•Physical and chemical properties of nanoscale bamboo charcoal were systematically investigated.•Nanoscale bamboo charcoal was tested for phenanthrene sorption in aqueous and soil-water systems.•Nanoscale bamboo charcoal had high ability for phenanthrene sorption in soil-water system, even at a low addition rate of 0.2% in soils.•Nanoscale bamboo charcoal would be more competitive than some biochars in aqueous and soil-water systems.•This finding increases our knowledge of nanoscale bamboo charcoal for organic pollutants remediation in soil.This study investigated the characteristics of nanoscale bamboo charcoal (NBC), and made a comparison with microscale bamboo charcoal (MBC) on how they impact on the sorption abilities of different soils. The two charcoals contained similar elemental contents (e.g., high C, low H and low N) and various functional groups on their surfaces (e.g., aromatic structure, carboxyl, and hydroxyl). However, NBC had a larger total pore volume than that of MBC and was more likely to generate multi-layer sorption of phenanthrene. Controlled by van der Waals forces and electrostatic forces, NBC formed meso-and macropores (intra-particle porosity) and a more intricate pore structure. The performance of NBC in aqueous and soil-water systems was conspicuous and impressing. In aqueous system, by virtue of its larger pore volume, surface area and nonprotonated aromatic carbon, the Kd (sorption coefficient) of NBC reached up to 1.24 × 106, almost 10 times higher than that of MBC. In soil-water systems, although it could aggregate and react with compounds in soil, the performance of NBC was not weakened by the complicated soil properties, and was still more capable of phenanthrene sorption than MBC, even at an extremely low addition rate 0.2% in soils. Additionally, in comparison with some other common biochars, NBC still showed a promising capacity for phenanthrene sorption in two systems. This finding increases our knowledge of NBC for the remediation of organic pollutants in soil and indicates that the addition rate of charcoals in soils could be reduced by lessening the particle size. Therefore, NBC provides a new possibility for soil pollutant remediation and deserves further research.Download high-res image (222KB)Download full-size image

Soil acidification is universal in soybean-growing fields. The aim of our research was to evaluate the effects of soil additives (N fertilizers and biochar) on crop performance and soil quality with specific emphasis on ameliorating soil acidity.Four nitrogen treatments were applied as follows: no nitrogen (N0), urea (N1), potassium nitrate (N2), and ammonium sulfate (N3), each providing 30 kg N ha−1. Half plot area of the N1, N2, and N3 treatments was also treated with biochar (19.5 t ha−1) to form N-biochar treatments (N1C, N2C, N3C). Both bulk and rhizosphere soils were sampled separately for the following analyses: pH, exchangeable base cations (EBC), exchangeable acidity (EA), total inorganic N (IN), total N (TN), and microbial phospholipid fatty acids (PLFAs). Soybean biomass and nutrient contents were also determined. Correlation analysis was applied to analyze the relationships between soil chemical properties and soybean plant parameters.With N-biochar additions (N1C, N2C, N3C), soil chemical properties changed as follows: pH increased by 0.6–1.2 units, EBC, IN, and TN increased by 175–419, 38.5–54.7, and 136–452 mg kg−1, respectively, and PLFAs increased by 23.6–40.9 nmol g−1 compared to the N0 in the rhizosphere. Microbial PLFAs had positive correlations with soil pH; EBC; exchangeable K, Ca, Na, and Mg; TN; IN; NH4+; and NO3− (r = 0.66–0.84, p < 0.01). There were negative correlations between PLFAs and EA or exchangeable Al (r = −0.64, −0.66, p < 0.01), which indicated that the additives increased microbial biomass by providing a suitable environment with less acid stress and more nutrients. The additives increased soil NH4+ and NO3− by promoting soil organic N mineralization and reducing NH4+ and NO3− leaching. Moreover, the soybean seed biomass and the nutrient contents in seeds increased with N-biochar additions, especially in the N3C treatment.N-biochar additions were effective in ameliorating soil acidity, which improved the microenvironment for more microbial survival. N-biochars influenced N transformations at the plant–soil interface by increasing organic N mineralization, reducing N leaching, and promoting N uptake by soybeans. The soil additive ammonium and biochar (N3C) were best in promoting soybean growth.

•High-ash biochars can reduce DNA extraction efficiency from soil.•Hydrophobic interactions may cause low extraction efficiencies with biochar.•DNA extraction efficiencies from biochar particles increase over time.•Biochar decreases extraction efficiency of surrounding soil over time.Biochar additions to soil have, in some cases, been shown to reduce the DNA extraction efficiency, but the mechanisms remain unclear and commonly used high-ash biochars have not been investigated. We studied the effects of pyrolysis temperatures (300 or 700 °C), post-pyrolysis extractable organic carbon (separating acetone extractable C, AeC), and soil incubation on DNA extraction efficiency using high-ash swine manure biochar. We used quantitative PCR to measure the extraction efficiency of an internal DNA standard (Aliivibrio fischeri) added to samples before extraction. DNA extraction efficiency from biochars decreased by 39% as pyrolysis temperature increased from 300 to 700 °C (p < 0.05). AeC from biochar 300 °C increased DNA extraction efficiency for biochars made at both pyrolysis temperatures and when added to biochar 700 °C, the extraction efficiency increased by 52% (p < 0.05). Incubation in soil increased DNA extraction efficiency from isolated biochar particles by up to 28% (main effect p < 0.05). However, biochar-soil mixtures had up to 24% lower DNA extraction efficiency compared to what would be predicted based on a simple mixing model of incubated soil and separated biochars. Biochar pyrolysis temperature, extractable C, and incubation with soil were all associated with changes in DNA extraction efficiency. The differences in DNA extraction efficiency indicated that caution must be exercised when comparing microbial abundance and diversity with different biochar additions, even for high-ash biochars.Download high-res image (168KB)Download full-size image

•On-going soil acidification is an important global issue.•Biochar is of great potential value in decreasing soil acidification.•Effectiveness and mechanism of biochars on acid soil improvement are discussed.•Biochar is as effective as other soil additives as acid soil amendment.A large number of soils, worldwide, are acid (normally pH < 5.5) and suffering from on-going soil acidification. Acid soils or soils undergoing acidification generally have low fertility and low crop productivity. Biochars have been reported to be of potential value in agriculture for improving soil properties and in reducing the hazards caused by soil acidification and in naturally acidic soils. However, the ameliorant effects of biochars on acid soils and the mechanisms involved have not previously been critically reviewed. Here we summarize the phenomena, and mechanisms involved in the improvement of soil acidity by biochars, the alleviation of aluminum toxicity, the enhancement of nutrient availability, and changes in nitrification by collating data in the literature. In addition, the agronomic effectiveness and environmental concerns in the incorporation of biochar and other soil additives (i.e. lime, industrial by-products, organic wastes and plant residues) to acid soils are systemically compared. We conclude that biochar is a potentially effective amendment to reverse or to prevent acidification in acid soils. Finally, perspectives for further research in terms of soil acidification are presented to address some issues that are still poorly understood and/or highly controversial.Download high-res image (247KB)Download full-size image

Soil microbiota play a critical role in soil biogeochemical processes and have a profound effect on soil functions. Recent studies have revealed microbial co-occurrence patterns in soil microbial communities, yet the geographic pattern of topological features in soil microbial co-occurrence networks at the continental scale are largely unknown. Here, we investigated the shifts of topological features in co-occurrence networks inferred from soil microbiota along a continental scale in eastern China. Integrating archaeal, bacterial and fungal community datasets, we inferred a meta-community co-occurrence network and analyzed node-level and network-level topological shifts associated with five climatic regions. Both node-level and network-level topological features revealed geographic patterns wherein microorganisms in the northern regions had closer relationships but had a lower interaction influence than those in the southern regions. We further identified topological differences associated with taxonomic groups and demonstrated that co-occurrence patterns were random for archaea and non-random for bacteria and fungi. Given that microbial interactions may contribute to soil functions more than species diversity, this geographic shift of topological features provides new insight into studying microbial biogeographic patterns, their organization and impacts on soil-associated function.

