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Since Chernozems are among the most fertile soils in the world, the study of their degradation is of great interest. However, the microstructure and composition of the soil organic matter (SOM) in eroded Chernozems have not yet been sufficiently studied. We studied the SOM and aggregate states of eroded Chernozems using the example of two catenas with arable Haplic Chernozems in the Kursk region of Russia. In the plow horizons (the part of the soil most susceptible to water erosion), we determined the mean-weighted aggregate diameter (MWD), structure and water stability coefficients (SC and WS; dry and wet sieving, respectively), soil organic carbon (SOC) content, and SOM composition and content (qualitative and quantitative micromorphological analyses, respectively). It was shown that with an increase in the degree of erosion, the content of SOC decreased significantly, according to both chemical and micromorphological methods of evaluation. No significant relationships were found between the degree of erosion and the indicators of the structure (except for WS, which was significantly lower in non-eroded Chernozem than in slightly and moderately eroded soils). With the increasing degree of erosion, the humus state of these soils deteriorates at the microlevel, the intensity of humification decreases, the depth of the appearance of assimilated biogenic aggregates with finely dispersed calcite in the profile increases, the structure is destroyed, lumpy aggregates form, and the proportion of planar voids increases. The downslope transport of the soil solid phase under the impact of erosion is accompanied by the accumulation of the transformation products of carbohydrates in the Chernozems in the lower part of the catena. In the Chernozems located in the transit position of the slope, the composition of SOM is characterized by the predominance of lipids and nitrogen-containing compounds. Our unique results contribute to a deeper understanding of the formation of structure and water resistance in eroded soils. [ABSTRACT FROM AUTHOR]

Mollisols are highly fertile soils and function as significant carbon reservoirs. However, determining their ages and formation processes is challenging due to extensive pedoturbation, which undermines conventional dating methods. Here, we employed luminescence, a light‐sensitive property of minerals widely used in geological dating, to investigate and quantify soil mixing. We analyzed over 2,400 luminescence ages of individual K‐feldspar grains from a Mollisol profile in Northeast China, and for the first time, we were able to determine the intensity of pedoturbation in the Mollisol profile over the past 50,000 years. The results showed that the current pedoturbation can penetrate to a depth of approximately 80 cm, with the intensity decreasing with depth. By identifying a significant intensification in historical pedoturbation, we inferred that the paleoenvironment might be suitable for the formation of Mollisols 16,400 years before present. Plain Language Summary: Mollisols, also known as a type of black soils, are highly fertile soils characterized by a thick, dark surface layer rich in soil organic matter. Mollisols are not only crucial for food security but also serve as a significant carbon pool. To predict the future evolution of these valuable soil resources, it is important to understand when and how they formed. However, due to intensive mixing by animals, plants, and freeze‐thaw processes, it is challenging to accurately obtain soil ages using traditional dating methods that rely on undisturbed sedimentation layers. Here, we utilized luminescence, a light‐sensitive property of minerals, to address the challenge of soil mixing. We analyzed more than 2,400 luminescence ages of individual K‐feldspar grains from a Mollisol profile in Northeast China. The results showed that the upper 80 cm of the soil body is currently mixed, with the mixing intensity being most intense at the soil surface and decreasing with depth. Additionally, we observed evidence of historical soil mixing over the past 50,000 years. The intensity of soil mixing increased around 16,400 years ago. We infer that the paleoenvironment might be favorable for forming Mollisols since then. Key Points: Single‐grain luminescence was used to quantify the intensity of pedoturbation in the Mollisol profile over the past 50,000 yearsDust accumulation fostered the formation of the thick, dark, humus‐rich surface layer of the Mollisol profileThe formation processes of the Mollisol profile were traced back to 16,400 years before present [ABSTRACT FROM AUTHOR]

The discovery of complete ammonia oxidizers (comammox) challenged our cognition of the nitrification process. Ammonia oxidizing archaea (AOA), ammonia oxidizing bacteria (AOB) and comammox can carry out soil autotrophic nitrification process together. However, the differentiation of the ecological niche of three types of ammonia oxidizers in different environments has not been fully discovered. In this study, a typical black soil collected from northeast China was adjusted to different pH (original and adjusted pH were 4.29 and 7, respectively) and NH4+-N concentrations (weekly adding and without adding 100 mg NH4+-N kg− 1 soil). The activities of AOA, AOB and comammox were examined using DNA stable isotope probing approach with 13CO2, the phylogenetic information of active ammonia oxidizers was detected by high-throughput sequencing. The results showed that niche differentiation of AOA, AOB and comammox in black soils differed with soil pH. AOA dominated the nitrification process in acidic soils, while AOA, AOB and comammox Clade A taken part in the nitrification process in neutral soils. Among them, AOB showed strong activity in the soils with the high N treatment. The active AOA mainly belonged to Nitrososphaera in acidic and neutral soils. The active AOB and comammox Clade A mainly belonged to Nitrosospira and Clade A.2 in neutral soils, respectively. Taken together, the results highlighted the significance of canonical ammonia oxidizers in nitrification process of black soils, and comammox Clade A played an active role in neutral condition. [ABSTRACT FROM AUTHOR]

Purpose: Soil erosion and deposition are natural occurrences that can greatly affect the functions of soil. Currently, soil erosion has become an important cause of soil degradation in the northeast China, which severely limits the sustainable development of agriculture. Therefore, understanding the effects of soil erosion and deposition on multiple soil ecosystem functions and soil microbial communities can facilitate a comprehensive assessment of their influence on soil quality and fertility of this region. Materials and methods: This study investigated the effects of soil erosion and deposition on microbial diversity and community in agroecosystems with Mollisols (black soil) at different sites of a slope in northeastern China. The study involves comparison of four slope sites with different erosion intensities and a deposition site. Firstly, a multifunctionality index was generated after determination of a number of soil physicochemical and microbiological parameters. Then, the soil bacteria were determined by 16 s rRNA gene sequencing technology. Finally, the above data were analyzed to investigate the relationship among microbial community characteristics, soil multifunctionality, and soil erosion and deposition. Results and discussion: Erosion reduces while deposition enhances soil multifunctionality and microbial diversity. Soil multifunctionality decreased from 0.52 (TS) to –0.83 (LS) and increased to 0.85 (FS). Erosion and deposition significantly changed the abundance of Desulfobacterota, Geobacteraceae, Methylomirabilota, and others, which may be related to soil physicochemical properties and hydrothermal conditions. Erosion reduced the complexity and stability of the co-occurrence network of bacteria, whose node and robustness respectively decreased from 540 and 0.1936 (TS) to 488 and 0.1881 (LS), and the vulnerability increased from 0.0006 (TS) to 0.0013 (LS). Moreover, the complexity and stability showed positive correlations with soil multifunctionality and microbial diversity. Overall, our results indicated that erosion and deposition can significantly affect soil multifunctionality and microbial diversity, which will further alter soil microbial communities and their functions. Conclusions: Soil degradation caused by soil erosion may be reflected not only by the reduction of soil nutrients and destruction of soil structure, but also by decreases in soil microbial diversity, network complexity, and stability. Soil degradation caused by erosion includes a decline in soil multifunctionality and microbial characteristics, both of which should be taken into account when treating and rehabilitating degraded soils caused by erosion. [ABSTRACT FROM AUTHOR]

