Abstract:Healthy soil is the foundation for food security, farmland productivity, and high-quality agricultural development. Currently, soil health assessment has globally become the focus and hotspot of the soil science discipline. The selection of soil health assessment methods and indicators has been systematically summarized. However, there is still a lack of practical suggestions for specific evaluation processes. This paper focuses on analyzing the characteristics of soil health and multifunctionality, the general principles of soil health evaluation, the n+X model for selecting indicators, and the selection and implementation of evaluation methods. We propose the soil health gap and benchmark, the selection of basic and restrictive indicators, as well as the adaptability of indicator selection. In addition, the establishment of a soil health indicator system needs to take into account factors such as soil texture, crop type, land use, and climate conditions. The implementation of soil health technology and paradigm needs to be integrated with relevant policies. In the future, it is necessary to further research the driving mechanisms of soil health and the cultivation of healthy soils. Based on long-term experiments and monitoring networks for farmland quality, the soil health indicator system, threshold, database, and decision support system were established depending on soil texture, crop type, land use, management objectives, and evaluation scales. Combined with relevant policies and regional environmental constraints, a consensus, convention, and action across regions and countries should be formed to promote the implementation of global soil health action and sustainable agricultural development.

Abstract:Polycyclic aromatic hydrocarbons (PAHs) are a class of persistent organic pollutants, which readily accumulate in the soil with significant toxicity. However, PAHs could be strongly adsorbed by the solid phase of soil, the exposure based on the total pollution mass will lead to the overestimation of human health risks. Based on 123 papers published from 2000 to 2020, this study summarized the distribution and composition characteristics of soil concentrations of 16 priority-controlled PAHs (Σ₁₆PAHs) in China, introduced 11 commonly used testing methods and main influencing factors for modelling bioaccessibilities, and summarized the ranges of bioaccessibility coefficients of PAHs. The results showed that the maximum and average concentrations of Σ₁₆PAHs in soil were 23 250 and 1 314.7 μ·kg^-1 respectively. In recent years, mainly based on the physiologically-based extraction tests (PBET), the bioaccessibility test methods of PAHs are continuously improved and modified in enriched simulation of digestion processes and adsorbents, while the digestion conditions and soil properties etc. have a great impact on the bioaccessibility results. The average bioaccessibilities of 16 PAHs ranged from 13.2% to 72.4%, among which higher values were identified for chrysene and benzo (b) fluoranthene, contributing significantly to the total Σ₁₆PAHs exposure. This study therefore provided an important theoretical ground for undertaking detailed risk assessment of PAHs.

Abstract:Molecular hydrogen is a key intermediary in the metabolic interactions of a wide variety of microorganisms. The activities of hydrogen-producing and hydrogen-consuming microorganisms in the environment determine the global hydrogen cycle, which has a potential driving effect on the biogeochemical cycle of other important elements. Environmental functional microorganisms play an important role in maintaining the balance of ecosystems and eliminating secondary pollution. Therefore, understanding the impact of hydrogen metabolizing (production and consumption of hydrogen) microorganisms on the ecological environment and its role and function in environmental bioremediation has vital significance and practical value for understanding the ecological and environmental effects of hydrogen and its application to bioremediation. This paper systematically analyzed the hydrogen metabolism process and the classification and function of hydrogenase, summarized the various ways of hydrogen production and consumption by microorganisms and their effects on soil ecological environment and bioremediation. The scientific and technical challenges existing in current hydrogen metabolism processes and the application of hydrogenase in environmental bioremediation were summarized. Besides, it was also proposed research ideas and key directions in this field to promote hydrogen as a bioenergy since it has become a promising strategy for environmental pollution remediation.

Abstract:Rice is the staple food for about half the world's population and one of the most widely grown crops. Because long periods of flooding are needed during rice planting, paddy water is becoming an important sink of contaminants such as herbicides, pesticides and heavy metal (loid) s (e.g., arsenic). Compared with surface water, the concentrations of nitrite/nitrate and dissolved organic matter (DOM) in paddy water are usually higher, due to the extensive application of nitrogen fertilizers and release of DOM from microbial degradation of soil organic matter. Owing to long-term flooding during rice cultivation, desorption of soil humic substances, reductive dissolution of mineral–OM complexes, and root exudation release a large amount of DOM into paddy water, which can generate reactive intermediates (RIs) such as triple excited organic matter (³CDOM^*), singlet oxygen (¹O₂) and hydroxyl radicals (^·OH) under sunlight. These RIs usually exhibit high reactivity and play an important role in pollutant transformation and element cycling in paddy fields. In this paper, the generation process and mechanism of RIs in paddy water were reviewed and the type and concentration of RIs in different growth stages of rice were emphasized. Compared with the typical surface water, quantum yields of ³CDOM^* and ^·OH were comparable, while quantum yields of ¹O₂ were about 2.4-6.7 times higher than those of surface water. DOM in paddy water with lower molecular weight and humification extent generated more RIs, and nitrite contributed to 23.9%–100% of ^·OH generation. DOM with more saturated and less aromatic formulas could produce more ³CDOM^* under irradiation, while the polyphenolic components of DOM inhibited the formation of RIs. The effects of different environmental factors on the production of RIs were discussed. The application of straw and lime increased the RI concentrations by up to 16.8 and 11.1 times, respectively, while biochar addition had limited effects on RI generation from paddy water. Furthermore, the solar radiation directly affected the quantum yields of RIs in paddy water, and the radiation intensity showed a linear positive correlation with the concentration of free radicals. The mechanism of abiotic transformation of arsenic and different organic pollutants in paddy water was described and the degradation of contaminants, including As(III), 2, 4-dichlorophenol (2, 4-DCP), polycyclic aromatic hydrocarbons (PAHs), chlorotoluron, diuron, dimethomorph, and propanil, was significantly accelerated by photoinduced RIs generated in paddy water. Most of previous studies were conducted with stimulation experiments in the laboratory and the underlying mechanisms of RIs generation in paddy water have not been fully elucidated. Future studies should pay more attention to the generation of RIs in the paddy field and link global scale factors such as photoactive material flux, different soil properties and improvement measures, as well as the transformation of pollutants and material circulation to form a systematic understanding. In addition, future studies should not only focus on the degradation of these pollutants themselves, but also on the toxicity and ecological risks of the degradation products of these pollutants. More attention should be paid to the transformation of emerging pollutants, such as new pesticides, antibiotics and microplastics, in the paddy system.

