Nitrogen Assimilation Research Articles

Genomic insights into key mechanisms for carbon, nitrogen, and phosphate assimilation by the acidophilic, halotolerant genus Acidihalobacter members.

In-depth comparative genomic analysis was conducted to predict carbon, nitrogen, and phosphate assimilation pathways in the halotolerant, acidophilic genus Acidihalobacter. The study primarily aimed to understand how the metabolic capabilities of each species can determine their roles and effects on the microbial ecology of their unique saline and acidic environments, as well as in their potential application to saline water bioleaching systems. All four genomes encoded the genes for the complete tricarboxylic acid cycle, including 2-oxoglutarate dehydrogenase, a key enzyme absent in obligate chemolithotrophic acidophiles. Genes for a unique carboxysome shell protein, csoS1D, typically found in halotolerant bacteria but not in acidophiles, were identified. All genomes contained lactate and malate utilization genes, but only Ac. ferrooxydans DSM 14175T contained genes for the metabolism of propionate. Genes for phosphate assimilation were present, though organized differently across species. Only Ac. prosperus DSM 5130T and Ac. aeolianus DSM 14174T genomes contained nitrogen fixation genes, while Ac. ferrooxydans DSM 14175T and Ac. yilgarnensis DSM 105917T possessed genes for urease transporters and respiratory nitrate reductases, respectively. The findings suggest that all species can fix carbon dioxide but can also potentially utilize exogenous carbon sources and that the non-nitrogen-fixing species rely on alternative nitrogen assimilation mechanisms.

Overlapping Transcriptome Alterations Reveal the Mechanism of Interaction between Selenium and Zinc and Their Common Effect on Essential Nutrient Metabolism in Mung Bean (Vigna radiata L.).

Selenium (Se) and zinc (Zn) deficiencies have become serious global food security and public health problems. Biofortification through foliar fertilizer is a nonspecific, low-tech, and cost-effective strategy. Se and Zn have overlapping physiological roles and interacting relationships in plants. Mung bean is superior for Se enrichment and an excellent Zn carrier. However, the molecular mechanism underlying the interaction between Se and Zn in the mung bean remains unclear. Herein, Se and Zn accumulation, antioxidant activities, physiological determination, and transcriptomic analysis were performed under both Se and Zn treatments. Common essential roles of Se and Zn in mung bean were reflected by the comprehensively altered ten physiological indexes under both Se2 (24 g·ha-1) and Zn1 (1.2 kg·ha-1) treatments. Overlapping transcriptome changes and common DEGs in two compared groups revealed that the upregulated expression of sulfate transporters (SULTRs), phosphate transporters (PHTs), and Zinc-regulated/Iron-regulated-like protein (ZIP) family genes under Se and Zn treatments directly promoted both Se and Zn intakes. Furthermore, the altered Se/Sulfur, nitrogen, and carbohydrate metabolisms are closely interlinked with the uptake and assimilation of Se and Zn via the 20 key genes that we filtered through the protein-protein interaction (PPI) network analysis. Further analysis indicated that l-methionine γ-lyase (E 4.4.1.11) genes may play an important role in the transamination of selenomethionine and its derivatives; glutamine synthetase (GS), nitrate reductase (NR), and starch synthase (SS) genes may regulate the nitrogen assimilation and carbohydrate metabolism, which provide more carriers for Se and Zn; glutathione peroxidase (GPx), glutamate-cysteine ligase catalytic subunit (GCLC), and serine acetyltransferase (SAT) genes may accelerate the GSH-GSSH cycle and promote Se and Zn storages. This study provides new molecular insights into the comprehensive improvement of the nutritional quality of mung beans in Se and Zn biofortification productions.

