High Nitrogen Levels Research Articles

Marsh archive reveals human population history and future implications for estuarine health in Long Island Sound

Coastal marshes are efficient ecosystems providing a multitude of benefits for invertebrates, birds, fish and humans alike. Yet despite these benefits, wetlands are threatened by anthropogenic inputs such as human wastewater which contain high levels of nitrogen (N). Increased nitrogen loads cause eutrophication and hypoxia in estuaries leading to further degradation of these valuable ecosystems that are already stressed by sea level rise and climate change. Policies to protect wetlands via wastewater treatments are reactive rather than proactive and a growing body of research shows that characteristics associated with population health and economic activity can be identified in wastewater. Analysis of a 2-m salt marsh sediment core reveals δN15 signatures indicative of human population rise and connects human impact to ecosystem health. Using key X-ray fluorescence (XRF), pollen, sediment and nitrogen signatures along the core, a robust chronology was produced dating back to 1700. This result was coupled with population data to observe the relationship between δN15 levels and population over three centuries. There is a statistically significant positive correlation between δN15 and population. Other external factors such as federal government policies (regulating clean water) show a clear reduction in this association but the use of synthetic nitrogen fertilizer masks the strength of this relationship. Further research to refine the relationship between population and δN15 could be beneficial in predicting nitrogen loads as human population grows, which in turn would create a proactive system to protect our coastal ecosystems.

Groundwater nitrogen concentration changes in an urbanized area of Indonesia over ten years period

Nitrogen in groundwater poses environmental concerns in Bandung Region, Indonesia, due to natural and anthropogenic factors. The predominant component of the region’s aquifer is high-hydraulic-conductivity volcanic rock, one of the natural vital factors that make the aquifer vulnerable to contamination. Another factor is urbanization which has been reported to be an adverse effect of high nitrogen levels in the groundwater, particularly the unconfined system. This study’s objective was to evaluate urbanization’s impact on dissolved inorganic nitrogen concentrations over a 10-year period, which had not been explained by previous research. The evaluation focused on land-use changes in the southern part of the Bandung Region and their relation to dissolved inorganic nitrogen (DIN) in unconfined groundwater. A total of 88 samples were collected in 2009, 2015, and 2018 from three types of land-use: residential, plantations, and paddy fields. From 2009 to 2018, land use changes were visible, with an 8% and 6% increase in urban settlements and rice fields, respectively, and a 15% reduction in plantations. Furthermore, over a decade, agricultural and rice fields substantially impacted the NO3 − levels, contributing approximately 13.2 mg/L and 9.9 mg/L, respectively. In the meantime, the settlement area significantly contributed to the 3.25 mg/L increase in the NH4 + levels.

Fertigation under different irrigation and nitrogen levels modulates the growth, physiology, nitrogen and fruit productivity of greenhouse tomato

AbstractExperiments were conducted to evaluate the interactive effects of different nitrogen and irrigation levels in 2017 and 2018 (April–July) on greenhouse‐grown tomato considering irrigation water, growth, physiology and productivity parameters. A randomized block design with three replications and two factors, water (W1, 100% of the requirement; W2, 90%; W3, 70%) and nitrogen fertilizer (F1 225 kg/ha, F2 180 kg/ha), was established. The highest values of crop consumptive use (ET) were observed under the W1F1 treatment during both seasons (266 and 226 mm during 2017 and 2018, respectively). The highest values of stem and root biomass were also observed under W1F1 during both experimental seasons, followed by W1F2 and W2F1, without significant differences. Compared with W1F1, W1F2 and W2F1 had no significant difference, but other treatments decreased the photosynthesis rate and stomatal conductance significantly during both seasons. The highest irrigation level, W1, increased fruit yield under both nitrogen levels (W1F1 yielded 91 and 102 t ha−1, followed by W1F2, with 90 and 99 t ha−1 during 2017 and 2018, respectively). W2 increased fruit yield under higher nitrogen levels (F1) but decreased fruit yield under lower nitrogen levels (F2). W3 decreased yield drastically under both nitrogen levels. W3 significantly decreased water use efficiency and irrigation water use efficiency. The highest partial factor productivity values of 23% and 22% were obtained under W1F2 in 2017 and 2018, respectively, when compared with the control treatment. It was concluded that W1F2 could be the best strategy for improving greenhouse‐grown tomato productivity.