The production of large quantities of biochar from natural fires has been a part of human history for millennia, causing CO2 emissions to the atmosphere and exerting long-term effects on soil processes. Despite its potential importance and recent work reflecting the wide interest in biochar, a general review of our deep understanding of biochar functions within forest soils is currently lacking. Gaps in research knowledge in this field are identified in this paper.This paper summarizes recent research to provide a better understanding of the concentrations, distribution, and characteristics of biochar produced from forest wildfire and its influences on soil processes. Perspectives and recommendations for future research on biochar in post-fire forest soils are also discussed.The concentration, distribution, and characteristics of biochar produced from forest wildfire largely depend on forest landscapes, regional climates, and mostly its feedstock and fire history, like, its duration and severity. The influences of biochar on soil processes, particularly carbon and nitrogen transformations and cycling, like, nitrification and nitrous oxide emissions reduction (Clough and Condron, J Environ Qual 39:1218–1223, 2010), are also determined mainly by the fire temperature and raw materials. Mechanisms can be attributed to the adsorption of organic compounds and nutrients or changed microenvironment, termed as charsphere, by biochar. We also identify the microbial mechanisms involved in the biochar-containing soils.

Carbon isotopic analysis and molecular-based methods were used in conjunction with geochemical data sets to assess the dechlorination of pentachlorophenol (PCP) when coupled to biogeochemical processes in a mangrove soil having no prior history of anthropogenic contamination. The PCP underwent 96% dechlorination in soil amended with acetate, compared to 21% dehalogenation in control soil. Carbon isotope analysis of residual PCP demonstrated an obvious enrichment of 13C (εC, −3.01 ± 0.1%). Molecular and statistical analyses demonstrated that PCP dechlorination and Fe(III) reduction were synergistically combined electron-accepting processes. Microbial community analysis further suggested that enhanced dechlorination of PCP during Fe(III) reduction was mediated by members of the multifunctional family of Geobacteraceae. In contrast, PCP significantly suppressed the growth of SO42– reducers, which, in turn, facilitated the production of CH4 by diversion of electrons from SO42– reduction to methanogenesis. The integrated data regarding stoichiometric alterations in this study gives direct evidence showing PCP, Fe(III), and SO42– reduction, and CH4 production are coupled microbial processes during changes in soil redox.

An analytical procedure for determination of water- and methanol-extractable pentachlorophenol (PCP) in soils was developed using vortex-assisted liquid-liquid extraction (VALLE) and gas chromatography (GC). Significant extraction parameters such as vortex speed and liquid-liquid volume ratio were optimized for extracting PCP from solution. The recovery of PCP was the highest (97.4%) with good reproducibility and a small relative standard deviation (RSD, 0.5%) when the vortex speed was at 2000 rpm. Meanwhile, when the volume ratio of derivatization solution to n-hexane was at 10:4, the recovery of PCP was 103% with a RSD of 0.7%. The linearity of the calibration curve for PCP determination ranged from 1.25 μg L−1 to 4000 μg L−1, with a correlation coefficient (R2) of 0.9999. The detection limit of PCP in water samples was below 0.2 μg L−1 and the measuring range was relatively wide, and suitable for trace- and micro-analysis of PCP. Compared with traditional extraction methods (liquid-liquid and solid-phase), VALLE consumes less extractant, requires fewer steps, and achieves higher recovery (96.8%) and smaller RSD (3.7%). The reliability of VALLE was verified in four distinct types (paddy, red, black and alluvial) of soil samples spiked with 1 and 10 mg kg−1 PCP. The total recoveries of PCP in the soil samples were in the range of 89.5%–98.9% by water extraction and 88.7%–98.4% by 3 consecutive extractions with methanol in a sequential procedure. The results indicated that VALLE-GC satisfied the requirements for extracting and determining water- and methanol-extractable PCP in soils polluted by PCP at varying levels.An analytical procedure for determination of water- and methanol-extractable pentachlorophenol (PCP) in soils was developed using vortex-assisted liquid-liquid extraction (VALLE) and gas chromatography (GC). The VALLE-GC method satisfied the requirements for extracting and determining different fractions of PCP in soils at varying PCP pollution levels.

Understanding the adsorption processes of Escherichia coli O157:H7 in the soil–water system is important in order to protect public health from waterborne diseases. The aim of this study was to investigate the role of pH on E. coli O157:H7 adsorption on kaolinite and goethite.The adsorption of E. coli O157:H7 on kaolinite and goethite over a wide range of pH levels (3–10) was determined. Confocal microscopy, zeta potential, classic Derjaguin–Landau–Verwey–Overbeek (DLVO) theory, and Fourier transform infrared spectrometry were used to provide insights into the mechanisms that affect E. coli O157:H7 adsorption.E. coli O157:H7 adsorption was greater on the positively charged goethite than on the negatively charged kaolinite. The maximum adsorption of E. coli O157:H7 occurred on goethite at pH 3, and increasing pH resulted in decreased adsorption on kaolinite and goethite. Confocal microscopy images confirmed that higher affinities of E. coli O157:H7 occurred on kaolinite and goethite at low pH. Zeta potential, interaction energy, and Fourier transform infrared analysis indicated that electrostatic forces between the E. coli O157:H7 and goethite surfaces controlled the extent of E. coli O157:H7 adsorbed onto goethite surfaces at low pH, and hydrogen bonding and inner-sphere complexation play majors roles in E. coli O157:H7 adsorption to goethite at high pH levels. However, electrostatic force is not the main force for E. coli O157:H7 adsorption to kaolinite.Goethite displayed a larger adsorption capacity for E. coli O157:H7 than kaolinite. The adsorption of bacteria on kaolinite and goethite was pH dependent, and high percentages of E. coli O157:H7 adsorption to kaolinite and goethite occurred at low pH levels.

To compensate for the shortcomings of manure biochar, an lignocellulose-based feedstock (rice straw) was added into manure-based feedstock (swine manure) at 3:1, 1:1, and 1:3 (w/w) manure/straw ratios during biochar production within the pyrolysis temperature ranging from 300 to 700 °C. The results showed that the pyrolysis temperatures and the proportions of straw added both influenced the biochar properties. The overall properties of biochars at 300, 400, and 500 °C were thoroughly different from those at 600 and 700 °C by principal components analysis (PCA). The XRD, FTIR, and SEM spectra suggested that the addition of straw considerably changed the mineral crystals, functional groups, and porous structures in manure biochar, respectively. The Zn(II) adsorption batch experiments showed that the biochars with more proportions of manure had the largest Zn(II) adsorption capacity than other biochars at 300 °C, which was attributed to the mineral components, oxygen functional groups, and surface areas. To meet varied agronomic and environmental requirements, the different conditions including pyrolysis temperatures and proportions of straw added should be quantitated.

Vertical variations of pentachlorophenol (PCP) dissipation and microbial community were investigated in a paddy soil with the addition of electron acceptors (NO3–, SO42–) and donors (crop residues). Crop residues enhanced PCP dissipation by supplying dissolved organic carbon (DOC) as an electron donor, whereas NO3– and SO42– inhibited it. The dissipation of PCP in electron donor treatments resulted in the accumulation of 3,4,5-trichlorophenol (3,4,5-TCP) except for wheat residues. The abundance and diversity of phospholipid fatty acids (PLFAs) decreased with increasing soil depth. The succession of predominant PLFAs shifted from aerobic bacteria to anaerobic bacteria when electron acceptors were changed to electron donors. The saturated/monounsaturated fatty acids (S/M) ratio increased with soil depth, which probably implied that nutrient turnover rate declined after the accumulation of 3,4,5-TCP. The results showed that the addition of electron donors and acceptors modified the microbial communities, which then further influenced the degradation pathway of PCP.

A greenhouse experiment was conducted to investigate the effects of zucchini (Cucurbita pepo L.), inoculated with the arbuscular mycorrhizal (AM) species Acaulospora laevis, Glomus caledonium, and Glomus mosseae, on the soil bacterial community responsible for Aroclor 1242 dissipation. The dissipation rates of Aroclor 1242 and soil bacteria abundance were much higher with the A. laevis and G. mosseae treatments compared to the non-mycorrhizal control. The biphenyl dioxygenase (bphA) and Rhodococcus-like 2,3-dihydroxybiphenyl dioxygenase (bphC) genes were more abundant in AM inoculated soils, suggesting that the bphA and Rhodococcus-like bphC pathways play an important role in Aroclor 1242 dissipation in the mycorrhizosphere. The soil bacterial communities were dominated by classes Betaproteobacteria and Actinobacteria, while the relative proportion of Actinobacteria was significantly (F = 2.288, P < 0.05) correlated with the PCB congener profile in bulk soil. Our results showed that AM fungi could enhance PCB dissipation by stimulating bph gene abundance and the growth of specific bacterial groups.