Nitrogen Assimilation, Biomass, and Yield in Response to Application of Algal Extracts, Rhizobium sp., and Trichoderma asperellum as Biofertilizers in Hybrid Maize

Nitrogen is essential for plants’ growth, yield, and crop quality, and its deficiency limits food production worldwide. In addition, excessive fertilization and inefficient use of N can increase production costs and cause environmental problems. A possible solution to this problem is the application of biofertilizers, which improve N assimilation and increase biomass and yield. Therefore, the objective of this research was to evaluate the impact of the application of a combination of green and red algae (Ulva lactuca and Solieria spp.), Rhizobium sp., Trichoderma asperellum, and the combination of the above three biofertilizers on N assimilation. A completely randomized design was performed, with 10 plants per treatment and five treatments: T1 = control; T2 = algal extracts; T3 = Rhizobium sp.; T4 = T. asperellum; T5 = T2 + T3 + T4. Our analyses showed that the biofertilizers’ application was better than the control. The application of Rhizobium sp. had the best performance amongst all of the biofertilizers, with the highest nitrate reductase activity in maize leaves, which enhanced photosynthesis, increasing biomass and yield. The use of Rhizobium sp. showed increases in biomass (13.4%) and yield (11.82%) compared to the control. This research shows that biofertilizers can be a key component for sustainable agricultural practices.

Using Legume-Enriched Cover Crops to Improve Grape Yield and Quality in Hillside Vineyards

Natural covering (NATC) has spread on hillside vineyards of central Italy as a replacement for tillage to reduce soil erosion, although it increased nitrogen and water needs. Therefore, in the current context of global warming, using cover crops (CCs) that require less water and provide nitrogen becomes crucial. The effects of two low-competition legume-enriched CCs in a rainfed hillside vineyard—a perennial legume–grass mixture (PLGM) and an annual legume cover crop of Trifolium alexandrinum (ALTA)—were compared with NATC over three years. PLGM and ALTA provided good levels of soil coverage, slightly lower than NATC, which had a negligible presence of legumes. PLGM and ALTA, due to low competition, enhanced vine vigor, resulting in thicker and wider canopies (as indicated by total leaf area and leaf layer number), higher pruning weight, and increased yield. PLGM and ALTA led to good qualitative levels, with higher grapes acidities, lower pH and total soluble solids content and, additionally, significantly higher yeast assimilable nitrogen content. In conclusion, implementing low-competition legume species in CCs is an effective tool to avoid soil erosion in a climate change scenario, leading to increased productivity, higher acidity, and improved nitrogen content in the grapes.

Enhancing cold tolerance in tobacco through endophytic symbiosis with Piriformospora indica

Tobacco, a warm-season crop originating from the Americas, is highly susceptible to cold stress. The utilization of symbiotic fungi as a means to bolster crops’ resilience against abiotic stresses has been proven to be a potent strategy. In this study, we investigated the effect of endophytic fungus Piriformospora indica on the cold resistance of tobacco. When exposed to cold stress, the colonization of P.indica in tobacco roots effectively stimulates the activity of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX). This, in turn, reduces the accumulation of reactive oxygen species (ROS), thereby mitigating oxidative damage. Additionally, P. indica elevates the levels of osmolytes, such as soluble sugars, proline, and soluble proteins, thus facilitating the restoration of osmotic balance. Under cold stress conditions, P. indica also induces the expression of cold-responsive genes. Furthermore, this fungus not only enhances photosynthesis in tobacco by stimulating the synthesis of photosynthetic pigments, strengthening Rubisco activity, and elevating PSII efficiency, but also fortifies tobacco’s nitrogen assimilation by inducing the expression of nitrate transporter gene and activating enzymes related to nitrogen assimilation. Consequently, this synergistic optimization of nitrogen and carbon assimilation provides a solid material and energetic foundation for tobacco plants to withstand cold stress. Our study demonstrates that a mycorrhizal association between P. indica and tobacco seedlings provides multifaceted protection to tobacco plants against low-temperature stress and offers a valuable insight into how P. indica enhances the cold tolerance of tobacco.

Elevated CO2 Concentration Extends Reproductive Growth Period and Enhances Carbon Metabolism in Wheat Exposed to Increased Temperature.

