Soil respiration induces co-emission of greenhouse gases and methylated selenium from cold-region Mollisols: Significance for selenium deficiency.

Mollisols rich in natural organic matter are a significant sink of carbon (C) and selenium (Se). Climate warming and agricultural expansion to the cold Mollisol regions may enhance soil respiration and biogeochemical cycles, posing a growing risk of soil C and Se loss. Through field-mimicking incubation experiments with uncultivated and cultivated soils from the Mollisol regions of northeastern China, this research shows that soil respiration remained significant even during cold seasons and caused co-emission of greenhouse gases (CO2 and CH4) and methylated Se. Such stimulus effects were generally stronger in the cultivated soils, with maximum emission rates of 7.45 g/m2/d C and 1.42 µg/m2/d Se. For all soil types, the greatest co-emission of CO2 and dimethyl selenide occurred at 25 % soil moisture, whereas measurable CH4 emission was observed at 40 % soil moisture with higher percentages of dimethyl diselenide volatilization. Molecular characterization with three-dimensional fluorescence and ultra-high resolution mass spectrometry suggests that CO2 emission is sensitive to the availability of microbial protein-like substances and free energy from organic carbon biodegradation under variable moisture conditions. Predominant Se binding to biodegradable organic matter resulted in high dependence of Se volatilization on rates of greenhouse gas emissions. These findings together highlight the importance of dynamic organic carbon quality for soil respiration and consequent Mollisol Se loss risk, with implications for science-based management of C and Se resources in agricultural lands to combat with Se deficiency.

Mollisol Erosion-Driven Efflux of Energetic Organic Carbon and Microflora Increases Greenhouse Gas Emissions from Cold-Region Rivers.

Massive soil erosion occurs in the world's Mollisol regions due to land use change and climate warming. The migration of Mollisol organic matter to river systems and subsequent changes in carbon biogeochemical flow and greenhouse gas fluxes are of global importance but little understood. By employing comparative mesocosm experiments simulating varying erosion intensity in Mollisol regions of northeastern China, this research highlights that erosion-driven export and biomineralization of terrestrial organic matter facilitates CO2 and CH4 emission from receiving rivers. Stronger Mollisol erosion, as represented by a higher soil-to-water ratio in suspensions, increased CO2 efflux, particularly for the paddy Mollisols. This is mechanistically attributable to increased bioavailability of soluble organic carbon in river water that is sourced back to destabilized organic matter, especially from the cultivated Mollisols. Concurrent changes in microbial community structure have enhanced both aerobic and anaerobic processes as reflected by the coemission of CO2 and CH4. Higher greenhouse gas effluxes from paddy Mollisol suspensions suggest that agricultural land use by supplying more nitrogen-containing, higher-free-energy organic components may have enhanced microbial respiration. These new findings highlight that Mollisol erosion is a hidden significant contributor to greenhouse gas emissions from river water, given that the world's four major Mollisol belts are all experiencing intensive cultivation.

Biochar aided priming of carbon and nutrient availability in three soil orders of India.

In recent years biochar (BC) has gained importance for its huge carbon (C) sequestration potential and positive effects on various soil functions. However, there is a paucity of information on the long-term impact of BC on the priming effect and nutrient availability in soil with different properties. This study investigates the effects of BC prepared from rice husk (RBC4, RBC6), sugarcane bagasse (SBC4, SBC6) and mustard stalk (MBC4, MBC6) at 400 and 600 °C on soil C priming and nitrogen (N), phosphorus (P), and potassium (K) availability in an Alfisol, Inceptisol, and Mollisol. BC properties were analyzed, and its decomposition in three soil orders was studied for 290 days in an incubation experiment. Post-incubation, available N, P, and K in soil were estimated. CO2 evolution from BC and soil alone was also studied to determine the direction of priming effect on native soil C. Increasing pyrolysis temperature enhanced pH and EC of most of the BC. The pyrolysis temperature did not show clear trend with respect to priming effect and nutrient availability across feedstock and soil type. MBC6 increased C mineralization in all the soil orders while RBC6 in Alfisol and SBC6 in both Inceptisol and Mollisol demonstrated high negative priming, making them potential amendments for preserving native soil C. Most of the BC showed negative priming of native SOC in long run (290 days) but all these BC enhanced the available N, P, and K in soil. SBC4 enhanced N availability in Alfisol and Inceptisol, RBC4 improved N and P availability in Mollisol and P in Alfisol and MBC6 increased K availability in all the soils. Thus, based on management goals, tailored BC or blending different BC can efficiently improve C sequestration and boost soil fertility.

