Nitrogen Stress Research Articles

Regulation of potential denitrification rates in sediments by microbial-driven elemental coupled metabolisms

Microbial driven coupled processes between denitrification and methane/sulfur metabolism play a very substantial role in accelerating nitrogen removal in river sediments. Until now, little is known about how element coupling processes alter nitrogen metabolism by the microbial functional communities. The primary objective of this research was to clarify the contributory role of microbial-mediated coupled processes in controlling denitrification. Specifically, the study sought to identify the key bioindicators (or metabolic pathway) for preferably regulating and predicting potential denitrification rate (PDR). Here, a total of 40 sediment samples were collected from the inflow rivers of Chaohu Lake under nitrogen stress. The results revealed the ecological importance of methanogens and sulfate reducing bacteria in the microbial interaction network. Correlations between quantitative or predicted genes showed that the methanogenic gene (mcrA) was synergistic with denitrifying genes, further unraveling that the key role of methanogenesis in denitrification process for facilitating nitrogen removal. The PDR of sediments ranged from 0.03 to 133.21 μg N·g−1·h−1. The study uncovered specific environmental factors (NH4+ and OM) and microbial indicators (nosZ, mcrA, Paracoccus, Thauera, Methanobrevibacter and Desulfomicrobium) as potential contributors to the variations in PDR. Structural Equation Model (SEM) analysis revealed a significant direct effect of NH4+ on PDR, evidenced by a standardized coefficient (λ) of 0.77 (P < 0.001). Additionally, the findings also emphasized the salient role of methanogens (Methanobrevibacter) and methanogenic gene (mcrA) in indicating PDR. The research's aforementioned findings shed light on the substantial consequences of methanogenesis on nitrogen metabolism in coupled processes, enabling improved control of nitrogen pollution in river sediments. This study provided fresh perspectives on the effects of multiple functional taxa on denitrification, and reinforces the significance of coupling processes for nitrogen removal.

Genetic regions determine tolerance to nitrogen deficiency in European elite bread wheats grown under contrasting nitrogen stress scenarios.

Clustering 24 environments in four contrasting nitrogen stress scenarios enabled the detection of genetic regions determining tolerance to nitrogen deficiency in European elite bread wheats. Increasing the nitrogen use efficiency of wheat varieties is an important goal for breeding. However, most genetic studies of wheat grown at different nitrogen levels in the field report significant interactions with the genotype. The chromosomal regions possibly involved in these interactions are largely unknown. The objective of this study was to quantify the response of elite bread wheat cultivars to different nitrogen field stress scenarios and identify genomic regions involved in this response. For this purpose, 212 elite bread wheat varieties were grown in a multi-environment trial at different nitrogen levels. Genomic regions associated with grain yield, protein concentration and grain protein deviation responses to nitrogen deficiency were identified. Environments were clustered according to adjusted means for grain yield, yield components and grain protein concentration. Four nitrogen availability scenarios were identified: optimal condition, moderate early deficiency, severe late deficiency, and severe continuous deficiency. A large range of tolerance to nitrogen deficiency was observed among varieties, which were ranked differently in different nitrogen deficiency scenarios. The well-known negative correlation between grain yield and grain protein concentration also existed between their respective tolerance indices. Interestingly, the tolerance indices for grain yield and grain protein deviation were either null or weakly positive meaning that breeding for the two traits should be less difficult than expected. Twenty-two QTL regions were identified for the tolerance indices. By selecting associated markers, these regions may be selected separately or combined to improve the tolerance to N deficiency within a breeding programme.

Root-Knot-Nematode-Encoded CEPs Increase Nitrogen Assimilation.

C-terminally encoded peptides (CEPs) are plant developmental signals that regulate growth and adaptive responses to nitrogen stress conditions. These small signal peptides are common to all vascular plants, and intriguingly have been characterized in some plant parasitic nematodes. Here, we sought to discover the breadth of root-knot nematode (RKN)-encoded CEP-like peptides and define the potential roles of these signals in the plant-nematode interaction, focusing on peptide activity altering plant root phenotypes and nitrogen uptake and assimilation. A comprehensive bioinformatic screen identified 61 CEP-like sequences encoded within the genomes of six root-knot nematode (RKN; Meloidogyne spp.) species. Exogenous application of an RKN CEP-like peptide altered A. thaliana and M. truncatula root phenotypes including reduced lateral root number in M. truncatula and inhibited primary root length in A. thaliana. To define the role of RKN CEP-like peptides, we applied exogenous RKN CEP and demonstrated increases in plant nitrogen uptake through the upregulation of nitrate transporter gene expression in roots and increased 15N/14N in nematode-formed root galls. Further, we also identified enhanced nematode metabolic processes following CEP application. These results support a model of parasite-induced changes in host metabolism and inform endogenous pathways to regulate plant nitrogen assimilation.

