous supplementation of NaHS [sodium hydrosulfide (8µM); H2S donor] and SNP [sodium nitroprusside (10µM); NO donor] which showed substantial improvement on growth, pigments, nitrogen metabolism, and EPS layer and noticeably occurred as a consequence of a substantial reduction in Ni accumulation content which minimized the toxicity effects. The accumulation of Ni on both the cyanobacterial cell surface (EPS layer) are confirmed by the SEM-EDX analysis. Further, the addition of NO scavenger (PTIO; 20µM) and inhibitor of NO (L-NAME; 100µM); and H2S scavenger (HT; 20µM) and H2S inhibitor (PAG; 50µM) reversed the positive responses of H2S and NO and damages were more prominent under Ni stress thereby, suggesting the downstream signaling of H2S on NO-mediated alleviation. Thus, this study concludes the crosstalk mechanism of H2S and NO in the mitigation of Ni-induced toxicity in rice field cyanobacteria.

Biochar application regulating soil inorganic nitrogen and organic carbon content in cropland in the Central Europe: a seven-year field study

Biochar incorporation into soil has shown potential, in enhancing nitrogen fertilizer (N-fertilizer) efficacy and soil organic carbon content (SOC). This study addresses a critical gap in the literature by investigating the effects of biochar addition over a seven-year period (2014–2020) on inorganic N, SOC, and pH in Haplic Luvisol. The research involved a rain-fed field experiment, with a crop rotation comprising spring barley, maize, spring wheat, and pea. Biochar, applied at the rates of 0, 10, and 20 t ha−1 in 2014, was reapplied to specific plots in 2018. Biochar was also combined with N-fertilizer at three level (N0, N1, and N2). Results showed a significant interactive influence of biochar and N-fertilizer combination on NO3− and NH4+ contents. Intriguingly, the addition of 10 t biochar ha−1 consistently decreased soil inorganic N levels across most of the examined months. Increasing biochar application rates led to a significant rise in pH, establishing a clear, negative correlation between soil pH and inorganic N content. Biochar significantly increased SOC compared to the control, particularly after the reapplication in 2018. However, this effect showed a diminishing trend over time. The study suggests that incorporating biochar treatments may enhance N-fertilizer effectiveness. However, the long-term implications of biochar application with N-fertilizer on N mineralization are specific to individual soil and biochar combinations. Except the application of 20 t ha−1 biochar at N2 in 2019, biochar did not affect the crop yields. Studied soil properties, including those influenced by biochar had nuanced impact on different aspects of crop yield.Graphical

Improved Method for Extracting Nitrites in Soil

Soil nitrite (NO2−) is an important reactive intermediate in many nitrogen transformation processes, but it is unstable under acidic conditions and may be lost as gaseous N. The canonical extraction method of soil NO2− using a potassium chloride (KCl) solution greatly underestimates its concentration. To reflect the concentration more accurately, we optimized the extraction method of soil NO2− for three agricultural soils differing in soil texture and pH, an alkalic fluvo-aquic soil and acidic Mollisol and Ultisol soils, respectively. Both extractable soil ammonium (NH4+) and nitrate (NO3−) were systematically investigated to optimize the simultaneous extraction of soil inorganic nitrogen. The effects of different extractants (deionized water (DIW), un-buffered 2 mol L−1 KCl, and pH-buffered 2 mol L−1 KCl), shaking time (10 and 30 min), and storage duration of the extracts (stored at −20 °C for 1 day, and at 4 °C for 1, 3, and 6 days) on the determination of soil inorganic nitrogen were investigated. The results showed that the un-buffered KCl extractant significantly underestimated soil NO2− concentration compared to DIW. The highest recovery of NO2− was obtained by extracting with DIW at 10 min of shaking for all three soils. Compared with DIW, the concentration of NH4+ and NO3− in soil extracted from the KCl solution increased significantly. Furthermore, the soil inorganic nitrogen content of extracts stored at 4 °C for one day was closer to the direct measurements of fresh samples than with the other storage methods. Overall, the recommended analysis method for soil NO2− was extraction by DIW, shaking for 10 min, and filtering with a 0.45 µm filter, while soil NH4+ and NO3− were extracted with a KCl solution and shaken for 30 min. The extract should be stored at 4 °C and analyzed within 24 h. Our study provides an efficient extraction method for soil NO2− and supports studies on the biogeochemical nitrogen cycle, e.g., in the investigation of soil nitrous acid (HONO) and nitric oxide (NO) emissions.