Returning straw to the field, coupled with fertilizer application, is an effective means to improve the fertility of black soil in Northeast China. Previous studies have mainly focused on the physical and chemical properties of soil structure and fertility. However, few efforts have been made to study the impact of straw returning on the microbial community of black soil in Northeast China. Here, we studied the typical northeast black soil in Heilongjiang Province to characterize the effects of long-term chemical fertilizer application and straw returning on its bacterial community structure. High-throughput sequencing was conducted to characterize the bacterial community of northeast black soil under different agricultural fertilization treatments, and the main factors affecting the bacterial community of northeast black soil were revealed through bioinformatic analyses. The results of high-throughput sequencing analyses demonstrated that the main bacterial phyla in the black soil in Northeast China were Actinomycetes, Proteobacteria, Acidobacteria, Chloroflexus, and Bacteroidetes. Long-term application of chemical fertilizers significantly increased the fertility and crop yield of black soil in Northeast China but led to significant changes in bacterial community structure and a significant decrease in diversity. Although straw returning improved soil fertility, it did not alleviate the adverse effects of the long-term application of chemical fertilizers on soil bacterial communities. Furthermore, our results demonstrated that changes in soil pH were the main factor leading to variations in soil bacterial communities. Returning straw to the field based on fertilizer application can improve black soil fertility in Northeast China but fails to alleviate the adverse effects of fertilizer-induced soil acidification on the composition and diversity of soil bacterial communities. This suggests that returning straw to the field may not have a significant beneficial impact on the microbial ecology of the black soil of Northeast China. Therefore, further research is needed to establish new straw return strategies to maximize agricultural yields while minimizing ecological impacts. [ABSTRACT FROM AUTHOR]

[Display omitted] • Natural and human factors influencing SOC pattern were summarized in Mollisols. • Warming and elevated CO 2 may increase labile organic carbon fractions in Mollisols. • Forest restoration may be a more effective way to improve global ecological benefits. • Conservation tillage improves SOC stocks by increasing the labile OC and MAOC. • Straw amendment and combined organic–inorganic fertilization improve SOC storage. Soil organic carbon (SOC) is a key component of the global carbon pool, which is crucial to the fertility and health of soils and deeply influences global carbon cycling. "Mollisols belts" with high SOC storage are considered as the natural breadbasket of the world, and SOC transformation between the sources and sinks profoundly affects global climate change. In this review, based on the newest publications, the effects of both natural and anthropic factors on the decomposition, migration, and transformation of SOC and further influencing the spatial distribution of SOC and its fractions in Mollisols were summarized. Furthermore, we summarized the debates on the spatial changes of SOC and its fractions in Mollisols from publications and analyzed the causes of these debates. Generally, climate change, land use types, fertilization, tillage practices combined with topographic factors, hydrologic process, and soil erosion process significantly influence the spatial distribution of SOC. As well, in the Mollisols, (1) Global warming and elevated CO 2 may increase the content of labile organic carbon fractions and affect the soil-atmosphere carbon cycle. (2) The conversion of abandoned cropland to forest or grassland, and the conversion of dry cropland to paddy field may improve the carbon sequestration capacity of terrestrial ecosystems, while rational fertilization and organic inputs reduce the SOC loss of natural ecosystems converting to cropland. (3) Conservation tillage in cropland improves the SOC storage by increasing the pool of labile organic carbon in soils. (4) A reasonable combination ratio of organic and chemical fertilization is crucial for achieving the stability of the SOC pool and the increase of the SOC storage in soils. At the end of this review, the key issues on the spatial distribution of SOC and the driving mechanisms were prospected in the future. [ABSTRACT FROM AUTHOR]

Moreover, soil acidification, with soil pH ranging from 4.0 to 4.5, simplified network structure and compelled denitrifiers to cooperate with each other in contrast with other soil pH ranges. Soil tillage practices and the resulting increase in water erosion is one of the most important anthropogenic processes to drive soil nutrients and SOC turnover in agricultural land. Abbreviations AOC aggregate-associated carbon iPOC intra-aggregate particulate organic carbon OC organic carbon SOC soil organic carbon SOM soil organic matter Mollisols are inherently productive and fertile soils that are extensively distributed on the steppes of North America, South America, Ukraine, and Northeast China. [Extracted from the article]

The return of straw is a widely used agricultural practice for increasing the soil organic carbon (SOC) content and improving soil structure in Mollisols, owing to the decline caused by continuous high-intensity tillage. We conducted a field experiment where corn straw was continuously returned for 10 years to investigate effects of the straw on the size distribution and stability of soil aggregates and on SOC density fractions. The treatments were no straw return (CK) and four rates of straw return: 6000 kg hm−2 (S1), 9000 kg hm−2 (S2), 12,000 kg hm−2 (S3), and 15,000 kg hm−2 (S4). SOC contents after straw return for bulk soil, a free light fraction (F-LF), an occluded light fraction (O-LF), and a heavy fraction (HF) were significantly higher by 27.0, 644.3, 720.0, and 69.2%, respectively, in S4 than CK. The contents of F-LF, O-LF, and HF in aggregates >2.00 mm were significantly higher by 194.2, 162.1, and 35.8%, respectively, in S4 than CK. Structural equation modeling indicated that SOC contents and aggregates >0.25 mm were directly correlated with the amount of straw returned. We conclude that returning 15,000 kg m−2 of straw would be an effective agronomic practice to restore Mollisol fertility. [ABSTRACT FROM AUTHOR]

Glomalin-related soil protein (GRSP), soil nutrients, and soil enzyme activities are closely related to soil fertility and land productivity, which play an important role in indicating soil quality. Little is known about the spatial variation in GRSP and its relationship with edaphic factors. Here, the spatial distribution of GRSP, soil chemical properties, and the soil enzyme activities of 0–20 cm depth farmland soil in the black soil region of northeast China were investigated, and the relationships among edaphic factors were analyzed collected from 41 sampling sites. The results indicate that GRSP, soil organic matter, total nitrogen, and acid phosphatase activities showed significant patterns of spatial variation, generally decreasing from north to south along a latitudinal gradient. Principal component analysis revealed that total GRSP (by 80.19%) and soil organic matter content (by 80.15%) were the greatest contributing factors accounting for the variations. Edaphic factors such as soil organic matter, total nitrogen, total phosphorus, and acid phosphatase were significantly positively correlated with GRSP, while urease was negatively correlated with GRSP. Mantel tests also showed that soil organic matter, total nitrogen, urease, and acid phosphatase were positively correlated with GRSP. The results reflect the soil fertility characteristics of the black soil region of northeast China and reveal the relationship among edaphic factors. These findings could be used to inform agricultural production and provide new insight into the role of GRSP in soil quality. [ABSTRACT FROM AUTHOR]

Soil internal forces can affect aggregate breakdown, and then impact splash detachment and transport of aggregate fragments. However, currently, the processes of soil splash detachment and transport under different soil internal forces are still not fully understood. Thus, to determine the effects of soil internal forces on the splash transport process, two soils (Binxian soil and Keshan soil) in the Mollisols (black soil) of Northeast China were selected to analyse the detachment and transport characteristics of aggregate fragments under different splash distances (0–10, 10–20, 20–30, 30–40 and 40–50 cm) through simulated rainfall experiments. Different concentrations of KCl electrolyte (from 1 to 10−5 mol L−1) were employed as rainfall materials to regulate soil internal forces. The results revealed that the net pressure of soil internal forces and splash amount presented the same trend with decreasing electrolyte concentration, that is, increased initially (from 1 to 10−2 mol L−1), followed by levelling off (from 10−2 to 10−5 mol L−1). The splash amount and net pressure had an exponential relationship (p < 0.01). Under the same electrolyte concentration, Binxian soil had a higher net pressure and splash amount than Keshan soil. The splash amount for the two soils was mostly distributed at a splash distance of 0–20 cm, and it exponentially decreased with increasing splash distance (p < 0.01). An empirical expression in our study was developed to predict the splash amount (M) based on the net pressure (N) and splash distance (S). The size distribution of splashed aggregates could be affected by the net pressure of soil internal forces, the greater the net pressure, the smaller size aggregates splashed. At each splash distance, the highest mass percentage was observed for the fragments <0.053 mm and accounted for 35.5% to 82.1% of the total splash amount. This study provides valuable information to better understand the processes and mechanisms of rainfall splash erosion in the Chinese Mollisol region. Highlights: The distribution characteristics of aggregate fragments under different soil internal forces were tested.Relations between soil internal forces and soil aggregate detachment were determined.The distribution of splashed aggregates size was greatly affected by soil internal forces.Soil internal forces had important effects on splash erosion in the Mollisols of Northeast China. [ABSTRACT FROM AUTHOR]

