Black Soil Of Northeast China Research Articles

Effects of Climate Warming on the Key Process and Index of Black Soil Carbon and Nitrogen Cycle During Freezing Period

As an critical part of the global biogeochemical cycle, the winter soil carbon and nitrogen cycles are extremely sensitive to climate warming. Furthermore, the black soil in northeast China is fertile and rich in organic matter and is a vital production base of commodity grains in China. For as long as half a year, the black soil is in a freezing-thawing state. Climate warming will change the snow cover thickness and soil freezing degree on the surface of the black soil in the winter and affect the freezing-thawing cycle frequency and timing of the soil, thus exerting a profound influence on the fixation, transformation, and release of soil carbon and nitrogen during the freezing period and throughout the year. To better understand the effects of climate warming on the black soil carbon and nitrogen dynamics during the freezing period, an experiment was conducted with two warming levels (W1 and W2) using an infrared radiometer to simulate soil warming. The warming increased the surface soil temperature (0 cm soil temperature) by 1.54℃ (W1) and 4.10℃ (W2), respectively, and significantly increased the soil moisture content compared with the control (C) during the freezing period, most likely because of the melting snow. The snow cover thickness, soil freezing depth, soil organic carbon (SOC), and labile organic carbon (LC) content were reduced by both warming treatments. However, the effect of the temperature increase during the freezing period on the key processes and indicators of the nitrogen cycle in black soil was relatively more complicated. With the increase in temperature, the content of nitrate nitrogen (NO3--N) decreased significantly, and the content of total nitrogen (TN) and net nitrogen nitrification rate increased significantly, while the ammonium nitrogen (NH4+-N), total inorganic nitrogen (TIN) content, and the net nitrogen mineralization rate exhibited a significant increase first and then decreased. In summary, climate warming will bring a warmer and more humid environment to the black soil during the freezing period, and the resulting changes in the soil carbon and nitrogen content and transformation processes will have a profound impact on the structure, productivity of the plants and microbial communities, and carbon and nitrogen cycles in the subsequent growing season. The results provide a scientific basis for studying the carbon and nitrogen cycle mechanisms of the northeast black soil during the freezing period.

Complex soil food web enhances the association between N mineralization and soybean yield – a model study from long-term application of a conservation tillage system in a black soil of Northeast China

Abstract. Long-term (10 years) application of conservation tillage following conversion from conventional tillage (CT) can achieve a new equilibrium in the soil environment, which is vital to reverse soil biodiversity declines and fulfil the goal of maintaining agroecosystem sustainability. However, in such a situation, how the soil community regulates nutrient cycling impacting crop yield is not well documented. Therefore, the relations between mineralized nitrogen (N) delivered by soil food web and soybean (Glycine max Merr.) yield were investigated after 14 years application of CT, reduced tillage (RT) and no tillage (NT) in a black soil (Typic Hapludoll) of Northeast China. We hypothesized that soil mineralizable N would increase with the complexity of the soil food web, and that the trophic groups involved in associating N mineralization with crop yield will vary with soil depth in the conservation tillage practice. During the soybean growing season, soil organisms, including bacteria, fungi, nematodes, mites and collembolans, were extracted and identified monthly from 0–5 and 5–15 cm soil depths to estimate the complexity of the food web indicated by the species richness and connectance indices, and to simulate the mineralized N using energetic food web modelling. The species richness and connectance of the food web at both soil depths were significantly affected by tillage practices, and their values decreased of the order of NT > RT > CT. A similar trend was also revealed for the simulated N mineralization, that is, the mineralized N released either from the functional feeding guilds or from the energy pathways of the food web were greater in RT and NT than in CT at both soil depths. Multiple linear regression analysis showed that soil organisms involved in coupling the mineralized N with soybean yield were different at different soil depths, in which fungal and root pathways at 0–5 cm and bacterial pathway at 5–15 cm were the driving factors for the supply of mineralized N to soybean in NT and RT soils. These results support our hypothesis and highlight the essential role of soil food web complexity in coupling N mineralization and crop yield after long-term application of conservation tillage. Additionally, the current modelling work provides basic hypotheses for future studies to test the impact of soil biodiversity or specific functional guilds on the fate of N in agro-ecosystems.

