Soil organic matter (SOM) stability in Arctic soils is a key factor influencing carbon sequestration and greenhouse gas emissions, particularly in the context of climate change. Despite numerous studies on carbon stocks in the Arctic, a significant knowledge gap remains regarding the mechanisms of SOM stabilization and their impact on the quantity and quality of SOM across different tundra vegetation types. The main aim of this study was to determine SOM characteristics in surface horizons of permafrost-affected soils covered with different tundra vegetation types (pioneer tundra, arctic meadow, moss tundra, and heath tundra) in the central part of Spitsbergen (Svalbard). Physical fractionation was used to separate SOM into POM (particulate organic matter) and MAOM (mineral-associated organic matter) fractions, while particle-size fractionation was applied to evaluate SOM distribution and composition in sand, silt, and clay fractions. The results indicate that in topsoils under heath tundra POM fractions dominate the carbon and nitrogen pools, whereas in pioneer tundra topsoils, the majority of the carbon and nitrogen are stored in MAOM fractions. Moreover, a substantial proportion of SOM is occluded within macro-and microaggregates. Furthermore, the results obtained from FTIR analysis revealed substantial differences in the chemical properties of individual soil fractions, both concerning the degree of occlusion in aggregates and across particle size fractions. This study provides clear evidence that tundra vegetation types significantly influence both the spatial distribution and chemical composition of SOM in the topsoils of central Spitsbergen.

Ecosystem carbon use efficiency (CUE) is a key indicator of an ecosystem's capacity to function as a carbon sink. While previous studies have predominantly focused on how climate and resource availability affect CUE through physiological processes during the growing season, the role of canopy structure in regulating carbon and energy exchange, especially its interactions with winter climate processes and nitrogen use efficiency (NUE) in shaping ecosystem CUE in semi-arid grasslands, remains insufficiently understood. Here, we conducted a 5-year snow manipulation experiment in a temperate grassland to investigate the effects of deepened snow on ecosystem CUE. We measured ecosystem carbon fluxes, soil nitrogen concentration, species biomass, plants' nitrogen concentration, canopy height and cover and species composition. We found that deepened snow increased soil nitrogen availability, while the concurrent rise in soil moisture facilitated nutrient acquisition and utilization. Together, these changes supported greater biomass accumulation per unit of nitrogen uptake, thereby enhancing NUE. In addition, deepened snow favoured the dominance of C3 grasses, which generally exhibit higher NUE and greater height than C3 forbs, providing a second pathway that further elevated community-level NUE. The enhanced NUE, through both physiological efficiency and compositional shifts, promoted biomass production and facilitated the development of larger canopy volumes. Larger canopy volumes under deepened snow increased gross primary production through improved light interception, while the associated increase in autotrophic maintenance respiration was moderated by higher NUE. Besides, denser canopies reduced understorey temperatures throughout the day, particularly at night, thereby suppressing heterotrophic respiration. Ultimately, deepened snow increased ecosystem CUE by enhancing carbon uptake while limiting respiratory carbon losses. Synthesis. These findings demonstrated the crucial role of biophysical processes associated with canopy structure and NUE in regulating ecosystem CUE, which has been largely overlooked in previous studies. We also highlight the importance of winter processes in shaping carbon sequestration dynamics and their potential to modulate future grassland responses to climate change.

Legumes are a vital component of agriculture, providing essential nutrients to both humans and soil through their ability to fix atmospheric nitrogen. However, the production of legume crops is often hindered by various biotic and abiotic stresses, limiting their yield and nutritional quality of crops by damaging plant tissues, which can result in lower protein content, reduced levels of essential vitamins and minerals, and compromised seed quality. This review discusses the recent advancements in technologies that are revolutionizing the field of legume crop improvement. Genetic engineering has played a pivotal role enhancing legume productivity. Through the introduction of genes encoding for enzymes involved in nitrogen fixation, leading to higher yields and reducing the reliance on synthetic fertilizers. Additionally, the incorporation of genes conferring disease and pest resistance has significantly reduced the need for chemical pesticides, making legume cultivation more sustainable and environmentally friendly. Genome editing technologies, such as CRISPR-Cas9, have opened new avenues for precision breeding in legumes. Marker-assisted selection and genomic selection are other powerful tools that have accelerated the breeding process. These techniques have significantly reduced time and resources required to develop new legume varieties. Finally, advancement technologies for legume crop improvement are aid and enhancing the sustainability, productivity, and nutritional quality of legume crops.

Climate change is driving permafrost thaw, releasing previously frozen resources, such as nitrogen, to the soil active layer. In low-nitrogen systems, like boreal peatlands, this novel nitrogen source may benefit plant productivity. However, other resource limitations (for example, light) may limit plant access to thaw-front nitrogen. We used a stable isotope experiment to explore variations in understory boreal plant species' ability to take up different forms of newly released nitrogen from permafrost thaw under different canopy covers. This experiment occurred in a peatland in the sporadic discontinuous permafrost zone of the Northwest Territories, Canada. We added N-15 labelled ammonium, nitrate, and the amino acid glycine at the thaw front (40 cm depth) at two sites differentiated by high and low canopy cover and determined uptake of N-15 in leaves of several common and abundant boreal plant species. We found that the probability of plant uptake of thaw-front nitrogen was significantly greater at low canopy cover sites; however, nitrogen form, plant species, and foliar N-mass had no effect. We further found that Rubus chamaemorus had the highest foliar N-mass followed by Rhododendron groenlandicum, Chamaedaphne calyculata, and Vaccinium vitis-idaea. Our results demonstrate that access to nitrogen released from permafrost thaw by boreal plants may be mediated by light availability. Understanding the variation in site response to permafrost thaw contributes to our understanding of how boreal peatlands will change with ongoing climate change.