Soil organic carbon (SOC) mineralization plays an important role in global climate change. Temperature affects SOC mineralization, and its effect can be limited by the substrate available. However, knowledge of the effects of temperature and substrate quality on SOC mineralization in the Mollisols of Northeast China is still lacking. In this study, based on a spatial transplant experiment, we conducted a 73-day incubation to examine the effects of temperature on SOC mineralization and its temperature sensitivity under different carbon levels. We found that the SOC content, incubation temperature and their interaction had significant effects on SOC mineralization. A higher SOC content and higher incubation temperature resulted in higher SOC mineralization. The temperature sensitivity of SOC mineralization was affected by the substrate quality. The temperature sensitivity of SOC mineralization, showed a downward trend during the incubation period, and the range of variation in the Q10 declined with the increment in the SOC content. The study suggested that there was a higher SOC mineralization in high levels of substrate carbon when the temperature increased. Further, SOC mineralization under higher SOC contents was more sensitive to temperature changes. Our study provides vital information for SOC turnover and the CO2 sequestration capacity under global warming in the Mollisols of Northeast China and other black soil regions of the world. [ABSTRACT FROM AUTHOR]

Soil organic matter (SOM) decreases after the conversion of native grasslands to croplands and increases after the conversion of croplands to plantations. However, the reasons for loss and/or accumulation of SOM fractions remain unclear. Hence, we investigated SOM fraction quantity and quality of soils from cropland (CL), a plantation (PL) converted from cropland, and native grassland (NG) all converted from the black soil (Mollisols) region of China. Results showed that: (1) across all sites, coarse particulate organic matter (cPOM), fine particulate organic matter (fPOM), and mineral‐associated organic matter (mSOM) formed successively, and the mSOM carbon (C) content accounted for more than 70% of the bulk SOM C content. (2) The cPOM C contents in CL and NG were similar, but the fPOM and mSOM C contents in CL were only 11.35% and 52.95% of those in NG, respectively. The C contents of cPOM, fPOM, and mSOM in PL were 53.77%, 27.72%, and 72.80% of those in NG, respectively. (3) The accumulation of mSOM was affected by the quantity of fPOM, but had no obvious relationship with the quality of fPOM. However, the accumulation of fPOM was affected by both quantity and quality of cPOM. In general, promoting the accumulation of fPOM may increase the mSOM and SOM contents of CL, and increasing cPOM may be a feasible way to increase the SOM content of PL. The study provides a fundamental reference for promoting SOM accumulation of croplands and plantations in the black soil region. [ABSTRACT FROM AUTHOR]

Black soil rich in organic matter is one of the most fertile soils in Northeast China, one of the four largest black soil regions in the world. However, the structure and function of black soil have seriously deteriorated after long-term cultivation in recent years. Much effort has been made to ensure the sustainable development of black soil. However, most previous studies were focused on the soil structure and nutrients in the year of the experiment. In this study, a systematic investigation was performed on the soil structure and function during the whole growth period of crops, thereby elaborating the dynamic evolution after the long-term conservation tillage. A field test was also conducted in the Hailun Monitoring and Research Station of Soil and Water Conservation, Chinese Academy of Sciences (47°26′N, 126°38′E), located at the Hailun City, Heilongjiang Province, the center of the typical Mollisols zone in Northeast China. Taking the corn-soybean rotation black soil as the research object, four tillage treatments were set (conservation tillage: NT (No-tillage with straw returning), RT (Reduced-tillage); traditional tillage: MT (Moldboard-tillage), Rot (Rotary-tillage)) during the different growth periods of soybean (SS (seedling stage), FlS (flowering stage), FiS (filling stage), and MS (maturity stage)). Some parameters were measured, including the soil bulk density, porosity, water status, and water-stable aggregate content in response to tillage. Once the soybean matured, the soil samples were collected to quantitatively characterize the soil organic carbon in the vertical direction of different tillage treatments, and the soil moisture infiltration rate in the plow layer. The results showed that: 1) The NT improved to stabilize the soil structure. The soil bulk density under the NT system was more stable than the other three treatments. The soil surface field capacity under the NT treatment was 4.56% ~ 23.07% higher than that of conventional tillage during the whole growth period of soybean. The NT treatment increased the content of large aggregates on the soil surface by 62.10%, and the Average Weight Diameter (MWD) reached 0.48 mm, higher than the rest. The NT also improved the soil water infiltration, where the initial infiltration rate was 1.26 to 1.63 times that of the rest treatments. 2) The NT significantly increased the accumulation of soil surface organic carbon. Specifically, the organic carbon content of soil surface under the NT treatment was 32.60%, 30.28%, and 25.79% higher than MT, RT, and Rot treatments, respectively. 3) The NT maintained the soil productivity. In short, the long-term no-tillage with the straw returning significantly determined the soil structure and organic carbon accumulation. The NT treatment performed better the structure and organic carbon accumulation in the lower layer soil, thereby promoting the sustainable development of black soil. This finding can provide a strong theoretical basis to explore the long-term effects of conservation tillage in the black soil area of Northeast China. [ABSTRACT FROM AUTHOR]

Biochar can affect soil microbial abundance and community structure due to its excellent physiochemical properties. Our previous study of soil bacterial community discovered that the relative abundance of Acidobacteria was significantly influenced by biochar. In this study, we further investigated the effect of biochar on acidobacterial community composition generated with Acidobacteria-specific primers ACIDO/342 R using Illumina MiSeq sequencing in the same black soil samples after 3 years of biochar application. The qPCR results showed that biochar addition increased the acidobacterial abundance, especially at the rates of 4% and 8%. There were 18 acidobacterial subgroups detected, and Gp4 and Gp6 were the most abundant subgroups. The relative abundance of Gp4 was positively correlated with soil total potassium and negatively correlated with soil pH, while Gp6 was on the opposite. Biochar addition did not influence the α-diversity but altered the acidobacterial community composition. Redundancy analysis revealed that changes in the soil acidobacterial community compositions were closely associated with soil properties, such as pH, total potassium and available potassium. Given that these soil properties were highly correlated with biochar addition, which suggested that the long-term impacts of biochar on the soil acidobacterial community were indirectly driven by changes in soil properties. [ABSTRACT FROM AUTHOR]

Chernozems or mollisols/black soils are 'reference soils' with a high content of organic matter, which ensures a high level of crop yield. In the article, we describe the structural characteristics of a typical medium‐thick Chernozem taken from Kursk region and their improvement via treatment by a 1 wt% aqueous solution/suspension of interpolyelectrolyte complex (IPEC), a product of electrostatic interaction between anionic potassium humates and cationic poly(diallyldimethylammonium chloride). The native Chernozem and polymer‐treated chernozem were characterized by laser diffraction, dry and wet sieving methods, transmission electron microscopy, soil washoff in a hydraulic erosion tray, gravimetry, visual control, and vegetation miniaturization in Petri dishes with the following main conclusions: (a) Deposition of a positively charged IPEC over the Chernozem sample led to an increase in a total amount of agronomically valuable 0.25–1 mm aggregates up to 28% in comparison with a 3% content of aggregates in the native Chernozem. (b) An average diameter of the air‐dry aggregates, treated by a cationic IPEC, was of 5.5 mm (cf. with 2.5 mm for the untreated). (c) An average diameter of the IPEC‐treated water‐resistant aggregates was of 2.1 mm (cf. with 0.5 for the untreated). (d) The Chernozem pretreated by the cationic IPEC showed a minimum removal of soil during several cycles of rewatering/drying. (e) All IPEC formulations, stimulated the growth of plants. The results are of interest for preparing low‐toxic polymer formulations capable of effective stabilizing fertile Chernozem soils. [ABSTRACT FROM AUTHOR]

