Soil In Southern China Research Articles

Effect of UV exposure and natural aging on the in vitro PAHs bioaccessibility associated with tire wear particles in soil

Tire wear particles (TWP), as an emerging type of microplastics, are a significant source of contaminants in roadside soils due to their high concentration of pollutants, including polycyclic aromatic hydrocarbons (PAHs). This study explored the impact of ultraviolet (UV) exposure and natural aging on the in vitro bioaccessibility of PAHs associated with TWP in soil on a China-wide scale. Our findings suggested that UV exposure amplified the negative charge of TWP by 75 % and increased the hydrophobic groups on the particle surface. The bioaccessibility of 3- and 4-ring PAHs in TWP was significantly (p < 0.05) heightened by UV exposure. After 20 types of soils containing 2 % UV-exposed TWP underwent natural aging, the bioaccessibility of PAHs saw a significant decrease (p < 0.05) to 16–48 %, compared to 28–96 % in the unaged group. Soil pH and electrical conductivity (EC) were the two primary soil properties positively influencing the reduction of in vitro PAHs concentration and PAHs bioaccessibility. According to the prediction results, soils in southern China presented the highest potential region for the release of bioaccessible PAHs from TWP, highlighting the regional specificity of environmental impact. Our study provides valuable insights into the biological impact of PAHs associated with TWP on a regional scale, and offers scientific evidence for targeted soil risk management strategies.

Straw removal reduces Cd availability and rice Cd accumulation in Cd-contaminated paddy soil: Cd fraction, soil microorganism structure and porewater DOC and Cd

The impacts of straw removal on rice Cd absorption, behaviour of Cd and microbial community in rhizosphere soil were investigated in paddy fields over two consecutive seasons. The results of the experiments in two fields revealed that straw removal promoted the transformation of soil Cd from acid-extractable and oxidisable fraction to residual fraction and reduced soil DTPA-Cd content with the reduction in DOC and Cd ions in soil porewater, thereby decreasing Cd content in rice. Specifically, the Cd content in brown rice was below 0.2 mg·kg−1 when all rice straw and roots were removed in the slightly Cd-contaminated soils. The α-diversity of soil microbial communities was less influenced by continuous straw removal, β-diversity was altered and the relative abundances of Anaeromyxobacter, Methylocystis and Mycobacterium microbes were increased. Redundancy analysis and network analysis exhibited that soil pH predominantly influenced the microbial community. Path analysis revealed that the Cd content in brown rice could be directly influenced by the soil Total-Cd and DTPA-Cd, as well as soil pH and OM. Straw removal, including roots removal, is an economical and effective technique to reduce Cd accumulation in rice plants.

Cadmium Phytoremediation Effect of Sweet Sorghum Assisted with Citric Acid on Typical Parent Soil in Southern China

Sweet sorghum has a large biomass and strong cadmium (Cd) absorption capacity, which has the potential for phytoremediation of Cd-contaminated soil. In order to study the Cd phytoremediation effect of sweet sorghum assisted with citric acid on the typical parent materials in southern China, a field experiment was carried out in two typical parent material farmland areas (neutral purple mud field and jute sand mud field) with Cd pollution in Hunan Province. The results showed that:① Citric acid had no inhibitory effect on the growth of sweet sorghum. After the application of citric acid, the aboveground biomass of sweet sorghum at the maturity stage increased by 10.1%-24.7%. ② Both sweet sorghum planting and citric acid application reduced the soil pH value, and the application of citric acid further reduced the soil pH value at each growth stage of sweet sorghum; this decrease was greater in the neutral purple mud field, which decreased by 0.24-0.72 units. ③ Both sweet sorghum planting and citric acid application reduced the total amount of soil Cd, and the decreases in the neutral purple mud field and jute sand mud field were 23.8%-52.2% and 17.1%-31.8%, respectively. The acid-extractable percentage of soil Cd in both places increased by 38.6%-147.7% and 4.8%-22.7%, respectively. ④ The application of citric acid could significantly increase the Cd content in various tissues of sweet sorghum. The Cd content in the aboveground part of the plant in the neutral purple mud field was higher than that in the jute sand mud field, and the Cd content in stems and leaves was 0.25-1.90 mg·kg-1 and 0.21-0.64 mg·kg-1, respectively. ⑤ After applying citric acid, the Cd extraction amount of sweet sorghum in neutral purple mud soil in the mature stage reached 47.56 g·hm-2. In summary, citric acid could enhance the efficiency of sweet sorghum in the phytoremediation of Cd-contaminated soil, and the effect was better in neutral purple mud fields. This technology has the potential for remediation coupled with agro-production for heavy metal-contaminated farmland.

