• Volume 58,Issue 4,2021 Table of Contents
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    • >Insights and Perspectives
    • Rhizobiont: An Interdisciplinary Innovation and Perspective for Harmonizing Resources, Environment, and Food Security

      2021, 58(4):805-813. DOI: 10.11766/trxb202012310722

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      Abstract:In recent years, the research on plant nutrition has gained significant achievements in improving nutrient use efficiency in molecular plant nutrition, plant-microbe interaction, rhizosphere interaction, micro-ecological regulation, and nutrient management. However, how to coordinate food security, resource efficiency, and environmental sustainability to implement agriculture green development still confronts great challenges. Here, we propose a new concept of "Rhizobiont" and the corresponding working strategies to address this key issue. Aiming at the major scientific questions of "rhizosphere interaction and nutrient efficiency", the core thinking of this concept is to develop a systemic theory of the "Rhizobiont" consortium. This is an integrated system consisting of plants, roots, rhizosphere, hypersphere, and their associated microbes, and then to decipher the underlying mechanisms of plant-microbe and microbe-microbe interactions that drive high nutrient use efficiency. Specifically, the objectives, in theory, are to clarify the structure and function of rhizobiont consortium and their roles in the mobilization, uptake, and utilization of nutrients. Also, we seek to establish comprehensive management strategies for enhancing the biological potentials of the rhizobiont consortium via multi-interface interactions, allowing for a significant increase in crop productivity and nutrient use efficiency towards sustainable development. This new conceptual theory opens up an innovative research field of plant-soil-microbe interactions. Moreover, this concept seeks a comprehensive understanding of these interactions for harnessing the second genome of plants (microbiome), which will be the frontiers of agricultural research. The rhizobiont theory will help solve the problem of multi-objective coordination of food security, resource efficiency, and environmental protection. Thus, it provides scientific support for achieving agriculture green development in China. We further point out the key research contents and perspectives.

    • From Suppressive Soil to Rhizosphere Immunity: Towards an Ecosystem Thinking for Soil-borne Pathogen Control

      2021, 58(4):814-824. DOI: 10.11766/trxb202003230038

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      Abstract:Soil-borne diseases have become a limiting factor for the development of sustainable intensive agriculture. To coordinate the integrative development of food security, resource efficiency, and ecological health, the construction of a systematic theory and integrated approach is vital for sustainably controlling soil-borne pathogens. As a hotspot where plants and soil closely interact, the rhizosphere inhabits diverse microbiomes. Since the rhizosphere is the only way for soil-borne pathogens to penetrate plant roots, interactions between soil, plants, microorganisms, and plant-pathogens harbored in the rhizosphere could affect pathogen invasion and plant health. Recently, the ability of the rhizosphere to act against the invasion of soil-borne pathogens was defined as "rhizosphere immunity". In this review, we introduced this concept in four important stages:1) the proposal and development of the concept of disease-suppressive soil, 2) the isolation of beneficial microorganisms and their mechanisms in controlling diseases, 3) the deciphering of the structure and function of core microbiomes in disease-suppressive soil, and 4) proposal and development of the concept rhizosphere immunity. Firstly, it was observed that soil microorganisms together with soil abiotic factors determine the ability of soil suppressiveness. Also, previous researchers isolated the key microorganisms and uncovered the underlying mechanisms in disease suppression. Secondly, typical mechanisms including antagonism, nutritional competition, parasitism, predation, induced systemic resistance, and interference of pathogenic signals of pathogenic microorganisms were revealed. In addition to beneficial fungi and bacteria, bacteriophages and protists have also been applied to control pathogens. Despite soil microorganisms playing an important role in disease suppression, application of a single beneficial biocontrol agent into the field usually did not achieve the goal of disease suppression because of its weak colonization ability in the rhizosphere. Therefore, deciphering the composition and functional characteristics of core microorganisms involved in disease suppression has become the hotspot during the past ten years. Thirdly, the core microbial groups and functional genes associated with disease suppression and the approaches to decipher the core microbiomes were identified. Given that the interactions between core microbiomes or with the pathogens are still difficult to verify in natural soil, we reviewed the use of synthetic microbial communities to overcome this limitation. Finally, the background of the concept of "rhizosphere immunity" was introduced. We expounded on the four core functions of rhizosphere immunity:prevention, recognition, response, and homeostasis. Consequently, we used the application of bio-organic fertilizer as an example to demonstrate that rhizosphere immunity could be improved. In the perspective and conclusion section, we appeal with researchers to pay more attention to the belowground micro-ecology, embrace interdisciplinarity, and underly the key mechanisms of rhizosphere immunity. This review could provide a theoretical basis and technical support for improving the health of the soil-plant system and in achieving the aims of sustainable development of modern agriculture and food security.

    • >Reviews and Comments
    • Cadmium Isotopes Fractionation in Soil-Plant Systems: A Review

      2021, 58(4):825-836. DOI: 10.11766/trxb202006010266

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      Abstract:Cd contamination of soils has aroused great concerns among the people the world over for its causing Cd concentration in food crops beyond the limit for food safety, thus posing a threat to human health via the food chain. Migration and transformation of cadmium in soil, uptake of cadmium by plant roots, transport and storage of cadmium in different organs of plants are critical processes of the biogeochemical cycling of cadmium in the soil-plant systems. In recent years, the technique of stable isotope fractionation has been applied to investigation of cadmium transfer and storage in soil-plant systems, providing new insights into the transformation of cadmium in different soil pools and plant compartments. In this study, a brief introduction is presented first to the fundamental principle and methodology of cadmium isotopic composition analysis. And then discussions in detail are made about directions and extents of the Cadmium isotopes fractionation in soil induced by a number of processes, such as dissolution of soil minerals, precipitation, adsorption, and chelation with organic matter, with special emphasis laid on mechanisms of the fractionation of Cd in different plant parts during the three critical processes, that is, cadmium uptake by plant roots, cadmium translocation from root to shoot and cadmium storage in grains. To the best of our acknowledge, fractionation of cadmium isotopes in soil-plant systems may be subject to impacts of a number of factors/processes, such as soil minerals, composition of organic matter, root exudates and microorganisms in the rhizosphere, type of plants, stage of plant growth, nutrient elements with antagonistic effect, and so on. However, it remains as of yet unclear as to how. In the end, based on the status quo of the research on cadmium isotopes fractionation in soil-plant systems, perspectives for future research are put forth to encourage a combined application with other techniques, such as spectroscopy-based speciation analyses, molecular biological analyses, and so on, in the hope that the future research may provide a better understanding of the mechanisms of cadmium transformation in soil-plant systems, and help develop regulation strategies and remediation technologies for safe production of crops in cadmium-contaminated soils.

    • Research Progress on Passivation Materials for Cadmium-Arsenic Co-Contamination in Soil

      2021, 58(4):837-850. DOI: 10.11766/trxb201912170575

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      Abstract:In China, heavy metal pollution in soils is very serious, especially cadmium(Cd)and arsenic(As)pollution. In Cd and As(Cd-As)co-contaminated soils, the two elements Cd and As act either antagonistically or synergically, and their effective concentrations are affected by soil pH, redox potential, and some other soil environmental factors, which makes it more difficult to remediate the Cd-As co-contaminated soil and seriously threatens food security in our country. In this paper, a review is presented to show the advantages and disadvantages of the passivation materials for Cd-As soil co-contamination, as well as their effects and mechanisms. Common passivating materials include biochar, phosphates, metals and their oxides, silicon-containing materials, clay minerals, organic fertilizers and some other new materials. Recently, a large amount of studies have demonstrated that biochar is a good adsorbent for Cd, but modified biochar is usually used in combination with other materials, like metals or their oxides, clay minerals, poultry manure, compound fertilizer, etc. to passivate Cd and As simultaneously. The mechanism of modified biochar to passivate Cd and As was ion exchange, coprecipitation and surface complexation. Phosphate is mainly applied together with iron salt or iron powder to passivate Cd by adsorption and isomorphic substitution, and to passivate As by site-competition; metals and their oxides are mostly combined with biochar, lime or clay minerals to passivate Cd through specific adsorption and coprecipitation, and to passivate As through redox and complexation. Iron silicon fertilizer, silicon calcium fertilizer or silicon potassium fertilizer is used to passivate Cd via coprecipitation, and to passivate As through specific adsorption and site competition mechanism. In clay minerals, sepiolite is widely used, mainly combined with metal oxide, calcium magnesium phosphate fertilizer, etc., to passivate Cd and As through ion exchange, precipitation and complexation. Sludge and animal manure, which contain organic matter with high degree of humification, are used to passivate Cd and As mainly through adsorption, redox, organic complex and microbial interaction. In addition, the materials rich in sulfhydryl-and amino-groups, glutamate, S and Se can also effectively immobilize Cd and As simultaneously. The passivation materials used in Cd-As co-contaminated soil are reviewed and characterized in this study to provide some guidance for the remediation of Cd and As co-contaminated soils.

