Interactive effects of salinity and nitrogen forms on plant growth, photosynthesis and osmotic adjustment in maize

Reactive oxygen species (ROS) modulate nitrogen signaling using temporal transcriptome analysis in foxtail millet

Reactive oxygen species (ROS) is a chemically reactive chemical substance containing oxygen and a natural by-product of normal oxygen metabolism. Excessive ROS affect the growth process of crops, which will lead to the decrease of yield. Nitrogen, as a critical nutrient element in plants and plays a vital role in plant growth and crop production. Nitrate is the primary nitrogen source available to plants in agricultural soil and various natural environments. However, the molecular mechanism of ROS-nitrate crosstalk is still unclear. In this study, we used the foxtail millet (Setaria italica L.) as the material to figure it out. Here, we show that excessive NaCl inhibits nitrate-promoted plant growth and nitrogen use efficiency (NUE). NaCl induces ROS accumulation in roots, and ROS inhibits nitrate-induced gene expression in a short time. Surprisingly, low concentration ROS slight promotes and high concentration of ROS inhibits foxtail millet growth under long-term H2O2 treatment. These results may open a new perspective for further exploration of ROS-nitrate signaling pathway in plants.

Optimization of irrigation and fertilization of apples under magnetoelectric water irrigation in extremely arid areas

Apple (Malus pumila Mill.) is one of the important economic crops in the arid areas of Xinjiang, China. For a long time, there has been a problem of high consumption but low yield in water and fertilizer management, prevent improvements in apple quality and yield. In this study, 5-year-old 'Royal Gala' apple trees in extremely arid areas of Xinjiang were used as experimental materials to carry out field experiments. considering 5 irrigation levels (W1, 30 mm; W2, 425 mm; W3, 550 mm; W4, 675 mm; W5, 800 mm) and 5 fertilization levels (F1, 280 kg·ha-1; F2, 360 kg·ha-1; F3, 440 kg·ha-1; F4, 520 kg·ha-1; F5, 600 kg·ha-1) under magnetoelectric water irrigation conditions. The results demonstrated that magnetoelectric water combined with the application of 675 mm irrigation amount and 520 kg·ha-1 fertilization amount was the most effective combination. These results occurred by increasing net photosynthetic rate of apple leaves, improved the quality of apples, increased apple yield, and promoted the improvement of water and fertilizer use efficiency. Additionally, the quadratic regression model was used to fit the response process of yield, IWUE and PFP to irrigation amount and fertilization amount, and the accuracy was greater than 0.8, indicating good fitting effects. The synergistic effect of water and fertilizer has a positive effect on optimizing apple water and fertilizer management. Principal component analysis showed that the magnetoelectric treatment combined water and fertilizer mainly affected apple yield, water and fertilizer use efficiency and vitamin C content related to quality. This study provides valuable guidance for improving water and fertilizer productivity, crop yield and quality in extreme arid areas of Xinjiang by using Magnetoelectric water irrigation.

Inoculum and pH effects on ammonium removal and microbial community dynamics in aquaponics systems

Understanding the ecology of microorganisms is essential for optimizing aquaponics systems. Effects of pH and inoculum on ammonium removal and dynamics of microbial community composition from all compartments of lab-scale aquaponics systems were examined. Initial ammonium accumulation in systems with comammox-enriched inocula were 47% and 69% that of systems enriched with ammonia-oxidizing bacteria (AOB), with higher rates of ammonium removal and transient nitrite accumulation measured in the latter systems. By the end of operation, Nitrosomonas and Nitrosospira AOB were dominant nitrifiers in systems at pH 7.6-7.8, whereas comammox (Nitrospira) nitrifiers and plant growth-promoting microbes were abundant in systems operating at pH 5.8-6.0. Lower pH systems supported more robust plant growth with no significant effects on fish health. This study demonstrated functional redundancy of aquaponics microbiota, with selectivity of nitrifying taxa as a function of pH. The results suggest that inoculum and pH are important considerations for aquaponics system initiation and optimization.

Moderate salinity and high ammonium/nitrate ratio enhance early growth in "summer wonder" lettuce cultivar

Because its impact in plant development and growth and its interaction with Na+ and Cl-, the supply of different N-forms to crops can be an easy-to-use tool with effective results on salinity tolerance. Here the effect of four N-NO3-/N-NH4+ ratios (mM; 2/0, 1.6/0.4, 0.4/1.6, 0/2) on adaptation to salt conditions (15 mM NaCl in a first experiment and 40 mM NaCl in a second experiment) was studied in young lettuce (cv "Summer wonder") plants. The experiments were carried out in greenhouse and under hydroponics conditions. The results show that this cultivar tolerates and adapts to moderate salinity by deploying several structural and physiological mechanisms; (i) increasing allocation of biomass to the root, (ii) increasing root Na+ uptake and storing it in the shoot and root tissues, (iii) increasing intrinsic water use efficiency and (iv) increasing root N and P uptake. The beneficial effect of salt exposure on growth was greater when the predominant N-form was N-NO3-. These plants with higher tissue N-NO3- concentration, decreased Cl- uptake and shoot and root Cl- concentration. Regardless of salt conditions, plants with a high proportion of N-NH4+ (1.6 mM) and a low proportion of N-NO3- (0.4 mM) had a greater growth and nitrogen use efficiency, that was associated with the improved uptake of nutrients, and the maintenance of water status.

More N fertilizer, more maize, and less alfalfa: maize benefits from its higher N uptake per unit root length

Root plasticity is fundamental to soil nutrient acquisition and maximizing production. Different soil nitrogen (N) levels affect root development, aboveground dry matter accumulation, and N uptake. This phenotypic plasticity is well documented for single plants and specific monocultures but is much less understood in intercrops in which species compete for the available nutrients. Consequently, the study tested whether the plasticity of plant roots, biomass and N accumulation under different N levels in maize/alfalfa intercropping systems differs quantitatively. Maize and alfalfa were intercropped for two consecutive years in large soil-filled rhizoboxes and fertilized with 6 different levels of N fertilizer (0, 75, 150, 225, 270, and 300 kg ha-1). Root length, root surface area, specific root length, N uptake and yield were all increased in maize with increasing fertilizer level, whereas higher N rates were supraoptimal. Alfalfa had an optimal N rate of 75-150 kg ha-1, likely because the competition from maize became more severe at higher rates. Maize responded more strongly to the fertilizer treatment in the second year when the alfalfa biomass was much larger. N fertilization contributes more to maize than alfalfa growth via root plasticity responses. Our results suggest that farmers can maximize intercropping yield and economic return by optimizing N fertilizer management.

Smart reprograming of plants against salinity stress using modern biotechnological tools

Climate change gives rise to numerous environmental stresses, including soil salinity. Salinity/salt stress is the second biggest abiotic factor affecting agricultural productivity worldwide by damaging numerous physiological, biochemical, and molecular processes. In particular, salinity affects plant growth, development, and productivity. Salinity responses include modulation of ion homeostasis, antioxidant defense system induction, and biosynthesis of numerous phytohormones and osmoprotectants to protect plants from osmotic stress by decreasing ion toxicity and augmented reactive oxygen species scavenging. As most crop plants are sensitive to salinity, improving salt tolerance is crucial in sustaining global agricultural productivity. In response to salinity, plants trigger stress-related genes, proteins, and the accumulation of metabolites to cope with the adverse consequence of salinity. Therefore, this review presents an overview of salinity stress in crop plants. We highlight advances in modern biotechnological tools, such as omics (genomics, transcriptomics, proteomics, and metabolomics) approaches and different genome editing tools (ZFN, TALEN, and CRISPR/Cas system) for improving salinity tolerance in plants and accomplish the goal of "zero hunger," a worldwide sustainable development goal proposed by the FAO.

Nitrogen Journey in Plants: From Uptake to Metabolism, Stress Response, and Microbe Interaction

Plants uptake and assimilate nitrogen from the soil in the form of nitrate, ammonium ions, and available amino acids from organic sources. Plant nitrate and ammonium transporters are responsible for nitrate and ammonium translocation from the soil into the roots. The unique structure of these transporters determines the specificity of each transporter, and structural analyses reveal the mechanisms by which these transporters function. Following absorption, the nitrogen metabolism pathway incorporates the nitrogen into organic compounds via glutamine synthetase and glutamate synthase that convert ammonium ions into glutamine and glutamate. Different isoforms of glutamine synthetase and glutamate synthase exist, enabling plants to fine-tune nitrogen metabolism based on environmental cues. Under stressful conditions, nitric oxide has been found to enhance plant survival under drought stress. Furthermore, the interaction between salinity stress and nitrogen availability in plants has been studied, with nitric oxide identified as a potential mediator of responses to salt stress. Conversely, excessive use of nitrate fertilizers can lead to health and environmental issues. Therefore, alternative strategies, such as establishing nitrogen fixation in plants through diazotrophic microbiota, have been explored to reduce reliance on synthetic fertilizers. Ultimately, genomics can identify new genes related to nitrogen fixation, which could be harnessed to improve plant productivity.