Co-enrichment of selenium and cadmium in soils of southern China and its implication for the safe utilisation of selenium-rich lands

Dietary deficiency of selenium (Se) is a global health threat related to low Se concentrations in crops. Southern China has abundant Se-rich land resources, but the cadmium (Cd) pollution problem is prominent, which may lead to Cd exceeding the safety standard in Se-rich crops. Therefore, it is important to delineate Se-rich land without Cd pollution in order to develop green Se-rich agriculture. Based on soil/sediment geochemical survey data covering 2.3 million km2 of southern China, this study analysed the concentration and spatial distribution of Se and Cd, discussed their enrichment mechanisms and proposed suggestions for the safe use of Se-rich land. The results showed that the soil/sediments in southern China were significantly enriched in Se and Cd, and the median values were 0.31 mg·kg−1 and 221 μg·kg−1, which were 1.8 times and 2.5 times the national soil background values, respectively. In addition, a significant positive correlation was observed between Se and Cd, indicating that Cd contamination in Se-rich soils frequently exceeded the pollution limit. According to statistics, Se-rich land accounted for 32.13 % of southern China. However, due to the co-enrichment of Se and Cd, areas without Cd pollution accounted for only one-third of the total Se-rich area. In particular, the areas with co-enrichment of SeCd are primarily distributed in Yunnan, Guizhou, Guangxi, western Hubei, northwestern Zhejiang, western Hunan, southern Hunan and northern Guangdong. The enrichment of Se is predominantly associated with parent rocks (black and carbonate rocks). At the same time, the enrichment of Cd is influenced by the parent rocks and PbZn mineralisation and mining activities. Three recommendations for managing Se-rich land were proposed: imposing restrictions on the utilisation of heavily contaminated Se-rich land for agricultural production, adopting a rational approach towards utilising lightly polluted Se-rich land and actively promoting the development of Se-rich agriculture in uncontaminated Se-rich areas. In the future, it is necessary to develop technologies that simultaneously enhance Se absorption while inhibiting Cd absorption in order to safely exploit Se-rich lands affected by Cd pollution.

Magnesium fertilizer application increases peanut growth and pod yield under reduced nitrogen application in southern China

This study investigated the effect of magnesium application on peanut growth and yield under two nitrogen (N) application rates in acidic soil in southern China. The chlorophyll content, net photosynthetic rate and dry matter accumulation of the N-sensitive cultivar decreased under reduced N treatments, whereas no effect was observed on the relevant indicators in the N-insensitive variety GH1026. Mg application increased the net photosynthetic rate by increasing the expression of genes involved in chlorophyll synthesis and Rubisco activity in the leaves during the pegging stage under 50%N treatment, while no effect on the net photosynthetic rate was observed under the 100%N treatment. The rate of dry matter accumulation at the early growth stage, total dry matter accumulation and pod yield at harvest increased after Mg application under 50%N treatment by increasing the transportation of assimilates from stems and leaves to pods in both peanut varieties, whereas no effect was found under 100%N treatment. Moreover, Mg application increased the NUE under 50%N treatment. No improvement of NUE in either peanut variety was found under 100%N treatment, while Mg application under the 50%N treatment can obtain a higher economic benefit than the 100%N treatment. In acidic soil, application of 307.5 kg ha−1 of Mg sulfate fertilizer under 50% reduced nitrogen application is a suitable fertilizer management measure for improving carbon assimilation, NUE and achieve high peanut yields in southern China.