This study was conducted to compare between two methods of soil organic matter determination for main soil orders in Kurdistan region/Iraq, for this purpose forty-five soil samples were taken then the organic matter was determined using chemical (Walkley-Black (wet) method and loss-on-ignition method (dry) combustion method. The results indicated the significant correlation (r = 0.88**) between the studied methods It means there is good adjustment to convert organic matter by loss-onignition method (dry) to Walkley-Black (wet) method organic matter by this linear equation (organic matter by loss-on-ignition =1.651* Walkley-Black method organic matter +2.1877) this equation can be used to convert organic matter by two methods for Mollisols(M), Vertisols(V) and Aridisols(A) in Hawler(H), Sulaimani(S) and Duhok(D) governorates, this equation is very important and economic to determine and convert dry method to wet method, the amount of organic matter for M, V, A was recorded the highest value (49.5, 24.8, 20 gkg-1) respectively for Mollisols, Vertisols, and Aridisols at Hawler (H), Sulaimani (S), and Duhok(D) respectively for (DM5, SV4, DA1) in Duhok Mollisols, Sulaimani Vertisols and Duhok Aridisol respectively for walk- black (wet) method, the highest value for dry method organic matter in Mollisols, Vertisols, Aridisols was recorded (97.6, 77.9, 50.3 g kg-1) ) for soil orders (MD3, VD4, AD4) respectively. [ABSTRACT FROM AUTHOR]

Phytoremediation is an ecologically sustainable method for remediating contaminated soils, however, research on phytoremediation and its mechanisms are still rarely reported. The highest dibutyl phthalate (DBP) dissipation rate was 91% in 0–3mm bok choy rhizosphere via a 45-day rhizo-box experiment, and bok choy could regulate soil nutrients by increasing soil ammonia nitrogen (AN) and available phosphorus (AP). The biochemistry mechanism of interaction between dissolved organic matter (DOM) and DBP was also elucidated by various spectroscopy techniques. It was found that the alkyl ester in DBP produced the fastest response during the binding process, and the aromatic, hydroxyl and phenolic groups of the DOM humic-like substances preceded amide in DOM protein-like substance. It was found that DBP pollution reduced the Chao1 richness and Shannon index of bacteria in black soil via a pot experiment and high-throughput sequencing, which disturbed the metabolic activities and functional diversity of microorganisms in Mollisol. The microbial abundance increased in bok choy amendments, which has a specific microbial community structure and a high abundance of Actinobacteria and Acidobacteria. We concluded that some enriched genera were responsible for DBP dissipation, Alsobacter , Lacibacter , Myceligenerans , Schrenkiella parvula and Undibacterium. The findings of this study revealed that the possible biochemistry and microbial mechanisms of phytoremediation promoting the DBP dissipation in rhizosphere Mollisol and provided more useful information for phytoremediation of organic pollutants. Image 1 • Bok choy rhizosphere DOM was one of the main factors affecting the dissipation of DBP. • The order of binding DOM to DBP was alkyl ester > aryl > hydroxyl > carboxylic acid > phenolic > amide. • Bok choy can be used as a potential germplasm for DBP phytoremediation. [ABSTRACT FROM AUTHOR]

Wide longitudinal ridge tillage has significant effects for increasing crop yield. Field observation shows that in the black soil region of Northeast China, wide longitudinal ridge tillage has been widely promoted in the intensive farms on which large agricultural machines are used. However, hillslope soil erosion of wide longitudinal ridge tillage is seldom studied. Therefore, in typical black soil region, in this study, two large natural runoff plots with gentle slope gradient were established in Liangshigou watershed in Keshan County, Heilongjiang Province. One was wide longitudinal ridge tillage with 320 m slope length and 3-m slope width and another was narrow longitudinal ridge tillage with 320 m slope length and 2 m slope width. Ridges were established on a field of silty clay loam (USDA classification). The slope gradients ranged from 2°-7°. According to literature review and field measurements of the wide and narrow ridges in black soil region of Northeast China, the used wide ridges were 15-cm high, 110-cm wide; the used narrow ridges were 15- cm high, 65 cm wide. A laboratory simulated rainfall experiment was conducted in the simulated rainfall hall of the State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Yangling City, China. The soil used in the laboratory simulated rainfall experiment was collected in the natural runoff plot. According to the standard of erosive rainfall in Northeast black soil region of China, the simulated rainfall intensities were 50, 75 and 100 mm/h. Each rainfall experiment lasted 60 min. The wide and narrow ridges used in the simulated experiments were consistent with the large natural runoff plot in Keshan County. Based on the runoff plot observation and laboratory simulated rainfall experiments, the differences of hillslope soil erosion between wide and narrow longitudinal ridge tillage in black soil region of China were analyzed. The results showed that under both field runoff observation and laboratory simulation, hillslope soil losses from the wide longitudinal ridge tillage hillslope were 64.4% - 90.4% and 33.2% - 57.9% lower than that from the narrow longitudinal ridge tillage. Field observation indicated that there were significant or strong significant positive correlations among the soil loss, runoff and PI30. The increment of soil loss with runoff and PI30 in narrow ridge-tillage system was larger (P< 0.05) than that in wide ridge-tillage system. The relationship between soil loss and PI30 was power function, while the relationship between soil loss and runoff was linear function (R²＞0.99). Indoor simulated experiments showed that there were linear relationships between soil loss and runoff under two longitudinal ridge tillage systems (R²≥0.81). The increment of soil loss from the wide longitudinal ridge tillage system was lower (P< 0.05) than that from the narrow longitudinal ridge tillage system. Compared with the narrow longitudinal ridge tillage, the reduction of soil loss by wide longitudinal ridge tillage decreased with the increase of PI30; when PI30 was 433.9 - 605.1, the reduction of soil loss by the wide longitudinal ridge tillage was 74.8%-90.4% and when PI30 were 1520.6 and 1708.6, the reduction of soil loss by the wide longitudinal ridge tillage was 64.4%-66.5%. Both field observation and simulated experiments displayed that the wide longitudinal ridge tillage had better effects on controlling hillslope soil erosion, compared with the traditional narrow ridge tillage. Therefore, promotion of wide ridge tillage system might have great significance in protecting Mollisol resources in the black soil region of Northeast China. [ABSTRACT FROM AUTHOR]

The effects of chemical fertilizers on soil microbial communities have been well studied in a variety of terrestrial systems. However, the individual effects of N, P, and K fertilizers and their combinations (NP, NK, PK and NPK) on bacterial community structure in black soils have not been fully understood. In this study, we applied Illumina MiSeq sequencing and network analysis targeting 16S rRNA gene to comprehensively characterize the effects of 35 years of these inorganic fertilizers on community diversity and composition in the black soil. The results of α-diversity indices and principal coordinates analysis (PCoA) indicated that the N-addition treatments had larger effects than the others. The network analysis showed that the N fertilizer shifted the network structure, topological roles of individual OTUs and key bacterial populations, contributing to a simple network under the N-fertilizer treatments compared with non-N fertilizers treatments. These findings suggested that N fertilizer reduced the bacterial diversity and simplified the interactions among key bacterial members in Mollisol. The results of this study could provide basis for further researches balancing different N application levels, the bacterial community network and crop yield to maintain the ecosystem function and stability. Abbreviations: N: nitrogen fertilizer; P: phosphorus fertilizer; K: potassium fertilizer; NP: nitrogen and phosphorus fertilizers; NK: nitrogen and potassium fertilizers; PK: phosphorus and potassium fertilizers; NPK: phosphorus and potassium fertilizers; TC: total carbon; TN: total nitrogen; TP: total phosphorus; TK: total potassium; AP: available phosphorus; AK: available potassium; OTUs: operational taxonomic Units; ACE: abundance-based coverage estimator; Chao1: estimated OTU richness; PCoA: principal coordinates analysis [ABSTRACT FROM AUTHOR]

