Fixation Capacity Research Articles

Enhanced adsorption and regulation mechanism of ball milling-modified biochar on Cd and atrazine in soil.

In order to improve the adsorption and immobilization capacity of biochar for Cd and atrazine in soil, the biochar was prepared from corn straw and modified by dry ball milling under various conditions. Compared with the pristine biochar (PB), the ball-milled biochar (BB) had a larger specific surface area and more pores, the number of oxygen-containing functional groups increased significantly, and the adsorption capacity of Cd and atrazine increased by 9.0% and 139.4%, respectively. Compared with a single pollutant, the adsorption capacity of PB and BB for Cd increased by 4.6% and 9.3%, respectively, and the adsorption capacity of atrazine increased by 97.1% and 11.5%, respectively. The increase of atrazine adsorption after modification was higher than that of Cd. In the desorption test, ball-milled modification decreased the desorption rate of Cd and atrazine, while the desorption rate of atrazine was much lower than that of Cd. Therefore, the biochar modified by ball-milled had stronger adsorption and fixation capacity for Cd and atrazine, which provides a basis for more effective remediation of soil polluted by Cd and atrazine.

Mechanism of pore structure on carbonation properties of cement with high carbon fixation capacity

Mechanism of pore structure on carbonation properties of cement with high carbon fixation capacity

Nitrogen fixation rates and aerial root production among maize landraces

In Mexico, the center of maize origin (Zea mays ssp. mays), there are landraces from the highlands that develop extensive aerial root systems which secrete a carbohydrate-rich mucilage. This mucilage produces a favorable environment for nitrogenase activity by diazotrophs. This plant-microbial interaction enables the fixation of nitrogen (N) from the atmosphere, reducing the required N that otherwise must come from the soil and/or fertilizers. The objective of this research was to investigate the degree to which other landraces of maize and nutrient management affect aerial root growth and the ability of maize to perform and benefit from N2 fixation. In two replicated field experiments in Columbus, Ohio, USA in 2019 and 2020, we planted 21 maize landraces and three improved varieties with and without fertilizer to measure their growth, production of aerial roots, and rate of atmospheric N2 fixation using the 15N natural abundance method. Maize accessions varied in the growth rate and number of nodes with aerial roots. Up to 36% of plant N was derived from the atmosphere, with values varying by accession, the reference plant used, and the fertilizer level. Moreover, there was a positive relationship between early growth parameters and numbers of nodes with aerial roots, which, in turn, predicted the amount of N derived from the atmosphere. Thus, larger seedlings may experience enhanced root growth and thereby benefit more from N fixation. By phenotyping a diverse set of maize accessions with and without fertilizer, this study explores both environmental and quantitative genetic variation in the traits involved in N fixation capacity, clarifying that N fixation found in the Sierra Mixe landrace is more broadly distributed than previously thought. In sum, farmers stewarding genetic diversity in a crop center of origin have preserved traits essential for biological symbioses that contribute to maize's nutrient requirements. These traits may enable maize crops grown by Mexican farmers, and farmers globally, to benefit from N fixation from the atmosphere.

Cytological Characterization of vrnp 1, a Pollen-Free Male Sterile Mutant in Mung Bean (Vigna radiata)

Mung bean (Vigna radiata) plays a significant role in agricultural trade, food processing and utilization, and cropping structure adjustment due to its abundant nutritional components, medicine-food homology, capacity for nitrogen fixation, and soil improvement. The low yield level is a crucial limitation factor in the mung bean industry, while heterosis is an efficient path for increasing crop yields. The flexible utilization of male sterile mung bean materials may solve this pressing demand in the industry. This study identified a completely male-sterile mutant, vrnp 1, in the EMS-mutagenized mung bean cultivar Jilv 10 population, which is controlled by a single recessive nuclear gene. Furthermore, we employed a series of microscopical and histological techniques and observed that the tapetal cells in the vrnp 1 mutant did not perform as expected when reaching stage 8 of anther development, notably exhibiting a delay in entering PCD. This was accompanied by a failure to deposit cell wall components onto the pollen wall, culminating in a complete absence of mature pollen and the manifestation of male sterility. In conclusion, the vrnp 1 mutant could potentially serve as a promising candidate for male sterility in exploiting hybrid vigor in mung bean. Our research may elucidate how the delayed initiation of programmed cell death in tapetal cells contributes to a factor implicated in mung bean male sterility. Furthermore, the phenotypic data collected during pivotal developmental phases may have contributed to a better grasp of mung bean microspores and anther development.