    • Interaction Between Bacteria and Soil Minerals and Application of Bacterial-Mineral Composites in Remediation of Heavy Metals Polluted Soil

      2021, 58(4):851-861. DOI: 10.11766/trxb202007280143

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      Abstract:The use of functional bacteria to assist phytostabilization is nowadays a practical and eco-friendly method commonly applied to remediation of heavy metals-contaminated farmland soils. The application can effectively control the migration of heavy metal pollutants, reduce the concentration of available heavy metals in the soil, and further on ensure safety of the agricultural production. However, bacteria do not exist independently in soil. Nearly 80%~90% of the microorganisms exist on and adhere to the surface of soil minerals or mineral-organic complexes. Within this in-situ soil remediation process, the interplay between bacteria and minerals, including the formation of bacterial-mineral complexes, the dissolution of minerals by bacteria metabolites and the influence of minerals on bacterial activity, which runs through the whole remediation, should be taken in consideration and show extensive interferences. First, the interplay will affect the surface characteristics of bacteria, such as chargeability, type and concentration of the surface functional groups, etc., which in turn affect biosorption behavior of the bacteria to heavy metals; Secondly, minerals can affect bacterial activity by destroying integrity of the bacterial biofilm, dissolving out mineral ions to poison bacteria and buffering pH in the environment, etc., and disrupt internal physiological regulation mechanisms of the bacteria, which ultimately affect colonization ability of the bacteria on the surface of minerals, growth-promoting function of the bacteria on plants, and ability of the bacteria to immobilize heavy metals. Moreover, the composites formed by combination of bacteria and minerals differ in behavior in immobilization of heavy metals from a single component of bacteria or minerals. This process might promote formation of soil aggregates, improve soil physical structure, and slow down soil degradation, which is conducive to the sustainable use of remedied farmlands, and hence plays an important role in remediation of heavy metals-contaminated soils. At present, the research on relationships between soil minerals, bacteria and heavy metals is still limited, and most of them focus on apparent phenomena. Therefore, this paper is oriented to comprehensively review the combination of bacteria and minerals, the dissolution effect of bacteria on minerals and the influence of minerals on bacterial activity, and expound the application potential of bacteria-soil mineral(mineral material)complexes in remediation of heavy metal polluted soils, so as to provide a theoretical basis for the application of bacteria-mineral complexes in the heavy metals -contaminated soil environment.

    • Advancement of Research on Application of Microbial Mineralization Technology in Remediation of Arsenic Contaminated Environment

      2021, 58(4):862-875. DOI: 10.11766/trxb202006150207

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      Abstract:In recent years, application of the technology of microbial mineralization has become one of the research hotspots in the field of environmental pollution control. Application of the technology of microbial mineralization has an excellent potential to remove arsenic from water and reduce arsenic bioavailability in soil. Here is a review to summarize mechanisms of the technology of microbial arsenic mineralization and applications of the technology in remediation of arsenic contaminated environments based on the relationship between typical mineralizing bacteria and arsenic mineralization:(1) Carbonate mineralizing bacteria, Fe/Mn oxidizing bacteria and sulfate reducing bacteria in the environment can directly promote formation of arsenic containing minerals or generation of some minerals capable of adsorbing arsenic. Mechanisms, characteristics and formation conditions of the microbial mineralization were explored, through analysis of products and factors of the arsenic mineralization. Microbial induced carbonate precipitation(MICP) can remove As from water or soil solution through adsorption or coprecipitation. Iron-oxidizing bacteria (FeOB) can oxidize Fe(II) into Fe(III) and induce formation of iron oxide and other minerals that adsorb As or reaction of arsenate with Fe(III) to form scorodite(FeAsO4·2H2O). Manganese-oxidizing bacteria(MnOB) can remove As in a similar way as FeOB do. Under sulfate reducing conditions, arsenic can be removed from water through precipitating in orpiment-like phase (As2S3), realgar-like phase(AsS) or arsenopyrite-like phase (FeAsS) with the presence of sulfate reducing bacteria(SRB). Alternatively, arsenic can be removed through being adsorbed in biogenic mackinawite-like phase(FeS), greigite-like phase(Fe3S4) and pyrite-like phase(FeS2) in the presence of iron; (2) Researches at home and abroad on application of the microbial mineralization technology to treating arsenic contamination of water and soil are summarized. The technology can reduce solubility or concentration of extractable arsenic in water and soil and subsequently increase As concentration markedly in the mineral fractions therein after bioremediation; (3) Initial As concentration, coexisting metal ions, pH, temperature and nutrient concentration can affect efficiency of the microbial mineralization. Microbial mineralization is a potential technology to treat arsenic pollution in the environment. However, further studies need to be done as to how to effectively apply the technology to actual treatment of arsenic pollution. And further efforts need to be devoted to exploration of more stable methods to prevent arsenic dissolution from minerals, and development of theories of the application of the microbial mineralization technology to environmental pollution control in combination with practical problems.

    • >Research Articles
    • The Correlation of Soil Color Relative to Clay and Iron Oxides in Alfisol of the Loess Plateau and Its Genetic Explanation—A Case Study of the 31 Argillic Horizons Covered in the Soil Series Survey of Shanxi Province

      2021, 58(4):876-886. DOI: 10.11766/trxb202001190693

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      Abstract:[Objective] Clay content and soil color are the most basic physical properties of soil. And soil color, including its hue, value and chroma, is highly influenced by type, content and state of the ferric oxides in the soil. As a result of the intense erosion during the later period of the development of the Loess Plateau, the ancient red clay layer, originally buried down in the lower part of the plateau has emerged up close to or even out of the surface, which is of high significance in the researches on soil genesis and ancient environment. But so far little has been reported about any systematic studies on relationships of soil color with clay content and iron oxides in the ancient red clay soil of the Loess Plateau. The purpose of this paper is to provide certain scientific basis for further studies of soil classification, paleosol and paleoenvironment in the plateau.[Method] Soil samples were collected from the thirty one argillic horizons of the Alfisol profiles in Shanxi Province on the Loess Plateau for analysis of contents of total iron, free iron oxide, amorphous iron oxide and clay and soil color, and further for quantitative exploration of relationships of soil color (hue, value and chroma) with the first three indices, respectively.[Result] Results show that clay content in the argillic horizons was positively related to the content of iron oxides (P<0.01), and so was soil color, and especially soil redness (P<0.01), of which free iron oxide contributed the most. The other soil color parameters, like hue, brightness and chroma, were also significantly related to total iron oxides and free iron oxides, which indirectly indicates that clay content had a certain relationship with soil color. It was also found in field observations that the surfaces of some argic horizons were redder than the matrix inside the horizons, which demonstrates that iron oxide migrates with clay through soil pores and accumulates on the surface.[Conclusion] In Alfisols of the Loess Plateau, the reddish argillic horizons develop mainly from the Tertiary red soil of the Baode series and the Quaternary red clay that outcrop or lie close underneath the surface as a result of intense soil erosion. Their contents of clay and color indicate that the paleoclimate was hotter and wetter in the Tertiary than in the Quaternary in the Loess Plateau region.

