Soil Nitrogen Content Research Articles

Siderophore Production Capability of Nitrogen-Fixing Bacterium (NFB) GXGL-4A Regulates Cucumber Rhizosphere Soil Microecology

Many nitrogen-fixing bacteria can produce siderophores for iron acquisition in soil, but the impact of their siderophore-producing capabilities on the rhizosphere soil microecology is not well understood. To explore the effects of root inoculation with NFB strains with different siderophore-producing capabilities on the rhizosphere soil microecology and deeply evaluate the application value of a high-yielding siderophore strain in promoting crop growth, the wild-type nitrogen-fixing bacterial strain Kosakonia radicincitans GXGL-4A and its Tn5 mutants M107 (high siderophore-producing ability) and M246-2 (deficient in siderophore production) were used as biofertilizers in cucumber rhizosphere soil. Iron is important for the growth of bacterial cells, and the mutant M246-2 showed the slowest growth rate compared to the other strains when incubated in an A15 nitrogen-free medium supplied with different levels of iron. The mutant M107 had the strongest chelating ability for iron, with the largest yellow halo on the CAS detection plate. There were statistically significant differences in the halo diameters among the three NFB groups. Compared with the control group, the application of NFB significantly increased the activities of soil peroxidase and dehydrogenase and altered the soil nitrogen contents. Fertilization with the mutant M107 significantly improved the cucumber biomass and reduced the abundance and diversity of bacterial communities in the rhizosphere soil compared to the other groups. The contents of soil ammonium nitrogen and total nitrogen and soil dehydrogenase showed significant correlations with the abundance of the top 50 dominant genera in the soil. The soil TN content was the essential factor affecting the abundance of Kosakonia bacteria in the cucumber rhizosphere.

Soil Aggregate Stability and Characteristics of Nitrogen, Phosphorus, and Potassium Contents in Cut Slope Soils With Different Aspects in Plateau Areas

ABSTRACTSlope aspects can affect the soil‐forming process. The implementation of road construction projects in plateau regions has resulted in the formation of numerous cut slopes. However, the soil aggregate stability and the characteristics of soil nitrogen (N), phosphorus (P), and potassium (K) nutrients under different cut slope aspects (east‐facing slope (EFS), west‐facing slope (WFS), south‐facing slope (SFS) and north‐facing slope (NFS)) are still unclear. In this context, the present study aims to assess the characteristics and influencing factors of soil aggregate stability, as well as N, P, and K contents, under different slope aspects in typical cut slope soils with the four different aspects in the southwestern plateau of China. In addition, the relationships of the soil aggregate stability with the soil N, P, and K contents were further explored in this study. The results showed significant differences in the soil aggregate stability (MWD, mean weight diameter) between the four slope aspects. The MWD values of the WFS and SFS were 1.18 and 1.16, respectively, which were significantly higher than those of the EFS and NFS (p < 0.05). Large macroscopic aggregates (LMA) showed the greatest contribution to the MWD values. The soil total phosphorus (TP), total nitrogen (TN), total potassium (TK), alkali‐hydrolyzed nitrogen (AN), available phosphorus (AP), available potassium (AK), and soil organic carbon (SOC) contents showed significant differences between the four slope aspects and soil particle sizes. However, comparatively lower SOC contents were observed in the silt and clay fraction (SCA). The SOC contents and soil pH were the major factors influencing the LMA and SCA, which, in turn, affected the soil aggregate stability and contents of N, P, and K. The current study provides a useful reference for improving the quality of cut slope soils.

Moderate grazing reduces while mowing increases greenhouse gas emissions from a steppe grassland: Key modulating function played by plant standing biomass.