Effects of Intercropping and Mowing Frequency on Biological Nitrogen Fixation Capacity, Nutritive Value, and Yield in Alfalfa (Medicago sativa L. cv. Vernal).

Intercropping with legume forages is recognized as an effective strategy for enhancing nitrogen levels in agroforestry, while mowing may influence nitrogen fixation capacity and yield. This study investigated the rooting, nitrogen fixation, nutritive value, and yield of alfalfa (Medicago sativa L.) under intercropping and varying mowing frequencies (CK, 2, and 3) from 2021 to 2023, using walnut (Juglans regia L.) and alfalfa as experimental subjects. The results indicated that intercropping suppressed root growth, whereas increased mowing frequency stimulated root development in the topsoil (0-20 cm). Specifically, the average root length density, root surface area, and root volume from the twice- and thrice-mowed treatments increased by 18.26, 17.45, and 4.15%, respectively, in comparison to the control. The δ15N values of the intercropped alfalfa were significantly lower than those of the monocropped alfalfa (p < 0.05), with the δ15N values of the mowing-thrice treatment increasing by an average of 38.61% compared to the control. Intercropping suppressed alfalfa yield but did not affect the total nitrogen content in the leaves or the nutritive value, and all mowing treatments resulted in land equivalent ratios (LERs) greater than 1. Furthermore, increased mowing frequency enhanced both the nutritive value and yield of alfalfa. Our study suggests that intercropping with walnut can improve biological nitrogen fixation in alfalfa, and that adopting a mowing-thrice regime can optimize yield and nutritive value.

Spatial characteristics of soil potassium in the early stage of vegetation restoration and influencing factors in southwest China’s karst region

The study established experimental transects in undisturbed areas of the Caohai Nature Reserve in Weining, Guizhou Province. The study aims to examine complete successional transects in different landscapes: non-karst, karst, and vegetation restoration, using the spatiotemporal substitution method. It analyzes the distribution patterns of Total potassium (TK) and Avail potassium (AK) in the soil and employs a Generalized Linear Mixed Model (GLMM) to investigate the effects of geomorphology, soil aggregates, and their interactions on the changes in soil potassium(K) elements. Furthermore, it explores the synergistic effects of K cycling during the vegetation restoration process in karst soils. The findings indicated that: (1) In karst areas, the overall TK content was higher than in non-karst areas, while the AK content in the topsoil was higher in non-karst areas. The TK content in the karst areas tended to approach that of the vegetation restoration zone. (2) After restoration, the dominant plants changed from Gramineae to Gramineae + Asteraceae, and the vegetation richness increased, thereby improving the soil fertility and potassium fixation capacity. (3) The GLMM showed that the karst landscape had a significant effect on the TK and AK contents of surface soil. In the early stage of vegetation restoration, the joint effect of soil and vegetation affected the TK and AK contents in soil.

Sea urchin intestinal bacterial communities depend on seaweed diet and contain nitrogen-fixing symbionts.

Kelp deforestation by sea urchin grazing is a widespread phenomenon globally, with vast consequences for coastal ecosystems. The ability of sea urchins to survive on a kelp diet of poor nutritional quality is not well understood and bacterial communities in the sea urchin intestine may play an important role in digestion. A no-choice feeding experiment was conducted with the sea urchin Strongylocentrotus droebachiensis, offering three different seaweeds as diet, including the kelp Saccharina latissima. Starved sea urchins served as experimental control. Amplicons of the 16S rRNA gene were analyzed from fecal pellets. One dominant symbiont (Psychromonas marina) accounted for 44% of all sequence reads and was especially abundant in the sea urchins fed seaweed diets. The starved and field captured sea urchins consistently displayed higher diversity than the seaweed-fed sea urchins. Cloning and sequencing of the nifH gene revealed diverse nitrogen fixers. We demonstrate that the sea urchin intestinal microbiome is dynamic, with bacterial communities that are plastic depending on diet and have the capacity for nitrogen fixation. This reflects the dietary flexibility of these sea urchins, and their intestinal microbiota could be a key component in understanding catastrophic kelp forest grazing events.