Abstract:【Objective】Pedology begins with the observation of soil profile and its morphological characteristics. The division of the soil profile horizon and description of the characteristics of the horizon boundary are the basis of soil investigation. The division of soil horizon in the field requires rich practical experience in pedology and is more subjective, which makes it difficult to form a set of unified division standards. 【Method】In this paper, the purple soil profile image was taken as the research object, and using K-means clustering and image segmentation technology, combined with the color (CIE Lab color space) and texture characteristics (Entropy) of the image, we identified the horizon boundary of the purple soil profile, by comparing with the results of field division. 【Result】The results show that (1) the a and b channels of CIE Lab color space and Entropy texture characteristics can delineate the master horizon (A , B , and C) and bedrock(R)of the profile; the a channel values range from 7-22, the b channel values range from 7-19, and the Entropy values were 4 or 5; the Munsell colors converted by the CEL XYZ system had a certain deviation from the colors visually discerned in the field using colorimetric cards, with a hue range of 10R-2.5Y, a value range of 4-8, and a chroma range of 3-8. (2) The number of soil horizon and the depth of soil horizon identified by clustering were consistent with the results of field identification; the difference between the lower boundary depth of soil horizon identified by clustering identification and those identified in the field was within 3 cm, except for C in profile Z2 and the Ap in profile Z6, where the difference was larger (13 cm and 8 cm, respectively). (3) The topography of the soil horizon identified by clustering was more irregular and the distinctness was more blurred. The clustering algorithm can identify more subtle differences in the soil profile image and reflect the local variation of soil properties in more detail. 【Conclusion】K-means clustering and image segmentation techniques achieved the identification of the horizon boundary of purple soil, and this study provides a scientific reference for the development of an intelligent identification system for soil profiles.

Abstract:【Objective】The black soil region of Northeast China is an important commodity grain production base in China. However, long-term high-intensity reclamation and unprotected utilization have led to serious soil erosion and continuous reduction of black soil thickness. In some areas, the low-nutrient loess parent material was exposed, resulting in decreased land productivity, and food production was seriously threatened. However, determination of the distribution of soil thickness on the slope is challenging. The traditional soil thickness measurement methods, including the soil profile method, soil probes, and the drilling method, are inefficient and cannot ensure continuity along the slope. Therefore, this study aims to apply a new method, ground penetrating radar (GPR), to measure the continuous variation of black soil thickness on slopes. 【Method】In this study, the GPR was used to continuously measure the black soil thickness on three slopes (straight, convex, and concave) in northeast China. Firstly, two types of soil, black soil and loess parent material were probed in a wood box to investigate the effect of soil moisture and bulk density on the soil permittivity and to prove the feasibility of GPR determination for black soil thickness. Then, the accuracy of the GPR in measuring black soil thickness was verified in conjunction with field trial excavation profiles and pre-buried iron pipes. 【Result】 (1) The soil permittivity increased and decreased with the increasing bulk density and soil moisture, respectively. The relationships among soil moisture, bulk density, and soil permittivity for both black soil and loess parent material can be represented by logarithmic equations with an accuracy of 95.26%～99.66%. (2) Compared with the actual thickness of the soil profile, the accuracy of GPR measurements for black soil thickness was 87.05%～95.58%. (3) The spatial distribution of black soil thickness differed among the three slopes. However, the overall wave-like variation was observed. Deposition occurred at the slope foot and the black soil thickness was thick, while the black soil thickness at the shoulder and back of the slope was thin where soil erosion was more serious. 【Conclusion】Soil moisture content and bulk density had a significant effect on soil permittivity and the soil permittivity decreased with the increasing clay content. Also, there were differences in the permittivity of black soil and loess parent material. It was observed that electromagnetic waves could be reflected at their interfaces, which means that GPR can be applied to detect the black soil thickness on loess parent material. Our analysis revealed that topographic factors significantly affected the spatial variation of black soil thickness among the three slope types studied. Based on these results, this study could provide an efficient and accurate method to investigate soil thickness for further evaluation and conservation of black soil resources.

Abstract:【Objective】To elucidate the effects of freeze-thaw cycles and initial water content on soil structure, rare earth oxides(REOs)were used as tracers to separate soil aggregates formation and breakdown processes. 【Method】REOs-labelled soil was reformed and investigated herein. Two initial water contents(50% field water holding capacity(T50)vs. 100% field water holding capacity (T100)) and five freeze-thaw cycles (0, 3, 6, 12 and 20 cycles) were involved in the simulation experiments. Soil aggregates distribution, mean weight diameter (MWD), and the aggregate turnover process were measured accordingly. 【Result】The results showed that freeze-thaw cycles significantly reduced MWD, > 0.25 mm aggregates and < 0.053 mm aggregates proportions, but increased the contents of 0.25～0.053 mm aggregates under the same initial water content. After 6 freeze-thaw cycles, MWD was significantly (P< 0.05) higher under T50 compared with that under T100, but there were no significant differences between the contents of 5～2 mm and < 0.25 mm aggregates. Except for 5～2 mm aggregates, the intensive transformation between neighboring size aggregates was observed during the whole simulation experiments. In the same freeze-thaw cycles, the transformation proportions from 5～2 mm to 0.25～0.053 mm aggregate were significantly (P < 0.05) higher under T100 compared with T50 treatment. The freeze-thaw cycles promoted the breakdown of > 0.25 mm aggregates and the formation of 0.25～0.053 mm aggregates both under T50 and T100 treatments. Also, MWD was significantly positively correlated with the relative formation of soil aggregates and negatively related with the relative breakdown of soil aggregates (P < 0.05). The turnover time of soil aggregate remarkably increased with the freeze-thaw cycles (P < 0.05) and the aggregate turnover time of > 0.25 mm aggregates was higher than that of < 0.25 mm aggregates. Comparatively, the aggregate turnover time was significantly higher under T100 than that under T50 with the same freeze-thaw cycle (P < 0.05). 【Conclusion】The freeze-thaw cycles and soil initial water content significantly affect the aggregate turnover. Both parameters change the stability of soil structure by affecting the aggregate formation and fragmentation processes. The results provide a theoretical basis for further exploration of the structural changes of black soil under freeze-thaw cycles.