Polyphosphate fertilizer impacts the enzymatic and non-enzymatic antioxidant capacity of wheat plants grown under salinity

By 2050, the predicted global population is set to reach 9.6 billion highlighting the urgent need to increase crop productivity to meet the growing demand for food. This is becoming increasingly challenging when soils are saline and/or deficient in phosphorus (P). The synergic effect of P deficiency and salinity causes a series of secondary stresses including oxidative stress. Reactive Oxygen Species (ROS) production and oxidative damage in plants caused either by P limitation or by salt stress may restrict the overall plant performances leading to a decline in crop yield. However, the P application in adequate forms and doses could positively impact the growth of plants and enhances their tolerance to salinity. In our investigation, we evaluated the effect of different P fertilizers forms (Ortho-A, Ortho-B and Poly-B) and increasing P rates (0, 30 and 45 ppm) on the plant's antioxidant system and P uptake of durum wheat (Karim cultivar) grown under salinity (EC = 3.003 dS/m). Our results demonstrated that salinity caused a series of variations in the antioxidant capacity of wheat plants, at both, enzymatic and non-enzymatic levels. Remarkably, a strong correlation was observed between P uptake, biomass, various antioxidant system parameters and P rates and sources. Soluble P fertilizers considerably enhanced the total plant performances under salt stress compared with control plants grown under salinity and P deficiency (C+). Indeed, salt-stressed and fertilized plants exhibited a robust antioxidant system revealed by the increase in enzymatic activities of Catalase (CAT) and Ascorbate peroxidase (APX) and a significant accumulation of Proline, total polyphenols content (TPC) and soluble sugars (SS) as well as increased biomass, Chlorophyll content (CCI), leaf protein content and P uptake compared to unfertilized plants. Compared to OrthoP fertilizers at 45 ppm P, Poly-B fertilizer showed significant positive responses at 30 ppm P where the increase reached + 18.2% in protein content, + 156.8% in shoot biomass, + 93% in CCI, + 84% in shoot P content, + 51% in CAT activity, + 79% in APX activity, + 93% in TPC and + 40% in SS compared to C+. This implies that PolyP fertilizers might be an alternative for the suitable management of phosphorus fertilization under salinity.

Response of Soil Microenvironment and Crop Growth to Cyclic Irrigation Using Reclaimed Water and Brackish Water

The scarcity of freshwater resources has increased the use of nonconventional water resources such as brackish water, reclaimed water, etc., especially in water-scarce areas. Whether an irrigation cycle using reclaimed water and brackish water (RBCI) poses a risk of secondary soil salinization to crop yields needs to be studied. Aiming to find an appropriate use for different nonconventional water resources, pot experiments were conducted to study the effects of RBCI on soil microenvironments, growth, physiological characteristics and antioxidation properties of crops. The results showed the following: (1) compared to FBCI, the soil moisture content was slightly higher, without a significant difference, while the soil EC, sodium and chloride ions contents increased significantly under the RBCI treatment. With an increase in the reclaimed water irrigation frequency (Tri), the contents of EC, Na⁺ and Cl^- in the soil decreased gradually, and the difference was significant; the soil moisture content also decreased gradually. (2) There were different effects of the RBCI regime on the soil's enzyme activities. With an increase in the Tri, the soil urease activity indicated a significant upward trend as a whole. (3) RBCI can alleviate the risk of soil salinization to some extent. The soil pH values were all below 8.5, and were without a risk of secondary soil alkalization. The ESP did not exceed 15 percent, and there was no possible risk of soil alkalization except that the ESP in soil irrigated by brackish water irrigation went beyond the limit of 15 percent. (4) Compared with FBCI, no obvious changes appeared to the aboveground and underground biomasses under the RBCI treatment. The RBCI treatment was conducive to increasing the aboveground biomass compared with pure brackish water irrigation. Therefore, short-term RBCI helps to reduce the risk of soil salinization without significantly affecting crop yield, and the irrigation cycle using reclaimed-reclaimed-brackish water at 3 g·L^-1 was recommended, according to the experimental results.

2-Oxoglutarate contributes to the effect of foliar nitrogen on enhancing drought tolerance during flowering and grain yield of soybean

Drought severely affects the growth and yield of soybean plants especially during the flowering period. To investigate the effect of 2-oxoglutarate (2OG) in combination with foliar nitrogen (N) at flowering stage on drought resistance and seed yield of soybean under drought stress. This experiment was conducted in 2021 and 2022 on drought-resistant variety (Hefeng 50) and drought-sensitive variety (Hefeng 43) soybean plants treated with foliar N (DS + N) and 2-oxoglutarate (DS + 2OG) at flowering stage under drought stress. The results showed that drought stress at flowering stage significantly increased leaf malonaldehyde (MDA) content and reduced soybean yield per plant. However, superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) activities were significantly increased by foliar N treatment, and 2-oxoglutarate synergistically with foliar N treatment (DS + N + 2OG) was more beneficial to plant photosynthesis. 2-oxoglutarate significantly enhanced plant N content, glutamine synthetase (GS) and glutamate synthase (GOGAT) activity. Furthermore, 2-oxoglutarate increased the accumulation of proline and soluble sugars under drought stress. Under drought stress, soybean seed yield was increased by DS + N + 2OG treatment by 16.48-17.10% and 14.96-18.84% in 2021 and 2022, respectively. Thus, the combination of foliar N and 2-oxoglutarate better mitigated the adverse effects of drought stress and could better compensate for the yield loss of soybean under drought stress.

Growth, nutrient uptake and transcriptome profiling of rice seedlings in response to mixed provision of ammonium- and nitrate-nitrogen

Nitrogen (N) is a principal macronutrient and plays a paramount role in mineral nutrition of rice plants. Mixed provision of ammonium- and nitrate-nitrogen (MPAN) at a moderate level could enhance N uptake and translocation and promote growth of rice, but current understanding of their molecular mechanisms is still insufficient. Two rice lines of W6827 and GH751, with contrasting ability of N uptake, were subjected to four levels of MPAN (NH₄⁺/NO₃^- = 100:0, 75:25, 50:50, 25:75) in hydroponic experiments. In terms of plant height, growth rate and shoot biomass, growth of GH751 tended to increase firstly and then decrease with enhancement in NO₃^--N ratio. It attained maximal level under 75:25 MPAN, with an 8.3% increase in shoot biomass. In general, W6827 was comparatively less responsive to MPAN. For GH751, the uptake rate of N, phosphor (P) and potassium (K) under 75:25 MPAN was enhanced by 21.1%, 20.8% and 16.1% in comparison with that of control (100:0 MPAN). Meanwhile, the translocation coefficient and content in shoots of N, P and K were all increased significantly. In contrast to transcriptomic profile under control, 288 differentially expressed genes (DEGs) were detected to be up-regulated and 179 DEGs down-regulated in transcription under 75:25 MPAN. Gene Ontology analysis revealed that some DEGs were up-regulated under 75:25 MPAN and they code for proteins mainly located in membrane and integral component of membrane and involved in metal ion binding, oxidoreductase activity and other biological processes. KEGG pathway enrichment analysis indicated that DEGs related to nitrogen metabolism, carbon fixation in photosynthetic organisms, photosynthesis, starch and sucrose metabolism, and zeatin biosynthesis were up- or down-regulated in transcription under 75:25 MPAN, and they are responsible for improved nutrient uptake and translocation and enhanced growth of seedlings.

Glycine betaine capped ZnO NPs eliminate oxidative stress to coriander plants grown under NaCl presence

Salinity is one of the major abiotic stresses for sustainable agriculture. The use of mineral nutrients in form of nanoparticles can be a novel strategy to fight against abiotic stresses. An in vitro study has been conducted to investigate the effect of zinc oxide nanoparticles (ZnO NPs) capped with glycine betaine (ZnOBt) on coriander plants exposed to saline (NaCl) stress. SEM and XRD analysis revealed 14.73 nm and 17.34 nm size of ZnO and ZnOBt NPs, respectively with spherical to hexagonal structures. Coriander plant length and biomass increased by the application of ZnO and ZnOBt NPs. ZnOBt NPs depicted promising results at 100 mg/L where, shoot and root length increased up to 14 cm and 13 cm, respectively as compared to plants grown under saline stress. ZnOBt NPs also increased fresh and dry weight of shoots and roots as compared to other treatments. The results depict that ZnOBt NPs mitigated stress condition. This is evident from concentration of phenolic and flavonoid contents that decreased in both roots and shoots. Free radical scavenging activity, total antioxidant capacity and total reducing power also decreased in plants by ZnOBt NPs when applied with stress. The concentration of superoxide and peroxide dismutase also decreased by application of ZnOBt NPs to salt stress plants. Glycine betaine with ZnO NPs, in conclusion, can be an effective remedy for salinity-exposed plants. These nanoparticles can be encouraged as a viable technique to overcome the detrimental effects of saline stress on plants.

