Nitrite Reductase Activity Research Articles

Trichoderma asperellum boosts nitrogen accumulation and photosynthetic capacity of wolfberry (Lycium chinense) under saline soil stress.

Trichoderma can promote plant growth under saline stress, but the mechanisms remain to be revealed. In this study, we investigate photosynthetic gas exchange, photosystem II (PSII) performance, nitrogen absorption and accumulation in a medicinal plant wolfberry (Lycium chinense) in saline soil supplemented with Trichoderma biofertilizer (TF). Larger nitrogen and biomass accumulation were found in plants supplemented with TF than with organic fertilizer (OF), suggesting that Trichoderma asperellum promoted plant growth and nitrogen accumulation under saline stress. T. asperellum strengthened root nitrogen (N) absorption according to greater increased root NH4+ and NO3- influxes under supplement with TF than OF, while nitrogen assimilative enzymes such as nitrate reductase, nitrite reductase and glutamine synthetase activities in roots and leaves were also stimulated. Thus, the elevated N accumulation derived from the induction of T. asperellum on nitrogen absorption and assimilation. Greater increased photosynthetic rate (Pn) and photosynthetic N-use efficiency under supplement with TF than OF illustrated that T. asperellum enhanced photosynthetic capacity and N utilization under saline stress. Although increased leaf stomatal conductance contributed to carbon (C) isotope fractionation under TF supplement, leaf 13C abundance was significantly increased by supplement with TF rather than OF, indicating that T. asperellum raised CO2 assimilation to a greater extent, reducing C isotope preference. Trichoderma asperellum optimized electron transport at PSII donor and acceptor sides under saline stress because of lower K and J steps in chlorophyll fluorescence transients under supplement with TF than OF. The amount of PSII active reaction centers was also increased by T. asperellum. Thus, PSII performance was upgraded, consistent with greater heightened delayed chlorophyll fluorescence transients and I1 peak under supplement with TF than OF. In summary, TF acted to increase N nutrient acquisition and photosynthetic C fixation resulting in enhanced wolfberry growth under saline soil stress.

Influence of organism stimulation with bacterial lipopolysaccharide on nitric oxide production and metabolism in rat heart on the background of metabolic syndrome

Aim. The aim of the study was to establish the changes in nitric oxide production and metabolism in rat heart during combined influence of organism stimulation with bacterial lipopolysaccharide (LPS) and modeling of metabolic syndrome (MetS).
 Materials and methods. The study was conducted on 24 mature male Wistar rats weighing 200–260 g. Experiment lasted 60 days. The animals were divided into 4 groups of 6 animals each: control group, MetS group, LPS stimulation group, LPS + MetS group. MetS was reproduced by using a 20 % fructose solution as the only source of drinking water. LPS of Salmonella typhi was administered at a dose of 0.4 μg/kg intraperitoneally. Animals from LPS + MetS group received a 20 % fructose solution as the only source of drinking water and were administered LPS. In 10 % tissue homogenate of rat heart we studied: total activity of NO-synthases (NOS), activity of constitutive (cNOS) and inducible (iNOS) isoforms, activity of nitrate (NaR) and nitrite (NiR) reductases, concentration of peroxynitrites (ONOO-), nitrites, nitrosothiols and hydrogen sulfide.
 Results. Combination of MetS and stimulation of organism with LPS led to increase in total NOS activity by 32.72 % compared to control group. Activity of cNOS did not change compared to control group. Activity of iNOS increased by 33.76 %. Arginase activity decreased by 23.53 %. NaR activity and NiR activity were increased by 86.67 % and by 149.29 %, respectively. Combination of MetS and stimulation of organism with LPS led to decrease in nitrite and nitrosothiols concentration by 38.73 % and by 54.79 %, respectively. Under these conditions concentration of ONOOelevated by 398.0 % compared to control group. Concentration of H S decreased by 27.56 %.
 Conclusions. Combination of metabolic syndrome and stimulation of organism with bacterial lipopolysaccharide leads to prevalence of peroxynitrite formation during increased nitric oxide production NO-synthase-dependent and nitrate-nitrite-NO pathways in rat heart.

Using soil nitrogen amendments in mitigating ozone stress in agricultural crops: a case study of cluster beans.