Long-term fertilization enhanced carbon mineralization and maize biomass through physical protection of organic carbon in fractions under continuous maize cropping

Long-term fertilization has been recognized as a key factor controlling soil organic carbon (SOC) and crop yields at various scales. Therefore, the impact of long-term nutrient management on SOC contents, fractional distribution, C-mineralization, and crop productivity under maize mono-cropping was investigated in the present work. For this, a typical black soil in northeast China was collected and analysed to measure the organic carbon (OC) content in the bulk soil, the distribution and OC contents of the different SOC fractions including, coarse particulate organic carbon (cPOC) and free particulate organic carbon (fPOC), intra-aggregate particulate organic carbon (iPOC), free silt plus clay (s + c_f) and micro-aggregate derived silt plus clay (s + c_m), and the SOC mineralization dynamics under different fertilizer treatments. Treatments included: 1) unfertilized control (CK), 2) balanced mineral fertilization (NPK), 3) NPK combined with manure (MNPK), 4) NPK combined with high dose (1.5 times) of manure (1.5MNPK), and 5) NPK combined with crop straw (NPKS). Manure treatments (1.5MNPK and MNPK) led to the largest increase in the SOC content of bulk soil (97% for 1.5MNPK and 41% for MNPK respect to CK). In addition, the long-term fertilization improved the proportions of the cPOC, fPOC and iPOC, especially in the case of manure treatments. In this same way, in comparison to CK, manure treatments (1.5MNPK and MNPK) significantly increased the SOC contents in cPOC (by 96 and 57%, respectively), fPOC (by 146 and 91%, respectively), iPOC (by 160 and 113%, respectively), s + c_f (by 51 and 39%, respectively) and s + c_m (by 56 and 50%, respectively) fractions. Similarly, higher values of SOC mineralization were associated with the 1.5MNPK and MNPK treatments as compared to CK, NPKS, and NPK alone. Finally, the application of 1.5MNPK and MNPK resulted in the highest increase in maize grain yield and in straw biomass yield. Therefore, the results obtained clearly indicate that long-term fertilization using manure combined with mineral fertilizer is the best choice to improve the SOC sequestration and mineralization, as well as the crop yields. All these facts can be considered relevant from points of view related to environmental management, soil fertility, and cleaner crop production.

Effects of Fertilization Methods on Chemical Properties, Enzyme Activity, and Fungal Community Structure of Black Soil in Northeast China

Understanding the influence of fertilizer on soil quality is vital to agricultural management, yet there are few studies, particularly in black soil. In this study, soils under various treatments, namely no fertilizer, bio-organic + humic acid, bio-organic + chemical, and chemical fertilizer, were sampled to identify their major physiochemical properties, and to investigate the fungal community structure using environmental sequencing techniques. Physiochemical properties and fungal community structure were examined at four important stages of the maize life cycle: seedling, jointing, heading period, and maturity. We found that chemical fertilizer in the mature stage increased the soil available phosphorous (AP) content. Organic matter content was greatly affected by bio-organic + chemical fertilizer during the mature stage. Bio-organic + humic acid significantly increased soil phosphatase activity in maturing maize, whilst chemical fertilizers reduced invertase activity. Taken together, our results clearly illustrated that bio-organic + humic and chemical fertilization indirectly alter fungal community structure via changing soil properties (especially AP). Chemical fertilizer markedly heightened the AP content, thereby decreasing specific fungal taxa, particularly Guehomyces. OM was of positive connection with bio-organic + humic acid and Mortierella abundance, respectively, through RDA analysis, which are in agreement with our result that bio-organic + humic acid fertilization to some extent increased Mortierella abundance. Additionally, bio-organic + humic acid decreased the abundance of Fusarium and Humicola, suggesting that bio-organic + humic acid possibly could help control crop disease. These results help to inform our fundamental understanding of the interactions between fertilizers, soil properties, and fungal communities.