Physiological and Morphological Responses of Blackberry Seedlings to Different Nitrogen Forms

Blackberries are an emerging third-generation fruit that are popular in Europe, and specific nitrogen (N) supply is an important factor affecting their growth and development. To study the optimal N fertilizer for blackberry seedlings, no N (CK), nitrate (NO₃^-)-N, ammonium (NH₄⁺)-N and urea were applied to one-year-old 'Ningzhi 4' blackberry plants at a key growth period (from May to August) to explore the effects of different N forms on the physiological characteristics. Correlation and principal component analysis were used to determine the relationships between various indexes. Ammonium (NH₄⁺) or urea-fed plants had a better growth state, showed a greater plant height, biomass, SPAD values and enhanced antioxidant enzyme activities and photosynthesis. In addition, NH₄⁺ was beneficial to the accumulation of sugars and amino acids in leaves and roots, and promoted the transport of auxin and cytokinin to leaves. NO₃^- significantly inhibited root growth and increased the contents of active oxygen, malondialdehyde and antioxidants in roots. Correlation and principal component analysis showed that growth and dry matter accumulation were closely related to the antioxidant system, photosynthetic characteristics, amino acids and hormone content. Our study provides a new idea for N regulation mechanism of blackberry and proposes a scientific fertilization strategy.

Sustaining nitrogen dynamics: A critical aspect for improving salt tolerance in plants

In the current changing environment, salt stress has become a major concern for plant growth and food production worldwide. Understanding the mechanisms of how plants function in saline environments is critical for initiating efforts to mitigate the detrimental effects of salt stress. Agricultural productivity is linked to nutrient availability, and it is expected that the judicious metabolism of mineral nutrients has a positive impact on alleviating salt-induced losses in crop plants. Nitrogen (N) is a macronutrient that contributes significantly to sustainable agriculture by maintaining productivity and plant growth in both optimal and stressful environments. Significant progress has been made in comprehending the fundamental physiological and molecular mechanisms associated with N-mediated plant responses to salt stress. This review provided an (a) overview of N-sensing, transportation, and assimilation in plants; (b) assess the salt stress-mediated regulation of N dynamics and nitrogen use- efficiency; (c) critically appraise the role of N in plants exposed to salt stress. Furthermore, the existing but less explored crosstalk between N and phytohormones has been discussed that may be utilized to gain a better understanding of plant adaptive responses to salt stress. In addition, the shade of a small beam of light on the manipulation of N dynamics through genetic engineering with an aim of developing salt-tolerant plants is also highlighted.

A systematic literature review of data envelopment analysis implementation in agriculture under the prism of sustainability

Safeguarding natural resources and energy is essential to ensure food security for future generations. Given the increase of published papers in the agricultural field applying Data Envelopment Analysis (DEA), this review seeks to address the special requirements of this methodology when implemented in the agricultural sector as well as to classify papers under sustainability aspects (economic, environmental, social). More specifically, 120 papers from Scopus and Web of Science databases were included in this review by using PRISMA methodology, and they were tested in the following groups (i) General information, (ii) DEA implementation, (iii) DEA extensions, (iv) Data type, (v) Data collection and processing, and (vi) Sustainability dimensions. Results indicate that there is a great need for weights use when performing DEA in the agricultural sector, to acquire results with greater explanatory power. Moreover, systematic data collection of multiple factors could lead to the implementation of complex methodologies, providing feasible solutions to the involved stakeholders. Lastly, the social aspect is the least represented dimension out of the three aspects of sustainability, indicating the need for the integration of social factors in such analyses, especially when DEA is used to create a policy framework in a specific area.

Integrative physiological, metabolomic and transcriptomic analysis reveals nitrogen preference and carbon and nitrogen metabolism in blackberry plants

Nitrogen (N) is an indispensable element for plant growth and development. To understand the regulation of underlying carbon (C) and N metabolism in blackberry plants, we performed integrated analyses of the physiology, metabolome and transcriptome. Blackberry plants were subjected to no N, nitrate (NO₃⁻)-N, ammonium (NH₄⁺)-N and urea treatments. Our results showed that the NH₄⁺-N treatment yielded higher values for the biomass, chlorophyll, antioxidants, N contents and antioxidant enzyme activities, as well as lower levels of free radicals and the C/N ratio compared with other treatments. Transcriptome analysis showed that different N forms significantly affected photosynthesis, flavonoid biosynthesis and the TCA cycle. Metabolome analysis indicated that the levels of lipids, carbohydrates, flavonoids and amino acids were markedly changed under different N treatments. Integrated transcriptomic and metabolomic data revealed that amino acids, including proline, arginine, L-isoleucine, L-aspartate, threonine, and L-glutamate, played important roles in maintaining normal plant growth by regulating N metabolism and amino acid metabolism. Overall, blackberry plants preferentially take up NH₄⁺-N. Under the NH₄⁺-N treatment, N assimilation was stronger, flavonoid biosynthesis was decreased, and the promoting influence of NH₄⁺-N on N metabolism was better than that of NO₃⁻-N. However, the NO₃⁻-N treatment enhanced the C/N ratio, accelerated the process of C metabolism and increased the synthesis of flavonoids, thereby accelerating the flow of N metabolism to C metabolism. These results provide deeper insight into coordinating C and N metabolism and improving N use efficiency in blackberry plants.

Proteomic Approaches to Uncover Salt Stress Response Mechanisms in Crops

Salt stress is an unfavorable outcome of global climate change, adversely affecting crop growth and yield. It is the second-biggest abiotic factor damaging the morphological, physio-biochemical, and molecular processes during seed germination and plant development. Salt responses include modulation of hormonal biosynthesis, ionic homeostasis, the antioxidant defense system, and osmoprotectants to mitigate salt stress. Plants trigger salt-responsive genes, proteins, and metabolites to cope with the damaging effects of a high salt concentration. Enhancing salt tolerance among crop plants is direly needed for sustainable global agriculture. Novel protein markers, which are used for crop improvement against salt stress, are identified using proteomic techniques. As compared to single-technique approaches, the integration of genomic tools and exogenously applied chemicals offers great potential in addressing salt-stress-induced challenges. The interplay of salt-responsive proteins and genes is the missing key of salt tolerance. The development of salt-tolerant crop varieties can be achieved by integrated approaches encompassing proteomics, metabolomics, genomics, and genome-editing tools. In this review, the current information about the morphological, physiological, and molecular mechanisms of salt response/tolerance in crops is summarized. The significance of proteomic approaches to improve salt tolerance in various crops is highlighted, and an integrated omics approach to achieve global food security is discussed. Novel proteins that respond to salt stress are potential candidates for future breeding of salt tolerance.

Nitrogen Promotes the Salt-Gathering Capacity of Suaeda salsa and Alleviates Nutrient Competition in the Intercropping of Suaeda salsa/Zea mays L

Nitrogen accelerates salt accumulation in the root zone of an euhalophyte, which might be beneficial for inhibiting the salt damage and interspecific competition for nutrients of non-halophytes in intercropping. However, the variations in the effect of euhalophyte/non-halophyte intercropping with nitrogen supply are poorly understood. Here, we selected the euhalophyte Suaeda salsa (suaeda) and non-halophyte Zea mays L. (maize) as the research objects, setting up three cropping patterns in order to explore the influence of nitrogen application on the intercropping effect in the suaeda/maize intercropping. The results showed that the biomass of maize in the intercropping was significantly lower than that in the monoculture, while for suaeda, it was higher in the intercropping than that in the monoculture. The biomass of maize under NO₃^--N treatment performed significantly higher than that under no nitrogen treatment. Moreover, under suitable NO₃^--N treatment, more salt ions (Na⁺, K⁺) gathered around the roots of suaeda, which weakened the salt damage on maize growth. In the intercropping, the effect of NO₃^--N on the maize growth was enhanced when compared with the non-significant effect of NH₄⁺-N, but a positive effect of NH₄⁺-N on suaeda growth was found. Therefore, the disadvantage of maize growth in the intercropping suaeda/maize might be caused by interspecific competition to a certain extent, providing an effective means for the improvement of saline-alkali land by phytoremediation.