Response of soil erosion resistance to straw incorporation amount in the black soil region of Northeast China.

Straw incorporation has been considered as an effective environmental management application to improve soil erosion resistance (SER) and organic carbon sequestration. SER is useful to evaluate soil erosion subjected to concentrated flow. Nevertheless, few studies have been performed to examine how SER varied with the amount of straw incorporation on sloping croplands in high latitude and cool regions. In the current study, the fixed bed scouring tests were conducted in a large hydraulic flume using undisturbed soil samples taken from Hebei small watershed in the black soil region of Northeast China. The response of SER to different straw incorporation amounts (0, 1.125, 2.25, 4.5, 6.75, 9.0 and 13.5 t ha-1) was quantified after three months of straw decomposition. The major influencing factors and the corresponding mechanisms were determined. The findings demonstrated that rill erodibility firstly decreased exponentially with straw incorporation amount (R2 = 0.93), while it slightly increased when straw incorporation amount was more than 9.0 t ha-1. Critical shear stress firstly increased logarithmically (R2 = 0.90) and then slightly decreased when the amount exceeded 9.0 t ha-1. Compared to the treatment of 0 t ha-1, rill erodibility reduced by 17.0%-92.8% and critical shear stress increased by 59.6%-127.2% across different treatments of straw incorporation. Rill erodibility had significant and negative correlations with soil organic matter content, aggregate stability, cohesion, root mass density, straw mass density and straw decomposition amount. The key mechanisms for promoting SER were derived by the direct and indirect effects of straw incorporation and its decomposition on soil physicochemical properties and crop roots. The amount of 9.0 t ha-1 was recommended as the optimum amount of straw incorporation in croplands in Northeast China. These findings are useful to understand how soil erosion resistance responds to the amount of straw incorporation and make rational environmental management policy for semi-humid and cool regions.

Soil nitrogen availability and microbial carbon use efficiency are dependent more on chemical fertilization than winter drought in a maize-soybean rotation system.

Soil nitrogen (N) availability is one of the limiting factors of crop productivity, and it is strongly influenced by global change and agricultural management practices. However, very few studies have assessed how the winter drought affected soil N availability during the subsequent growing season under chemical fertilization. We conducted a field investigation involving snow removal to simulate winter drought conditions in a Mollisol cropland in Northeast China as part of a 6-year fertilization experiment, and we examined soil physicochemical properties, microbial characteristics, and N availability. Our results demonstrated that chemical fertilization significantly increased soil ammonium and total N availability by 42.9 and 90.3%, respectively; a combined winter drought and fertilization treatment exhibited the highest soil N availability at the end of the growing season. As the growing season continued, the variation in soil N availability was explained more by fertilization than by winter drought. The Mantel test further indicated that soil Olsen-P content and microbial carbon use efficiency (CUE) were significantly related to soil ammonium availability. A microbial community structure explained the largest fraction of the variation in soil nitrate availability. Microbial CUE showed the strongest correlation with soil N availability, followed by soil available C:P and bacteria:fungi ratios under winter drought and chemical fertilization conditions. Overall, we clarified that, despite the weak effect of the winter drought on soil N availability, it cannot be ignored. Our study also identified the important role of soil microorganisms in soil N transformations, even in seasonally snow-covered northern croplands.

[Impacts of upslope inflow and soil pipe collapse on slope water erosion in the typical Chinese Mollisol region]. / å ¸åž‹é»‘åœŸåŒºå¡é¢ä¸Šæ–¹æ±‡æµå’ŒåœŸå£¤ç®¡é“å´©å¡Œå¯¹å¡é¢æ°´èš€çš„å½±å“.