Three-dimensional fluorescence technology was applied to analyze the components and structures of the water extractable organic matter (WEOM) in the topsoil (0-20 cm) and a 20-40 cm depth of Mollisol of an uncultivated land or the land after of 5, 20, 50 and 100 years of reclamation, respectively. With the continuous reclamation, the content of the WEOM in the black soil has a tendency of decreasing at first but increasing subsequently. The WEOM reaches its maximum and minimum contents at 86.65 mg/kg and 47.81 mg/kg. The fluorescence intensity of the area III was enhanced. After the reclamation of 100 years, the fluorescence intensity of the areas III and Vreached to the top values, suggesting the maximum contents of fulvic acid-like and humic acid-like organic matters. The emitting lights at the fluorescence peak of the fluorescence area of humic acid-like organic matters also show red shift, indicating the increase of molecular weight, aromaticity and degree of polycondensation. However, the area Ⅳ remained unchanged. The research results showed that: with the reclamation, the components and structure, and the variation of WEOM in soil varies are related to the years of reclamation; the molecular weights, aromaticity and degrees of polycondensation in the WEOM increase evidently with the reclamation. [ABSTRACT FROM AUTHOR]

Bacillus -like species are gram-positive bacteria that are ubiquitous in soils. Many of Bacillus -like bacteria are demonstrated as beneficial microbes widely used in industry and agriculture. However, the knowledge related to their diversity and distribution patterns in soils is still rudimentary. In this study, we developed a combined research method of using culture-dependent and high-throughput sequencing to investigate the composition and diversity of cultivable Bacillus -like bacterial communities across 26 soil samples obtained from the black soil zone in northeast China. Nearly all bacterial 16S rDNA sequences were classified into the order Bacillales. Fifteen genera were detected, with Bacillus , Paenibacillus , and Brevibacillus being the three most abundant genera. Although more than 2,000 OTUs were obtained across all samples, 33 OTUs were confirmed as the abundant species with a relative abundance over 5% in at least one sample. Pairwise analysis showed that the diversity of Bacillus -like bacterial communities were significantly and positively correlated with soil total carbon contents and soil sampling latitudes, which suggests that a latitudinal gradient diversity of Bacillus -like bacterial communities exists in the black soil zone. The principal coordinates analysis revealed that the Bacillus -like bacterial communities were remarkably affected by soil sampling latitudes and soil total carbon content. In general, this study demonstrated that a distinct biogeographic distribution pattern of cultivable Bacillus -like bacterial communities existed in the black soil zone, which emphasizes that the strategy of local isolation and application of beneficial Bacillus -like strains is rather important in black soil agriculture development. [ABSTRACT FROM AUTHOR]

This study investigated the effects of 35 years of application of inorganic fertilizers containing nitrogen (N), phosphate (P), or potassium (K) alone or in combination on the abundance and composition of diazotrophic community in a black soil (Mollisol) in northeast China. The abundance and composition of diazotrophic community were analyzed using qPCR and Illumina MiSeq sequencing targeting nifH genes. Nitrogen fertilization decreased the abundance and Shannon diversity of nifH genes. The diazotrophic community was dominated by Alphaproteobacteria (Bradyrhizobium at the genus level), with relatively higher abundance in the N fertilization treatments than in the non-N fertilization treatments. All diazotrophic communities were clustered into two groups with and without N fertilization history, and the soil pH, total C, total N, and NO 3 −-N significantly influenced the structure of the whole diazotrophic community. Moreover, random matrix theory analysis elucidated a clear difference in network structures between the N and non-N fertilization treatments, with N fertilization causing a less stable network structure. These results highlighted that it was N fertilizer, but not P and K fertilizers, contributed to great changes in the diazotrophic community in this black agricultural soil. [ABSTRACT FROM AUTHOR]

Improving soil carbon sequestration and reducing greenhouse gas emissions in farmland require understanding how the microbial communities that control the agroecosystem function. Here, we surveyed the soil microbial communities in neighboring pairs of dryland and paddy fields in the black soils of northeastern China. Soil moisture, mean weight diameter of aggregates, fluorescence index and biological index of dissolvable organic matter, total anion concentration, and prokaryotic community α-diversity were higher in paddy soils than in dryland soils, while soil saturated hydraulic conductivity (SHC), dissolvable total nitrogen, and fungal community α-diversity were lower in paddy soils than in dryland soils. Moreover, soil moisture (P < 0.01) and SHC (P < 0.05) had significantly positive correlations with the α-diversity of prokaryotic and fungal communities, respectively. The co-occurrence network complexity of microbial communities was lower in paddy fields than in dryland fields, while the co-occurrence network tightness and cooperation of microbial communities were higher in paddy fields than in dryland fields, which may help paddy microbiome resist environmental disturbances. Taken together, both dryland and paddy fields had their own advantages in evaluating soil biological health from microbial community diversity and network stability. Additionally, the differential groups of CH 4 production, S cycle, and Fe cycle (e.g., Bathyarchaeota, Bacteroidetes, and Geobacter) increased, while those of environmental remediation and biological control (e.g., Blastococcus and Roseiflexus) decreased after the change from dryland to paddy fields. Further combined with metagenomic analysis, the functions of CH 4 production, CO 2 fixation, N fixation, and sulfur reduction were enhanced in paddy soils, while those of CH 4 oxidation, nitrification, and N 2 O production were reduced. In conclusion, the ecological functioning of the differential groups may lead to the increase of CH 4 emission and CO 2 fixation, and the decrease of N 2 O emission in paddy fields of black soil, even in non-flooding period. [Display omitted] • The microbial-mediated potential of soil CO 2 fixation was enhanced in paddy soils. • The microbial-mediated potential of soil N fixation was enhanced in paddy soils. • The microbial-mediated potential of soil nitrification was reduced in paddy soils. • The microbial-mediated potential of soil N 2 O production was reduced in paddy soils. • The microbial-mediated potential of soil CH 4 production was enhanced in paddy soils. [ABSTRACT FROM AUTHOR]

Although biochar amendment has been extensively evaluated as a promising strategy to improve soil quality, most evaluations have been conducted in the laboratory or under short-term field conditions, which restricted us to understand the long-term effects of biochar as a soil amendment. As the residence time of biochar in soils is expected to be hundreds to thousands of years, this study focused on revealing whether biochar addition influences soil physiochemical properties and fungal community composition in a black soil of northeast China over the long term. Biochar was added to the micro-plots at 0%, 2%, 4%, and 8% of the total mass of the top 20 cm of the soil in the spring of 2012, and soil samples were collected seasonally four times in 2014. The results indicate that soil pH, moisture, total C, total N, total P, NO 3 − -N, available K and the C/N ratio significantly increased but soil bulk density and total K content decreased with biochar addition. The soil fungal abundance determined using quantitative real-time PCR showed that the number of fungal ITS gene copies increased with biochar addition. The soil fungal community composition determined using the Illumina MiSeq sequencing method showed that community diversity was not influenced by biochar addition but the community composition was influenced. The impact of biochar on changes in community composition was not reflected at the phylum level, but at the genus and operational taxonomic units (OTU) levels. The relative abundance of Fusarium decreased, but Guehomyces increased with biochar addition over the first three sampling dates. The relative abundances of several OTUs classified as potential crop pathogens decreased with biochar addition, suggesting that biochar amendment may be beneficial in terms of suppressing the occurrence of crop disease over the long term. In addition, canonical correspondence analysis indicated that fungal community composition was associated with soil parameters such as pH, soil moisture, total C, total N, total K and available K. The changes in these soil characteristics were highly correlated with the amounts of biochar addition, suggesting that the impacts of long-term biochar amendment on the soil fungal community occurred indirectly as a result of the alteration of soil physiochemical properties. [ABSTRACT FROM AUTHOR]