Photosynthetic performance and nutrient uptake under salt stress: Differential responses of wheat plants to contrasting phosphorus forms and rates

Salt stress impacts phosphorus (P) bioavailability, mobility, and its uptake by plants. Since P is involved in many key processes in plants, salinity and P deficiency could significantly cause serious damage to photosynthesis, the most essential physiological process for the growth and development of all green plants. Different approaches have been proposed and adopted to minimize the harmful effects of their combined effect. Optimising phosphorus nutrition seems to bring positive results to improve photosynthetic efficiency and nutrient uptake. The present work posed the question if soluble fertilizers allow wheat plants to counter the adverse effect of salt stress. A pot experiment was performed using a Moroccan cultivar of durum wheat: Karim. This study focused on different growth and physiological responses of wheat plants grown under the combined effect of salinity and P-availability. Two Orthophosphates (Ortho-A & Ortho-B) and one polyphosphate (Poly-B) were applied at different P levels (0, 30 and 45 ppm). Plant growth was analysed on some physiological parameters (stomatal conductance (SC), chlorophyll content index (CCI), chlorophyll a fluorescence, shoot and root biomass, and mineral uptake). Fertilized wheat plants showed a significant increase in photosynthetic performance and nutrient uptake. Compared to salt-stressed and unfertilized plants (C+), CCI increased by 93%, 81% and 71% at 30 ppm of P in plants fertilized by Poly-B, Ortho-B and Ortho-A, respectively. The highest significant SC was obtained at 45 ppm using Ortho-B fertilizer with an increase of 232% followed by 217% and 157% for both Poly-B and Ortho-A, respectively. The Photosynthetic performance index (PI_tot) was also increased by 128.5%, 90.2% and 38.8% for Ortho-B, Ortho-A and Poly B, respectively. In addition, Poly-B showed a significant enhancement in roots and shoots biomass (49.4% and 156.8%, respectively) compared to C+. Fertilized and salt-stressed plants absorbed more phosphorus. The P content significantly increased mainly at 45 ppm of P. Positive correlations were found between phosphorus uptake, biomass, and photosynthetic yield. The increased photochemical activity could be due to a significant enhancement in light energy absorbed by the enhanced Chl antenna. The positive effect of adequate P fertilization under salt stress was therefore evident in durum wheat plants.

The performance of Miscanthus hybrids in saline-alkaline soil

Cultivating the dedicated biomass crop Miscanthus on marginal land is a sustainable means of avoiding competition with food crops for arable land. A large proportion of global marginal land is saline-alkaline; however, little is known about the performance of Miscanthus in saline-alkaline soil. In this study, Miscanthus × giganteus and ten other Miscanthus hybrids grown in the Yellow River Delta were exposed to low and saline-alkaline soils during the 2016-2018 growing season to evaluate the agronomic traits, biomass quality and the potential productive index of eleven Miscanthus genotypes. Plant biomass, plant height, and tiller number significantly decreased in high saline-alkaline soil. In particular, the average plant biomass of ten Miscanthus hybrids in low saline-alkaline soil in 2017 and 2018 were 0.21 and 2.25 kg per plant, respectively, and in high saline-alkaline soil were 0.13 and 0.65 kg per plant, respectively. Cell wall, cellulose, and nitrogen content of all genotypes significantly decreased in high saline-alkaline soil, while hemicellulose, ash, sodium, potassium, magnesium, and calcium content significantly increased. However, high saline-alkaline soil had no observable impact on lignin content of Miscanthus biomass. The effect of high saline-alkaline on biomass quality parameters could provide important information for the application of Miscanthus biomass in saline-alkaline soil. The selected genotypes (A5) could be considered as breeding materials in saline-alkaline soil.

Comparison and interpretation of freshwater bacterial structure and interactions with organic to nutrient imbalances in restored wetlands

Chemical oxygen demand to nitrogen (COD/N) and nitrogen to phosphorus (N/P) ratios have distinct effects on bacterial community structure and interactions. However, how organic to nutrient imbalances affect the structure of freshwater bacterial assemblages in restored wetlands remains poorly understood. Here, the composition and dominant taxa of bacterial assemblages in four wetlands [low COD/N and high N/P (LH), low COD/N and low N/P (LL), high COD/N and high N/P (HH), and high COD/N and low N/P (HL)] were investigated. A total of 7,709 operational taxonomic units were identified by high throughput sequencing, and Actinobacteria, Proteobacteria, and Cyanobacteria were the most abundant phyla in the restored wetlands. High COD/N significantly increased bacterial diversity and was negatively correlated with N/P (R2 = 0.128; p = 0.039), and the observed richness (Sobs) indices ranged from 860.77 to 1314.66. The corresponding Chao1 and phylogenetic diversity (PD) values ranged from 1533.42 to 2524.56 and 127.95 to 184.63. Bacterial beta diversity was negatively related to COD/N (R2 = 0.258; p < 0.001). The distribution of bacterial assemblages was mostly driven by variations in ammonia nitrogen (NH4+-N, p < 0.01) and electrical conductivity (EC, p < 0.01), which collectively explained more than 80% of the variation in bacterial assemblages. However, the dominant taxa Proteobacteria, Firmicutes, Cyanobacteria, Bacteroidetes, Verrucomicrobia, Planctomycetes, Chloroflexi, and Deinococcus-Thermus were obviously affected by variation in COD/N and N/P (p < 0.05). The highest node and edge numbers and average degree were observed in the LH group. The co-occurrence networkindicated that LH promoted bacterial network compactness and bacterial interaction consolidation. The relationships between organic to nutrient imbalances and bacterial assemblages may provide a theoretical basis for the empirical management of wetland ecosystems.

Differential sensitivity of metabolic pathways in sugar beet roots to combined salt, heat, and light stress

Plants in nature commonly encounter combined stress scenarios. The response to combined stressors is often unpredictable from the response to single stresses. To address stress interference in roots, we applied salinity, heat, and high light to hydroponically grown sugar beet. Two main patterns of metabolomic acclimation were apparent. High salt of 300 mM NaCl considerably lowered metabolite amounts, for example, those of most amino acids, γ-amino butyric acid (GABA), and glucose. Very few metabolites revealed the opposite trend with increased contents at high salts, mostly organic acids such as citric acid and isocitric acid, but also tryptophan, tyrosine, and the compatible solute proline. High temperature (31°C vs. 21°C) also frequently lowered root metabolite pools. The individual effects of salinity and heat were superimposed under combined stress. Under high light and high salt conditions, there was a significant decline in root chloride, mannitol, ribulose 5-P, cysteine, and l-aspartate contents. The results reveal the complex interaction pattern of environmental parameters and urge researchers to elaborate in much more detail and width on combinatorial stress effects to bridge work under controlled growth conditions to growth in nature, and also to better understand acclimation to the consequences of climate change.

Growth and nitrogen metabolism in Sophora japonica (L.) as affected by salinity under different nitrogen forms

Sophora japonica is a leguminous tree species native to China. To explore the nitrogen (N) source preference and its impact on stress tolerance, a hydroponic experiment was designed in which S. japonica seedlings were supplied with sole ammonium (NH₄⁺) or sole nitrate (NO₃^-) nutrition under 75 mM NaCl-induced salt stress. The growth and N metabolism performance were investigated. In the absence of NaCl, plants fed NH₄⁺ showed better root growth than those fed NO₃^-, but there was no difference in aerial part growth. Salinity inhibited the root growth of NH₄⁺-fed plants and the shoot growth of NO₃^--fed plants, while the total N accumulation was suppressed under either N form. Specifically, in NH₄⁺-fed plants, salinity significantly increased the net photosynthetic rate, root NH₄⁺ content and root antioxidant enzyme activities. Higher nitrate reductase (NR) activities but lower glutamate synthetase (GS) activities were observed in both leaves and roots. Leaf AMT1.1 and AMT2.1a in NH₄⁺-fed plants positively reacted to salt stress, whereas the expression of four AMTs was reduced or remained unchanged in roots. In contrast, salinity suppressed the net photosynthetic rate, antioxidant enzyme activities, and GS activity in the leaves of NO₃^--fed plants. Upregulation of NPF1.2, NPF2.11, NPF4.6 and NPF7.3, as well as unaltered NR activity, caused higher NO₃^- content in the leaves. Moreover, NR and glutamate synthase (GOGAT) activities together with the transcription of most NRTs were promoted by salinity in the roots of NO₃^--fed plants. Additionally, compared to those treated with NH₄⁺, in response to salinity, NO₃^--treated seedlings showed more intensive repression of the net photosynthetic rate, chlorophyll content, and both shoot and root growth. Overall, these results suggest that S. japonica plants grew better in NH₄⁺ medium than in NO₃^- medium, and the different N metabolism responses improved S. japonica tolerance to salinity with NH₄⁺ application. This study provides new insights for understanding the mechanism of salt tolerance, breeding resistant varieties of S. japonica, and developing scientific fertilization management strategies during the seedling cultivation period.