Grassland represents one of the most expansive terrestrial ecosystems, exerting a profound influence on atmospheric greenhouse gas (GHG) levels within the broader context of global change. Both climate and land use changes play important roles in modulating grassland GHG emissions by directly or indirectly altering soil physical and chemical properties, especially soil temperature and inorganic nitrogen content. The optimal grassland management practices need to simultaneously meet the requirements of reducing GHG emissions, maintaining biological biodiversity, and ensuring productivity. However, the information on the management effects on GHG emissions from natural grasslands is still insufficient. Here we conducted a six-year grazing and mowing experiment in a semi-arid steppe grassland in central Inner Mongolia, and employed the static chamber method to investigate the effects of three major management measures, fencing, grazing and mowing, on ecosystem respiration (CO2 emission), methane uptake (CH4), and nitrous oxide emission (N2O) patterns in the experimental grassland. The results demonstrated that: (i) moderate grazing reduced plant aboveground standing biomass and CO2 emissions, but promoted belowground nutrient cycling and CH4 uptake; (ii) mowing enhanced plant biomass production, increased soil carbon and nitrogen content, and also increased CO2 emission; (iii) reducing grazing frequency reduced plant biomass loss and N2O emissions. We conclude that grazing at a moderate intensity and frequency is the best for mitigating GHG emissions while maintaining grassland production, and that mowing enhancement of plant production and GHG emissions should be considered in optimizing grassland management.

Fire-driven disruptions of global soil biochemical relationships

Fires alter the stability of organic matter and promote soil erosion which threatens the fundamental coupling of soil biogeochemical cycles. Yet, how soil biogeochemistry and its environmental drivers respond to fire remain virtually unknown globally. Here, we integrate experimental observations and random forest model, and reveal significant divergence in the responses of soil biogeochemical attributes to fire, including soil carbon (C), nitrogen (N), and phosphorus (P) contents worldwide. Fire generally decreases soil C, has non-significant impacts on total N, while it increases the contents of inorganic N and P, with some effects persisting for decades. The impacts of fire are most strongly negative in cold climates, conifer forests, and under wildfires with high intensity and frequency. Our work provides evidence that fire decouples soil biogeochemistry globally and helps to identify high-priority ecosystems where critical components of soil biogeochemistry are especially unbalanced by fire, which is fundamental for the management of ecosystems in a world subjected to more severe, recurrent, and further-reaching wildfires.

Interaction between arbuscular mycorrhizal fungi and dark septate endophytes in the root systems of Populus euphratica and Haloxylon ammodendron under different drought conditions in Xinjiang, China

Background and AimsArbuscular mycorrhizal fungi (AMF) and dark septate endophytes (DSE) are known to enhance the tolerance of host plants to biotic and abiotic stresses, but the mechanism of their interaction under natural conditions has not been extensively studied.MethodsWe analyzed the endophytic fungal diversity and colonization characteristics in the typical desert plants Populus euphratica and Haloxylon ammodendron and the relationship between them and environmental factors.ResultsExcept for DSE in the roots of H. ammodendron, the colonization rates of AMF and DSE were significantly positively correlated with drought severity. The abundance of AMF and DSE under medium and mild drought conditions was greater than that under severe drought conditions. The root colonization rate and abundance of AMF were lower than those of DSE under the same drought conditions. The species diversity and abundance of AMF and DSE in P. euphratica were greater than those in H. ammodendron. AMF were more susceptible to soil factors such as soil water content, soil nitrogen and phosphorus content, and urease, whereas DSE were more affected by pH.ConclusionDrought stress has different effects on AMF and DSE in the roots of P. euphratica and H. ammodendron. DSE have a greater advantage in extremely arid environments. This study demonstrates the interaction between AMF and DSE with the host plants P. euphratica and H. ammodendron as well as their effects on the adaptation of host plants to the desert environment, which can provide a basis for strengthening desert vegetation management.

Effects of green manuring on chemical characteristics and microecology of tobacco-growing soil in central henan

