• Volume 59,Issue 1,2022 Table of Contents
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    • >Insights and Perspectives
    • The Role of Soil in the Formation of Plant Biodiversity and Its Research Significance

      2022, 59(1):1-9. DOI: 10.11766/trxb202106170314

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      Abstract:Soil scientists well know the role of biological factor as one of the five major natural factors driving soil formation and evolution, but they rarely ask about the role of soil in the origin and evolution of plants. I believe that the origin and evolution process of land plants is essentially an adaptation process to the soil environment. It means that the soil environment has a "mold effect" on the formation and evolution of the plants. The diversity of soil environments in profile thickness and layer configuration, physical, chemical and biological properties provides a basis of the formation of the plant diversity. Since plant roots grow in the soil, by absorbing nutrients from the soil to meet their growth demands, the role of soil environment on the formation of plant characteristics is mainly reflected in the genetic characteristics of plant root phenotype, nutritional physiology and resistant physiology to the stress of soil environments. Soil-plant diversity builds diverse habitats for different types of organisms and plays a key role in the formation and maintenance of biodiversity. Protecting the diversity of soil environment is crucial for biodiversity protection, and the key is to protect the heterogeneity of soil environment. In order to enhance crop yields, the cultivation processes of cropland soils are, in essence, the homogenization processes of soil properties, hence, it is not conducive to biodiversity protection. It is of great significance to trace the soil environment in which crops originate, understand the crop genetic characteristics formed by the originated soil environment for the crop allocation, breeding, and crop nutrient management, and so on. However, the research requires not only rich knowledge in soil science, but also rich knowledge in other disciplines, particularly in molecular genetics. Therefore, conducting research in the field will expand research fields of soil science, re-understand the importance of soil resources, and promote the cross-integration of soil science and other disciplines.

    • >Reviews and Comments
    • Research on Salt-affected Soils in China: History, Status Quo and Prospect

      2022, 59(1):10-27. DOI: 10.11766/trxb202110270578

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      Abstract:Taking salt-affected soils and salt-affected habitat as the main research objects, salt-affected soil research is a field focusing on genesis and evolution process of salt-affected soils and salinization, on impact and mechanism of environmental factors and human activities on salinization, and on theory and technology of salt-affected soils management, improvement and utilization. With huge area and a wide variety, salinization has prominent impact on agricultural production and ecological environment in China. On salt-affected soil research, the theories and technical methods proposed by Chinese scientists, such as "water and salt regulation", "water and salt balance", "salt-free fertile layer" and "obstacle reduction", have played a positive role in developing agricultural production, improving land productivity, ensuring food security and expanding cultivated land resources. Recently, China has made positive progress and achievements in monitoring the evolution process of soil salinization and multi-source data fusion, simulation and scale expansion of soil water and salt transport process, nutrient circulation-loss control-efficiency increase of salt-affected farmland, ecological reduction of saline obstacles, microbial remediation of saline obstacles, optimal management of irrigation and drainage of saline farmland and safe utilization of marginal water. It is suggested to carry out theoretical and technical research on efficient and safe water use theory and technology for precise salt control of salt-affected soils, green reduction and health conservation of soil salinity barriers, expansion of nutrient storage capacity of saline farmland, carbon increase and emission reduction, coupling response and collaborative adaptation of soil salinization and regional ecology. We should strive to expand the theoretical research and develop new technology for agriculture resources, ecology, environment and other industries and fields, and play more important role in the country's agricultural upgrading, food security, cultivated land security, ecological security and high-quality development. This paper reviews the development process of salt-affected soils research in China and the relationship between domestic and foreign research, systematically analyzes the characteristics and progress of recent salt-affected soils related research, and puts forward the research prospect of salt-affected soils in China in combination with the frontier hotspots and national needs of relevant research at home and abroad.

    • New Perspectives about Health Risk Assessment of Soil Heavy Metal Pollution-Origin and Prospects of Probabilistic Risk Analysis

      2022, 59(1):28-37. DOI: 10.11766/trxb202009120516

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      Abstract:Health hazard assessment of soil heavy metal pollution is the paramount premise of soil environmental risk management. Probabilistic risk assessment (PRA) that upholds the idea of uncertainty and variability of characterization has opened up new perspectives about health risk assessment of soil heavy metal pollution. In order to strengthen the theoretical cognition of PRA and to promote in-depth application of PRA in the field of soil heavy metals exposure risk assessment, this paper systematically elaborated the theoretical basis and connotation evolution of PRA, with the aid of the bibliometric and integrating analysis methods, and compared PRA with the traditional deterministic risk assessment (DRA), with emphases on dynamics of its application and development and trends and directions of the research on PRA in future. The research indicates that being an important supplement to DRA, PRA is an integration of a set of concepts and technologies that include both variability and uncertainty into the environment risk assessment. It has broken through the limit of the traditional conservative single-point risk estimation, and is applicable to fine assessment of the risk of soil heavy metals exposure to human health. However, the current PRA framework fails to explain clearly the definition of parameter boundaries and uncertainty handling of exposure scenarios, thus leading to arguments over its accuracy, applicability and resource costs. Another challenge originates from its integration with source apportionment and biomarkers analysis of soil heavy metals and development towards a multi-media, multi-receptor and multi-scale PRA framework. It is, therefore, essential for us to unfold in-depth research on PRA from the aspects of theoretical basis, technology and practical application, so as to enhance the policy implications in drafting benchmarks and developing management systems of soil environment risks.

    • Advancement in Researches on Technical Systems and Modes for Risk Management and Control of Contaminated Sites at Home and Aborad

      2022, 59(1):38-53. DOI: 10.11766/trxb202010120569

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      Abstract:With risk management as basic principle, sustainable remediation and safe utilization of contaminated sites has become an urgent environmental and developmental issue worldwide. To promote the application of rapid, economical and effective risk management and control technologies at the early stage of the soil pollution prevention and control drive in China, while specifying attributes of the broad and narrow connotations of risk management and control of contaminated sites, the paper elaborated systematically the technical theory, engineering implementation and applicable conditions of the risk management technologies in narrow connotation, including engineering control, institutional control and monitored natural attenuation, analyzed the risk management and control systems in developed countries, with reference to the risk management and control mode supported by the technical system and policy system established on the reality of the soil environmental management in China. In the end, aiming at the problems of weak foundation, unsound system and insufficient technical support of the risk management and control system in China, the authors put forth an overall layout of "prevention-control-remediation-management" for risk management and control of contaminated sites in consistence with the idea of green sustainability and the theory of life cycle management, which is expected to be of great practical significance to promotion of application of the technology and improvement of the risk management level.