Asynchronous characteristics of Feammox and iron reduction from paddy soils in Southern China

Recently, the newly discovered anaerobic ammonium oxidation coupled with iron reduction (i.e., Feammox) has been proven to be a widespread nitrogen (N) loss pathway in ecosystems and has an essential contribution to gaseous N loss in paddy soil. However, the mechanism of iron-nitrogen coupling transformation and the role of iron-reducing bacteria (IRB) in Feammox were poorly understood. This study investigated the Feammox and iron reduction changes and microbial community evolution in a long-term anaerobic incubation by 15N isotope labeling combined with molecular biological techniques. The average rates of Feammox and iron reduction during the whole incubation were 0.25 ± 0.04 μg N g−1 d−1 and 40.58 ± 3.28 μg Fe g−1 d−1, respectively. High iron oxide content increased the Feammox rate, but decreased the proportion of Feammox–N2 in three Feammox pathways. RBG-13-54-9, Brevundimonas, and Pelomonas played a vital role in the evolution of microbial communities. The characteristics of asynchronous changes between Feammox and iron reduction were found through long-term incubation. IRB might not be the key species directly driving Feammox, and it is necessary to reevaluate the role of IRB in Feammox process.

Cadmium toxicity to and accumulation in a soil collembolan (Folsomia candida): major factors and prediction using a back-propagation neural network model.

Accurate prediction of cadmium (Cd) ecotoxicity to and accumulation in soil biota is important in soil health. However, very limited information on Cd ecotoxicity on naturally contaminated soils. Herein, we investigated soil Cd ecotoxicity using Folsomia candida, a standard single-species test animal, in 28 naturally Cd-contaminated soils, and the back-propagation neural network (BPNN) model was used to predict Cd ecotoxicity to and accumulation in F. candida. Soil total Cd and pH were the primary soil properties affecting Cd toxicity. However, soil pH was the main factor when the total Cd concentration was < 3mgkg-1. Interestingly, correlation analysis and the K-spiked test confirmed nutrient potassium (K) was essential for Cd accumulation, highlighting the significance of studying K in Cd accumulation. The BPNN model showed greater prediction accuracy of collembolan survival rate (R2 = 0.797), reproduction inhibitory rate (R2 = 0.827), body Cd concentration (R2 = 0.961), and Cd bioaccumulation factor (R2 = 0.964) than multiple linear regression models. Then the developed BPNN model was used to predict Cd ecological risks in 57 soils in southern China. Compared to multiple linear regression models, the BPNN models can better identify high-risk regions. This study highlights the potential of BPNN as a novel and rapid tool for the evaluation and monitoring of Cd ecotoxicity in naturally contaminated soils.

Analysis of physiological response and differential protein expression of Paramichelia baillonii saplings under phosphorus deficiency.

Paramichelia baillonii is a rare and fast-growing tree species in subtropical China. The acidic red soil in southern China severely limits its growth as it lacks sufficient available phosphorus (P), resulting in declining soil fertility and nutrient availability. The effect of P deficiency on P. Baillonii growth, root attributes, and physiological response has not yet been reported. Understanding the adaptability of P. baillonii to low-P conditions can improve afforestation and soil management in southern China. Therefore, we conducted a pot experiment on 2-year-old saplings and treated them with different P levels. Results showed that P deficiency (0-5 mg L-1 ) decreased growth attributes, root morphological traits, and nutrient uptake of P. baillonii saplings compared to control (CK). Similarly, reduction in chlorophyll a, b, total chlorophyll, net photosynthetic rate (Pn), transpiration rate (Tr), and Gs were seen in low P treatment saplings compared to CK. Whereas superoxide dismutase, peroxidase, malondialdehyde, acid phosphatase activity, and soluble protein content increased with increasing P-deficiency up to 5 mg L-1 , and soluble sugar showed oppsite trend. Moreover, the proteomics analysis identified 2721 proteins, 196 showing differential expression, with 90 up- and 106 down-regulated. Importantly, the metabolic activities increased in the pentose phosphate pathway, starch and sucrose metabolism, amino sugar and nucleotide sugar metabolism, and phenylpropanoid biosynthesis pathways to sustain regular plant growth under P deficiency. This study delves into the dynamic morpho-physiological and proteomic changes in response to P deficiency. Overall, growth and nutrient uptake were reduced, countered by adaptive biochemical and proteomic shifts, including heightened antioxidant activities and modifications in metabolic pathways, highlighting the resilient strategies of P. baillonii saplings under P deficiency.