Both elevated atmospheric CO2 concentration ([CO2]) and increased temperature exert notable influences on wheat (Triticum aestivum L.) growth and productivity when examined individually. Nevertheless, limited research comprehensively investigates the combined effects of both factors. Winter wheat was grown in environment-controlled chambers under two concentrations of CO2 (ambient CO2 concentration and ambient CO2 concentration plus 200 µmol mol-1) and two levels of temperature (ambient temperature and ambient temperature plus 2°C). The phenology, photosynthesis, carbohydrate and nitrogen metabolism, yield and quality responses of wheat were investigated. Elevated [CO2] did not counteract warming-induced shortening of wheat phenological period but prolonged grain filling. Even though photosynthetic adaptation occurred during the reproductive growth period, elevated [CO2] still significantly enhanced carbohydrate accumulation under warming, particularly at the grain filling stage, thereby increasing yield by 20.1% compared with the ambient control. However, elevated [CO2] inhibited nitrogen assimilation at the grain filling stage under increased temperature by downregulating the expression levels of TaNR, TaNIR, TaGS1 and TaGOGAT and reducing glutamine synthetase activity, which directly led to a significant decrease of 19.4% in grain protein content relative to the ambient control. These findings suggest that elevated [CO2] will likely increase yield but decrease grain nutritional quality for wheat under future global warming scenarios.

Acute copper stress showed toxic effects on the physiological metabolism of Ulva lactuca, a common green macroalgae

The pollution by heavy metals in coastal waters has gradually intensified due to industrial development. In this study, physiological responses of Ulva lactuca, one of the most common green seaweeds with important ecological and economic value in the global intertidal zone, to acute copper stress were investigated. Results showed that an increase in copper ions concentration significantly inhibited photosynthetic activity and inorganic nitrogen utilization by U. lactuca but, increased its respiration. Copper stress limited the activity and gene expression of enzymes related to carbon and nitrogen assimilation of U. lactuca. Under moderate copper stress, U. lactuca had higher soluble carbohydrate and soluble protein contents, whereas under high copper stress, these components decreased sharply. Copper stress increased malonaldehyde content, and relative electrical conductivity in U. lactuca, but changes in antioxidant enzyme activities were not significant and even slightly decreased. Moreover, the contents of 8-hydroxy-deoxyguanosine and polyADP ribose polymerase in U. lactuca increased by high Cu2+ concentration culture, indicating that oxidative damage caused by high Cu2+ level involved its DNA damage and interfered with DNA repair in the alga. Copper stress seemed to be more damaging to the carbon assimilation process of U. lactuca, resulting in weakened resistance to copper stress and lower growth rate. This reflected the threat of coastal high copper stress to intertidal biodiversity. This provided ecological reference for the assessment of offshore heavy metal pollution represented by copper.

Response and adaptation of Chlorella pyrenoidosa to 6PPD: Physiological and genetic mechanisms

The extensive contamination of the tire antidegradant N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD) in aquatic environments have raised concerns about its potential threats to aquatic organisms. Here, the responses of green algae Chlorella pyrenoidosa (C. pyrenoidosa) to 6PPD exposure were investigated for the first time. The growth of C. pyrenoidosa experienced three sequential phases, including inhibition, recovery and stimulation. Physiological and transcriptome analysis suggested that the growth inhibition was associated with the suppressed nitrogen assimilation and amino acid biosynthesis pathways, among which nitrate transporter (NRT) 2.1 was a key target of 6PPD. Molecular docking revealed the steadily binding of 6PPD to the substrate entry region of NRT 2.1 via hydrogen bonds and π − cation interaction, blocking the acquisition of extracellular inorganic nitrogen. Along with the removal of 6PPD through abiotic processes and biodegradation, an adaptive metabolic shift in cells not only facilitated growth recovery but also triggered a compensatory stimulation phase. With regard to microalgal adaptation, upregulated DNA replication and repair pathways served to maintain the integrity of the genetic information, enhanced photosynthesis cascades and central carbon metabolism improved carbon flux and energy conversion to microalgal biomass, recovered amino acid biosynthesis produced essential proteins for multiple metabolisms. The results provide new insights into microalgal molecular responses to 6PPD exposure, facilitating a better understanding of ecological consequences of 6PPD in the environment.