The Escherichia coli (E. coli) O157:H7 survival dynamics in original and pH-modified agricultural soils were investigated to determinate how E. coli O157:H7 survival responded to the pH values of different soils, identify the relationships between E. coli O157:H7 survival time (td) and soil properties, and assess the potential pathogen contamination after soil pH changed.The six soil samples were collected from different provinces of China, and 18 pH-modified soil samples were obtained from original soils by treating the original soils with direct electric current. The E. coli O157:H7 cells were inoculated into 24 soils and incubated at soil moisture of −33 kPa and 25 °C. The soils were sampled for determining the numbers of E. coli O157:H7 at given time intervals over the incubation. The effects of soil pH change and other properties on the td values were analyzed.The td values in the test soils were between 7.1—24.7 days. Results indicate that soil pH, texture, and free Fe2O3 (Fed) were the most important factors impacting the td values in the test soils. Further, the response of E. coli O157:H7 survival to pH change varied with different soils. In the acidic soils (shorter td values), the td values decreased as the pH decreased and Fed increased, while in the neutral or alkaline soils (pH ≥ 6.45, longer td values), the td values did not change significantly with pH.The changes of amorphous and free sesquioxides induced by pH change might strengthen the response of E. coli O157:H7 survival to soil pH. Closer attention should be paid to E. coli O157:H7 long survival in soils and its potential environmental contamination risk.

Field survey and sampling of vegetable greenhouse soils were conducted in Shouguang, Shandong Province, and Ningbo, Zhejiang Province to study the acidification and salinization characteristics of soils with different initial soil pH values and greenhouse cultivation time.The pH, electrical conductivity (EC), and ion composition of 74 composite soil samples were analyzed to evaluate their relation to soil acidification and salinization.Compared with their corresponding open-field soils, acidification and salinization of the greenhouse soils occurred in both 0-20 cm and 20-40 cm soil layers for the Shouguang and Ningbo soils. The soil pH decreased gradually at different rates as greenhouse cultivation time increased in the two surveyed regions, but the opposite trend was observed for soil EC. For the Shouguang soils, while the percentages of K+ and NO3− increased dramatically and Ca2+ and HCO3- decreased significantly after the soils were converted to greenhouse use, the correlation between soil pH and EC was significant, and the stepwise multiple regression analysis further showed that there was a significant correlation between pH and the percent of Ca2+ and HCO3−.Soil acidification and salinization are common in greenhouse soils with different initial soil pH. Soil acidification in the Shouguang soils is a result of decrease in the percent of Ca2+, HCO3− due to over application of N and K fertilizers. Future research should be devoted to understanding the relevant mechanisms in greenhouse soils with lower initial soil pH values to assess if there are correlations between soil acidification and salinization under greenhouse cultivation.

A laboratory incubation under constant temperature and humidity was conducted to estimate the impacts of nitrogen (N) fertilizers on the acidification of two acid soils (Plinthudult and Paleudalfs) in south China.The experiment had three treatments, i.e., control (CK), addition of urea (U), and addition of ammonium sulfate (AS). We measured soil pH, nitrate (NO3−), ammonium (NH4+), exchangeable hydrogen ion (H+), and aluminum ion (Al3+) concentrations at various intervals during the 90 days of incubation. Soil buffering capacity (pHBC) was also measured at the end of the experiment.The application of N fertilizers resulted in soil acidification. The U treatment caused greater acidification of the Plinthudult soil than the AS treatment, while there were no differences between U and AS treatments on the acidification of the Paleudalfs. At the end of the trial, the pHBC of Plinthudult in AS treatment was greater than that in CK and U treatments, which may be due to the buffering system of NH4+ and NH4OH. However, the pHBC of Paleudalfs was unchanged between treatments. The dynamics of exchangeable H+ and Al3+ corresponded to that of soil pH. Correlation analysis showed that both soil exchangeable H+ and soil exchangeable Al3+ were significantly related to soil pH.Application of urea and ammonium sulfate caused acidification in both soils and increased soil exchangeable Al3+ and H+ concentrations in the Paleudalfs. The application of urea increased exchangeable Al3+, and ammonium sulfate increased pHBC in the Plinthudult.

Initial soil pH determines the direction and magnitude of pH change after residue addition. This study aimed to evaluate the relative importance of initial soil pH and rate of residue application in determining subsequent pH change, nitrogen (N) mineralization, and soil-exchangeable aluminum (Al).An incubation experiment was conducted for 102 days on a Plinthudult soil and a Paleudalf soil, where pH gradients were produced after application of direct current (DC). Rates of vetch applications were 0, 5, 15, 30, and 50 g kg−1 soil.Increasing rates of vetch application caused greater increases in soil pH, but no consistent increase in soil pH at higher initial pH range (4.40∼6.74), because of nitrification. There was a positive correlation between alkalinity production and the initial soil pH at day 14, while correlations became negative at days 56 and 102. Mineral N accumulated as NH4+–N in low pH soils, due to limited nitrification, while NO3−–N dominated in higher pH soils. Application of vetch decreased KCl-extractable Al, probably because of complexation of Al by organic matter and precipitation of Al as a result of increased pH, reductions in Al concentration increased with increasing rates of vetch application. However, this amelioration effect on Al concentration weakened with time in higher pH soils.Application of vetch residue can significantly increase soil pH and concentrations of mineral N and reduce exchangeable Al. These amelioration effects are enhanced with increased rate of vetch addition and vary with time depending on the initial pH of the soil.

The aim of the research was to explore the effect of Chinese milk vetch (CM vetch) addition and different water management practices on soil pH change, C and N mineralization in acid paddy soils.Psammaquent and Plinthudult paddy soils amended with Chinese milk vetch at a rate of 12 g kg−1 soil were incubated at 25 °C under three different water treatments (45 % field capacity, CW; alternating 1-week wetting and 2-week drying cycles, drying rewetting (DRW) and waterlogging (WL). Soil pH, dissolved organic carbon, dissolved organic nitrogen (DON), CO2 escaped, microbial biomass carbon, ammonium (NH4+) and nitrate (NO3−) during the incubation period were dynamically determined.The addition of CM vetch increased soil microbial biomass concentrations in all treatments. The CM vetch addition also enhanced dissolved organic N concentrations in all treatments. The NO3–N concentrations were lower than NH4–N concentrations in DRW and WL. The pH increase after CM vetch addition was 0.2 units greater during WL than DRW, and greater in the low pH Plinthudult (4.59) than higher pH Paleudalfs (6.11) soil. Nitrogen mineralization was higher in the DRW than WL treatment, and frequent DRW cycles favored N mineralization in the Plinthudult soil.The addition of CM vetch increased soil pH, both under waterlogging and alternating wet–dry conditions. Waterlogging decreased C mineralization in both soils amended with CM vetch. Nitrogen mineralization increased in the soils subjected to DRW, which was associated with the higher DON concentrations in DRW than in WL in the acid soil. Frequent drying–wetting cycles increase N mineralization in acid paddy soils.

