Yellow-brown Soil Research Articles

Geochemical Characteristics and Influencing Factors of Selenium in the Xichang Area, Southwest China

Taking the Xichang area of China as an example, this study investigated factors affecting the geochemical characteristics of Se element by analyzing and comparing the environmental geochemical characteristics and temporal and spatial changes of Se in different rock formations, soil types, parent material layers, and soil layers. Analytical and statistical tests revealed that the content of Se in the soil of the study area ranged from 0.01 to 0.57 mg·kg-1, with an average value of 0.12 mg·kg-1, corresponding to a relatively low content. The orders of Se content in different materials are as follows: soil layer > soil parent material layer > rock layer in terms of the profile; Triassic continental clastic > Neogene-Quaternary continental clastic > Mesozoic intermediate-acid > Proterozoic intermediate-acid > Jurassic-Cretaceous continental clastic > Permian basic-ultrabasic = Sinian marine carbonate = Proterozoic volcanic clastic in terms of rock formations (parent rocks); and brown soil > yellow brown soil > dark brown soil > black felt soil > red soil > purple soil. The spatial distribution of Se exhibits distinct zoning and a good spatial coupling relationship with geological formations, rivers, topography, and geomorphology. The selenium content is mainly controlled by geological factors such as parent rock and parent material under different geological tectonic units, followed by clay minerals, organic matter such as Corg, S, N and element adsorption and fixation.

Reducing Moisture Effects on Soil Organic Carbon Content Estimation in Vis-NIR Spectra With a Deep Learning Algorithm

When estimating soil organic carbon (SOC) using visible and near-infrared (Vis-NIR) spectra measured in situ, the interference of soil moisture content (SMC) needs to be eliminated. The existing SMC removal methods are mainly based on spectral transformation, but they change the original form of the soil spectrum. In this paper, a new deep learning-based SMC influence removal network (MIRNet) is proposed to establish the relationship between the spectra of moist soil and that of dry soil. This method constructs a spectral extraction module (SEM) with two one-dimensional (1-D) ghost modules to extract soil spectral characteristics and a context extraction module (CEM) with a two-layer dilated convolutional neural network (DiCNN) to extract the context information of the spectra. Then these extracted features are combined to reconstruct the SMC influence with a two-layer deconvolution using residual learning (Res). Finally, a new loss function that combining spectral distance and spectral shape measurement (D-S loss) is proposed. The input of MIRNet is the moist soil spectra, and the output is the dry soil spectra. Black soil collected from Harbin and yellow-brown soil collected from Nanjing are selected as the research objects. The <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$R^{2}$</tex-math></inline-formula> reaches 0.703, 0.747, 0.907, 0.892, 0.866, 0.907, and 0.926, respectively, when using spectra processed by external parameter orthogonalization (EPO), orthogonal signal correction (OSC), support vector regression (SVR), convolutional neural network (CNN), deep neural network (DNN), denoising convolutional neural network (DnCNN), and MIRNet. Therefore, the proposed MIRNet achieves competitive results compared with these state-of-the-art methods.

Divergent responses and ecological risks of wheat (Triticum aestivum L.) to cerium oxide nanoparticles in different soil types

Cerium oxide nanoparticles (nCeO2), as a common component for sustainable agriculture, have been broadly investigated due to their potential threat to the soil biodiversity and health. However, few studies considered the impacts of soil types on response of ecotoxicity of nCeO2 to plants. This study aimed to explore the effects of soil properties on ecological response of nCeO2 to wheat (Triticum aestivum L.) and assess the ecological risks of nCeO2 (0–1000 mg/kg) in red soil, yellow-brown soil, and brown soil by applying a multi-biomarker approach. The results showed that the clay content had the extremely significant correlation with acid solute fraction Ce in soil. Ce accumulation in wheat largely depended on acid-soluble fraction Ce, but not the total Ce. Both urease and invertase activities were highest in brown soil among the three soils, after exposure to diverse concentration nCeO2. Although wheat has a stronger antioxidant capacity in red soil, integrated biomarker response index proved that nCeO2 showed least toxicity to wheat in brown soil (IBRv2 = 34.3) among the three soils. These results indicated that the toxicity level of nCeO2 to wheat was not only related to contaminated concentration, but also greatly depended on soil properties. The soil types are important factors governing ecological risk of nCeO2 in soil, which needs to be adequately assessed and properly controlled.