Transcriptome analysis expands underlying mechanisms of quorum sensing mediating heterotrophic nitrification-aerobic denitrification process at low temperature

Quorum sensing (QS) could regulate the behavior of microbial communities and help them resist adverse low-temperature environments. A newly isolated heterotrophic nitrification-aerobic denitrification (HN-AD) bacterium, strain YB1107, exhibited strong tolerance to harsh cold environments, removing 93.5 % of ammonia within 36 h and achieving a maximum specific growth rate of 0.28 h−1 at 10 °C. Strain YB1107 secreted large amounts of N-butanoyl-L-homoserine or N-octanoyl-L-homoserine lactones in response to cold stimuli. The add-back experiments indicated that these two signaling molecules jointly manipulated microbial physiological behavior by improving ammonia oxidation and biofilm formation, while inhibiting aerobic denitrification. The transcriptome analysis revealed that QS systems enhanced the cold resistance of HN-AD bacteria by promoting nitrogen assimilation and reducing dissimilation through regulating related genes. This study provided new molecular insights into how QS mediated HN-AD at low temperatures and laid the foundation for the potential applications of psychrophilic HN-AD bacteria in wastewater treatment.

The ammonium transporter AmtB is dispensable for the uptake of ammonium in the phototrophic diazotroph Rhodopseudomonas palustris

Ammonium (NH4+) transport across cell membranes plays an important role in assimilation or removal of the environmental nitrogen. The membrane protein AmtB has been considered to be the NH4+ transporter that is responsible for the NH4+ uptake. The phototrophic diazotroph Rhodopseudomonas palustris harboring two amtB genes has been widely used in wastewater treatment and bioremediation. However, the role of AmtB in NH4+ uptake remains unclear in R. palustris. Here, we employed an innovative approach combining stable isotope probing (SIP) with Raman spectroscopy to determine the physiological functions of AmtB1 and AmtB2 in R. palustris. This powerful technique allowed us to investigate NH4+ uptake at the single-cell level. The generated R. palustris ΔamtB1 ΔamtB2 mutant lacking AmtB1 and AmtB2 proteins was still capable of utilizing 15NH4+ even the 15NH4+ concentration was as low as 5 μM. These data demonstrate that both of the AmtB proteins are not essential for R. palustris to take up NH4+ regardless of environmental NH4+ levels. However, both AmtB1 and AmtB2 can contribute to NH4+ uptake under nitrogen-limiting conditions. Given that R. palustris primarily expresses AmtB2 in these conditions, AmtB2 plays a more important role in NH4+ uptake compared to AmtB1. In addition, transcriptomic analysis showed that the deletion of the amtB1 and amtB2 genes resulted in the upregulation of many transporter genes, providing potential targets for future investigation of alternative NH4+ uptake systems.

Integrative physiological and transcriptome analysis unravels the mechanism of low nitrogen use efficiency in burley tobacco.

Burley tobacco, a chlorophyll-deficient mutant with impaired nitrogen use efficiency (NUE), generally requires three to five times more nitrogen fertilization than flue-cured tobacco to achieve a comparable yield, which generates serious environmental pollution and negatively affects human health. Therefore, exploring the mechanisms underlying NUE is an effective measure to reduce environmental pollution and an essential direction for burley tobacco plant improvement. Physiological and genetic factors affecting tobacco NUE were identified using two tobacco genotypes with contrasting NUE in hydroponic experiments. Nitrogen use inefficient genotype (TN90) had lower nitrogen uptake and transport efficiencies, reduced leaf and root biomass, lower nitrogen assimilation and photosynthesis capacity, and lower nitrogen remobilization ability than the nitrogen use efficient genotype (K326). Transcriptomic analysis revealed that genes associated with photosynthesis, carbon fixation, and nitrogen metabolism are implicated in NUE. Three nitrate transporter genes in the leaves (NPF2.11, NPF2.13, and NPF3.1) and three nitrate transporter genes (NPF6.3, NRT2.1, and NRT2.4) in roots were down-regulated by nitrogen starvation, all of which showed lower expression in TN90 than in K326. In addition, the protein-protein interaction (PPI) network diagram identified eight key genes (TPIP1, GAPB, HEMB, PGK3, PSBO, PSBP2, PSAG, and GLN2) that may affect NUE. Less advantageous changes in nitrogen uptake, nitrogen assimilation in combination with nitrogen remobilization, and maintenance of photosynthesis in response to nitrogen deficiency led to a lower NUE in TN90. The key genes (TPIP1, GAPB, PGK3, PSBO, PSBP2, PSAG, and GLN2) were associated with improving photosynthesis and nitrogen metabolism in tobacco plants grown under N-deficient conditions.