Latitudinal responses of wetland soil nitrogen pools to plant invasion and subsequent aquaculture reclamation along the southeastern coast of China

The impact of invasive species and land use change on soil nitrogen pools in coastal wetlands has been reported at local scale, but uncertainty persists for regional pattern due to geographical variability and limited field data. This study measured the top soil (upper 20 cm) organic nitrogen (SON), inorganic nitrogen (SIN) and total nitrogen (STN) concentrations and stocks across 21 coastal wetland sites in China (20°42′N-31°51′ N) that had undergone the same sequence of transformation from mudflats (MFs) to invasive Spartina alterniflora marshes (SAs) then to earthen aquaculture ponds (APs). Results showed that the conversion of MF to SA significantly increased SON and SIN concentrations and stocks by 37.7–86.1%, but subsequent conversion to APs significantly decreased them by 13.5–34.6%. SON/SIN ratio decreased upon invasion by S. alterniflora and it had a negative effect on STN accumulation, whereas conversion of SAs to APs showed the opposite trends. The change rates of SON, SIN and STN stocks showed clear decreasing trends with increasing latitude in the MF-to-SA conversion scenario, reflecting the strong influence of environmental temperatures, but weaker or insignificant trends were observed in the SA-to-AP conversion scenario, likely because of mitigating anthropogenic activities in aquaculture ponds. Our findings can be used to inform strategies to control invasive species and reduce the greenhouse gas nitrous oxide (N2O) emissions, and support global N model for climate change in response to habitat modifications in coastal wetlands.

Potential benefits of Bacillus subtilis-mediated bioflocs in supplementary feeding on triangle sail mussels Hyriopsis cumingii: a pilot study of fluorescence-labeled floc-forming bacteria

As micro-particle aggregates, bioflocs may be potential baits for ingestion by triangle sail mussels and supplementary feeding raises more concerns. Besides, a plasmid carrying the green fluorescent protein (GFP) gene was transformed into floc-forming Bacillus subtilis (GFP-B. subtilis) to visualize its colonization during the bioflocs ingestion. To investigate the potential benefits of bioflocs on H. cumingii, Chlorella vulgaris diets were supplemented with nothing (control group, CG) or bioflocs accounting for the microalgae biomass at 25% (T1), 50% (T2), and 100% (T3) respectively. The community composition of bioflocs was analyzed and some species like phylum Proteobacteria, order Rhodobacterales and genus Paracoccus with potentials to improve water quality were found. Furthermore, supplementary bioflocs could reduce the concentrations of inorganic nitrogen in the aquacultural environment. Differences in growth traits across all groups were insignificant, but the digestion, metabolic and immune response of H. cumingii were promoted remarkably. Interestingly, some colonies of GFP-B. subtilis were detected in the intestines of H. cumingii from T1, suggesting H. cumingii could uptake bioflocs efficiently and intestinal colonization of B. subtilis might be accomplished. Besides, supplementary bioflocs with the highest ratio (T3) could improve the physiological status of organs and suppress the dominance of potential pathogens such as Aeromonas and Pseudomonas. It was assumed that B. subtilis might stimulate the healthy intestine development via intestinal colonization. Overall, B. subtilis-mediated bioflocs is beneficial to H. cumingii and more feeding strategies of bioflocs in H. cumingii farming are expected to be developed in future.