Biochars have been considered as useful soil amendments due to their beneficial properties in improving soil fertility, carbon (C) sequestration, and soil decontamination. In our study, a series of biochars produced from different types of feedstocks at two pyrolysis temperatures (300 and 500 °C) were characterized to evaluate their different potentials as soil amendments.Ten types of feedstocks were used to prepare biochars at the pyrolysis temperatures of 300 and 500 °C, for 2 h. Chemical and physical analyses, X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier Transform Infrared (FTIR) analyses were conducted to determine differences in biochar properties. Then, soil incubation studies were used to investigate the relationships between these biochar properties and their different ameliorant values in soil.The pH, ash, total C, total potassium, total phosphorus, total base cation concentrations, surface areas, and total pore volumes of biochars produced at 500 °C were higher than at 300 °C, while the reverse applied for yields, total oxygen and total hydrogen, and average pore widths and particle sizes. Cluster analysis suggested that biochars derived from similar feedstock types belonged in the same category. The SEM, XRD, and FTIR analyses of typical biochars from the different categories suggested both variations and similarities in their characteristics. In addition, the results from soil incubation experiments were consistent with the conclusions made from biochar characteristics analysis.Biochars derived from swine manures, fruit peels, and leaves with high pH and macro-nutrients appeared appropriate to increase soil pH and soil nutrient availability; whereas, biochars from wetland plant residues with high C concentrations and Brunauer–Emmett–Teller were better for soil C sequestration and contaminant adsorption.

The objective of the present study was to explore the effect of initial pH on the decomposition rate of plant residues and the effect of residue type on soil pH change in three different paddy soils.Two variable charge paddy soils (Psammaquent soil and Plinthudult soil) and one constant charge paddy soil (Paleudalfs soil) were used to be incubated at 45 % of field capacity for 105 days at 25 °C in the dark after three plant residues (Chinese milk vetch, wheat straw, and rice straw) were separately added at a level of 12 g kg−1 soil. Soil pH, CO2 escaped, DOC, DON, MBC, MBN, NH4+, and NO3− during the incubation period were dynamically determined.Addition of the residues increased soil pH by 0.1–0.8 U, and pH reached a maximum in the Psammaquent and Plinthudult soils with low initial pH at day 105 but at day 3 in the Paleudalfs soil with high initial pH. Incorporation of Chinese milk vetch which had higher concentration of alkalinity (excess cations) and nitrogen increased soil pH more as compared with incorporation of rice and wheat straws. Microbial activity was the highest in Chinese milk vetch treatment, which resulted in the highest increase of soil pH as compared with addition of rice and wheat straws. However, nitrification seemed to be inhibited in the variable charge soils of Psammaquent and Plinthudult but not in the constant charge soil of Paleudalfs.The effectiveness of increasing soil pH after incorporation of the plant materials would be longer in low initial pH soils of Psammaquent and Plinthudult than in high initial pH soil of Paleudalfs. In order to achieve the same degree of pH improvement, higher amounts of plant residues should be applied in constant charge soils than in variable charge soils.

Sorption and desorption of butachlor were simultaneously investigated on synthesized pure amorphous hydrated Fe oxides (AHOs Fe), and soils both with and without surface coating of AHOs Fe, with special interest towards how amorphous sesquioxides affect and contribute to butachlor retention in soils.The AHOs Fe was artificially synthesized pure materials. Two soils with contrasting physicochemical properties selected for study were black soil and latosol, belonging to permanent charged soil and variable charged soil, respectively. Both soils were further treated using AHOs Fe for detecting the differentiation from native soils regarding butachlor retention produced after the soils were surface-coated by AHOs Fe. A sorption experiment was conducted using a batch equilibrium technique, and desorption was carried out immediately following sorption by three sequential dilution. Hysteresis index (HI) values were calculated to investigate desorption hysteresis by developing desorption isotherms concentration dependent and time dependent, respectively.The sorption capacity for butachlor increased in the order of AHOs Fe, uncoated soils, and soils with surface coating of AHOs Fe. The sorption capacity of both soils significantly increased after surface coating by AHOs Fe (p < 0.01), with a bigger increase achieved by black soil (52.0 %) as compared with that by latosol (45.3 %). Desorption of butachlor was coincidently hysteretic on AHOs Fe, and soils both uncoated and coated, whereas variation in desorption hysteresis was different between AHOs Fe and soils with increasing butachlor sorption loading, indicating different sorption mechanisms were operative for AHOs Fe and soils across the entire butachlor concentration range. Hysteresis of butachlor desorption was weakened after the soils were surface coated by AHOs Fe, as suggested by the changed HI values.With high specific surface area and highly reactive surfaces, the “active” AHOs Fe originally has a relatively high sorption capacity and affinity for butachlor. While in natural soils, where the inevitable association derived from soil organic matter (SOM) would restrain AHOs Fe from sequestrating butachlor directly, AHOs Fe may likely contribute in a mediator way by coordinating active sites both on and within SOM. This may enhance the availability of sorption domains both on and within soils, thereby achieved an enhanced but more reversible retention for butachlor in soils after their surfaces were coated by AHOs Fe. This study has extended the observations of the role of noncrystalline sesquioxides in retention of pesticides such as butachlor from pure clay mineral systems to natural soils.

The purpose of the present study are to analyze the temporal and spatial trends of the pesticide use on almond crops and assess their associated risk to soil, surface water, and air, and to investigate the impacts of pesticide risk on biodiversity.California Pesticide Use Report database was used to determine the organophosphate (OP) and pyrethroid use trends in the San Joaquin Valley for almonds from 1992 to 2005. Environmental potential risk indicator for pesticides model was employed to evaluate associated environmental relative risks in soil and in surface water. Emission potential of pesticide product was used to estimate the air relative risk. Geographical Information System was used to delineate the spatial distribution patterns of environmental risk evaluation in almonds and biodiversity.OP pesticide use has been declined in any measurement in almonds. However, a converse result was found for pyrethroid pesticide. Pesticide use trends reflect the profound changes in pest management strategies in the California almond farm community. The model results in this study showed evidence that pyrethroid posed less environmental risks to soil, air, and water resources than OP. The physiochemical properties of pyrethroid reflect a strong tendency to adsorb to organic carbons, and therefore, potentially move off-site attached to sediment. Once in sediments, they can be bioavailable to the aquatic food web. So, more future study on environmental model should address pyrethroid environmental risk on sediment. Ecologists revealed that endangered species diversity has good correlation with total species diversity, so we developed a biodiversity index by using the survey data of endangered and rare animals in California. The results showed a negative relationship between count of animal occurrence and predicted environmental risk. This result would be useful to help conserve California’s biological diversity by providing information to promote agricultural management and land-use decisions.Pesticide use trend is directly related to environmental risk. Pyrethroid posed less environmental risk than OP in this study. And also, this study got a noticeable result that pesticide uses in intensive agriculture and their associated environmental risks pose negative impacts on biodiversity.

Although the bioavailability of heavy metals has been widely investigated, little information is available on the spatial correlations of heavy metals in soil–rice systems at a regional scale. A study of heavy metals in soil–rice systems at a present rice production area could provide valuable information on the safety of rice production and provide guidelines beneficial to agriculture management and strategic sustainable agriculture in China and other rapidly developing regions in the world. The overall goals of this study were to identify the characteristics of metal fractions and their bioavailability to rice plants in the paddy fields of a present rice production region.In the rice harvest season (October 2006), 96 pairs of rice grain and rooted soil samples were collected from rice production area of Wenling in southeast Zhejiang province, China, which is one of the well-known electronic and electric waste (E-waste) recycling centers. Soil samples were analyzed for total heavy metal concentrations, metal fraction concentrations, and soil properties. Soil properties analyzed in this study included soil pH, electrical conductivity, organic matter, Fe oxides, and soil particle size distribution. Rice grain samples were analyzed for heavy metal concentrations. Multivariate statistical and geostatistical methods were applied to study the spatial dependence characteristics of metal fractions and their spatial correlation with uptake by rice plants in the rice production area and to identify the bioavailability of metal fractions to rice plants.The paddy soils of the studied area showed Cd contamination and some paddy soils presented a potential Cu, Ni, and Zn risk. The elevated levels of Cd were predominantly in non-residual (extractable) fractions. The percentage of Cd in fractions decreased in the order of exchangeable > Fe–Mn oxide bound > residual > organic bound fraction. In contrast, soil Cu, Ni, Pb, and Zn were mainly in the residual (non-extractable) fractions. The fractions of Ni, Pb, and Zn followed the order of residual > Fe–Mn oxide bound > organic bound > exchangeable fraction; the fractions of Cu decreased in the order of residual > organic bound > Fe–Mn oxide bound fraction. The spatial distribution patterns of non-residual fractions exhibited similarities with the highest metal concentrations in the northwest area owing to the industries and E-waste recycling activities. Most metals in rice grain were the strongest spatially correlated with the exchangeable fraction, followed by the organic bound fraction, indicating that exchangeable and organic bound fractions had the highest bioavailability. Rice Cd and Zn were strong spatially correlated with exchangeable, Fe–Mn oxide, and organic bound fractions; rice Ni and Cu were strongly spatially correlated with the exchangeable and organic bound fractions, respectively. The principal component analysis results also confirmed that exchangeable, Fe–Mn oxide, and organic bound soil fractions can be considered as bioavailable fractions to rice for Cd and Zn, while exchangeable and organic fractions were more important sinks for Ni and Cu, respectively.Due to a comparatively high input of Cd in the paddy soils, soil Cd was predominantly associated with non-residual fractions, especially with the exchangeable fraction. The soil Cu, Ni, Pb, and Zn were largely associated with the residual fraction while little associated with the exchangeable fraction. The bioavailability of the fractions to rice varied with metal fractions. In general, the exchangeable fraction had the highest bioavailability to rice plants, followed by the organic bound fraction. The bioavailability of the fractions to rice also varied with heavy metals. The exchangeable, Fe–Mn oxide, and organic bound fractions had high bioavailability to rice for Cd and Zn; the exchangeable and organic bound fractions had highest bioavailability for Ni and Cu, respectively.