The climate change scenario in the coming years is liable to have serious negative consequences on agricultural productivity. Increasing tropospheric ozone concentration is an important aspect of climate change, which, due to its oxidative nature, is injurious to the plants. Due to the multifarious nature and continuously increasing concentration of tropospheric ozone, it is prerequisite to develop strategies to manage ozone stress in plants. Present study not only evaluates the potential of soil nitrogen amendments in ameliorating ozone stress in plants, but also focuses upon the mechanistic approaches adopted by the different plant cultivars to combat ozone stress. Three doses of nitrogen amendments, recommended (N1), 1.5× recommended (N2) and 2× recommended (N3), were given to two cultivars (S-151 and PUSA-N) of Cymopsis tetragonoloba exposed to ambient ozone stress. Control plants were also maintained in which no nitrogen treatment was given. Nitrogen supplementation reduced the root nodulation frequency and leghaemoglobin content, which subsequently increased the cellular nitrogen metabolism as evident through increase in the activities of nitrate reductase and nitrite reductase in both the test cultivars. The positive effects of nitrogen amendments are clearly evident in the 1D protein profile studies which showed a greater accumulation of larger sub-units of RuBisCO in nitrogen amended plants. The results clearly indicate that N2 treatment effectively enhanced the yield of both the cultivars (84.8% and 76.37%, in S-151 and PUSA-N, respectively); however, the mechanistic approach adopted by the two cultivars was different. Whereas the yield quantity showed higher increments in S-151, the yield quality parameters (carbohydrates and nitrogen contents) responded more positively in PUSA-N.

LED red and blue light intensity affected productivity and nitrogen metabolisms of ryegrass

Light intensity plays a critical regulatory role in determining plant yield and quality, and energy consumption in plant factory with artificial light (PFAL). The effects of different light intensities (200, 300, 400, 500, and 600 µmol·m−2·s−1) of light-emitting diodes (LED) red and blue light with ratio 4:1 on growth, quality, nitrogen and amino acid metabolisms of ryegrass were investigated. The results showed the tiller number and shoot fresh weight in ryegrass were increased, while plant height and stem diameter remained stable with the improvement of light intensity. The highest levels of soluble protein, free amino acid, and DPPH free radical clearance rate in photon flux density (PPFD) at 500 µmol·m−2·s−1, and then significantly decreased with light intensity increased. The highest soluble sugar content was found at PPFD of 600 µmol·m−2·s−1, while malondialdehyde (MDA) content remained stable in all treatments. As the light intensity increased, nitrate content decreased, while nitrate reductase (NR) activity and the ammonium content increased. As light intensity was increased from 200 to 600 µmol·m−2·s−1, nitrite reductase (NiR) activity first decreased and then increased. Moreover, glutamate and cysteine contents increased first and then decreased, while glutamate synthase (GOGAT), glutamine synthase (GS), glutamate dehydrogenase (GDH), and cysteine synthases (CS) activities increased continuously with light intensity. Light intensity was significantly correlated with the parameters of growth, quality, nitrogen and amino acid metabolisms in ryegrass. It was recommended that PPFD at 400–500 µmol·m−2·s−1, photoperiod of 16 h/d was suitable for ryegrass high-efficient production in PFAL with relatively low energy cost.

Exogenous hydrogen sulphide alleviates senescence of postharvest pakchoi through regulating antioxidant system, endogenous hydrogen sulphide and nitric oxide metabolism

Previous studies showed that hydrogen sulphide (H2S) fumigation retarded the yellowing of detached pakchoi leaves. However, whether H2S regulated specific metabolic pathways and gene expression levels in this process remained unclear. In this study, the effect of H2S, DL-propargylglycine (PAG, H2S synthetic inhibitor) on antioxidant capacity, endogenous H2S synthesis, and endogenous NO synthesis in pakchoi was investigated. After H2S fumigation (40 L L−1, 6 h), the pakchoi stored at 20 °C ± 1 °C with 90–95% relative humidity exhibited the best quality, with the highest chlorophyll content and the lowest respiration rate and malondialdehyde content. Contrarily, PAG accelerated pakchoi senescence. H2S treatment reduced superoxide anion and hydrogen peroxide by increasing the activities of superoxide dismutase, catalase, ascorbate peroxidase, and peroxidase, partially up-regulating the expression of enzyme genes. The increased expression of BcLCD, BcDCD and BcCAS C1 activated L- and D-cysteine desulfhydrase activities so that more endogenous H2S were retained in the pakchoi. Meanwhile, H2S treatment increased cysteine content in pakchoi via up-regulating BcSAT5 expression and enhancing the activities of sulfite reductase and serine acetyltransferase. Moreover, H2S increased endogenous NO primarily by preserving the activities of nitrate reductase and nitrite reductase instead of NO synthase (NOS)-like activity and decreased nitrate and nitrite as well. Overall, exogenous H2S alleviated the senescence of postharvest pakchoi via positively regulating antioxidant system, endogenous H2S and NO metabolism. Moreover, this work described a putative regulatory mechanism and provided some relevant information for future research into the interaction of H2S and NO in this process.