Outwelling of reduced porewater drives the biogeochemistry of dissolved organic matter and trace metals in a major mangrove‐fringed estuary in Amazonia

AbstractMangrove‐fringed estuaries are intertidal ecosystems discharging significant amounts of dissolved organic matter (DOM) into coastal oceans. DOM in these ecosystems is derived from autochthonous production, fluvial input, and mangrove porewater outwelling; however, differentiating between these sources remains challenging. Our incomplete understanding of the biogeochemical factors controlling DOM dynamics and its relationship with nutrient and trace metal cycling still hinders the formulation of elemental budgets in coastal environments. Here, we relate the DOM composition in a mangrove‐fringed estuary in North Brazil (Amazonia) to the redox conditions at the formation sites. We combined molecular DOM analyses via ultrahigh‐resolution mass spectrometry (FT‐ICR‐MS) with parallel factor analysis of excitation–emission fluorescence matrices (EEM‐PARAFAC), nutrient and redox‐sensitive trace metal analyses. During low tide, the influx of oxygen‐depleted porewater carried terrigenous DOM, inorganic nutrients, and trace metals into the mangrove‐fringed creeks. Precipitation of metal(hydr)oxides and microbial turnover controlled nutrient and trace metal dynamics in the estuary. The highest inorganic nitrogen concentrations within the upper mangrove‐fringed estuary indicated outwelling from mangrove sediments as an essential source. Phosphate concentrations were highest within the lower mangrove‐fringed estuary, where available phosphate likely exceeded precipitation with iron(hydr)oxides. We tracked the DOM transport to the coastal ocean using a novel molecular index derived from sulfidic porewater (ISuP). Outwelling of recalcitrant DOM from mangrove habitats is relevant in the context of blue carbon storage. Therefore, applying our molecular proxy (ISuP), together with trace‐metal and optical DOM analyses, is a powerful approach for differentiating contributions of diverse DOM sources in highly complex coastal ecosystems.

Impact of soil inorganic nitrogen on bacterial phylogeny in estuarine intertidal zones: a study of nitrogen metabolism.

Here we investigated the potential impacts of soil inorganic nitrogen (SIN) content on the phylogenetic characteristics and ecological functions of soil bacterial communities in estuarine intertidal zones in China, aiming to comprehend the response mechanism of soil microorganisms to variations in SIN content within estuarine wetlands. Our results show that SIN in estuarine areas has a significant spatiotemporal variation on spatial and seasonal scales, in this study and is significantly associated with the phylogenetic diversity and phylogenetic turnover of soil bacterial communities. In addition, the results of the metagenomic analysis showed that the relative abundance of nitrogen-cycling functional genes in bacterial communities did not differ significantly in sampling sites and seasons, and weakly correlated with SIN content. Further, the results based on structural equation modeling (SEM) analysis showed that SIN directly and significantly regulated the phylogenetic characteristics of bacterial communities, thereby indirectly affecting the potential of bacterial nitrogen metabolism. This study emphasizes the key influence of SIN variations on the phylogenetic dissimilarity in soil bacterial communities. Moreover, although there was a weak direct relationship between the functional characteristics of the bacterial nitrogen metabolism and SIN content, the spatiotemporal variation of bacterial nitrogen metabolic potential may be indirectly regulated by SIN content by influencing the phylogenetic diversity in bacterial communities. Our study unravels the pivotal mechanisms through which SIN content influences bacterial communities, thereby offering novel insights into the microbial intricacies governing nitrogen metabolism within estuaries.

Nitrogen enrichment decreases seagrass contributions to refractory organic matter pools