The purpose of the present study was to investigate the composition and structure of microbial communities in rhizosphere soils in response to the presence of Aroclor 1242 with low (8 mg kg−1 soil) and high (16 mg kg−1 soil) concentrations in the hope to provide more information on potential dissipation of polychlorinated biphenyls (PCBs) at contaminated sites.A greenhouse experiment was conducted in a specially designed rhizobox, in which ryegrass (Lolium multiflorum L.) was grown for 90 days in the soil contaminated with Aroclor 1242 (a commercial mixture of PCBs) at 8.0 and 16.0 mg kg−1 soil. At the end of the experiment, Aroclor 1242 residues were extracted with hexane–acetone (v:v = 1:1, 30 mL) twice by ultrasonic agitation for 30 min. Microbial biomass was estimated from the total extractable phospholipid fatty acids (PLFAs) and PLFA profiles were analyzed to determine microbial community composition.Aroclor 1242 was moderately lost from both high (16.0 mg kg−1) and low PCBs levels (8.0 mg kg−1) at the end of the screening experiment. The PCBs concentrations had a great impact on the PLFAs total concentrations and profiles. The total PLFAs concentrations within each compartment of the control soils were higher than in the corresponding compartment of the contaminated soils at both high and low PCBs rates. Pollution may lead to a decrease in microbial diversity due to the elimination of species which lack sufficient tolerance to the stress imposed and enhanced population of other species which thrive under stress. Total bacterial and Gram-positive bacterial PLFA concentrations in each compartment were highest in control soils. The rapid disappearance of bacteria in the high-level PCBs treatment could be explained by the high concentrations of pollutant which were sufficiently toxic to suppress their growth. It further showed that bacteria were more sensitive to persistent organic pollutants pollution. Fungal concentrations were observed to increase with the increase in PCBs concentrations. This may be because fungal growth is C limited and probably lives on the PCB-killed bacteria.Microbial biomass and profiles responses to PCBs contamination levels varied. The greatest fungal biomass in the high PCBs pollution treatment indicated that soil fungi have a high tolerance to pollutants and therefore a great potential for the bioremediation of toxic chemicals. The largest PLFAs concentration occurred at the near rhizosphere, not the root compartment, which fits well with PCBs dissipation.

Temperature is an important environmental factor regulating soil microbial biomass, activity, and community. Soils from different climatic regions may have very different dominant soil microbes, which are acclimated to the local conditions like temperature. Changing soil temperature especially warming has been shown to increase the mortality rate of soil microbes. However, little is known about the responses of soil microbes coming from different climatic regions to different incubation temperatures. The objective of this study was to examine the temperature effects on microbial biomass and community of soils collected from cold, intermediate, and hot natural sites.Soils were collected from northern (Heilongjiang province), central (Jiangsu province), and southern (Guangxi province) China, these soils having very different temperature histories. The Heilongjiang soil was from the coldest region with a mean annual temperature of 1.2°C, the Jiangsu soil was intermediate with a mean annual temperature of 15.7°C, and Guangxi soil was from the hottest area, with a mean annual temperature of 21.2°C. These three soils were incubated at 4°C, 15°C, 25°C, and 35°C for up to 56 days. Phospholipid fatty acid (PLFA) analyses were conducted on days 0, 3, 7, 14, 28, and 56 to track the dynamics of soil microbes.Soil microbial biomass indexed by total phospholipid fatty acid concentration decreased with increasing incubation temperature, with that of the Heilongjiang soil decreasing most. At the end of incubation, the biomass at 35°C in the Heilongjiang, Jiangsu, and Guangxi soils had declined to 65%, 72%, and 96% of the initial biomass, respectively. The PLFA patterns shifted with increasing temperatures in all the soils, especially at 35°C; the change was biggest in the Heilongjiang soil.History does have effects on soil microbes responding to environmental stress. Soil microbial biomass and PLFA profiles shifted least in the Guangxi soil with the hottest temperature history and most in the Heilongjiang soil with the coldest temperature, indicating that the distribution of free-living microorganisms is influenced by climatic factors. The majority of soil microorganisms coming from the hot regions are more adapted to high temperature (35°C) compared to those from the cold area. There are some regular changes of PLFA profiles when increasing incubation temperature to 35°C. However, the effect of incubation temperature on soil microbial community structure was inconclusive. As PLFA profile community structure is the phenotypic community structure. Genotype experiments are required to be done in future studies for the better understanding of soil microbes in different climate regions with concerning temperature variation.With the increasing incubation temperature, soil microbial biomass and PLFA profiles shifted most in the soil with the coldest temperature history and least in the soil with the hottest temperature. History does matter in determining soil microbial dynamics when facing thermal stress.

The assessing bias of rhizosphere effect on polycyclic aromatic hydrocarbons (PAHs) degradation in soils would come out from formation of nonextractable PAHs and extractability difference of various solvents. The aim of this study was to evaluate the role of rhizosphere effect in long-term PAHs polluted soils by using sequential extraction approach.The scheme of sequential extraction included methanol/water extractable PAHs, butanol extractable PAHs, DCM extractable PAHs, humic acid-bound PAHs, crude humin-bound PAHs, and organic-C enriched humin-bound PAHs. PAHs in plant tissues were extracted by dichloromethane after saponifying. The correlations between PAHs in plant tissues and sequentially extracted fractions were generated by partial least squares regression.The profiles of sequentially extracted PAHs varied with plant species. The discrepancy of toxicity equivalency concentrations between rhizosphere and bulk soils was much more significant than that of total PAHs concentrations. In partial least squares regression models, the concentration of PAHs in plant tissues was correlated with fractions strongly associated with soil.The novelty of this study is the evaluation of concentration and toxicity equivalency concentration of PAHs in rhizosphere of crops sampled in a field polluted with PAHs for long term. This study has highlighted more significant role of rhizosphere in cleanup of cancerogenic toxicity of soil than amount of PAHs in polluted soils.