Salinity of irrigation water selects distinct bacterial communities associated with date palm (Phoenix dactylifera L.) root

Saline water irrigation has been used in date palm (Phoenix dactylifera L.) agriculture as an alternative to non-saline water due to water scarcity in hyper-arid environments. However, the knowledge pertaining to saline water irrigation impact on the root-associated bacterial communities of arid agroecosystems is scarce. In this study, we investigated the effect of irrigation sources (non-saline freshwater vs saline groundwater) on date palm root-associated bacterial communities using 16S rDNA metabarcoding. The bacterial richness, Shannon diversity and evenness didn’t differ significantly between the irrigation sources. Soil electrical conductivity (EC) and irrigation water pH were negatively related to Shannon diversity and evenness respectively, while soil organic matter displayed a positive correlation with Shannon diversity. 40.5% of total Operational Taxonomic Units were unique to non-saline freshwater irrigation, while 26% were unique to saline groundwater irrigation. The multivariate analyses displayed strong structuring of bacterial communities according to irrigation sources, and both soil EC and irrigation water pH were the major factors affecting bacterial communities. The genera Bacillus, Micromonospora and Mycobacterium were dominated while saline water irrigation whereas contrasting pattern was observed for Rhizobium, Streptomyces and Acidibacter. Taken together, we suggest that date-palm roots select specific bacterial taxa under saline groundwater irrigation, which possibly help in alleviating salinity stress and promote growth of the host plant.

Influence of chromium and sodium on development, physiology, and anatomy of Conilon coffee seedlings

Some components found in the composition of the tannery sludge are nutrients for the plants; it can be considered an alternative source of fertilization as they have favorable agronomic characteristics. However, it is reported in some studies that the presence of chromium and sodium in this residue causes physiological and anatomical disturbances that inhibit the development of the plants. The objective of this study was to evaluate the influence of chromium and sodium on the physiology, anatomy, and development of Conilon coffee seedlings grown on substrates produced with tannery sludge and equivalent doses of chromium and sodium. The experiment was carried out in nursery using randomized block design, containing 5 treatments and 7 repetitions. The treatments consisted of the application of a 40% tannery sludge dose and equivalent doses of chromium and sodium mixed with a conventional substrate. Notably, the presence of sodium in the substrate caused greater damage to the plants, negatively influencing the physiology, anatomy, and, consequently, development of the plants, while the presence of chromium suggests that it does not influence much the evaluated characteristics. The treatment with tannery sludge, on the other hand, despite containing the same chromium and sodium contents, revealed a more pronounced negative influence on the physiology, anatomy, and development patterns of the seedlings. This shows that sodium and chromium alone are not the only factors responsible for the lowest growth indicators studied.

Nitrogen form differently modulates growth, metabolite profile, and antioxidant and nitrogen metabolism activities in roots of Spartina alterniflora in response to increasing salinity

Sodium tolerance and nitrogen-source preferences are two of the most fascinating and ecologically important areas in plant physiology. Spartina alterniflora is a highly salt-tolerant species and appears to prefer ammonium (NH₄⁺) over nitrate (NO₃^-) as an inorganic N source, presenting a suite of aboveground physiological and biochemical mechanisms that allows growth in saline environments. Here, we tested the interactive effects of salinity (0, 200, 500 mM NaCl) and nitrogen source (NO₃^-, NH₄⁺, NH₄NO₃) on some physiological and biochemical parameters of S. alterniflora at the root level. After three months of treatments, plants were harvested to determine root growth parameters and total amino acids, proline, total soluble sugars, sucrose, and root enzyme activity. The control (0 mM NaCl) had the highest root growth rate in the medium containing only ammonium and the lowest in the medium containing only nitrate. Except for NO₃^--fed plants, the 200 mM NaCl treatment generally had less root growth than the control. Under high salinity, NH₄⁺-fed plants had better root growth than NO₃^--fed plants. In the absence of salinity, NH₄⁺-fed plants had higher superoxide dismutase, ascorbate peroxidase, glutathione reductase, and guaiacol peroxidase activities than NO₃^--fed plants. Salinity generally promoted the activity of the principal antioxidant enzymes, more so in NH₄⁺-fed plants. Nitrogen metabolism was characterized by higher constitutive levels of glutamate dehydrogenase (GDH) activity under ammonia nutrition, accompanied by elevated total amino acids levels in roots. The advantage of ammonium nutrition for S. alterniflora under salinity was connected to high amino acid accumulation and antioxidant enzyme activities, together with low H₂O₂ concentration and increased GDH activity. Ammonium improved root performance of S. alterniflora, especially under saline conditions, and may improve root antioxidant capacity and N-assimilating enzyme activities, and adjust osmotically to salinity by accumulating amino acids.

Graded Moisture Deficit Effect on Secondary Metabolites, Antioxidant, and Inhibitory Enzyme Activities in Leaf Extracts of Rosa damascena Mill. var. trigentipetala

Drought affects plant growth and yield in many agricultural areas worldwide by producing negative water potentials in the root zone that reduce water availability, affecting plant development and metabolism. This study investigated the effect of varying moisture regimes (100% field capacity (FC), well-watered plants, 50% FC (moderate water stress), and 25% FC (severe water stress)) on growth parameters, chlorophyll content, and bioactive molecule patterns, and the impact on antioxidant, lipoxygenase (LOX), and acetylcholinesterase (AChE) activities in Rosa damascena. The water deficit treatments reduced biomass production for both treatments (−29 and −33%, respectively, for MWS and SWS) and total chlorophyll (−18 and −38% respectively for MWS and SWS), relative to the control. The 50% FC treatment had the greatest effect on the phenolic profiles and their respective functionalities, with significant increases in the levels of total phenolic, benzoic (gallic, p-coumaric, and syringic acids) (+32%), and cinnamic (caffeic and trans-cinnamic acid) acids (+19%) and flavonoids (epicatechin-3-O-gallate) (+15%) compared to well-watered leaves (control leaves). The 50% FC treatment also exhibited the highest potential antioxidant activities (apart from NO-quenching activity), evidenced by the lowest IC50 and EC50 values. The inhibitory LOX and AChE capacities varied depending on the severity of stress, with superior activity in the 50% FC treatment. Overall, the drought tolerance in rose was associated mainly with its suitable manipulation of antioxidant production and orderly regulation of LOX and AChE activities.

Sex-specific nitrogen allocation tradeoffs in the leaves of Populus cathayana cuttings under salt and drought stress

Nitrogen (N) partitioning within a leaf affects leaf photosynthesis and adaptation to environmental fluctuations. However, how plant sex influences leaf N allocation and its tradeoffs in acclimation to drought, excess salt and their combination remains unknown. Here, leaf N allocation between the photosynthetic and non-photosynthetic apparatus and among the components of the photosynthesis in Populus cathayana Rehder females and males were investigated under drought, salt and their combination to clarify the underlying mechanism. We found that males with a lower leaf N allocation (N_L) into non-protein N (N_np), showed a greater leaf N allocation into photosynthetic apparatus, especially into the carboxylation component under all treatments, and a greater leaf N allocation into cell wall under drought and salt stress alone, consequently causing higher photosynthetic N use efficiency (PNUE) and tolerance to stresses. Conversely, females had a greater leaf N allocation into N_np under all treatments than males and a lower leaf photosynthetic N (N_P) allocation. There was a tradeoff in leaf N allocation among photosynthetic apparatus (N_P/N_L), cell wall (N_CW/N_L) and N_np, which explained plant responses to drought, salt and their combination. Moreover, the leaf N allocation into the carboxylation component could explain the intersexual difference in responses to all treatments, while leaf cell wall N (N_CW) and N_np reflected intrasexual differences among treatments in both sexes. These findings indicate sex-specific strategies in coping with drought, salt and their combination that relate to leaf N allocation, which may contribute to sex-specific photosynthesis and niche segregation.

Ammonium and nitrate affect sexually different responses to salt stress in Populus cathayana

Nitrogen (N) fertilization is a promising approach to improve salt tolerance. However, it is poorly known how plant sex and inorganic N alter salt stress-induced Na⁺ uptake, distribution and tolerance. This study employed Populus cathayana Rehder females and males to examine sex-related mechanisms of salt tolerance under nitrate (NO₃ ^- ) and ammonium (NH₄ ⁺ ) nutrition. Males had a higher root Na⁺ efflux, lower root-to-shoot translocation of Na⁺ , and higher K⁺ /Na⁺ , which enhanced salt tolerance under both N forms compared to females. On the other hand, decreased root Na⁺ efflux and K⁺ retention, and an increased ratio of Na⁺ in leaves relative to shoots in females caused greater salt sensitivity. Females receiving NH₄ ⁺ rather than NO₃ ^- had greater net root Na⁺ uptake, K⁺ efflux, and translocation to the shoots, especially in leaves. In contrast, males receiving NO₃ ^- rather than NH₄ ⁺ had increased Na⁺ translocation to the shoots, especially in the bark, which may narrow the difference in leaf damage by salt stress between N forms despite a higher shoot Na⁺ accumulation and lower root Na⁺ efflux. Genes related to cell wall synthesis, K⁺ and Na⁺ transporters, and denaturized protein scavenging in the barks showed differential expression between females and males in response to salt stress under both N forms. These results suggested that the regulation of N forms in salt stress tolerance was sex-dependent, which was related to the maintenance of the K⁺ /Na⁺ ratio in tissues, the ability of Na⁺ translocation to the shoots, and the transcriptional regulation of bark cell wall and proteolysis profiles.