Microbial induced calcium precipitation by Zobellella denitrificans sp. LX16 to simultaneously remove ammonia nitrogen, calcium, and chemical oxygen demand in reverse osmosis concentrates

In recent years, with the rapid development of industrial revolution and urbanization, the generation and treatment of a large number of salt-containing industrial wastewater has attracted wide attention. A novel salt-tolerant Zobellella denitrificans sp. LX16 with excellent nitrogen removal and biomineralization capabilities was isolated in this experiment. Kinetic experiments were conducted to determine the optimal condition. Under this condition, chemical oxygen demand (COD) can be entirely removed together with ammonia nitrogen, and the removal efficiency of calcium was 88.09%. Growth curves and nitrogen balance tests showed that strain LX16 not only had good HNAD and MICP capabilities, but also had high nitrite reductase and nitrate reductase activities during this process. Three-dimensional fluorescence results reflected that when external carbon sources were lacking or salinity was high, humic acid could effectively enhance the metabolic activity of heterotrophic nitrifying aerobic denitrifying microorganisms through extracellular electron transfer, and the substances produced in the metabolic process could promote biommineralization. Moreover, combined with SEM, SEM-EDS, XRD and FTIR analysis, it is concluded that the microbial surface can provide nucleation sites to form calcium salts, and with the increase of alkalinity to generate Ca5(PO4)3OH. The theoretical basis for the use of biological treatment in reverse osmosis wastewater have been proved by this experiment.

Incubation study on remediation of nitrate-contaminated soil by Chroococcus sp.

The possibility of using the non-nitrogen-fixing cyanobacterium (Chroococcus sp.) for the reduction of soil nitrate contamination was tested through Petri dish experiments. The application of 0.03, 0.05 and 0.08mg/cm2 Chroococcus sp. efficiently removed NO3--N from the soil through assimilation of nitrate nutrient and promotion of soil denitrification. At the optimal application dose of 0.05mg/cm2, 44.06%, 36.89% and 36.17% of NO3--N were removed at initial NO3--N concentrations of 60, 90 and 120mg/kg, respectively. The polysaccharides released by Chroococcus sp. acted as carbon sources for bacterial denitrification and facilitated the reduction of soil salinity, which significantly (p < 0.05) stimulated the growth of denitrifying bacteria (Hyphomicrobium denitrificans and Hyphomicrobium sp.) as well as significantly (p < 0.05) elevated the activities of nitrate reductase and nitrite reductase by 1.07-1.23 and 1.15-1.22 times, respectively. The application of Chroococcus sp. promoted the dominance of Nocardioides maradonensis in soil microbial community, which resulted in elevated phosphatase activity and increased available phosphorus content. The application of Chroococcus sp. positively regulated the growth of soil bacteria belonging to the genera Chitinophaga, Prevotella and Tumebacillus, which may contribute to increased soil fertility through the production of beneficial enzymes such as invertase, urease and catalase. To date, this is the first study verifying the remediation effect of non-nitrogen-fixing cyanobacteria on nitrate-contaminated soil.