A comparative analysis of root traits in diverse wheat seedlings screened under optimum and low nitrogen stress in hydroponics

A comparative analysis of root traits in diverse wheat seedlings screened under optimum and low nitrogen stress in hydroponics

Evaluating the Antioxidant Properties of the Leaves and Stems of Alpinia oxyphylla In Vitro and Its Growth-Promoting, Muscle Composition Change, and Antioxidative Stress Function on Juvenile Litopenaeus vannamei.

Alpinia oxyphylla is a homology of medicine and food. This study aims to investigate the dominant chemical composition and explore the antioxidant properties of the ethanol extract of the leaves and stems of A. oxyphylla (AOE) on juvenile shrimp, Litopenaeus vannamei. An in vitro test showed that AOE and its dominant chemical composition procyanidin B-2 (1) and epicatechin (2) presented DPPH and ABTS radical scavenging activities. A shrimp feeding supplement experiment revealed that shrimp growth parameters and muscle composition were improved significantly when fed with a 200 mg/Kg AOE additive. Meanwhile, the activities of antioxidant enzymes (CAT, GSH-Px, SOD, and T-AOC) in serum and the liver and the expression of related genes (LvMn-SOD, LvCAT, LvproPo, and LvGSH-Px) were enhanced with various degrees in different AOE additive groups while the content of MDA was significantly decreased. Moreover, the antioxidative effect of AOE additive groups on shrimp was also observed in an acute ammonia nitrogen stress test.

QTL mapping and transcriptome analysis identify candidate genes influencing water–nitrogen interaction in maize

Water and nitrogen fertilization are the key factors limiting maize productivity. The genetic basis of interactions between maize genotype, water, and nitrogen is unclear. A recombinant inbred line (RIL) maize population was evaluated for seven yield and five agronomic traits under four water and nitrogen conditions: water stress and low nitrogen, water stress and high nitrogen, well-watered and low nitrogen, and well-watered and high nitrogen. Respectively eight, six, and six traits varied in response to genotype–water interactions, genotype–nitrogen interactions, and genotype–water–nitrogen interactions. Using a linkage map consisting of 896 single-nucleotide polymorphism markers and multiple-environmental quantitative-trait locus (QTL) mapping, we identified 31 QTL, including 12 for genotype–water–nitrogen interaction, across the four treatments. A set of 8060 genes were differentially expressed among treatments. Integrating genetic analysis, gene co-expression, and functional annotation revealed two candidate genes controlling genotype–water–nitrogen interactions, affecting both leaf width and grain yield. Genes involved in abscisic acid biosynthesis and bZIP, NAC, and WRKY transcription factors participated in maize response to water and nitrogen conditions. These results represent a step toward understanding the genetic regulatory network of maize that responds to water and nitrogen stress and provide a theoretical basis for the genetic improvement of both water- and nitrogen-use efficiency.

Ammonia nitrogen stress damages the intestinal mucosal barrier of yellow catfish (Pelteobagrus fulvidraco) and induces intestinal inflammation.

Nitrogen from ammonia is one of the most common pollutants toxics to aquatic species in aquatic environment. The intestinal mucosa is one of the key mucosal defenses of aquatic species, and the accumulation of ammonia nitrogen in water environment will cause irreversible damage to intestinal function. In this study, histology, immunohistochemistry, ultrastructural pathology, enzyme activity analysis and qRT-PCR were performed to reveal the toxic effect of ammonia nitrogen stress on the intestine of Pelteobagrus fulvidraco. According to histological findings, ammonia nitrogen stress caused structural damage to the intestine and reduced the number of mucous cells. Enzyme activity analysis revealed that the activity of bactericidal substances (Lysozyme, alkaline phosphatase, and ACP) had decreased. The ultrastructure revealed sparse and shortened microvilli as well as badly degraded tight junctions. Immunohistochemistry for ZO-1 demonstrated an impaired intestinal mucosal barrier. Furthermore, qRT-PCR revealed that tight junction related genes (ZO-1, Occludin, Claudin-1) were downregulated, while the pore-forming protein Claudin-2 was upregulated. Furthermore, as ammonia nitrogen concentration grew, so did the positive signal of Zap-70 (T/NK cell) and the expression of inflammation-related genes (TNF, IL-1β, IL-8, IL-10). In light of the above findings, we conclude that ammonia nitrogen stress damages intestinal mucosal barrier of Pelteobagrus fulvidraco and induces intestinal inflammation.