Enhanced photorespiratory and TCA pathways by elevated CO2 to manage ammonium nutrition in tomato leaves

Plants grown under exclusive ammonium (NH4+) nutrition have high carbon (C) demand to sustain proper nitrogen (N) assimilation and energy required for plant growth, generally impaired compared to nitrate (NO3-) nutrition. Thereby, the increment of the atmospheric carbon dioxide (CO2) concentration, in the context of climate change, will potentially allow plants to better face ammonium nutrition. In this work, tomato (Solanum lycopersicum L.) plants were grown under ammonium or nitrate nutrition in conditions of ambient (aCO2, 400 ppm) or elevated CO2 (eCO2, 800 ppm) atmosphere. Elevated CO2 increased photosynthesis rate and tomato shoot growth regardless of the N source. In the case of NH4+-fed leaves the positive effect of elevated CO2 occurred despite of the high tissue NH4+ accumulation. Under eCO2 ammonium nutrition triggered, among others, the modulation of genes related to C provision pathways (including carbonic anhydrase and glyoxylate cycle), antioxidant response and cell membranes protection. The enhanced photosynthate production at eCO2 facilitated C skeleton provision through the TCA cycle and anaplerotic pathways to promote amino acid synthesis. Moreover, photorespiratory activity was stimulated by eCO2 and contributed to yield serine as additional sink for NH4+ excess. Overall, these changes denote a connection between the respiratory and the photorespiratory pathways linked to ammonium nutrition. This metabolic strategy may allow crops to grow efficiently using ammonium as fertilizer in a future climate change scenario, while mitigating N losses.

Foliar application of carbon dots enhances nitrogen uptake and assimilation through CEPD1-dependent signaling in plants

The use of nitrogen (N) fertilizers increases crop yield, but the accumulation of residual N in agricultural soils poses significant environmental risks. Improving the N use efficiency (NUE) of crops can help reduce N pollution. While nanomaterials have been shown to enhance crop agronomic traits, more research is needed to clarify the regulatory mechanisms involved. In this study, foliar spraying of carbon dots (CDs, 1 mg·mL−1) derived from Salvia miltiorrhiza increased the activity of plasma membrane H+-ATPase in Arabidopsis thaliana roots, promoting the uptake, transport, and assimilation of NO3- and NH4+. The upregulation of N metabolism-related genes, such as AtAMTs and AtNRTs, was also observed in A. thaliana roots. Transcriptome analysis suggested that this regulatory effect is mediated by the shoot-to-root mobile polypeptide CEPD1 (C-terminally encoded peptide DOWNSTREAM 1) signaling pathway. Additionally, foliar application of CDs increased the NUE of sweetpotato (Ipomoea batatas (L.) Lam.) from 2.5% to 8.1%. The upregulation of genes such as CEPD1 in leaves was observed following CDs application under different N conditions. Finally, foliar spraying of CDs significantly increased field yield and enhanced tolerance to low N stress in sweetpotato. Overall, this study demonstrated that foliar application of CDs improved NUE in plants through CEPD1-dependent signaling.