The relationship between plant absorption and accumulation of heavy metals and the effect of iron plaque on roots of wetland plants are unknown, especially for plants grown in heavy metal-contaminated soil. This experiment was designed to study the effects of iron addition on the formation of iron plaque in the rhizosphere of the wetland plant species Iris pseudacorus L. in artificial Pb-contaminated soil and the effects of iron plaque on Pb accumulation by plants.Soil was collected from 0- to 30-cm depth of a clayey illitic thermic typic epiaqualfs in an abandoned paddy field in Jiaxing of Zhejiang Province, China. The seeds of yellow flag (I. pseudacorus L.) were germinated in soil mixed with vermiculite and grown for 30 days. Three treatments of iron (0, 100, and 500 mg Fe kg−1 as FeSO4) were added when uniform seedlings were transplanted into plastic pots filled with 1.0-kg soil, which had been previously treated with four treatments of Pb [0, 100, 500, and 1,000 mg Pb kg−1 as Pb(NO3)2] and waterlogged for 72 days. The yellow flags were grown in a greenhouse for 60 days. The plaque on roots was extracted using the cold DCB (dithionite–citrate–bicarbonate) technique. The plant samples were digested with 10 mL concentrated nitric acid by microwave digestion. The concentration of Fe and Pb were determined using atomic spectrophotometry (NovAA300, Germany).The amount of iron plaque on the roots of yellow flag (I. pseudacorus L.) was markedly affected by Fe addition but not by Pb addition. The total Pb accumulated in plants was increased initially and then decreased with the addition of Fe in three lower Pb treatments (0, 100, and 500 mg Pb kg−1) but decreased with more Fe addition in the 1,000 mg Pb kg−1 treatment. The pH value was decreased with the addition of more iron, which increases Pb availability, and heavy doses of iron caused iron toxicity. Plant growth decreased due to iron toxicity at higher iron additions (500 mg kg−1), while Pb accumulation decreased. Intermediate levels of iron supply (100 mg kg−1) enhanced Pb absorption in roots, which improved phytoremediation effectiveness.Iron supply enhanced the amount of iron plaque and increased both Pb adsorbed on the roots and Pb uptake by plants. However, plant growth was inhibited by iron toxicity at high iron dose (500 mg kg−1) and biomass decreased. The intermediate iron dose (100 mg kg−1) generally enhanced Pb absorption and accumulation, which enhances the ability of yellow flag to remove Pb from Pb-contaminated soils.

Longjing (Dragon Well) tea from the West Lake region of Hangzhou, China, is one of the highest quality green teas prized for drinking and is often called the national drink of China. However, the ever-increasing accumulation of lead (Pb) in Westlake Longjing tea has been continually reported in the recent decades, while the exact Pb sources still remain unclear. Our purpose is to investigate the key factors that account for the concentration increase of Pb accumulated in Longjing tea based on a broad regional scale.Eighty-one young tea leaves and corresponding soil and air samples where the tea plants grow in and around, respectively, were collected from three typical Longjing tea gardens for illustrating the sources of Pb that accumulated in Longjing tea. The sampling lines were arranged with the proximity to the traffic area. Pb concentrations in the tea leaves and soil and air samples were determined, respectively. Wash procedures were also conducted to trace the removable possibility and rates of Pb in young tea leaves. Simple statistical analysis and spatial geostatistics were further applied for the investigation of the potential relationship of Pb levels among young tea leaves and the relevant soil and air samples.The regional differences and seasonal variation of Pb concentration were found for young tea leaves, with the order of Longwu > Meijiawu > Longjing and spring > summer (p < 0.05), respectively. The significant positive correlation was found only for the Pb concentration between young tea leaves and air samples (r = 0.34, p < 0.01). The results from wash experiment showed that a substantial portion of Pb in young tea leaves could be removed by wash, and the removable rates of Pb showed an obvious decrease with the increasing distance from the traffic area in Longwu and Meijiawu. A similar geographic distribution tendency of Pb between young tea leaves and air was also revealed by further geographic spatial analysis taking Longwu as a case. The significant correlations and similar distribution tendency of Pb concentration between young tea leaves and air suggested that atmospheric deposition could be an important, even predominant, source for Pb accumulated in Longjin tea. This non-edaphic contribution was further validated in wash experiment and testified to be distance dependent on the proximity to the main traffic area. This might be attributed to the large rough pubescent surface of tea leaves which are conducive to foliar deposition and/or absorption of Pb. The lack of correlations between young tea leaves Pb and soil Pb indicated that the contribution of soil Pb would be limited (especially near the traffic area where the influence of atmospheric Pb was dominant) and might be attributed to the low bioavailability of Pb in soils and finite uptake and transport of Pb from roots to shoots. Meanwhile, the higher Pb concentration in spring teas (compared with summer teas) might be due to the long growth period that allowed for a long time interception of Pb by young tea leaves through atmospheric deposition.The Pb that rooted in air was suggested as the main source accounting for the accumulation of Pb in Longjing Tea of the tested tea gardens. This non-edaphic contribution of atmospheric deposition was distance dependent on the proximity to the main traffic area. For alleviating the accumulation and elevation of Pb amount in Longjing Tea, efforts should be made especially during the period of spring tea growth. The additional wash procedure was also recommended before the tea leaf processing in factories.

The combined pollution of bensulfuron-methyl (BSM) and heavy metal Pb has been a common problem in agro-ecological environment in southern China. As an important natural clay mineral, the kaolinite structure possesses great advantages in many processes due to its high chemical stability and low expansion coefficient. The adsorption of BSM on kaolinite was therefore investigated at varying Pb2+ concentrations (0, 100, 500 and 1,000 mg kg−1) and different pH levels (3, 4 and 5) using the batch equilibration experiment.BSM was purchased from Aldrich Chemical Co. (purity, 98%), used as the model compound in this study. The experimental kaolinite was sampled from Yuhang in Zhejiang Province. The metal salts used in the study are Pb(NO3)2. The kaolinite samples were spiked with Pb at a rate of 100, 500 and 1,000 mg kg−1 air-dried soil, respectively. The adsorption of BSM on kaolinite was investigated using the batch equilibration experiment. The BSM concentration of the filtrate was determined by high-pressure liquid chromatography.The adsorption of BSM on kaolinite could be described by the Freundlich isotherm equation, with the R2 values greater than 0.959 in all experimental treatment. The presence of Pb2+ in kaolinite promoted the adsorption of BSM, and the higher Pb would generally lead to the stronger sorption of BSM by kaolinite based on the observed Kf values. The adsorption of BSM on kaolinite declined with the increase of pH, and the spiked Pb2+ aggravated the reduction of adsorption of BSM. The exclusion between BSM and kaolinite was strengthened with the increase of pH, which partially elucidated the adsorption of BSM decreasing with increasing pH of the solution. Some adsorption of Pb2+ took place along the outer hydroxyl plane, therefore releasing H+ ions located there. The spiked Pb2+ would promote the adsorption of BSM onto kaolinite by increasing the hydrogen (H+) ions concentration in solution. The interactions of the heavy metal cations with the kaolinite could affect the structure and other properties such as swelling capacity, compaction capability and the double-layer behaviour of kaolinite. In addition, the substitution of H+ ions for metal ions could change the Van der Wals force within the kaolinite structure. All these might lead to the increased sorption of BSM onto kaolinite at the presence of Pb2+.The addition of Pb2+ and the reduction of pH in solution would enhance the retention of BSM and thus effectively retard BSM from entering the aqueous phase. The mechanisms involved in the promotion effects of the spiked Pb2+ on adsorption might be primarily attributed to the increased hydrogen (H+) ions as a consequence of the addition of Pb2+. Further investigation would be required to give insight into the specific mechanism controlling the adsorption of BSM on kaolinite.

Four wetland plants were selected to study the effect of Fe plaque formation on phosphorus (P) accumulation in the rhizosphere and P uptake. There were significant positive correlations between the sorbed Fe content in the rhizosphere and the Fe plaque concentration (r2 = 0.8454, p < 0.01) and between P accumulation and the amount of the sorbed Fe in the rhizosphere (r2 = 0.8460, p < 0.01). The concentration of the Fe plaque on the root surface of four wetland plants species tested followed the order of Zizania cedu Ciflora Turez > Scirpus tabernaemontani Gmel > Iris pseudacorus Linn > Canna indica Linn. The Fe plaque formation increased P uptake, apparently through enhancing the diffusion of P into the roots of the wetland plants; this resulted in increased P concentration in shoots. However, this effect decreased in the higher Fe plaque concentration status, apparently due to physical blocking and immobilization of P by Fe plaque. Therefore, adequate surface coverage of roots of wetland plant by the Fe plaque would increase the uptake of P by wetland plants, which depend on the optimum amendment of Fe. These effects also varied with wetland plant species.