Microscale Spatiotemporal Variation and Generation Mechanisms of Reactive Oxygen Species in the Rhizosphere of Ryegrass: Coupled Biotic-Abiotic Processes.

Reactive oxygen species (ROS) play key roles in soil biogeochemical processes, yet the occurrence and accumulation of ROS in the rhizosphere are poorly documented. Herein, we first developed a ROS-trapping membrane to in situ determine ROS in the ryegrass rhizosphere and then quantified the temporal and spatial variations of representative ROS (i.e., O2•─, H2O2, and •OH). Fluorescence imaging clearly visualized the production of ROS in the rhizosphere. Both O2•─ and H2O2 content increased first and then declined throughout the life cycle of ryegrass, while •OH concentration decreased continuously. Spatially, ROS contents remained at a relatively high level at 0-5 mm and then descended with increasing distance. The concentrations of ROS in different soils followed the order of black soil > latosol soil > yellow-brown soil > tier soil ∼ red soil. Analysis of soil properties suggested that both biotic factors (microbial community) and abiotic factors (Fe(II) and water-soluble phenols) played critical roles in ROS production. The combined processes, including Fe(II) and water-soluble phenol-mediated electron transfer, microbial community-driven extracellular O2•─ release, and Fe(II)/Fe(III) cycling, may be responsible for ROS production. These findings provide insights into ROS-associated rhizosphere effects and inspiration for the phytoremediation of pollutants and element cycling.

Microplastics can affect soil properties and chemical speciation of metals in yellow-brown soil

Although the influence of microplastics (MPs) in different soil environments has been investigated, their effects on the physiochemical properties and chemical speciation of heavy metals in yellow-brown soil remains unknown. This study aimed to determine the effects of various concentrations of linear low-density polyethylene (LLDPE), polyamide (PA), polyurethane (PU), polystyrene (PS), and low-density polyethylene (LDPE) MPs on the yellow-brown soil environment and chemical speciation of the heavy metals cadmium (Cd), copper (Cu), lead (Pb), and zinc (Zn). MPs influenced the physicochemical properties and chemical speciation of heavy metals in yellow-brown soil. The physicochemical properties of yellow-brown soil can be altered by changing the concentrations of LDPE MP. The relationship between changes in field capacity (FC) and LDPE concentrations was approximately linear. The physiochemical properties of yellow-brown soil containing added PA, PU, and LDPE MPs were substantially improved (control vs. MPs): FC, 39 % vs. 42.50 % for PU, cation exchange capacity (CEC) 45.77, 56.65, and 57.44 cmol.kg−1 for PA, PU, and LDPE respectively, and organic matter (OM) content, 40.16 vs. 51.68 g.kg−1 for PA. The LLDPE and PU MPs also simultaneously affected the chemical speciation of heavy metals in yellow-brown soil. The LLDPE MPs increased the acid-soluble (45.17–54.67 % (Cd-F1), 7.24–11.30 % (Cu-F1), 4.20–7.23 % (Pb-F1), 21.21–31.47 % (Zn-F1)) and reducible (24.02–29.41 % (Cd-F2), 25.69–34.95 % (Cu-F2), 74.29–81.07 % (Pb-F2), 28.77–34.19 % (Zn-F2)) fractions of heavy metals, which increased their bioavailability. However, PU MPs reduced the ecological risk of heavy metals in yellow-brown soil by increasing the content of the residual fraction (26.11–40.21 % (Cd-F4), 47.63–59.67 % (Cu-F4), 17.25–26.76 % (Pb-F4), 32.63–50.46 % (Zn-F4)). Changes in the properties of yellow-brown soil and the impact of MPs on heavy metals, might change the chemical speciation of heavy metals. The impact of MPs on heavy metals in yellow-brown soil requires further investigation.