Engineering neuroglobin nitrite reductase activity based on myoglobin models

Neuroglobin is a hemoprotein expressed in several nervous system cell lineages with yet unknown physiological functions. Neuroglobin presents a very similar structure to that of the related globins hemoglobin and myoglobin, but shows an hexacoordinate heme as compared to the pentacoordinated heme of myoglobin and hemoglobin. While several reactions of neuroglobin have been characterized in vitro, the relative importance of most of those reactions in vivo is yet undefined. Neuroglobin, like other heme proteins, can reduce nitrite to nitric oxide, providing a possible route to generate nitric oxide in vivo in low oxygen conditions. The reaction kinetics are highly dependent on the nature of the distal residue, and replacement of the distal histidine His64(E7) can increase the reaction rate constants by several orders of magnitude. However, mutation of other distal pocket positions such as Phe28(B10) or Val68(E11) has more limited impact on the rates. Computational analysis using myoglobin as template, guided by the structure of dedicated nitrite reductases like cytochrome cd1 nitrite reductase, has pointed out that combined mutations of the residues B10 and CD1 could increase the nitrite reductase activity of myoglobin, by mimicking the environment of the distal heme pocket in cytochrome cd1 nitrite reductase. As neuroglobin shows high sequence and structural homology with myoglobin, we hypothesized that such mutations (F28H and F42Y in neuroglobin) could also modify the nitrite reductase activity of neuroglobin. Here we study the effect of these mutations. Unfortunately, we do not observe in any case an increase in the nitrite reduction rates. Our results provide some further indications of nitrite reductase regulation in neuroglobin and highlight the minor but critical differences between the structure of penta- and hexacoordinate globins.

Responses of plant carbon and nitrogen assimilations to nitrogen addition in a subtropical forest: Canopy addition vs. understory addition

The global atmospheric nitrogen (N) deposition has intensified in recent years, resulting in a complex impact on forest ecosystems. This study investigated the effects of canopy (CAN) and understory additions of N (UAN) on leaf carbon (C) and N assimilations, as well as growth parameters of representative woody plant species in an evergreen broad-leaved forest, i.e. Castanea henryi, Schefflera heptaphylla, Blastus cochinchinensis, and Lasianthus chinensis. The results showed that leaf N assimilation key enzyme nitrate reductase (NR) activities of B. cochinchinensis and S. heptaphylla were significantly decreased by UAN, and were significantly decreased by CAN for C. henryi. CAN significantly decreased the nitrite reductase activity of C. henryi, while significantly increased that of L. chinensis. However, the Amax values of each woody species were not significantly different among control (CK), CAN, and UAN. Community surveys demonstrated that CAN and UAN inhibited the growth (diameter at breast height, height, or crown width) of the representative large tree, C. henryi, while promoting the growths of understory woody species (B. cochinchinensis and L. chinensis). Overall, N addition was found to change the physiological processes of N and C metabolisms of the dominant woody species in an evergreen broad-leaved forest. The community of subtropical evergreen broad-leaved forests may further decline and its C fixation capacity may be detrimentally changed under N deposition in the future.

Application fruit tree hole storage brick fertilizer is beneficial to increase the nitrogen utilization of grape under subsurface drip irrigation.

It is very important to promote plant growth and decrease the nitrogen leaching in soil, to improve nitrogen (N) utilization efficiency. In this experiment, we designed a new fertilization strategy, fruit tree hole storage brick (FTHSB) application under subsurface drip irrigation, to characterise the effects of FTHSB addition on N absorption and utilization in grapes. Three treatments were set in this study, including subsurface drip irrigation (CK) control, fruit tree hole storage brick A (T1) treatment, and fruit tree hole storage brick B (T2) treatment. Results showed that the pore number and size of FTHSB A were significantly higher than FTHSB B. Compared with CK, T1 and T2 treatments significantly increased the biomass of different organs of grape, N utilization and 15N content in the roots, stems and leaves, along with more prominent promotion at T1 treatment. When the soil depth was 15-30 cm, the FTHSB application significantly increased the soil 15N content. But when the soil depth was 30-45 cm, it reduced the soil 15N content greatly. T1 and T2 treatments obviously increased the activities of nitrite reductase (NR) and glutamine synthetase (GS) in grape leaves, also the urease activity(UR) in 30 cm of soil. Our findings suggest that FTHSB promoted plant N utilization by reducing N loss in soil and increasing the enzyme activity related to nitrogen metabolism. In addition, this study showed that FTHSB A application was more effective than FTHSB B in improving nitrogen utilization in grapes.

Natural mutations of human XDH promote the nitrite (NO2−)-reductase capacity of xanthine oxidoreductase: A novel mechanism to promote redox health?