Suffer or Survive: Decoding Salt-Sensitivity of Lemongrass and Its Implication on Essential Oil Productivity

The cultivation of lemongrass (Cymbopogon flexuosus) crop is dominated by its medicinal, food preservative, and cosmetic demands. The growing economy of the lemongrass market suggests the immense commercial potential of lemongrass and its essential oil. Nevertheless, the continuous increase of the saline regime threatens the growth and productivity of most of the plant life worldwide. In this regard, the present experiment explores the salt sensitiveness of the lemongrass crop against five different levels of salt stress. Metabolomic analyses suggest that lemongrass plants can effectively tolerate a salt concentration of up to 80 mM and retain most of their growth and productivity. However, extreme NaCl concentrations (≥160 mM) inflicted significant (α = 0.05) damage to the plant physiology and exhausted the lemongrass antioxidative defence system. Therefore, the highest NaCl concentration (240 mM) minimised plant height, chlorophyll fluorescence, and essential oil production by up to 50, 27, and 45%. The overall data along with the salt implications on photosynthetic machinery and ROS metabolism suggest that lemongrass can be considered a moderately sensitive crop to salt stress. The study, sensu lato, can be used in reclaiming moderately saline lands with lemongrass cultivation converting such lands from economic liability to economic asset.

Phosphorus Fertilization Enhances Productivity of Forage Corn (Zea mays L.) Irrigated with Saline Water

Salinity is a major problem affecting crop production in many regions in the world including Morocco. Agricultural practices such as fertilization could be useful to overcome this problem and improve crop productivity. The objective of our study was to evaluate the combined effect of phosphorus fertilization and irrigation water salinity on growth, yield, and stomatal conductance of forage corn (Zea mays L.) cv. "Sy sincerro". Field experiments were carried out for two years testing four levels of irrigation water salinity (ECw = 0.7; 2, 4, and 6 dS·m^-1) and three rates of phosphorus (105, 126, and 150 kg P₂O₅·ha^-1) fertilization conducted in a split-plot design with three replications. The obtained results show that irrigation water salinity had a negative effect on all monitored parameters. For instance, the dry matter yield reduced by an average of 19.3 and 25.1% compared to the control under saline irrigation with an EC value equal to 4 and 6 dS·m^-1, respectively. The finding also showed that phosphorus applications tend to increase root weight, root length, stem length, leaf stomatal conductance, grain yield and dry matter yield under salinity conditions. For example, the addition of phosphorus with a rate of 126 and 150 kg P₂O₅·ha^-1 respectively improved dry matter yield by an average of 4 and 9% under low salinity level (ECw = 2 dS·m^-1), by 4 and 15% under medium salinity (4 dS·m^-1), and by 6 and 8% under a high salinity level (6 dS·m^-1). Our finding suggests that supplementary P application could be one of the best practices to reduce the adverse effects of high salinity on growth and development of forage corn.

Examination of the Productivity and Physiological Responses of Maize (Zea mays L.) to Nitrapyrin and Foliar Fertilizer Treatments

Nutrient stress has been known as the main limiting factor for maize growth and yield. Nitrapyrin, as a nitrification inhibitor-which reduces nitrogen loss-and foliar fertilizer treatments have been successfully used to enhance the efficiency of nutrient utilization, however, the impacts of these two technologies on physiological development, enzymatic responses, and productivity of maize are poorly studied. In this paper, the concentration of each stress indicator, such as contents of proline, malondialdehyde (MDA), relative chlorophyll, photosynthetic pigments, and the activity of superoxide dismutase (SOD) were measured in maize leaf tissues. In addition, biomass growth, as well as quantitative and qualitative parameters of yield production were examined. Results confirm the enhancing impact of nitrapyrin on the nitrogen use of maize. Furthermore, lower activity of proline, MDA, SOD, as well as higher photosynthetic activity were shown in maize with a more favorable nutrient supply due to nitrapyrin and foliar fertilizer treatments. The obtained findings draw attention to the future practical relevance of these technologies that can be implemented to enhance the physiological development and productivity of maize. However, this paper also highlights the importance of irrigation, as nutrient uptake from soil by the crops decreases during periods of drought.

Plastidial Expression of 3β-Hydroxysteroid Dehydrogenase and Progesterone 5β-Reductase Genes Confer Enhanced Salt Tolerance in Tobacco

The short-chain dehydrogenase/reductase (SDR) gene family is widely distributed in all kingdoms of life. The SDR genes, 3β-hydroxysteroid dehydrogenase (3β-HSD) and progesterone 5-β-reductases (P5βR1, P5βR2) play a crucial role in cardenolide biosynthesis pathway in the Digitalis species. However, their role in plant stress, especially in salinity stress management, remains unexplored. In the present study, transplastomic tobacco plants were developed by inserting the 3β-HSD, P5βR1 and P5βR2 genes. The integration of transgenes in plastomes, copy number and transgene expression at transcript and protein level in transplastomic plants were confirmed by PCR, end-to-end PCR, qRT-PCR and Western blot analysis, respectively. Subcellular localization analysis showed that 3β-HSD and P5βR1 are cytoplasmic, and P5βR2 is tonoplast-localized. Transplastomic lines showed enhanced growth in terms of biomass and chlorophyll content compared to wild type (WT) under 300 mM salt stress. Under salt stress, transplastomic lines remained greener without negative impact on shoot or root growth compared to the WT. The salt-tolerant transplastomic lines exhibited enhanced levels of a series of metabolites (sucrose, glutamate, glutamine and proline) under control and NaCl stress. Furthermore, a lower Na+/K+ ratio in transplastomic lines was also observed. The salt tolerance, mediated by plastidial expression of the 3β-HSD, P5βR1 and P5βR2 genes, could be due to the involvement in the upregulation of nitrogen assimilation, osmolytes as well as lower Na+/K+ ratio. Taken together, the plastid-based expression of the SDR genes leading to enhanced salt tolerance, which opens a window for developing saline-tolerant plants via plastid genetic engineering.

Arbuscular mycorrhizal symbioses alleviating salt stress in maize is associated with a decline in root-to-leaf gradient of Na+/K+ ratio

BACKGROUND

Inoculation of arbuscular mycorrhizal (AM) fungi has the potential to alleviate salt stress in host plants through the mitigation of ionic imbalance. However, inoculation effects vary, and the underlying mechanisms remain unclear. Two maize genotypes (JD52, salt-tolerant with large root system, and FSY1, salt-sensitive with small root system) inoculated with or without AM fungus Funneliformis mosseae were grown in pots containing soil amended with 0 or 100 mM NaCl (incrementally added 32 days after sowing, DAS) in a greenhouse. Plants were assessed 59 DAS for plant growth, tissue Na⁺ and K⁺ contents, the expression of plant transporter genes responsible for Na⁺ and/or K⁺ uptake, translocation or compartmentation, and chloroplast ultrastructure alterations.

RESULTS

Under 100 mM NaCl, AM plants of both genotypes grew better with denser root systems than non-AM plants. Relative to non-AM plants, the accumulation of Na⁺ and K⁺ was decreased in AM plant shoots but increased in AM roots with a decrease in the shoot: root Na⁺ ratio particularly in FSY1, accompanied by differential regulation of ion transporter genes (i.e., ZmSOS1, ZmHKT1, and ZmNHX). This induced a relatively higher Na⁺ efflux (recirculating) rate than K⁺ in AM shoots while the converse outcoming (higher Na⁺ influx rate than K⁺) in AM roots. The higher K⁺: Na⁺ ratio in AM shoots contributed to the maintenance of structural and functional integrity of chloroplasts in mesophyll cells.

CONCLUSION

AM symbiosis improved maize salt tolerance by accelerating Na⁺ shoot-to-root translocation rate and mediating Na⁺/K⁺ distribution between shoots and roots.