Soil Nutrient, Salinity, and Alkalinity Responses of Dendrocalamopsis oldhami in High-Latitude Greenhouses Depending on Planting Year and Nitrogen Application

This study explored the viability of greenhouse cultivation of Dendrocalamopsis oldhami under the “South Bamboo North Transplanting” initiative. In this study, the effects of planting year and nitrogen application on changes in soil nutrient levels, salinity, and alkalinity over the plant growth period were explored. After the introduction and planting of bamboo in 2017, a soil layer with a thickness of 0–40 cm was sampled at the end of the shooting stage in the greenhouse between 2017 and 2019 (late August), and the bamboo shoot yield and standing culm density were measured. Following the application of nitrogen to the bamboo groves in 2019, three nitrogen levels were established: no nitrogen (N1:0 g grove−1), medium nitrogen (N2:540 g grove−1), and high nitrogen (N3:1080 g grove−1). Soil layers at depths of 0–20 and 20–40 cm were sampled during the shoot elongation stage (late May) and at the end of the shooting stage (late August). The yield and nutrient content of bamboo shoots under different nitrogen treatments were also investigated. The results showed that Ca2+ and HCO3− were the main salt ions in greenhouse soil. With later planting years, the total number of cations (Ca2+, Na+, Mg2+, and K+) decreased, whereas the total number of anions (HCO3−, SO42−, NO3−, and Cl−) increased, resulting in a decrease in the percentage of exchangeable sodium (ESP), pH, and electrical conductivity (EC). The diameter at breast height, individual weight, and quantity of bamboo shoots increased annually, and the standing culm density increased by 1.4 times. Each year, the total nitrogen content decreased, whereas the alkali-hydrolyzed nitrogen, available phosphorus, and available potassium contents increased. Nitrogen application resulted in a significant decrease in ESP and pH and an increase in the total anion, cation, and EC values. It also reduced soil organic carbon, total nitrogen, total phosphorus, total potassium, available phosphorus, and available potassium. Nitrogen application increased the number of bamboo shoots, total yield, and accumulation of N and P; however, there was no significant difference between N2 and N3. In conclusion, the salinization of calcareous soil was alleviated, and the available nutrients were activated following the introduction of D. oldhami from south to north. The mineralization rates of organic matter and soil fertility increased. Soil acidification and EC decreased at the end of the shoot stage. Nitrogen application acidified the soil, and the yield and soil salt accumulation increased with increasing nitrogen levels. The nutrient uptake efficiencies of nutrients at high nitrogen levels were lower than those at medium nitrogen levels. Therefore, soil salt concentrations with values 0.26 < EC < 0.42 hindered the nutrient uptake of D. oldhami.

A novel type of biochar from chitinous Hermetia illucens waste with a built-in stimulating effect on plants and soil arthropods

The breeding of insects generates waste in the form of insect excrement and feed residues. In addition, a specific chitinous waste in the form of insect larvae and pupae exuvia is also left. Recent research tries to manage it, e.g., by producing chitin and chitosan, which are value-added products. The circular economy approach requires testing new, non-standard management methods that can develop products with unique properties. To date, the possibility of biochar production from chitinous waste derived from insects has not been evaluated. Here we show that the puparia of Hermetia illucens are suitable for biochar production, which in turn exhibits original characteristics. We found that the biochars have a high nitrogen level, which is rarely achievable in materials of natural origin without artificial doping. This study presents a detailed chemical and physical characterization of the biochars. Moreover, ecotoxicological analysis has revealed the biochars’ stimulation effect on plant root growth and the reproduction of the soil invertebrate Folsomia candida, as well as the lack of a toxic effect on its mortality. This predisposes these novel materials with already built-in stimulating properties to be used in agronomy, for example as a carriers for fertilizers or beneficial bacteria.

