Background and aimsCalcium salts are prevalent in soils, and excessive amounts of these salts can subject crops to abiotic stress, leading to yield reduction or death. While the effects of Ca2+ in calcium salt stress have been widely reported, the role of the anions remains unclear.MethodsThe response of the calcium-secreting plant Ceratostigma willmottianum to five (0, 25, 50, 100, and 200 mM) equimolar concentrations (also iso-osmotic) of Ca(NO3)2 and CaCl2 in terms of growth, morpho-anatomy, photosynthesis, physiology and biochemistry, and ion content was evaluated.ResultsPlants were more sensitive to CaCl2 than to equal concentrations of Ca(NO3)2, which caused more severe water deficit, oxidative damage, and inhibition of photosynthesis and growth. The CaCl2 sensitivity may be related to the toxicity of Cl-, which accumulates in large amounts in leaves (661-2149 mM); however, under the Ca(NO3)2 treatments, the leaf NO3- concentrations were 42-210 mM. Cl- inhibited chlorophyll synthesis and accelerated chlorophyll degradation, leading to photosystem disruption, and its inhibition of photosynthesis may involve both stomatal and nonstomatal limitation. In contrast, NO3- was not ionotoxic but rather promoted nitrogen assimilation and chlorophyll synthesis. The inhibition of photosynthesis by 100-200 mM Ca(NO3)2 originated mainly from stomatal limitation triggered by osmotic water loss. In addition, the Ca2+ secretion rate increased under calcium salt stress, which may represent a strategy for adaptation to high-calcium environments.ConclusionThe present study provides valuable information for a comprehensive understanding of calcium salt injury mechanisms and plant adaptation to high-calcium environments.

Grain protein content (GPC) often increases with nitrogen (N) fertilizer; however, low GPC is preferred for soft wheat (Triticum aestivum L.). The combined effects of decreasing N and increasing seed rate (SR) on soft wheat quality, economic benefits (Eb), apparent N recovery (ARN), and soil nitrate-N residual (SNR) are poorly understood. Field experiments were conducted with three SRs (SR135, SR180, and SR225) and two N levels (N235 and N290) in 2017-2018, and three N levels (N290, N235, and N180) with a control (N0) in 2018-19. The results showed that storage proteins, GMP, HMW-GS, and Zeleny sedimentation value significantly decreased with lower N levels and increased with higher SR. At the same SR, the significant difference for the parameters mentioned were greater at a low N rate than at a high rate. Furthermore, grain yield (GY), Eb, ARN, and SNR were significantly affected by N and SR. Increasing SR from 135 to 180 resulted in an average Eb increase of 13.32%, while increasing from 180 to 225 led to a decline of 3.75%. Compared to N290, N235 decreased SNR and GPC by 27.5% and 4.7%, respectively, but increased ARN by 18.3%. The highest Eb (13,914 CNY) and ARN value (57.5%) were observed with the treatment (N235SR180). Additionally, optimal combination for maximizing GY (90%), Eb (87.8%), and ARN (97%) was found at N235SR198, according to regression and spatial analysis. This study confirmed that optimizing N and SR can improve soft wheat quality and resource use efficiency without decreasing yield.

AimsPlant yield, nitrate accumulation risk, and the potential pathogenic microorganism are critical parameters in evaluating soil fertility management. The nitrate content in the soil-plant system is substantially driven by soil abiotic properties and soil and endophytic microorganisms which are also potential resources of plant pathogenicity. This study aimed to quantify the effects of citric acid (CA), alone or with dicyandiamide (DCD) and 3, 4-dimethylpyrazole phosphate (DMPP), on plant yield, nitrate accumulation risk and potential pathogenicity of soil-plant system.MethodsOur study contained six treatments: (1) control without CA or nitrification inhibitor (CK); (2) sole DCD application treatment (DCT); (3) sole DMPP application treatment (DMT); (4) sole CA application treatment (CAT); (5) CA + DCD application treatment (CADCT) and (6) CA + DMPP application treatment (CADMT). The nitrate contents, plant yields, and bacterial communities in soil and plant samples were analyzed.ResultsThe CA significantly reduced soil nitrate contents by 29.8%. Relative to sole CA application, extra nitrification inhibitor application significantly enhanced plant yields and decreased plant nitrate contents. The exclusive CA application could significantly stimulate the soil Actinobacteriota but reduce the soil pathogenicity, but extra nitrification inhibitors led to higher potential soil pathogenicity.ConclusionsThe single CA application could decrease nitrate accumulation risk and mitigating potential soil pathogenicity damage, while extra nitrification inhibitor application would intensify the performances of CA in decreasing plant nitrate accumulation but potentially enhancing the pathogenic. It deserves to emphasize the consideration of the tradeoffs among plant yield, nitrate accumulation risk, and potential pathogen risk when evaluating the effects of CA and nitrification inhibitors.