    • The Abiotic and Biotic Transformation Processes of Soil Iron-bearing Minerals and Its Interfacial Reaction Mechanisms of Heavy Metals: A Review

      2022, 59(1):54-65. DOI: 10.11766/trxb202010300268

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      Abstract:Iron (Fe) minerals are widely distributed in soil and are an important component of soils, which play an important role in regulating soil health, pollutant behavior, and element biogeochemical cycles. These minerals are of great importance since they can influence many key chemical processes. For instance, they can affect the bioavailability and toxicity of heavy metals via a series of physical and chemical processes, such as physical encapsulation, adsorption, complexation, and co-precipitation. Additionally, soil organic substances can affect the transformation of iron minerals and lead to changes in the structure and surface properties of the products. Besides, the resultant products of such interactions have been reported to show a varied affinity for heavy metals and demonstrate contrasting effects on the environmental behaviors of heavy metals. In this review, we considered the following three points:(i) the effect of reaction pH, reaction temperature, and the added ferrous iron activity and concentrations on the abiotic transformation rates, degree, and pathways; (ii) the influence of soil root exudates such as oxalate acid, citric acid, and phenols on the accumulation, reduction, nucleation, dissolution and coprecipitation of Fe oxides; and lastly (iii) the surface complexation, and redox reactions of heavy metals at iron minerals-water interface. Here, the influence of iron mineral transformation on (a) the distribution of heavy metals, (b) the reaction process and molecular mechanism of heavy metals at the interface of iron mineral-organic matter, and (c) the use of kinetic models to evaluate and predict the environmental behavior of heavy metals is given in detail. It was observed that the ferrous oxidation is mediated by anaerobic photoautotrophic ferric oxidizing bacteria, and the bacteria affect the iron oxidation process through nitrate-reducing ferrous oxidation and biomineralization. Also, iron-reducing bacteria influence the iron reduction process primarily through chelating reagents, redox-active electron shuttling substances, and the c-type cytochrome of the outer membrane. Additionally, soil organic matters (e.g., fulvic acids and humic acids) can affect the aggregation and stability of soil aggregates. They can interact with iron minerals packaged in soil aggregates by electrostatic attraction, coordination exchange, van der Waals force, hydrophobic interaction, and hydrogen bonding, thereby affecting the biotic and abiotic transformation process of iron minerals. Nevertheless, this study can only serve as a reference for detail understanding of iron mineral-organic matter-heavy metal dynamic interaction mechanism at the microscale and the interaction molecular mechanisms of heavy metal at the soil multi-component interface. We suggest that future researchers should provide (i) an in-depth analysis revealing the molecular mechanism of the soil heavy metals environmental behavior under the dynamic interaction of iron minerals, soil organic matter and microorganisms, (ii) a clear picture of the soil interfacial reaction processes and mechanism at the atomic and molecular level, and (iii) a path for developing an in-situ dynamic monitoring method and technology for soil-water interface reaction process in the microscale, simulating the complex biogeochemical reactions, and predicting and assessing the trend of heavy metals in the complex natural environment by coupled kinetics models.

    • Progress of Impact of Plant Domestication on Composition and Functions of Microbiome

      2022, 59(1):66-78. DOI: 10.11766/trxb202006090210

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      Abstract:The plant microbiome plays crucial roles in nutrient acquisition, growth and health of plants, and has the potential to reduce dependence of the crops on fertilizers and pesticides. Plant domestication shows a significant impact on composition and functions of the microbiome. However, the mechanisms underlying this process are not well understood. Here, the paper is presented to summarize impacts of the variation of the plant in cultivar and genotype, root exometabolite and habitat, while the plants are being domesticated on composition and functions of the microbiome. Multifaceted comparison shows:(1) that domestication affects microbial diversity significantly and most of the plant microbial communities decrease in diversity during domestication; wild crops might attract more microbial communities that are beneficial to the resistance of pathogenic bacteria:and variation of the plant in cultivar and genotype affects composition of the rhizosphere microbiome and symbiotic relationship of the microbiome with the plant; (2) that changes in root exometabolite affect nutrient acquisition of the microbes and domestication weakens chemical defense of the plant; (3) Relative to the microbiome in the soil of croplands, the one in the virgin soil habitat is composed of more diverse and unique microbes. To sum up, the change in the plant rhizosphere microbiome is the result of the comprehensive interactions of multiple factors during the plant domestication process. Revealing the impacts of plant domestication on functions of the microbiome and restoring the beneficial plant-microbe connections and properties that may have got lost during plant domestication, can facilitate the development of new microbiome-based breeding strategies.

    • >Research Articles
    • Pedogenetic Characteristics and Paleoenvironment Significance of Mesozoic Paleosols in Sichuan Basin

      2022, 59(1):79-91. DOI: 10.11766/trxb202004300208

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      Abstract:[Objective] Detailed inversion of paleoclimates facilitates a better understanding of variation of the climate in the history and provides a basis for predicting future changes triggered by human activities in climate. Paleosol, formed on the Earth's surface during its geological period, is a direct record of the information about the terrestrial environmental conditions when it was formed. Quite a volume of paleosols are found developed within the Mesozoic strata across the Sichuan Basin and they may serve as an important terrestrial archive available for the research on global or regional deep-time paleoclimate.[Method] In this paper, a total of four hundred and thirteen deep-time paleosol profiles were identified in the Mesozoic strata of the Sichuan Basin, southwest China based on the pedogenic characteristics of paleosols. Of the paleosol profiles, observations and analyses were performed for their morphology, micromorphology, mineral composition, particle size composition and geochemical properties, for summarization of their pedogenic characteristics, for researches on their classification, and for discussion of their environmental significance as indicators.[Result] These profiles with distinct pedogenic features, such as presence of root traces and/or animal burrows, accumulation of pedogenic carbonate nodules, vertical variation of color, and development of soil horizons and soil structures, could be sorted into four different types of paleosols (i.e., Paleosol A, Paleosol B, Paleosol C, and Paleosol D). All the paleosol horizons are predominantly composed of quartz and calcite in mineralogy with minor proportions of feldspar, muscovite, illite and/or smectite. And content of the minerals varies with type of the paleosol. The paleosols are obviously lower than their corresponding modern ones in TOC and vary in a similar trend. And moreover, the two are basically consistent in element composition, and do not differ much in geochemical weathering index, leaching index, clayeyness, salinization index, and barium/strontium ratio, which indicate that the paleosols vary in chemical weathering degree with geological period and type of the soil.[Conclusion] According to the standards of the Chinese Soil Taxonomy, the paleosols, observed within the Mesozoic strata of the Sichuan Basin, are analogous to the four orders of modern soil, that is, Primosols, Cambosols, Aridosols, and Argosols, and the proportion of the last is relatively low. The development of the different types of paleosols indicates that the environment of the Sichuan Basin experienced repeated alternations between aridity and humidity during the Mesozoic Era, however, it was mainly under semi-arid and arid weathers.

    • Application of Seismic Refraction Tomography in Stratigraphic Division of Critical Zones in Red Soil Area

      2022, 59(1):92-104. DOI: 10.11766/trxb202008080247

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      Abstract:[Objective] It is of great significance to identify structure of the critical zones (CZs) of the earth for better understanding the geochemical, ecological and hydrological processes occurring in the CZs. However, previous studies relied mainly on borehole drilling and profiles, which is far from enough to help draw a full picture of the underground structure of the CZs. To overcome this problem, in this study, attempts were made to combine borehole drilling with the seismic refraction tomography (SRT) method to test if the seismological method can effectively detect the structure of CZs of highly weathered regolith.[Method] To that end, case studies were carried out of the Sunjia Catchment of Yingtan and the terraces of slat bedrock along the Yangtze River in Changsha. The study areas are both located in the red soil region, but different in bedrock composition. The bedrock is red sandstone in the Sunjia Catchment and sedimentary slate in the terraces along the Yangtze River. Ten seismic lines were arranged in the two study areas, and each had a detection depth ranging between 25~30 m. In addition, a total of 13 boreholes were drilled in the two study areas. In the field investigation recognition capability and error range of the SRT method were evaluated.[Result] Results show:SRT can effectively discern propagation velocity of p-wave at different depths in the CZs, and determine depth of key interfaces. In Yingtan, the identified lower boundary of the Overburden layer varies in the range of 3.0~5.2 m, with root mean square error (RMSE) being 1.7 m, and the identified bedrock surface does in the range between 8.2 and 22.0 m, with RMSE being 7.0 m. In Changsha, the identified lower boundary of the first layer falls in the range of 8.1~13.2 m, with RMSE being 2.4 m, and the identified bedrock surface does between 18.8 and 22.9 m, with RMSE being 0.9 m. The prediction is in good agreement with the drilling observation. The seismic wave travels at 2400 m/s in red sandstone and at 2 000 m·s-1 in sedimentary slate. Under flat terrain the overburden and bedrock are stable, while under sloping terrain, the overburden is thick on the top slope, and gets thinner on the mid slope. Landfills reduce the precision of seismograph in predicting underground structure for they have great impacts on the structure of the overburden layer, but not much on the structure of the deep underground. Groundwater in aquifers makes the overburden of the critical zones divided with the seismic refraction method tend to be thinner.[Conclusion] The longitudinal wave traveling through the subterranean layers of the CZs varies in velocity with the layer, which is the key to identification of the structural layers of the CZs by seismograph. SRT can not only improve the efficiency of field investigations, but also advance the development of the CZ three-dimensional mapping.