Intelligent detection and behavior tracking under ammonia nitrogen stress

In this paper, a novel YOLO-based detection model with deformable convolution network (DCN-YOLOv5) is developed, which is concerned with the object and key points detection and behavior tracking problem for Oplegnathus punctatus in the ammonia nitrogen environment. The proposed model can adapt to the posture change of the object by deforming the receptive field, which solves the problem of false and missed detection caused by the movement and occlusion. Moreover, a new multi-object multi-category tracking algorithm (MOMC-Tracking) is proposed to track and plot the trajectory and calculate the key behavioral characteristics parameters. In addition, an executable software which integrates the proposed DCN-YOLOv5 model and the MOMC-Tracking algorithm is proposed. Extensive experiments show that compared with the typical YOLO series of algorithms, the proposed model in this paper performs the best with the highest accuracy and the fastest convergence speed, where the mAP@0.5 and mAP@0.5:0.95 of the proposed DCN-YOLOv5 model are 93.71% and 57.45%, which are respectively improved by 1.78% and 24.77% as compared with those obtained by the original YOLOv5 model.

Nitrogen removal characteristics of anammox biofilm and analyses of the dynamic network structure of functional microbes under gradient nitrogen stress

The universal porous gel/vertical fixed bed-anaerobic ammonia oxidation (UPG/VFB-A) is a complex efficient denitrification symbiotic system of microorganisms for leachate. However, the different gradient nitrogen loading lead to dynamic correlation and difference in biofilm formation remain unclear. Therefore, the UPG/VFB-A was operated for 300 days under gradient total nitrogen loading rate (TNLR) conditions, and its biofilm biomass characteristics, bacterial population succession and functional denitrification gene dynamic network were investigated to achieve strong impact resistance and recovery of the reactor for landfill leachate. The results showed that the total nitrogen removal efficiency (TNRE) was 92.4 ± 2.7% and the nitrogen removal (NR) up to 487.0 ± 20.5 mg/L. The system was highly resistant and resilient to high concentrations of FA (11.68 mg/L) and FNA (0.0467 mg/L) with total nitrogen removal rate (TNRR) up to 1.12 kg/m3/d. Candidatus Kuenenia (from 0.09% to 17.2%) with high tolerance to FA and FNA was superior to Candidatus Brocadia (from 9.7% to 4.7%) as the main AnAOB. Meanwhile, the gradient nitrogen had a significant effect on the abundance of genes related to nitrogen conversion, and the relative abundance of typical anammox genes hzs and hdh was highest at a feedwater load of 1.34 kg/m3/d, reaching 20.7% and 16.5%, respectively. This study can provide guidance for anammox treatment of landfill leachate in practical engineering.

Large latitudinal difference in soil nitrogen limitation on global vegetation response to elevated CO2

This study is the first to evaluate latitudinal characteristics of the coupled impacts of atmospheric-CO2 fertilization and soil nitrogen limitation on global plant photosynthesis for 2001–2019 by using a remote sensing-based light use efficiency model (DTECM-l-CN). It predicted that the global GPP should have increased by 0.40 Pg C a − 2 (PMK < 0.001) from 2001 to 2019. Leaf area index change contributed 55.0% to this predicted increase in the global GPP trend, followed by coupled CO2 and soil nitrogen effects (32.5%) and the effects from the climate forcing (12.5%). Without CO2 fertilization effects, the global GPP trend was predicted lower by 32.5%. With CO2 fertilization effects included but without a nitrogen constraint, the model would predict global GPP trend higher by 67.5%. These contrasting changes strongly imply the need to consider all these effects simultaneously to estimate future GPP. Comparing the annual mean CO2 fertilization factor with and without soil nitrogen stress showed that the fertilization factor under soil nitrogen stress was only 62.5% of that with no soil nitrogen stress.As a result of soil nitrogen stress, annual mean CO2 response metric (RCO2), indicating the CO2 fertilization effect, declined from 2002 to 2019. Soil nitrogen stress was found to attenuate the positive effect of CO2 fertilization on GPP trend with a large latitudinal difference, i.e., the tropics had a weaker CO2 fertilization effect than the extratropics. This study highlights that soil nitrogen has progressively become limiting on plant response to CO2 fertilization with a large latitudinal divergence.