The rapeseed genotypes with contrasting NUE response discrepantly to varied provision of ammonium and nitrate by regulating photosynthesis, root morphology, nutritional status, and oxidative stress response

Ammonium (NH₄⁺) and nitrate (NO₃^-) are the two predominant inorganic nitrogen (N) forms available to crops in agricultural soils. However, little is known about how the NH₄⁺:NO₃^- ratio affect the growth of Brassica napus. Here, we investigated the impact of five NH₄⁺:NO₃^- ratios (100:0, 75:25, 50:50, 25:75, 0:100) on plant growth, photosynthesis, root morphology, ammonium uptake, nutritional status, oxidative stress response, and relative expression of genes involved in these processes in two rapeseed genotypes with contrasting N use efficiency (NUE). Application of NO₃^- as a N source extremely improved rapeseed growth compare to NH₄⁺. However, the best growth of the N-inefficient genotype was observed under 75:25 NH₄⁺/NO₃^- ratio, while it happens for the N-efficient genotype only under the sole NO₃^- environment. The low-NUE genotype exhibited a more developed root system, higher photosynthetic capacity, higher nutrient accumulation, and better NH₄⁺ uptake ability under the 75:25 NH₄⁺/NO₃^- ratio, resulting in a decrease of malondialdehyde (MDA) in root. However, the high-NUE genotype performed better in the above aspects under the NO₃^--only condition. Nitrate decrease MDA by reducing the activities of superoxide dismutase, peroxidase, and catalase in root of the N-efficient genotype. Moreover, significant differences were detected for the expression levels of genes involved in N uptake and oxidative stress response between the two genotypes under two NH₄⁺/NO₃^- ratios. Taken together, our results indicate that the N-inefficient rapeseed genotype prefers mixed supply of ammonium and nitrate, whereas the genotype with high NUE prefers sole nitrate environment.

Drought and salinity: A comparison of their effects on the ammonium-preferring species Spartina alterniflora

Drought and salinity are the most serious environmental factors affecting crop productivity worldwide; hence, it is important to select and develop both salt- and drought-tolerant crops. The perennial smooth cordgrass Spartina alterniflora Loisel is unusual in that it is highly salt-tolerant and seems to prefer ammonium (NH₄ ⁺ ) over nitrate (NO₃ ^- ) as an inorganic N source. In this study, we determined whether Spartina's unique preference for NH₄ ⁺ enhances performance under salt and drought stress. Greenhouse experiments were conducted to compare the interactive effects of N source, salinity, and low water availability on plant performance (growth and antioxidant metabolism). Drought significantly reduced growth and photosynthetic activity in S. alterniflora, more so with NH₄ ⁺ than NO₃ ^- ; in contrast, NH₄ ⁺ enhanced growth under high salinity. The increased tolerance of S. alterniflora to salt stress in the presence of NH₄ ⁺ was linked to a high level of antioxidant enzyme activity, combined with low MDA content, EL, and H₂ O₂ production. In contrast, drought stress negated the growth advantages for S. alterniflora exposed to salt stress in the presence of NH₄ ⁺ . The susceptibility of S. alterniflora to drought was partly due to reduced antioxidant enzyme activities, thereby reducing the defense against the oxidative damages induced by osmotic stress. In conclusion, in contrast to salt stress, drought stress negates the beneficial effects of ammonium as an N source in the C₄ plant Spartina alterniflora.

Biochemical, Physiological, and Molecular Aspects of Ornamental Plants Adaptation to Deficit Irrigation

There is increasing concern regarding global warming and its severe impact on the farming sector and food security. Incidences of extreme weather conditions are becoming more and more frequent, posing plants to stressful conditions, such as flooding, drought, heat, or frost etc. Especially for arid lands, there is a tug-of-war between keeping high crop yields and increasing water use efficiency of limited water resources. This difficult task can be achieved through the selection of tolerant water stress species or by increasing the tolerance of sensitive species. In this scenario, it is important to understand the response of plants to water stress. So far, the response of staple foods and vegetable crops to deficit irrigation is well studied. However, there is lack of literature regarding the responses of ornamental plants to water stress conditions. Considering the importance of this ever-growing sector for the agricultural sector, this review aims to reveal the defense mechanisms and the involved morpho-physiological, biochemical, and molecular changes in ornamental plant’s responses to deficit irrigation.

Adaptation of cucumber seedlings to low temperature stress by reducing nitrate to ammonium during it's transportation

BACKGROUND

Low temperature severely depresses the uptake, translocation from the root to the shoot, and metabolism of nitrate and ammonium in thermophilic plants such as cucumber (Cucumis sativus). Plant growth is inhibited accordingly. However, the availability of information on the effects of low temperature on nitrogen transport remains limited.

RESULTS

Using non-invasive micro-test technology, the net nitrate (NO3-) and ammonium (NH4+) fluxes in the root hair zone and vascular bundles of the primary root, stem, petiole, midrib, lateral vein, and shoot tip of cucumber seedlings under normal temperature (NT; 26 °C) and low temperature (LT; 8 °C) treatment were analyzed. Under LT treatment, the net NO3- flux rate in the root hair zone and vascular bundles of cucumber seedlings decreased, whereas the net NH4+ flux rate in vascular bundles of the midrib, lateral vein, and shoot tip increased. Accordingly, the relative expression of CsNRT1.4a in the petiole and midrib was down-regulated, whereas the expression of CsAMT1.2a-1.2c in the midrib was up-regulated. The results of 15N isotope tracing showed that NO3--N and NH4+-N uptake of the seedlings under LT treatment decreased significantly compared with that under NT treatment, and the concentration and proportion of both NO3--N and NH4+-N distributed in the shoot decreased. Under LT treatment, the actual nitrate reductase activity (NRAact) in the root did not change significantly, whereas NRAact in the stem and petiole increased by 113.2 and 96.2%, respectively.

CONCLUSIONS

The higher net NH4+ flux rate in leaves and young tissues may reflect the higher NRAact in the stem and petiole, which may result in a higher proportion of NO3- being reduced to NH4+ during the upward transportation of NO3-. The results contribute to an improved understanding of the mechanism of changes in nitrate transportation in plants in response to low-temperature stress.

Ammonium supply induces differential metabolic adaptive responses in tomato according to leaf phenological stage

Nitrate (NO3-) and ammonium (NH4+) are the main inorganic nitrogen sources available to plants. However, exclusive ammonium nutrition may lead to stress characterized by growth inhibition, generally associated with a profound metabolic reprogramming. In this work, we investigated how metabolism adapts according to leaf position in the vertical axis of tomato (Solanum lycopersicum cv. M82) plants grown with NH4+, NO3-, or NH4NO3 supply. We dissected leaf biomass composition and metabolism through an integrative analysis of metabolites, ions, and enzyme activities. Under ammonium nutrition, carbon and nitrogen metabolism were more perturbed in mature leaves than in young ones, overall suggesting a trade-off between NH4+ accumulation and assimilation to preserve young leaves from ammonium stress. Moreover, NH4+-fed plants exhibited changes in carbon partitioning, accumulating sugars and starch at the expense of organic acids, compared with plants supplied with NO3-. We explain such reallocation by the action of the biochemical pH-stat as a mechanism to compensate the differential proton production that depends on the nitrogen source provided. This work also underlines that the regulation of leaf primary metabolism is dependent on both leaf phenological stage and the nitrogen source provided.

Salinity induced physiological and biochemical changes in plants: An omic approach towards salt stress tolerance

Salinity is one of the major threats to sustainable agriculture that globally decreases plant production by impairing various physiological, biochemical, and molecular function. In particular, salinity hampers germination, growth, photosynthesis, transpiration, and stomatal conductance. Salinity decreases leaf water potential and turgor pressure and generates osmotic stress. Salinity enhances reactive oxygen species (ROS) content in the plant cell as a result of ion toxicity and disturbs ion homeostasis. Thus, it imbalances nutrient uptake, disintegrates membrane, and various ultrastructure. Consequently, salinity leads to osmotic and ionic stress. Plants respond to salinity by modulating various morpho-physiological, anatomical, and biochemical traits by regulating ion homeostasis and compartmentalization, antioxidant machinery, and biosynthesis of osmoprotectants and phytohormones, i. e, auxins, abscisic acid, brassinosteroids, cytokinins, ethylene, gibberellins, salicylic acid, jasmonic acid, and polyamines. Thus, this further modulates plant osmoticum, decreases ion toxicity, and scavenges ROS. Plants upregulate various genes and proteins that participate in salinity tolerance. They also promote the production of various phytohormones and metabolites that mitigate the toxic effect of salinity. Based on recent papers, the deleterious effect of salinity on plant physiology is discussed. Furthermore, it evaluates the physiological and biochemical responses of the plant to salinity along with phytohormone response. This review paper also highlights omics (genomics, transcriptomics, proteomics, and metabolomics) approach to understand salt stress tolerance.