    • Prediction of Spatial Distribution of Soil Organic Carbon in Farmland Based on Multi-Variables and Random Forest Algorithm—A Case Study of A Subtropical Complex Geomorphic Region in Fujian as An Example

      2021, 58(4):887-899. DOI: 10.11766/trxb202001140623

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      Abstract:[Objective] Soil organic carbon (SOC) plays an important role in soil fertility and the terrestrial ecosystem carbon cycle. A detailed understanding of the spatial distribution of SOC is vital to management of the soil resources and mitigation of the global climate change. With the development of the 3S technology, the models for predicting soil properties based on environmental variables are getting increasingly popular. The purpose of our study is to try to simulate the complex and nonlinear relationship between SOC and environmental variables, and evaluate the importance of soil attributes to accuracy in SOC mapping.[Method] For this purpose, machine learning methods and a random forest (RF) model was applied to map the spatial distribution of topsoil organic carbon contents for farmlands in the high-yield agricultural areas in Southeast Fujian. A set of environmental variables (including 5 hard-to-obtain quantitative soil attributes such as hydrolysable nitrogen, available phosphorus, pH, etc) and 11 easy-to-obtain variables (i.e. topography factors, vegetation indexes and climate factors) were acquired through analysis of a large number of soil samples collected from that region, and then processed with the RF algorithm to predict spatial distribution of SOC content in the topsoil layers of the farmlands of that region. Two different combinations of the above variables were entered as input to RF-S model and RF-A model separately. The RF-S model functioned only on the basis of easy-to-obtain variables and the RF-A model did on the basis of all the variables, both easy-to-or hard-to-obtain ones, for predicting SOC. Root mean square errors (RMSE), mean absolute errors (MAE), Pearson correlation coefficients (r), coefficients of variation (CV), relative errors (RE) and relative root mean square errors (RRMSE) of the two models were worked out for evaluation of accuracy of their predictions, and screening-out of an optimal RF model for mapping SOC in the study area based the raster datasets of all variables. Then cross-validation was performed to compare the optimal RF model with the Ordinary Kriging (OK) interpolation model.[Result] Results show that of the two models, different in input of environmental variables, the RF-A model that functioned based on remote sensing variables, climate factors and soil attributes was much better than the other in performance and could explain the most of the spatial heterogeneity of SOC. Compared with the RF-S model, the RF-A model significantly improved in fitting and prediction (r increased by 7.95% and RMSE decreased by 45.13%). The SOC contents of the farmlands of the region predicted with the RF-A model varied in the range of 14.70±2.95 g·kg-1 and were quite similar to what was obtained with the OK model in spatial distribution, i.e. an ascending trend from the east coastal area to the western inland of the study area. And despite sampling percentage, the RF-A model was generally higher than the OK model in prediction accuracy, and in capability of capturing spatial heterogeneity, and preferred especially in the case of relatively fewer sampling sites. Among the variables, hydrolysable nitrogen (N) was the most important one for the RF-A model, and followed by elevation(DEM). Both of them significantly affected spatial heterogeneity of the SOC, exhibiting positive relationships with SOC.[Conclusion] It is therefore concluded that the random forest model that functions based on remote sensing variables, climate factors as well as soil attributes is a promising approach to predicting spatial distribution of SOC in Southeast Fujian. In addition, soil attributes variables, such as N and P, should be taken into account for improving prediction accuracy for mapping of SOC in regions with complex geomorphology.

    • Establishment and Validation of the Model for Prediction of Nutrient Loss with Runoff on Bare Slopes in the Loess Plateau

      2021, 58(4):900-910. DOI: 10.11766/trxb202002240069

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      Abstract:[Objective] Under natural rainfall conditions, a large amount of soil nutrients are losing with overland flow or surface runoff on sloping farmlands in the loess area, which exacerbates the decline of soil quality and productivity of the farmlands and causes serious agricultural non-point source pollution to the environment. Therefore, it is particularly important to accurately predict how soil nutrients loing with surface runoff in the loess areas. However, the existing nutrient loss prediction model focuses on estimating the total nutrient loss over a long period of time in an area, but neglects the effect of infiltrating water diluting the nutrients in the exchange layer before runoff starts.[Method] In this study, according to the characteristics of nutrient migration in different time periods of a rainfall event, the entire process of a rainfall event is divided into three phases:(1) from the beginning of rainfall (t0) to the time when the exchange layer is completely saturated (tsa), (2) from the time when the exchange layer is completely saturated (tsa) to the time when runoff occurs (tp), and (3) from first runoff (tp) to the end of the rainfall. Based on the approximate analytical solution of the motion wave model, an approximate analytical model of nutrient loss was established, which integrated the effects of raindrop splashing, diffusion and infiltration;and then a simulated rainfall experiment was conducted to determine parameters of the model and verify reliability of the model.[Result] Results show the values of surface runoff and nutrient loss predicted with the model accurately matched the measured values (R2> 0.8, Nash-Sutcliffe efficiency coefficient> 0.347). In this nutrient loss model, the raindrop-induced water transfer rate er was valued in the range of 0.006~0.023 cm·min-1, and the exchange layer depth de in the range of 0.68~1.32 cm. The former significantly affected peak rate of the nitrate nitrogen and ammonium nitrogen loss, whereas the latter did range of the overall variation of the loss rate and boosted total loss of the nutrients. The model was found to be more sensitive to de than to er.[Conclusion] Some field management measures, such as revegetation, deep fertilization, etc. should be adopted to reduce raindrop kinetic energy and lower the content of nutrients in the exchange layer, so as to realize the purpose of reducing nutrient loss. In general, this approximate semi-analytical model has fully considered the influence of water infiltration in unsaturated soil on nutrient transport in the exchange layer, so it can be used to predict nutrient loss processes on bare slopes in arid and semi-arid regions. However, it should be emphasized that accurate calculation of runoff process is the basis of the nutrient loss simulation, so it is advisable to select an appropriate infiltration formula and solute adsorption coefficients in the light of soil texture, nutrient type, and nutrient concentration in rainwater.

    • Saline Water Infiltration Process and Water-salt Distributions in Coastal Saline Soil Relative to Concentration of the Saline Water

      2021, 58(4):911-920. DOI: 10.11766/trxb202004090037

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      Abstract:【Objective】To irrigate fields of heavily salinized-alkalinized soil with water from melting saline ice is found to have an apparent soil ameliorating effect. Melting of saline ice is a dynamic process of meltwater in quality and quantity. 【Method】To explore feasibilities of using saline water to irrigate fields of saline soil for soil amelioration, in this paper an experiment was designed to simulate infiltration process of water from melting saline ice into coastal saline soil. A soil column experiment was conducted in this study. The experiment was designed to have three treatments and a CK, i.e. gradient saline water infiltration (GSI), mere saline water infiltration (DSI), melting saline ice infiltration (MSI) and fresh water infiltration as control (CK). The saline water used in the experiment was set to be 15 g·L-1 in salinity and 314.3 mm in volume. Besides, according to the variation of meltwater in salinity and volume during the melting process of saline ice, four batches of infiltration were designed for treatment GSI, with melted water different in salinity and volume (81 g·L-1, 19 g·L-1, 3 g·L-1 and 0 g·L-1 and 25 mm, 125.8 mm, 94.3 mm and 69.2 mm, respectively, for S1, S2, S3 and S4). The four batches of water were charged one after another when the previous batch totally infiltrated. 【Result】Results show that infiltrating water went down deeper and faster in all the three treatments than in CK within the same time period, and in treatment GSI than in treatment DSI during the initial infiltration stage. In treatment DSI, each batch infiltration significantly increased the next batch in infiltration rate for the first two batches, but for the last two, treatment GSI fell significantly behind treatment DSI in infiltration rate, owing to the lowering salinity of the infiltration water. At the end of the infiltration, the treatments were found following an order of DSI > GSI > MSI in water and salt content in the 0-40 cm soil layer; treatment GSI and treatment MSI were quite similar in soil water and salt distribution and reached up to 92.87% and 91.38% respectively in desalinization rate, which were apparently higher than 74.74% in treatment DSI. 【Conclusion】The above findings have made clear the characteristics of the infiltration of saline water varying in salinity in coastal saline soil, and batch infiltration of saline water had an effect similar to that of infiltration of melting saline ice on desalinization, which provides an useful means to simulate infiltration process of meltwater, changing in salinity and volume with the saline ice melting, and a theoretical basis for the technology of irrigating saline soil with saline and fresh water alternative.