ObjectiveThis study explored green manuring effects on microecology, carbon/nitrogen levels, and enzyme activity in tobacco-growing soils.MethodsAfter 30,000 kg·hm⁻² overpressure and 28 days of natural decomposition, plants (Hordeum vulgare L. (DM), Secale cereale L. (HM), Medicago sativa L. (MX), Vicia dasycarpa Ten. (SZ), Brassica napus L. (YC), and Astragalus sinicus L. (ZY)) were grown in a lab to analyze changes in carbon and nitrogen components, microbial community structure, and enzyme activities in the soil.ResultsThe results showed improved soil nutrition and increased organic matter, nitrate-nitrogen, and ammonium-nitrogen levels. Except for MX, the other treatments markedly enhanced carbon/nitrogen in the soil microbial biomass. Compared to the CK treatment, the HM treatment boosted alkaline phosphatase and catalase activities by 20.54% and 61.98%, respectively, and increased the soil microbial biomass carbon and nitrogen content by 99.59% and 61.07%, respectively. Green manuring altered bacterial and fungal community structures. Proteobacteria, Actinobacteria, Chloroflexi, Firmicutes, Acidobacteria, Planctomycotes, and Gemmatimonadetes were the dominant bacterial communities. MX significantly increased the abundance of Bacteroidetes. Over half of all soil fungi were Ascomycota, with SZ substantially increasing their abundance. LEfSe analysis revealed 29 differential bacterial and fungal species (LDA > 3.5); fungi comprised 29 distinct species in six treatments (LDA > 4), with the exception of the YC treatment. Fusarium and Mortierella were positively correlated with sucrase and urease activities and negatively correlated with other markers, whereas Sphingomonas was strongly negatively correlated with UE and positively correlated with other indicators. HM showed the highest relative abundance of genes related to the tricarboxylic acid cycle (icd), starch breakdown (malZ), nitrification process (amoABC, hao), and nitrogen fixation process (nifK, nifD, nifH). Secale cereale L. manuring effectively improved the carbon sequestration and nitrogen mineralization capacity of soil microorganisms.ConclusionGreen manuring improved soil nutrition and microecology, controlling bacterial community composition, with optimal results when turning Secale cereale L. first.

Effects of Herbaceous Plant Encroachment on the Soil Carbon Pool in the Shrub Tundra of the Changbai Mountains

Under global warming, vegetation composition changes induced by plant encroachment have a significant impact on the carbon balance of tundra ecosystems. The encroachment of herbaceous plants into indigenous shrub communities has changed the aboveground and belowground litter carbon input and the characteristics in the shrub tundra of the Changbai Mountains. However, the impact of variations in litter characteristics and litter carbon input on the dynamics of soil organic carbon (SOC) pool concentrations and SOC stability remains ambiguous. In this study, aboveground and belowground litter and soil samples were collected for lab experiments. Our results showed that the increase in aboveground litter and belowground litter due to Deyeuxia purpurea encroachment increased the SOC concentration. Simultaneously, D. purpurea encroachment decreased the soil C/N by decreasing the components of both aboveground and belowground litter that were resistant to decomposition (C/N and lignin/N) and increased the soil mineralization ability and available N concentrations, increased the CO2 release rate, and ultimately decreased the SOC concentration. D. purpurea encroachment enhanced soil decomposition capacity by increasing the concentration of organic carbon molecular structures, such as carbohydrates, in the aboveground and belowground litter, thereby increasing the concentration of decomposable organic carbon molecular structures and active organic carbon in the soil, while simultaneously reducing the concentration of recalcitrant organic carbon. Even more, D. purpurea encroachment reduced the recalcitrant components of the aboveground and belowground litter enhanced soil mineralization capability and increased soil nitrogen concentration, which collectively increased the carbon oxidation state (COX) and decreased SOC stability. In general, global warming has led to herbaceous plant encroachment, which changes the aboveground and belowground litter carbon inputs and properties in the tundra, in turn reducing the SOC concentration and soil carbon pool stability, enhancing soil carbon emission capacity, and increasing atmospheric CO2 concentration, forming a vicious cycle.

Phenotypic Profiling of Selected Cellulolytic Strains to Develop a Crop Residue-Decomposing Bacterial Consortium.

Slow decomposition rates of cereal crop residues can lead to agronomic challenges, such as nutrient immobilization, delayed soil warming, and increased pest pressures. In this regard, microbial inoculation with efficient strains offers a viable and eco-friendly solution to accelerating the decomposition process of crop residues. However, this solution often focuses mostly on selecting microorganisms based on the appropriate enzymic capabilities and neglects the metabolic versatility required to utilize both structural and non-structural components of residues. Therefore, this study aimed to address these limitations by assessing the metabolic profiles of five previously identified cellulolytic bacterial strains, including Bacillus pumilus 1G17, Micromonospora chalcea 1G49, Bacillus mobilis 5G17, Streptomyces canus 1TG5, and Streptomyces achromogenes 3TG21 using Biolog Phenotype Microarray analysis. Moreover, this study evaluated the impact of wheat straw inoculation with single strains and a bacterial consortium on soil organic carbon and nitrogen content in a pot experiment. Results revealed that, beyond the core subset of 12 carbon sources, the strains exhibited diverse metabolic capacities in utilizing 106 carbon sources. All strains demonstrated effective straw biomass degradation compared to the negative control, with significant differences detected only in oil seed rape straw biodegradation estimations. Furthermore, wheat straw inoculated with a bacterial consortium showed a significant increase in soil organic carbon content after 180 days in the pot experiment. Overall, these findings underscore the critical role of metabolic profiling in gaining a deeper understanding of microbial capabilities and addressing the complexities of residue composition and environmental variability.