    • Influence of Soil Erosion on the Obstacle Factors of Cultivated Layer in Purple Sloping Farmland

      2022, 59(1):105-117. DOI: 10.11766/trxb202011090401

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      Abstract:[Objective] Purple soil sloping farmland is an important cultivated land resource in the upper reaches of the Yangtze River. Therefore, clarifying the change characteristics and main obstacle factors influencing purple soil sloping farmland under different erosion degrees is important.[Method] In a cultivated layer of sloping farmland, five erosion degrees (0, 5, 10, 15, 20 cm) were set up in situ. The cultivated layer quality index (CLQI) and obstacle degree (Mij) were calculated by selecting 10 quality indexes, including bulk density, total porosity, saturated hydraulic conductivity, soil compactness, soil shear strength, organic matter, total nitrogen, total phosphorus, pH and cation exchange capacity. Thus, the change characteristics of cultivated layer quality and obstacle degree under different erosion degrees were quantitatively evaluated.[Result] Soil erosion destroyed the structure of the cultivated layer, resulting in deterioration of cultivated layer quality index. Total porosity, saturated hydraulic conductivity, shear strength, cation exchange capacity, total nitrogen and total phosphorus decreased with the increase of erosion degree, while bulk density and soil compaction increased with the increase of erosion degree. The order of obstacle degree from cultivated layer quality was soil compaction (17.04%) > saturated hydraulic conductivity (15.83%) > total nitrogen (11.49%) > organic matter (11.47%) > total phosphorus (10.73%). The main obstacle factors of cultivated layer quality were soil compaction, saturated hydraulic conductivity, total nitrogen, organic matter and total phosphorus. The effect of soil erosion and management measures on soil compaction was significant (P < 0.01) while the effect of management measures on organic matter and saturated hydraulic conductivity was extremely significant (P < 0.01). Also, the interaction between soil erosion and management measures had a significant (P < 0.05) effect on saturated hydraulic conductivity and organic matter.[Conclusion] The main obstacles of cultivated layer types of purple soil sloping farmland can be divided into soil nutrient-poor obstacle and soil acidification obstacle. All the findings above can provide a theoretical basis for quality control of purple soil sloping farmland.

    • Effects of Temperature on Soil Atterberg Limit in Soil of Collapsing Gully Wall in the Hilly Granitic Region of South China

      2022, 59(1):118-128. DOI: 10.11766/trxb202007300287

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      Abstract:[Objective] Collapsing gully, one of the most serious soil erosion problems in the tropical and subtropical areas of South China, occurs mainly in the hilly red soil regions as triggered off by the interaction of runoff and gravity. A collapsing gully generally consists of five parts:an upper catchment, a collapsing wall, a colluvial deposit, a scour channel, and an alluvial fan. Stability of a collapsing gully wall determines the scale of the collapsing gully and the volume of the colluvial deposit. Rainfall and temperature not only determine weathering rate of soils, but also affect the mechanical state of granite red soils. Liquid and plastic limits are the most commonly tested mechanical indices. However, few studies have been reported about investigation of the effects of temperature on soil Atterberg limits in collapsing gullies.[Method] In this study, soil samples were collected from the three soil layers in a soil profile, i.e. red soil layer, sandy soil layer and detritus layer, of a typical collapsing gully located in Anxi County, Fujian Province. The soil profile was subdivided into three soil layers in the light of their colors and structures. Four levels of temperature (15, 25, 40 and 60℃) were set to investigate their effects on soil liquid and plastic limits and soil bound water content.[Result] The red soil layer was found to be the highest in soil liquid limit, plastic limit and plastic index and followed by the sandy soil layer and the detritus layer. Liquid and plastic limits positively and linearly related to contents of fine clay, organic matter and iron oxide. When temperature rose from 15℃ to 40℃, soil liquid and plastic limits in the three soil layers all decreased, as well as the soil bound water content. When temperature rose from 40℃ to 60℃, soil plastic limit increased in the red soil layer and the detritus layer, and soil liquid limit increased in the red soil layer and sandy soil layer. The effect of temperature on soil bound water content was consistent with the changes in soil liquid and plastic limits.[Conclusion] The soil liquid limit of the detritus layer is approximate to its saturated water content, and decreases gradually with the rising soil temperature. In the case of high temperature and heavy rain in summer in this region, flow deformation is the most likely to occur in the detritus layer, which might be one of the main reasons causing the collapse of a collapsing gully wall.

    • Hydraulic Characteristics of Rills of Non-eroded and Eroding on Saturated Purple Soil

      2022, 59(1):129-138. DOI: 10.11766/trxb202005280259

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      Abstract:[Objective] Rill hydraulics is an important dynamic factor affecting slope soil erosion. Rill morphology affects flow dynamics characteristics at all erosion stages, and further on development and morphology evolution of rill erosion.[Method] Scouring experiments were conducted on flumes packed with saturated purple soil for determination of runoff velocity in non-eroded and eroding rill, relative to flow discharge (2, 4, and 8 L·min-1) and slope gradient (5°, 10°, 15°, and 20°). The electrolyte pulse boundary model method was used to measure rill flow velocity (V), On such a basis, calculation was done of the hydraulic parameters of rills of non-eroded and eroding (including mean flow depth (h), Reynolds number (Re), Froude number (Fr), Darcy-Weisbach friction coefficient (f) and Manning roughness coefficient (n)), and then comparison was made of the hydraulic characteristics between the rills of the two states.[Result] Results show that the flow velocity in the rills of non-eroded state (VN) ranged from 0.170 to 0.778 m·s-1, and that in the rills of eroding state (VE) did from 0.156 to 0.619 m·s-1. VN varied with flow discharge to the power of 0.524 and with slope gradient to the power of 0.601, while VE varied with flow discharge to the power of 0.474 and with slope gradient to the power of 0.530, and their determination coefficient was 0.910 and 0.905, respectively. The mean flow depth of the rills of non-eroded state (hN) ranged from 0.078 to 0.413 cm, and that of the rills of eroding state (hE) did from 0.107 to 0.450 cm. hN varied with flow discharge to the power of 0.502 and with slope gradient to the power of -0.505, while hE varied with flow discharge to the power of 0.558 and with slope gradient to the power of -0.415, and their determination coefficients were both 0.942. When the flow discharge was 2 L·min-1, Re was < 500, and when the flow discharge was 4 or 8 L·min-1, Re varied between 500 and 2 000. Fr was always >1 regardles of working conditions, and ranged from 1.237 to 6.026 in the rills of non-eroded (FrN), and from 1.079 to 4.274 in the rills of eroding state (FrE). f ranged from 0.079 to 0.856, n did from 0.011 to 0.035, fN (in the rills of non-eroded state) did from 0.079 to 0.592, and fE (in the rills of eroding state) did from 0.156 to 0.856.[Conclusion] The parameter h is positively related to flow discharge in the power function, but negatively to the slope gradient. The influences of flow discharge and slope gradient on V decrease in all the rills regardless of state, and that of the former on h increases, while that of the latter on h decreases. The flow regime is dominated by transition flow and rarely by laminar flow, all belonging to rapids. Re does not differ much between rills different in state; FrEremaints almost a constant while approaching 1; f varies as affected by the interaction between V and h, in which V is the dominant one in the rill of non-eroded state, while h is in the other rills. During the development of the rills from the non-eroded state to the eroding state, V decreases, while h increases, so that Re increases, Fr decreases, and both f and n increase, and the erosion of the rills of eroding state caused by rill flow is lower than that of the rills of non-eroded state in intensity. This is because variation of the rills in morphology promotes energy dissipation, which in turn retards rill flow, reduces flow velocity, but increases the mean flow depth, thus eventually leading to changes in flow regime and resistance. All the findings in this study may hopefully help determine hydraulic characteristics of saturated purple soils with rills different in state and be of certain reference value to the establishment of a physical model for researches on soil erosion.