Exploring Appropriate Preprocessing Techniques for Hyperspectral Soil Organic Matter Content Estimation in Black Soil Area

Black soil in northeast China is gradually degraded and soil organic matter (SOM) content decreases at a rate of 0.5% per year because of the long-term cultivation. SOM content can be obtained rapidly by visible and near-infrared (Vis–NIR) spectroscopy. It is critical to select appropriate preprocessing techniques for SOM content estimation through Vis–NIR spectroscopy. This study explored three categories of preprocessing techniques to improve the accuracy of SOM content estimation in black soil area, and a total of 496 ground samples were collected from the typical black soil area at 0–15 cm in Hai Lun City, Heilongjiang Province, northeast of China. Three categories of preprocessing include denoising, data transformation and dimensionality reduction. For denoising, Svitzky-Golay filter (SGF), wavelet packet transform (WPT), multiplicative scatter correction (MSC), and none (N) were applied to spectrum of ground samples. For data transformation, fractional derivatives were allowed to vary from 0 to 2 with an increment of 0.2 at each step. For dimensionality reduction, multidimensional scaling (MDS) and locally linear embedding (LLE) were introduced and compared with principal component analysis (PCA), which was commonly used for dimensionality reduction of soil spectrum. After spectral pretreatments, a total of 132 partial least squares regression (PLSR) models were constructed for SOM content estimation. Results showed that SGF performed better than the other three denoising methods. Low-order derivatives can accentuate spectral features of soil for SOM content estimation; as the order increases from 0.8, the spectrum were more susceptible to spectral noise interferences. In most cases, 0.2–0.8 order derivatives exhibited the best estimation performance. Furthermore, PCA yielded the optimal predictability, the mean residual predictive deviation (RPD) and maximum RPD of the models using PCA were 1.79 and 2.60, respectively. The application of appropriate preprocessing techniques could improve the efficiency and accuracy of SOM content estimation, which is important for the protection of ecological and agricultural environment in black soil area.

Beneficial Effects of Mixing Kentucky Bluegrass With Red Fescue via Plant-Soil Interactions in Black Soil of Northeast China.

Continuous monoculture of cool-season turfgrass causes soil degradation, and visual turf quality decline is a major concern in black soil regions of Northeast China. Turf mixtures can enhance turfgrass resistance to biotic and abiotic stresses and increase soil microbial diversity. Understanding mechanism by plant-soil interactions and changes of black soil microbial communities in turf mixture is beneficial to restoring the degradation of urbanized black soils and maintaining sustainable development of urban landscape ecology. In this study, based on the previous research of different sowing models, two schemes of turf monoculture and mixture were conducted in field plots during 2016–2018 in a black soil of Heilongjiang province of Northeast China. The mixture turf was established by mixing 50% Kentucky bluegrass “Midnight” (Poa pratensis L.) with 50% Red fescue “Frigg” (Festuca rubra L.); and the monoculture turf was established by sowing with pure Kentucky bluegrass. Turf performance, soil physiochemical properties, and microbial composition from rhizosphere were investigated. Soil microbial communities and abundance were analyzed by Illumina MiSeq sequencing and quantitative PCR methods. Results showed that turfgrass quality, turfgrass biomass, soil organic matter (SOM), urease, alkaline phosphatase, invertase, and catalase activities increased in PF mixture, but disease percentage and soil pH decreased. The microbial diversity was also significantly enhanced under turf mixture model. The microbial community compositions were significantly different between the two schemes. Turf mixtures obviously increased the abundances of Beauveria, Lysobacter, Chryseolinea, and Gemmatimonas spp., while remarkably reduced the abundances of Myrothecium and Epicoccum spp. Redundancy analysis showed that the compositions of bacteria and fungi were related to edaphic parameters, such as SOM, pH, and enzyme activities. Since the increasing of turf quality, biomass, and disease resistance were highly correlated with the changes of soil physiochemical parameters and microbial communities in turf mixture, which suggested that turf mixture with two species (i.e., Kentucky blue grass and Red fescue) changed soil microbial communities and enhanced visual turfgrass qualities through positive plant-soil interactions by soil biota.

Does biochar application enhance soil salinization risk in black soil of northeast China (a laboratory incubation experiment)?