Understanding the effects of upslope runoff and soil pipe collapse on slope water erosion can provide scien-tific basis for preventing Mollisol degradation caused by soil erosion. We conducted an experiment to investigate the effects of upslope inflow rate and soil pipe collapse on slope water erosion and to quantify the contribution of soil pipe erosion to slope soil erosion. The experiment included three inflow rates (30, 40, and 50 L·min-1) and three near-surface soil hydrological conditions (without soil pipe: NP; with soil pipe but no pipe flow: PF0; with pipe flow: PF1). The results showed that: 1) Slope soil erosion increased with increasing inflow rates; when the inflow rate increased from 30 L·min-1 to 40 and 50 L·min-1, slope soil erosion increased by 100.0%-111.5% and 214.8%-289.2%, respectively. 2) The soil pipe occurrence and pipe flow formation aggravated the slope water erosion process. At inflow rates of 30, 40, and 50 L·min-1, slope soil loss under the PF0 and PF1 treatments were 1.4-1.6 times and 1.7-2.1 times of that under the NP treatment. The contribution of soil pipe erosion to slope soil loss was 26.7%-37.6% under the PF0 treatment and 40.5%-51.9% under the PF1 treatment. 3) Soil pipe collapse intensified the rill erosion process. Compared with the NP treatment at 30, 40, and 50 L·min-1 inflow rate, rill erosion amounts under the PF0 and PF1 treatments increased by 38.1%-66.0% and by 93.7%-128.4%, respectively. Our results suggested that increasing upslope inflow rate resulted in higher surface runoff velocity, which promoted runoff detachment and transport capacity, and then aggrandized the amount of slope soil erosion. Moreover, soil pipe collapse exacerbated rill erosion process. When the soil pipe collapsed, all surface runoff was converted to soil pipe flow, which accelerated flow velocity and slope soil erosion process, and then increased the amount of slope soil erosion.

Loss of Selenium from Mollisol Paddy Wetlands of Cold Regions: Insights from Flow-through Reactor Experiments and Process-Based Modeling.

Mollisols are critical agricultural resources for securing global food supply. Due to its health importance, selenium (Se) fate in the Mollisols attracts growing concerns. Land use change from conventional drylands to paddy wetlands impacts Se bioavailability in the vulnerable Mollisol agroecosystems. The underlying processes and mechanisms however remain elusive. Here, results of flow-through reactor experiments with paddy Mollisols from northern cold-region sites indicate that continuous flooding with surface water for 48 d induced redox zonation that facilitated the loss of Mollisol Se by up to 51%. Further process-based biogeochemical modeling suggests largest degradation rates of dissolved organic matter (DOM) in 30 cm deep Mollisols that contained the highest-level labile DOM and organic-bound Se. Electron shunting from degradation of Se-bearing DOM coupled to reductive dissolution of Se-adsorbed Fe oxides accounts mainly for Se(IV) release into the pore water. Consequent changes in DOM molecular composition make the reservoir of organic-bound Se vulnerable to flooding-induced redox zonation and likely enhance Se loss through destruction of thiolated Se and emission of gaseous Se from the Mollisol layer. This study highlights a neglected scenario where the speciation-driven loss of bioavailable Se from the paddy wetlands can be a significant consequence in the cold-region Mollisol agroecosystems.

Characteristics of spring maize sap flow and its environmental influencing factors in typical mollisol area.

Clarifying the variations of sap flow rate of spring maize in the typical mollisol area and its main control factors is of great significance to explore water consumption from transpiration and regulate field water management. In this study, we installed the wrapped sap flow sensors and TDR probes to continuously monitor the sap flow rate of spring maize during filling-maturity stage and soil water and heat conditions of topsoil. In combination with meteorological data collecting from a nearby automatic weather station, we analyzed the correlation between the sap flow rate of spring maize and environmental factors at different time scales. The results showed that the sap flow rate of spring maize in typical mollisol area had an obvious fluctuation of high diurnal and low nighttime. The instantaneous sap flow rate peaked at daytime, with a value of 139.9 g·h-1, but being weak at nighttime. The starting time, closing time, and peak values of spring maize sap flow were significantly inhibited in cloudy and rainy days, compared with that in sunny days. On hourly scale, the sap flow rate was significantly correlated to solar radiation, saturated vapor pressure deficit (VPD), relative humidity, air temperature, and wind speed. On daily scale, only solar radiation, VPD, and relative humidity were significantly correlated with sap flow rate, with the absolute values of correlation coefficient being all above 0.7. Due to high soil water content during the observation period, the sap flow rate was not significantly correlated with soil water content and soil temperature of 0-20 cm layer, with the absolute values of correlation coefficient being less than 0.1. Under the condition without water stress, solar radiation, VPD, and relative humidity were the top three influencing factors of sap flow rate in this region, on both hourly scale and daily scale.