    • Distribution and Application of Soil Electrical Resistivity in Slope Land and Dam Land in the Loess Region

      2022, 59(1):139-147. DOI: 10.11766/trxb202004260196

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      Abstract:[Objective] Soil moisture is one of the most important factors for plant growth and solute transport in arid and semi-arid areas. An accurate and effective measurement of profile soil moisture is a critical issue of soil hydrology. The technology of electrical resistivity tomography (ERT) based on soil electrical properties provides a new geophysical method for measuring soil moisture content in the profile, which has been widely applied in the studies of soil water dynamics, groundwater recharge and root-water interactions in many regions in the world. However, little is known yet about the applicability of ERT to monitoring soil moisture or groundwater in the loess area, and the lack of information on profile soil resistivity (ρ) as affected by land use inhibits progress of the research on hydro-geophysics. This study was conducted to (1) explore characteristics of profile ρ, as affected by land use and slope position, in slope land and dam land in the northern part of the Loess Plateau, (2) determine effects of slope position and land use type on ρ and (3) examine applicability of ERT to monitoring soil moisture and groundwater dynamics in the loess area.[Method] Profile ρ in slope lands and dam land, different in land use type (including cropland, natural grassland, artificial grassland and caragana shrubland) was measured with a high-density ERT (Advanced Geosciences, Inc.) in the Liudaogou catchment in the northern part of the Loess Plateau. Variation of profile ρ with land use type and slope position was analyzed with ANOVA.[Results] Results show that land use type and slope position had significant effects on ρ in slope land. In terms of mean profile ρ, lands different in land use type followed an order of caragana shrubland > artificial grassland > natural grassland > cropland. Furthermore, mean profile ρ was the lowest in the bottom of the slope, followed by the middle and top of the slope. These findings suggest that profile ρ was closely related to soil moisture condition. Profile ρ in the dam land exhibited obvious horizontal and vertical variation in distribution. Vertically, ρ displayed a curve of high-low-high from the top to the deep loess layer, and the upper boundary of the low-resistance zone was consistent with the table of shallow groundwater in the dam land, while horizontally, profile ρ was closely related to land use type and geological position. Compared with the head dam land, the tail dam land had a low-resistance zone significantly thicker and penetrating the high-resistance zone in the shallow soil layer, which may be ascribed to crops' lower water consumption.[Conclusion] Spatial distribution of profile ρ varies significantly with land use type and slope position in the loess area. The geophysical method of ERT is recommended for monitoring and studying spatial and temporal characteristics of dry and wet conditions of soil profiles different in land use type, as well as shallow groundwater dynamics in the loess area of China. It can also be used to study relationships between precipitation, vegetation, soil moisture and groundwater, particularly for areas thick in sediment deposits.

    • Spatial Distribution of Shajiang Content in Shajiang Black Soil of Huaibei Plain and Its Influencing Factors

      2022, 59(1):148-160. DOI: 10.11766/trxb202004280202

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      Abstract:[Objective] Shajiang black soil (Vertisol), one of the major soil types in China with low or medium productivity, is mainly distributed in the Huaibei plain. As the name suggests, in soil configuration, the soil is composed of a black soil layer and a Shajiang layer, with the former overlaid with the latter. Although the black soil layer is dark in color, it is very low in organic matter content (< 1%). "Shajiang", a special kind of calcareous concretion, is a major component and a typical feature of Shajiang black soil. The presence of Shajiang leads to high heterogeneity of the soil and significantly influences physical and chemical properties of the soil, thus restraining root growth and crop yield. Shajiang is a byproduct of soil-forming process, and shows high spatial variability. However, little is yet known about spatial distribution of Shajiang and its driving factors in the Huaibei Plain. The objective of this study was to investigate spatial distribution of Shajiang its driving factors in the Plain.[Method] Based on the classical statistics and geo-statistics, this study selected two bands of Shajiang black soil, typical of the area, extending from west to east and from north to south in the plain for investigation of contents of Shajiang in the 0~100 cm soil layer, therein. Meanwhile, soils in the 0~20 cm soil layer were sampled for analysis of physico-chemical properties. Besides, topographic and climate data of the sampling sites were collected too. The west-east band extended from Shangcai County in Henan Province to Sixian County in Anhui Province (360 km long, and a total of 35 samples collected), and the north-south band did from Luyi County in Henan Province to Huaiyuan County in Anhui Province (195 km long and a total of 29 samples collected).[Result] (1) the two bands showed a general increasing trend from west to east and from north to south, separately in Shajiang content, but a decreasing one in depth of their burial; (2) Shajiang content increased with soil depth in both bands, and peaked in the 20~60 cm soil layer. The analysis of particle size composition of Shajiang shows that the 2~5 mm fraction of Shajiang accounted for 40%~44% of the total; (3) Similar to Shajiang content in variation trend, increasing from west to east and from north to south in the two bands, the proportion of montmorillonite, MAT and MAP increased too, but MAE and elevation did reversely. However, the content of total calcium only showed a decreasing trend from north to south in the north-south band; and (4) Pearson correlation analysis shows that Shajiang content was positively related to montmorillonite content (r=0.321, P < 0.01), MAP (r=0.416, P < 0.01), and MAT (r=0.369, P < 0.01), but negatively to total calcium content (r=-0.279, P < 0.05), elevation (r=-0.387, P < 0.01), and MEA (r=-0.392, P < 0.01). Principal component analysis shows that topography (37.4%) and climate conditions (38.4%) were factors more important than soil properties affecting Shajiang content (24.1%).[Conclusion] Therefore, it can be concluded that Shajiang content in the Huaibei Plain is mainly regulated by topography, climate conditions and soil properties together, thus forming a spatial distribution pattern of "low in the northwest, and high in the southeast".