Effects of Artificial Soil Fertility Gradient Strategy on the Soil Fertility, Nutrient Uptake and Growth Attributes of Chakravarthi Keerai (Chenopodium album)

The effect of artificial soil fertility gradient techniques on crop growth attributes, nutrient uptake, soil fertility and soil biological properties were studied in a field trial conducted in 2023 at Horticulture Research Station, Ooty, Nilgiris, Tamil Nadu. It was done using an inductive methodology. The field was split into three equal strips, with three graded levels of fertilizers viz., N (Urea), P2O5 (Single Super phosphate) and K2O (Muriate of Potash) applied to strip I (N0P0K0), II (N1P1K1) and III (N2P2K2). The N1 level has been determined on the basis of the blanket recommendation to Chakravarthi keerai, while the P1 and the K1 levels have been determined based on the fixing capacity of the soil phosphorus (250 kg ha-1) and the potassium (100 kg ha-1). Gradient crop, Chakravarthi keerai variety Ooty 1 was cultivated and green yield of Chakravarthi keerai was observed at the time of harvesting. At the time of harvesting, plant samples were taken and examined for N, P &amp; K content and the uptake of N, P &amp; K was calculated. The results showed that graded levels of fertilizer N, P2O5, K2O had a significant impact on soil fertility status and NPK uptake, as well as plant growth parameter. The article clearly shows a significant influence of the organic carbon, chlorophyll content, soil enzymes activity, microbial population, and Microbial biomass carbon.

Unusual Genomic and Biochemical Features of Paenarthrobacter lasiusi sp. nov-A Novel Bacterial Species Isolated from Lasius niger Anthill Soil.

The black garden ant (Lasius niger) is a widely distributed species across Europe, North America, and North Africa, playing a pivotal role in ecological processes within its diverse habitats. However, the microbiome associated with L. niger remains poorly investigated. In the present study, we isolated a novel species, Paenarthrobacter lasiusi, from the soil of the L. niger anthill. The genome of P. lasiusi S21 was sequenced, annotated, and searched for groups of genes of physiological, medical, and biotechnological importance. Subsequently, a series of microbiological, physiological, and biochemical experiments were conducted to characterize P. lasiusi S21 with respect to its sugar metabolism, antibiotic resistance profile, lipidome, and capacity for atmospheric nitrogen fixation, among others. A notable feature of the P. lasiusi S21 genome is the presence of two prophages, which may have horizontally transferred host genes involved in stress responses. P. lasiusi S21 synthesizes a number of lipids, including mono- and digalactosyldiacylglycerol, as well as steroid compounds that are typically found in eukaryotic organisms rather than prokaryotes. P. lasiusi S21 exhibits resistance to penicillins, lincosamides, fusidins, and oxazolidinones, despite the absence of specific genes conferring resistance to these antibiotics. Genomic data and physiological tests indicate that P. lasiusi S21 is nonpathogenic to humans. The genome of P. lasiusi S21 contains multiple operons involved in heavy metal metabolism and organic compound inactivation. Consequently, P. lasiusi represents a novel species with an intriguing evolutionary history, manifesting in distinctive genomic, metabolomic, and physiological characteristics. This species may have potential applications in the bioaugmentation of contaminated soils.

Divergent Effects of Monoculture and Mixed Plantation on the Trade-Off Between Soil Carbon and Phosphorus Contents in a Degraded Hilly Land