Abstract:【Objective】 Antecedent moisture content is a critical factor affecting soil aggregate stability. However, its influence on the aggregate stability of lateritic soils developed from basalt has not been systematically investigated. To unravel the intricate interplay between soil properties, antecedent moisture content, and the water stability of lateritic soils developed from basalt, a meticulous investigation was undertaken. This study delved into the diverse land use types, aiming to shed light on the intricate relationship between these factors and aggregate water stability. 【Method】 In the latosol region of Hainan, a comprehensive study was conducted to examine the influence of three prevalent land use types, forest, cropland, and wasteland, on the soil properties and aggregate size distribution. Through a preliminary investigation, the tested soils were meticulously analyzed. The LB method, specifically the Fast Wetting variant, was employed to determine the aggregate size distribution within the 3-5 mm range across the various land use types. This assessment was performed under five distinct antecedent moisture contents of 3%, 5%, 10%, 15%, and 20%. Subsequently, water stability indices, including Water Stability Index (WSA), Mean Weight Diameter (MWD), and Geometric Mean Diameter (GMD), were meticulously calculated to provide valuable insights into aggregate water stability. 【Result】Distinctive variations in soil properties, encompassing pH, organic carbon, cation exchange capacity, and some exchangeable base cations, were prominently observed across different land use types. The distribution of water-stable aggregates in the lateritic soil exhibited either an unimodal or bimodal pattern, with peaks predominantly observed at 2-1 mm and 0.5-0.25 mm size fractions. Notably, forest soils displayed the highest aggregate stability among surface soils, while cultivated soils exhibited relatively weaker aggregate stability. Furthermore, subsurface soils demonstrated significantly lower aggregate stability (P<0.05) compared to surface soils. When considering air-dry conditions, characterized by moisture content during air-drying, the water stability of surface soil aggregates consistently exhibited high values(WSA>90%, MWD>1.5, GMD>1.2). As the antecedent moisture content increased, the proportion of macro aggregates (>2 mm) following aggregate fragmentation displayed varying degrees of change, ultimately resulting in an overall increase in the content of macro aggregates (>2 mm). It is noteworthy that the influence of land use type on aggregate water stability outweighed that of antecedent moisture content (F >56, P<0.01). Soil organic carbon (SOC) emerged as the primary factor explaining the variation in aggregate stability (R²=80.6%,PR² = 66.0%, P<0.01), while capillary porosity demonstrated a noteworthy negative correlation. Among the soil sesquioxides, aluminum oxides (Al_d, Al_o) exerted a considerably larger impact on aggregate stability compared to other sesquioxides. In contrast, the influence of antecedent moisture content on aggregate stability was relatively modest, displaying a significant negative correlation (R²= 24.0%, P<0.01). 【Conclusion】The water stability of lateritic soil aggregates, which developed from basalt, exhibited pronounced sensitivity to land use, with forested areas surpassing wastelands and croplands surpassing cultivated land in terms of water stability. Additionally, the water stability of these lateritic soil aggregates showed an initial increase followed by a subsequent decrease as the antecedent moisture content increased. Notably, when compared to red soil, lateritic soil aggregates displayed a lower sensitivity to dissipative effects. The primary determinant influencing the stability of lateritic soil aggregates is the concentration of SOC. Variations in the stability of these aggregates across different land uses can be attributed to fluctuations in SOC levels.

Abstract:【Objective】Soil hydrothermal parameters are fundamental physical parameters for studying soil thermal and hydraulic transport. Currently, the heat pulse probe HPP) method can synchronously measure soil hydrothermal parameters. However, but this method is limited to point-scale measurements, while the active heated fiber optic (AHFO) method holds the potential to extend the measurement scale to field-scale kilometers. 【Method】To investigate the errors of AHFO, we conducted comparative experiments between the AHFO and the HPP methods for measuring soil hydrothermal parameters. 【Result】 The results showed that, using the HPP method as a reference, the root mean square error (RMSE) of thermal conductivity measured by the AHFO method was 0.13 W·m^–1.·℃^–1. The thermal conductivity measured by the AHFO was significantly higher than that by the HPP method. This difference was attributed to the significant increase in temperature during the measurement by fiber optic which led to a temperature effect on the soil thermal conductivity around the fiber optic.【Conclusion】The measurement of error order of soil hydrothermal parameters using the AHFO method mainly originates from the contact thermal resistance between multiple interfaces (fiber optic core-air layer-metal layer-sheath-soil), the temperature sensitivity of the fiber optic, noise interference, and moisture migration under temperature gradients. This study can provide a theoretical reference for improving the accuracy of soil hydrothermal parameter determination by the AHFO method.

Abstract:【Objective】Undisturbed woodland and cultivated land soils from vertical and horizontal directions were collected across different latitudes in typical black soil regions in Northeast China for this research. The objective was to investigate the effects of long-term tillage in cultivated land on the black soil hydrological degradation. 【Method】 Nine typical cultivated land units were selected across three latitudes, including Jiusan Farm Management Area in Nenjiang (48°46′N), Hailun (47°30′N), and Bayan County in Harbin (46°23′N). Intact soil cores were collected from 0-15 and 15-30 cm depths in vertical and horizontal directions to determine soil penetration resistance (SPR), and hydraulic properties (water retention and saturated hydraulic conductivity (K_s). 【Result】 Results showed that soil SPR significantly increased in cultivated land compared to woodland, and the SPR in tillage pan layer (15-30 cm) (897.04 kPa) was 1.89 times higher than that in woodland. Soil hydraulic properties also significantly decreased in cultivated land, whose soil available water decreased to 0.15 (0.10-0.21) cm³·^–3 compared to 0.19(0.14-0.23) cm³·^–3 in woodland. Using soil physical quality index S to assess the over black soil quality showed that S value decreased from excellent 0.061 (0.041-0.094) in woodland to poor 0.025 (0.009-0.040) in cultivated land. The degradation of cultivated land quality was attributed to the significant reduction in soil organic matter content and significant increase in soil bulk density (1.31 g·cm^–3 in cultivated land vs. 1.03 g·cm^–3 in woodland). Long-term ridge tillage resulted in a 10 times reduction in Ks in tillage pan layer (6.61 cm·d^–1), and this can be attributed to the disruption of balance between tillage and tillage pan layer and enlargement of magnitude difference for Ks and bulk density between two layers. Tillage resulted in a lower K_s in the vertical direction (64.67 cm·d^–1)than in the horizontal direction (82.84 cm·d^–1) in the tillage layer. The K_s decreased in a larger degree in the vertical direction and less degree in the horizontal direction. Thus, this heterogeneity of K_s in directions interfered the original water movement direction in tillage layer. The low hydraulic conductivity of the plough pan tends to accumulate precipitation and produce lateral interflow.【Conclusion】 Generally, long-term tillage has severely degraded the physical and hydraulic properties of the soil. The huge difference of soil compactness and K_s between the tillage layer and plough pan produced an artificially stratified soil in cultivated land. The limitation of water infiltration is a dominant reason for the "furrow effect" in cultivated land.

Abstract:【Objective】This study aimed to understand the erosion mechanism of typical grassland in the Loess Plateau by analyzing the mechanical mechanism of soil detachment. 【Method】The representative grassland with tap roots and fibrous roots was selected as the research object in this study. Undisturbed soil samples were collected and subjected to flow scouring, and the relative soil detachment capacity (RSD) was calculated. The soil shear strength and root tensile force were determined, and the root cohesion was estimated based on Wu's model. 【Result】The RSD of grassland with fibrous roots was 77.27% significantly lower than that of grassland with tap roots, while the soil cohesion (C_r) was 14.84% higher than that of grassland with tap roots. The expression effect of C_ron RSD in the grassland with tap roots was better than that of root length density, and this effect was not obvious in the grassland with fibrous roots. The correlation between the RSD and soil shear strength under normal stress of 200 Kpa (τ₂₀₀) was better than the shear strength under other normal stresses. In the root-soil composite, the effect of C_ron soil detachment was stronger than that of τ₂₀₀. Additionally, the soil detachment capacity of the root-soil composite in the grassland with tap roots, could be effectively predicted by the mechanical parameters, but the prediction of soil detachment capacity in the grassland with fibrous roots need to be further explored. 【Conclusion】Thus, this study presents an effective way to analyze the soil detachment mechanism by mechanical properties of root-soil composites. The results could provide a reference for the study of the erosion reduction mechanism of roots in the Loess Plateau.