Investigating the dynamic responses of Aegilops tauschii Coss. to salinity, drought, and nitrogen stress: a comprehensive study of competitive growth and biochemical and molecular pathways.

Aegilops tauschii (Coss.) is a highly deleterious, rapidly proliferating weed within the wheat, and its DD genome composition exhibits adaptability toward diverse abiotic stresses and demonstrates heightened efficacy in nutrient utilization. Current study investigated different variegated impacts of distinct nitrogen concentrations with varied plant densities, scrutinizing the behavior of Ae. tauschii under various salinity and drought stress levels through multiple physiological, biochemical, and molecular pathways. Different physiological parameters attaining high growth with different plant density and different nitrogen availability levels increased Ae. tauschii dominancy. Conversely, under the duress of salinity and drought, Ae. tauschii showcased an enhanced performance through a comprehensive array of physiological and biochemical parameters, including catalase, peroxidase, malondialdehyde, and proline content. Notably, salinity-associated traits such as sodium, potassium, and the sodium-potassium ratio exhibited significant variations and demonstrated remarkable tolerance capabilities. In the domain of molecular pathways, the HKT and DREB genes have displayed a remarkable upregulation, showcasing a comparatively elevated expression profile in reaction to different levels of salinity and drought-induced stress. Without a doubt, this information will make a substantial contribution to the understanding of the fundamental behavioral tendencies and the efficiency of nutrient utilization in Ae. tauschii. Moreover, it will offer innovative viewpoints for integrated management, thereby enabling the enhancement of strategies for adept control and alleviation.

Different genotypes of tartary buckwheat can regulate the transformation of nitrogen through the secretion of organic acids under low nitrogen stress

Roots respond to nitrogen deficiency by altering their physiological and metabolic responses. Soil nitrogen invertase activity and the diversity of nitrifying microorganisms (AOA and AOB) significantly affect the nitrogen cycle in soil. As an important part of root exudates, organic acids can reflect the dynamic changes of plant roots in soil. However, it is not clear how the barren-tolerant genotype plant varieties show their stress resistance through organic acids regulating nitrogen transformation under low nitrogen environment. Here, we selected two Tartary buckwheat varieties: HeiFeng1 (HF, low nitrogen sensitive cultivar) and DiQing (DQ, low nitrogen tolerance cultivar) for a two-year experiment. The urea addition levels of 0, 80, and 160 mg kg−1 soil were respectively set as nitrogen sources, and ozone sterilization experiments were designed to completely remove microbial effects to distinguish the contribution of plant roots and microorganisms to nitrogen invertase and organic acids (400 ml 1 mol L−1 ozone water daily, 0 nitrogen fertilizer, O3). The results showed that malic acid and tartaric acid were the main organic acids secreted by tartary buckwheat. The total amount and richness of organic acids in Diqing were higher than those in Heifeng, and organic acids directly affected the diversity of ammonia-oxidizing microorganisms (AOA and AOB), changed the soil environment by affecting soil water content, and indirectly affected the activity of nitrogen invertase. At the same time, it was found that the increase of nitrogen application rate would increase the proportion of key bacteria such as Nirtrosomonas and Nitrosospira in AOB of tartary buckwheat soil. Finally, Diqing tartary buckwheat was proved to be more suitable for planting in the nitrogen-deficient Loess Plateau, but attention should be paid to the negative effects of AOB and organic acids.