Moss Cover Modulates Soil Fungal Functional Communities and Nutrient Cycling in Alpine Forests

Moss–cyanobacteria associations serve as significant nitrogen fixers and represent the primary nitrogen sink in boreal forests. Fungi, which are essential for soil biogeochemical cycling, have community structures intrinsically linked to forest ecosystem health and productivity. Using high-throughput sequencing, we investigated differences between moss-covered and non-moss soils in two alpine forests (both plantation and natural forests) by examining soil nitrogen contents, fungal community structure, composition, and functional guilds. Results demonstrated that moss cover enhanced soil nutrient contents, including total carbon, total nitrogen, and inorganic nitrogen. It also altered fungal community characteristics, resulting in higher Chao1 and Shannon diversity indices, as well as a more complex fungal network. Notable changes in functional guilds included an increase in saprotrophic fungi abundance and a decrease in ectomycorrhizal fungi. Our findings support the concept that moss cover creates distinct soil environments: moss-covered soils attract decomposers and nutrient-mobilizing fungi (particularly saprotrophs and ectomycorrhiza), while non-moss soils favor ectomycorrhizal fungi that relieve nutrient limitation through extensional mycelial networks. These findings highlight the critical role of moss cover in sustaining forest soil health and resilience, positioning it as a cornerstone of carbon and nutrient cycling within forest ecosystems.

Long-term nitrogen fertilization alters the partitioning of amino acids between citrus leaves and fruits.

The growth of evergreen fruit trees is influenced by the interaction of soil nitrogen (N) and leaf amino acid contents. However, information on free amino acid contents in leaves of fruiting and non-fruiting branches during long-term N fertilizer application remains scarce. Here, a four-year field experiment (2018-2021) in a citrus orchard revealed consistently lower total N and amino acid contents in leaves of fruiting compared to non-fruiting branches. Appropriate N fertilizer application increased free amino acid and total N contents in leaves of both types of branches and fruits, but excessive amounts led to decreases. Correlation analysis showed that, in the early stage of fruit development, leaves on both types of branches can meet the N requirements of the fruit (R²=0.77 for fruiting, R²=0.82 for non-fruiting). As fruits entered the swelling stage, a significant positive correlation emerged between fruiting branch leaves and fruit total N content (R²=0.68), while the R² for leaves on non-fruiting branches dropped to 0.47, indicating a shift in N supply towards leaves on fruiting branches. Proline and arginine are the most abundant amino acids in these leaves. At fruit maturity, these amino acids account for more than half of the total amino acids in the fruit (29.0% for proline and 22.2% for arginine), highlighting their crucial role in fruit development. Further research is needed to investigate amino acid transport and distribution mechanisms between citrus leaves and fruits.

Response of Plant Leaf Traits to Environmental Factors in Climax Communities at Varying Latitudes in Karst Regions.

Exploring the changes in plant functional traits and their relationship with the environment in karst climax communities across different latitudes can enhance our understanding of how these communities respond to environmental gradients. In this study, we focus on climax karst climax plant communities in Guizhou Province, China. We selected three sample sites located at varying latitudes and analyzed the variations in functional traits of the plant communities at these latitudes. Additionally, we examined the relationship between functional traits and environmental factors, integrating species characteristics and community structure into our analysis. The results indicated that (1) there were significant differences in both the community leaf aspect ratio and the community-specific leaf area. (2) Soil organic carbon content exhibited significant variations across different latitudes, while soil nitrogen content was notably higher in mid-latitude and low-latitude regions compared to high-latitude areas. The distribution of soil factors was more concentrated in high and mid-latitude regions, whereas low-latitude areas displayed more pronounced variability. (3) The primary environmental factors influencing the climax community in the karst study area included soil water content (SPMC), soil bulk density (BD), soil organic carbon content (SOC), soil nitrogen content (SNC), and soil phosphorus content (SPC). Our findings suggest that karst plant communities exhibit specific combinations of functional traits at distinct latitudes. With increasing latitude, the community demonstrated a gradual shift in ecological strategy from conservative to more opportunistic. Most environmental factors imposed limiting effects on plant functional traits, with plants primarily constrained by BD during growth. Among the responses of plant functional traits to environmental factors, community-weighted leaf area and community-weighted chlorophyll content were the most sensitive to soil conditions.