Several rare genetic variations of human XDH have been shown to alter xanthine oxidoreductase (XOR) activity leading to impaired purine catabolism. However, XOR is a multi-functional enzyme that depending upon the environmental conditions also expresses oxidase activity leading to both O2·- and H2O2 and nitrite (NO2−) reductase activity leading to nitric oxide (·NO). Since these products express important, and often diametrically opposite, biological activity, consideration of the impact of XOR mutations in the context of each aspect of the biochemical activity of the enzyme is needed to determine the potential full impact of these variants. Herein, we show that known naturally occurring hXDH mutations do not have a uniform impact upon the biochemical activity of the enzyme in terms of uric acid (UA), reactive oxygen species (ROS) and nitric oxide ·NO formation. We show that the His1221Arg mutant, in the presence of xanthine, increases UA, O2·- and NO generation compared to the WT, whilst the Ile703Val increases UA and ·NO formation, but not O2·-. We speculate that this change in the balance of activity of the enzyme is likely to endow those carrying these mutations with a harmful or protective influence over health that may explain the current equipoise underlying the perceived importance of XDH mutations. We also show that, in presence of inorganic NO2−, XOR-driven O2·- production is substantially reduced. We suggest that targeting enzyme activity to enhance the NO2−-reductase profile in those carrying such mutations may provide novel therapeutic options, particularly in cardiovascular disease.

Reveal molecular mechanism on the effects of silver nanoparticles on nitrogen transformation and related functional microorganisms in an agricultural soil

Silver nanoparticles (AgNPs) are widely present in aquatic and soil environment, raising significant concerns about their impacts on creatures in ecosystem. While the toxicity of AgNPs on microorganisms has been reported, their effects on biogeochemical processes and specific functional microorganisms remain relatively unexplored. In this study, a 28-day microcosmic experiment was conducted to investigate the dose-dependent effects of AgNPs (10 mg and 100 mg Ag kg−1 soil) on nitrogen transformation and functional microorganisms in agricultural soils. The molecular mechanisms were uncovered by examining change in functional microorganisms and metabolic pathways. To enable comparison, the toxicity of positive control with an equivalent Ag+ dose from CH3COOAg was also included. The results indicated that both AgNPs and CH3COOAg enhanced nitrogen fixation and nitrification, corresponding to increased relative abundances of associated functional genes. However, they inhibited denitrification via downregulating nirS, nirK, and nosZ genes as well as reducing nitrate and nitrite reductase activities. In contrast to high dose of AgNPs, low levels increased bacterial diversity. AgNPs and CH3COOAg altered the activities of associated metabolic pathways, resulting in the enrichment of specific taxa that demonstrated tolerance to Ag. At genus level, AgNPs increased the relative abundances of nitrogen-fixing Microvirga and Bacillus by 0.02 %–629.39 % and 14.44 %–30.10 %, respectively, compared with control group (CK). The abundances of denitrifying bacteria, such as Rhodoplanes, Pseudomonas, and Micromonospora, decreased by 19.03 % to 32.55 %, 24.73 % to 50.05 %, and 15.66 % to 76.06 %, respectively, compared to CK. CH3COOAg reduced bacterial network complexity, diminished the symbiosis mode compared to AgNPs. The prediction of genes involved in metabolic pathways related to membrane transporter and cell motility showed sensitive to AgNPs exposure in the soil. Further studies involving metabolomics are necessary to reveal the essential effects of AgNPs and CH3COOAg on biogeochemical cycle of elements in agricultural soil.

Changes of Soil Nitrogen Fractions and nirS-Type Denitrifier Microbial Community in Response to N Fertilizer in the Semi-Arid Area of Northeast China

The denitrification process is one of the important processes in the soil nitrogen (N) cycle, and is closely related to the loss of soil N fertilizer. Five treatments were included in this study: N0 (control, no N application); N90 (N application rate 90 kg ha−1); N150 (N application rate 150 kg ha−1); N210 (N application rate 210 kg ha−1); and N270 (N application rate 270 kg ha−1), to study the effect of different N application rates on the soil nirS-type denitrifying bacterial community structure, the influence of key enzyme activities during the denitrification process, and the main environmental factors affecting the variation of the denitrifying bacterial community in maize field soil under the mulched fertigation system in the semi-arid region of Northeast China. The results showed that increasing N fertilizer application significantly increased the contents of soil inorganic N and acid-hydrolyzable organic N, but significantly decreased pH. N fertilizer significantly increased nitrate reductase (NAR) activity and nitrite reductase (NIR) activity. Excessive application of N fertilizer significantly increased the nirS gene copy numbers, and, at the same time, significantly decreased the diversity of nirS-type soil denitrifying bacteria. Proteobacteria was the dominant denitrifying phylum in all treatments, and N application promoted the growth of Bradyrhizobium belonging to this phylum. The application of N fertilizer significantly changed the community structure of nirS denitrifying bacteria, and the NO3−-N content was the most important factor for this observation. Soil organic matter (SOM) and non-hydrolyzable N (NHN) indirectly affected the denitrifying bacterial community structure through NAR activity and NIR activity, while soil total N (TN) and nitrate N (NO3−-N) indirectly affected yield through denitrifying bacterial community structure. Although increasing N fertilizer was beneficial in increasing soil nutrients, the community structure of nirS-type denitrifying bacteria changed significantly. This is attributed to the increase in soil NO3−-N accumulation caused by a large amount of N application. The results of this research provide an important scientific basis for further research on the response mechanism of farmland soil denitrifying microorganisms to different N fertilizer managements under the mulched fertigation system in the semi-arid region of Northeast China.