Carbon (C) and phosphorus (P) in soil are closely related to plantation types in afforestation practices. However, the trade-off between soil C and P in response to different restoration models on degraded hilly land is still not clear. In this study, four restoration patterns, including natural recovered shrubland (NS), Castanopsis hystrix plantation (CH), 10-species mixed plantation (10MX), and 30-species mixed plantation (30MX) were selected, and the physicochemical properties and readily oxidized carbon (ROC) in different layers of 1 m depth soil were measured to understand the effects of natural restoration and artificial afforestation on soil P and C pool and their trade-off on degraded hilly land in southern China. The results indicate that the total P (TP) content in each soil layer was observed to follow the order of CH &gt; 10MX &gt; 30MX &gt; NS, with monoculture (CH) exhibiting higher levels of TP than mixed plantation. However, the soil C storage of NS (59.61 t hm−2) and 30MX (57.71 t hm−2) was similar, while 10MX boasted the highest C storage (64.99 t hm−2) of the four restoration patterns, with CH being the lowest (42.75 t hm−2). In deep soil layers (20–100 cm), the 10MX plantation presented the highest for both the C pool index (CPI) and C pool management index (CMI). Moreover, the structural equation model (SEM) revealed that the soil CMI was directly regulated by the levels of soil available P and total N, while soil C pool activity was directly influenced by soil pH. Thus, our study suggests that compared to mixed plantations, the monoculture plantation (CH) demonstrates lower P uptake and utilization, resulting in a higher soil P content. Furthermore, 10MX plantation showed a superior C fixation capacity over those with 30MX and monoculture plantations. These suggests that the trade-off between soil C and P contents was commonly observed among different plantation restoration patterns. Therefore, afforestation with different tree composition and nutrient regulation is necessary for maintaining the balance between soil C and P and keeping the sustainability of plantation management in the degraded hilly lands.

Optimizing water‐nitrogen regulation for enhanced carbon absorption and reduced greenhouse gas emissions in greenhouse tomato cultivation

AbstractTo study the impact of different water‐nitrogen regulation modes on the carbon cycle of greenhouse tomatoes and determine optimal irrigation and nitrogen application levels to enhance carbon absorption and minimize greenhouse gas emissions. This study employed three irrigation levels (100%, 80%, and 60% of ET0) and three nitrogen application levels (240, 192, and 144 kg·ha−1), along with a control group (W1N1, i.e., 100% ET0‐240 kg·ha−1). Gas‐chromatography methods were used to monitor CH4 and soil CO2 emissions, while assessing dry matter, carbon content, and carbon fixation capacity of tomato organs throughout the growth period. Additionally, a system for evaluating the net ecosystem carbon budget of facility tomatoes was developed based on net primary productivity. Results indicated reduced CH4 and soil CO2 emissions with decreased irrigation and nitrogen application. Dry matter, carbon content, and carbon fixation of tomato organs initially increased with reduced nitrogen and irrigation but then declined. The W2N2 (80% ET0‐192 kg·ha−1) treatment showed maximal values for dry matter, carbon content, carbon fixation, net primary productivity (NPP), and gross primary productivity (GPP). Findings suggest a positive net ecosystem carbon budget under reduced water and nitrogen conditions, indicating carbon absorption. Specifically, the W2N2 treatment outperformed others in net carbon absorption, highlighting its potential as an effective mode for enhancing carbon sequestration in the region.

A Study on the Effect of Indirect Nitrate Supply on the Nitrogen Fixation Capacity of Soybean Nodules.

In this study, dual-root soybean (Glycine max L. Merr.) plants, with one side nodulated and the other nonnodulated, were used as experimental materials. The nonnodulated lateral roots were treated with excessive nitrate (200 mg·L-1 nitrogen) for three days, followed by a three-day nitrate withdrawal, and then subjected to excessive nitrate again for another three days. Meanwhile, the nodulated side was continuously supplied with nitrogen-free nutrient solution. We measured the nitrogenase activity, nodule quantity, and concentrations of sucrose, starch, and soluble sugars, along with the microstructure of the nodules. By analyzing these data, we aim to provide theoretical insights into how indirect nitrate supply affects the nitrogen fixation capacity of nodules. The results demonstrated that indirect supply of nitrate to the soybean nodules reduced the nodule nitrogen fixation ability, which was manifested in the decrease in nodule dry weight, nodule number, and nitrogenase activity. The reason was found to be related to the decrease in carbon sources (sucrose, starch, and soluble sugar) allocated to the nodules. Further observation of the internal structure of the nodules found that the number of infected cells in the nodules decreased with the addition of nitrate, and increased with its withdrawal. However, the addition and withdrawal of nitrate did not change the effect of nitrate on the structure of infected cells around the nodules after the first addition of nitrate. These may be one of the important reasons why nitrate indirectly affects the activity of nitrogenase in nodules.