Monitoring soil mercury content based on hyperspectral data and machine learning methods

Mercury (Hg) is a heavy metal pollutant characterized by global migration, high bioaccumulation, and high biological toxicity. Soil Hg pollution seriously harms soil environmental quality and human health. The higher the content of Hg in the soil, the more serious the harm. Therefore, the acquisition of soil Hg content information is crucial for soil monitoring and restoration, and human health. The purpose of this study is to establish the best hyperspectral prediction model of soil Hg content in the study area. A total of 90 soil samples were collected from the mining areas and suburbs, and the Hg content was analyzed. Several preprocessing methods were applied to the hyperspectral data. Partial least-squares regression (PLSR), orthogonalized PLSR, random forest, and back propagation neural network (BPNN) were used to establish the relationship between soil hyperspectral data and soil Hg content to predict the soil Hg content. Specifically, the transferability of the best prediction model in yellow-brown and cinnamon soil data was discussed. The results showed that BPNN + standard normal variable + full-band (4 nm) is the optimum method to predict soil Hg content (Rtrain2=0.94, Rtest2=0.85). The transferability of the model is the best in yellow-brown soil. This research provides technical support for the rapid monitoring of soil Hg pollution information in central and eastern Shaanxi-Province, and the results enrich prediction models of soil Hg content in different soil types.

Characteristics of Soil Erodibility K Value and Its Influencing Factors in the Changyan Watershed, Southwest Hubei, China

Soil erodibility K factor is an important parameter for evaluating soil erosion vulnerability and is required for soil erosion prediction models. It is also necessary for soil and water conservation management. In this study, we investigated the spatial variability characteristics of soil erodibility K factor in a watershed (Changyan watershed with an area of 8.59 km2) of Enshi, southwest of Hubei, China, and evaluated its influencing factors. The soil K values were determined by the EPIC model using the soil survey data across the watershed. Spatial K value prediction was conducted by regression-kriging using geographic data. We also assessed the effects of soil type, land use, and topography on the K value variations. The results showed that soil erodibility K values varied between 0.039–0.052 t·hm2·h/(hm2·MJ·mm) in the watershed with a block-like structure of spatial distribution. The soil erodibility, soil texture, and organic matter content all showed positive spatial autocorrelation. The spatial variability of the K value was related to soil type, land use, and topography. The calcareous soil had the greatest K value on average, followed by the paddy soil, the yellow-brown soil (an alfisol), the purple soil (an inceptisol), and the fluvo-aquic soil (an entisol). The soil K factor showed a negative correlation with the sand content but was positively related to soil silt and clay contents. Forest soils had a greater ability to resist to erosion compared to the cultivated soils. The soil K values increased with increasing slope and showed a decreasing trend with increasing altitude.

Long-term fertilization with high nitrogen rates decreased diversity and stability of diazotroph communities in soils of sweet potato

Sweet potato (Ipomoea batatas Lam) could produce acceptable root yield in low-nitrogen (N) soils, with substantial N uptake potentially attributed to supplies provided via biological N2-fixation by free-living diazotrophs. However, dynamics of diazotrophic communities as influenced by soil properties across the N fertilization gradients are still largely unclear. Long-term fertilization experiment under wheat-sweet potato rotation was established in an acid yellow brown soil since 2011. Soil samples were collected after sweet potato harvest (October 2018). The nitrogenase (nifH) gene real-time polymerase chain reaction (RT-PCR) and Hiseq high-throughput sequencing technologies were applied to soil samples from four N fertilizer treatments (0, 60, 120 and 180 kg ha−1). The results showed that long-term N fertilization significantly decreased abundance of the nifH gene, which was closely related to decreases in the content of available phosphorus (AP). The long-term high-N (120 and 180 kg ha−1) fertilization dramatically altered structure of soil diazotrophic community and lead to in decreased diversity of diazotrophs, whereas low-N (60 kg ha−1) fertilization maintained diazotrophic community diversity and stability. Compared with the low-N fertilizer inputs (0 and 60 kg ha−1), the high rates of N fertilization (180 kg ha−1) significantly decreased the relative abundance of nifH-harboring microorganisms, especially the phylum Cyanobacteria known as potential N2-fixers that could sustain fertility of sweet potato soils. There were negative correlations between N fertilization rates and the relative abundance of Proteobacteria, whereas the Bacteroidetes and Firmicutes showed a positive correlation. Moreover, the structural equation model (SEM) results suggested that the diazotrophic community diversity and structure were influenced mostly by soil pH rather than SOM and N forms (TN, NH4+-N and NO3−-N), and diazotrophs abundance mainly regulated by soil AP content. Our results implied that appropriate N fertilization is beneficial to sustain the stability and diversity of the diazotrophic community.