Intraspecific variation in reproductive traits and embryo elemental composition of the crab Hemigrapsus crenulatus (Milne Edwards, 1837) across fluctuating coastal environments along Chilean coasts

The estuarine crab Hemigrapsus crenulatus has a wide distribution range along the coast of the South Pacific Ocean (from 20 °S to 53 S°). This decapod is abundant in these coastal and estuarine habitats and plays a key ecological role as prey of the snook fish (Eleginops maclovinus) and kelp gull (Larus dominicanus). Its diet consists of detritus, dead fish, and crustaceans, and the macroalgae Ulva sp. In response to contrasting environmental conditions and anthropogenic impacts along the Chilean coast, H. crenulatus may present intraspecific variations in its reproductive traits and changes in the elemental composition of its embryos, directly affecting its biological fitness. Along the Chilean coast, female individuals were collected during late spring 2019 and early summer 2020 (from November 2019 to February 2020) in six areas of Chile (north: Tongoy (30°S); south-central: Lenga (36°S), Tubul (37°S); south austral: Calbuco (41°S), Castro (42°S), Quellón (43°S). The environmental conditions (i.e. sea surface temperature, precipitation and chlorophyll α) present during each sampling event were also recorded. We evaluated the reproductive parameters of females (fecundity, reproductive output (RO)) as well as their body size (carapace width and dry weight), volume, water content, dry weight, elemental composition (carbon, hydrogen, nitrogen: CHN), and finally the energy content of their embryos. Our results indicated that the environmental conditions of the sea water temperature, precipitation (proxy of water salinity) and chlorophyll α (proxy of food availability) have direct effects on the reproductive parameters of females and the characteristics of their embryos. We observed a low fecundity and high RO in Calbuco and Quellón, where precipitation was high (i.e. diluted salinity) and temperatures and productivity was low. For embryo traits, the highest values of volume and water content were observed in female crabs from the estuarine areas (i.e. Tongoy, Lenga, Tubul), values much higher than those found in the internal sea of Chile (i.e. Calbuco, Castro, Quellón). For the elemental composition, we observed high nitrogen levels and a low C:N proportion in embryos from female crabs from Lenga (a nitrogen enriched area). Fluctuating environmental variables among localities proved to modulate intraspecific variations in females and embryos of H. crenulatus, revealing different reproductive strategies, particularly in the quality and energy investment per embryo, which subsequently influenced successful embryogenesis and larval survival.

Interspecific interactions between crops influence soil functional groups and networks in a maize/soybean intercropping system

Despite increasing evidence that intercropping systems may increase crop productivity, little is known about whether and how soil biota change under interspecific competition among plants. A field experiment with maize/soybean intercropping and the corresponding monoculture systems was conducted under four nitrogen fertilization regimes to investigate the effects of interspecific plant interactions on grain yield, soil properties (β-glucosidase and water-soluble carbohydrates), and biotic communities (bacteria, fungi, and nematodes). The soils under maize and soybean in the intercropping system were sampled separately to represent intercropped maize and intercropped soybean, respectively. Compared to monocultures, the complexity and robustness of soil networks comprising bacterial, fungal, and nematode communities increased in intercropped maize soils, but densities of plant parasitic nematodes and β-glucosidase activity were reduced. Intercropped soybean soils had lower C availability due to chronic shading by maize, but a significant increase was found in saprophytic fungi, and plant parasitic nematodes compared to soybean monoculture soils. Although intercropped soybean suffered from interspecific competition with maize, the interactions within the fungal community increased for both crop species in the intercropping system. Our study demonstrates that increased carbon uptake in maize due to increased light capture in the intercropping system can facilitate nutrient cycling by altering the abundance of functional groups of soil organisms, such as saprophytic fungi, and enhancing network complexity and stability. We detected a trade-off between productivity and soil nematode diversity in the intercropping system under nitrogen fertilization, the yield of maize increased but soil nematode richness decreased at low nitrogen level, while the yield of soybean decreased but the nematode richness increased at high nitrogen level. These findings show that both trade-offs and benefits occur in intercropping systems and highlight the role of plant-soil biota interactions in such systems.