Microorganisms play essential roles in soil phosphorus (P) cycling and the regulation of P bioavailability, however, genetic information on microbial P cycling in response to nutrient inputs is largely unclear. Here, metagenomic sequencing and genome binning were used to investigate microbial functional traits under chemical and organic fertilization in three long-term field experiments across black soil region of Northeast China. The results revealed that manure amendments strongly affected microbial P cycle-related functional gene patterns, which were significantly and positively correlated with the contents of soil total P (TP) and available P (AP). Manure addition directly increased soil AP concentrations, and indirectly acted through the alterations of microbial functional genes involved in soil P cycling. Specifically, manure amendments consistently decreased abundances of phnC gene and increased gene abundances of phnP , opd , and phoN across three locations, suggesting the potentially inhibition of soil microbial P-uptake and transport and the promotion of soil microbial organic P- mineralization. Manure addition promoted microbial inorganic P-solubilization by enriching the ppa , gcd , and pqqC genes at two out of three locations, while chemical fertilizer (CF) addition slightly stimulated the functional gene abundances involved in microbial P-uptake and transport and P-starvation response regulation. In addition, soil AP content was negatively correlated with the phnC gene abundance but positively correlated with the gene abundances of opd and phoN. Moreover, 23 metagenome-assembled genomes (MAGs) were reconstructed covering all soil samples, all of which contained the phnC gene with the copy numbers varying from 1 to 19. Nevertheless, only bin44 had a negative correlation with soil AP (r = −0.361, P = 0.030) and could be considered as a potential indicator regulating microbial P-uptake and transport. Taken together, manure inputs positively accelerated microbial P-transformations, which was beneficial for the establishment of efficient P management strategies in sustainable-intensive agriculture. [Display omitted] • Manure significantly influenced microbial P cycle-related functional profiles. • Manure decreased phnC gene abundance that inhibited microbial P-uptake and transport. • Soil microbial inorganic and organic P mobilization was promoted by manure amendments. • phnC gene was found as a biomarker for soil P cycling in black soils. • Bin44 containing phnC gene was a potential indicator regulating microbial P-uptake and transport. [ABSTRACT FROM AUTHOR]

Although Acidobacteria are ubiquitous and are commonly one of the most abundant bacterial phyla in soils, knowledge regarding their diversity and distribution is still limited. Our previous studies discovered the biogeographical distribution patterns of bacterial and fungal communities in the black soil zone of northeast China. In this study, we further investigated the diversity and composition of acidobacterial communities generated with the Acidobacteria-specific primers ACIDO/342r in the same soil samples using quantitative PCR and Illumina MiSeq sequencing methods. A total of 412,203 acidobacterial 16S rRNA gene sequences were obtained from 26 soil samples that were collected from arable lands across the black soil zone. These sequences belonged to 21 subgroups, and GP1, GP3, GP4 and GP6 were the most abundant subgroups, accounting for 22.63%, 17.17%, 23.82% and 27.47% of acidobacterial sequences across all soils, respectively. The abundance of Acidobacteria displayed a more significant positive correlation with soil carbon content than with soil pH, and the relative abundance of certain subgroups was significantly positive or negative related with soil pH. The OTU richness, phylogenetic diversity and community composition of Acidobacteria were significantly correlated with soil pH. A variance partitioning analysis showed that the soil pH contributed 25% of the community variation, while the geographic distance explained only approximately 5% of the variation. These results indicated that soil pH was a main factor structuring acidobacterial communities in the black soil zone of northeast China. Our results also suggested that the Acidobacteria-specific primers could be better used for studying the distribution of acidobacterial communities in soils. [ABSTRACT FROM AUTHOR]

Black soils (Mollisols) are among the most important soil resources for crop production and food security. In China, they are mainly distributed in the northeastern region. To investigate soil antibiotic resistance distribution patterns and monitor soil quality, we randomly chose nine corn fields in Northeast China and analyzed the antibiotic resistance gene (ARG) distribution and co-occurrence patterns on the basis of high-throughput approaches and network analyses. High genetic diversity (136 unique genes) and low ARG abundances (10−5–10−2 copies/16S rRNA gene copy) were detected, with relatively few interactions among ARGs. Type I integron genes were prevalent in the soil and were positively correlated with ARGs, which may increase the risk of ARG transmission. Most ARGs were strongly associated with microorganisms. Moreover, several ARGs were significantly correlated with antibiotics, nutrients, and metal elements. The generation and dissemination of ARGs, which were most likely mediated by mobile genetic elements (MGEs) and bacteria, were affected by environmental conditions. These results provide insights into the widespread co-occurrence patterns in soil resistomes. [Display omitted] • 136 ARGs were detected in black soil in Northeast China (10−5–10−2 copies/16 S rRNA gene copy). • Network analyses revealed positive correlations and few interactions among ARGs. • ARG generation and spread by bacteria and MGEs are influenced by antibiotics and inorganic and metal elements. [ABSTRACT FROM AUTHOR]

The degree of soil compaction is affected not only by the agricultural machinery but also by the soil physical, chemical, and mechanical properties. We hypothesized that the changes in the soil physical (clay content) and chemical properties (soil organic matter, SOM) due to long-term tillage operations would cause corresponding variations in the soil mechanics properties. The in-situ undisturbed soil samples were firstly adopted to detect soil properties as affected by long-term conventional tillage of Mollisol (black soil), and explore the relationship between soil physico-chemical properties and mechanical properties with 4 different cultivation duration croplands (0, 17, 30, and 40 yr). Then, artificial modified soil samples were further used to verify this relationship and confirm the predominate factor influencing compression-rebound behavior at 3 levels of SOM and clay contents, respectively, at 2 levels of gravimetric water contents. The compression index (C c) and rebound index (C r) were determined using a fast oedometer test. We found that with cultivation duration extending, the clay content and soil bulk density increased, while the SOM, C c and C r gradually decreased. The laboratory simulation tests also showed that the compressibility was higher when SOM or clay content was higher; while the soil resilient capacity was lower when the SOM was lower or clay content was higher. In conclusion, the decrease of SOM and the increase of clay content due to long-term cultivation could increase the risk of soil compaction and weaken its recovery capacity. SOM is predominant in influencing the soil mechanical properties relative to clay content. Maintaining and/or increasing SOM may improve the mechanical properties of arable Mollisols. • Long-term conventional tillage decreases SOM and increases clay content. • Both SOM and clay content affect the compression and rebound behavior. • SOM is predominant in governing the mechanical properties of Mollisols. • SOM acts as an early warning signal for evaluating mechanical properties. • In-situ and indoor simulated test can be complemented and verified mutually. [ABSTRACT FROM AUTHOR]

Black soils (Mollisols) are one of the most important soil resources for maintaining food security of China and are mainly distributed in northeast China. To understand which environmental factors influence the microbial communities and how the communities are distributed in the black soils, we collected 26 soil samples with different soil carbon contents across the black soil zone in northeast China, and the soil bacterial community compositions were estimated using high resolution bar-coded pyrosequencing. A total of 355,813 bacterial 16S rDNA sequences were obtained, which were classified into at least 35 bacterial groups. The dominant groups across all samples (>5% of all sequences) were Acidobacteria, Actinobacteria, Proteobacteria, Bacteroidetes, Chloroflexi, Gemmatimonadetes and Planctomycetes. The composition and diversity of the soil bacterial community were dominantly affected by both soil pH and soil total carbon content, and the effect of soil pH was stronger than that of soil carbon content. Variance partitioning analysis showed that geographic distance contributed 14.75% of the bacterial community variation, and soil environmental factors explained approximately 37.52% of the variation. Pairwise analysis showed that a relatively higher diversity of the bacterial community was observed at lower latitudes, suggesting that a latitudinal diversity gradient of the bacterial community might be present in the black soil zone. In general, our results indicated that contemporary factors, such as soil pH and soil carbon content, were more important than the historical factor of geographic distance in shaping the bacterial community in the black soil zone in northeast China. [ABSTRACT FROM AUTHOR]