Effect of biochar on immobilization remediation of Cd⁃contaminated soil and environmental quality

PurposeField experiments were conducted to explore the remediation effects of ordinary biochar and PEI-modified biochar on the Cd-contaminated yellow brown soil, and the improvement of soil environment quality in southern Shaanxi province, so as to provide theoretical basis and technical support for in-situ remediation of Cd-contaminated soil in southern Shaanxi province. Results and discussionBiochar applied in soil could increase the soil pH value, EC, ECEC, and SOC, and improve the soil physical and chemical properties to a certain extent. Biochar in soil could change the chemical form of Cd in soil, effectively passivate Cd in soil and reduce its bio-availability. Biochar could enhance the activities of catalase, urease, alkaline phosphatase and sucrase in soil to different degrees, and the four soil enzymes could be used as indicators of passivation effects of soil Cd by biochar. With biochar treatment, soil aggregates MWD and GMD increased to different degrees, so biochar could enhance soil stability. The biochar could decrease the content of Cd in different parts of wheat, the content of Cd in wheat grains had a highly significant positive correlation with the available content of Cd in soil, and highly significant or significant negative correlations with pH, SOC, EC, ECEC, and the activities of phosphatase, urease and sucrase in soil. Compared with ordinary biochar, the passivation effect of PEI-modified biochar on Cd was more significant. ConlusionsThe results of the study indicated that ordinary biochar and PEI-modified biochar could passivate the Cd in soil, and remediate Cd-contaminated soil, and improve the soil environmental quality effectively, compared with ordinary biochar, the PEI-modified biochar produced batter.

Effects of Soil Type on Trace Element Absorption and Fruit Quality of Pepper.

The inbred “SJ11-3” pepper was cultured in yellow brown soil, paddy soil, fluvo-aquic soil, and pastoral soil, and the factors affecting the absorption of trace elements and fruit quality were analyzed. The results showed that the physicochemical properties of the soils were significantly different, which led to differences in the nutritional quality of pepper fruits. The pH value had a significant effect on the absorption of trace elements in pepper. The increase of pH promoted the absorption of magnesium and molybdenum but inhibited the absorption of zinc, copper, manganese, and iron. The stepwise multivariable regression analysis showed that the amount of molybdenum in soil was the main factor affecting the total amino acid content of pepper. Total nitrogen, zinc, and copper were the main factors that contributed to the soluble sugar content of pepper, and the available potassium was the major determinant of the vitamin C content of pepper. This study provides new insight on the pepper fruit quality grown on different types of soil with varying levels of trace elements.