Degradability of Vicia ervilia Grain Using In Situ and CNCPS Methods, and Model-Based Analysis of Its Ruminal Degradation

Using nylon bag techniques, Cornell net carbohydrates and protein systems (CNCPS), and scanning electron microscopy, the authors examined the digestibility and structure of Vicia ervilia (ervil, bitter vetch) after steam flaking, roasting, and microwave processing. During the in situ technique, the samples were incubated at 0, 2, 4, 6, 8, 12, 16, 24, 36, and 48 h. For the description of the ruminal DM (dry matter) and CP (crude protein) degradation kinetics of treated and untreated Vicia ervilia, different models were selected as the best fit for the dry matter (DM) and crude protein (CP) degradation parameters of steam flaked samples. The results showed that both the steam flaking and microwave treatment samples contained high levels of non-protein nitrogen and buffer soluble protein, respectively. In comparison with steam flaking and microwave treatment, roasting decreased and increased the buffer soluble protein and neutral detergent insoluble protein, respectively. The control treatments showed the highest levels of neutral detergent soluble protein and the lowest levels of acid detergent soluble protein. Moreover, steam flaking and roasting decreased and increased the amount of acid detergent insoluble protein, respectively. When using dry heat (microwave and roasting), the acid detergent soluble and insoluble protein fractions were increased. As a result of this experiment, the nitrogen fractions were altered using heat processing. Hence, protein fermented feed and ruminal fermentation conditions can be expressed using these results.

Linkages between bacteria and nutrient availabilities in slash‐and‐burn tropical soils vary with feeding‐habit ants

AbstractAs important structuring forces in forest ecosystems, ants can drive above‐ and belowground food‐webs and ecosystem functionality. It remains uncertain, however, about how different foraging‐habit ants shape symbiotic bacterial assemblies and nutrient cycling in nest soils. This study quantified the impacts of predatory and honeydew‐feeding ants on soil bacterial communities and nutrient pools in Xishuangbanna tropical forests restored from slash‐and‐burn agriculture. In contrast to reference soils, all ant nests increased the relative abundances of dominant copiotrophs and decreased those of preponderant oligotrophs in the bacterial communities, which was closely associated with the high levels of carbon (C) and nitrogen (N) in the nests. Honeydew‐feeding ants harbored a high abundance of bacterial trophic groups (i.e., γ‐Proteobacteria, Firmicutes, and Bacteroidetes) preferring low‐quality resource, owing to high increment (103%) in C concentration and low increase (69%) in N level compared to reference soils. In contrast, predatory ants sheltered a high assemblage of bacterial taxa (i.e., β‐Proteobacteria and δ‐Proteobacteria) favoring high‐quality resource, due to increased N level (135%) and decreased C:N ratio (35%) compared to reference soils. We concluded that the foraging‐habit ants shaped symbiotic bacterial assemblages primarily through differential modifications on level and allocation of soil C and N pools. Our results would further the understanding of the fauna roles in driving soil food‐webs as well as nutrient cycling.

Development and validation of a predictive model for diarrhea in ICU patients with enteral nutrition.

The aim of this study was to build and validate a risk prediction model for diarrhea in patients in the intensive care unit (ICU) receiving enteral nutrition (EN) by identifying risk factors for diarrhea in these patients. The risk factors for diarrhea were analyzed to build a prediction model for EN diarrhea in patients in the ICU based on the data collected from 302 patients receiving EN in the ICU. Subsequently, the model was validated by the area under the curve. In this study, the collected data were divided into two groups: a derivation cohort and a validation cohort. The results showed that 54.03% (114) of patients had diarrhea in the derivation cohort and 56.04% (51) of patients had diarrhea in the validation cohort. Moreover, days of EN, high urea nitrogen levels, probiotics, respiratory system disease, and daily doses of nutrient solution were included as predictive factors for diarrhea in patients receiving EN in the ICU. The predictive power of the model was 0.81 (95% CI, 0.752~0.868) in the derivation cohort and 0.736 (95% CI, 0.634~0.837) in the validation cohort. In accordance with the predictive factors, the model, characterized by excellent discrimination and high accuracy, can be used to clinically identify patients in the ICU with a high risk of EN diarrhea.