    • Effects of Deep Straw Incorporation on Subsoil Physical Properties and Aggregate Distribution in Black Soil

      2021, 58(4):921-934. DOI: 10.11766/trxb202003180714

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      Abstract:[Objective] In order to improve soil structure of the subsoil layer of black soil and solve the problem of how to return maize straw in Northeast China, a three-year (2015—2018) field experiment was carried out.[Method] The field experiment was designed to have three treatments in returning pattern, i.e. CK (no straw return), QS (returning of chopped straw) and KL (returning of pelletized straw), and three treatments in straw returning dosage, i.e. low dosage (15 000 kg·hm-2), medium dosage (45 000 kg·hm-2, 3 times as much as the low dosage) and high dosage (75000 kg·hm-2, 5 times as much as the low dosage), and all had the straw buried in the soil 30-40 cm depth. Effects of the treatments on soil bulk density, soil compactness and soil water content were explored, and effects of soil aggregate distribution regulating soil physical properties was analyzed.[Result] The tests of the soil samples collected at the maize maturity stage of the three year experiment show:1) The practice of deep straw returning reduced soil bulk density and soil compactness and increased soil water content, and the effects were more significant in the 20-40 cm layer than in the 0-20cm soil layer. Moreover, the effects become more significant with increasing of straw dosage, and less with the time going on, and the effects of straw returning once at a high rate might last for a few years. In the third year of the experiment, only QS5 reduced soil bulk density significantly or by 10.9% (P < 0.05), and QS5 and KL5 lowered soil compactness by 24.1% and 22.0% (P < 0.05), but raised soil water content by 8.9% and 7.4% (P < 0.05), respectively; 2) The treatments of medium and high in dosage significantly increased the content of macroaggregates and reduced the content of microaggregates in the subsoil, and the fractions of > 0.25 mm water stable aggregates and of the > 2 mm large aggregates increased significantly with rising straw dosage. What's more, the return of pelletized straw tended to promote the formation of macroaggregates than the return of chopped straw. The first and second years of straw returning were the main period for formation of macroaggregates, of which the highest content reached up to about 5 times and 1.5 times than that in CK, respectively; 3) Significant relationships were observed of 0.25-0.053 mm micro aggregate and > 0.25 mm water stable aggregate with soil bulk density, soil compactness and soil water content in the subsoil layer (P < 0.05), and the 0.25-0.053 mm, > 2 mm, and > 0.25 mm fractions of aggregates were the key factor driving changes in soil physical properties in 2016 and 2017, but the 1-0.5 mm fraction of aggregates was found to be the key factor driving the changes in soil physical properties in 2018.[Conclusion] Therefore, from the perspective of recycling maize straw in Northeast China, the return of chopped straw with a rate of 75 000 kg·hm-2 is a good management to regulate the distribution of soil aggregates and improve the physical properties of subsoil. The finding may provide a theoretical basis and technical guidance for improvement of soil structure of the black soil in China.

    • Effects of Planting Patterns on Soil Structure and Fertility of Calcareous Purple Soil in Hilly Areas of Central Sichuan Basin

      2021, 58(4):935-947. DOI: 10.11766/trxb202002210685

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      Abstract:[Objective] Planting pattern is an important factor affecting soil physico-chemical properties, dietary preference of soil fauna, and hence soil water and nutrient movement in a soil profile. This study aims to evaluate characteristics of the common planting patterns in the basin and screen out one suitable to the calcareous purple soil in the central Sichuan basin.[Method] Based on a long-term in situ field experiment, three planting patterns, i.e. maize-wheat (MW), maize-oil rape (MR) and maize-sweet potato-wheat (MWP), were selected for comparison in this study. Using laboratory analysis in combination with the computer tomography micro-scanning technology, analysis was performed of effects of the planning patterns on soil physical properties, nutrient status and soil fauna and on calcareous purple soil quality and productivity as well. Moreover, pros and cons of the planting patterns were distinguished to select suitable planting patterns[Result] Number of the pores 25~500 μm in equivalent aperture in the cultivated layer, was ultra-significantly and positively related to content of soil organic matter, total nitrogen (N) and available N, separately, which implies that the pores contribute greatly to storage of soil organic matter, total N and available N in the cultivated layer. However, number of the pores > 500 μm in equivalent aperture was ultra-significantly and positively related to content of available phosphorus (P), which indicates that large-size pores are conducive to retention of available P. In terms of organic matter, total N, available N and available potassium (K) in the cultivated soil layer, the three planting patterns all exhibited an order of MW > MR > MWP. Treatment MW was higher than the other two in compactness of the 0~20 cm soil layer and in looseness of the >35cm soil layer; with pores 25~1 000 μm and > 1 000 μm in equivalent aperture accounting for 50.2% and 49.8%, respectively, of the total pore volume, forming a proper proportion of pores, evenly distributed and well connected, which contributes greatly to soil structure and soil quality. However, in Treatment MW, soil fauna was lower in total population than in the other two. Consequently the treatment was the lowest in annual total yield and economic output. Treatment MR was quite similar to Treatment MW in soil physical properties with pores 25~1 000 μm and > 1 000 μm in equivalent aperture accounting for 31.6%, and 68.4%, respectively of the total and being poorly connected; however, the treatment was significantly higher than the other two in total population and species of scavenger soil animals and more significant in soil available P accumulation. Treatment MWP had a plough layer loose in texture, and was significantly higher than that in the other two Treatments in saturated water content, saturated conductivity, mean porosity soil fauna abundance and annual crop yield and economic output; in the Treatment pores 25~1000μm and > 1000μm in equivalent aperture accounted for 20.5% and 79.5%, respectively, and higher proportion of the latter facilitated downward movement of water and nutrients, thus leading to lower contents of soil available P and readily available K and exposure to higher risks of nutrient consumption and loss; moreover, the treatment was much higher in abundant and species variety of soil animals.[Conclusion] The three planting patterns are the traditional ones in the area and all have their own advantages and disadvantages. It is advisable to choose site-specific ones and to make full use of the pros and avoid the cons. The MW pattern leads to formation of a plough layer with soil pores reasonable in proportion and good in connectivity, which is conducive to water and nutrient conservation and soil sustainable utilization, however, the pattern tends to be lower in soil fauna abundance and economic benefits than MR and MWP. Though MR is worse in soil pore structure than MW, it is conducive to abundance of saprophytic soil fauna, which helps improve the soil structure and hence higher in economic benefit than MW. MWP is the highest in economic benefit and its crop types and pore structure are good to the survival and reproduction of soil fauna, however, the pattern causes soil pore structure unfavorable to water and nutrient retention. So it may need higher nutrient input to keep high stable yields, which is negative to soil nutrient accumulation and long-term fertility.