Responses of soil N-cycle enzyme activities to vegetation degradation in a wet meadow on the Qinghai-Tibet Plateau

Soil enzymes play a vital role in the functioning of wetland ecosystems, driving energy flow and material cycling processes. Gahai wet meadow, one of the important components of alpine wetlands on the Qinghai-Tibet Plateau, has suffered serious degradation in the last 30 years due to climate change and human activities. We studied the spatial and temporal heterogeneity of soil nitrogen content and nitrogen (N)-cycle enzyme activities (i.e., urease, protease, nitrate reductase and nitrite reductase) in four degraded wet meadows in the Gahai wetlands. Our results suggested that with increasing wet meadow degradation, there was a significant decrease in soil water content, total nitrogen, ammonium nitrogen, microbial biomass nitrogen content, protease activities, and nitrite reductase activities; Conversely, soil temperature, nitrate nitrogen content, urease activities, and nitrate reductase activities increased significantly. Soil urease, protease, and nitrite reductase activities significantly decreased with increasing soil depth;The highest activity levels of the three N-cycle enzymes were observed in July and August. The linear mixed modeling results indicated that there were significant effects of degradation level and soil depth and their interactions on soil nitrate reductase and nitrite reductase activities (p &amp;lt; 0.01), while soil depth had significant effects only on soil urease and protease activities (p &amp;lt; 0.01). Redundancy analyses showed that soil ammonium and nitrate nitrogen were the main drivers of changes in soil N-cycle enzyme activity during the degradation of wet meadows. In summary, our study sheds light on the processes of soil enzyme activity in an alpine wetland ecosystem and provides valuable information for understanding the N cycling in these complex systems.

Enhancement patterns of potassium on nitrogen transport and functional genes in cotton vary with nitrogen levels

The application of potassium (K) in conjunction with nitrogen (N) has been shown to enhance N use efficiency. However, there is still a need for further understanding of the optimal ratios and molecular regulatory mechanisms, particularly in soil-cotton systems. Here, a field trial was conducted, involving varying rates of N and K, alongside pot and hydroponic experiments. The objective was to assess the impact of N-K interaction on the absorption, transport and distribution of N in cotton. The results showed that K supply at 90 and 240 kg ha−1 had a beneficial impact on N uptake and distribution to both seed and lint, resulting in the highest N use efficiency ranging from 22% to 62% and yield improvements from 20% to 123%. The increase in stem and root diameters, rather than the quantify of xylem vessels and phloem sieve tubes, facilitated the uptake and transport of N due to the provision of K. At the molecular level, K supply upregulated the expression levels of genes encoding GhNRT2.1 transporter and GhSLAH3 channel in cotton roots to promote N uptake and GhNRT1.5/NPF7.3 genes to transport N to shoot under low-N conditions. However, under high-N conditions, K supply induced anion channel genes (GhSLAH4) of roots to promote N uptake and genes encoding GhNRT1.5/NPF7.3 and GhNRT1.8/NPF7.2 transporters to facilitate NO3- unloading from xylem to mesophyll cell in high-N plants. Furthermore, K supply resulted in the upregulation of gene expression for GhGS2 in leaves, while simultaneously downregulating the expression of GhNADH-GOGAT, GhGDH1 and GhGDH3 genes in high-N roots. The enzyme activities of nitrite reductase and glutamine synthetase increased and glutamate dehydrogenase decreased, but the concentration of NO3- and soluble protein exhibited a significant increase and free amino acid decreased in the shoots subsequent to K supply.