Developmental-specific regulation promotes the free amino acids accumulation in chlorotic tea plants (Camellia sinensis)

Chlorophyll-deficient tea plant exhibits a significantly higher accumulation of free amino acids (FAAs) than normal tea plants. This study focused on the impact of leaf color and the developmental stage on FAAs in six tea germplasms while maintaining all other conditions. The total FAAs content initially increased as the leaf matured during the one-bud-two-leaves (1B2L) and one-bud-three-leaves (1B3L) stages in green germplasms, then decreased or stabilized in the one-bud-four-leaves (1B4L) stage. In contrast, chlorotic germplasms showed continuous FAAs’ content increase from 1B2L to 1B4L, thus being significantly positively correlated with total chlorophyll content. Interestingly, ethylamine content decreased with leaf maturation in both chlorotic and green germplasms, thus showing a significant negative correlation with L-theanine content only in chlorotic germplasms. Comparative RNA-seq analysis linked FAAs accumulation in chlorotic germplasm’s 1B3L to photosynthesis inhibition and in 1B4L to nitrogen assimilation promotion. Feeding experiments revealed higher L-theanine synthesis and degradation abilities in chlorotic shoots versus green shoots, with synthesis efficiency exceeding degradation efficiency. Overall, this study uncovers a developmental-specific FAAs accumulation pattern in chlorotic germplasms and offers novel insights into the precise regulation by leaf color and developmental stage.

Nutrition for commercial flower production of Longiflorum asiatica (LA) hybrid under northern plains

The study was conducted during the winter seasons, comprising the various combinations of inorganic fertilizers (N, P2O5, and K2O) and organic manure (FYM). Treatment T24 [(25 t FYM+160 kg N+120 kg P2O5+100 kg K2O)/ha] emerged as the statistically significant treatment, outperforming others in respect of tallest plant (122.43 cm), leaf count per plant (79.33), leaf length (7.90 cm), and early flower bud initiation (28.01 days), bud initiation to colour shown (47.11 days), and colour shown to flower opening (6.10 days). This treatment also tended to show the longest flower retention on plant (15.30 days), number of flower buds per plant (4.20), bud length (8.96 cm), stalk length (110.10 cm), stalk diameter (0.96 cm), flower diameter (22.98 cm), total chlorophyll content (6.50 mg/g), leaf nitrogen (4.70%), potassium (4.10%), and net assimilation ratio (NAR) (0.0065 mg/cm2/ day). Treatment T23 [(25 t FYM+120 kg N+90 kg P2O5+75 kg K2O)/ha] proved next best treatment. The lowest value was recorded in T25 (Control). Overall, treatment T24 proved to be the most effective treatment statistically for the commercial flower production of LA hybrid lilium for northern Indian plains.

Cover crop root exudates impact soil microbiome functional trajectories in agricultural soils

BackgroundCover cropping is an agricultural practice that uses secondary crops to support the growth of primary crops through various mechanisms including erosion control, weed suppression, nutrient management, and enhanced biodiversity. Cover crops may elicit some of these ecosystem services through chemical interactions with the soil microbiome via root exudation, or the release of plant metabolites from roots. Phytohormones are one metabolite type exuded by plants that activate the rhizosphere microbiome, yet managing this chemical interaction remains an untapped mechanism for optimizing plant-soil-microbiome interactions. Currently, there is limited understanding on the diversity of cover crop phytohormone root exudation patterns and our aim was to understand how phytochemical signals selectively enrich specific microbial taxa and functionalities in agricultural soils.ResultsHere, we link variability in cover crop root exudate composition to changes in soil microbiome functionality. Exudate chemical profiles from 4 cover crop species (Sorghum bicolor, Vicia villosa, Brassica napus, and Secale cereal) were used as the chemical inputs to decipher microbial responses. These distinct exudate profiles, along with a no exudate control, were amended to agricultural soil microcosms with microbial responses tracked over time using metabolomes and genome-resolved metatranscriptomes. Our findings illustrated microbial metabolic patterns were unique in response to cover crop exudate inputs over time, particularly by sorghum and cereal rye amended microcosms. In these microcosms, we identify novel microbial members (at the genera and family level) who produced IAA and GA4 over time. Additionally, we identified cover crop exudates exclusively enriched for bacterial nitrite oxidizers, while control microcosms were discriminated for nitrogen transport, mineralization, and assimilation, highlighting distinct changes in microbial nitrogen cycling in response to chemical inputs.ConclusionsWe highlight that root exudate amendments alter microbial community function (i.e., N cycling) and microbial phytohormone metabolisms, particularly in response to root exudates isolated from cereal rye and sorghum plants. Additionally, we constructed a soil microbial genomic catalog of microorganisms responding to commonly used cover crops, a public resource for agriculturally relevant microbes. Many of our exudate-stimulated microorganisms are representatives from poorly characterized or novel taxa, revealing the yet to be discovered metabolic reservoir harbored in agricultural soils. Our findings emphasize the tractability of high-resolution multi-omics approaches to investigate processes relevant for agricultural soils, opening the possibility of targeting specific soil biogeochemical outcomes through biological precision agricultural practices that use cover crops and the microbiome as levers for enhanced crop production.BPG5Z_iDvqR4KrAs2TcSTiVideo