Environmental Behaviors of Procymidone in Different Types of Chinese Soil

Procymidone is a widely used fungicide in the prevention and treatment of fungal diseases on many crops in China. Part of the procymidone will enter the soil during the application process. Procymidone may exhibit environmental behavior diversity in different soils. Therefore, it is extremely important to clarify the environmental behavior of procymidone in soil for its environmental safety evaluation. Here, the degradation, adsorption, and mobility behaviors of procymidone in four typical types of Chinese soil were investigated for the first time. The half-lives of procymidone in the soils ranged from 14.3 d to 24.1 d. The degradation rates of procymidone in the soils were promoted by organic matter content, moisture content, and microorganisms. Furthermore, the degradation of procymidone on the soil surface was promoted by light. The desorption rates of procymidone in laterite soil, yellow brown soil, black soil, and chestnut soil were 27.52 ± 0.85%, 16.22 ± 0.78%, 13.67 ± 1.29%, and 7.62 ± 0.06%, respectively, which were contrary to the adsorption ability. The mobility order of procymidone in the soils was: laterite soil &gt; yellow brown soil &gt; black soil &gt; chestnut soil, with the Rf values of 0.28, 0.22, 0.18, and 0.16, respectively. Three degradation products of procymidone were identified by liquid chromatography coupled with quadrupole/time-of-flight mass spectrometry, and the degradation pathway of procymidone in the soil was speculated. The results will provide a theoretical basis for the removal of procymidone in the soil environment.

Effects of biochar on heavy metal bioavailability and uptake by tobacco (Nicotiana tabacum) in two soils

Biochar, as a soil conditioner, not only improves soil fertility but also changes the bioavailability of heavy metals in soil-crop systems, which may lead to certain environmental issues. To investigate the effect of biochar on the bioavailability of heavy metals (Cd, Cu, Ni, and Pb) in soils, a two-year field experiment with five biochar rates (0, 5, 15, 20, and 40 Mg ha−1) was conducted in yellow-brown soil (pH 5.32) and yellow soil (pH 6.39) in southwestern China with tobacco as an example crop. The results showed that, in the acidic soil, available Cd content increased with biochar rate when the rate exceeded 15 Mg ha−1, whereas in neutral yellow soil, the Cd content increased significantly only at the rate of 40 Mg ha−1. Biochar application did not cause any significant increase in Cd content or accumulation in the crop. The soil available Cu, Ni, and Pb contents decreased with increasing biochar rate, and the decrement varied with soil pH and time after biochar application. Cu, Ni and Pb contents and their accumulations in tobacco decreased with higher biochar application rate. The decreases in soil available Cu, Ni and Pb contents may result from immobilization of these heavy metals by electrostatic attraction, ion exchange, surface precipitation, complexation, while the increase in soil available Cd content resulted from high Cd content in feedstock of the biochar. The biochar derived from tobacco stem contained 7.63 mg kg−1 Cd, which added 6.20, 30.0, 93.0, 124, and 248 ug kg−1 to the top 10 cm soils for the application rate of 1, 5, 15, 20, and 40 Mg ha−1, respectively. It is important to identify heavy metal contamination in biochar before it is used as a soil amendment. In conclusion, biochar application can decrease soil available and plant total Cu, Ni, and Pb content, and the degrees of decrease varies with soil pH and biochar application rate. Meanwhile, we should be careful about the possible heavy metal pollution from feedstock of biochar.

Combined passivators regulate the heavy metal accumulation and antioxidant response of Brassica chinensis grown in multi-metal contaminated soils.

Passivation of heavy metals is one of the most efficient techniques to remediate soil pollution. However, passivators with single component are usually unsatisfactory in the case of multi-metal contaminated soils. To resolve this problem, a series of combined passivators containing different ratios of Fe-Mn ore, Fe powder, zeolite, bentonite, etc. were designed and used to study their effects on the growth, heavy metal accumulation, and the antioxidant response of Chinese cabbage (Brassica chinensis L.) as well as the soil available forms of heavy metals in a copper refinery's multi-metal (As, Cd, Pb, Cu) contaminated yellow-brown soil and an artificially contaminated (As, Cd, Pb, Cu) calcareous alluvial soil. The results showed that compared with the control, the addition of combined passivators significantly promoted cabbage growth, with the biomass increase up to 1.77 and 3.54 times in yellow-brown soil and calcareous alluvial soil, respectively. The activity of antioxidant enzymes (SOD, CAT, POD) and the content of malondialdehyde (MDA) and glutathione (GSH) decreased, while the chlorophyll content increased significantly, as compared with no passivators. In addition, passivator application decreased As, Cd, Pb, and Cu contents in shoots and roots by 34.8%, 45.6%, 34.9%, and 11.1% and 49.2%, 63.8%, 38.6%, and 46.4% in yellow-brown soil and by 29.8%, 27.3%, 26.8%, and 25.5% and 45.8%, 55.2%, 61.8%, and 5.7% in calcareous alluvial soil, respectively. Besides, the content of soil available heavy metals was reduced by 8.0-17.1% in yellow-brown soil and 3.3-19.1% in calcareous alluvial soil after the application of passivators. The results indicated that the combined passivators formulated in this experiment could efficiently reduce the content of the multi-metals in cabbage and relieve the oxidant stress and could be used as a way to remediate multi-metal polluted soils.