Side dressing nitrogen fertilization in soybean in association with inoculation

The soybean is a crop that demands high levels of nitrogen (N) to express its productive potential. Supplemental fertilization with N can be a management strategy to increase the yield. This study aims to assess the effect of the N side dressing fertilization at the V4 stage of soybean, with and without inoculation, as well as its effects on the process of biological nitrogen fixation (BNF). The experimental design was randomized complete-block design with four replications in factorial scheme 2 × 5, where the seeds were either inoculated or not and received 5 doses of N: 0, 10, 20, 30, and 40 kg ha−1. Vegetative growth, nodulation, and yield components were evaluated. The stem diameter, plant height, and grain yield were not affected by inoculation, only by the N doses, with positive linear responses to the N supply. The leaf area responded positively to the seed inoculation and to the N supply. The node mass and viable node mass were not altered by seed inoculation or the supply of mineral N; and, until the dose of 40 kg ha−1, the node formation did not decrease. The number of pods per plant and the thousand-grain weight showed an interaction between inoculation and doses of N. The side dressing N fertilization at the V4 stage, until the dose of 40 kg ha−1, did not affect the vegetative growth and BNF, while it contributed to increase grain yield, even in the presence of inoculation.

Effects of Nitrogen Fertilization and Soil Water Content on Seed and Oil Yield in Perennial Castor in a Mediterranean Environment

Castor (Ricinus communis L.) is an oilseed species that can be grown as a semi-perennial in Mediterranean environments, including the coastal areas of Sicily. The present study investigated the optimization of cultivation techniques for castor, with the crop being maintained over a two-year period, through the evaluation of different agronomical inputs in order to increase seed yield. The effects of irrigation (I) and nitrogen fertilization (N) on the seed and oil yield and their components were assessed in castor cultivated in a typical semi-arid environment. Four levels of irrigation (I0, I30, I60, and I100: 0, 30, 60, and 100% of crop evapotranspiration—ETm restoration, respectively) as the main plot and three levels of nitrogen fertilization (N) (0, 60, and 120 kg N ha−1) as the sub-plot were considered. Irrigation mostly affected the number of racemes per plant, the number of capsules per raceme, and the seed weight. The oil content was, on average, 39.2% and 45.6% for the first and second year, respectively. The highest seed yield was obtained by I100N120 treatment (4154.0 kg ha−1); however, the combination of a high soil nitrogen level (N120) and medium water availability (I60) resulted in satisfactory seed and oil yields. The reduction in the irrigation water to an intermediate level could be also an environmentally friendly strategy not significantly affecting yields.

Membrane distillation for separation and recovery of valuable compounds from anaerobic digestates