    • Effect of Intermittent Rainfall on Size Distribution and Phosphorus, Copper and Zinc Enrichment of Soil Aggregates

      2021, 58(4):948-956. DOI: 10.11766/trxb202001080611

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      Abstract:[Objective] Effects of the soil wetting-drying alternations induced by intermittent rainfall on the temporal dynamics of soil aggregate size distribution (ASD) in the soil were studied in this paper, which is of great significance to in-depth understanding of the mechanisms of sediment transport and fractionation and revealing rules of associated trace elements transfer with runoff.[Method] In this study, a field experiment was carried out having the field of Cambisol subjected to five separate artificial rainfall events within 37 days. During the experiment, soil aggregate breakdown process triggered by the rainfall events and dynamic change in particle size distribution of the soil aggregates were observed. And through analysis of dynamic changes in the contents of P, Cu and Zn in soil aggregates of various particle size fractions, evaluation of impacts of intermittent rainfall on enrichment of pollutants in the soil was performed.[Result] Results show that soil wetting and drying cycles caused by the intermittent rainfall triggered drastic turnover in ASD, which consequently declined in stability as a whole with the experiment going on, especially the fraction of >250 μm, which as a result decreased in proportion (P<0.05), while the fraction of <250 μm increased. Changes in ASD also led concurrently to variations of P, Cu and Zn concentrations in the various aggregate size classes. The three elements gradually moved from aggregates of >250 μm to those of <63 μm, and peaked in concentrations in aggregates of <63 μm towards the end of the experiment. This shows that the intermittent rainfall triggered breakdown of aggregate structure, increased in the fraction of <250 μm aggregates, and enrichment of trace elements in the fraction (<250 μm), which in turn aggravated the risk of increasing soil and water loss and associated discharge of pollutants.[Conclusion] The experiment revealed how intermittent rainfall affect soil aggregate structure, fractionation of sediments and element transfer processes, which may serve as certain theoretical reference for better understanding the mechanisms of lateral transfer of soil materials caused by soil erosion.

    • Impacts of Combined Pollution of Copper and Doxycycline on Activities of Soil Microbes and Enzymes

      2021, 58(4):957-967. DOI: 10.11766/trxb202002200514

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      Abstract:[Objective] Nowadays, more attention should be paid to the situation of agricultural environment and the quality and safety issues of agricultural produces because more and more various pollutants are entering into the agricultural soil. Among the pollutants, heavy metals and antibiotics are two of the most important types of pollutants in the farmland soil. In this study, soil microorganisms are used as indicators to illustrate impacts of combined pollution of heavy metals and antibiotics on soil environment.[Method] An in-lab analogue incubation experiment was conducted in this study, with the soil spiked with doxycycline (DOX, 0, 8 and 15 mg·kg-1) and copper (Cu, 0, 100 and 400 mg·kg-1), singly or combinedly, at a varying rate as the representative pollutants of antibiotic and heavy metal, respectively. Effects of the pollutants on respiration of soil microbes, activities of soil enzymes, like urease, sucrase and catalase, and abundance of tet ARGs (tetracycline-resistance genes) were investigated.[Result] Results show that throughout the whole incubation period (30 days), the pollution of DOX and Cu, either singly or combinedly, inhibited significantly respiration of soil microbes in intensity, and activities of sucrase and catalase, but stimulated that of urease, and the effect was apparently catalase than on sucrase. To sum up, the effects of combined pollutions is much higher than that of singe pollutions and the addition of DOX stimulated the initial effect of Cu on respiration of soil microbes or activities of soil enzymes. Correlation analysis shows that the activity of catalase/urease was significantly and negatively related to Cu concentration and urease activity significantly and negatively correlated with sucrase activity. Besides, it was also found that the total relative abundance of four types of antibiotic resistance genes (ARGs) decreased first and then turned backwards, which was probably owing to the tie lag of about 7-15 days the soil system needs to adapt and age after the addition of the pollutants. Compared with other treatments, the addition of high concentrations of Cu and DOX significantly increased the abundance of ARGs at the mid-and late-stages of the incubation, especially the relative abundance of tetA and tetW. The addition of a high concentration (400 mg·kg-1) of Cu improved the ability of DOX to induce high relative abundance of tet ARGs.[Conclusion] All the findings in this study indicate that combined pollution of Cu and DOX has dramatic impacts on functions of the soil microbial system.

    • Determination of 1, 9-Decanediol in Soil with Ultrasonic Extraction-Gas Chromatography

      2021, 58(4):968-977. DOI: 10.11766/trxb201911210536

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      Abstract:[Objective] The application of biological nitrification inhibitors (BNIs) is considered an important new strategy to reduce nitrogen loss from agricultural systems. Recently, a new BNI, 1,9-decanediol, has been identified in rice root exudates and the substance is found to be contributive to improvement of nitrogen (N)-use efficiency (NUE) and reduction of N2O emissions in agriculture. In order to evaluate its stability and effect in soil, an efficient, fast and accurate extraction and detection method needs to be developed. Thus, this study was oriented to develop a method of using ultrasonic extraction-gas chromatography (GC) to determine 1,9-decanediol in soil.[Method] Soil samples were collected from a paddy soil at Yixing (31°17' N, 119°54' E), Jiangsu Province of China for extraction of 1,9-decanediol using different methods, including different extractants (water, acetonitrile, methanol, acetone, ethyl acetate, dichloromethane, hexane, and petroleum ether), different liquid to solid ratios (varying in the range of 10-50 mL·g-1), different durations of ultrasonic processing (in the range of 10-50 min), different frequency of extraction (in the range of 1-3 times), and different gas chromatography detection parameters, including inlet temperature (in the range of 200-280℃), detector temperature(in the range of 260-320℃), and four heating procedures for optimization. Spike recovery of the substance in soil was determination relative to its concentration (10, 100 and 1 000 mg kg-1).[Result] Results show that:(1) the method of ultrasonic extraction using methanol as extractant, 40 mL·g-1 in liquid/solid ratio, and going only one round that lasted 30 min was the optimal one; (2) In using the Agilent 8890 gas chromatographer to determine the substance, the optimal conditions were 250 ℃ at the inlet, 310 ℃ at the FID detector, 60 ℃ in the column kept for the first 2 min, and then raised up to 150 ℃ at 20 ℃·min-1 and to 180℃ at 3℃·min-1, kept for 2 min. and in the end, raised to 270 ℃ at 20℃·min-1; (3) under such conditions, determination of 1,9-decanediol, 10-100.00 μg·mL-1 in concentration exhibited good linearity, standard curve of y=26.81x-9.678(R2=0.999), detection limit of 0.03 μg·mL-1, recovery rate of 93.99%-96.91%, intraday precision 1.78% and interday precision of 1.52%; and (4) under such optimal extraction and determination conditions, the spike recovery rate of 1, 9-decanediol in soil samples, regardless of concentration, varied in the range of 90.58%-94.55% with relative standard deviation(RSD)varying in the range of 0.30%-3.41%.[Conclusion] This method, low in detection limit, high in sensitivity and precision, and good in reproducibility, and this experiment may lay down a foundation for evaluation of stability and environmental impacts of 1, 9-decanediol in agricultural soils, and provide a good reference for developing methods for extracting other BNIs in soil in future.