Comparison of Various Nitrogen and Water Dual Stress Effects for Predicting Relative Water Content and Nitrogen Content in Maize Plants through Hyperspectral Imaging

Water and nitrogen (N) are major factors in plant growth and agricultural production. However, these are often confounded and produce overlapping symptoms of plant stress. The objective of this study is to verify whether the different levels of N treatment influence water status prediction and vice versa with hyperspectral modeling. We cultivated 108 maize plants in a greenhouse under three-level N treatments in combination with three-level water treatments. Hyperspectral images were collected from those plants, then Relative Water Content (RWC), as well as N content, was measured as ground truth. A Partial Least Squares (PLS) regression analysis was used to build prediction models for RWC and N content. Then, their accuracy and robustness were compared according to the different N treatment datasets and different water treatment datasets, respectively. The results demonstrated that the PLS prediction for RWC using hyperspectral data was impacted by N stress difference (Ratio of Performance to Deviation; RPD from 0.87 to 2.27). Furthermore, the dataset with water and N dual stresses improved model accuracy and robustness (RPD from 1.69 to 2.64). Conversely, the PLS prediction for N content was found to be robust against water stress difference (RPD from 2.33 to 3.06). In conclusion, we suggest that water and N dual treatments can be helpful in building models with wide applicability and high accuracy for evaluating plant water status such as RWC.

Remodeling of the 3D chromatin architecture in the marine microalga Nannochloropsis oceanica during lipid accumulation

BackgroundGenomic three-dimensional (3D) spatial organization plays a key role in shaping gene expression and associated chromatin modification, and it is highly sensitive to environmental stress conditions. In microalgae, exposure to nitrogen stress can drive lipid accumulation, yet the associated functional alterations in the spatial organization of the microalgal genome have yet to be effectively characterized.ResultsAccordingly, the present study employed RNA-seq, Hi-C, and ChIP-seq approaches to explore the relationship between 3D chromosomal architecture and gene expression during lipid accumulation in the marine microalga Nannochloropsis oceanica in response to nitrogen deprivation (ND). These analyses revealed that ND resulted in various changes in chromosomal organization, including A/B compartment transitions, topologically associating domain (TAD) shifts, and the disruption of short-range interactions. Significantly higher levels of gene expression were evident in A compartments and TAD boundary regions relative to B compartments and TAD interior regions, consistent with observed histone modification enrichment in these areas. ND-induced differentially expressed genes (DEGs) were notably enriched in altered TAD-associated regions and regions exhibiting differential genomic contact. These DEGs were subjected to Gene Ontology (GO) term analyses that indicated they were enriched in the ‘fatty acid metabolism’, ‘response to stress’, ‘carbon fixation’ and ‘photosynthesis’ functional categories, in line with the ND treatment conditions used to conduct this study. These data indicate that Nannochloropsis cells exhibit a clear association between chromatin organization and transcriptional activity under nitrogen stress conditions. Pronounced and extensive histone modifications were evident in response to ND. Observed changes in chromatin architecture were linked to shifts in histone modifications and gene expression.ConclusionsOverall, the reprogramming of many lipid metabolism-associated genes was evident under nitrogen stress conditions with respect to both histone modifications and chromosomal organization. Together these results revealed that higher-order chromatin architecture represents a new layer that can guide efforts to understand the transcriptional regulation of lipid metabolism in nitrogen-deprived microalgae.

Mechanisms governing the impact of nitrogen stress on the formation of secondary metabolites in Artemisia argyi leaves

Nitrogen is a key factor in various physiological and metabolic processes in plants. Providing an adequate supply of nitrogen is essential for improving the total yield and quality of the medicinal plant Artemisia argyi (A. argyi), but the underlying mechanisms of how this nutrient alters the crop remains unclear. In this study, we conducted a series of pot experiments to investigate the agronomic traits and active components in the leaves of A. argyi plants under low and high nitrogen stress. Additionally, we used transcriptome analysis and RT-qPCR to explore the molecular pathways associated with nitrogen stress. Our results demonstrate a dramatic increase in the accumulation of phenolic acids and flavonoids in the low nitrogen (LN) stress group compared to the control (CK), with increases of 40.00% and 79.49%, respectively. Interestingly, plants in the high nitrogen (HN) stress group exhibited enhanced plant growth with larger leaves, thicker stems, and a 3% increase in volatile oil content compared to the CK. Moreover, A. argyi in the HN group displayed a 66% increase in volatile oil concentration compared to the LN group. Our combined transcriptome and q-PCR results indicate that LN stress promotes the expression of genes involved in flavonoid synthesis, while HN stress promotes the expression of genes related to terpene skeleton production and photosynthesis. Taken together, these findings suggest that different gene expression levels under LN and HN stress contribute to the photosynthesis capacity and the accumulation of active ingredients in A. argyi leaves. Our results elucidate the physiological and molecular mechanisms of nitrogen stress on A. argyi secondary metabolites and guide fertilization strategies for plant cultivation.