Digestate - the wet by-product of the anaerobic digestion (AD) of organic waste - is composed of a mixture of residual organic matter, microbial biomass and inorganic compounds. Although digestate is rich in nutrients, the occurrence of high levels of salinity and soluble ammoniacal nitrogen (N-NH4+) limits its direct exploitation as organic fertilizer and imposes a complex disposal.This study assesses at laboratory-scale the potential of Direct Contact Membrane Distillation (DCMD) for the separation of nutrients and the recovery of water from the liquid phase of the digestate produced by a digester that treats cattle manure and agricultural residues. Experimental tests, carried out at different feed temperature (50–70 °C) and initial pH (6–8.2) of the liquid digestate, aimed at investigating the effect of the operating conditions on the transmembrane flux of water vapor, the concentration of N-NH4+, P-PO3-, and Chemical Oxygen Demand (COD) in both permeate (also referred to as distillate) and retentate streams.For raw digestate, the initial transmembrane flux enhanced from 1.83 L·m−2·h−1 to 5.55 L·m−2·h−1, in response to increasing temperature gradient. Overall, the highest achieved water recovery factor was 40% at a feed temperature of 70 °C. The pH had a limited impact on the transmembrane flux, whereas notably affected the DCMD performance in terms of separation efficiency. In particular, a pH reduction from 8.2 (raw digestate) to 6 was able to completely avoid the transfer of N-NH4+ into the distillate. Compared to the concentration in the raw digestate, the reduction of COD and P-PO3- in the distillate was 99.0% and 99.9%, respectively. Regardless feed temperature, the performance of the process was subjected to a significant decline of evaporation rate due to occurrence of membrane fouling; however, cycles of cleaning with citric acid allowed to partially regenerate the membrane by removing the reversible cake of foulants accumulated on the surface. The results demonstrate an adequate performance of MD process for recovering water and nutrients, leading to a dehydrated fraction of the digestate phase that can be easily stored and used in agronomic practices.

Aplikasi Kompos Azolla (Azolla sp.) dan Pupuk Hayati Pada Budidaya Selada (Lactuca sativa L.) Organik

Organic fertilizer plays an essential chemical role such as in providing macro and micro nutrients. One of many plants which is able to be used as organic fertilizer which contains high level of nitrogen for the soil is Azolla pinnata. Biofertilizer is defined as a fertilizer which contains beneficial bacteria which may improve plant’s yield. The aims of this research is to study the application of composted Azolla and M-Bio Biofertilizer on lettuce (Lactuca sativa L.) cultivation. This research was conducted at the research field of Faculty of Agriculture, Siliwangi University by an altitude of 356 m above sea level on August to October 2022. This research was arranged based on Completely Randomized Design in factorial patterns, consisted of two factors. The first factor was the dosage of composted Azolla fertilizer, consisted of three dosages, i.e 10 ton/ha, 15 ton/ha, 20 ton/ha. The second factor was the consentration of M-Bio biofertilizer, consisted of the levels, i.e 10 ml/L, 15 ml/L, 20 ml/L. Each treatment was replicated 3 times, therefore, there were 27 experimental plots. Data were analysed by using the analysis of variance with F test and continued by Duncan’s Multiple Range Test with 5% of critical value. The result of this research shows that there is no interraction between composted Azolla fertilizer and M-Bio consentration on growth and yield of lettuce (Lactuca sativa L.).

Treatment of High-Ammonia-Nitrogen Wastewater with Immobilized Ammonia-Oxidizing Bacteria Alcaligenes sp. TD-94 and Paracoccus sp. TD-10

In this study, modified granular activated carbon (GAC) and immobilized cells were used to improve the biological efficiency of high-ammonia-nitrogen wastewater treatment using microorganisms. The results showed that using sodium-hydroxide-modified activated carbon (NaOH-GAC) greatly increased the immobilized numbers of the ammonia-oxidizing bacteria Alcaligenes sp. TD-94 and Paracoccus sp. TD-10. Using NaOH-GAC increased the number of immobilized cells by 63.27% over GAC. Compared with free cells, those immobilized on modified activated carbon were more effective in the removal of high ammonia nitrogen levels from wastewater. In wastewater with an ammonia nitrogen concentration of 100 mg·L−1, the ammonia nitrogen removal efficiencies of NaOH-GAC-immobilized cells and free cells within 24 h were 100% and 4.17%, respectively. After 45 cycles, NaOH-GAC-immobilized cells maintained an ammonia nitrogen removal efficiency of 79.24%. After 70 days of storage at 4 °C, the ammonia nitrogen removal efficiency was still as high as 100%. The removal efficiencies of ammonia nitrogen (NH4+-N), total nitrogen (TN), and chemical oxygen demand (COD) in high-ammonia-nitrogen wastewater from petrochemical enterprises reached 99.27%, 88.39%, and 69.85%, with removal rates of 75.21, 69.43, and 1117.40 mg·L−1·d−1, respectively. The findings demonstrated that NaOH-GAC improved the capacity of the biological treatment to remove ammonia nitrogen from wastewater and provide a practical option for the remediation of environmental pollution.