Experiences with grassland aerator with blades in Karcag

In 2023-24, we examined the effects of a lawn aerator with blades on plant structure, nitrogen, and total organic carbon content in a near-natural grass association in Karcag, characterized by saline soil. Following the aeration in October, by the following May, the nitrogen and total organic carbon content of the grass soil decreased. There was a decline in species diversity and the cover value of leguminous grass species. In contrast, the cover proportion of moderately oligotrophic, community-forming Festuca pseudovina increased. Additionally, the cover value of the dominant grass species, Alopecurus pratensis, also rose due to the two-time intervention with the blade roller. Summarizing our results, the application of lawn aeration in sensitive plant structures of near-natural grass associations is justified with great care.

Challenges in alpine meadow recovery: The minor effect of grass restoration on microbial resource limitation.

Microorganisms play a vital role in restoring soil multifunctionality and rejuvenating degraded meadows. The availability of microbial resources, such as carbon, nitrogen, and phosphorus, often hinders this process. However, there is limited information on whether grass restoration can alleviate microbial resource limitations in damaged slopes of high-altitude regions. This study focused on alpine bare land impacted by engineering activities, with the goal of using grass seeds to improve soil resource availability and multifunctionality. High-throughput sequencing and enzyme stoichiometry (vector analyses) were employed to analyze microbial community composition and assess resource limitations. Our findings suggested that soil carbon, nitrogen, and phosphorus contents were low, ranging from 7.67 to 12.6gkg-1for carbon, 0.61 to 0.98gkg-1,for nitrogen, and 0.65 to 0.78gkg-1for phosphorus. Nevertheless, the standardized scores for high yield and resource acquisition strategies remained at 0.26 and 1.36 in the four groups, which were lower than those of the stress tolerance strategy. Microorganisms primarily employed the stress tolerance strategy, focusing on repairing injured cells rather than promoting cell growth, which suggests that microbial growth and metabolism were only marginally enhanced. Because of this strategy's limited impact on enhancing microbial community diversity and fostering a co-occurrence network, the resultant levels remained comparable to those observed in degraded meadows. In this case, microbial resource limitations persisted, with phosphorus remaining a constraint. Consequently, grass restoration alone offered limited relief for microbial resource limitations in alpine meadows, underscoring the challenges of solely relying on grass seeds to recover damaged alpine ecosystems.

Assessment In Depth on the Anti‐seasonal Water Fluctuations and Vegetation Dynamic Trends in a Plateau Lake, Southern China

ABSTRACTHuman activities, such as dam construction for flow regulation, modify the natural hydrological regimes of lakes and rivers. The altered flow regimes substantially influence plant growth in the water level fluctuation zone, impacting both vegetation patterns and success. The relationships among above‐ground vegetation, soil seed bank and soil microorganisms remain unexamined. This study was performed in Lashi Lake, a plateau lake in southern China characterized by anti‐seasonal water level fluctuations, and Jizi Reservoir, a reference site exhibiting natural seasonal water level variations. The primary aim was to assess the distribution pattern of plant, soil seed bank and their corresponding soil microorganism over the three flood gradients, and the relationships among them were analysed simultaneously. The findings indicated that both plant community variety and seed bank diminished as the area of soil flooding increased. The soil seed bank was a strong indication of community diversity, particularly throughout late spring and late summer. Additionally, significant correlations between the alpha diversity of soil microorganisms and the concentrations of soil carbon, nitrogen and moisture were found across the flooding gradients. The organization and diversity of soil microbial communities were significantly correlated with the alpha diversity of the plant community and the soil seed bank. The findings demonstrate that both seed banks and soil bacteria play a dynamic role in the restoration of vegetation in areas experiencing anti‐seasonal water fluctuations.