Improvement of soil acidification and ammonium nitrogen content in tea plantation by long-term use of organic fertilizer.

Soil acidification was common in Chinese tea plantations, which seriously affected the growth of tea trees, and it was of great significance to explore soil remediation in acidified tea plantations for the sustainable development of tea industry. We sought to determine how different fertilizers improve acidified soil and their nitrogen transformation in tea plantation. Different fertilizers were used to treat acidified soils in tea plantations for 4 consecutive years from 2017 to 2021, and the changes in soil pH, indexes related to soil nitrogen transformation and tea yield were analyzed to construct interaction networks of the above indexes and obtain the indexes with the greatest influence on the fertilization effect. Long-term use of sheep manure fertilizer in tea plantation improved soil acidification, increased the soil pH value, enhanced the number and intensity of nitrogen-fixing bacteria and ammonifying bacteria, urease, protease, asparaginase and N-acetamide glucose ribosidase activities, nifH gene expression, reduced the number and intensity of soil nitrifying bacteria and denitrifying bacteria, nitrate reductase and nitrite reductase activities, and the expressions of amoA-AOA, nirK, nirS, narG and nosZ genes, which in turn increased ammonium nitrogen content of the soil, reduced nitrate nitrogen content, and enhanced tea yield. Topsis index weight analysis showed that ammonium nitrogen content in soil had the greatest impact on the fertilization effect. Long-term use of sheep manure fertilizer was beneficial to restore the balance of micro-ecosystem of acidified soil. This study provided an important practical basis for soil remediation and fertilizer management in acidified tea plantation soils.

Metagenomics and proteomics profiling of extracellular polymeric substances from municipal waste sludge and their application for soil and water bioremediation

This study assessed the components of anaerobically digested sludge, activated sludge, and microbial and extracellular polymeric substance (EPS) enzymes to identify the mechanisms underlying nitrogen removal and soil regeneration. 16S rRNA gene amplicon-based sequencing was used to determine the microbial community composition and the related National Center for Biotechnology Information (NCBI) protein database was used to construct a conventional library from the observed community. EPS components were identified using gel-free proteomic (Liquid Chromatography with tandem mass spectrometry-LC/MS/MS) methods. Alginate-like EPS from aerobically activated sludge have strong potential for soil aggregation and water-holding capacity, whereas total EPS from anaerobic sludge have significant potential for ammonia removal under salt stress. Fourier transform infrared spectroscopy (FTIR) revealed that both EPS may contain proteins, carbohydrates, humic compounds, uronic acid, and DNA and determined the presence of O–H, N–H, C–N, CO, and C–H functional groups. These results demonstrate that the overall enzyme activity may be inactivated at 30 g L-1 of salinity. An annotation found in Kyoto Encyclopedia of Genes and Genomes (KEGG)- KEGG Automatic Annotation Server (KAAS) revealed that the top two metabolic activities in the EPS generated from the anaerobic sludge were methane and nitrogen metabolism. Therefore, we focused on the nitrogen metabolism reference map 00910. EPS from the anaerobically digested sludge exhibited nitrate reductase, nitrite reductase, and dehydrogenase activities. Assimilatory nitrate reduction, denitrification, nitrification, and anammox removed ammonia biochemically. The influence of microbial extracellular metabolites on water-holding capacity and soil aggregation was also investigated. The KAAS-KEGG annotation server was used to identify the main enzymes in the activated sludge-derived alginate-like extracellular EPS (ALE-EPS) samples. These include hydrolases, oxidoreductases, lyases, ligases, and transporters, which contribute to soil fertility and stability. This study improves our understanding of the overall microbial community structure and the associated biochemical processes, which are related to distinct functional genes or enzymes involved in nitrogen removal and soil aggregation. In contrast to conventional methods, microbial association with proteomics can be used to investigate ecological relationships, establishments, key player species, and microbial responses to environmental changes. Linking the metagenome to off-gel proteomics and bioinformatics solves the problem of analyzing metabolic pathways in complex environmental samples in a cost-effective manner.

Effects of low nitrogen supply on biochemical and physiological parameters related to nitrate and water, involving nitrate transporters and aquaporins in Citrus macrophylla.