A New Perspective on the Applicability of Diffuse Reflectance Spectroscopy for Determining the Hematite Content of Fe-Rich Soils in the Tropical Margins of China

Hematite and goethite are widely occurring chromogenic iron oxides in soils and sediments that are sensitive to climatic dry/wet shifts. However, only by accurately quantifying the content or ratio of hematite and goethite can they be applied reliably to palaeoclimate reconstruction. Compared to the Loess Plateau of China, hematite in the soils of southern China has not been sufficiently studied. We used diffuse reflectance spectroscopy (abbreviation DRS, including the first-derivative curves and the second-derivative curves of the Kubelka–Munk remission functions), combined with ignition at 950 °C, and X-ray fluorescence (XRF) to quantify the hematite content of four tropical-margin iron-rich soil profiles with different matrix compositions in the Leizhou Peninsula, China. We also examined the application of hematite quantification parameters in soils with different matrix compositions under the same climatic conditions. Our main findings are as follows: (i) DRS first-derivative curves can reflect the presence of goethite and hematite in soils, and their relative contents can be compared within the same profile. (ii) The second-derivative curve of the Kubelka–Munk remission functions can reflect the relative proportions of goethite and hematite and provide information about the degree of Al substitution. (iii) Combined with calibration equations, soil redness can reliably quantify the hematite content, but it is necessary to consider the effect of mucilage envelopes in the process of hematite formation. Additionally, we summarize various methods used for quantifying hematite, and the influence of soil matrix compositions, with the aim of providing a reference for hematite quantification elsewhere. We also propose a new indicator (ΔHmRed/HmRed) to help detect iron hydroxide/iron oxide changes in soils.

Thermal Effects on the Soil Water Retention Curves and Hydraulic Properties of Benggang Soil in Southern China

Soil hydraulic properties significantly affect the occurrence and development of collapsing gully walls. The effect of temperature on the hydraulic properties of soil in collapsing gully walls remains unclear. In this study, the hydraulic properties of the red soil layer, the sandy soil layer and the detritus layer in a collapsing gully wall were investigated using the filter paper method, and the soil water retention curves of the different soil layers at 25 and 40 °C were determined. The aim of this study was to investigate the impact of temperature on the soil hydraulic properties of different soil layers in collapsing gully walls. The study found that when the water content in the red soil layer and sandy soil layer exceeded 20% and in the detritus layer exceeded 10%, the soil’s matric suction significantly decreased as the temperature increased from 25 to 40 °C. Additionally, the parameters of θs, α, n and m all exhibited a decreasing trend, and the soil water content in the detritus layer was primarily influenced by the temperature change, which resulted in a decrease of 38.10%. The unsaturated hydraulic conductivity of the detritus layer exhibited higher values than that of the sandy layer and red soil layer under identical temperature conditions. Moreover, the unsaturated hydraulic conductivity of the red soil layer, sandy soil layer and detritus layer increased with increasing temperature. It was observed that the unsaturated hydraulic conductivity of the detritus layer increased by 0.18 cm h−1 at a soil water content of 44%. This increase in conductivity was more pronounced than the corresponding changes in the red soil layer and sandy soil layer. An elevated temperature caused the water-holding capacity of the different soil layers of the collapsing gully wall to decrease and the unsaturated hydraulic conductivity to increase. However, the influence of the clay particle content within the soil of the collapsing gully wall rendered the temperature effect more distinct. Therefore, the destabilizing deformation of the soil in the collapsing gully wall during the summer under high temperatures and precipitation may have played a key role in its collapse.

Effects of oilseed rape green manure on phosphorus availability of red soil and rice yield in rice-green manure rotation system.