Elevated CO2 and temperature increase arbuscular mycorrhizal fungal diversity, but decrease root colonization, in maize and wheat.

Anthropogenic climate change threatens ecosystem multifunctionality. Arbuscular mycorrhizal (AM) fungi are important symbionts that participate in mediating many ecosystem processes, and thus being potentially essential link in the chain of responses to climate change. Yet, how climate change affect the abundance and community structure of AM fungi associated with different crops remains elusive. Here, we investigated the changes in rhizosphere AM fungal communities and growth performance of maize and wheat grown in Mollisols under experimentally elevated CO2 (eCO2, +300 ppm), temperature (eT, +2 °C) and both in-combination (eCT) with open-top chambers, representing a scenario likely to occur by this century's end. The results showed that eCT significantly shifted AM fungal communities in both rhizospheres compared with control, but with no remarkable variation of the overall communities in maize rhizosphere, suggesting their greater resistance to climate change. Both eCO2 and eT increased rhizosphere AM fungal diversity, and conversely they reduced mycorrhizal colonization of both crops, probably since AM fungi had distinct adaptive strategies to climate change in rhizospheres (i.e., r-strategy) and roots (K-strategy), while the colonization intensity positively correlated with a decreased phosphorus (P)-uptake in two crops. Furthermore, co-occurrence network analysis showed that eCO2 strongly decreased the modularity and betweenness centrality of network structure than that of eT and eCT in both rhizospheres, along with the reduced network robustness, implied their destabilized communities under eCO2, while root stoichiometry (C:N and C:P ratio) was the most important factor associating with taxa in networks regardless of climate change. Overall, those findings suggest that rhizosphere AM fungal communities in wheat appear to be more sensitive to climate change than that in maize, further highlighting the importance of effective monitoring and managing AM fungi, which may allow crops to maintain critical levels of mineral nutrients (at least P) under future global change.

Fluvial Deposition and Land Use Change Control Selenium Occurrence in Mollisols of Cold Region Agroecosystems.

Mollisols support the most productive agroecosystems in the world. Despite their critical links to food quality and human health, the varying distributions of selenium (Se) species and factors governing Se mobility in the mollisol vadose zone remain elusive. This research reveals that, in northern mollisol agroecosystems, Se hotspots (≥0.32 mg/kg) prevail along the regional river systems draining the Lesser Khingan Mountains, where piedmont Se-rich oil shales are the most probable source of regional Se. While selenate and selenite dominate Se species in the water-soluble and absorbed pools, mollisol organic matter is the major host for Se. Poorly crystalline and crystalline Fe oxides are subordinate in Se retention, hosting inorganic and organic Se at levels comparable to those in the adsorbed pool. The depth-dependent distributions of mollisol Se species for the non-cropland and cropland sites imply a predominance of reduced forms of Se under the mildly acidic and reducing conditions that, in turn, are variably impacted by agricultural land use. These findings therefore highlight that fluvial deposition and land use change together are the main drivers of the spatial variability and speciation of mollisol Se.

Mechanisms of changing speciation and bioavailability of selenium in agricultural mollisols of northern cold regions.

The distribution, speciation, and bioavailability of selenium (Se) - an essential micronutrient for human beings - in agricultural soils influence the resource recovery of agricultural benefits and the sustainable use of Se in agroecosystems. Quantitative understanding in this regard however remains limited in the world's mollisol agroecosystems, despite their critical importance in securing global food supply. Herein, a systematic investigation of Se in the river sediment-irrigation water-mollisols-rhizosphere-rice seeds continuum, at the core zone of the northern mollisol regions, was conducted to elucidate the hydrological-hydrogeochemical processes and mechanisms responsible for the distribution and bioavailability of Se. The content of total Se in the mollisols ranged between 0.12 and 0.54 mg/kg with an average of 0.31 mg/kg. At the riverside flood plains, humic-acid bound Se accounted on average for 39 % of total Se. This pool of Se can be transformed to water-soluble and ion-exchangeable Se(VI), supporting a higher potential of Se bioavailability at riparian agricultural mollisols. For mollisol lands far from the river channels, the topography affects the speciation and partitioning of Se presumably through regulating water retention and organic matter transport. Moreover, altering pH and redox conditions in response to irrigation with the river water may boost Se bioavailability in weakly acidic and high Eh mollisols. It can be in part ascribed to the transformation of organic-bound Se along with infiltrated oxygenated water that leads to the increase of water-soluble and ion-exchangeable Se. These findings reinforce that hydrological-hydrogeochemical perturbations due to irrigation with surface water need to be assessed carefully in the management of Se resources in the mollisol agroecosystems.