LUCC study under different geological conditions in Nanjiang district, Sichuan Province

With the development of the times, more and more people begin to pay attention to land use change. This paper analyses the influence of different geological background conditions on the dynamic change of land use in Nanjiang County, Sichuan Province, and attempts to establish a land use model that meets the geological conditions of each region. According to different geological conditions, the purple soil of Cretaceous and Jurassic tilted single-sided low mountains and eroded terrace like narrow valley low mountains in the south is suitable for planting and breeding; the yellow soil of Jurassic and Triassic single-sided low and middle mountain purple soil in the middle is suitable for developing multi economic crops dominated by forest land; the limestone of yellow brown soil of Triassic, Sinian, Cambrian and middle mountain yellow soil in the north can be used for forestry and animal husbandry Industry.

Effects of sulfur application on selenium uptake and seed selenium speciation in soybean (Glycine max L.) grown in different soil types

AimsThe objective of the present study was to elucidate the effects of sulfur (S) application on selenium (Se) uptake and seed Se speciation in high-protein soybean (Glycine max L.) grown in different soil types. MethodsPot experiments were conducted with soybean plants grown in yellow-brown soil (pH 5.68) and in calcareous alluvial soil (pH 7.87). Sodium selenate (Na2SeO4, 2 mg kg−1) was applied to soil with or without S fertilizer (S, 100 mg kg−1). ResultsSoybean grain yield and total biomass in calcareous alluvial soil were both approximately 1.3-fold the levels in yellow-brown soil. Following Se application, seed Se concentration in calcareous alluvial soil was 3.2-fold the concentration in yellow-brown soil, although additional S application reduced the corresponding seed Se concentrations by 55.6% and 38.6%, respectively. Generally, Se application facilitated Se translocation and enrichment in soybean seeds. Organic Se accounted for 92% of seed total Se and Se-methionine (>90%) was always the major Se species. Available Se (soluble and exchangeable fractions) accounted for 50.7% (yellow-brown soil) and 70.1% (calcareous alluvial soil) of soil total Se under Se treatment, while additional S application decreased the corresponding proportion of soluble Se by 12.6% and 14.4%. ConclusionsThe bioavailability of selenate in calcareous alluvial soil was higher than the bioavailability in yellow-brown soil and was more negatively affected by S application. Although S application inhibited Se uptake in soybean plants in both soil types, it did not influence seed Se speciation and Se-methionine was the major Se species.

Rhizospheric pore-water content predicts the biochar-attenuated accumulation, translocation, and toxicity of cadmium to lettuce

Metal bioavailability controls its behaviors in soil-plant system, especially involved in biochar amendment. This study compared a rhizospheric pore-water extraction against a BCR sequential extraction method to understand cadmium (Cd) bioavailability in two typical Chinese soils. Soils were spiked with five levels of Cd (CdCl2) and remediated with 3% corn-straw derived biochar. After 60 days of lettuce growth, Cd accumulation and enzyme activities in tissues were analyzed. Results showed that biochar increased soil properties (pH, CEC and SOM) compared to un-amended soils, but decreased contents of bioavailable Cd in soil pore-water (Cdpore-water) and BCR extracted Cd (CdFi+Fii). Contents of Cdpore-water were lower in yellow-brown soils than that in red soils. Pearson analysis showed that bioavailable Cd is negatively correlated with soil pH and CEC (p < 0.05). Cd accumulation in lettuce roots and leaves both were decreased by biochar addition, and the established linear equations proved that soil Cdpore-water is the best predictor for Cd accumulation in lettuce roots (r2 = 0.964) and in leaves (r2 = 0.953), followed by CdFi+Fii. Transfer factor (TF) values of Cd from roots to leaves were lower than 1, and slightly better correlated with soil Cdpore-water (r = −0.674, p < 0.01) than CdFi+Fii (r = −0.615, p < 0.01). Aggregated boosted tree (ABT) analyses indicated that soil properties together with Cdpore-water contribute more than 50% to root enzyme activities. Collectively, soil Cdpore-water is a promising predictor of Cd bioavailability, accumulation and toxicity in soil-plant system with biochar addition.