Abstract:【Objective】The contents of background chromium(Cr) and manganese(Mn) oxides in latosols are high. The dissolution of Cr and subsequent oxidation of Cr(III) in the soils may occur to produce Cr(VI) with high toxicity, thus, posing a threat to the surrounding environment and humans. Therefore, this study aimed to study the dissolution of Cr and the oxidation of Cr(III) in latosols collected from Yunnan, Hainan, and Guangdong Provinces to understand the ecological and environmental risks associated with chromium in latosols.【Method】The dissolution of Cr was investigated using batch experiment , while both batch and incubation experiments were used to investigate the oxidation of Cr(III) in the soils. The concentration of Cr in extractants was determined by an atomic absorption spectrometer. Also, dithionite-citrate-bicarbonate(DCB) extraction and electron probe scanning were used to examine the forms of Cr in the soils.【Result】The results of DCB extraction and electron probe scanning showed that Cr in latosols was mainly combined with iron oxides and silicates. Acidification by hydrochloric acid and complexation by citric acid promoted the dissolution of Cr from the soils. However, even in 1 mol·L^–1 hydrochloric acid, only 3.68% and 3.54% of total Cr was dissolved from the latosols of Hainan 3 and Guangdong 9, respectively, suggesting that Cr in latosols is stable and presents a low environmental risk. The oxidation of Cr(III) was observed in the soils during a 42-day incubation experiment. Based on the net production of Mn (II), Cr(VI) content, and organic matter content, it is probable that the Cr(VI) generated in the soils might be reduced to Cr(III) again by soil organic matter. The results of the batch experiment showed that the exogenous Cr(III) was oxidized to Cr(VI) in the latosols with organic matters removed, and the amount of Cr(III) oxidized was determined by the content of easily reducible Mn(III/IV) oxides in the soils. With the increase of suspension pH, the oxidized amount of Cr(III) increased firstly, reached the largest amount at pH 4.5 and then decreased. At this pH, only 1.48% of Cr(III) added was oxidized to Cr(VI). Although exogenous Cr(III) can be oxidized to Cr(VI) by soil Mn(III/IV) oxides in the latosols, the percentage of Cr(III) oxidized to Cr(VI) in the latosols was small, indicating that the risk of exogenous Cr(III) oxidization in the soils was very low.【Conclusion】Despite the high contents of background Cr and easily reducible Mn (III/IV) oxides in the latosols, the dissolution of Cr and oxidation of Cr(III) were difficult. This shows that under the experimental conditions, it was not easy to convert Cr(III) to Cr(VI) through oxidation reactions, therefore, the risk of background Cr in latosols is low.

Abstract:【Objective】 This study aimed to understand the soil stable organic carbon (SSOC) storage of natural grassland in the hinterland of the Qinghai-Tibet Plateau, and clarify its carbon fixation capacity and potential for increasing sinks. 【Method】The soil in the Three-River Source Region was divided according to regional space and three typical grassland types and the active layer soil was taken as the object. The soil total organic carbon (TOC) and Iron (aluminum)-bounded carbon [Fe(Al)-C] were analyzed, the relationship model was established with the geographical and climatic data, and the temporal and spatial variation law in recent 60 years(1961-2020) was retrieved. 【Result】The results show that: 1) The average content of Fe(Al)-C is 6.07 g·kg^–1and the average content of[Fe(Al)-C]/TOC is 16.87% in the Three-River Source Region, with obvious zonal characteristics. Also, the content in the central and eastern regions was significantly higher than that in the western region (P < 0.05); 2) The contents of Fe(Al)-C and[Fe(Al)-C]/TOC in the three types of grassland were 2.35～8.81 g·kg^–1and 11.99%～20.52%, respectively, and the alpine shrub meadow and alpine meadow were significantly higher than those in alpine steppe (P < 0.05). Fe(Al)-C was positively correlated with TOC in the three typical natural grassland types (P < 0.01). 3) The results of analog-digital mapping showed that the distribution area change of Fe(Al)-C in the Three-River Source Region has changed in the recent 20 years (2001-2020). Compared with the past two periods; 1961-1980 and 1981-2000, the distribution area with its content >5.75 g·kg^–1 and increased by 1.64% on average. 【Conclusion】From our analysis, it was deduced that whole area is in a state of carbon sink, and the C fixation potential of Fe(Al)-C in soils in the Three-River Source Region can not be overlooked.

Abstract:【Objective】Little or no research has been done on the carbon footprint and economic benefits of different rice planting patterns at the provincial level. Thus, a systematic analysis of the carbon footprint and economic benefits of different rice planting patterns is of great significance for carbon emission reduction of rice production and the development of low-carbon agriculture.【Method】Based on the survey data of rice farming in Jiangsu Province, the carbon footprint and economic benefits of different rice planting patterns in Jiangsu Province were quantitatively analyzed by using the life cycle assessment method.【Result】The results showed that from 2016 to 2020, the carbon footprint per unit area, the carbon footprint per unit yield, and the carbon footprint per unit value were 11.28-14.39 t·hm^–2,, 1.30-1.52 kg·kg^–1 and 0.49-0.58 kg·yuan^–1, respectively. The carbon footprint per unit area, per unit yield and per unit output value of different rice production and planting patterns were in order of broadcasted seeding rice or manual transplanting rice, mechanical transplanting rice, direct seeding rice. The carbon footprint per unit area of mechanical transplanting rice and manual transplanting rice production showed a decreased trend with the increase of years. Also, the carbon footprint per unit yield of mechanical transplanting rice, manual transplanting rice, and direct seeding rice production showed a decreased trend with the increase of years. Methane emissions from rice fields accounted for the largest proportion, followed by carbon footprints caused by nitrogen fertilization, nitrous oxide emissions from rice fields and carbon footprints caused by irrigation electricity. Nitrogen fertilizer and irrigation electricity were the main driving factors affecting the regional differences in the carbon footprint of different rice planting patterns. The total income of different rice planting patterns was between 2.51×10³- 2.75×10³ yuan·hm^–2, the resource input cost was 1.88×10³- 1.99×10³ yuan·hm^–2, the carbon emission cost was 0.20×10³- 0.25×10³ yuan·hm^–2, and the net income (NI_-CO2) considering carbon emissions was 0.39×10³- 0.64×10³ yuan·hm^–2. The NI_-CO2 of mechanical transplanting rice was lower than that of manual transplanting rice, broadcasted seeding rice and direct seeding rice. This was mainly caused by the higher total income and the lower resource input cost and carbon emission cost of mechanical transplanting rice.【Conclusion】In conclusion, direct seeding rice was the lowest carbon emission rice planting pattern. Considering the carbon emission and economic benefits, machinal transplanting rice was superior to manual transplanting rice, direct seeding rice and broadcasted seeding rice.