Pollution caused by mining reshaped the structure and function of bacterial communities in China’s largest ion-adsorption rare earth mine watershed

Ion-adsorption rare earth mining results in the production of high levels of nitrogen, multiple metals, and strong acidic mine drainage (AMD), the impacts of which on microbial assembly and ecological functions remain unclear. To address this knowledge gap, we collected river sediments from the watershed of China's largest ion-adsorption rare earth mine and analyzed the bacterial community's structure, function, and assembly mechanisms. Results showed that bacterial community assembly was weakly affected by spatial dispersion, and dispersal limitation and homogeneous selection were the dominant ecological processes, with the latter increasing with pollution gradients. Bacterial alpha diversity decreased with pollution, which was mainly influenced by lead (Pb), pH, rare earth elements (REEs), and electrical conductivity (EC). However, bacteria developed survival strategies (i.e., enhanced acid tolerance and interspecific competition) to adapt to extreme environments, sustaining species diversity and community stability. Community structure and function showed a consistent response to the polluted environment (r = 0.662, P = 0.001). Enhanced environmental selection reshaped key microbial-mediated biogeochemical processes in the mining area, in particular weakening the potential for microbial denitrification. These findings provide new insights into the ecological response of microbes to compound pollution and offer theoretical support for proposing effective remediation and management strategies for polluted areas.

The effects of cultivation patterns and nitrogen levels on fertility and bacterial community characteristics of surface and subsurface soil.

The cropping system affects the physicochemical property and microbial community of paddy soil. Previous research mostly focused on the study of soil 0-20 cm underground. However, there may be difference in the laws of nutrient and microorganism distribution at different depths of arable soil. In surface (0-10 cm) and subsurface (10-20 cm) soil, a comparative analysis including soil nutrients, enzymes, and bacterial diversity was carried out between the organic and conventional cultivation patterns, low and high nitrogen levels. Analysis results suggested that under the organic farming pattern, the contents of total nitrogen (TN), alkali-hydrolyzable nitrogen (AN), available phosphorus (AP), and soil organic matter (SOM) as well as alkaline phosphatase and sucrose activity increased in surface soil, but the SOM concentration and urease activity decreased in subsurface soil. A moderate reduction of nitrogen applied to soil could enhance soil enzyme activity. It was demonstrated by α diversity indices that high nitrogen levels remarkably undermined soil bacterial richness and diversity. Venn diagrams and NMDS analysis manifested great difference in bacterial communities and an apparent clustering tendency under different treatment conditions. Species composition analysis indicated that the total relative abundance of Proteobacteria, Acidobacteria, and Chloroflexi retained stable in paddy soil. LEfSe results revealed that a low nitrogen organic treatment could elevate the relative abundance of Acidobacteria in surface soil and Nitrosomonadaceae in subsurface soil, thereby tremendously optimizing the community structure. Moreover, Spearman's correlation analysis was also performed, which proved the significant correlation of diversity with enzyme activity and AN concentration. Additionally, redundancy analysis disclosed that the Acidobacteria abundance in surface soil and Proteobacteria abundance in subsurface soil exerted conspicuous influence on environmental factors and the microbial community structure. According to the findings of this study, it was believed that reasonable nitrogen application together with an organic agriculture cultivation system could effectively improve soil fertility in Gaoyou City, Jiangsu Province, China.