Improving the nutrient content of red soils in southern China is a priority for efficient rice production there. To assess the effectiveness of oilseed rape as green manure for the improvement of soil phosphorus nutrient supply and rice yield in red soil areas, a long-term field plot experiment was conducted comparing two species of rape, Brassica napus (BN) and Brassica juncea (BJ). The effects of returning oilseed rape on soil phosphorus availability, phosphorus absorption, and yield of subsequent rice under rice-green manure rotation mode were analyzed, using data from the seasons of 2020 to 2021. The study found that compared with winter fallow treatment (WT) and no-tillage treatment (NT), the soil available phosphorus content of BN was increased, and that of BJ was significantly increased. The content of water-soluble inorganic phosphorus of BJ increased, and that of BN increased substantially. Compared with the WT, the soil organic matter content and soil total phosphorus content of BN significantly increased, as did the soil available potassium content of BJ, and the soil total phosphorus content of BJ was significantly increased compared with NT. The soil particulate phosphorus content of BJ and BN was significantly increased by 14.00% and 16.00%, respectively. Compared with the WT, the phosphorus activation coefficient of BJ was significantly increased by 11.41%. The rice plant tiller number under the green manure returning treatment was significantly increased by 43.16% compared with the winter fallow treatment. The green manure returning measures increased rice grain yield by promoting rice tiller numbers; BN increased rice grain yield by 9.91% and BJ by 11.68%. Based on these results, returning oilseed rape green manure could augment the phosphorus nutrients of red soil and promote phosphorus availability. Rice-oilseed rape green manure rotation could increase rice grain yield.

Effects of Vegetation Restoration on Soil Nitrogen Fractions and Enzyme Activities in Arable Land on Purple Soil Slopes.

Purple soils are greatly representative of ecologically fragile soils in southern China, yet the impact of vegetation restoration processes on the nitrogen (N) availability in purple soil ecosystems is still unclear. In this study, the soil nutrient content, available N fractions (including microbial biomass N (MBN), ammonium N (NH4+-N), nitrate N (NO3--N), and total dissolved N (TDN)), and enzyme activities (including urease (URE), nitrate reductase (NR), and nitrite reductase (NIR)) involved in N mineralization and immobilization were investigated across the three vegetation-restoration measures: Camellia oleifera monoculture, Camellia oleifera ryegrass intercropping, and Camellia oleifera intercropping with weeds. The results showed that the Camellia oleifera monoculture mode considerably enhanced the accumulation and availability of soil N and modified the proportion of available N fractions in arable land situated on purple soil slopes, compared to the intercropping mode, the physical, chemical, and microbiological properties of soil demonstrated more pronounced effects due to the Camellia oleifera monoculture vegetation-restoration measures. However, soil nutrient loss is faster on set-aside land and in crop monocultures, and intercropping restoration measures are more beneficial for soil and water conservation under timely fertilization conditions. The soil URE, NR, and NIR activities and MBN content in the Camellia oleifera monoculture model were significantly higher than in the control check sample. Soil N transformation occurs through the combined influence of chemical and biological processes. The relationships between the activities of the three soil enzymes studied and the contents of various components of soil nutrients and effective N displayed significant differences. Notably, URE had a highly significant positive correlation with TOC. There is a strong positive correlation between NR and TN, NIR and TDN, NO3--N, and NH4+-N. Our findings suggest that vegetation restoration improved the soil N availability and its enzyme activities in purple soils, making an essential contribution to the restoration and sustainability of purple soil ecosystem functions.

Various green manure-fertilizer combinations affect the soil microbial community and function in immature red soil.

Green manure application is a common practice to improve soil fertility in China. However, the impact of different green manure-fertilizer combinations on the soil microbial communities in the low-fertility immature red soil in southern China remains unclear. In this study, we conducted a pot experiment using two common green manure crops, ryegrass (Lolium perenne L.) and Chinese milk vetch (Astragalus sinicus L.), along with a fallow treatment. We also considered three combined fertilizer management strategies, including mineral, humic acid, and organic manure fertilizers. We evaluated the soil microbial biomass, activity, communities, functional prediction and their correlation with soil properties during green manure growth and incorporation periods, to assess the potential alterations caused by different green manure and fertilizer combinations. Our findings indicate that green manure application, particularly in combination with organic fertilizers, increased the alpha diversity of the soil bacterial community, while the opposite trend was observed in the fungal community. The application of green manure altered the soil microbial communities during both growth and incorporation periods, especially the taxa that participate in carbon, nitrogen and sulfur cycles. Notably, ryegrass significantly increased the relative abundance of bacterial phylum Firmicutes and fungal phylum Ascomycota, whereas Chinese milk vetch significantly stimulated the bacterial phylum Acidobacteria and fungal phylum Glomeromycota. Compared with fallow treatments, green manure application significantly increased the soil pH by 4.1%-12.4%, and microbial biomass carbon by 29.8%-72.9%, regardless of the types of combined fertilizer. Additionally, the application of green manure resulted in a 35.6%-142.6% increase in urease activity and a 65.9%-172.9% increase in β-glucosidase activity compared to fallow treatments, while led to a 22.5%-55.6% decrease in catalase activity. Further analysis revealed that the changes in both bacterial and fungal communities positively correlated with soil pH, soil organic matter, total nitrogen and alkali hydrolyzed nitrogen contents. Moreover, the relationship between the soil microbial community and soil enzyme activities was regulated by the specific green manure species. In conclusion, our results provide insight into the effects of different green manure-fertilizer combinations on soil microorganisms and their underlying mechanisms in improving soil fertility in the low-fertility immature red soil.