• Biogeographic distance rather than fertilization dominated microbial functional profiles in Mollisols. • Chemical fertilization promoted processes of methane oxidation, soil N degradation, nitrification and anammox. • Manure fertilization shifted C fixation and degradation processes and facilitated nitrate reduction. • Chemical plus manure fertilization could potentially enhance N2O emission via denitrification. • Soil P contents were the most influential factor in controlling microbial functional profiles. The long-term effects of different fertilization regimes on the microbial functional potential of soils involving nutrient cycling remain largely unknown. Here, metagenomic sequencing was applied to investigate the influences of long-term chemical and organic fertilization on soil microbial C and N cycling across southern, middle and northern sites of black soil region in Northeast China. The results showed that biogeographic distance induced the most influential on the microbial functional profiles of soil C and N cycling, and significant effects of manure fertilization were detected across three experimental sites. Organic fertilization enriched the relative abundances of Proteobacteria and Planctomycetes that carry C and N cycling genes, while inhibited the growth of oligotrophic groups such as Verrucomicrobia. Chemical fertilization increased the gene abundances involved in methane oxidation, but had little effect on soil C degradation and fixation. Contrarily, manure fertilization, particularly the combination of chemical and organic fertilizers (CFM), significantly decreased the abundance of cooC (reductive acetyl-CoA pathway) and coxS (CO oxidation) while enhanced the abundance of icd (rTCA cycle), which are involved in C fixation. Additionally, chemical fertilization enriched the gene abundance that involved in soil N degradation, nitrification and anammox, whereas manure fertilization was beneficial for the functional potentials of assimilatory and dissimilatory nitrate reductions across the black soils. However, CFM significantly promoted the soil denitrification potential, possibly due to excess N input, which might result in soil N loss via the emission of nitrogenous gas in this region. Furthermore, the substantial enhancement in soil P contents induced by manure addition predominantly affected the C and N cycling profiles, abundance of functional genes and microbial taxa. Moreover, diverse correlations between C and N cycling genes suggested the synergetic or antagonistic interactions of C and N metabolic potentials in the black soils. Overall, this study provided in-depth insights into distinct microbial functional potentials under long-term chemical and organic fertilization that may have predictable consequences for soil nutrient cycling in agroecosystems of black soil region. [ABSTRACT FROM AUTHOR]

Although autotrophic ammonia oxidizing archaea (AOA) and bacteria (AOB) and comammox coexist in soils, their abundances and contributions to nitrification are not well addressed, especially in arable black soils. In this study, using the nitrification inhibitors acetylene and octyne, the contributions to nitrification potential provided by different ammonia oxidizers and heterotrophic nitrifiers in four long-term fertilization treatments, i.e. , no fertilization (NoF), manure fertilization (M), chemical fertilization (CF), and chemical fertilization plus manure (CFM), were investigated in samples collected from the northern, middle and southern black soil regions of northeast China. The amoA gene abundances of AOA, AOB, comammox Clade A and comammox Clade B in these soils were quantified by qPCR. The results showed that the amoA gene abundances of the three ammonia oxidizers tended to increase from the northern to southern sites, while the opposite trend was observed in the ratios of AOA/AOB and comammox Clade B/Clade A; the different fertilization treatments significantly influenced the amoA abundances, and the effects varied with the ammonia oxidizers and across the sites. Autotrophic ammonia oxidizers accounted for 62%–100% of the gross soil nitrification potential across all soils. Among them, AOB dominated soil autotrophic nitrification in the fertilized soils, while no fertilization may have increased the nitrification potential provided by AOA plus comammox. Pairwise analysis showed that the amoA gene abundances of AOA and AOB were significantly and positively correlated with their respective nitrification-driven potentials. Correlation heatmaps indicated that soil pH and inorganic nitrogen content were the main soil factors related to nitrification activities and the abundances of the ammonia oxidizers. Our findings highlight that AOB are the dominant ammonia oxidizers contributing to nitrification in arable fertilized black soils, although AOA and comammox are highly abundant. • Autotrophic nitrification is the main process in black soils of northeast China. • AOA and comammox dominate the autotrophic nitrification in non-fertilized acid soils. • AOB dominates the autotrophic nitrification in non-fertilized neutral soils. • Long-term fertilization increases the nitrification contributed by AOB. • The abundances and activities of AOMs are mainly driven by soil pH and inorganic N. [ABSTRACT FROM AUTHOR]

Labile organic carbon (LOC) is a fraction of soil organic carbon (SOC) with rapid turnover time and is affected by soil fertilization. This investigation characterized the SOC content, LOC content and LOC distribution in the treatment plots of surface soil erosion at five levels (0-, 5-, 10-, 20- and 30-cm erosion). The soil had received contrasting fertilizer treatments (i.e., chemical fertilizer or chemical fertilizer + manure) for 6 years. This study demonstrated that both SOC and various LOC fractions contents were higher in the plots with fertilizer + manure than in those with fertilizer alone under the same erosion conditions. The SOC and LOC contents decreased as the erosion depth increased. Light fraction organic carbon, particulate organic carbon, easily oxidizable organic carbon (KMnO 4-oxydizable organic carbon), and microbial biomass carbon were 27%–57%, 37%–47%, 20%–25%, and 29%–33% higher respectively in the fertilizer + manure plots, than in the fertilizer alone plots. Positive correlations ( p < 0.05) between SOC content and different fractions contents were observed in all plots except the correlation between total SOC content and water-soluble organic carbon content in the different fertilization treatments. Obviously, fertilizer + manure treatments would be conducive to the accumulation of LOC and SOC in the Black soil of Northeast China. [ABSTRACT FROM AUTHOR]

Long-term fertilization has shown a high relevance as regards soil organic carbon (SOC) sequestration, but the degree of stability of the sequestered SOC has not been widely studied up to now. Using physical fractionation combined with laboratory incubation and NMR spectroscopy, we evaluated the differences in SOC stability caused by long-term fertilization. Four SOC fractions were isolated and examined for contents and chemical composition and cumulative amount of CO 2 –C respired from the fractions under six fertilization treatments: control (CK); balanced inorganic fertilization (NPK); NPK combined with pig manure (MNPK); NPK combined 1.5 times of pig manure (1.5MNPK); and NPK combined with high amount of manure (M2NPK). The highest contents of SOC were recorded for the coarse particulate organic carbon (cPOC) fraction, ranging from 17.25 to 30.47 g kg−1 under CK and M2NPK. The highest cumulative amount of CO 2 –C was released from the cPOC fraction under manure treatments (M2NPK and 1.5NPKM), which was 56 and 43% higher than that from CK, whereas the lowest amount of CO 2 –C was released from the mineral associated-C (MOC) fraction under the same treatments, being 65 and 49% higher than that released from CK, suggesting low SOC stability in cPOC and high SOC stability in MOC fractions. However, manure treatments (M2NPK and 1.5NPKM) greatly lowered the specific amount of C-mineralized (C-mineralized per unit total SOC) in fractions and whole soil, suggesting the ability of manure to accumulate more SOC by reducing SOC losses. Moreover, carbonyl-C was found to be the form of SOC experiencing major degree of sequestration under current fertilization practices. The SOC stability indices; aromaticity index (AI), hydrophobicity index (HI) and alkyl-C/O-alkyl-C were found to be higher in manure treated plots further suggesting higher stability of SOC under manure addition. Thus, long-term manure combined with mineral fertilizers would enhance SOC stability through minimizing SOC losses and promoting accumulation of stable C forms in a Chinese Mollisol. • SOC stability evaluated in fractions by laboratory incubation and 13C NMR analysis. • CPOC was more decomposable/less stable and MOC was less decomposable/more stable. • Carbonyl-C was the main sequestered C functional group in the black soil studied. • Manure + mineral fertilizer enhanced SOC stability more than mineral fertilizer. [ABSTRACT FROM AUTHOR]