    • Inversion of Leaf Area Index in Winter Wheat by Merging UAV LiDAR with Multispectral Remote Sensing Data

      2022, 59(1):161-171. DOI: 10.11766/trxb202007130239

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      Abstract:[Objective] In order to further tap the potential of unmanned aerial vehicle (UAV) carried LiDAR to monitor crop growth and to explore effect of merging UAV LiDAR with multispectral data in inversing leaf area index (LAI) in winter wheat, this study was carried out.[Method] In this study, with the aid of UAV LiDAR scanners and visible-near infrared multispectral cameras, UAV LiDAR point cloud and multispectral data of the winter wheat at the booting stage in experiment zone were collected. From the data, four LiDAR point cloud structure parameters, i.e., three-dimensional volumetric parameters (BIOVP), mean plant height (Hmean), 75 percentile plant height (H75) and laser penetration index (LPI), and six vegetation indices, i.e., NDVI, SAVI, MCARI, TVI, NDRE and RVI were extracted. Then correlation analysis was performed of these parameters for screening suitable modeling parameters. With the aid of the multiple linear regression (MLR) and the partial least squares regression (PLSR), a LAI inversion model was constructed through merging the LiDAR point cloud structure parameters with vegetation indices as input parameters of the model. In applying the MLR method, the two vegetation indices, NDVI and SAVI, that are the most closely correlated with the field-observed LAI and the two point cloud structure parameters, H75 and BIOVP, that are the most closely correlated with the field-observed LAI, were used as input parameters of the model. While in adopting the PLSR method, the number of principal components in modeling was determined in the light of the result of the cross-validation. Before modeling, the experimental dataset had been randomly divided into a modeling set (n=32) and a validation set (n=16) at a ratio of 7:3 in all treatments. A LAI inversion model was built up based on the modeling dataset and then the validation dataset was used to evaluate effect of the model. Meanwhile, in order to determine whether the inversion with the LiDAR point cloud data merged with the multispectral data was better than that based on multispectral data alone, LAI inversion models were constructed using the same modeling method with vegetation indices as input parameters of the model only.[Result] The evaluation of the model using the coefficient of determination (R2) and the root mean square error (RMSE) shows that the inversion model using the LiDAR point cloud data merged with the multispectral data well reflect the LAI in winter wheat, with R2 of the modeling set being all > 0.900 and RMSE being < 0.400 and R2 of the validation set being all > 0.800, and RMSE being < 0.500. In addition, no matter whether using MLR or PLSR, the models with the LiDAR point cloud data and vegetation indices (MLR:R2=0.901, RMSE=0.480; PLSR:R2=0.909, RMSE=0.445 (n=16)) are all superior to the models using vegetation indices only (MLR:R2=0.897, RMSE=0.492; PLSR:R2=0.892, RMSE=0.486 (n=16)).[Conclusion] In conclusion, although the LAI data in this research were too scattered, leading to insignificant difference between models in comparison, it could still be seen that the addition of UAV LiDAR data could make up for the defect of using the multispectral data alone that insufficient information could be extracted along the vertical direction of the crop, and improve accuracy of the inversion of LAI in winter wheat. Therefore, the model with UAV LiDAR data merged with multispectral data is a superior means for inversion of LAI in winter wheat and even other crops smaller in plant type.

    • In Vitro Test-based Study on Health Risks of Arsenic in Typical Soils of China and Their Influencing Factors

      2022, 59(1):172-182. DOI: 10.11766/trxb202005140100

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      Abstract:[Objective] This study aimed at accurate assessment of health risks of arsenic (As) in typical soils of China and comprehensive investigation of their influencing factors, based on oral bioaccessibility/bioavailability of soil As.[Method] Samples of five typical soils of the country, i.e. red soil, black soil, cinnamon soil, brown soil and yellow soil, were collected and prepared into As-contaminated samples by spiking As at 600 mg·kg-1. After one-month aging, bioaccessibility/bioavailability of soil As in the gastrointestinal tract of a human being were studied, and its health risk was evaluated by means of in vitro test (PBET-UF model). Besides, from the perspective of soil properties (soil basic physicochemical properties and As fractions), influencing factors of As bioaccessibility/bioavailability were explored and variation of As bioaccessibility/bioavailability with the soil analyzed.[Result] Results show that As bioaccessibility/bioavailability significantly varied between soils, as As bioaccessibility ranged from 37.2% to 71.8% in the gastric phase and from 49.0% to 73.3% in the small intestinal phase, while As bioavailability in the small intestinal phase ranged from 48.6% to 72.1%. It was indicated that from the stomach to the small intestine soil As was gradually dissolved by digestive fluids, and almost all the dissolved As in the small intestine could pass through the specific ultrafiltration membrane used to simulate small intestinal epithelium. Also, health risks of soil As through oral ingestion significantly varied with the soil. Based on the estimated As bioaccessibility in the gastric phase, carcinogenic and non-carcinogenic risks of As in the five soils varied in the range of 4.28×10-4~8.26×10-4and in the range of 14.86~28.69, respectively; and based on the estimated As bioavailability in the small intestinal phase, they did in the range of 5.59×10-4~8.30×10-4and in the range of 19.40~28.81, respectively. The carcinogenic risk and non-carcinogenic risk was two orders and one order of magnitude respectively higher than their respective acceptable limit. In addition, correlation analysis shows that between bioaccessibility/bioavailability of soil As was significantly related to certain soil properties.[Conclusion] Oral bioaccessibility/bioavailability of soil As is significantly and positively related to soil pH, migration coefficientS and migration coefficientW, but negatively to content of free Fe and Al oxides. Migration coefficientS is the main influencing factor determining bioaccessibility of soil As in the gastric phase, whereas soil pH is in the small intestinal phase. Although free Fe and Al oxides in the soils are not the determining factors directly affecting bioaccessibility/bioavailability of soil As in the gastric phase, they form new minerals with As, thus reducing the activity and consequent bioaccessibility/bioavailability of soil As. It is expected that all the findings in this study may contribute positively to making future field investigations of soil environmental quality of China more in line with the reality, and consummation of the methodologies for health risk assessment of heavy metal (loid) -contaminated soil.

    • Effect of Reductive Soil Disinfestation Mitigating Adverse Factors for Growth of Replanted Longya Lily (Lilium brownii var. viridulum)

      2022, 59(1):183-193. DOI: 10.11766/trxb202007220410

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      Abstract:[Objective] Longya Lily (Lilium brownii var. viridulum) is a perennial herb aboriginal of Longhui County, Shaoyang City, Hunan Province, with edible and medicinal values. It is of great significance to sustain cultivation of the crop for farmers' income and local economic development. However, soil borne diseases and weeds are the two key adverse factors affecting growth of replanted Longya Lily, and hence threatening stability and development of the local Lily industry. Reductive soil disinfestation (RSD) refers to a technology of pre-planting soil treatment designed to effectively eliminate soil-borne pathogens, degrade allelochemicals, and improve soil physicochemical properties, etc., but how much RSD could control weeds and soil weed seed bank is still unclear. Therefore, this study was oriented to explore effects of RSD on soil borne pathogens and weed seed bank in Longya Lily fields.[Method] A field experiment, designed to have three treatments, i.e. CK (control without soil treatment); MO[RSD incorporated with 6 t·hm-2liquid organic material (C/N 21)]; SB[RSD incorporated with 15 t·hm-2 solid organic material (C/N 94)], was conducted in a field planted with Longya Lily for one year. Real-time PCR was used to determine populations of the bacteria, fungi and soil-borne pathogens in the soil. Species of the weeds in the field were identified and density and biomass of the weeds were recorded.[Result] Results show that RSD effectively suppressed Fusarium oxysporum, Fusarium solani and Rhizoctonia solani, and significantly lowered the proportion of genus Fusarium in the fungal community as compared to CK, with disinfestation efficacy up to 98.8%. Furthermore, RSD also effectively inhibited germination of most of the weeds in the soil weed seed bank, and significantly reduced density and biomass of the weeds in the field, by 94.1%~96.0% and 71.0%~94.7%, respectively. And treatment MO was higher than treatment SB in weed control effect. In addition, RSD significantly changed structure and reduced diversity, richness and dominance of the weed community.[Conclusion] Therefore, it can be concluded that RSD can significantly reduce soil borne pathogens, weeds and other adverse factors in the field of replanted Longya Lily. It is a promising agricultural measure with the potential to reduce the occurrence of both soil borne diseases and weed infestation. The findings in this study could provide a theoretical basis and certain technical support for reducing the use of pesticide and realizing sustainable development of the green agriculture.