Physically separated soil organic matter pools as indicators of carbon and nitrogen change under long-term fertilization in a Chinese Mollisol.

Isolation and quantification of soil organic matter (SOM) pools under the influence of management practices is needed for assessing the changes in soil fertility. However, the knowledge on how the active, slow and passive pools of SOM respond to long-term fertilization is scarce. Therefore, the present study was designed to isolate the active, slow, and passive pools of soil organic matter through physical fractionation under long-term fertilization. The treatments included; inorganic fertilization (NPK) either alone or combined with a normal dose of manure (MNPK) or a high dose of manure (1.5MNPK) with an unfertilized control (CK) for comparison. The isolated pools were analyzed and compared for their sizes, SOC and TN storage and their contribution to total SOC and TN sequestration. The results revealed that the fertilization enhanced the active, slow and passive pools of SOC and TN and their storage under applied treatments was patterned as 1.5MNK > MNPK > NPK > CK. The highest SOC and TN storage was observed in the active pool, while, greater response to fertilization (in terms of response ratio) was associated with the slow pool. Results show that fertilization enhanced the proportion of SOC and TN stocks to bulk SOC and TN stocks in active and slow pools, while a diminishing trend was found for passive pools. Moreover, the highest response ratio was found for TN sequestration in each pool as compared to SOC, suggesting preferential accumulation of TN over SOC in the studied soil. Nevertheless, the highest SOC and TN storage took place in the active pool. The slow pool showed greater response to applied fertilizer, with the highest values being observed under 1.5MNPK. This study concluded that long-term manure + inorganic fertilization is crucial for enhancing C and N sequestration by altering the size and response of SOM pools.

[Effects of soil erosion and deposition on the spatial distribution of soil microbial quantity in Mollisol area of Northeast China.] / å ¸åž‹é»‘åœŸåŒºä¾µèš€-沉积对土壤微生物数量空间分布的影响.

Revealing the responses of soil microbial community to soil erosion can provide guidance for agricultural ecosystem management. We investigated the impacts of soil erosion intensity on soil microbial quantity at the Binzhou River Basin, a typical thin layer Mollisol area in Bin County of Heilongjiang Province, using 137Cs tracer. The results showed that there were seasonal variations in soil microbial quantity. The abundance of soil microbes in summer was considerably higher than that in autumn. Bacteria was more sensitive to seasonal variation than fungi and actinomycetes, which was increased by 1.4-2.6 times and 1.4-2.2 times in summer compared with autumn in different parts of slope and watershed, respectively. The spatial variation of soil erosion intensity had an important effect on the spatial distribution of soil microbial community. The highest proportion of bacteria was found at lower deposition area of slope (84.4%) and at the lightly eroded area of the downstream (85.4%). The numbers of soil microbes, soil bacteria and actinomycetes were negative linearly correlated with soil erosion modulus, with correlation coefficients of -0.595, -0.554 and -0.291, respectively. Soil erosion and deposition induced spatial differences in soil physical and chemical properties, with consequences on spatial distribution of soil microbial community.

Influence of environmental factors on soil organic carbon in different soil layers for Chinese Mollisols under intensive maize cropping.