Abstract:【Objective】CH₄ is the second most potent greenhouse gas only next to CO₂. Continued CH₄ and CO₂ emissions by human activities pose a major challenge to the mitigation of global climate change. Rice paddy, a main form of artificial wetland, accounts for～8% of anthropogenic sources of CH₄. The elevated atmospheric CO₂(eCO₂) affect the cycling of nutrients and elements in paddy fields mainly through the changes in plant-soil-microbe interactions, which also influence net CH₄ flux associated with both the methanogenic and methanotrophic processes. However, how eCO₂ affects aerobic methane oxidation in paddy soils has rarely been examined, and the adaptative mechanisms of active methane-oxidizing bacteria(MOB)for eCO₂ remain unclear. This study aimed to explore the changes in methane-oxidizing rates and identify the active MOB phylotypes in paddy soil under the eCO₂ treatment.【Method】We collected paddy soil samples from China’s FACE(Free Air CO₂ Enrichment)experiment station, with FACE treatment and ambient CO₂ concentration treatment (aCO₂). The CH₄-feeding microcosm incubation was applied to learn the methane-oxidizing rates in the two soils. DNA-based stable isotope probing (DNA-SIP) combined with quantitative polymerase chain reaction (qPCR) of methane-oxidizing functional gene pmoA was used to identify the ¹³C-labeled DNA. High-throughput sequencing and phylogenetic analysis for the 16S rRNA gene amplicons of the ¹³C-DNA were used to identify the active microbiomes during methane oxidation.【Result】The results showed that eCO₂ significantly stimulated aerobic methane-oxidizing rate when compared to the ambient CO₂ treatment, with 302 and 243 nmol CH₄·g^–1 d.w.s·h^–1, respectively. The abundance of MOB increased by 1.1 folds -1.2 folds under eCO₂. A group of MOB assimilated ¹³CH₄ and synthesized ¹³C-DNA, which were separated into heavy fractions during DNA-SIP. The result of high-throughput sequencing for ¹³C-DNA showed that Methylobacter and Methylosarcina predominated the active MOB phylotypes. The relative abundance of Methylobacter increased by 16.2%-17.0% while the relative abundance of Methylosarcina decreased under eCO₂. eCO₂ also stimulated the activity of non-methanotrophic bacteria, such as Acidovorax and Pseudomonas, which implies a methanotrophy-induced microbial community response to eCO₂.【Conclusion】This study reveals positive effects of elevated atmospheric CO₂ on aerobic methane oxidation in paddy soil, with the predominant and active MOB of Methylobacter playing crucial roles, indicating an improved potential of methane oxidation under the scenarios of global climate change.

Abstract:【Objective】Sheath blight (ShB) is a soil-borne disease, whose occurrence and development seriously threatens rice (Oryza sativa L.) production. However, it is still unclear how elevated CO₂ concentration ([CO₂]) and temperature affect pathogenesis-related proteins (PR proteins) and defense enzymes in plants infected with Rhizoctonia solani.【Method】In this study, temperature by free-air CO₂ enrichment(T-FACE) system was used with four treatments: ambient condition; elevated [CO₂]([CO₂] up to 590 μmol·mol^–1); elevated temperature (temperature increased 2℃); the combination of elevated [CO₂] and elevated temperature. Two cultivars(a susceptible variety, Lemont and a resistant variety, YSBR1) were planted to explore the response of PR proteins and defense enzymes activities in leaves and stems for two cultivars by artificial inoculation of R. solani, as well as basic physical and chemical properties of soil.【Result】Results indicated that there was no significant difference in the growth rate of R. solani on soil extract medium, which was made by bulk soil under elevated [CO₂] and temperature. After inoculation with R. solani, the development rate of the ShB lesion was not related to the basic physical and chemical properties of soil. The combination of elevated [CO₂] and elevated temperature induced different effects on PR proteins and defense enzymes activities in the leaves of two cultivars. For the PR proteins and defense enzymes in stems, the combination of elevated [CO₂] and elevated temperature obviously increased the catalase (CAT), phenylalanine ammonia-lyase (PAL), β-1, 3-glucanase (GLU) or superoxide dismutase (SOD) activities for both Lemont and YSBR1. For different cultivars, after being infected with R. solani, the activities of PR proteins and defense enzymes in the leaves and SOD and CAT in the stems for YSBR1 were significantly higher than those for Lemont under different treatments, and the development rate of ShB lesion for YSBR1 was significantly lower than that for Lemont. During the whole disease infection, elevated [CO₂] and the combination of elevated [CO₂] and elevated temperature both significantly increased the development rate of rice ShB for Lemont by 21%-45%, but not for YSBR1. The correlation analysis showed that under different [CO₂] and temperature treatments, the development rate of ShB was significantly positively correlated with GLU activity in stems for Lemont and YSBR1.【Conclusion】After inoculated R.solani, the defense reaction formed by PR proteins and defense enzymes in resistant cultivar can effectively reduce the effect of elevated [CO₂] and temperature on the development rate of ShB in the future. This study can provide applications for breeding ShB-resistant cultivars to ensure global rice production under future climate change.

Abstract:【Objective】There are about 0.66 million hectares of coastal saline-sodic soil in Jiangsu that have not been developed and used as arable land for agriculture. This is because the saline-sodic soil has a higher concentration of salt that requires urgent ameliorating. 【Method】This study used waste phosphogypsum (PG), a kind of by-product from the phosphate industry, to conduct an amelioration experiment of saline-sodic soil in the field. Eight treatments were employed in the field experiment: no fertilizer and PG, fertilizer but no PG, and compound fertilizer + different amounts of PG. 【Result】Results showed that pH was decreased by 0.07～0.40 pH units in the depth of 0～20 cm topsoil treated with PG compared to the control. Soil bicarbonate and sodium ions decreased by 15.81%～43.53% and 17.25%～89.83%, respectively. The concentration of potassium ion, calcium ion, and organic matter in the amended soil treated with PG was increased by 8.17%～384.90%, 59.51%～1977.72%, and 4.51%～19.50%, respectively. Also, the amounts of total N and P in the wheat leaves in the PG treatment were increased by 7.85%～26.21% and 5.02%～35.97%, respectively, and the wheat grain yield increased by 11.41%～45.26%. Overall, PG can be used to ameliorate costal saline-sodic soil with better effectiveness. Mechanistically, the increase in calcium ions occurred as PG exchanged with sodium ions adsorbed in soil, and the sodium ions were leached underground during irrigation and rain to decrease the soil pH. Also, some acid-containing groups in PG were able to neutralize the bicarbonate ions to decrease the soil pH. PG increased the N uptake in wheat leaves and the yield of wheat grain due to the increased P from PG which induced a proportionate uptake of nutrients by the plant. Comprehensively, the best performance was the treatments of 30% compound fertilizer (1050 kg`hm<sup>-2</sup>)＋ PG (1125 kg`hm^-2) and 30% compound fertilizer (1050 kg`hm<sup>-2</sup>)＋ PG (2250 kg`hm^-2).【Conclusion】The positive effect of PG should not be considered proportional to the amount applied, because trace hazardous elements in PG could accumulate in the soil which will result in environmental risks and grain safety issues. Thus, proper care should be taken when using high doses of PG for soil amendment.