Growth and physiological responses of Pennisetum sp. to cadmium stress under three different soils.

Pennisetum sp. was employed as a model species to detect the growth and physiological response to cadmium (Cd) stress at different Cd concentrations (0, 20, 50, and 100 mg kg-1) in three types of soils (yellow brown soil, yellow soil, and red soil). Results showed that the growth of Pennisetum sp. was not significantly influenced by Cd in 20 mg kg-1, but significantly inhibited at higher Cd concentrations in three types of soils. Besides, the higher Cd concentrations, the lower root, stem, and leaf biomass. With Cd concentration of soil increasing, Cd content of root, stem, and leaf increased. Compared with no Cd, high Cd concentrations (50 and 100 mg kg-1) induced the physiological indices (photosynthetic rate, stomatal conductance, transpiration rate) and biochemical indices (nitrate reductase, glutamine synthetase, and glutamate synthase activities) decreasing, but the concentration of NO3- and NH4+ increasing. The activity of antioxidative enzymes (SOD, POD, and CAT) was disrupted and the content of malondialdehyde (MDA) increasing. Pennisetum sp. could protect cells from damage and maintain normal physiological metabolism via increasing the production of soluble sugar and soluble protein, but soluble proteins and soluble sugars were limited in high concentrations of Cd (50 and 100 mg kg-1). Moreover, the growth and physiological response to Cd are different in the three types of soils. The growth of Pennisetum sp. in yellow brown soil was better than that in other two soils, and the gas exchange rate, antioxidant enzyme activity, and nitrogen metabolism in yellow soil and red soil were more affected by Cd stress than that in yellow brown soil. Overall, Pennisetum sp. had certain tolerance and biosorption ability to Cd in different Cd concentrations and different types of soil. Hence, Pennisetum sp. was a suitable choice for Cd remediation, especially in yellow brown soil.

Synergistic effects of organic fertilizer coupled with phosphate-solubilizing and nitrogen-fixing bacteria on nutrient characteristics of yellow-brown soil under carbon deficiency

Understanding the dynamics of phosphate-solubilizing and N2-fixing bacteria on soil nutrient and related enzyme activity under different organic fertilizer proportions (OFP) could provide references for screening appropriate inoculant type, OFP, and fertilization period. Here, we set four OFP levels (mass ratio: 0%, 4%, 8%, 12%) and inoculated two phosphate-solubilizing bacteria (Bacillus megaterium, Pseudomonas fluorescens) and two N2-fixing bacteria (Azotobacter chroococcum, Azospirillum brasilence) in the subtropical yellow-brown barren soil. After a 60-day soil incubation under controlled conditions (28 ℃, darkness), we examined the impacts of single/mixed applications of beneficial bacteria on soil available nutrients and related enzyme activities at different OFP levels and different sampling times (3rd, 8th, 16th, 30th, 45th, 60th day). The results showed that soil available nutrient contents increased with the elevated OFP levels, and exhibited as 12%>8%>4%>0%. With the extension of culture time, soil nutrient contents in all treatments first increased and then decreased. Compared with the single application of organic fertilizer, combined application of organic fertilizer and bacterial inoculants resulted in higher and longer improvement of soil nutrient contents and enzyme activities. The effects of inoculants on soil nutrient properties varied across four OFP levels. When the OFP was low (0-4%), inoculation significantly increased soil available nutrient contents, with no the differences between inoculants at the initial stage. However, with the extension of the culture time and the elevation of OFP, phosphate-solubilizing bacteria (especially for B. megaterium) significantly increased available phosphorus content while N2-fixing bacteria (especially for A. brasilence) significantly increased available nitrogen content. The mixed inoculant with four strains showed phosphate-solubilizing effect on soil and performed better than the single application of phosphate-solubilizing bacteria, but without prominent effect on nitrogen fixation. Soil nutrient contents were positively correlated with enzyme activity, which was affected by both cultural time and carbon-nitrogen ratio. Bacterial inoculations could significantly increase nutrient contents in the short term, but the specific functions of beneficial bacteria on soil were highly dependent on organic carbon input and carbon-nitrogen ratio. Coupled application of inoculants and organic fertilizer at an appropriate OFP level (8%-12%) could increase and extend the soil-remediating effects, while the inoculation should be conducted with an interval of 45-60 days to ensure the survival rate and the consecutive effect on soil.