Soil micronutrients are essential for plant growth and human health. Spatial variability and evaluation of soil micronutrient status are the research hotspot. The plain of northern Zhejiang Province, around Taihu Lake, China, is a key agriculture production area. With the rapid development of agriculture in Zhejiang Province, the management of soil micronutrients is of increasing concern to sustain crop productivity and human health. Soil-available micronutrients in the study region have not previously been studied in detail. Primary objective of this research was to examine the spatial distribution and evaluation of soil-available micronutrients in the arable land in this agriculturally important region using geostatistics. The controlling factors for the spatial variability of available micronutrients were interpreted. The research findings attained in the present study are of fundamental significance in providing a guideline for precise agriculture management practice and sustaining food security.Amounts of available Fe, Mn, Cu, Zn, B and Mo in 1893 soil samples taken from the arable land in nine counties in northern Zhejiang Province, around Taihu Lake, were measured and their spatial distribution patterns were investigated. Available Mn, Fe, Cu, and Zn were extracted with DTPA and analyzed by inductively coupled plasma–atomic emission spectroscopy. Available B was extracted with boiled water, then determined by inductively coupled plasma–optical emission spectroscopy. Available Mo was extracted with Tamm reagent and was then determined by inductively coupled plasma-mass spectrometry. Geostatistics was conducted for the data processing.More than 50% of the arable land were deficient in available Mo, while more than 70% had extremely low amount of available B. Amounts of available Cu, Zn and Mn were relatively high, whereas the soils are extremely sufficient in available Fe. The geostatisticical data shows that Mn, Cu, Zn, and Mo were best fit with an exponential model, while Fe and B were best fit with a spherical and linear model, respectively. Copper and Mo had strong spatial dependency, which is attributable to the effects of natural factors including parent material, topography, and soil type; Fe, Mn, and Zn had medium spatial dependency; however, B had weak spatial dependency, indicating an involvement of anthropogenic factors. Nevertheless, the six micronutrients studied all show spatial distribution trend to a certain extent.Based on the provincial classification standard of soil micronutrients and the results of the present study, regionalized management of soil micronutrients was recommended. We divided the soil micronutrients investigated in the present study into three types: Type I (Fe), Type II (Mn, Cu, and Zn) and Type III (B and Mo). Type I is sufficient, and its amount needs to be controlled; otherwise, it will be toxic to crops. Type II is enough and its amount does not need to be increased currently through micronutrient fertilization. However, Type III is deficient in substantial areas in the region studied and its cause of deficiency needs to be investigated; its availability needs to be improved to sustain the crop production and food quality. The availability of B and Mo in the north of Zhejiang Province should be regionally managed. Over the past two decades, the spatial variability of soil-available micronutrients in the study region was attributable to the soil formation factors as well as anthropogenic activities such as fertilization, cultivation, and other soil management practices. The lower available B and Mo concentrations in the arable land were apparently due to continuous cropping and intensive applications of fertilizers without adequate supply of micronutrients. The high available Fe and Mn concentrations in the soils were attributed to increasing soil acidification and relatively high soil organic matter contents. The high available Cu and Zn levels of the soils in this region were attributed to intensive utilization of animal manure as fertilizers.Based on the provincial classification standard and the results from the present study, regionalized management of soil micronutrients was recommended. Moreover, the present study would provide an insight into understanding the basis for the development of innovative strategies for land management practices such as precision farming and environmental risk assessment.The research findings attained in the present study would help to improve our understanding of spatially variable availability of soil micronutrients and providing a quantitative basis for decision and policy making to develop innovative agricultural management strategies to sustain micronutrient nutrition. Further research should be conducted to elucidate the relationship between soil micronutrient and plant growth and human health.

•We explore the bacterial and fungal communities in a paddy soil chronosequence.•The Illumina MiSeq was applied to the microbial community structure studies.•Soil microbial PLFAs were higher under paddy management than arable cropping.•Bacterial succession of paddy and arable soil were similar.•Orderly succession of soil bacterial and fungal communities occurred.In agroecosystems, soil bacterial and fungal communities are crucial for soil and plant health because of their diverse metabolic functions. However, little is known about the effect of long term paddy management on microbial communities. This study was conducted to assess the responses of the soil bacterial and fungal communities to cultivation history along a paddy soil chronosequence by using phospholipid fatty acid (PLFA) profiling and Illumina HiSeq sequencing. Soil samples were collected from the paddy fields (50, 100, 300, 1000, and 2000 years of paddy use; P50-P2000-), the adjacent arable chronosequence (50, 100 and 300 years of land use; NP50-NP300) and mudflat (estuarine sediment, representing the parent material for paddy and arable soil reclamation). The results showed that soil microbial biomass PLFAs increased significantly with increasing soil organic C which accumulated more under paddy than arable management. Bacterial taxonomic groups assigned to Proteobacteria and Acidobacteria changed relatively in the transition from tidal wetland to agricultural land. The relative abundances of dominant bacterial phyla in paddy soil orderly changes with cultivation time. The dominant fungal phyla in all samples were Ascomycota, Chytridiomycota, Basidiomycota, Glomeromycota and Zygomycota, representing 18.50%, 18.46%, 10.02%, 7.34%, and 7.19%, respectively. The succession of fungal community structure was mainly associated with changes in Ascomycota. Correlation analysis showed that higher soil total carbon and nitrogen related to long-term cultivation were associated with lower Proteobacteria and Ascomycota, but higher Verrucomicrobia. Furthermore, different land use type differed significantly in their fungal composition, but likely had similar effects on the succession of bacterial composition, mainly the Proteobacteria and Acidobacteria. Our results indicate that orderly succession of soil bacterial and fungal communities occurred along the long-term development of paddy soil, which in turn was associated with changes in soil physicochemical properties over time.

To understand root–soil–microbe interactions in rhizo-depletion of xenobiotics, we conducted a glasshouse study using specially designed laminar rhizoboxes which allow intact layers of near- (1–5 mm) and far- (>5 mm) rhizosphere soil to be harvested separately from root surfaces without the removal of the root material itself. Plant (Lolium perenne L.) seedlings were grown for 90 days in a soil treated with PCP at 20 and 50 mg kg−1. Changes in PCP depletion, soil microbial biomass and community structure (as indicated by phospholipid fatty acids (PLFAs) profiles) with increasing distance from the root surfaces were then assessed after harvesting. Surprisingly, depletion of PCP in the planted rhizoboxes exhibited a nonlinear dependence on the distance to root surfaces, with the most rapid loss in the 2 or 3 mm near-rhizosphere layers, contrasting to the well-known linear gradient of root exudates and mineral nutrients etc. (generally, the extent gradually decreased with increasing distance from the root surface). Soil microbial biomass carbon, however, decreased linearly as expected with increasing distance from the roots. The microbial community structures as indicated by PLFA profiles showed distance-dependent selective enrichment of competent species that may be responsible for efficient PCP depletion. The results suggest that root exudates induced modifications of microbial communities in the PCP contaminated rhizosphere and spatially modified the dominant species within these communities, resulting in the nonlinear PCP depletion pattern.

Little information is available on the interactive effects of inorganic and organic pollutants on carbon utilization by soil microorganisms. This study examined the effects of two common soil pollutants, lead (Pb) and bensulfuron-methyl herbicide (BSM), on decomposition of an adscititious carbon source (14C-glucose). Two contrasting paddy soils, a silty clay soil and a clay loam soil, were incubated with different concentrations and combinations of pollutants for 60 days. Orthogonal rotatable central composite design was adopted to design the combinations of the pollutant concentrations so that rate response curves could be derived. Rapid decomposition of 14C-glucose occurred in the first three days for both soils where no Pb or BSM was added (control). Overall, 63%–64% of the added 14C-glucose was decomposed in the control over the 60-day incubation. The addition of Pb or BSM significantly decreased the decomposition of 14C-glucose during the first week but increased the decomposition thereafter; as a result, the percentages of 14C-glucose decomposed (57%–77%) over the 60-day period were similar to or higher than those of the control. Application of the pollutants in combination did not further inhibit decomposition compared with the control. Overall, decomposition rates were lower in the silty clay soil than in the clay loam soil, which was related to the soil texture, cation exchange capacity, and pH. The relationship between the decomposition rates and the pollutants could be well characterized by the quadratic regression orthogonal rotation model. The initial antagonistic effects of the pollutants followed by the synergistic effects on microbial activity might result from changes of the concentrations of the pollutants.