Effect of biogas slurry on the nutrient cycling and micro-organisms community in two types of soil

The biogas slurry (BS) generated through the anaerobic fermentation of biogas in pig farms is extensively employed as an organic fertilizer in Northeast China. BS is often used in large amounts because of fragmented farmland ownership resulting from previous local policies. In this work, 20 m3 · 667m-2 of BS was applied to black soil twice and to aeolian sandy soil once to explore microbial-driven nutrient cycling. The results indicated that BS increased organic carbon, total nitrogen, and total phosphorus contents in black soil. The activities of C-cycling and P-cycling enzymes in black soil were enhanced, while the activities of P-cycling enzymes in aeolian sandy soil were reduced. The BS application increased the abundance ratio of fungi to bacteria in both soil types. Total carbon, total nitrogen, and total phosphorus primarily influenced the microbial community structure in black soil, while pH was the key factor in aeolian sandy soil. However, the excessive increase of heavy metals in black soil treated twice BS posed a potential risk to the environment. Utilizing BS as fertilizer is a viable strategy applicable for Northeastern China’s agriculture, and application dosages must be adjusted according to experimental results.

Examining the Impact of Microbial Compost from Anaerobic Digestion on Soil Fertility and Maize Crop Nutrient Uptake

This research study was to evaluate the effects of combining microbial compost and mineral fertilizer on soil properties, maize growth, and nutrient uptake. Therefore, after selecting normal soil, 10 kg of soil was placed in each pot. Nine treatments with three replications were applied by using a Completely Randomized Design (CRD) for the study layout. The results revealed that the maximum plant height (101.73 cm), shoot fresh weight (69.36 g), shoot dry weight (128.6 g), root fresh weight (1.68 g), and root dry weight (0.89 g), as well as the highest content of nitrogen (1.66%), the highest phosphorus concentration (1.04%), and the maximum potassium concentration (2.13%) were noted in SF+MM + ½ NPK, while contents of iron (80.2 mg/kg), zinc (98.46 mg/kg), copper (78.66 mg/kg), and manganese (67.7 mg/kg) were also recorded in SF+MM + ½ NPK compared to other treatments. After harvesting maize crops, the lowest pH (7.27), highest EC (0.38 dS/M), and the highest contents of organic matter (1.03%) were recorded in SF+MM + ½ NPK. Maximum nitrogen content in soil (37 mg/kg), phosphorus content in soil (19.7 mg/kg), and potassium content in soil (105.8 mg/kg) were recorded in T8, while maximum contents of iron (4.88 mg/kg), zinc (1.80 mg/kg), copper (0.51 mg/kg), and manganese (1.95 mg/kg) were recorded in SF+MM + ½ NPK. The combination of SF+MM + ½ NPK showed to be the most effective treatment, whereas the usage of compost and chemical fertilizer alone remained the least effective.

Ammonia-Assimilating Bacteria Promote Wheat (Triticum aestivum) Growth and Nitrogen Utilization.

Nitrogen fertilizers in agriculture often suffer losses. Ammonia-assimilating bacteria can immobilize ammonia and reduce these losses, but they have not been used in agriculture. This study identified an ammonia-assimilating strain, Enterobacter sp. B12, which assimilated ammonia via the glutamate dehydrogenase (GDH) pathway at low levels (5 mM) and the glutamine synthetase (GS)-glutamine-2-oxoglutarate aminotransferase (GOGAT) pathway at high levels (10 mM). Inoculating wheat with B12 increased seedling dry weight, nitrogen accumulation, rhizosphere soil nitrogen content, and root enzyme activities, including GDH, superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD), under both conditions. However, root GS, GOGAT enzyme activities, and ammonia assimilation-related gene expressions were lower than the controls. The results suggest that the ammonia-assimilating bacterium promotes wheat growth, nitrogen accumulation, and soil nitrogen immobilization by establishing an ammonia and amino acid exchange with roots and enhancing root antioxidant capacity, making it a potential plant growth-promoting rhizobacteria (PGPR).