ABSTRACT Generally, application of biochar is an important management practice that can affect soil physico-chemical and biological properties. However, biochar is characterized by high pH and ash content, and due to this, little is known of potential salinization risk of application of biochar to soil. Laboratory incubation experiments were conducted with three replications comprising five treatments according to application rates of biochar (0, 50, 100, 200 and 400 g kg−1 (wt/wt)). The results indicated that application of corn straw biochar to black soil at the rate of 400 g kg−1 resulted in significant increases in soil pH, electrical conductivity (EC) and exchangeable K+ and soluble K+, Ca2+ and Mg2+, and decreases in cation exchange capacity (CEC) and exchangeable Ca2+ in comparison to untreated soil. Based on stepwise regression analysis, the dominant independent variable that affected soil pH was exchangeable K+ saturation percentage. In addition, EC was significantly positively related to potassium adsorption ratio (PAR). It was concluded that increased soil pH and EC are related to biochar (pyrolysis temperature of 600 °C) with higher concentration of K+ and lower CEC. This is due to increased exchangeable and soluble K+ and decreased soil buffering capacity from high application rate of biochar.

Effects of different agronomic practices on the selective soil properties and nitrogen leaching of black soil in Northeast China

Considering the large amount and high frequency application of concentrated fertilizer nitrogen in the Black Soil Region of Northeast China, the current laboratory/field simulation study aimed to explore the pollution risk of added nitrogen in black soil to groundwater and identify effective measures to prevent and control soil nitrogen leaching with an undisturbed soil column. The results showed that the saturated nitrogen adsorption capacities increased by 1.7%, 7.7% and 18.5% in ploughing, impervious agent (starch grafted polyacrylic acid) addition, and corn straw returning treatments, respectively, relative to the control (no-till). When the collection volume of the leaching solution reached the experimental maximum (4,000 mL), the total amount of nitrogen leaching from the control soil column (i.e., the no-tillage treatment) accounted for more than 50% of the added nitrogen, indicating a great risk of nitrogen pollution in groundwater. Compared with the no-tillage treatment, the amount of nitrogen leaching from the ploughing treatment increased insignificantly, and the amount of nitrogen leaching in the following spring in the corn straw returning treatment increased by 11.2%. The amount of nitrogen leaching decreased by 12.5% in the soil sampled in autumn of the second year. The total amount of nitrogen leaching in the soil with impervious agents decreased by 40.1%. Therefore, the permeability-reducing agent could significantly reduce underground water pollution risk posed by nitrogen leaching.

Influence of 37 Years of Nitrogen and Phosphorus Fertilization on Composition of Rhizosphere Arbuscular Mycorrhizal Fungi Communities in Black Soil of Northeast China

Increased inorganic nitrogen (N) and phosphorus (P) additions expected in the future will endanger the biodiversity and stability of agricultural ecosystems. In this context, a long-term fertilizer experiment (37 years) was set up in the black soil of northeast China. We examined interaction impacts of elevated fertilizer and host selection processes on arbuscular mycorrhizal fungi (AMF) communities in wheat rhizosphere soil using the Illumina MiSeq platform. The soil samples were subjected to five fertilization regimes: no fertilizer (CK) and low N (N1), low N plus low P (N1P1), high N (N2), and high N plus high P (N2P2) fertilizer. Long-term fertilization resulted in a significant shift in rhizosphere soil nutrient concentrations. The N fertilization (N1 and N2) did not significantly change rhizosphere AMF species diversity, but N plus P fertilization (N1P1 and N2P2) decreased it compared with CK. Non-metric multidimensional scaling showed that the rhizosphere AMF communities in CK, N1, N2, N1P1 and N2P2 treatments were distinct from each other. The AMF communities were predominantly composed of Glomeraceae, accounting for 30.0–39.1% of the sequences, and the relative abundance of family Glomeraceae was more abundance in fertilized soils, while family Paraglomeraceae were increased in N1 and N2 compared with CK. Analysis shown that AMF diversity was directly affected by soil C:P ratio but indirectly affected by plant under long-term fertilization. Overall, the results indicated that long-term N and P fertilization regimes changed rhizosphere AMF diversity and community composition, and rhizosphere AMF diversity was both affected by soil C:P ratio and plant.

Changes of diazotrophic communities in response to cropping systems in a Mollisol of Northeast China.