The degradation of black soil is a serious problem with the decrease in soil organic matter (SOM) content in northeast China, and animal manure as a reservoir of antibiotic resistance genes (ARGs) is commonly amended into soil to sustain or increase the SOM content. However, the potential effect of SOM content on soil resistome remains unclear. Here, a soil microcosm experiment was established to explore the temporal succession of antibiotic resistance genes (ARGs) and bacterial communities in three black soils with distinct difference in SOM contents following application of poultry manure using high-throughput qPCR (HT-qPCR) and MiSeq sequencing. A total of 151 ARGs and 8 mobile genetic elements (MGEs) were detected across all samples. Relative abundance of ARGs negatively correlated with SOM content. Manure-derived ARGs had much higher diversity and absolute abundance in the low SOM soils. The ARG composition and bacterial community structure were significantly different in three soils. A random forest model showed that SOM content was a better predictor of ARG pattern than bacterial diversity and abundance. Structural equation modeling indicated that the negative effects of SOM content on ARG patterns was accomplished by the shift of bacterial communities such as the bacterial diversity and abundance. Our study demonstrated that SOM content could play an important role in the dissemination of ARGs originated from animal manures, these findings provide a possible strategy for the suppression of the spread of ARGs in black soils by increasing SOM content. • The number of detected ARGs was abundant in the low SOM soil. • The low SOM soil enriched the absolute abundance of manure-derived ARGs. • Soil ARG composition was significant related to bacterial community. • Soil bacterial diversity influenced by SOM plays a vital role in the dissemination of ARGs. [ABSTRACT FROM AUTHOR]

The black land is a precious strategic soil resource in nature. Arbuscular mycorrhizal fungi (AMF, phylum Glomeromycota) have a critical role in the agricultural ecosystem functioning. However, the black land remains largely unexplored. This study adopted MiSeq sequencing to predict the AMF community distribution and diversities in 41 farmland sites from northeast China's black land. According to findings in this work, all sequences in those 41 soil sites were categorized as one phylum, one class, four orders, eight families, and night genera in the black land of China. Glomus , Paraglomus and Claroideoglomus were the most abundant genera. The diversity of AMF communities was increased with increasing latitude. Moreover, canonical correspondence and pairwise analysis were performed, which suggested that the AMF community structures and diversities were susceptible to latitude, soil organic matter (SOM), soil pH and N. Variance partitioning analysis and Mantel test showed that both soil properties and geographic distance contributed to AMF community structure. It was concluded that the AMF communities showed relatively pronounced diversity at high latitudes, with soil properties and latitude were the important predictors in determining the AMF community structure in the black land of China. Findings in this work shed more lights on the AMF community diversity and distribution and the important factors influencing it at region spatial scale, and suggest that AMF could be used for improving plant growth and sustainable agriculture. • Distribution of AMF communities increase with increasing latitude. • Glomus and Paraglomus are the most abundance genera in the black soil zone. • AMF community diversity and structure are affected by pH, C, N and latitude. • Soil properties and geography shape the composition of AMF communities. [ABSTRACT FROM AUTHOR]

• 40-year fertilizers increased yield and soil fertility, and decreased soil pH. • 40-year fertilizations enhanced bacterial α-diversity. • β-diversity significantly changed varying by different types of fertilizations. • Yield, soil pH and fertility significantly correlated with bacterial diversity. The impacts of long-term fertilization on soil bacterial communities remain unclear due to non-consistent results from different studies, which may be attributed to different soil types and field managements. Therefore, we studied the responses of bacterial communities and soil properties to different inorganic and inorganic-organic fertilizer treatments after 40-year (1980–2019) operation of a maize agroecosystem established on a black soil (typical Mollisols) in Changchun, Jilin Province, China. Ten fertilizer treatments have been set up since 1980, including the application of no fertilizer (CK), nitrogen (N) fertilizer (N), N and phosphate (P) fertilizer (NP), N and potassium (K) fertilizer (NK), P and K fertilizer (PK), NPK fertilizer (NPK), NPK plus straw (NPKS), and NPK plus manure in three combinations (NPKM1, NPKM2, and NPKM3). The results showed that maize yield and soil nutrients significantly increased by fertilizations, especially when organic incorporation. Soil pH significantly decreased by inorganic fertilizers but alleviated when organic incorporation. Fertilizations significantly enhanced bacterial α-diversity due to the increased nutrient availabilities. The bacterial β-diversity was also significantly changed the changed by fertilizations, especially manure-added. The three dominant bacteria were Proteobacteria, Acidobacteria and Actinobacteria, accounting for 50-70 % of the total bacteria. Fertilizers, especially manure-added, significantly increased Proteobacteria and Acidobacteria and decreased Actinobacteria. The other top 7 bacteria taxa, were significantly correlated with soil pH. The Mantel test showed yield, and soil pH and nutrients were all significantly related to the overall bacterial community structure. The soil pH contributed to 14.3 %, and the yield and soil nutrients contributed to 5.6 % and 15.8 % of bacterial community changes based on a partial CCA-based variation partitioning analysis. [ABSTRACT FROM AUTHOR]

• "Black soils" contribute to ecosystem services, especially as a major carbon store. • We evaluated the taxonomic distances between the centroids of the "black soils". • "Black soils" roughly correspond to Mollisols order in the US Soil Taxonomy. • Vertisols and Andisols should be excluded from the concept of "black soils". • We recommend establishing a fuzzy definition of "black soils" for general public. "Black soils" recently proposed by the FAO Global Soil Partnership, include fertile soils, characterized by a thick, dark-colored soil horizon rich in organic matter. This study addressed the proposed concept of "black soils", in terms of taxonomic relationship of their corresponding soil types of existing soil classifications. Similarity studies were based on the calculation of taxonomic distances between selected soil groups with organic matter–enriched horizons of the Russian Soil Classification System, the United States Soil Taxonomy and the World Reference Base for Soil Resources. In the process, we used the so called "centroids", which are the calculated mean values of several soil properties for each of the soil groups using legacy data derived from national and international databases. The results indicated that the Great Groups of the Mollisol Order in the US Soil Taxonomy had small taxonomic distances within the order, except some soils with shallow depth to the hardpan or permafrost. Dark-colored Vertisols and Andisols were found to differ from the Mollisols and similar soils found in similar environments mainly under grasslands. We recommend excluding Vertisols and Andisols from the "black soils" cluster due to the peculiarity in their properties, potential use and management. While the Vertisols and Mollisols of the Soil Taxonomy were completely dissimilar in properties, the WRB Vertisol Reference group and Russian dark-humus compact soils fitted well the Mollisols cluster, presumably due to the different concept of the Vertisols in the studied system. The soil types of the "black soils" of the Russian soil classification had a short distance to the corresponding Reference Groups of the World Reference Base. Also, the similarity was high with the Great Groups of the US Soil Taxonomy for all soil types except of Kastanozems, but the relationship in places was not well interpreted from a pedogeographic point of view. We ascribed the phenomenon to the geographical bias of the databases. Though "black soils" form a distinct cluster that roughly corresponds to the Mollisols Order of the US Soil Taxonomy, the taxonomic distance within the group may be significant, contributing to the pedodiversity of soilscapes of "black soils". [ABSTRACT FROM AUTHOR]

• Diversity and abundance of antibiotic resistance genes were influenced by different types and amounts of animal manures. • Multidrug was the most dominant type of antibiotic resistance genes in the black soils. • Composition of Antibiotic resistance genes had no clear geographic patterns. • aadA-1-01 and mexF were the major indicators. Black soils (Mollisols) are important soil resources for crop production and maintain food safety in China. For keeping soil fertility, the application of animal manure is commonly practiced in black soils. However, the impact of this application on abundance and diversity of antibiotic resistance genes (ARGs) in black soils of China remains unclear. Here, we surveyed the profiles of ARGs in 72 soil samples collected from four long-term experimental stations with different fertilization regimes and from open farmlands in two sites across northeast China using high-throughput quantitative PCR. Results showed that a total of 178 ARGs including mobile genetic elements (MGEs) were detected, and the diversity and abundance of ARGs were significantly increased with manure application. Additionally, the finding of a significant positive correlation between relative abundance of ARGs and MGEs (P < 0.0001), suggesting that horizontal gene transfer may potentially impact the transmission of ARGs. Furthermore, two genes aadA-1-01 and mexF , encoding resistance to aminoglycoside and multidrug, respectively, were recognized as indicators to estimate the abundance of other co-occurring ARGs. These findings provided insights into the soil resistome in black soils of northeast China and also highlighted the environmental risks caused by manure application should not be ignored. [ABSTRACT FROM AUTHOR]