Abstract:【Objective】The objective of this study was to disclose the structural characteristics and the relationship with phosphorus validity in the promoted phosphate rocks (PPR), which were made by mixing low-grade phosphate rock powder and natural humic material materials.【Method】Continuous water extraction, X-ray diffraction (XRD), fourier transform infrared spectrometry (FTIR), and pot experiment were carried out to explore the phosphorus validity mechanism of PPR from dynamic release, structural characteristics and fertilizer effects. 【Result】The results showed that the release of water-soluble phosphorus showed an increasing trend with the increase of activator addition. After five leachings, the total water-soluble phosphorus released was 1.54 and 1.72 times higher than that of the control treatment when the mass ratio of natural humic material or HNO₃-treated natural humic material mixed with low-grade phosphate rock powder was 20: 80. X-ray diffraction analysis showed that the characteristic diffraction peaks corresponding to P₂O₅ and Ca(PO₃)₂ showed a significant decrease after five leaching of natural humic material or HNO₃-treated natural humic material mixed with low-grade phosphate rock powder. The results of FTIR spectral analysis showed that the disappearance of the PO₄^3- symmetric stretching vibration v₁ at 966 cm^-1 was evident after five leaching cycles of natural humic material or HNO₃-treated natural humic material mixed with low-grade phosphate rock powder, while the intensity of the PO₄^3- asymmetric stretching vibration v₃, H₂PO₄^- associated absorption peaks, and HPO₄^2- associated absorption peaks at 1 127, 673 and 612 cm^-1 were significantly decreased. The pot experiment further showed that natural humic material or HNO₃-treated natural humic material as a high-quality organic material applied at 6 g`kg<sup>-1</sup> or 9 g`kg^-1 while mixed with low-grade phosphate powder at a 20: 80 mass ratio could significantly increase the available phosphorus content of the soil, while rapidly increasing the soil organic matter content. When natural humic material was applied at 9 g`kg^-1 and mixed with low-grade phosphate powder at a mass ratio of 20: 80, soil available phosphorus was increased by 29.86%, 29.47%, and 36.48% while soil organic matter was increased by 34.16%, 8.05%, and 47.40%, respectively, compared to control treatment on days 14, 30, and 60 after sowing. Also, when HNO₃-treated natural humic material was applied under similar conditions, soil available phosphorus was increased by 36.97%, 94.44%, and 34.51% while soil organic matter was increased by 27.29%, 14.57%, and 45.41%, respectively, compared with control treatment on days 14, 30, and 60 after sowing.【Conclusion】Natural humic material or HNO₃-treated natural humic material with acidic pH, high specific surface area, high humus content and a high number of active functional groups were responsible for enhancing the water-soluble phosphorus content of low-grade phosphate rock powder and soil available phosphorus.

Abstract:【Objective】China depends heavily on agricultural potassium fertilizer imported from abroad. Thus, it is important to improve potassium utilization efficiency by changing the existing forms of potassium.【Method】In this paper, a two-year field trial (in 2020 and 2021) was set up using Virginia-type peanut Huayu 22 to investigate the effects of inorganic potassium (free ionic state) and sorbitol chelated potassium on peanut yield, dry matter accumulation, potassium accumulation, and bacterial community structure in peanut rhizosphere soil by a completely randomized block design. Under the premise of conventional fertilization, peanut spraying experiments were carried out at different growth stages and with five treatments: CK, water control; IK, inorganic potassium; MK, sorbitol mixed inorganic potassium; SK, sorbitol chelated potassium (self-made); and LK, commercially available chelated potassium (Canada).【Result】The results showed that foliar topdressing potassium fertilizer on leaves could significantly increase the peanut yield. Compared with the treatment of IK or LK treatments, the two-year average yield of SK treatments increased by 18.9% and 14.97%, respectively. The yield components of 100-seed weight, 100-pod weight, and full fruit rate were all significantly improved. Also, the dry matter accumulation and potassium accumulation of peanut plants treated with sorbitol-chelated potassium were significantly increased. Compared with CK, IK, and LK treatments, the total dry matter of peanut plants treated with SK increased by 19.5%, 19.1%, and 15.7% in the stage of the full pod, and increased by 22.8%, 27.4%, and 11.7% at the mature stage, respectively. Potassium accumulation in peanut kernels increased by 30.6%, 49.8% and, 44.8% in the stage of full pod, and increased by 30.8%, 59.1%, and 10.8% at the mature stage, respectively. The above results showed that self-made sorbitol-chelated potassium could promote the absorption and distribution of potassium nutrients in plants. Furthermore, the microbial diversity and richness of peanut rhizosphere soil increased under SK treatment compared with the other treatments. Compared with CK, MK, and LK treatments, the Sobs index of microbial communities in SK treatment increased by 10.7%, 12.5%, and 10.7%, respectively. The species significantly enriched in SK treatment were p-Verrucomicrobiota_g-Roseimicrobium and p-Planctomycetota_c-vadinHA49. The correlation analysis showed that the increase in production was significantly related to the absorption and distribution of potassium and the changes in rhizosphere microorganisms.【Conclusion】In summary, compared with inorganic potassium form, sorbitol-chelated potassium could promote the absorption and accumulation of potassium in peanuts at the same potassium application level, which is comprehensively reflected in production. The research results could provide theoretical and practical references for improving potassium efficiency.