Nitrogen-fixing microorganisms play important roles in N cycling. However, knowledge related to the changes in the diazotrophic community in response to cropping systems is still rudimentary. In this study, the nifH gene was used to reveal the abundance and community compositions of diazotrophs in the cropping systems of continuous cropping of corn (CC) and soybean (SS) and soybean-corn rotation for growing corn (CSC) and soybean (SCS) in a black soil of Northeast China. The results showed that the abundance of the nifH gene was significantly higher in cropping soybean than in cropping corn under the same cropping system, while remarkably increased in the rotation system under the same crop. The Shannon index in the CC treatment was significantly higher than that in the other treatments, but the OTU number and Chao1 index had no significant change among the four treatments. Bradyrhizobium japonicum was the dominant diazotrophic species, and its relative abundance was at the lowest value in the CC treatment. In contrast, Skermanella sp. had the highest relative abundance in the CC treatment. A PCoA showed that the diazotrophic communities were separated between different cropping systems, and the variation caused by continuous corn cropping was the largest. Among the tested soil properties, the soil available phosphorus was a primary factor in determining diazotrophic community compositions. Overall, the findings of this study highlighted that the diazotrophic communities in black soils are very sensitive to cropping systems.

Response of acidobacterial communities to 3 years of biochar addition in a black soil of northeast China

ABSTRACT 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.

Effects of soil erosion and land use patterns on the characteristics of soil water and gas transport in the black soil region

Soil erosion is one of the main causes for the degradation of black soil in Northeast China. Understanding the differences of soil water and air transport under different land use patterns can provide scientific basis for efficient utilization and protection of soil and water resources in the black soil area. In this study, we examined the in-situ soil saturated hydraulic conductivity, air permeability and relative gas diffusion of 0-5 cm soil layer in three typical land use patterns (cropland, woodland, abandoned land) in the Northeast black soil area and explored the impacts of soil erosion and land use pattern on water and gas transport. Results showed that there were significant differences in soil water and air transport between different eroded croplands and between different land use patterns. Soil bulk density of serious erosion cropland was higher than that of other lands, and that of ungraded cropland was significantly lower than other lands. Compared with the ungraded cropland, soil bulk density in the light erosion cropland, the moderate erosion cropland and the serious erosion cropland increased by 12.7%, 17.6% and 39.2%, saturated hydraulic conductivity decreased by 84.4%, 53.7% and 12.7%, air permeability decreased by 94.6%, 64.4% and 14.0%, and relative gas diffusion decreased by 91.3%, 82.6% and 4.3%, respectively. The saturated hydraulic conductivity, air permeability and relative gas diffusion of pine forest decreased by 86.5%, 83.0% and 91.3% respectively compared with that of ungraded cropland, saturated hydraulic conductivity, air permeability and relative gas diffusion of sea-buckthorn forest decreased by 51.7%, 45.6% and 82.6%, and saturated hydraulic conductivity, air permeability and relative gas diffusion of abandoned land decreased by 16.2%, 1.4% and 73.9% respectively compared with that of ungraded cropland. In addition, the measured result of soil air permeability and relative gas diffusion could be used to estimate saturated soil hydraulic conductivity. Soil water and gas transport characteristics were significantly affected by soil erosion and land use pattern.

Dynamics of ammonia oxidizers and denitrifiers in response to compost addition in black soil, Northeast China.

Organic fertilizer application could have an impact on the nitrogen cycle mediated by microorganisms in arable soils. However, the dynamics of soil ammonia oxidizers and denitrifiers in response to compost addition are less understood. In this study, we examined the effect of four compost application rates (0, 11.25, 22.5 and 45 t/ha) on soil ammonia oxidizers and denitrifiers at soybean seedling, flowering and mature stage in a field experiment in Northeast China. As revealed by quantitative PCR, compost addition significantly enhanced the abundance of ammonia oxidizing bacteria (AOB) at seedling stage, while the abundance of ammonia oxidizing archaea was unaffected across the growing season. The abundance of genes involved in denitrification (nirS, nirK and nosZ) were generally increased along with compost rate at seedling and flowering stages, but not in mature stage. The non-metric multidimensional scaling analysis revealed that moderate and high level of compost addition consistently induced shift in AOB and nirS containing denitrifers community composition across the growing season. Among AOB lineages, Nitrosospira cluster 3a gradually decreased along with the compost rate across the growing season, while Nitrosomonas exhibited an opposite trend. Network analysis indicated that the complexity of AOB and nirS containing denitrifiers network gradually increased along with the compost rate. Our findings highlighted the positive effect of compost addition on the abundance of ammonia oxidizers and denitrifiers and emphasized that compost addition play crucial roles in shaping their community compositions and co-occurrence networks in black soil of Northeast China.