    • Effect of Increased or Decreased Application of Organic Manure on Aggregates Stability and Soil Cement in Red Paddy Soil

      2021, 58(4):978-988. DOI: 10.11766/trxb201912040540

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      Abstract:[Objective] This paper is oriented to explore effects of increased or decreased application of organic manure on stability and cement (e.g. organic carbon and iron-aluminium oxides) of soil aggregates stability in red paddy soil of a long-term field fertilization experiment.[Method] In the 35-year-old long term field experiment, on the premise of guaranteeing normal development of the original stationary experiment, the treatments, which used to be applied with chemical fertilizer, changed to be applied with organic manure instead and the treatments, which used to be applied with original manure, changed to be applied with chemical fertilizer or remained to be applied with organic manure, but at a higher rate. Soil samples were collected from the tillage soil layers of the treatments and analyzed for changes in fractionation, stability, contents of total organic carbon (TOC) and its fractions, and content of iron-aluminium oxides of soil aggregates. Based on the analysis of the relationship between aggregates stability and cement, mechanism of their interactions was explored with correlation analysis and path analysis methods.[Result] Results show that there was no obvious changes in average weight diameter (MWD) of the soil aggregates after application of organic manure at a higher rate in Treatment CF (application of chemical fertilizer) and Treatment NOM (application of organic manure at a normal rate), but there were in content of oxidizable organic carbon (EOC), which increased by 87.44% and 20.53%, respectively, in the organic carbon fraction, and in content of fine particulate organic carbon (fPOC), which increased by 26.94%, in Treatment N-H (treatments changed from normal to high in organic manure application rate); MWD decreased significantly or by 8.39% and 6.80%, respectively, in Treatment H-C (treatment changed from application of organic manure at a high rate to application of chemical fertilizer) and treatment N-C(treatments changed from application of organic manure at a normal rate to application of chemical fertilizer); TOC, coarse particulate organic carbon (cPOC) and light organic carbon(LFOC) decreased by 23.48%, 30.09% and 25.29%, respectively, in treatment H-C (treatment changed from application of organic manure at a high rate to application of chemical fertilizer), but TOC and its fraction did not vary much in Treatment N-C (treatment changed from application of organic manure application of chemical fertilizer treatment); and no matter whether in treatments with application of organic manure increased or decreased in rate, the content of Fe-Al oxides varied irregularly. Correlation analysis and analysis using the structural equation model (SEM) show that the content of >0.25 mm aggregates increased along with growing organic carbon fraction and with rising free iron oxide (Fed) content, but decreased with rising chelated oxide (Fes) content, and >0.25 mm aggregates were the only factor directly affecting MWD; changes in organic manure application rate induced the content of light organic carbon (LFOC) and EOC raised or declined in red paddy soils, resulted in the synergistic variation of Fed and Fes, which eventually led to changes in content of >0.25 mm aggregates. In terms of effect coefficients of the factors affecting MWD and >0.25 mm aggregates, an order of EOC > LFOC > Fed> Fes,was observed and organic carbon and its fractions were the principal affecting factors in the red paddy soil.[Conclusion] The fraction of >0.25 mm aggregates in the red paddy soil plays a key role in aggregate stability, and the fraction of active organic carbon is the major factor affecting formation and destruction of large-sized soil aggregates.

    • Release of Exogenous Carbon and Nitrogen in Rice Root, Stem and Leaf in Paddy Soil

      2021, 58(4):989-997. DOI: 10.11766/trxb201909260505

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      Abstract:[Objective] The climate in Northeast China is very cold, so that the paddy fields therein have a long fallow period when the soil is frozen for most of the time. Rice is quite short in life cycle and calls for high soil temperature and seasonal flooding for healthy growth. The practice of rice straw returning is quite popular, but little is known about how the exogenous rice straw is decomposed and how carbon (C) and nitrogen (N) in the decomposing rice straw is released during the fallow season and the rice-growing period as affected by hydrothermal condition in Northeast China.[Method] In this study, an outdoor incubation experiment was carried out using dual-isotope-labeled (13C and 15N) rice root, stem and leaf for tracing of the elements with the stable isotope mass spectrum analysis technique, to characterize dynamics of the decomposition rate of the incorporated rice root, stem and leaf and the release rate of C and N from the decomposing rice root, stem and leaf in the paddy soil. Isotope-labeled rice root, stem and leaf were added to the paddy soil in autumn.[Result] Decomposition rates of the straw in Treatment S1 (labeled root + unlabeled stem and leaf) and Treatment S2 (unlabeled root + labeled stem and leaf) was determined to be 30.2% and 34.5%, C release rate to be 30.9% and 38.2%, and N release rate to be 7.4% and 35.0%, respectively, at the end of the fallow period (November to May). One year after the amendment, decomposition rate of the straw reached 66.5% and 66.6%, C release rate did 63.7% and 65.8%, and N release rate 28.6% and 51.1% in Treatment S1 and S2, respectively. The N release rate of root was significantly lower than that of stem and leaf (P< 0.05).[Conclusion] One year after the amendment of rice root, stem and leaf into the paddy soil, the decomposition rates of rice roots, stem and leaf all reached about 65%. The release of C from the rice root, stem and leaf varied synchronously with the decomposition of the materials in rate. However, the release of N from the rice root, stem and leaf was relatively slow, especially that from the root. Higher temperature obviously promoted decomposition of and C and N release from the straw in the soil. This study is expected to be of great significance for scientific evaluation of the recycling of C and N in the incorporated rice straw in the paddy soil in Northeast China.

    • Rhizosphere Effects of Maize on Inorganic and Organic Carbon Release in Calcareous Soils

      2021, 58(4):998-1007. DOI: 10.11766/trxb201911210581

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      Abstract:[Objective] In calcareous soil, CO2in rhizosphere soil comes from at least three sources, i.e., respiration of roots, decomposition of soil organic C (SOC) and dissolution of soil inorganic C (SIC). Owing to technical limitations in partitioning CO2 by source, how rhizosphere effects affect SOC decomposition and SIC dissolution is still an issue not yet clarified. Therefore, an in-lab pot experiment using calcareous soil collected from a farmland of North China to grow maize in an attempt to investigate rhizosphere effects of summer maize plants on release of CO2 from SOC and SIC, using the IsoSource model to partition CO2 in the rhizosphere by source.[Method] At the end of the elongation (24-53 days), heading (54-66 days) and grain-filling (67-99 days) stages of the summer maize, destructive sampling of maize rhizospheres was carried out separately for analysis of content of 13C from root, SOC and SIC, separately. During the period from the beginning of the elongation stage to the end of the maize growth stage, soil respiration and 13C content in the soil with or without maize planted was monitored at a three-day interval with the aid of the IsoSource software.[Result] Results show that to the total soil CO2 emission, root respiration contributed 48.0%, SOC did 31.2% and SIC did 20.8%. During the period from the elongation stage to the end of the summer maize season, CO2 emission from SOC and from SIC in the pot with maize planted was 65% and 156% higher than their respective ones in the pot without maize planted.[Conclusion] This experiment indicates that SIC plays a significant role in stabilizing global C pool and regulating atmospheric CO2 concentration. If the contribution of SIC to soil CO2 emission in calcareous soils is ignored, the amount of CO2from SOC decomposition may be overestimated, which will inevitably affect quantification of the priming effects of SOC. This study will help reduce uncertainties in of soil C budgeting for farmlands of calcareous soil in North China.

    • Composition of Humus in Forest Soils of Yunnan Province, China and Its Influencing Factors

      2021, 58(4):1008-1017. DOI: 10.11766/trxb202003240513

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      Abstract:[Objective] Yunnan Province is rich in forest resources, thus posing an important part of China's forest carbon pool. Its forest ecosystem plays an irreplaceable role in the global carbon cycle and balance, and its organic carbon pool in the forest soil does too in regulating the global carbon balance and slowing down the rising concentration of atmospheric chamber gas. Though soil humus is known to be the main body of soil carbon, it is still unclear as to characteristics of its composition and influencing factors. Therefore, it is of great significance to strengthen the study of composition of the forest soil humus and its influencing factors to the efforts of regulating forest soil carbon balance and improving soil fertility.[Method] A total of 88 soil samples were collected from the topsoil layers of different forest zones in Yunnan province. Environmental factors of the sampling sites, such as soil type, latitude and longitude, elevation, slope degree and slope aspect, were measured through field investigations. The soil samples were analyzed in lab for contents of soil carbon and soil humus and its components, of which regression analysis and descriptive statistics were employed to quantify relative contributions of elevation, soil type, slope degree, slope aspect, annual mean precipitation and annual mean temperature to the variation of soil humus composition. In the end, soil humus composition and distribution in the forest soils of Yunnan were characterized.[Result] Results show:in the top soils of the forests, SOC content varied in the range from 8.40 to 199.73 g·kg-1, with a mean of 51.37 g·kg-1; HE-C content in the range from 2.54 to 84.02 g·kg-1, with a mean of 24.52 g·kg-1; HA-C content in the range from 0.99 to 33.64 g·kg-1, with a mean of 9.35 g·kg-1; FA-C content in the range from 1.40 to 57.16 g·kg-1, with a mean of 15.17 g·kg-1; and H/F in the range from 0.17 to 4.59, with a mean of 0.78; soil humus in the samples was fairly low in polymerization degree, with C/N ranging from 4.68 to 41.72 and averaged to be 14.25. The contributions of soil type, elevation and annual mean temperature to soil humus composition were significant(P<0.01 or 0.05), but those of annual precipitation, slope degree and slope aspect were not so significant(P<0.05). The environmental factors varied in explanation of the spatial variation of total organic carbon, extractable humic carbon, humic acid carbon, fulvic acid carbon, and carbon-nitrogen ratio in the soil with soil type explaining 30.1%, 29.6%, 30.9%, 24.3% and 11.5%; annual mean temperature doing 22.2%, 19.5%, 13.7%, 18.8% and 18.0%; elevation doing 13.3%, 9.4%, 11.1%, 8.7% and 13.9%, respectively.[Conclusion] The content of soil organic carbon in the forest soils of Yunnan is found to be relatively high in the northeast and northwest parts of the province, and relatively low in the south and central parts. Soil type, elevation and average mean temperature are the key factors regulating spatial variability of the soil humus in the forests of Yunnan Province. In terms of contribution degree, the factors exhibit an order of soil type > annual mean temperature > elevation. Soil type plays an important role in the accumulation of humus in the forest surface soil.