Abstract:【Objective】The low availability of iron in calcareous soil leads to serious iron-deficiency chlorosis in plants. Thus, it is important to screen highly efficient iron-solubilizing bacteria and explore their collaboration with mycorrhizal fungi (AM) to increase the available iron content and improve plant iron nutrition. 【Method】Pot experiments were conducted with calcareous soil and tomato (Lycopersicon esculentum) as test materials. They were inoculated with Advenella kashmirensis(B1), Arthrobacter cupressi (B2), Klebsiella variicola(B3), Variovorax guangxiensis (B4) and Enterobacter ludwigii (B5), and treatment with no bacteria inoculation as the control group (CK). Efficient iron-solubilizing bacterial strains B1, B2 and B3 were screened and combined with AMF (Rhizoshagu irregularis, Ri)as B1+Ri, B2+Ri, B3+Ri and B1+B2+B3+Ri treatments. Also, AM fungi were inoculated alone (Ri) to explore the mechanism of synergistic effect between different iron-solubilizing bacteria and AMF to mobilize insoluble iron in calcareous soil and promote iron absorption in plants. 【Result】The results showed that compared with the control treatment, inoculation with B1, B2 and B3 strains could significantly increase the tomato biomass and the total iron accumulation in root and shoot increased by 6.48 and 2.61, 4.11 and 2.03, 4.37 and 2.25 times, respectively. The active iron content in new leaves increased by 74.21%, 1.33 times and 1.75 times. Compared with inoculation with AMF alone, different co-inoculation combinations significantly increased the tomato biomass, and the average total iron accumulation in different parts of the plant increased by 58.32%-119.43%. Under B3+Ri and B1+B2+B3+Ri treatments, the active iron content in tomato roots increased by 41.47% and 44.30%, and new leaves increased by 12.61% and 12.77%, respectively. Different co-inoculation combinations could effectively improve the root architecture of the plant, and the mycorrhizal infection rates of AM fungi under different co-inoculation treatments were 13.35%-30.99% higher than those under inoculation alone. The root iron reductase activity was significantly increased by 9.86%-22.07% compared with the inoculation with AM fungi alone, and the relative expressions level of LeFIT1,LeFRO2 and LeMYB72 in tomato roots was significantly up-regulated. Compared with exclusive AMF inoculation, B3+Ri and B1+B2+B3+Ri treatments reduced the rhizosphere soil pH value by 0.21 and 0.09, respectively, but increased the soil available Fe content by 15.78% and 55.23%.【Conclusion】It was concluded that the synergistic effect of AM fungi and three high-efficiency iron-solubilizing bacteria could significantly improve iron availability in calcareous soil and enhance plant iron nutrition. However, the synergistic mechanism between different types of iron-solubilizing bacteria and AMF was different and provided a microbial approach to solve the problem of low iron availability in calcareous soil.

Abstract:【Objective】This study aimed to investigate the long-term and synergistic effects of Biochar and organic fertilizer on dissolved organic matter (DOM) in paddy soil. 【Method】Several fertilization treatments were tested over five years, including a control (CK), biochar (BC), fertilizer(N), biochar+fertilizer (N+BC), manure+fertilizer (MF, 25% nitrogen replacement), and manure+fertilizer+biochar(MF+BC, 25% nitrogen substitution). The effects of these treatments on soil pH, total nitrogen, available phosphorus, accessible potassium, soil organic carbon (SOC), readily oxidizable organic carbon (ROC), and dissolved organic carbon were examined. The spectral properties and fluorescence components of DOM were characterized using the ultraviolet-visible spectrum (UV-Vis), fluorescence spectrum, and parallel factor analysis. Also, the specific UV absorbance, UV absorption slope rate, fluorescence index, biological index, humification index, and relative amounts of fulvic acid, tryptophan, and humic acid of the DOM were examined. 【Result】The results showed that by utilizing biochar and organic fertilizer, soil acidity could be decreased and rice productivity effectively increased. The MF+BC treatment had the highest rice productivity and soil available phosphorus of all the treatments. Significantly(P＜0.05)favorable correlations between rice yield and DOM's bioavailability, aromatization, humification, tryptophan concentration, and hydrophilicity were found. The order of the degree of humification and bioavailability increase in DOM was manure > biochar. Furthermore, biochar significantly increased DOM, fulvic acid, and tryptophan components and promoted the conversion of ROC to dysoxidizable-organic carbon, whereas organic fertilizer increased ROC, fulvic acid, tryptophan, and humic acid components. The application of Biochar and organic fertilizer had an interaction effect on the increase of rice production, ROC, DOM, fulvic acid, tryptophan, aromatization, humification, and DOM bioavailability. 【Conclusion】Thus, the combined application of biochar and organic fertilizers increased rice yield while also enhancing the functional diversity of organic carbon and DOM components in paddy soil.

Abstract:【Objective】The combined application of crop straw with chemical fertilizers and chicken manure can change soil microbial community structure and the interaction between microorganisms. However, whether there is a correlation between these changes and wheat yield remains unclear.【Method】A 7-year field experiment was used as the research platform, and this included five management strategies: (1) N0S0: no fertilizer or crop straw returning, (2) N0S: crop straw returning, (3) NS0: traditional chemical fertilization, (4) NS: crop straw returning with chemical fertilizer, and (5) NSM: crop straw returning with chemical fertilizer and the nitrogen was substituted 20% by chicken manure. The effects of different management strategies on microbial community composition in bacterial-fungal co-occurrence networks and the correlation between key microorganisms and wheat yield were studied.【Result】The results showed that compared with N0S0 treatment, the grain yield of wheat under NS0, NS and NSM treatments increased by 539.20%, 611.56% and 676.56%, respectively, while there was no significant change under N0S treatment. The bacterial and fungal community compositions were divided into three significantly different groups: N0S0 and N0S, NS0, and NS and NSM, respectively, indicating that the microbial community composition was significantly different with or without chemical fertilizer application. Under both chemical fertilizer applications, there was a significant difference in whether organic materials were applied. Ranked from high to low importance, we found that available phosphorus, electrical conductivity, microbial biomass nitrogen, soil organic carbon, readily oxidizable organic carbon, and particulate organic carbon were the main soil physicochemical properties that caused the changes in bacterial community composition under different treatments. Also, electrical conductivity, microbial biomass nitrogen, readily oxidizable organic carbon, particulate organic carbon, available phosphorus, and soil organic carbon were the main soil physicochemical properties that caused the changes in fungal community composition under different treatments. In the bacterial-fungal co-occurrence network, two key modules (module 1 and module 4) were significantly correlated with wheat yield changes. NS+NSM treatments increased the relative abundance of beneficial microorganisms in module 4, including Nocardioides, Cellulomonas, Pir4_lineage, Chrysosporium,Acaulium, and Schizothecium, which were positively correlated with wheat yield. These beneficial microorganisms could degrade cellulose and lignin, promote nutrient conversion and recycling, or inhibit the growth of the potential pathogen. NS+NSM treatments also significantly reduced the relative abundance of plant pathogenic fungi in module 1, including Stachybotrys,Achroiostachys, and Fusicolla, which were negatively correlated with wheat yield and were detrimental to soil health and crop growth.【Conclusion】Therefore, crop straw returning with chemical fertilizer and crop straw returning with chemical fertilizer and chicken manure were beneficial to the increase of key beneficial microorganisms and the decrease of pathogenic fungi. The function and the relative abundance of key microorganisms had effects on wheat yield.