In recent years, excessive accumulations of iron (Fe), manganese (Mn), and nitrogen (N) have been observed in the groundwater of agricultural regions, particularly in flood irrigation areas. Nevertheless, the causes of this phenomenon and the associated hydrobiogeochemical processes remain elusive. This study demonstrated that redox fluctuations instigated by flood irrigation triggered a synergistic interaction between the N cycles and the activation of Fe and Mn oxides, thereby resulting in elevated concentrations of Fe, Mn, and N simultaneously. Static experiments revealed that the properties of the topsoil exerted a profound influence on the N induced release of Fe and Mn. The black soil (TFe: 1.5-2.3 times, Mn(II): 1.1-1.5 times, nitrate: 1.3-1.4 times) had greater release potential than meadow and dark brown soils due to higher electron donors/acceptors and substrates. Dynamic column experiments further elucidated that the wet-dry cycles induced by agricultural cultivation regulated the release process through the formation of zonal redox gradients and the structuring of microbial community. Organic nitrogen mineralization, chemolithotrophic nitrification, and Feammox/Mnammox were identified as the primary mechanisms responsible for the reductive dissolution of Fe-Mn oxides. On the other hand, autotrophic denitrification, with nitrate serving as the electron acceptor, constituted the main process for the reoxidation of Fe and Mn. Furthermore, the agricultural activities exerted a significant impact on the nitrate attenuation process, ultimately resulting in the recurrence of TFe (black soil: 1.5-6.3 times) and nitrate (black soil: 1.4-1.6 times) pollution during the phase after harvesting of rice (days 40-45) in saturated zone. The findings of this study not only deepened the understanding of the intricate interactions and coupled cycles between primary geochemical compositions and anthropogenic pollutants, but also provided a scientific foundation for the effective management and prevention of groundwater pollution stemming from agricultural cultivation processes.

Moderate nitrogen addition can enhance plant growth performance under salt stress. However, the regulatory effects of nitrogen addition on the growth of the leguminous halophyte medicinal plant, Sophora alopecuroides, under salt stress remain unclear. In this study, a two-factor pot experiment with different NaCl levels (1 g/kg, 2 g/kg, 4 g/kg) and NH4NO3 levels (0 mg/kg, 32 mg/kg, 64 mg/kg, 128 mg/kg) was set up to systematically study the response of S. alopecuroides plant phenotype, nodulation and nitrogen fixation characteristics, nitrogen (N), phosphorus (P), potassium (K) nutrient absorption and utilization efficiency, plant biomass and nutrient accumulation to nitrogen addition under salt stress. The results demonstrated that under mild (1 g/kg NaCl) and moderate (2 g/kg NaCl) salt stress, S. alopecuroides exhibited a relatively low nitrogen demand. Specifically, low (32 mg/kg N) and medium (64 mg/kg N) nitrogen levels significantly enhanced nodule nitrogenase activity and nitrogen fixation capacity. Furthermore, the uptake of essential nutrients, including N, P, and K, in the aboveground biomass was markedly increased, which in turn promoted the accumulation of major nutrients such as crude protein, crude fat, and alkaloids, as well as overall biomass production. However, under severe (4 g/kg NaCl) salt stress, S. alopecuroides exhibited a preference for low nitrogen levels (32 mg/kg N). Under S3 conditions, excessive nitrogen application (e.g., 64 mg/kg and 128 mg/kg N) exacerbated the damage caused by salt stress, leading to significant inhibition of nitrogen fixation and nutrient uptake. Consequently, this resulted in a substantial reduction in biomass. This study provides a theoretical basis for nitrogen nutrition management of S. alopecuroides under salt stress conditions and offers valuable insights for optimizing fertilization and nutrient management strategies in saline-alkali agricultural production.

Permafrost is increasingly vulnerable to thaw and collapse because of Arctic climate warming and wildfire activity. Arctic permafrost holds one third of global soil carbon (C) and large nitrogen (N) pools. A majority of permafrost organic matter is in the Russian Yedoma Domain. Soils in this remote region have high mineral soil C and N concentrations and massive, patterned ice wedges susceptible to degradation after disturbance. Yet, how Yedoma C and N pools will respond to the interaction of climate warming, wildfire, and permafrost thaw remains unknown. Here, we examined fire and permafrost thaw impacts in the Yedoma Domain of far northeast Siberia forests burned in 2001. We measured C and N pools, soil characteristics, and foliar chemistry and productivity. We found burning reduced soil organic layer depth, promoted active layer deepening, and initiated ground subsidence. Active layer permafrost thaw resulted in a 50% reduction in soil C pools in the top 125 cm, supported by evidence of increased decomposition from soil C isotope signatures and declining C:N. Burning and subsidence similarly diminished total soil N pools 50%, labile N pools 75%, and foliar N. Foliar N isotope signatures became more depleted after disturbance, suggesting greater reliance on mycorrhizal uptake and/or NO3-. Collectively, permafrost thaw mobilized soil organic matter, reducing soil C storage, N pools, and overall nutrient capital. Permafrost collapse is not only a significant atmospheric C source but N cycle restrictions could further diminish long-term C sequestration potential which balances permafrost C loss as the ecosystem recovers from disturbance.