The Nitrogen Fixation Characteristics of Terrestrial Nitrogen-Fixing Cyanobacteria and Their Role in Promoting Rice Growth

Cyanobacteria, ubiquitous phototrophic prokaryotes, can enhance soil fertility and crop productivity by promoting biological nitrogen fixation, phosphate dissolution, and mineral release. In this study, five nitrogen-fixing cyanobacteria were isolated and purified from paddy soil in Jilin Province. The effects of nitrogen-fixing cyanobacteria on soil fertility and rice seedling growth were examined through a pot experiment to clarify their growth and nitrogen-fixing characteristics. The results showed that the application of nitrogen-fixing cyanobacteria led to a significant increase in soil nitrogen content. GD2 and GD8 have the highest nitrogenase activity, at 75.33 U·mg−1 and 50.34 U·mg−1, respectively. It also enhanced the activities of urease, sucrase, phosphatase, and catalase in rice soil. In addition, it significantly promoted root development and plant height in rice plants. The total number of microorganisms in rice soil increased by 133–366%. Remarkably, the Desmonostoc muscorum GD2 strain was found to exhibit higher growth state indicators, including the growth curve, chlorophyll content, carbon and nitrogen content, and biomass accumulation, compared to other algae strains. The total nitrogen content of rice leaves treated with GD2 increased by 48.73%, and the soluble protein content increased by 52.89%. GD2 has great potential as an excellent nitrogen-fixing cyanobacteria inoculant for rice, suitable for agricultural production. In conclusion, the application of these nitrogen-fixing cyanobacteria significantly increased soil nitrogen levels and activated key enzyme activities involved in plant nitrogen metabolism. Moreover, it improved nitrogen utilization rates and promoted plant growth.

Optimization of Irrigation and Fertilization in Maize–Soybean System Based on Coupled Water–Carbon–Nitrogen Interactions

Effective water and nitrogen management plays a pivotal role in enhancing crop yields while simultaneously reducing greenhouse gas emissions. This study differs from previous research by investigating the effects of water–nitrogen co-regulation involving organic carbon on the yield increase and emission mitigation in a soybean–maize system. A dryland experiment was conducted, employing 20 distinct combinations of water and nitrogen treatments that were meticulously designed for the maize–soybean system. The DSSAT crop model was employed to quantitatively elucidate the intricate interactions between water and nitrogen. A multi-objective optimization model, integrating experimental data and mechanistic insights, was constructed and refined using the NSGA-III genetic algorithm to identify the optimal water and nitrogen application ratios. An analysis of maize and soybean data from Acheng in Heilongjiang, China, indicates that optimized irrigation and nitrogen application regimes—152.2 mm and 247.1 kg·ha−1 for maize and 91.7 mm and 106.2 kg·ha−1 for soybean—substantially enhanced the net economic returns within the dryland ecosystem. There is a significant positive correlation between the yield (Y), soil nitrogen content, and soil organic carbon (SOC). Nitrate nitrogen has a significant positive correlation with CO2 gas emissions. Organic carbon changes the soil’s carbon to nitrogen ratio by participating in the water and nitrogen cycles, thereby affecting nitrogen and phosphorus loss and carbon emissions. This study presents a sustainable method for regulating water and nitrogen in the maize–soybean system.

Impacts of Vetiver Grass and DT2008 Soybean Cover Crop Practices on Soil Quality in Citrus Orchards in Cao Phong, Hoa Binh

This study investigated the efficiency of biomass management, residue quantity, and quality from Vetiver grass and DT2008 soybean cover crops in improving soil quality, including carbon and nitrogen content and soil physiochemical properties. Mesocosm experiments in pots were conducted with six treatments, each was replicated three times: CT0 (control), CT1 (2% Vetiver grass mulch), CT2 (2% DT2008 mulch), CT3 (1% Vetiver grass and 1% DT2008 mulch), CT4 (1% Vetiver grass and 1% DT2008 buried), and CT5 (2% DT2008 buried). After 12 months, significant increases in total carbon, nitrogen, and humic and fulvic acids were observed, indicating enhanced soil physiochemical properties. CT5 and CT4 showed the highest carbon, nitrogen, and cation exchange capacity (CEC) improvements. Soil moisture, pH in water (pHH2O), pH in KCl (pHKCl), and hydrolytic acidity were higher in CT1, CT2, and CT3. Nitrogen accumulation efficiency was relatively lower than carbon (24.44% to 86.67%), while carbon accumulation efficiency was much higher (41.94% to 91.72%). The most effective methods were to bury soybean biomass or mulch Vetiver grass over a soybean plant mulching layer, with Vetiver grass mulch recommended for enhancing and conserving soil fertility.