Soil Greenhouse Gas Emissions and Nitrogen Dynamics: Effects of Maize Straw Incorporation Under Contrasting Nitrogen Fertilization Levels

Straw is widely incorporated into conservation agriculture around the world. However, its effects on greenhouse gas emissions (GHGs) and nitrogen dynamics under soils formed by the long-term application of different amounts of nitrogen (N) fertilizer are still unclear. An incubation experiment was conducted on soils collected from a field study after 6 years of contrasting N fertilization of 0 (low N), 187 (medium N), and 337 kg N ha−1 (high N), with and without maize straw. Straw amendment significantly stimulated both nitrous oxide (N2O) and carbon dioxide (CO2) fluxes (p &lt; 0.05), and increased cumulative emissions by 0.8 and 19.0 times on average compared to those without straw incorporation. Medium-N soil observably weakened N2O emissions (23.8 μg kg−1) compared to high-N soil (162.7 μg kg−1), and increased CO2 emissions (1.9 g kg−1) compared to low-N soils (2.3 g kg−1) with straw amendment. Soil NH4+-N and NO3−-N invariably increased with rising soil N level, whereas straw promoted the turnover of mineral N by enhancing soil N fixation capacity. From the first day until the end of incubation, NH4+-N decreased by 79.0% and 24.7%, while NO3−-N showed a decrease of 58.8% or an increase of 75.2%, depending on whether straw was amended or not, respectively. Moreover, partial least squares path modeling and random forest mean predictor importance were used to find that straw affected GHGs by altering the N turnover capacity. Straw amendment increased GHGs and diminished the risk of losing mineral N by enhancing its turnover. Combining straw with medium-N soil could mitigate the greenhouse effect and improve the N and carbon (C) balance in farming systems compared to low- and high-N soils. This is recommended as a farmland management strategy in Northeast China.

Different Species and Cultivars of Broad Beans, Lupins, and Clovers Demonstrated Varying Environmental Adaptability and Nitrogen Fixation Potential When Cultivated as Green Manures in Northeastern Portugal

The success of growing legumes as green manure depends on their spatial and temporal integration within agroecosystems, which minimizes competition with cash crops, and on their nitrogen (N) fixation potential. This study evaluated seven legume species for biomass production, N fixation, and suitability for use in cropping systems in northern Portugal. Oats (Avena sativa L.) were grown to estimate the N fixation using the difference method, as a non-legume reference crop is required for this purpose, and oats are widely grown in the region. The study was conducted over four cropping cycles (2021–2024) in two climate zones across four land plots. The results indicated that the biomass production and N fixation varied by the species/cultivar and cropping cycle, which was significantly influenced by spring precipitation. Broad beans (Vicia faba L.) failed to develop in one cycle on highly acidic soil (pH 4.9), showing negative N fixation values when calculated by the difference method. Conversely, the lupins maintained a relatively high level of N fixation across all the conditions, demonstrating strong environmental adaptability. Thus, the N fixation values across the four cycles ranged from −5.4 to 419.4 kg ha−1 for broad bean (cv. Favel), while yellow lupin (Lupinus luteus L.) exhibited average values between 204.0 and 274.0 kg ha−1. The percentage of N derived from the atmosphere (%Ndfa) ranged from −13.3 to 91.6, −39.4 to 85.8, 83.8 to 94.7, 74.9 to 94.3, 72.8 to 92.2, 23.1 to 75.8, and 11.7 to 21.7 for these species/cultivars. Due to their environmental adaptability, biomass production, and N fixation capacity, these legumes could be used as green manure in inter-rows of woody crops or in summer annual crops like tomatoes and maize, grown in winter as an alternative to fallow land. The lupins showed strong promise due to their environmental resilience.