Distribution, origin and speciation of soil selenium in the black soil region of Northeast China.

Selenium (Se) is an essential trace element within human beings that hold with crucial biological functions. Investigating the complex origin of soil Se is of great importance to scientifically approach the land use of Se-rich land use, and the respective promotion of regional economic development. In this study, 160 soil samples from 10 profiles in farmland and woodland were collected in Hailun city, which is a typical black soil region in Northeast China, in order to characterize the distribution and speciation of Se in the black soil, and to identify the origin of soil Se. The total selenium content in the soil ranges from 0.045 to 0.444μgg-1, with an average selenium content in black soil (0.318μgg-1) of three times greater than that found in the yellow-brown soil (0.114μgg-1). The land-use type has a significant influence on the distribution of selenium in the black soil. Moreover, Se and heavy metals have a significant (positive or negative) correlation, in which TOC plays an important role. The black soil presents a consistent REE distribution pattern with underlying yellow-brown soil indicating black soil originates from yellow-brown soil. REE geostatistical analysis suggests that the soil Se partly originates from shale weathering and enriches in black soil. Moreover, elemental geochemical analysis and XRD results show that the paleoclimate change from humid and warm to dry and cold is favorable for organic matter accumulation, resulting in less leaching and enhanced adsorption of selenium into the black soil.

Physiological and biomass partitioning shifts to water stress under distinct soil types in Populus deltoides saplings

Abstract Aims Although soil environments exist extensive heterogeneity for many plants with a wide range of distribution, researches about effects of soil conditions on plants’ tolerance and adaptation are particularly inadequate. In our study, the aims are to reveal physiological strategies of Populus deltoides against drought stress under different soil conditions and to select the most suitable soil type for P. deltoides plantation. Methods Under controlled conditions, we used P. deltoides as a model species to detect differences in gas exchange rate, antioxidative capacity, nitrogen metabolism and biomass accumulation and partitioning in response to drought stress under three mineral soil types with distinct physicochemical characters, i.e. red soil (RS), yellow soil (YS) and yellow-brown soil (BS). Important Findings Exposure to 25% of field water holding capacity in soil for 3 months had significantly decreased biomass of all organs, photosynthetic rate, enzyme activities related to N assimilation, but increased H2O2, malondialdehyde and content of both NO3− and NH4+, when P. deltoides was planted in both RS and YS. In contrast, under BS, there are slightly negative effects exerted by water deficit on total biomass, gas exchange rate, activities of enzymes related to nitrogen metabolism and membrane damage caused by reactive oxygen species, which can be associated with a consistent increase in superoxide dismutase, peroxidase and catalase, and a higher ratio of root mass to shoot mass. It is concluded that, such higher capacity in tolerance and adaptation against drought stress under BS relative to both RS and YS could be accounted for more sufficient nutrient provision in soil parental materials and better soil aeration conditions which play a vital role in plant acclimation to water shortage. Our study also revealed that, distribution areas of BS might be preferable for cultivation of P. deltoides, when compared with those of RS and YS.