Effects of nitrogen stress on uptake and translocation of organophosphate esters by watermifoil (Myriophyllum aquaticum L.) in an aquatic ecosystem.

Although organophosphate esters (OPEs) and nitrogen (N) are normally present in aquatic environments, the effects of the plant uptake, accumulation, and translocation of OPEs in different levels of N remain ambiguous. To better understand these processes, watermifoil (Myriophyllum aquaticum L.) as tested plant was chosen to investigate the effects of different N levels on the uptake and translocation of OPEs by plants in matched water-sediment-plant samples. After two months, we found the root-water concentration factors, root-sediment concentration factors, and translocation factors (TFs) were significantly changed with the levels of N (p < 0.05), implying that the presence of N could alter uptake, accumulation, and translocation of OPEs in M. aquaticum, particularly the process of root absorption. Low concentrations of N could remarkably promote the uptake of OPEs by M. aquaticum. However, when the concentrations of N in water were higher than 200 mg/L, the plants' growth and OPE accumulation by M. aquaticum were obviously inhibited with the elevated N contents. Moreover, the enrichment and environmental transport of OPEs in M. aquaticum seemed to be closely associated with physicochemical parameters; the octanol-water partition coefficient had significant relationships with measured organic carbon-normalized sediment-water partition coefficients and TFs in the present study. Additionally, the substituents and structures of OPEs could also affect the accumulation and translocation of OPEs in M. aquaticum, including the chlorination degree and alkyl chain length. This study could improve our understanding of uptake and translocation of OPEs in aquatic plants under different levels of N.

Cooperative adaptation strategies of different tissues in blunt snout bream (Megalobrama amblycephala) juvenile to acute ammonia nitrogen stress.

Ammonia-nitrogen is a common stress factor for aquatic organisms in their habitation environment, which is enriched in water due to high-density farming and environmental pollution. Ammonia nitrogen can enter fish body through gill, epidermis, digestive tract, and other tissues, causing fish ammonia poisoning. In the present study, juvenile blunt snout bream (average weight, 45 ± 5g) were exposed to high concentrations of ammonia-nitrogen stress (25.0 ± 0.5mg/L) for six different treatment times (0, 3, 6, 12, 24, 48, and 72h); the tissue ultrastructure, mRNA levels of antioxidation system, and apoptosis patterns were studied. The antioxidant systems of malondialdehyde (MDA), catalase (CAT), acid phosphatase (ACP), and reduced glutathione (GSH) in various tissues were highly transcripted at 6 or 12h (hpt) after treatment under high ammonia-nitrogen, which may play a role in preventing cells from being attacked by highly toxic reactive oxygen species (ROS). After 24 hpt, the antioxidant capacity threshold is breached, followed by the decline of antioxidant enzyme activity. Thus, with the prolonging of high ammonia-nitrogen processing time, ammonia-nitrogen stress caused irreversible damage of organs (gill, liver, and kidney). Furthermore, the expression of caspase-3 apoptotic pathway was highly induced in different tissues, implying the apoptotic system is activated, which causes extensive cell apoptosis in different tissues as shown using TUNEL analysis. In conclusion, we observed that, in response to acute ammonia-nitrogen stress, blunt snout bream enhances antioxidant capacity and cell apoptosis.

Quantifying water productivity and nitrogen uptake of maize under water and nitrogen stress in arid Northwest China

Water and nitrogen (N) are critical determinants of crop water productivity (WP) and N uptake (Nuptake), and are also key factors in crop modelling. Through a two-year field experiment with three irrigation levels (full irrigation (W1), moderate water stress (W0.75), and severe water stress (W0.5)), three N application rates (150, 75, and 0 kg N ha−1, i.e., N150, N75, and N0) and three replications for each treatment in Northwest China, we quantified the effects of water and N stress on the growth, yield, and water and N use efficiency (WP and NUE) of hybrid seed maize (Zea mays L. cv. Tianruifeng). Furthermore, nonlinear dynamic water productivity (WP) models and water (ET)-based Nuptake models were developed. The results showed that water stress had a larger impact than N stress on the growth and yield of maize, with water stress reducing yield (Y), final aboveground biomass (B), and N uptake by 36.5%, 15.4%, and 25.7% on average, respectively, and N stress decreasing them by 18.7%, 12.3%, and 13.6%, respectively. Biomass-based water productivity (WPB-ET) and yield-based water productivity (WPY-ET) at the end of the growth period responded differently to water stress but similarly to N stress because of a higher decrease of harvest index (HI) under water stress than under N stress. Specifically, WPY-ET decreased significantly while WPB-ET kept relatively stable as water stress increased. The variation of the measured WP during the growth period presented a single peak trend. The Logistic, Sigmoid, and Linear models showed similar high accuracy for quantifying the relationship between evapotranspiration accumulation and biomass growth. However, the derived WP values from the nonlinear dynamic models were more in line with the single peak variation of the measured WP during the growth period, with the agreement index (d) improved from 0.21 to 0.65–0.75 in comparison to the Linear model. The developed ET-based N accumulation models can quantify N uptake through evapotranspiration. The results can contribute to improving the accuracy of crop modelling under drought stress conditions, and the design of irrigation and N management in arid and semi-arid regions.