Formation of biogenic amines in soy sauce and reduction via simple phytochemical addition

Biogenic amines (BAs) are of great concern as endogenous contaminants. In this study, the BA level and its formation in soy sauce were analyzed, and an efficient BAs reduction strategy was also explored via simple phytochemical addition. The results indicated that phenylethylamine (PHM), histamine (HM), tyramine (TYM) and putrescine (PUT) were the dominant BAs in soy sauce products, and the total BA levels were within the range 6.46 mg/L to 317.49 mg/L. In general, the total BA contents were low in soy sauces that had high amino nitrogen levels. Moreover, we found a good linear relationship between the HM and TYM contents in soy sauce products and fermented moromi. The content of BAs in the fermented moromi first increased, reaching a maximum content of 628.51 mg/L after 90 d of fermentation, then decreased. The inhibition effects of seven phytochemicals on BAs formation were tested. Quercetin showed a good result in BAs inhibition, and the contents of PUT and HM decreased were by 37.72% and 34.34%, respectively. Notably, quercetin had a negligible effect on BA degradation in the fermentation anaphase and on the quality of the soy sauce, indicating it is a promising additive for controlling BA levels in soy sauce.

Influence of Nitrogen Application Rate on Stem Lodging Resistance Rice under Dry Cultivation

High grain yields of rice (Oryza sativa) under dry cultivation are primarily obtained through high levels of nitrogen (N) input. However, excessive inputs of N increase the risk of lodging. This study aimed to clarify the effect of N application rates on crop morphology, mechanical mechanisms of the stem, and chemical components in the basal stems of rice and their underlying mechanism in association with lodging resistance under dry cultivation. In this study, field experiments on rice were conducted under dry cultivation in early May to early October 2019 and 2020. Six rates of N applied at 0, 70, 140, 210, 280 and 350 kg ha−1 were set at a sowing rate of 150 kg ha−1 with Suijing 18 as the test material. The increased risk of lodging represented by lodging index (LI) and lodging rate with increasing N application was observed under both growing seasons. The plant height, basal internode length, particularly the second internode, and center of gravity height, which positively correlated with the LI, increased significantly with the increase in N application rates. In contrast, internode fullness and carbohydrate content of the basal second (S2) internode, which negatively correlated with LI, decreased significantly with increasing N application rates. A quadratic regression model between N application rates and grain yield showed that better grain yield could be achieved under an N application rate ranging from 210 to 228 kg ha−1. Therefore, the N application rate of (i.e., 210–228 kg N ha−1) could be recommended for the Suijing18 variety under dry cultivation in central Jilin Province for achieving high grain yield and great lodging resistance.

Effect of Low R:FR Ratio on Nitrogen Assimilation and NRT Gene Expression in Pakchoi under Excessive Nitrate Stress

Nitrate accumulation is a major factor for the secondary salinization of greenhouse soil in China. Our previous study pointed out that a low ratio of red:far-red light (R:FR) can improve salt tolerance in pakchoi under excessive nitrate stress. However, the nitrogen metabolism mechanism is still unclear. To detect the effect of a low R:FR ratio on nitrogen metabolism of pakchoi under excessive nitrate stress, two extra additions of nitrogen of 80 mmol·L−1 NO3− (H80) and 160 mmol·L−1 NO3− (H160) with/without a low R:FR ratio (R:FR = 0.7) were set, and the growth index, chlorophyll content, key enzymes in nitrogen metabolism, nitrate and glutamic acid content and NRT gene expression level of pakchoi leaves were examined. The results indicated that a low ratio of R:FR could alleviate the reduction in growth and chlorophyll content in pakchoi under high-level nitrogen stress (H80 and H160). The activity of nitrate reductase (NR), glutamine synthetase (GS) and glutamine synthetase (GOGAT) decreased under H80 and H160 conditions, except of NR with the H80 treatment. The activity of glutamate dehydrogenase (GDH) increased under H80 treatment, but decreased under H160 treatment. However, the activity of GDH decreased further by reducing the ratio of R:FR. Excessive nitrate stress increased the nitrate content, and a low R:FR ratio could inhibit nitrate accumulation. However, the change in glutamic acid content was significantly increased under a low R:FR ratio without stress. Under the high-nitrogen level treatment (H160), the use of a low ratio of R:FR increased NRT gene expression. Therefore, a low R:FR ratio (R:FR = 0.7) could effectively promote the growth of pakchoi and improve its nitrogen metabolism, thus alleviating the stress effect of a high level of nitrogen in pakchoi.