Study on the intelligent protection of cement-based materials through the synergistic action of lactate intercalated double metal hydroxides and microorganisms

The effective protection of cement-based materials in marine environments was an important way to enhance the durability of marine engineering structures. In this study, the feasibility of integrating bimetallic hydroxides with microorganisms as an intelligent protection effect for cracked cement-based materials was fully demonstrated. Firstly, the calcination method was utilized to prepare double metal hydroxides with lactate intercalated layers (MgAl-LDHs-C3H5O3−). Simultaneously, systematic characterization of the prepared MgAl-LDHs-C3H5O3− was conducted, confirming the successful intercalation of inter layer ions. Secondly, the fixing capacity of MgAl-LDHs-C3H5O3− for erosive ions was tested in a simulated aqueous environment. The experimental findings demonstrated that through ion exchange, the fixation rate of SO42− reached 100 %, while that of Cl− reached 44 %. Meanwhile, C3H5O3− was exchanged into the solution system. The MgAl-LDH-C3H5O3− immobilized with erosive ions were subjected to comprehensive characterization. The outcomes unveiled a thorough elucidation of the mechanism underlying the fixation of erosive ions by MgAl-LDH-C3H5O3−. Finally, the microorganisms were cultured in a simulated solution system. The results showed that C3H5O3− exchanged into the solution was decomposed and utilized by microorganisms. A significant quantity of CaCO3 produced through microbial mineralization was identified. Based on the experimental results, it could be inferred that the combination of MgAl-LDH-C3H5O3− with microorganisms played a role in ion immobilization and mineralization improving. This study provided new insights into the intelligent protection of cracked cement-based materials in marine environments.

Analysis of Microbial Community Heterogeneity and Carbon Fixation Capabilities in Oil-Contaminated Soils in Chinese Onshore Oilfields.

This study selected 27 soil samples from four representative horizontally distributed onshore oilfields in China to explore the diversity of soil microbial communities and their carbon fixation capacity, with a focus on the potential interaction between pollution and carbon fixation under oil pollution stress. The analysis of the soil physicochemical properties and microbial community structures from these oilfield samples confirmed a clear biogeographic isolation effect, indicating spatial heterogeneity in the microbial communities. Additionally, the key factors influencing microbial community composition differed across regions. The dominant bacterial phyla of soil microorganisms under soil pollution stress were Proteobacteria, Actinobacteriota, Chloroflexi, Acidobacteriota, Firmicutes, Bacteroidota, and Gemmatimonadota. A correlation network analysis identified Immundisolibacter, Acinetobacter, Blastococcus, Truepera, and Kocuria as key players in the microbial network, with most showing positive correlations. The results of the KEGG database functional annotation showed that degradation and carbon fixation metabolic pathways coexist in soil samples and maintain a balanced relative abundance. These metabolic pathways highlight the functional diversity of microorganisms. Among them, prokaryotic and eukaryotic carbon fixation pathways, along with benzoate degradation pathways, are predominant. These findings establish a theoretical basis for further exploration of the synergistic mechanisms underlying pollution reduction and carbon sequestration by microorganisms in petroleum-contaminated soils.

Effects of Deep Tillage on Rhizosphere Soil and Microorganisms During Wheat Cultivation.

The production of wheat is fundamentally interconnected with worldwide food security. The practice of deep tillage (DT) cultivation has shown advantages in terms of soil enhancement and the mitigation of diseases and weed abundance. Nevertheless, the specific mechanisms behind these advantages are unclear. Accordingly, we aimed to clarify the influence of DT on rhizosphere soil (RS) microbial communities and its possible contribution to the improvement of soil quality. Soil fertility was evaluated by analyzing several soil characteristics. High-throughput sequencing techniques were utilized to explore the structure and function of rhizosphere microbial communities. Despite lowered fertility levels in the 0-20 cm DT soil layer, significant variations were noted in the microbial composition of the DT wheat rhizosphere, with Acidobacteria and Proteobacteria being the most prominent. Furthermore, the abundance of Bradyrhizobacteria, a nitrogen-fixing bacteria within the Proteobacteria phylum, was significantly increased. A significant increase in glycoside hydrolases within the DT group was observed, in addition to higher abundances of amino acid and carbohydrate metabolism genes in the COG and KEGG databases. Moreover, DT can enhance soil quality and boost crop productivity by modulating soil microorganisms' carbon and nitrogen fixation capacities.

Cyanobacteria's power trio: auxin, siderophores, and nitrogen fixation to foster thriving agriculture.