Abstract:【Objective】This study aimed to understand the role of glomalin in maintaining soil organic carbon (SOC) balance and soil aggregate stability, and construct management strategies for improving soil structure and soil quality. 【Method】 To fully understand glomalin, published data in recent years (332 sets of data from 19 literature) were collected, the distribution characteristics of glomalin in soil aggregates were quantitatively analyzed, and its influencing factors were systematically analyzed. Moreover, the distribution of glomalin in soil aggregates under different land uses was compared. 【Result】The results showed that the mass percentages of the > 2 000 μm and 2 000-250 μm aggregates (about 40%, respectively) were significantly higher than that of the 250-53 μm aggregates ( about 20%). The proportion of easily extractable glomalin in total glomalin was 20% in<53 μm aggregates, which was lower than other particle sizes (> 30%). There was no significant difference in the glomalin-C in SOC in different aggregates. The proportion of easily extractable glomalin-C in aggregates of different particle sizes was about 2%, while the proportion of total glomalin-C was about 8%.【Conclusion】In the >250 μm aggregates, GRSP (glomalin related soil protein) increased with the increase of temperature and precipitation, but decreased with the increase of pH. Although these correlations were not found in <250 μm aggregates, there was a significant positive correlation between glomalin and SOC. By comparing different land use patterns, it was found that the glomalin in the aggregates of forest soil was more than those in farmland and grassland, which indicated that forest soil was more conducive to the accumulation of glomalin than farmlands and grasslands.

Abstract:Temperature and exogenous arsenic are important factors affecting rice growth. Due to climate warming, rice growth is affected by a combination of temperature and arsenic in rice fields contaminated by arsenic. Clarifying the combination can provide a theoretical basis for rice management and safety production.【Method】Germination and culture experiments were carried out in the artificial climate chamber under the condition of different exogenous arsenic concentrations [0(As0), 0.5(As0.5) and 1(As1) mg`L^-1] and different temperature simulations [daytime/nighttime 30℃/25℃(T0) and 35℃/30 ℃(T1)] using eight common rice varieties in Jiangsu Province. Seed germination, seedling growth and arsenic uptake of different rice varieties were analysed. 【Result】The results showed that exogenous arsenic inhibited sprout length and vigor index of rice. Compared with T0As0, T0As1 reduced the sprout length and vigor index of different rice varieties by 13.69%-43.34% and 28.14%-52.88%, respectively, and the effect of temperature on rice seed germination was related to rice varieties. Under the condition of T1 treatment, the germination rate, sprout length and vigor index of Yanliangyou 1618 were better than those of other varieties. The interaction of temperature and exogenous arsenic significantly decreased the sprout length (P < 0.05). Compared with T0As0, T1As1 decreased sprout length by 5.66%-43.34%. Also, single temperature or exogenous arsenic had a significant effect on rice root length and root vigor. Compared with T0As0, T0As1 reduced root vigor by 3.01%-58.21%. The interaction of temperature and exogenous arsenic inhibited rice root length and root vigor. Compared with T0As0, T1As1 significantly reduced root vigor of different rice varieties by 53.80%-89.01%. The seedling height and root vigor of different rice varieties had significant differences (P < 0.05) under the same treatment of temperature or exogenous arsenic, among which the seedling height and root vigor of Yanliangyou 888 were at higher levels. The arsenic concentration in rice stems and leaves increased significantly under exogenous arsenic while the arsenic concentration in rice stems and leaves decreased under the increase in temperature. Furthermore, compared with single arsenic treatment, arsenic concentration in rice stems and leaves decreased under the interaction of temperature and exogenous arsenic. 【Conclusion】From the above results, it can be concluded that temperature and exogenous arsenic affected rice growth and arsenic uptake. However, rice growth conditions and arsenic concentration were significantly different among rice varieties. The germination and growth of Yanliangyou 888 and Yanliangyou 1618 were better than other rice varieties under the condition of temperature and exogenous arsenic.

Abstract:【Objective】This study examined the effect and mechanism by which nano-sized iron oxide regulates crop tolerance to salt. 【Method】Nanoparticle Fe₃O₄(Fe₃O₄NPs) with a particle size of about 10 nm was synthesized by the coprecipitation method and characterized by X-ray diffractometry and electron microscopy. Selected tomato seeds were soaked in 0, 1, 10, 50, 100, 200, 300, and 400 mg·L^-1of Fe₃O₄NPs solution and the effects on seed germination, seedling growth and antioxidant system under NaCl stress were evaluated. 【Result】 Fe₃O₄NPs with a particle size of 10 nm were synthesized and successfully passed the characterization analysis and identification. It was found that under salt stress, soaking tomato seeds in 1 mg·L^-1Fe₃O₄NPs reduced seed germination. However, seed germination was improved as the concentration of Fe₃O₄NPs was increased. Under 100 mmol·L^-1NaCl stress, the seed germination potential and hypocotyl length after soaking in 200 mg·L^-1Fe₃O₄NPs reached the peak, which was significantly higher than those treated with salt stress only. Salt stress of 100 mmol·L^-1NaCl significantly reduced the seedling rate, fresh biomass and water content of tomato seedlings, and this negative trend was intensified after soaking the seeds in 1 mg·L^-1Fe₃O₄NPs. With an increase in the concentration of Fe₃O₄NPs, the negative impact of salt stress was alleviated and the fresh biomass and water content of seedlings soaked with 200 mg·L^-1Fe₃O₄NPs reached the peak, which was significantly higher than those treated only with salt. Under salt stress, the activities of superoxide dismutase (SOD) and peroxidase (POD) in tomato seedlings soaked in 1 mg·L^-1Fe₃O₄NPs increased significantly, while the activity of catalase (CAT) decreased significantly. With an increase in the concentration of Fe₃O₄NPs, the activities of SOD and POD gradually decreased and then gradually increased while that of CAT gradually increased and then decreased. Specifically, the activities of SOD and POD in seedlings treated with 100-200 mg·L^-1 Fe₃O₄NPs were the lowest, while the activity of CAT was the highest. Also, the contents of malondialdehyde (MDA), proline (Pro), superoxide anion (O₂^·－) and hydrogen peroxide (H₂O₂) in seedlings treated with 200 mg·L^-1Fe₃O₄NPs were the lowest of all treatments. The correlation analysis showed that the fresh biomass and seedling rate of seedlings were significantly negatively correlated with the activities of SOD and POD, as well as the contents of MDA and reactive oxygen species. 【Conclusion】 Fe₃O₄NPs with a particle size of 10 nm were prepared by the coprecipitation method. It was found for the first time that the germination and emergence of tomato seedlings under salt stress could be mitigated by Fe₃O₄NPs and the effect was proportional to the concentrations of Fe₃O₄NPs. For example, treating seeds with 1 mg·L^-1 Fe₃O₄NPs inhibited germination due to increased oxidative stress whereas 200 mg·L^-1 Fe₃O₄NPs showed significant promotion of germination, seedling formation and seedling strength. This study provides scientific basis and technical support for the application of nanomaterials to improve agriculture in saline soil.