The Mollisol region of Northeast China has a large soil organic carbon (SOC) storage which is important for maintaining soil fertility. SOC is susceptible to various environmental factors; however, the responses of SOC content to environmental factors in different soil layers of cropland remain unclear, particularly in deep soil layers. In this study, we collected 138 soil samples from the surface, subsurface, and subsoil layers among 46 sample sites with monocropping maize and intensive conventional tillage in this region. We assessed the relative importance and effect paths of 12 environmental factors (including geography, climate, and soil properties) on SOC content in different layers using redundancy analysis (RDA), structural equation model (SEM), and variation partitioning analysis (VPA). The VPA results showed that SOC content was mainly affected by climatic factors that explained 68% and 57% for the surface and subsurface layers, respectively. However, SOC content in the subsoil layer was greatly affected by soil properties that explained 27%. Furthermore, the SEMs results suggested that geographical factors indirectly affected SOC content by influencing the climatic factors. Mean annual temperature was the most important factor affecting SOC content directly or indirectly, and its negative effects significantly diminished with soil depth, as it explained 63%, 52%, and 17% of the variation in SOC content for the surface, subsurface and subsoil layers, respectively. In addition, the effects of soil water-holding capacity on SOC content also decreased with soil depth, whereas pH and clay content showed a contrasting pattern. This implies that pH and clay content play important roles in the sequestration of SOC in deep soil layers. Moreover, the organic C content within >53 µm aggregates was more sensitive to environmental factors. This study can be useful for forecasting SOC dynamics and establishing reasonable C management strategies under climate change conditions.

Stability of soil organic carbon under long-term fertilization: Results from 13C NMR analysis and laboratory incubation.

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 CO2-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 CO2-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 CO2-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.

Rhizosphere Soil Bacterial Communities of Continuous Cropping-Tolerant and Sensitive Soybean Genotypes Respond Differently to Long-Term Continuous Cropping in Mollisols.

The continuous planting of soybeans leads to soil acidification, aggravation of soil-borne diseases, reduction in soil enzyme activity, and accumulation of toxins in the soil. Microorganisms in the rhizosphere play a very important role in maintaining the sustainability of the soil ecosystem and plant health. In this study, two soybean genotypes, one bred for continuous cropping and the other not, were grown in a Mollisol in northeast China under continuous cropping for 7 and 36years in comparison with soybean-maize rotation, and microbial communities in the rhizosphere composition were assessed using high-throughput sequencing technology. The results showed that short- or long-term continuous cropping had no significant effect on the rhizosphere soil bacterial alpha diversity. Short-term continuous planting increased the number of soybean cyst nematode (Heterodera glycines), while long-term continuous planting reduced these numbers. There were less soybean cyst nematodes in the rhizosphere of the tolerant genotypes than sensitive genotypes. In addition, continuous cropping significantly increased the potential beneficial bacterial populations, such as Pseudoxanthomonas, Nitrospira, and Streptomyces compared to rotation and short-term continuous cropping, suggesting that long-term continuous cropping of soybean shifts the microbial community toward a healthy crop rotation system. Soybean genotypes that are tolerant to soybean might recruit some microorganisms that enhance the resistance of soybeans to long-term continuous cropping. Moreover, the network of the two genotypes responded differently to continuous cropping. The tolerant genotype responded positively to continuous cropping, while for the sensitive genotype, topology analyses on the instability of microbial community in the rhizosphere suggested that short periods of continuous planting can have a detrimental effect on microbial community stability, although this effect could be alleviated with increasing periods of continuous planting.

[Characteristics of soil fertility during soil fertilization from parent material of a Mollisol in Northeast China]. / 东北黑土成土母质培肥过程中土壤肥力变化特征.

Based on a long-term field experiment located in the central region of Mollisol in Northeast China, we examined the changes of soil fertility and nutrient supply capacity of the newly-formed soils with pot experiment after 14-year different agricultural management practices from parent material (PM) (down to 2.0-3.0 m depth) of a Mollisol, and finally tried to optimize pre-ferential agricultural practices improving soil fertility of seriously eroded PM. After 14-year different agricultural practices, soil organic carbon, total nitrogen, stability of soil aggregate and other rela-ted soil nutrient contents improved compared with PM. Soil fertility level of the newly-developed soils significantly affected nutrient supply capacity for wheat in the pot experiment. Results from principal component analysis showed that soil fertility developed toward to the surface Mollisol after 14 years of different agricultural practices from PM. Surface soils with higher organic carbon inputs in arable soil with chemical fertilizer plus all aboveground biomass incorporated and those in no-tilled alfalfa soil were much approached to surface Mollisol, followed by arable soil with fixed amount of organic inputs and natural fallow soil, while soils without and with only chemical fertilizer were much closed to PM. Our results indicated that 14-year organic carbon inputs improved soil aggregate structure and the decomposition of organic carbon entering into soil, changed soil physical and biochemical properties, and hence caused maturing of soil fertility of PM. Straw returning, organic manure application, and planting alfalfa were recommended for improving soil fertility of eroded soil. These findings would give a better scientific basis for high-efficient fertilization and management practices in eroded Mollisol region.