Cyanobacteria, often overlooked in traditional agriculture, are gaining recognition for their roles in enhancing plant growth and soil health through diverse mechanisms. This review examines their multifaceted contributions to agricultural systems, highlighting their proficiency in auxin production, which promotes plant growth and development. Additionally, we examined cyanobacteria's ability to produce siderophores that enhance iron absorption and address micronutrient deficiencies, as well as their capacity for nitrogen fixation, which converts atmospheric nitrogen into a form that plants can utilize, all with the goal of reducing reliance on synthetic fertilizers. A meta-analysis of existing studies indicates significant positive effects of cyanobacteria on crop yield, although variability exists. While some research shows considerable yield increases, other studies report non-significant changes, suggesting benefits may depend on specific conditions and crop types. The overall random-effects model estimate indicates a significant aggregate effect, with a few exceptions, emphasizing the need for further research to optimize the use of cyanobacteria as biofertilizers. Although cyanobacteria-based products are limited in comparison to seaweed-derived alternatives, for instance, ongoing challenges include regulatory issues and production costs. Integrating cultivation with wastewater treatment could enhance competitiveness and viability in the agricultural market.

Glucose addition in natural forest soils has higher biological nitrogen fixation capacity than other types of soils

Land use changes soil microbial and chemical properties, but the mechanism of biological nitrogen fixation under different land use patterns is rarely reported, so we used four types of soil: Natural forest soil (NS), healthy banana soil (HS), diseased banana soil (DS) and paddy soil (PS). Treatments included the control (CK), addition of glucose (G), addition of glucose and ammonium nitrate (GN), addition of banana straw (BS), addition of banana straw and ammonium nitrate (BSN), addition of banana root (BR), and addition of banana root and ammonium nitrate (BRN). The study found that the change of soil utilization types, glucose addition increased carbon dioxide emissions (Compared with the control, increased by 963.11%, 508.39%, 794.77% and 511.34%, respectively) and enhanced the ability of soil microbial nitrogen fixation. Importantly, natural forest soil microorganisms have a higher biological nitrogen fixation capacity compared to other types of soils. Glucose addition caused the accumulation of ammonium nitrogen (Compared with the control, increased by 426.08%, 934.21%, 420% and 1065.95%, respectively), indicating that microorganisms had higher utilization efficiency of soluble carbon and enhanced the biological nitrogen fixation capacity, and nitrogen addition caused the accumulation of ammonium nitrogen, thereby weakening the biological nitrogen fixation capacity. At the same time, glucose significantly increased the Fimicutes phylum (83.73%, 66.38%, 67.18% and 70.36%) and lowered the level of other bacterial phylums, thereby reducing the bacterial network structure, and the stability of the soil environment has decreased. Forest analysis showed that CO2 was an important factor in predicting the bacterial community structure of different soil types, an increase in CO2 content can predict drastic changes in the bacterial community. Bacteria at the Fimicutes phylum level preferred glucose, which may also have a negative effect on bacteria at the level of other phylums.

Coupled iron and heavy metal accumulation in karst soils in Southwestern China: Iron isotope perspective

Heavy metals (HMs) are abundant in the karst soils of Southwest China, posing significant health risks to millions of people. Iron (Fe) (hyr)oxides serve as critical carriers of HMs in these soils; however, the processes governing Fe oxide formation and transformation associated with HM accumulation during carbonate weathering in karst region is less understood. In this study, we present Fe isotope compositions from a carbonate–derived profile to investigate the major factors controlling Fe migration. In the saprolite layer, strong correlations between δ56Febulk and the proportions of extracted FeNH2OH.HCl or Feresidue fractions suggest that the formation of goethite and phyllosilicate may be responsible for variations in δ56Febulk. The positive correlations between δ56FeNH2OH.HCl values and HM concentrations in this layer suggest an enhanced capacity for HM fixation by goethite in these soils. In contrast, the fractionation of Fe isotopes in the soil layer appears to be influenced by vegetation, as indicated by the correlation between total organic carbon and δ56Febulk. The negative correlations between δ56Febulk values and HM concentrations in the soil layer likely indicate that vegetation litter enhances the retention capacity of Fe oxides for HMs. This study highlights the trajectory of Fe and its connection to HM accumulation in karst soil with high geological background levels.