AbstractCoastal nitrogen enrichment significantly contributes to the decline of seagrass health and habitat, thereby diminishing its capacity to capture and sequester carbon (i.e., Blue Carbon). However, the consequences to blue carbon stocks due to sublethal changes in chemical recalcitrance of seagrass organic matter (OM) caused by nitrogen enrichment is unknown. In this study, we investigated the effects of nitrogen‐loading on the chemical composition of meadow‐forming Thalassia hemprichii. We found that the amino acid content in seagrass leaves and rhizomes increased with nitrogen loading, while the total labile OM and refractory OM (i.e., cellulose and lignin) content in seagrass leaves, sheaths, and roots generally decreased with nitrogen loading. Additionally, cellulose and lignin within sheath tissues showed a threshold response whereby refractory OM dropped when leaf nitrogen content (i.e., indicator of nitrogen loading) exceeded 2.2%. The rhizome labile OM and cellulose content also peaked at 2.2% leaf nitrogen content but subsequently reduced to a minimum at ~2.9% leaf nitrogen. The threshold of 2.2% leaf nitrogen content, equivalent to 43~72 μM dissolved inorganic nitrogen concentration in sediment pore water, may be utilized to forecast the contribution of seagrass refractory OM to sediments. It was estimated that high nitrogen loading could result in a loss of 309–645 kg ha−1 of refractory OM inputs in this study sites. The findings underscore that nitrogen enrichment has sublethal but significant negative impacts on carbon cycling via the reduction of refractory OM in seagrass biomass, consequently weakening the autochthonous contribution of seagrass to long‐term carbon sequestration.

Characteristics of Cyanobacteria at Different Stages of Existence of the Kyiv Reservoir

The paper deals with the patterns of Cyanobacteria long-term succession at different stages of existence of the Kyiv Reservoir. The main ecological factors responsible for Cyanobacteria succession include current velocity, hydromorphological characteristics of the reservoir, the content of inorganic nitrogen (primarily of ammonium) and phosphorus, &amp;#931;N : P ratio, global climate changes, and the competition with higher aquatic plants in the shallow water zone. The trophic state of the hydroecosystem changed from mesotrophic (at the stage of the non-regulated river) to eutrophic (at the present time) depending on the intensity of Cyanobacteria development. With possible further deterioration of water quality, possible climate changes with an increase in water temperature within the range of even 1-2&amp;deg;C, the intensity of Cyanobacteria development will increase, especially in the pelagic zone of the reservoir, where they have practically no natural biological competitors.

Acidification and hypoxia in seawater, and pollutant enrichment in the sediments of Qi’ao Island mangrove wetlands, Pearl River Estuary, China

Mangrove forests are crucial in absorbing, storing, and purifying pollutants while maintaining ecological balance. A study was conducted in 2020 to investigate the biogeochemical processes of seawater and sedimentary environmental factors in the Qi'ao Island mangrove wetland. The study comprised two survey sections and ten survey stations within the mangrove forest and 16 large-scale survey stations in the adjacent sea area. During ebb tides, the mean concentrations of inorganic nitrogen and phosphate in Section D1 of the mangrove forest were 0.63 mg/L and 0.003 mg/L, respectively. These levels were significantly lower than the results observed in the adjacent sea area and Section D2 of the mangrove forest during flood tides. The mangrove forest efficiently absorbed and consumed nutrients, with the nitrogen-to-phosphorus ratio of consumed nutrients being notably higher than that typically utilized by plants during growth. We identified various biogeochemical processes, including nitrogen fixation, mineralization, nitrification, and denitrification, occurring within the mangrove forest. Seawater measurements in Section D1 during ebb tides showed the mean pH of 7.58 and dissolved oxygen levels of 4.52 mg/L, resulting in a dissolved oxygen saturation level of only 57.0 %. The low dissolved oxygen levels were attributed to organic matter degradation in the forest. Consequently, the longer the water retention time, the more obvious the trend of hypoxia and acidification was observed. In the adjacent sea area, the sedimentary environment was deemed healthy, with pollutants primarily originating from runoff and ship discharge from waterways and ports. However, within the mangrove forest, the sediments exhibited higher enrichment factors for organic carbon and sulfide, indicating significant pollution compared to the adjacent sea area. The sediments were conducive to the accumulation and burial of total Hg, Zn, and Cu, while other heavy metals did not show prominent deposition and enrichment. Notably, the enrichment factor of oils was as high as 4.37, leading to the formation of an oil pollution zone at the forest edge, and the enrichment of pollutants in sediment may inhibit the growth and expansion of mangroves. Overall, this study shed light on the occurrence of seawater acidification, hypoxia, and the behavior of sediment pollutants within the mangrove forest. The findings provide valuable insights to support efforts aimed at promoting and maintaining the ecosystem health of mangrove forests.