    • Effects of Rapeseed/Wheat-Rice Rotation and Fertilization on Soil Nutrients and Distribution of Aggregate Carbon and Nitrogen

      2022, 59(1):194-205. DOI: 10.11766/trxb202004090091

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      Abstract:[Objective] In China, upland-paddy rotation systems are mainly distributed in the Yangtze River Basin, with rapeseed-rice (RR) and wheat-rice (WR) rotations being the main systems. It was noticed that rice productivity varied with the rotation system. Therefore, a long-term experiment, designed to have different treatments concerning rotation system and fertilization pattern, was carried out. The study aimed to explore differences in soil nutrients and distribution of aggregate carbon and nitrogen between RR and WR rotations and between different fertilization methods. It is hoped that the study may providing a scientific basis for optimizing the paddy-upland rotation systems and the fertilization methods as well in the rapeseed-wheat interlaced area of the middle reaches of the Yangtze River.[Method] The field experiment was designed to have two treatments in rotation system (i.e., RR and WR) and three treatments in fertilization, i.e., CK (no fertilization), NPK (chemical fertilization), and NPK+S (chemical fertilization combined with straw returning). Soil samples were collected from the 0-20cm soil layer of each treatment after harvest of the upland crops of the fourth year for analysis of physical and chemical properties, such as soil organic matter, nutrient content, porosity, distribution and stability of soil aggregates, and contribution rate of soil aggregate organic carbon and nitrogen to the soil total.[Result] Compared with WR, RR was 13.1%-19.2% and 18.8%-59.5% higher in content of soil organic matter and available phosphorus when fertilized. Treatment NPK+S was 28.1% than CK and 29.2% higher than Treatment NPK in content of soil total nitrogen. In the group of Treatment NPK, Treatment RR was significantly or 8.1% (in CK) and 10.3% (in Treatment NPK) higher and 11.7% and 10.5%, respectively, higher than Treatment WR in total porosity and capillary porosity. In the group of fertilization treatments (either NPK or NPK+S), Treatment WR was significantly higher than Treatment RR in mean weight diameter (MWD) and geometric mean diameter (GMD) of the water-stable soil aggregates and content of water-stable macroaggregate (WSMA), and in contribution rate of large-sized soil aggregates to total organic carbon and total nitrogen as well. In terms of soil organic matter and nutrient contents the fertilization treatments displayed an order of CK < NPK < NPK+S, and Treatments NPK and NPK+S were significantly higher than CK in soil aggregate stability and contribution rate of large-sized aggregates to total organic carbon and total nitrogen, regardless of rotation patterns. In the group of Treatment WR, Treatment NPK + S was significantly higher than CK and NPK in soil total porosity and capillary porosity, while in the group of Treatment RR, no significant difference was observed in soil porosity between different fertilizer treatments.[Conclusion] All the findings show that under the rapeseed-rice rotation system, application of chemical fertilizer combined with straw returning can increase contents of soil organic matter and soil nutrients, improve bulk density and porosity of the soil, and stabilize soil aggregate structure. Hence, the combination of rapeseed-rice rotation and application of NPK coupled with straw returning could be deemed as an important measure to achieve sustainable development of rice fields.

    • Effects of Mortierella on Nutrient Availability and Straw Decomposition in Soil

      2022, 59(1):206-217. DOI: 10.11766/trxb202006020213

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      Abstract:[Objective] Saprophytic fungi can convert complex organic substances into available components, which is closely related to soil nutrient availability and carbon (C) sequestration. Mortierella has been reported to be substantially enhanced after long-term fertilization in agricultural soils. Studies in the past demonstrated that some species of Mortierella did make important contributions to soil nutrient transformation and availability, and were able to degrade hemicellulose, cellulose and lignin, and hence could directly affect straw decomposition and alter nutrient status of the soil. Furthermore, Mortierella species show great ability to excrete a large volume of polyunsaturated fatty acids, which contained abundant C sources, thus altering the soil microhabitat. It was therefore, presumed that Mortierella inoculants could affect soil microbial communities in part by changing their nutrient uptake, thus indirectly influencing soil nutrient transformation and availability in the soil. However, empirical evidence of the effects of Mortierella inoculants on the soil microbial communities under planting conditions is seldom available. The objective of this study was to explore how indigenous strains of Mortierella affect soil nutrient availability during the process of straw decomposition.[Method] Two strains of Mortierella (Mortierella alpina and Mortierella elongata) were isolated from two types of agricultural soils (red soil and Shajiang black soil) that had been applied with organic manure for decades. A pot experiment, designed to have three treatments, i.e. no inoculation (Control); inoculation with Mortierella alpina (Ma); and inoculation with Mortierella elongata (Me), and three replicates for each treatment, was conducted with the two soils packed in the pots separately and incorporated with straw. Availability of C, nitrogen (N) and phosphorus (P) and activities of β-glucosidase, N-acetyl-β-glucosaminidase and phosphatase were determined. Chemical C structure of the residual straw and bacterial community composition in the soil was analyzed with the aid of the solid state 13C-nuclear magnetic resonance (13C-NMR) spectroscopy and the technique of 16S rRNA gene amplicon sequencing, respectively.[Result] In red soil, Treatment Ma increased the content of soil available P by 29.0%, while Treatment Me did the content of soil available N and the activity of β-glucosidase by 15.5% and 81.3%, respectively. In Shajiang black soil, both Mortierella treatments notably increased the content of soil available N and the activity of β-glucosidase. In addition, Treatment Ma significantly increased the activity of phosphatase, while Treatment Me did the content of dissolved organic C and soil available P by 16.2% and 11.5%, respectively. In red soil, Mortierella inoculants inhibited straw decomposition and significantly altered composition and metabolic functions of the bacterial community, while in Shajiang black soil, they promoted straw degradation but had little effect on bacterial community structure. Ochrobactrum, Achromobacter and Streptomyces were the most influential taxa contributing to differences in bacterial community between the treatments and the control in red soil. Network analysis showed that the interactions between soil microbes were more complex connectedness in red soil than in Shajiang black soil. Lysobacter, Stenotrophomonas, Pantoea, Phyllobacteriaceae and Solirubrobacterales were identified as the keystone taxa in red soil, while Comamonadaceae, Lysobacter, Cytophagaceae and Serpens flexibilis were in Shajiang black soil. These keystone taxa acted as decomposers or biocontrol agents, and played important roles in maintaining microbial interactions and in potential processes of straw decomposition.[Conclusion] The present study has demonstrated that Mortierella alpina and Mortierella elongata can improve soil C, N and P availability and associated enzyme activities, and provide evidence of roles of indigenous strains of Mortierella strains on straw decomposition and nutrient transformation in agricultural soils.