A reduction in chemical N-based fertillizer was investigated in Citrus plants. As N and water uptake are connected, the relationship between the physiological response to reductions in N was studied in relation to N metabolism and water. We examined the response of new and mature leaves and roots of Citrus macrophylla, grown under controlled conditions, and given different concentrations of N: 16, 8 or 4 mM. Differences in growth and development were determined for biochemical (mineral content, photosynthetic pigments, proteins and nitrate and nitrite reductase activity), physiological (photosynthesis and transpiration), and molecular (relative expression of nitrate transporters and aquaporins) parameters. Only plants given 4 mM N showed a reduction in growth. Although there were changes in NR activity, protein synthesis, and chlorophyll content in both 8 and 4 mM N plants that were highly related to aquaporin and nitrate transporter expression. The results revealed new findings on the relationship between aquaporins and nitrate transporters in new leaves of Citrus, suggesting a mechanism for ensuring growth under low N when new tissues are being formed.

Effects of UV-B Radiation on the Chemical Composition of Azolla and Its Decomposition after Returning to the Field and Nitrogen Transformation in Soil

In the present research, the effects of UV-B radiation (5.00 kJ·m−2) on the chemical composition of Azolla were investigated, and the decomposition of Azolla residues after UV-B radiation, the nitrogen form, enzyme activity, and bacterial community in paddy soil were analyzed. Compared to the natural light treatment, the total nitrogen content of Azolla was significantly increased by 17.0% under UV-B radiation treatment. Compared to returned Azolla grown under natural light, the decomposition rate of cellulose, lignin, and total nitrogen of returned Azolla grown under UV-B radiation significantly increased, which led to an increase in the activities of nitrogen transformation enzymes, including neutral protease, ammonia monooxygenase, nitrogenase, nitrate reductase, and nitrite reductase, and the contents of different nitrogen forms (NH4+-N, NO3−-N, soluble organic nitrogen, and microbial biomass nitrogen) in paddy soil, while N2O emission flux was significantly reduced by 20–30%. The dominant bacteria in soil supplied with Azolla grown under natural light were Firmicutes, Clostridia, Clostridiales, and Lachnospiraceae. However, returning Azolla grown under UV-B radiation to the soil significantly changed the bacterial community structure in soil, resulting in a decrease in the number of ammonifying bacteria, nitrifying bacteria, and nitrogen-fixing bacteria and an increase in the number of denitrifying bacteria, inducing changes in the dominant bacteria to Methanomicrobiales, Methanoregulaceae, and Methanoregula. According to the structural equation model, returning Azolla to the field would reduce N2O emissions by increasing Azolla lignin decomposition and ammonia monooxygenase activity, reducing the number of nitrifying bacteria and reducing nitrite reductase activity in soil. Thus, UV-B radiation can directly change the phytochemical components and their decomposition in soil, thus indirectly affecting the bacterial community structure, enzyme activity, and nitrogen transformation, which play important ecological roles in regulating the nutrient transformation of terrestrial ecosystems.

The effect of silver nanoparticles on aerobic denitrifying bacteria during biological nitrogen removal: A new perspective based on morphological effects

The morphological effect-dependent biotoxicity of silver nanoparticles (AgNPs) toward aerobic denitrifying bacteria is unclear. In this study, the behavior and biotoxicity of spherical and flaky AgNPs on aerobic denitrifier Pseudomonas stutzeri were investigated based on morphological effects. The three-dimensional fractal dimension of flaky AgNPs with a rough surface and complex structure was 2.73, which was higher than that of spherical AgNPs. Flaky AgNPs more significantly inhibited the growth and nitrogen removal of P. stutzeri than spherical AgNPs, with average inhibition rates of 50.4% and 76.4%, respectively. Flaky AgNPs resulted in higher secretion of extracellular polymeric substances, lower activity of electron transport system and higher concentrations of reactive oxygen species and lactate dehydrogenase in P. stutzeri than spherical AgNPs, indicating that flaky AgNPs displayed stronger inhibitory effects on P. stutzeri. The results of flow cytometry and scanning electron microscopy revealed that flaky AgNPs caused more damage to the cell surface of P. stutzeri, resulting in a higher proportion of cell death. Furthermore, flaky AgNPs more significantly inhibited the expression of napAB and nirS in P. stutzeri than spherical AgNPs, up to 67.7%, resulting in lower nitrate and nitrite reductase activities and worse nitrogen removal efficiency. The results of this study can elucidate the morphology-dependent toxicity of AgNPs and provide new insights into the negative impacts of AgNPs on aerobic denitrification wastewater treatment.