Cadmium resistance mechanisms of a functional strain Enterobacter sp. DNB-S2, isolated from black soil in Northeast China

Enterobacter sp. DNB-S2 is an efficient DBP-degrading bacterial strain, which was proved to be highly resistant to cadmium (MIC was 12.5 mM) and the involved mechanisms were verified in this study. The results showed the maximu values of extracellular adsorbed and intracellular accumulated Cd2+ contents accounted for 24.67% and 4.78% of the initial Cd2+ content in the medium. The extreme low intracellular Cd accumulation reduced the risk of cadmium interfering with normal cell metabolism. TEM exhibited cell structure of DNB-S2 kept intact even at high Cd concentrations. Some precipitation particles were formed inside cells, which were further identified to be Cd–O–P, Cd (OH)2, CdCO3, and CdS by XPS. Furthermore, Cd resistant genes were predicted on DNB-S2 genome, and the presence of 11 alkaline phosphatase encoding genes provided genetic basis for the formation of cadmium phosphate precipitation, which illustrated intracellular precipitation is one of the important intracellular Cd detoxification mechanisms in strain DNB-S2. Noteworthily, 8 efflux proteins were annotated possibly responsible for cadmium efflux and they were all predicted located on cytoplasmic membrane. In a word, integrity of cell structure, the formation of cadmium precipitation and efficient exclusion primarily constitute Cd tolerance mechanisms of strain DNB-S2. This strain exhibits promising application to the bioremediation of cadmium-DBP contaminated bites.

Soil aggregates stability and storage of soil organic carbon respond to cropping systems on Black Soils of Northeast China

Monoculture and improper management may reduce soil fertility and deteriorate soil structure in Black soils (Mollisols) of Northeast China. The experiment was carried out from 2015 to 2016 in Black Soils comprising five cropping systems: continuous corn (CC), soybean-corn rotation (SC), corn-soybean rotation (CS), fallow-corn (FC), and fallow-soybean (FS). Our results showed that CS and FS treatments significantly increased mean weight diameter (MWD) and fractal dimension (D) in mechanical stability aggregates (MSAs), and increased MWD and geometric mean diameter (GMD) in water-stable aggregates (WSAs) compared with CC treatment. These two treatments were also significantly increased water-stable aggregates stability rate (WSAR), but decreased percentage of aggregates destruction (PAD) than CC treatment. Meanwhile, CS and FS treatments exhibited a higher carbon accumulation than CC treatment in bulk soils. Soil organic carbon (SOC) concentration in WSA0.106-0.25,WSA2-5 mm and WSA0.5-1 mm had a dominant effect on aggregate stability. Simutaneously, SOC in WSA>5 mm affected SOC concentration in bulk soils. As a whole, the CS and FS treatments can increase the percentage of macro-aggregates, enhance aggregate stability, as well as increase SOC concentration in bulk soils and all soil aggregate sizes.

Arbuscular mycorrhizal fungal community was affected by tillage practices rather than residue management in black soil of northeast China

Arbuscular mycorrhizal (AM) fungi are one of the most important soil microbes in an agrarian ecosystem, and consequently affected by various agricultural practices. To elucidate the effects of tillage practices and residue management on AM fungi, a field trial was conducted on the Songnen Plain, Northeast China. We examined the effects of different tillage practices including no-tillage (NT), rotary tillage (RT), subsoil tillage (ST) and deep tillage (DT) on the AM fungal biomass, diversity and community under residue removal and residue retention. AM root colonization and extraradical hyphal (ERH) density were significantly higher in DT treatment compared with NT treatment, whereas an opposite trend was observed for AM fungal spore density. Structural equation modeling indicated that AM fungal spore density was directly affected by tillage practices. Albeit, the effect of tillage practices on ERH density was mainly mediated through root length of maize. By Miseq sequencing of 18S rDNA, 66 AM fungal operational taxonomic units (OTUs) were identified and Glomeraceae was the most abundant group in this study. AM fungal OTU richness was highest in treatment NT, and significantly higher than that in treatment DT. Non-metric multidimensional scaling analysis indicated that treatment DT and ST induced a distinct AM fungal community composition compared with treatment NT. On the other hand, residue did not significantly influence AM fungal biomass, OTU richness and community composition. Overall, our findings indicated that tillage practice is a stronger determinant than residue management in AM fungal development and community composition in black soil on the Songnen Plain.