    • Molecular Ecological Network of Bacteria and Fungi in Paddy Soil Profile of Typical Red Soil

      2021, 58(4):1018-1027. DOI: 10.11766/trxb202001170025

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      Abstract:[Objective] Soil environmental factors are highly spatially heterogeneous, especially soil pH, nutrient availability, soil temperature and soil microbes, which vary with soil depth, and hence affect the distribution of soil microbial communities. Soils in deep soil layers may have microbial communities that have adapted to the environments of deep soil layers, and consequently are different in structure from those in topsoil layers. Microbial communities decrease in biomass and diversity with depth in the soil profile, which alters structures of the soil microbial communities and affects their functions. Microbes in deep soil play an important role in soil formation, biogeochemical reactions and pollutant degradation. So deep soil has significant influences on quality indices of the soil and hence productivity of the vegetation on the surface. Interactions between species of the microbes may be more important than richness and diversity to ecosystem function of the microbial community, especially in complex ecosystems. Interactions between microbial communities are a part of the microbial network of a terrestrial ecosystem, and the basis of biochemical cycles. Ecological network analysis is a new analysis method to visualize interactions between microbial communities and explore co-existence patterns of the species in microhabitats and their main influencing factors. Network analysis can be used to explore mechanisms of microbial interactions driving biogeochemical coupling of important elements in soil, and hence is an important means to improve service functions of a soil ecosystem. However, most of the previous studies on soil microbial communities focused on those in the topsoil (0-20 cm) layer or on abundance of microbial species. Therefore, the information available in the literature about potential relationships between microbial interactions and soil depth, and their determining environmental factors.[Method] After late rice was harvested, soil samples were collected from a paddy field in Yingtan (116°54' E, 28°13' N, 34-62 m in elevation), South China. For the sampling, five sampling sites were set randomly as five replicates. At each site, a soil sample was collected from each of the five soil layers, 0-10, 10-20, 20-40, 40-60, 60-80 and 80-100 cm with an auger, making up a total of 30 samples for analysis, separately, of soil geochemical properties and DNAs.[Result] Contents of soil nutrients, including total nitrogen (TN), total carbon (TC) and NH4+-N, and species richness of soil microbes decreased significantly with soil depth. Network analysis shows that with increasing soil depth, the average. number of neighbors, clustering coefficient and Network density of the microbial interaction network increased, indicating that the associations between microbial communities became more complex in the microbial co-existence network with positive interactions intensified, and interactions within the bacterial community and within the fungal community enhanced, but the interactions between bacteria and fungi communities reduced. TC and TN were the main factors contributing to soil microbial interactions according to the random forest analysis. Variance partitioning analysis of the soil microbial network shows that microbial interactions were affected by carbon (TC + DOC) and nitrogen (TN + NO3--N+NH4+-N). Moreover, the effect of C intensified with soil depth.[Conclusion] The interactions between soil microbes become more intensive, more complicated and more modular with soil depth. The interactions within soil microbial communities are positively related to soil depth, and so were the interactions between bacterial and fungal communities. With the soil going down in depth, the contribution of soil C increased from 3.58% to 32.67% for the microbial interaction network.

    • Characterization of Population and Community Structure of Carbon-Sequestration Bacteria in Soils under Four Types of Forest Vegetations Typical of Subtropical Zone

      2021, 58(4):1028-1039. DOI: 10.11766/trxb202005110021

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      Abstract:[Objective] To alleviate the global climate change is one of the most important environmental challenges facing mankind. Autotrophic microorganisms, especially those in forest ecosystems, have been reported to have a strong ability to adapt to environmental changes and a high potential to sequestrate carbon. However, how their carbon-sequestrating effects vary with type of forests vegetation remains unclear. To explore this complex relationship, investigations were made of populations and community structures of soil carbon-sequestrating bacteria in the soils of four typical subtropical forests.[Method] Soil samples were collected from the surface (0-20 cm) and subsurface (20-40 cm) soil layers in the four types of forests, that is Moso banboo, Broad-leaved trees, Chinese fir and Masson pine for analysis of cbbL as indicator gene with the aid of quantitative PCR and MiSeq high-throughput sequencing technology.[Result] Abundance of the bacteria with 16S rRNA genes and those with cbbL genes varied in the range of 5.40×1010-2.81×1011 copies·g-1 dry soil and of 4.55×108to 3.53×109copies·g-1dry soil, respectively, in the four types of forest soils, and was the highest in the soil under bamboo groves (P<0.05); among soil physico-chemical properties, soil available P and soil pH was significantly related to the abundance of cbbL genes in the two soil layers under the broad-leaved forest (P<0.05). The soil under the Chinese fir forest was significantly lower than the others, and the subsurface soil was higher than the surface soil in diversity of carbon-sequestrating bacteria (P<0.05). Double factor variance analysis shows that the diversity of soil carbon-sequestrating bacteria varied significantly or ultra-significantly with forest type and soil layer. All the soils had similar dominant species of cbbL-carrying bacteria, which, however, differed in relative abundance beteween the four types of vegetations. The soil of the Moso bamboo groves and the Chinese fir forest was signiticantly higher than that of the Broad-leaved forest and Masson pine forest in proportion of Methylibium and Nocardia. Redundancy analysis (RDA) shows that soil pH, organic carbon, available P and total N were the main factors affecting the formation of community structure of the soil carbon-sequestrating bacteria in the soils.[Conclusion] To sum up, all the findings in this study indicate that population and community structure diversity of the soil carbonsequestrating microbes varied with type of the vegetation. Comparison of the four forest soils in soil physico-chemical property, and genetic abundance, diversity and community structure of the carbon-sequestrating bacteria shows Moso bamboo groves are the best type of vegetation benefitting soil fertility and carbon-sequestrating bacteria. Contribution of the bacteria to accumulation of organic matter was higher in the soil under bamboo groves than under broad-leaved forests, but as to how much, further investigations should be done.