Overexpression of PsAMT1.2 in poplar enhances nitrogen utilization and resistance to drought stress.

Ammonium is an important form of inorganic nitrogen, which is essential for plant growth and development, and the uptake of ammonium is mediated by different members of ammonium transporters (AMTs). It is reported that PsAMT1.2 is specially expressed in the root of poplar, and the overexpression of PsAMT1.2 could improve plant growth and the salt tolerance of poplar. However, the role of AMTs in plant drought and low nitrogen (LN) resistance remains unclear. To understand the role of PsAMT1.2 in drought and LN tolerance, the response of PsAMT1.2-overexpression poplar to polyethylene glycol (PEG)-simulated drought stress (5% PEG) under LN (0.001mM NH4NO3) and moderate nitrogen (0.5mM NH4NO3) conditions was investigated. The PsAMT1.2-overexpression poplar showed better growth with increased stem increment, net photosynthetic rate, chlorophyll content, root length, root area, average root diameter and root volume under drought and/or LN stress compared with the wild type (WT). Meanwhile, the content of malondialdehyde significantly decreased, and the activities of superoxide dismutase and catalase significantly increased in the roots and leaves of PsAMT1.2-overexpression poplar compared with WT. The content of NH4+ and NO2- in the roots and leaves of PsAMT1.2-overexpression poplar was increased, and nitrogen metabolism-related genes, such as GS1.3, GS2, Fd-GOGAT and NADH-GOGAT, were significantly upregulated in the roots and/or leaves of PsAMT1.2-overexpression poplar compared with WT under drought and LN stress. The result of this study would be helpful for understanding the function of PsAMT1.2 in plant drought and LN tolerance and also provides a new insight into improving the drought and LN tolerance of Populus at the molecular level.

Full-scale operation of an integrated aerated biofilter–denitrification shallow biofilter system for simultaneous nitrogen and phosphorus removal from low-carbon domestic sewage: Influencing parameters, microbial community and mechanism

At present the problem of not satisfying the increasingly strict emission standards in the biological treatment of domestic sewage characterized by high nitrogen and phosphorus stress has become prominent, especially under the insufficient carbon source. For the efficient treatment of low-carbon sewage, a full-scale integrated system was constructed and practically applied, which is based on a combination of an up-flow aerated biofilter and a denitrification shallow biofilter (UAB-DSB). The effects of operation parameters such as air/water ratio, hydraulic load, C/N ratio, and polyaluminum chloride (PAC) dosage on nitrogen and phosphorus removal were investigated. With the optimal parameters, the maximum removal efficiencies of chemical oxygen demand (COD), NH4+-N, total nitrogen (TN), and total phosphorus (TP) reached approximately 90%, 85%, 80%, and 92%, respectively, achieving an excellent quality effluent. Based on the water quality changes along the filter layer height, a dynamic equation for predicting NH4+-N removal was established, which can be applicable to different hydraulic loads. High-throughput sequencing analysis results indicated that the dominant bacteria genera were Longilinea, Nitrospira, and Terrimonas in UAB, while those in DSB were Longilinea, Ornatilinea, and Thauera. As proved by metagenomic analysis, the nxrA and nxrB genes encoded key enzymes in the nitrification, while narG, napA, nirS, norB, and nosZ genes were mainly responsible for the denitrification. By analyzing the spatial variations of the microbial communities and functions, the main mechanisms underlying the UAB-DSB system along the water flow direction were in turn carbon removal, ammoniation, synchronous nitrification and denitrification, aerobic denitrification, and heterotrophic denitrification.