Substation of vermicompost mitigates Cd toxicity, improves rice yields and restores bacterial community in a Cd-contaminated soil in Southern China

Cadmium (Cd) contamination in agricultural soil is a global concern for soil health and food sustainability because it can cause Cd accumulation in cereal grains. An in-situ stabilizing technology (using organic amendments) has been widely used for Cd remediation in arable lands. Therefore, the current study examined the influence of vermicompost (VC) on soil biochemical traits, bacterial community diversity and composition, Cd uptake and accumulation in rice plants and grain yield in a Cd-contaminated soil during the late growing season in 2022. Different doses of VC (i.e., V1 = 0 t ha−1, V2 = 3 t ha−1 and V3 = 6 t ha−1) and two concentrations of Cd (i.e., Cd1 = 0 and Cd2 = 50 mg Cd Kg−1 were used. We performed high-throughput sequencing of 16S ribosomal RNA gene amplicons to characterize soil bacterial communities. The addition of VC considerably affected the diversity and composition of the soil bacterial community; and increased the relative abundance of phyla Chloroflexi, Proteobacteria, Acidobacteriota, Plantomycetota, Gemmatimonadota, Patescibacteria and Firmicute. In addition, VC application, particularly High VC treatment, exhibited the highest bacterial diversity and richness (i.e., Simpson, Shannon, ACE, and Chao 1 indexes) of all treatments. Similarly, the VC application increased the soil chemical traits, including soil pH, soil organic carbon (SOC), available nitrogen (AN), total nitrogen (TN), total potassium (TK), total phosphorous (TP) and enzyme activities (i.e., acid phosphatase, catalase, urease and invertase) compared to non-VC treated soil under Cd stress. The average increase in SOC, TN, AN, TK and TP were 5.75%, 41.15%, 18.51%, 12.31%, 25.45% and 29.67%, respectively, in the High VC treatment (Pos-Cd + VC3) compared with Cd stressed soil. Redundancy analysis revealed that the leading bacterial phyla were associated with SOC, AN, TN, TP and pH, although the relative abundance of Firmicutes, Proteobacteria, Bacteroidata, and Acidobacteria on a phylum basis and Actinobacteria, Gammaproteobacteria and Myxococcia on a class basis, were highly correlated with soil environmental factors. Moreover, the VC application counteracted the adverse effects of Cd on plants and significantly reduced the Cd uptake and accumulation in rice organs, such as roots, stem + leaves and grain under Cd stress conditions. Similarly, applying VC significantly increased the fragrant rice grain yield and yield traits under Cd toxicity. The correlation analysis showed that the increased soil quantities traits were crucial in obtaining high rice grain yield. Generally, the findings of this research demonstrate that the application of VC in paddy fields could be useful for growers in Southern China by sustainably enhancing soil functionality and crop production.