    • Effects of Litters Different in Quality on Soil Microbial Community Structure in Cunninghamia lanceolata Plantation

      2021, 58(4):1040-1049. DOI: 10.11766/trxb201912260562

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      Abstract:[Objective] Litter is an important part of a forest ecosystem. It is of great significance for scientific regulation of a plantation ecosystem to study effects of litters different in quality on soil microbial community composition in the plantation.[Method] To that end, a three-year litter amendment experiment was carried out in a 7-year-old secondary Cunninghamia lanceolata plantation in Xiayang Forest Farm located in Nanping, Fujian, China. The experiment was designed to have eight treatments amended with litters different in quality, separately. Three years later, soil samples were collected from the treatments for analysis, separately, of variation of soil microbial community composition in each treatment.[Result] Results show:(1) the treatment of amending litter of Eucalyptus robusta, high in quality, was 27%, 35% and 19% higher than the treatment of amending litter of Cunninghamia lanceolata, respectively, in soil total microbial biomass, gram-positive bacterial biomass and gram-negative bacterial biomass, while the treatment of amending litter of Cinnamomum bodinieri low in quality, was 29% and 10% lower, respectively, than the treatment of amending litter of Cunninghamia lanceolate in soil total Phospholipid fatty acid and gram-negative bacterial biomass; (2) The soil fungi/bacteria ratio (0.14) was significantly higher in the treatment of amending litter of Eucalyptus robusta than in all the other treatments, and the Gram-positive/Gram-negative bacteria ratio (1.64) was significantly higher in the treatment of amending litter of Cinnamomum bodinieri than in all the others; (3) Amendment of litters, regardless of quality, had no significant effect on soil pH and soil carbon/nitrogen ratio, and the treatment of amending litter of Phyllostachys heterocycla was the highest in nitrate-N content; and (4) Correlation analysis shows that litter carbon content was positively related to total fatty acid, Gram-positive bacterial biomass, Gram-negative bacterial biomass, fungal biomass, and mycorrhizal fungal biomass. Alkyl carbon was positively related to total fatty acid, Gram-positive and -negative bacteria, bacteria, fungi and fungi/bacteria ratio. Methoxy carbon (N-alkyl C), oxy alkyl carbon(O-alkyl C) and aromatic carbon (Aryl C) was significantly and positively related to Gram-positive/Gram-negative bacteria ratio. Redundancy analysis shows that Alkyl C content was positively related to Gram-negative bacteria (16: 1ω7c, 18: 1ω7c) and fungi (18: 2ω6c, 18: 1ω9). Alkyl C content in the litter had a significant effect on soil microbial community structure.[Conclusion] The difference between the litters in alkyl carbon composition is an important index affecting soil microbial biomass and community composition.

    • Variation of Microbial Residues during Forest Secondary Succession in Topsoil and Subsoil

      2021, 58(4):1050-1059. DOI: 10.11766/trxb201912210508

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      Abstract:[Objective] Soil microbes are an important factor driving turnover of soil organic matter (SOM), through participating in SOM formation, linking aboveground and underground ecosystems in evolution process, and influencing the structure and function of ecosystems. However, it is still a hard nut to evaluate the contribution of soil microbes (especially microbial residues) to SOM, and a hotspot of research in this aspect, due to limitation in technology. In this study, efforts were dedicated to examining (1) how forest secondary succession influences the content of microbial residues and its contribution to soil organic carbon (SOC); (2) how soil depth affects content of microbial residues and its contribution to SOC; and (3) how fungal and bacterial residues regulate the contribution of microbial residues to SOC.[Method] To explore changes in the content of microbial residues and contribution of microbial residues to SOC, soil samples were collected from the topsoil (0-5 cm) and subsoil (5-15 cm) in five plots of secondary forests with different age or succession (i.e. 20 years, 80 years, 120 years, 200 years and ≥ 300 years) in the Changbai Mountain National Nature Reserve, Jilin, Northeast China for analysis of amino sugars, including glucosamine, galactoamine, and muramic acid, as biomarkers for microbial residues. Based on the analysis, contents of fungal and bacterial residues were worked out. Besides, soil organic matter in the sample was analyzed for composition (i.e. aromatic C, aliphatic C and polysaccharides) with fourier transform mid-IR spectroscopy.[Result] Our study showed significant increases in content of microbial residues and contribution of the residues to SOC in both topsoil and subsoil during the period of 80-200 years of the succession, whereas a reverse trend was found after 300 years. Path analysis showed that content of microbial residues was positively related to microbial biomass carbon (MBC) in the two soil layers during the succession, indicating that changes in MBC influence the accumulation of microbial residues. In the soils under secondary forests 80-200 years old, labile SOM (low in aromatic C/polysaccharides ratio) was relatively higher, which was beneficial to utilization of microbial carbon (high in MBC/SOC ratio) and accumulation of microbial residues, and promoted contribution of the residues to SOC, while in the soils under secondary forests >300 years old, recalcitrant SOM (high in aromatic C/polysaccharides ratio) was relatively higher, which inhibited utilization of microbial C, thus leading to decline in content of microbial residues and contribution of the residues to SOC. Content of microbial residues varied with soil depth, being higher in the topsoil than in the subsoil as SOC did. Higher content of SOC in the topsoil induced generation of more microbial biomass, thus leading to higher accumulation of microbial residues, whereas the existence of higher contents of recalcitrant fractions of SOM in the topsoil caused decrease in contribution of the residues to SOC. In addition, the variation of SOM utilization rate from low in the topsoil to high in the subsoil caused decline of fungal residue contribution to SOC, but a reverse trend with bacterial residues.[Conclusion] In summary, changes in availability of carbon resources (i.e. SOC concentration and SOM components) trigger variation of content and accumulation of microbial residues in SOC. All the findings in this study may provide certain theoretical support for us in exploring effects of microbial metabolites on SOM formation from the perspective of microbial ecology. Therefore, this study suggests that the anabolic pathways of soil microbes be integrated into the current terrestrial ecosystem carbon models, which will sure facilitate better prediction and evaluation of SOC response to ecosystem managements.

    • Effects of Intercropping on Fusarium Wilt Infection and Root Tissue Structure under Ferulic Acid Stress

      2021, 58(4):1060-1071. DOI: 10.11766/trxb201912300613

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      Abstract:[Objective] To explore roles of ferulic acid, a phenolic-acid-like autotoxic substance, in occurrence of a hazard to monocropping of faba bean, mechanism of ferulic acid promoting faba bean Fusarium wilt and effects of interplanting of wheat with faba bean alleviating ferulic acid stress, a field experiment was carried out.[Method] In the experiment faba bean was interplanted with wheat. Effects of the interplanting were investigated on occurrence of fusarium wilt, activities of root cell wall degrading enzymes (pectinase, cellulase, protease and amylase), lignin content, callose deposition and root ultrastructure in the presence of Fusarium oxysporum f. sp. fabae (FOF) and under the stress of ferulic acid varying in concentration (0, 50, 100 and 200 mg·L-1).[Result] Results show that in the monocropping group, compared with the controls (without ferulic acid stress), all the ferulic acid treatments, regardless of concentration, significantly increased incidence and index of the disease, activities of the cell wall degrading enzymes, lignin content and callose deposition, thus leading to distortion of cell structure, leakage of intracellular substances and worsening of the resistance of root tissue structure, which indicates that the synergistic effect of ferulic acid and the pathogen aggravated the hazard to monocropping of faba bean., while compared with the monocropping treatments, the interplanting treatments, though under the stress of 0-200 mg·L-1 ferulic acid, decreased incidence of the disease by 0.0%-31.7%, disease index by 28.3%-46.9%, root pectinase activity by 17.9%-60.1%, cellulase activity by 1.2%-28.2%, protease activity by 5.6%-60.3% and amylase activity by 16.8%-65.5%, but increased lignin content by 9.8%-57.7%, and reduced callose deposition, thus ensuring normal transportation of nutrients and alleviating deformation of cell structure. Intracellular substances of root cells, like membrane, nucleus and organelle, of the faba plants in the interplanting treatments were less damaged. Obviously the plants effectively prevented further invasion of FOF, reduced the damage of Fusarium wilt, and ensured normal growth of faba bean. The field experiment demonstrates that wheat and interplanting of faba bean with wheat can significantly reduce the damage of Fusarium wilt to the bean crop.[Conclusion] All the findings in this experiment suugest that faba been interplanted with wheat can improve the resistance of faba against FOF under ferulic acid sterss. Therefore, the practice of interplanting can be adopted as an effective strategy for management of Fusarium wilt of faba bean.

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