Periphyton-based biofertilizer have a high potential for soil remediation, particularly for controlling soil salinization. This global environmental problem leads to low soil utilization and insufficient crop yields. Efficient and sustainable methods of managing saline soils are needed to reduce salinization and improve soil fertility and crop quality. Traditional methods such as physical mulching and chemical amendments, while improving soil conditions, exhibit limited effectiveness and may damage soil structure. This study aims to evaluate the feasibility of algae-based fertilizers in remediating saline-alkali soils and improving crop performance. The review delves into the and application prospects of algae-based fertilizers, highlighting their potential from both sustainable development and economic perspectives. It further advocates integrating other emerging technologies with the production and application of algae-based fertilizers to address the increasingly severe challenges posed by degraded soil resources and environmental instability. The review found that algal fertilizers are more environmentally friendly than traditional chemical fertilizers but are not inferior in function. This approach offers more efficient and sustainable solutions for managing saline-alkaline soils and effectively achieves sus-tainable agricultural production. Furthermore, it is necessary to conduct experimental research and monitoring evaluations of algal fertilizers to formulate scientific and rational fertilization plans to meet the increasingly serious challenges facing soil resources and unstable environments. The findings of this study will provide theoretical and technical support for using algae biofertilizers for soil remediation, improving crop quality and sequestering carbon.

Nitrogen is an essential element for life but its excessive release into the environment in the form of reactive nitrogen causes severe damage, including acidification and eutrophication. One of the main sources of nitrogen pollution is the use of fertilizers in agricultural soils. Feammox is a recently described pathway that couples ammonium (NH4+) oxidation with iron (Fe) reduction. In this study, the enrichment and bioaugmentation of anaerobic sludge under conditions that promote Feammox activity were investigated. The first enrichment stage (E1) achieved 28% of ammonium removal after 28 days of incubation, with a production of 30 mg/L of Fe2+. E1 was then used as inoculum for two enrichments at 35 degrees C with different carbon sources: sodium acetate (E2) and sodium bicarbonate (E3). Neither E2 nor E3 showed significant NH4+ removal, but E2 was highly effective in iron reduction, reaching Fe2+ concentrations of 110 mg/L. Additionally, an increase in nitrate (NO3-) concentration was observed, which may indicate the occurrence of this pathway in the Feammox process. The Monod kinetic model, analyzed using AQUASIM software, showed a good fit to the experimental data for NH4+, NO3-, and Fe2+. Sequencing analysis revealed the presence of phyla associated with Feammox activity. Although there was only a slight difference in NH4+ removal between the bioaugmented and non-augmented control sludge, the bioaugmented sludge was statistically superior in nitrate production and iron reduction. This study provides valuable insights into the enrichment and bioaugmentation of the Feammox process potential large-scale wastewater treatment applications.

Drought and soil nitrogen (N) deficiency are the limiting factors for poplar plantation productivity improvement in semi-arid regions. N addition could alleviate the growth decline of trees caused by drought; however, the effectiveness under severe drought and the underlying ecophysiological understanding remains uncertain. To further clarify the mechanisms of N addition in regulating tree biomass accumulation under different drought levels, we investigated the effects of 6 g NH4NO3 per plant addition on the carbon and N assimilation and biomass accumulation of potted poplar seedlings under moderate or severe drought (40 % or 20 % of field capacity) conditions, with a particular emphasis on carbon and N interactions. We found that under moderate drought, N addition markedly promoted the activities of antioxidases, nitrate reductase (39 %), and N concentration (56 %) in leaves, significantly alleviated the damages of the membranes and photosystem II, and increased both leaf area (69 %) and chlorophyll content per unit leaf area, along with net photosynthesis rate (34 %), thereby significantly alleviating growth restrictions. However, under severe drought, although N addition increased the accumulation of both soluble sugars and N of the whole plant, it did not ameliorate the damage to membranes and photosystem II, nor did it improve chlorophyll content, leaf area, or biomass accumulation. Therefore, N addition could increase leaf area, enhance antioxidants, and positively influence leaf carbon assimilation (0.60, p < 0.001) in poplar seedlings under moderate drought. The restrictions on leaf area and carbon assimilation were exacerbated during severe drought, which mitigated the positive effects of N addition on carbon assimilation and biomass accumulation. The findings of this study suggest that the growth of hybrid poplar can be enhanced by applying N fertilizer under mild drought conditions. In contrast, N fertilization has no significant effect in severe drought conditions.