Construction and evaluation of pedotransfer functions for saturated hydraulic conductivity in the granite red soil regions of southern China

Study regionSix typical regions of granite red soil in southern China. Study focusRegional large-scale Ks analysis of granite red soil in South China is still limited to a large number of repetitive and expensive workloads. It is necessary to construct Ks PTFs suitable for the granite red soil region of South China. In this study, six different regions granite red soil in South China were used to validate the prediction of classical PTFs for Ks, the best combination of predictors was screened and PTFs developed based on stepwise regression methods and machine learning algorithms. New hydrologic insights for the region(1) The coefficient of variation for Ks is 69.87% in the granite red soil region of South China, with a large spatial variability. (2) The six typical PTFs of Ks were poor predictors of Ks for soils in southern China, R2 < 0.4. (3) "Clay+Silt+Sand+BD+SOM+NCP" is the best combination of predictors of soil Ks in the granite red soil region of South China, which can be used in different machine learning algorithms. (4) The constructed MLR model “Ks= 1.501 + 0.043 ×NCP-0.995 ×BD+ 0.034 ×SOM-0.013 ×Clay” with KNN, ANN and BRT machine algorithm models have a prediction accuracy R2 greater than 0.8. This study provides different prediction models for soil Ks in the granitic regions of southern China and lays a theoretical basis for hydrological research in the these regions.

Differences of SOC storage and stability between soil layers influenced by long-term fertilization in a typical paddy soil of Southern China

BackgroundThe contribution of long-term fertilization to soil organic carbon (SOC) storage has been of great concern. To assess the effects of long-term fertilization on SOC storage and stability in top and sub-soil layers, soil samples were collected from a 29-year field experimental station in a typical paddy soil in southern China. The SOC storage of whole soil and SOC fractions was quantified at three soil depths (0–20, 20–40, 40–60 cm) under four treatments: no fertilization (Control), a combination of nitrogen, phosphorus and potassium (NPK), double the rates of NPK (2NPK), NPK plus manure (NPKM).ResultsThe increase of Cinput-total was significantly higher than that of SOC storage among different treatments (p < 0.05), indicating that soil fixation of exogenous carbon is limited. Besides, the SOC accumulation and sequestration rates patterned as NPKM > 2NPK > NPK, and these rates were higher at 0–20 cm depth as compared to other depth intervals. Furthermore, for the whole profile, the SOC storage of active pool was higher in the Control (39.6 t C ha−1) than in other treatment (36.2 t C ha−1, p < 0.05). Whereas, fertilization increased the SOC storage of passive pool, ranked as NPKM > 2NPK≈NPK > Control (p < 0.05), indicating that fertilization, especially organic combined with inorganic fertilization, improved SOC stability. From the perspective of soil layers, the difference of SOC storage among treatments for passive pool was mainly resulted from the difference at surface soil, and for active pool were the deeper layers. Additionally, manure application increased the difference among soil layers.ConclusionThis study concluded that non-fertilized treatment could improve the SOC storage of active pool especially in deep soil layers, while fertilization especially manure application could improve the SOC storage and stability in surface soil and increased the difference among soil layers.Graphical

Boron decreases cadmium accumulation in water spinach by enhancing cadmium retention in the root cell walls.

Cadmium (Cd) contamination and boron (B) deficiency are two major challenges associated with the farmland soils in Southern China. Therefore, this study was conducted to examine the impacts of B supply on Cd accumulation in water spinach (Ipomoea aquatica) using a cultivar (T308) with high Cd accumulation. The study further investigated the physiological mechanism behind the changes in Cd accumulation due to B supply. The findings revealed that B supply substantially reduced the Cd concentration in the leaves of water spinach by 41.20% and 37.16% under the Cd stress of 10μM and 25μM, respectively. Subcellular distribution of Cd showed that the Cd content as well as its proportion in root cell wall (RCW) increased significantly after B supply. Fourier transform infrared spectroscopy showed significant enrichment of negatively charged groups (such as -OH, -COOH, and -NH2) in the RCW after B supply. Overall, B supply also enhanced covalently bound pectin (CSP) content as well as the Cd content linked with CSP under Cd stress. These observations revealed that B regulated the Cd chelation in RCW, thereby reducing the amassment of Cd in water spinach.