    • Effects of Nitrogen Deficiency on Microbial Community Structure in Rhizosphere Soil of Wheat

      2022, 59(1):218-230. DOI: 10.11766/trxb202005080225

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      Abstract:[Objective] Rhizosphere microorganisms play an essential role in the process of nutrients absorbing in crops. To improve nitrogen utilization efficiency in wheat production, it is of great significance to study effects of nitrogen deficiency on structure of the microbial community in the rhizosphere of wheat.[Method] Soil samples were collected from a nitrogen-depleted wheat field of Lou soil, which is typical of the Guanzhong Region, Shaanxi Province for a rhizobox experiment. The experiment was designed to have two treatments, one applied with nitrogen fertilizer at a normal rate (150 mg·kg-1) and the other with no nitrogen fertilizer to the wheat growing in the rhizoboxes. Soil microbial communities in the rhizosphere, near-rhizosphere and non-rhizosphere were analyzed with the technique of 16S rRNA gene amplicon high-throughput sequencing for comparison between the two treatments in soil microbial diversity and community structure in these sections of the rhizoboxes.[Result] Results show that the content of soluble inorganic nitrogen in the soil played a leading role in triggering changes in microbial community diversity and community structure. Compared with normal nitrogen supply, soil microbial community has higher α diversity index under nitrogen deficiency. The abundance of microorganisms, such as Firmicutes, Gracilibacteria, Candidatus Jorgensenbacteria and Elusimicrobia, was negatively related to soil nitrate content. Nitrososphaeria an ammonia-oxidizing class of archaea, was a critical node of the microbial co-occurrence network affected by nitrogen deficiency. Nitrogen deficiency induced a series of microbial metabolic processes, such as mRNA synthesis, glycolysis, peroxides, and phosphoinositol metabolism. Nitrosospira and Nitrospirae contributed the most to accuracy of the random forest classifier, and can be used as biomarker for prediction of nitrogen supply level in soil.[Conclusion] To sum up, the effects of nitrogen deficiency on diversity, community structure, and metabolic function of the soil microbes in the rhizosphere were significant, and more than the rhizosphere effect. It is helpful for the exploration of plant growth-promoting rhizobacteria and provides some theoretical basis for reducing the nitrogen fertilizer application and improving the utilization efficiency of nitrogen fertilizer in wheat production.

    • Effects of Paddy Periphyton Biofilms on Rice Germination and Seedling Growth Relative to Paddy Ecosystems

      2022, 59(1):231-241. DOI: 10.11766/trxb202004190180

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      Abstract:[Objective] Periphyton is ubiquitously distributed in paddy fields, directly affecting nutrient cycles and their bio-availabilities. However, no study regarding effects of periphyton on rice growth has been reported.[Method] In this study, model paddy ecosystems with three types of soils were simulated under controlled conditions to investigate the effects of periphyton on rice seed germination and seedling growth.[Result] Results show that periphyton of three types of soils was mainly composed of Proteobacteria, Cyanobacteria and Bacteroidetes, while the diversity of periphyton of the three soils was significantly different, and that grown in soil from Yanbian (YBP) had the highest OTU number and Chao1 index. Furthermore, there were significant differences in carbon metabolic activity among the three periphyton (P<0.05). The Pearson correlations indicated that periphyton composition and diversity was positively correlated with soil pH, TP, TOC and Mn contents (P<0.05). The carbon metabolism activity of YBP was the highest during the whole growth period, while that of soil from Yingtan (YTP) was the lowest. The presence of periphyton greatly increased the germination index of rice seed (by maximally 18%), and α-amylase activity in the presence of periphyton was increased significantly (P<0.05). Besides, the periphyton covering on paddy soil surface from Yanbian (YBP) significantly promote shoot length and its biomass (P<0.05). The Pearson correlations indicated that seed germination and survival rate was positively correlated with periphyton chemical properties.[Conclusion] To summarize, this study indicates that the presence of periohyton biofilm during seed germination period was propitious for rice growth. Results of this study provided an insight into understanding the periphyton-plant relationships with different soil-types and also new approaches to controlling plant phenology by regulating the growth of periphyton.

    • Effect of Planting System on Fertilization-induced Variation of Soil Denitrification Potential and Its Microbial Mechanism

      2022, 59(1):242-252. DOI: 10.11766/trxb202009250539

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      Abstract:[Objective] Soil denitrification potential (SDP) is generally higher in paddy field than in upland field. However, as the effect of fertilization on SDP in paddy field and upland field varies with climatic and soil type, accuracy of its assessment is often affected by external conditions.[Method] In this study, two adjacent fields, one paddy field and one upland field, both derived from the same parent material of Quaternary red clay, in a long-term field experiment were selected for exploration of effect of fertilization regime on SDP and its association with abundances of functional genes (narG, nirS, nirK, and nosZ) and community composition of nirS-type denitrifiers with the aid of in-lab incubation, real-time quantitative polymerase chain reaction (qPCR), and high-throughput sequencing technology.[Result] In the paddy field, compared with Treatment NPK, Treatment NP and PK was significantly or 33.01% and 23.57%, respectively, higher in SDP, while Treatment NK was 35.76% lower in SDP. The effects of Treatments NP and NK were related to the abundance of nirS gene, and the changes in content of soil available P (AP) and N:P ratio, while that of Treatment PK was associated with the community composition of nirS-type denitrifiers (Azospira sp. NC3H-14). In the upland field, compared with Treatment NPK, Treatment NP, NK and P was 13.94%, 26.51%, and 25.41%, respectively, higher in SDP. The effects of Treatments NK and P were significantly related to the abundance of narG gene and of nirS-type denitrifiers (Azospira sp. NC3H-14 and Ideonella sp. NC3L-43b for NK treatment; Azospira sp. NC3H-14, Rhodanobacter sp. D206a, Rubrivivax gelatinosus for P treatment). The content of amorphous iron oxide (Feo) was probably the main factor affecting the abundance of narG gene.[Conclusion] The above listed findings indicate that planting system affects the effect of fertilization on SDP. The variation of SDP in paddy field is mainly attributed to nirS-type denitrifiers, while that in upland field primarily to the abundance of functional gene and the community compostion of nirS-type denitrifiers.

    • Dissimilatory Nitrate Reduction to Ammonium Coupled to Fe2+ Oxidation in Paddy Soils as Affected by Oxygen Presence and Carbon Addition

      2022, 59(1):253-262. DOI: 10.11766/trxb202007100382

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      Abstract:[Objective] Dissimilatory nitrate reduction to ammonium (DNRA), a biological pathway converting NO3- to NH4+, provides ammonium for rice uptake and microbial immobilization, resulting in N retention in paddy soils. Recently, the coupling between DNRA and Fe2+oxidation has been reported occurring in freshwater lake or estuary sediments. However, so far little has been reported on this process in paddy soil, and its potential key factors are practically unknown.[Method] Using 15N-tracing technique in combination with membrane inlet mass spectrometer (MIMS), an in-lab incubation experiment was performed to investigate the process of DNRA coupled to Fe2+ oxidation as affected by oxygen presence and carbon addition in two types of paddy soils (CS and TY).[Result] Results showed that the process of DNRA coupled to Fe2+ oxidation was found in both paddy soils, where the potential rate of DNRA increased from N 0.36-0.38 to 0.81-2.35 nmol·g-1·h-1 with Fe2+ addition rising from 0 to 800 μmol·L-1. At the concentration of 800 μmol·L-1 Fe2+, potential rate of DNRA was significantly higher in CS soil than that in TY soil, which was in consistence with differences between the two tested soils in nrfA gene abundance. Effect of oxygen presence and/or lactic acid addition on the process of DNRA coupled to Fe2+ oxidation varied in the two tested paddy soils. In TY soil, regardless of singly or in combination applied, oxygen presence and lactic acid addition significantly promoted potential rate of DNRA at varying Fe2+concentrations. In CS soil, single oxygen presence or lactic acid addition significantly increased potential rate of DNRA at the concentration of 500 μmol·L-1 Fe2+, whereas, at the concentration of 800 μmol·L-1 Fe2+, either lactic acid singly applied or in combination with oxygen significantly decreased potential rate of DNRA.[Conclusion] Findings of this study suggest that the process of DNRA coupled to Fe2+ oxidation occurs in paddy soils and may be affected by presence of oxygen and carbon addition. Further studies are needed to deepen understanding of this process by including more types of soil and comprehensively evaluating the effects of environmental parameters and soil properties on the process.