Trichloroethylene inhibits nitrogen transformation and microbial community structure in Mollisol.

Trichloroethylene (TCE) is the most ubiquitous halogenated organic pollutant in the environment, it is one of the 129 priority control pollutants. In order to clarify the influence of TCE on microorganisms and nitrogen transformation in Mollisol is the core purpose of this study. Results showed that 10 mg kg-1 TCE is the concentration limit of ammonification in Mollisol. When the concentration of TCE reached 10 mg kg-1 and the effect lasted for over 7 days, the process of ammonia oxidation to nitric acid in Mollisol will be affected. TCE affected the process of nitrate (NO3-) transformation into nitrite (NO2-) by affecting the activity of nitrate reductase, thereby affected the denitrification process in soil. When the concentration of TCE is more than 10 mg kg-1 it reduced the ability of soil microorganisms to obtain nitrogen, thereby affecting soil nitrogen transformation. RDA (Redundancy analysis) showed that the activity of nitrate reductase and the number of nitrifying bacteria and denitrifying bacteria in soil was negatively correlated with the incubation of TCE. In addition, soil nitrate reductase, nitrite reductase, peroxidase activity, ammonifying bacteria, nitrifying bacteria and denitrifying bacteria were negatively correlated with TCE concentration. Beyond that PICRUSt (Phylogenetic Investigation of Communities by Reconstruction of Unobserved States) of functional gene structure depend on KEGG (Kyoto Encyclopedia of Genes and Genomes) showed that 20 mg kg-1 TCE significantly inhibited the metabolism of energy and other substances in Mollisol. Based on the above, it is found that TCE significantly affected nitrification and denitrification in Mollisol, thus the nitrogen transformation in Mollisol was affected by TCE contamination.

Effects of trichloroethylene stress on the microbiological characteristics of Mollisol.

Trichloroethylene (TCE), one of 129 kinds of priority pollutants, is the most common halogenated organic pollutant in the environment. To explore the changes in soil physicochemical properties and biological activities then clarify the effects of these factors on bacterial, fungal and actinomycetes communities in Mollisol under TCE stress is the significance of our research. The results indicated that when TCE concentration was greater than 10 mg kg-1, soil quality declined and soil decomposition of organic matter and cycling of mineral nutrients were inhibited through an effect on soil microbial biomass. Operational taxonomic units (OTUs) richness of the bacteria in Mollisol was altered by TCE contamination. The SChao1 and HShannon indices of bacterial communities in Mollisol decreased when 40 mg kg-1 TCE was applied. Meanwhile, the OTU richness of fungi in Mollisol was altered by TCE contamination. The HShannon indices of the fungal communities in Mollisol were inhibited by higher TCE concentrations (20 and 40 mg kg-1 TCE). TCE altered the content of some bacteria, fungi and actinomycetes involved in soil carbon and nitrogen cycling and metabolism, such as Acidobacteria, Proteobacteria, Planctomycetes, Chytridiomycota, Streptomycetales, Pseudonocardiales, Propionibacteriales and Rhizobiales, and thus influenced nutrient cycling and the process of energy metabolism in Mollisol. In addition, redundancy analysis (RDA) results indicated that physicochemical properties and biological activities under TCE contamination significantly affected soil microbial community composition thus confirming that TCE interfered with the carbon and nitrogen cycling and metabolism of soil microorganisms. The results of this study are of great importance for revealing the effects of TCE stress on the microbiological characteristics of Mollisol, and also provide more useful information for determining the potential ecological risk of organic pollutants in Mollisol.

Effects of bok choy on the dissipation of dibutyl phthalate (DBP) in mollisol and its possible mechanisms of biochemistry and microorganisms.

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.