The high levels of nitrate (NO3-) in the surface water have contributed to eutrophication and other eco-environmental damages worldwide. Although the excessive NO3- concentrations in rivers were often attributed to anthropogenic activities, some undisturbed or slightly disturbed rivers also had high NO3- levels. This study utilized multi-pronged approaches (i.e., river natural abundance isotopes, N-15-labeling techniques, and qPCR) to provide a comprehensive explanation of the reason for the high NO3- levels in a river draining forest-dominated terrene. The river natural abundance isotopes (delta N-15/delta O-18-NO3-) indicated that the soil source (i.e., soil organic nitrogen-SON and chemical fertilizer-CF) were the primary contributors to the NO3-, and the NO3- removal was probably prevalent in the basin scale. The N-15-labeling techniques quantitatively showed that denitrification and anammox were stronger than nitrification in the soils and sediments. Structural equation models suggested that nitrification in the soils was regulated by NH4+-N contents, which, in turn, were closely related to fertilization in spring. Denitrification and anammox were largely controlled by elevation and functional gene abundances (i.e., nirK and hzsB, respectively). The hydrological isotopes (i.e., delta D/delta O-18-H2O) indicated that the transport of NO3- from soil to the river was related to the intensity of runoff leaching to the soil, In contrast, the riverine NH4+ was largely from point sources; thus, increasing runoff led to a dilution effect. This study clearly showed that soil biogeochemistry and hydrological condition of a river basin jointly shaped the high NO3- levels in the almost undisturbed river.

Nitrate leaching from soil presents a significant threat to soil health, as it can result in nutrient loss, soil acidification, and structural damage. It is crucial to quantify the spatial heterogeneity of nitrate leaching and its drivers. A total of 509 observational data points regarding nitrate leaching in northern China were collected, capturing the spatial and temporal variations across crops such as winter wheat, maize, and greenhouse vegetables. A machine learning (ML) model for predicting nitrate leaching was then developed, with the random forest (RF) model outperforming the support vector machine (SVM), extreme gradient boosting (XGBoost), and convolutional neural network (CNN) models, achieving an R-2 of 0.75. However, the performance improved significantly after integrating the four models with Bayesian optimization (all models had R-2 > 0.56), which realized quantitative prediction capabilities for nitrate leaching loss concentrations. Moreover, the XGBoost model exhibited the highest fitting accuracy and the smallest error in estimating nitrate leaching losses, with an R-2 value of 0.79 and an average absolute error (MAE) of 3.87 kg/ha. Analyses of the feature importance and SHAP values in the optimal XGBoost model identified soil organic matter, chemical nitrogen fertilizer input, and water input (including rainfall and irrigation) as the main indicators of nitrate leaching loss. The ML-based modeling method developed overcomes the difficulty of the determination of the functional relationship between nitrate loss intensity and its influencing factors, providing a data-driven solution for estimating nitrate-nitrogen loss in farmlands in North China and strengthening sustainable agricultural practices.

The insufficient taking into account of groundwater as a basis for implementing protection measures for coastal wetlands can be related to the damage they are increasingly exposed to. The aim of this study is to demonstrate the pertinence of combining hydrogeological tools with assessment of pollutant fluxes and stable isotopes of O, H and N, as well as groundwater time-tracers to identify past and present pollution sources resulting from human activities and threatening shallow groundwater-dependent ecosystems. A survey combining physico-chemical parameters, major ions, environmental isotopes (O-18, H-2, N-15 and H-3), with emerging organic contaminants including pesticides and trace elements, associated with a land use analysis, was carried out in southern Italy, including groundwater, surface water and lagoon water samples. Results show pollution of the shallow groundwater and the connected lagoon from both agricultural and domestic sources. The N-isotopes highlight nitrate sources as coming from the soil and associated with the use of manure-type fertilizers related to the historical agricultural context of the area involving high-productivity olive groves. Analysis of EOCs has revealed the presence of 8 pesticides, half of which have been banned for two decades and two considered as pollutant legacies (atrazine and simazine), as well as 15 molecules, including pharmaceuticals and stimulants, identified in areas with human regular presence, including rapidly degradable compounds (caffeine and ibuprofen). Results show that agricultural pollution in the area is associated with the legacy of intensive olive growing in the past, highlighting the storage capacity of the aquifer, while domestic pollution is sporadic and associated with regular human presence without efficient modern sanitation systems. Moreover, results demonstrate the urgent need to consider groundwater as a vector of pollution to coastal ecosystems and the impact of pollutant legacies in planning management measures and policies, with the aim of achieving 'good ecological status' for waterbodies.