Simulated Nitrogen Deposition Decreases the Ratios of Soil C to P and N to P, Changes Soil Enzyme Activity, and Reduces Soil Microbial Biomass in Paddy Soil in Southern China

There have been few studies on the impact of nitrogen deposition on paddy field ecosystem; therefore, we evaluated the effects of different N deposition levels (0, 40, and 120 kg N·ha−1) with the conventional nitrogen rate (180 kg N·ha−1) on rice field ecosystem through two-season experiments. The results showed that 40 and 120 kg·ha−1 nitrogen deposition had no significant effect on rice yield, although the rice grains per panicle and the 1000-grain weight increased. The 40 and 120 kg·ha−1 nitrogen deposition levels had no significant effect on rice and soil total carbon/total nitrogen (TC/TN) in the two-season experiment; however, 40 and 120 kg·ha−1 nitrogen deposition significantly increased TP content of the rice root and soil in a short time, and continuous 120 kg·ha−1 nitrogen deposition significantly decreased TP content of the rice root and significantly increased TP content of the rice stem. In addition, nitrogen deposition significantly reduced total carbon/total phosphorus (TC/TP) and total nitrogen/total phosphorus (TN/TP) in the soil. The activities of soil acid phosphatase (S-ACP), β-glucosidase (S-β-GC), and N-acetyl-β-D-glucosidase (S-NAG) increased under 40 kg·ha−1 nitrogen deposition, while the activities of S-β-GC and S-NAG decreased under 120 kg·ha−1 nitrogen deposition compared with 40 kg·ha−1. The microbial carbon, microbial nitrogen, microbial phosphorus, and fungal microbial biomass reduced under 40 and 120 kg·ha−1 nitrogen deposition. These findings suggest that, under short-term N deposition, rice and soil can adjust the C, N, P, and even the nutrient balance by themselves; however, continuous nitrogen deposition may have adverse reactions to microorganisms, thereby disrupting this balance and ultimately leading to the deterioration of paddy soil environment and a reduction in rice yield in the long term.

Effect of boron supply on the uptake and translocation of cadmium in Capsicum annuum

Large areas of soil in southern China are contaminated with cadmium (Cd) and are deficient in boron (B). Previously, we suggested that B supplementation could reduce Cd accumulation in hot peppers (Capsicum annuum L.); however, the physiological mechanisms underlying this reduction remain unclear. In this study, the uptake and translocation of Cd in hot pepper plants were investigated using hydroponic experiments with different B and Cd treatments. A pot experiment was performed to verify whether B decreased the Cd concentration in hot peppers by minimizing the Cd translocation rate. The results of the dose- and time-dependent experiments showed that B supplementation reduced root Cd uptake and root-to-shoot Cd translocation. Additionally, B supplementation increased the root length, diameter, volume, surface area, and number of root forks and tips, as well as improving the relative absorbance of carboxyl groups under Cd exposure, leading to enhanced Cd fixation in the cell walls of the roots. As a result, the fruit Cd concentration decreased because B inhibited Cd translocation from the roots. Overall, the results demonstrate that B supplementation can reduce Cd accumulation in hot peppers by promoting normal root growth and development and by limiting the uptake and translocation of Cd.

Effects of slow- and controlled-release nitrogen fertilizers on bacterial and fungal community composition in a double-cropping rice system

Slow- and controlled-release (SCR) nitrogen (N) fertilizers improve crop production and N utilization efficiency. However, responses of biological soil characteristics to the long-term application of N fertilizer have received little attention. In this work, a five-year field experiment was performed to assess the influence of different N fertilizer treatments (no N fertilizer application [CK] and applications of polymer-sulfur coated urea [PSCU], conventional prilled urea [PU], and urea-formaldehyde [UF]) on soil microbial communities in yellow clayey paddy soils in southern China. The types of N fertilizers had a stronger impact on soil bacterial diversity and community structure than fungal diversity and community structure. The soil microbial communities of PU and UF treatments did not differ from those of CK regarding alpha diversity indices. However, the PSCU treatment significantly decreased the Shannon index by 2.16% for bacteria but had no significant effect on the Shannon index of fungi. This might be due to the application of PSCU significantly reducing the soil pH by 0.16 units compared to CK and leading to soil acidification. Co-occurrence network analysis determined the keystone species mainly belonging to Proteobacteria and Ascomycota. Notably, these keystone species played an important role in PSCU-treated soils. Soil Ca2+, Na+, and NH4+ were the main determinants of microbial network stability. These results contribute to our understanding of how SCR-N fertilizers impact soil microorganisms.