The role of Aspergillus flavus in modulating the physiological adjustments of sunflower to elevated CO2 and temperature

Exploring the interactions between plants and foliar endophytic fungi under varying climatic conditions is crucial for harnessing endophytes that enhance plant resilience to environmental stressors. This study examines the role of a specific strain of Aspergillus flavus as an endophyte in sunflowers under standard and altered CO2 and temperature regimes. We assessed the impact of this fungus on physiological traits such as chlorophyll and flavonoid content, gas exchange, and Chlorophyll a fluorescence using open-top chambers simulating ambient (∼420 µmol mol−1) and elevated (∼880 µmol mol−1) CO2 levels, along with a temperature increase of 3°C. The findings indicate that A. flavus promotes nitrogen assimilation and chlorophyll production under ambient conditions, potentially enhancing sunflower growth and photosynthetic performance. However, under elevated temperatures (eT), inoculation with A. flavus resulted in decreased biomass and reduced Photosystem II efficiency. Elevated CO2 (eCO2) conditions also led to unexpected negative effects, with reductions in foliar nitrogen, leaf area, and light capture efficiency, culminating in diminished biomass. When both elevated CO2 and temperature conditions were combined (eCO2eT), the interaction further impaired Photosystem II efficiency, suggesting exacerbated physiological stress. These results demonstrate that environmental modifications can transform A. flavus from a beneficial endophyte to a potential pathogen, highlighting the dual nature of plant-fungal interactions. This study underscores the complexity of these relationships under changing climatic conditions and suggests a cautious approach to the agricultural use of endophytes to ensure plant health and productivity.

Effect of copper on nitrogen uptake, transportation, assimilation processes, and related gene expression in Chinese cabbage [Brassica campestris L. ssp. Chinensis (L.)] under various nitrate-to-ammonium ratios.

Improving vegetable yield and optimizing its quality through nutrient management have long been central to plant nutrition and horticultural science. Copper (Cu) is recognized as an essential trace element that promotes plant growth and development. However, the mechanisms by which Cu influences nitrogen (N) metabolism remain largely unknown, with limited studies exploring the interaction between Cu and varying nitrate-to-ammonium (nitrate/ammonium) ratios. In this study, Chinese cabbage was exposed to two Cu concentrations (0 and 0.02 mg L-1) in combination with three nitrate/ammonium ratios (10/90, 50/50, and 90/10) under hydroponic conditions. The results showed that Cu application increased plant biomass, nitrate reductase (NR) and glutamine synthetase (GS) enzyme activities, the expression of NR (NIA) and GS2 (Gln2) genes, and N content in both shoots and roots. Additionally, Cu treatment decreased nitrate and free amino acid contents, as well as the expression of nitrate transporters NRT1.1 and NRT2.1 in roots while increasing these four parameters in shoots. Additionally, these effects were significantly modulated by the nitrate/ammonium ratios. In conclusion, Cu may facilitate nitrate transportation, enhance nitrate reduction, promote ammonium assimilation, and influence the transformation of organic N compounds, highlighting its potential role in improving N metabolism in Chinese cabbage.

Arbuscular mycorrhizal fungi enhance nitrogen assimilation and drought adaptability in tea plants by promoting amino acid accumulation.