The mechanism of resistance-reducing/anti-adhesion and its application on biomimetic disc furrow opener.

The black soil of Northeast China is sticky and agglomerates easily, which often adheres to the surface of a traditional furrow opener during the furrowing process. In this paper, biomimetic design principles in resistance-reducing, anti-adhesion and resistance-reducing mechanism of biomimetic disc furrow opener were studied. Nine kinds of singular convex hull, nine kinds of singular wedge and nine kinds of mixed convex hull and wedge structural biomimetic disc furrow opener were designed, and the furrowing process with the soil simulated by finite element method (FEM).Three types of biomimetic disc furrow opener with less resistance were manufactured by laser processing for comparative test in soil bin based on the simulation results. The test results showed that the resistance of the biomimetic disc furrow opener was less than that of the ordinary disc. The soil-disc stress, influence of biomimetic structures, moisture content and furrow speeds on resistance were discussed. The resistance-reducing rate of D-BC-3 reached the maximum value 15.36% at the furrow speed of 0.6 m/s and the soil moisture content of 20%. It is believed that the biomimetic design principles can provide the significant inspirations for the future design of disc furrow opener with drag reduction.

Synergistic effect of Klebsiella sp. FH-1 and Arthrobacter sp. NJ-1 on the growth of the microbiota in the black soil of Northeast China.

The application of Atrazine in soil has always been a main problem in agriculture because its residuals may maintain in the soil for a long term. In this paper, two strains of Atrazine degrading bacteria (Klebsiella sp. FH-1 and Arthrobacter sp. NJ-1) were used to make biological compound microbial inoculum to repair the Atrazine contaminated typical black soil in Northeast China. Grain chaff was chosen as the optimal carrier material for microbial inoculum. The dynamic changes of Atrazine were detected by gas chromatography. The half-life of Atrazine in soil containing microbial inoculum was shortened from 9.8d to 4.2d. The Atrazine sensitive crops grown in the repaired soil showed increased stem length, root length, and emergence rate. The effects of microbial remediation on the original bacterial and fungal biota in the typical black soil in Northeast China were analyzed using the metagenomic approach. Results showed that Atrazine inhibited the original bacteria and fungi populations. The total numbers of bacterial and fungal species in the soil were partially recovered by adding the microbial inoculum. Two genera (Sphingosinicella and Sphingomonas) were the dominant bacteria. The beneficial bacterial biota was recovered and the number of species of the beneficial bacteria was higher than that in the original soil after adding the microbial inoculum. The dominant fungi included genera Guehomyces and Chaetomella. There was a total of 113 unclassified fungal genera (22.6% of 499), indicating the potential utility of the unclassified fungal species in the assessment of the soil contamination by Atrazine.

Effects of different corn straw amendments on humus composition and structural characteristics of humic acid in black soil

ABSTRACT Straw returning to the field has become a common way to utilize crop residues. This method does not only solve the problem of rational utilization of straw but also improves soil organic carbon (SOC) quality and quantity. So far, various methods of straw return exist, but the comparison of these methods has not been sufficiently studied, especially in the black soil of Northeast China. The purpose of this study is to evaluate the effects of different corn straw amendments applied under equal carbon (C) mass on soil humus composition and structural characteristics of humic acid (HA). The pot experiment was carried out by simulating corn straw return, which included four treatments: no corn straw applied (CK), corn straw (CS), humidified corn straw (HCS) and corn straw biochar (Bc). Soil HA was characterized by Fourier transform infrared spectroscopy (FTIR), elemental analyzer and thermogravimetric analysis (TG). The results showed that CS, HSC, and Bc treatments increased SOC content by 7.51%, 31.03%, and 33.65%, respectively, compared to CK. Bc treatment showed a greater degree of humification (79.16%) and increased the C content of HA by 10.87% and 7.37% compared with CS and HCS, respectively. The FTIR spectra and elemental results revealed that CS and HCS treatments increased the aliphaticity of the HA structure, while Bc increased the aromaticity of C in HA structure, rendering HA structure complicated. It can, therefore, be inferred that the application of biochar will improve humus compositions, SOC content and enhances the stability of HA structure.

Profiles of antibiotic resistome with animal manure application in black soils of northeast China

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.