New insights into molecular targets of salt tolerance in sorghum leaves elicited by ammonium nutrition

This study investigated the proteome modulation and physiological responses of Sorghum bicolor plants grown in nutrient solutions containing nitrate (NO₃^-) or ammonium (NH₄⁺) at 5.0 mM, and subjected to salinity with 75 mM NaCl for ten days. Salinity promoted significant reductions in leaf area, root and shoot dry mass of sorghum plants, regardless of nitrogen source; however, higher growth was observed in ammonium-grown plants. The better performance of ammonium-fed stressed plants was associated with low hydrogen peroxide accumulation, and improved CO₂ assimilation and K⁺/Na⁺ homeostasis under salinity. Proteomic study revealed a nitrogen source-induced differential modulation in proteins related to photosynthesis/carbon metabolism, energy metabolism, response to stress and other cellular processes. Nitrate-fed plants induced thylakoidal electron transport chain proteins and structural and carbon assimilation enzymes, but these mechanisms seemed to be insufficient to mitigate salt damage in photosynthetic performance. In contrast, the greater tolerance to salinity of ammonium-grown plants may have arisen from: i.) de novo synthesis or upregulation of enzymes from photosynthetic/carbon metabolism, which resulted in better CO₂ assimilation rates under NaCl-stress; ii.) activation of proteins involved in energy metabolism which made available energy for salt responses, most likely by proton pumps and Na⁺/H⁺ antiporters; and iii.) reprogramming of proteins involved in response to stress and other metabolic processes, constituting intricate pathways of salt responses. Overall, our findings not only provide new insights of molecular basis of salt tolerance in sorghum plants induced by ammonium nutrition, but also give new perspectives to develop biotechnological strategies to generate more salt-tolerant crops.

Growth-promoting bacteria and natural regulators mitigate salt toxicity and improve rapeseed plant performance

Salinity is a major environmental stress that limits plant production and portraits a critical challenge to food security in the world. In this research, the impacts of plant growth-promoting bacteria (Pseudomonas RS-198 and Azospirillum brasilense RS-SP7) and foliar application of plant hormones (salicylic acid 1 mM and jasmonic acid 0.5 mM) on alleviating the harmful effects of salt stress in rapeseed plants (Brassica napus cv. okapi) were examined under greenhouse condition. Salt stress diminished rapeseed biomass, leaf area, water content, nitrogen, phosphorus, potassium, calcium, magnesium, and chlorophyll content, while it increased sodium content, endogenous salicylic and jasmonic acids, osmolyte production, H₂O₂ and O₂^•- generations, TBARS content, and antioxidant enzyme activities. Plant growth, nutrient content, leaf expansion, osmolyte production, and antioxidant enzyme activities were increased, but oxidative and osmotic stress indicators were decreased by bacteria inoculation + salicylic acid under salt stress. Antioxidant enzyme activities were amplified by jasmonic acid treatments under salt stress, although rapeseed growth was not generally affected by jasmonic acid. Bacterial + hormonal treatments were superior to individual treatments in reducing detrimental effects of salt stress. The best treatment in rectifying rapeseed growth under salt stress was combination of Pseudomonas and salicylic acid. This combination attenuated destructive salinity properties and subsequently amended rapeseed growth via enhancing endogenous salicylic acid content and some essential nutrients such as potassium, phosphorus, and magnesium.

Nitrogen Forms Alter Triterpenoid Accumulation and Related Gene Expression in Cyclocarya paliurus (Batalin) Iljinsk. Seedlings

Cyclocarya paliurus (Batalin) Iljinsk. is a multiple function tree species distributed in subtropical areas, and its leaves have been used in medicine and nutraceutical foods in China. However, little information on the effects of nitrogen (N) forms and ratios on growth and secondary metabolite accumulation is available for C. paliurus. The impact of five NO3−/NH4+ ratios on biomass production, triterpenoid accumulation and related gene expression in C. paliurus seedlings was evaluated at the middle N nutrition supply. Significant differences in seedling growth, triterpenoid accumulation and relative gene expression were observed among the different NO3−/NH4+ ratio treatments. The highest triterpenoid content was achieved in a sole NO3− or NH4+ nutrition, while the mixed N nutrition with equal ratio of NO3− to NH4+ produced the highest biomass production in the seedlings. However, the highest triterpenoid accumulation was achieved at the treatment with the ratio of NO3−/NH4+ = 2.33. Therefore, the mixed N nutrition of NO3− and NH4+ was beneficial to the triterpenoid accumulation per plant. The relative expression of seven genes that are involved in triterpenoid biosynthesis were all up-regulated under the sole NH4+ or NO3− nutrition conditions, and significantly positive correlations between triterpenoid content and relative gene expression of key enzymes were detected in the leaves. Our results indicated that NO3− is the N nutrition preferred by C. paliurus, but the mixture of NO3− and NH4+ at an appropriate ratio would improve the leaf triterpenoid yield per area.

Impact of drought on growth, photosynthesis, osmotic adjustment, and cell wall elasticity in Damask rose

The response of Damask rose to drought and the underlying mechanisms involved are not known. In this study, vegetative, propagated rose plants were grown under control and water-deficit conditions in a greenhouse at Taïf University, south-west of Saudi Arabia. Control plants were irrigated to field capacity (FC), while water-stressed plants were irrigated to either 50% FC (mild stress) or 25% FC (severe stress). After 60 days, leaf, stem and root fresh and dry weights (g plant^-1), photosynthetic activity, leaf water potential (Ψw), leaf water content (WC), apoplastic water fraction (AWF), osmotic potential at full turgor (Ψs¹⁰⁰) and turgor loss point (Ψs⁰), cell wall elasticity, osmotic adjustment (OA), and some solutes (K⁺, Ca²⁺, Cl^-, proline and soluble carbohydrates) were evaluated. Water stress significantly decreased fresh and dry weights of R. damascena and all photosynthetic parameters, apart from leaf temperature, which increased. Severe water stress (25% FC) resulted in more negative Ψs¹⁰⁰ and Ψs⁰ values than the mild water stress and control. The AWF did not significantly change in response to water stress. The leaf bulk modulus of elasticity (ε) increased from 2.5 MPa under well-watered conditions to 2.82 and 3.5 MPa under mild and severe water stress, respectively. R. damascena experienced OA in response to water stress, which was due to the active accumulation of soluble carbohydrates and, to a lesser degree, proline under mild stress, along with tissue dehydration (passive OA) under severe stress. Overall, we identified two important mechanisms of drought tolerance in R. damascena-osmotic and elastic adjustment-but they could not offer resistance to water stress beyond 25% FC.

Osmotic adjustment in cowpea plants: Interference of methods for estimating osmotic potential at full turgor

Osmotic adjustment is a persisting controversy in studies on the effect of salt and water stress in cowpea crops. Our hypothesis is that the osmotic potential determination method interferes with the osmotic adjustment calculation. The objective of this study was to consider the osmotic adjustment comparing results obtained by pressure-volume (P-V) curves and osmometry. The experiment was conducted in a randomized block design, with six salt water concentrations 0, 20, 40, 60, 80, and 100 mmol L^-1 of NaCl in a Fluvisol. The osmotic adjustment found through osmometry were lower than those found through P-V curves. The apoplastic water fraction of the cowpea had a dilution effect, denoting overestimation of the osmotic potential by the methodology based on osmometry. This may be the source of the different interpretations of osmotic adjustment in cowpea plants. Thus, osmotic adjustment should be calculated preferably using the osmotic potential determined by method of pressure-volume curves.

Stomatal and non-stomatal limitations are responsible in down-regulation of photosynthesis in melon plants grown under the saline condition: Application of carbon isotope discrimination as a reliable proxy

Salinity is one of the most severe environmental stresses limiting agricultural crop production worldwide. Photosynthesis is one of the main biochemical processes getting affected by such stress conditions. Here we investigated the stomatal and non-stomatal factors during photosynthesis in two Iranian melon genotypes "Ghobadlu" and "Suski-e-Sabz", as well as the "Galia" F1 cultivar, with an insight into better understanding the physiological mechanisms involved in the response of melon plants to increasing salinity. After plants were established in the greenhouse, they were supplied with nutrient solutions containing three salinity levels (0, 50, or 100 mM NaCl) for 15 and 30 days. With increasing salinity, almost all of the measured traits (e.g. stomatal conductance, transpiration rate, internal to ambient CO₂ concentration ratio (C_i/C_a), Rubisco and nitrate reductase activity, carbon isotope discrimination (Δ¹³C), chlorophyll content, relative water content (RWC), etc.) significantly decreased after 15 and 30 days of treatments. In contrast, the overall mean of water use efficiency (intrinsic and instantaneous WUE), leaf abscisic acid (ABA) and flavonol contents, as well as osmotic potential (Ψ_S), all increased remarkably with increasing stress, across all genotypes. In addition, notable correlations were found between Δ¹³C and leaf gas exchange parameters as well as most of the measured traits (e.g. leaf area, biomass, RWC, Ψ_S, etc.), encouraging the possibility of using Δ¹³C as an important proxy for indirect selection of melon genotypes with higher photosynthetic capacity and higher salinity tolerance. The overall results suggest that both stomatal and non-stomatal limitations play an important role in reduced photosynthesis rate in melon genotypes studied under NaCl stress. This conclusion is supported by the concurrently increased resistance to CO₂ diffusion, and lower Rubisco activity under NaCl treatments at the two sampling dates, and this was revealed by the appearance of lower C_i/C_a ratios and lower Δ¹³C in the leaves of salt-treated plants.