The development and quality of tea plants (Camellia sinensis (L.) O. Ktze.) are greatly hampered by drought stress (DS), which affects them in a number of ways, including by interfering with their metabolism of nitrogen (N). Arbuscular mycorrhizal fungi (AMF) are known to enhance water and nutrient absorption in plants, but their specific effects on tea plant N metabolism under DS and the associated regulatory mechanisms remain unclear. This study aimed to evaluate the impact of Claroideoglomus etunicatum inoculation on N assimilation in tea plants (C. sinensis cv. Fuding Dabaicha) under well-watered (WW) and DS conditions, and to explore potential molecular mechanisms. After 8 weeks of DS treatment, root mycorrhizal colonization was significantly inhibited, and the biomass of tea shoots and roots, as well as the contents of various amino acids (AAs) were reduced. However, AMF inoculation significantly increased the contents of tea polyphenols and catechins in leaves by 13.74%-36.90% under both WW and DS conditions. Additionally, mycorrhizal colonization notably increased N content by 12.65%-35.70%, various AAs by 11.88%-325.42%, and enzymatic activities associated with N metabolism by 3.80%-147.62% in both leaves and roots. Gene expression analysis revealed a universal upregulation of N assimilation-related genes (CsAMT1;2, CsAMT3;1, CsGS1, CsNADH-GOGAT, CsTS2, CsGGT1, and CsADC) in AMF-colonized tea roots, regardless of water status. Under DS condition, AMF inoculation significantly upregulated the expressions of CsNRT1;2, CsNRT1;5, CsNRT2;5, CsNR, CsGS1, CsGDH1, CsGDH2, CsTS2, CsGGT1, CsGGT3, and CsSAMDC in tea leaves. These findings suggest that AMF improved tea plant adaptability to DS by enhancing N absorption and assimilation, accompanied by the synthesis and accumulation of various AAs, such as Glu, Gln, Asp, Lys, Arg, GABA and Pro. This is achieved through the upregulation of N metabolism-related genes and the activation of related enzymes in tea plants under DS condition. These findings provide valuable insights into the role of AMF in regulating tea plant N metabolism and enhancing stress tolerance.

A novel approach to enhance high optically active L-lactate production from food waste by landfill leachate

The recycling of food waste (FW) through anaerobic fermentation into lactic acid (LA), with two isomers L-LA and D-LA, aligns with the principles of a bio-based circular economy. However, FW fermentation is often limited by competing pathways, acidification inhibition, and trace metals deficiency. This study investigates the introduction of landfill leachate, containing buffering agents (ammonia) and trace metals, into FW fermentation. Various dosages of landfill leachate, ranging from 90 (LN-90) to 450 mg/L (LN-450) based on inclusive ammonia calculation, were employed. Results showed that LA production peaked at 43.65 ± 0.57 g COD/L in LN-180 on day 6, with a high optical activity of L-LA at 92.40 ± 1.15 %. Fermentation pathway analysis revealed that landfill leachate amendment enhances hydrolysis (as evidenced by increased activity of amylase, α-glucosidase, and protease) and glycolysis (resulting in enhanced utilization of carbohydrates and glucose). The inclusive ammonia in leachate plays a crucial role as a buffer, maintaining optimal pH conditions (5–7), thereby reducing volatile fatty acid production and thus intensifying LA orientations. The increased activity of L-lactate dehydrogenase (L-LA generation) and decreased NAD-independent lactate dehydrogenase (LA consumption) in properly dosed leachate further explained the high accumulation of L-LA. Dominance of lactic acid bacteria, including Streptococcus, Enterococcus, Klebsiella, Bifidobacterium, Bavariicoccus, and Lacticaseibacillus, accounted for 91.08% (LN-90), while inhibitory effects were observed in LN-450 (4.45%). Functional gene analysis further supported the enhanced glycolysis, L-lactate dehydrogenase, and nitrogen assimilation. Finally, a network analysis indicates a beneficial effect on the genus Enterococcus and Klebsiella by landfill leachate addition. This study demonstrates the efficiency of utilizing landfill leachate to enhance LA recycling from FW fermentation, aligning with the concept of circular economy by transforming waste into valuable resources.