    • Impacts of Plantation of Winter Green Manure Crops on Soil Nitrification in Paddy Soil

      2022, 59(1):263-273. DOI: 10.11766/trxb202004050150

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      Abstract:[Objective] Utilization of green manure crops in winter is an effective practice to maintain high and stable yields in paddy fields in South China, and plays an important role in N management in the rice cropping system. Nitrification is a key process in N cycling and is highly related to N utilization of crops and to N leaching loss as well. Since nitrification process is a potential N loss pathway, it is worthwhile to study impacts of cultivation and incorporation of green manure crops on nitrification process and ammonia oxidizing microorganisms in paddy soil.[Method] A pot experiment having three crops a year, that is, green manure crop, early rice and later rice, was conducted in alkaline paddy soil and designed to have four treatments, i.e. winter fallow-double cropping rice (WF), milk vetch-double cropping rice (MV), ryegrass-double cropping rice (RG) and rape-double cropping rice (RP). Nitrification potential (NP) and recovered nitrification potential (RNP) of the soil in the pots were measured. Relative contributions of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) to RNP were explored using specific bacterial inhibitors (Kanamycin and Spectinomycin). Abundances of AOA and AOB were measured using the amoA gene-based real-time quantitative PCR method.[Result] Treatments MV and RG increased the N uptake of early rice and late rice, respectively. Plantation of winter green manure crops, no matter what, significantly lowered NP at the pre-transplanting, tillering and jointing stages of early rice. The NP at the jointing stage of early rice was the highest in Treatment WF, reaching up to 56.15 mg×kg-1×d-1. Compared to Treatment WF, the other three treatments were all higher in NH4+-N, and lower in NO3--N at most of the sampling stages. Soil NO3--N was significantly and positively related to NP. Compared to Treatment WF, all the green manure treatments were higher in copy numbers of AOA and AOB amoA genes at most of the sampling stages, especially the former, which was much higher than the latter. However, AOB was a dominating contributor to RNP at all the sampling stages, contributing relatively 61.02%-82.37%. The abundance of amoA genes had nothing to do with the contributions of AOA and AOB to nitrification. Utilization of green manure crops increased relative contribution of AOB to RNP (RNPAOB) at the tillering stage of early rice, but decreased that of AOA to RNP (RNPAOA) at the pre-transplanting and jointing stages of early rice. Soil properties were significantly related to nitrification process, especially soil pH, NH4+-N and NO3--N. Application of winter green manure crops decreased soil pH in alkaline soil, which may be one of the main causes of the practice inhibiting nitrification.[Conclusion] Application of winter green manure crops reduces soil NP, which is consistent with the variation of soil NO3--N, suggesting that the practice may mitigate the risk of NO3--N leaching loss. Therefore, it plays an important role in N management in paddy soil.

    • Strategies for Soil Microbes Utilizing Exogenous Substrates in Ultisol Based on Nucleic Acid Stable Isotope Probing Technique

      2022, 59(1):274-284. DOI: 10.11766/trxb202008100445

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      Abstract:[Objective] The input of exogenous active carbon (C) substrate strongly affects the growth of soil microorganisms. However, so far little knowledge is available about dynamic responses of soil microorganisms (bacteria and fungi) to the input of exogenous active carbon substrate and functional traits of the microorganisms in utilizing the substrate and their relationships with community structure of the microorganisms.[Method] Hence, an experiment was carried out using 13C-glucose as substrate in Ultisol for incubation of soil microorganisms (bacteria and fungi), which were sampled periodically for analysis with the aid of DNA-based stable isotope probing and high-throughput pyrosequencing techniques to explore dynamic traits of the microorganisms utilizing the carbon of glucose relative to species.[Result] It was found that in utilizing the substrate, the bacterial and fungal communities followed the r/K selection strategy in evolution from bacteria to fungi. Among the bacterial community, copiotrophic bacteria, like Proteobacteria and Actinobacteria, were higher than oligotrophic phyla, like Acidobacteria and Chloroflexi, in activated substrate utilization capacity. Different from bacteria in utilization of substrates, fungi, like Ascomycota and Basidiomycota, were low in selectivity and able to utilize both labile C and native soil organic matter.[Conclusion] Hence, bacteria retain their intrinsic life-history strategies controlled by their copiotrophic or oligotrophic natures, regardless of increase in C availability. Fungi can utilize a wide range of substrates and labile C input can induce copiotrophic Ascomycota to utilize heterogeneous recalcitrant C, thus accelerating decomposition of native soil C.

    • The Effect of Long-term Fertilization on the Abundance and Composition of Ammonia-oxidizing Archaea and Bacteria in Paddy Soil Profiles

      2022, 59(1):285-296. DOI: 10.11766/trxb202007140240

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      Abstract:[Objective] Nitrification is a critical process of the nitrogen cycle which is driven by ammonia-oxidizing archaea (AOA) and bacteria (AOB). It has been observed that long-term fertilization affect soil properties and nitrifying microbial community in paddy soils. However, the effect of long-term fertilization on the community structure of AOA and AOB along the depth in paddy soils has been given little attention.[Method] From a long-term experiment on fertilization management of a paddy field in Ningxiang, Hunan Province, we selected four treatments; no fertilization (CK), straw organic fertilizer (ST), organic-inorganic fertilizer (OM), and inorganic fertilizer (NPK), and used real-time fluorescent quantitative PCR and Illumina MiSeq sequencing technology to analyze the soil properties, and abundance and composition of AOA and AOB in the soil layers (0-10 cm, 10-20 cm, 20-30 cm, 30-40 cm).[Result] ST, OM and NPK treatments increased the contents of soil organic carbon, total nitrogen, available phosphorus and the nitrification potential in each soil layer, but decreased soil pH. The contents of soil organic carbon, total nitrogen, alkali hydrolyzable nitrogen, available phosphorus, and the nitrification potential decreased with an increase in soil depth, while the pH value showed an opposite trend. Importantly, NPK had a more significant effect on soil acidification (0-20 cm) compared to the other fertilizers. The AOB abundance in the control (no fertilization) treatment was higher than AOA abundance, with the ratio of AOB/AOA abundance in the range 9.24-29.19. Also, the application of fertilizers promoted the growth of AOA, with the AOA/AOB abundance ratio in the range 0.77-31.28. Long term application of fertilizers enriched the proportion of Nitrosocosmicus in AOA population and Nitrosolobus in AOB population. Redundancy analysis showed that available phosphorus and pH had a significant impact on the composition of AOA and AOB communities, with interpretive degrees of 31.5% and 46.7%, respectively. This indicated that available phosphorus and pH were the key factors driving the succession of AOA and AOB community structure. Additionally, the vertical distribution characteristics of AOA and AOB were affected by different fertilization measures and soil layers.[Conclusion] Long term fertilization can acidify paddy soil and change the main executor of ammonia oxidation in the nitrification process. Variations in carbon, nitrogen, phosphorus and pH along the paddy soil depth induced the observed changes in AOA and AOB abundance and community composition and then affected the nitrification ability of soil. This study can serve as a theoretical basis for improving nitrogen use efficiency and reducing greenhouse gas emission.

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