Agriculture is vital for global food security, and irrigation is essential for improving crop yields. However, irrigation can pose challenges such as mineral scarcity and salt accumulation in the soil, which negatively impact plant growth and crop productivity. While numerous studies have focused on enhancing plant tolerance to high salinity, research targeting various ecotypes of Arabidopsis thaliana has been relatively limited. In this study, we aimed to identify salt-tolerant ecotypes among the diverse wild types of Arabidopsis thaliana and elucidate their characteristics at the molecular level. As a result, we found that Catania-1 (Ct-1), one of the ecotypes of Arabidopsis, exhibits greater salt tolerance compared to Col-0. Specifically, Ct-1 exhibited less damage from reactive oxygen species (ROS) than Col-0, despite not accumulating antioxidants like anthocyanins. Additionally, Ct-1 accumulated more potassium ions (K+) + ) in its shoots and roots than Col-0 under high salinity, which is crucial for water balance and preventing dehydration. In contrast, Ct-1 plants were observed to accumulate slightly lower levels of Na+ + than Col-0 in both root and shoot tissues, regardless of salt treatment. These findings suggest that Ct-1 plants achieve high salinity resistance not by extruding more Na+ + than Col-0, but rather by absorbing more K+ + or releasing less K+. + . Ct-1 exhibited higher nitrate (NO3-) 3) levels than Col-0 under high salinity conditions, which is associated with enhanced retention of K+ + ions. Additionally, genes involved in NO3-transport 3transport and uptake, such as NRT1.5 and NPF2.3, , showed higher transcript levels in Ct-1 compared to Col-0 when exposed to high salinity. However, Ct-1 did not demonstrate significantly greater resistance to osmotic stress compared to Col-0. These findings suggest that enhancing plant tolerance to salt stress could involve targeting the cellular processes responsible for regulating the transport of NO3-and 3and K+. + . Overall, our study sheds light on the mechanisms of plant salinity tolerance, emphasizing the importance of K+ + and NO3-transport 3transport in crop improvement and food security in regions facing salinity stress.

Microplastic (MP) contamination in soil severely impairs plant growth. However, mechanisms underlying the effects of MPs on plant nutrient uptake remain largely unknown. In this study, we revealed that NO3- 3- content was significantly decreased in shoots and roots of wheat plants exposed to high concentrations (50-100 mg L-1)-1 ) of MPs (1 mu m and 0.1 mu m; type: polystyrene) in the hydroponic solution. Isotope labeling experiments demonstrated that MP exposure led to a significant inhibition of NO3- 3- uptake in wheat roots. Further analysis indicated that the presence of MPs markedly inhibited root growth and caused oxidative damage to the roots. Additionally, superoxide dismutase and peroxidase activities in wheat roots decreased under all MP treatments, whereas catalase and ascorbate peroxidase activities significantly increased under the 100 mg L- 1 MP treatment. The transcription levels of most nitrate transporters (NRTs) in roots were significantly downregulated by MP exposure. Furthermore, exposure to MPs distinctly suppressed the activity of nitrate reductase (NR) and nitrite reductase (NiR), as well as the expression levels of their coding genes in wheat shoots. These findings indicate that a decline in root uptake area and root vitality, as well as in the expression of NRTs, , NR , and NiR genes caused by MP exposure may have adverse effects on NO3- 3- uptake and assimilation, consequently impairing normal growth of plants.

Inadequate management of solid waste stands out as a primary cause of environmental contamination, leading to a decline in groundwater quality in the vicinity of landfill sites. Though landfills are required by federal regulation to have liners formed by plastic or clayey layers, these liners tend to have leaks, which can result in landfill leachate percolation into the soil and aquifers, contaminating nearby water sources and further damaging ecosystems. Currently, the elevated nitrate (NO3-) concentration in groundwater spurred by landfill leachates is becoming a growing global concern. Various regions across the world present groundwater NO3- concentrations exceeding the threshold limit (50 mg/L) of WHO for drinking purpose. In this scenario, it is requisite to consider and develop highly efficient and affordable solutions for the long-term management of groundwater resources. Therefore, a bibliographical review was conducted in this paper by searching literature in Web of Science, ScienceDirect, Google Scholar, SpringerLink, PubMed, and Scopus to analyze NO3- pollution in groundwater caused by landfill leachates and explore the impacts of landfills and NO3- pollution on the environment and human health. In addition, this review also presents an overview of the leachate treatment technologies to remove nitrogenous compounds, particularly NO3-. This review entails a worldwide appraisal of groundwater NO3- pollution to comprehend the human health risks and aid in optimizing groundwater quality. A resulting framework developed in this review provides an improved grasp of the link between inadequate landfill management and adverse environmental and health outcomes and urged all stakeholders to address the issue of solid waste to ensure environmental and human health. Overall, the results emphasize the need for immediate action and collaborative efforts to mitigate these impacts and ensure the long-term sustainability of waste management practices.

In savanna ecosystems, the seasonal effects of nitrogen forms and availability, as well as their utilization by plants, influence the abundance and distribution of herbaceous species in grassland communities. This study examines seasonal effects on nitrogen availability and utilization by native grass species in the Cerrado, a savanna ecosystem in Brazil. Ammonium and nitrate levels in soil, nitrate acquisition and transport, and Nitrate Reductase Activity (NRA) in different plant parts during dry and wet periods were assessed. Results indicated higher soil nitrate availability during the wet period, influenced by precipitation, with leaves showing a higher nitrate content compared to roots. There was seasonal modulation in nitrate reduction, with leaves being the primary site during the dry period and roots during the wet period. The studied grass species exhibited heterogeneous responses to seasonal nitrogen availability, potentially affecting community abundance patterns. Findings suggest that edaphoclimatic seasonality plays a crucial role in nitrogen distribution and utilization capacity by grass plants in the Cerrado, contributing to the understanding of these ecosystems' ecology.