Successful soil organic matter (SOM) quality assessment is needed to improve our ability to manage forest soils sustainably. Our objective was to use a multivariate data set to determine whether the land use conversion from native forest (NF) to hoop pine plantation and the following rotation and site preparation practices had altered SOM quality at three adjacent sites of NF, first (1R) and second rotation (2R, including tree planting row (2R–T) and windrow of harvest residues (2R–W)) of hoop pine plantations in southeast Queensland, Australia. Cross-polarization magic angle spinning 13C nuclear magnetic resonance (CPMAS 13C NMR) spectroscopy and sequential hot water and acid hydrolysis were conducted on SOM fractions separated by wet-sieving and density fractionation procedures to characterize SOM quantitative and qualitative relevant parameters, including carbon (C) functional groups, C and nitrogen (N) contents, C/N ratios, and C and N recalcitrant indices. Analysis of variance (ANOVA) and principal component analysis (PCA) of these multivariate parameters together indicated a complicated interaction between physical protection and biochemical recalcitrance, making the land use and management induced changes of SOM quality more complex. Knowledge of PCA based on the refined set of 41 SOM quantitative and qualitative parameters identified that principal component 1 (PC1), which explained 55.7% of the total variance, was most responsible for the management induced changes in soil processes. This was reflected by the dynamics of SOM regarding the aspects of total stock, soil basal and substrate induced respirations, gross and net N mineralization and nitrification, and microbial biomass, microbial diversity of C utilization patterns. Further, the macroaggregates (F250–2000 μm) and the C/N ratio of acid extracts of SOM physical fractions, which represented the most informative and unique variables loading on PC1, might be the most promising physical and chemical measures for SOM quality assessment of land use and management impacts in subtropical Australian forests.

Increased phosphorus (P) uptake during intercropping has been demonstrated previously between specific crop species, e.g. cereal–legumes, in P deficient alkaline or neutral soils. The evidence is less strong in P deficient acidic soils. To assess the interspecific effects of acidic soils on P uptake, and to determine the biochemical mechanisms involved, a field experiment with maize-based (Zea mays) intercropping was conducted with the legumes chickpea (Cicer arietinum) and soybean (Glycine max), as well as the cereal wheat (Triticum aestivum), respectively, in subtropical acidic soils of Southern China. The land equivalent ratio (LER) values (on an average of 1.20 and 1.07 for maize–chickpea and maize–soybean, respectively; and from 0.85 to 1.08 on average for maize–wheat after P fertilization) indicated that the interspecific stimulation of P uptake may be a general phenomenon i.e. controlled by soil P availability rather than crop species or soil type. Rhizosphere soil pH increased compared to that of non-rhizosphere even following the addition of the acidic calcium superphosphate (on an average of 0.16–0.56 pH units), suggesting rhizosphere acidification due to intercropping could not be the cause of increased P uptake in acid soils, unlike in alkaline or calcareous soils. The microbial phospholipids fatty acid (PLFA) profiles varied with both intercropping species and soil P status, indicating a selective enrichment of competent species (arbuscular mycorrhizal fungi, gram-negative bacteria, actinomycetes, and probably P solubilizing microorganisms) that may be responsible for increased P uptake during intercropping. The results suggest that root contact modified the microbial communities and the dominant microbial species in the intercropped rhizosphere, thereby contributing to increased P uptake during intercropping in acidic soils.Highlights► A field experiment with maize-based intercropping in acidic soils was conducted. ► Interspecific stimulation of P uptake was generally controlled by soil P status. ► Rhizosphere acidification was not the cause for increased P uptake in acid soils. ► Root contact modified the microbial community and dominant microbial species. ► Microbial interaction may contribute to increased P uptake during intercropping.

Our aim was to investigate rhizosphere effects on the chemical behavior of Cd. This was done in a glasshouse experiment, where two rice cultivars (Zhenong54 and Sixizhan) were grown in soil spiked with cadmium (Cd) at two levels, 3.9±0.5 and 8.3±0.5 mg kg−1 soil, placed in a rhizobox until ripening stage. Chemical forms of cadmium near the root surface were then assessed using a sequential extraction procedure (SEP). There were significant differences in Cd species, especially exchangeable Cd (EXC-Cd) between the two rice cultivars as affected by rice roots. The lowest EXC-Cd with Zhenong54 appeared in the near-rhizosphere area with little difference between tillering stage and ripening stage while Sixizhan had its lowest EXC-Cd concentration in the root compartment. Both cultivars had slight changes in the Fe/Mn oxide-bound fraction of Cd (FMO-Cd) at the grain ripening stage while the control treatments without plants had a significant increase in FMO-Cd at the same time, indicating a transformation from a less bioavailable form (FMO-Cd) to more bioavailable forms (EXC-Cd). Soil microbial biomass in the vicinity of the root surface had opposite trends to some extent with EXC-Cd, partly because of the root-induced changes to bioavailable Cd. Unlike Zhenong54, Sixizhan had a higher Cd concentration in the root, but only a small proportion of Cd translocated from the root to grain.Research highlights►We investigated genotypic effects on Cd speciation in the rhizosphere of rice. ►Zhenong54 (ZN) and Sixizhan (SX) were grown in rhizobox to show root-induced changes. ►Lowest exchangeable-Cd of ZN was in near-rhizosphere while SX in root compartment. ►Soil microbial biomass had opposite trends with exchangeable-Cd in both cultivars. ►Unlike ZN, SX had higher Cd content in roots, but lower Cd content in shoots.

Soil physical structure causes differential accessibility of soil organic matter (SOM), including carbon (C) and nitrogen (N) pools, to decomposer organisms and is an important determinant of SOM storage. Physical fractionation method of SOM in conjunction with elemental as well as isotopic analyses (C, N, δ13C, δ15N) of those soil fractions are used in this study to determine the land use and management-induced changes of SOM and associated processes in three adjacent sites of native forest (NF), first (1R) and second rotation (2R, including tree planting row (2R-T) and windrow of harvest residues (2R-W)) of hoop pine plantations in southeast Queensland, Australia. The results suggest that there is a greater accumulation of C and N in the light fraction (LF) of NF site than that of plantation sites (1R and 2R), and the C and N losses following conversion from mixed species NF to the single-species plantation are attributed to the reduction in C and N stocks for all physical fractions separated by wet sieving. In contrast, the C and N losses induced by the rotation practices (e.g., between 1R and 2R-T) are attributed to the C and N decreases in the LF and macroaggregates (250–2000 µm) only. The C and N increases upon the residue management (e.g., between 2R-W and 2R-T) are primarily attributed to the C and N increases in the LF and macroaggregates as well. Coupled with 30 soil chemical and biological parameters obtained in our previous studies, further principal component and multivariable regression analyses were conducted and the results showed that both the LF and macroaggregates were highly related to the status of C and N pools, the processes of N transformation and soil respiration, and the diversity of microbial communities, and thus could serve as diagnostic SOM fractions responsible for the changes of soil properties and processes within the tested ecosystem induced by the land uses and management practices. Knowledge of the interactive relationships between aggregate classes within SOM and soil chemical and biological processes in this study represents a further step towards diagnostically measuring and understanding important soil C and N processes in response to the land use and management changes in the soil ecosystems such as forests in subtropical Australia.

•We report genome of Massilia sp. WG5, a novel PHE-degrading strain.•The genome sequence was obtained by using PacBio RSII and Illumina Miseq systems.•Only 4 genes related to PAHs-degrading are found by KEGG pathway analysis.•It gives a foundation for PHE-degrading pathways of Massilia sp. WG5.Massilia sp. strain WG5 is a phenanthrene-degrading bacterium isolated from polycyclic aromatic hydrocarbons contaminated soil in Jiangsu, China. Here we present the features of the strain WG5 and its complete genome sequenced by two SMRTs-cell of PacBio RS II and corrected by Miseq. The genome contains one circular chromosome and two plasmids, which is including 6,049,576 nucleotides with 65.51% G + C content, 5,140 protein-coding genes, 111 RNA genes.

The present study was conducted to examine the dynamics of the extractable and bound residues and the mineralization rate of 14C-metsulfuron-methyl in six Chinese paddy soils held at 20, 40, and 50% water-holding capacity (WHC) and 35 °C for 84 days. The results showed that extractable residues were higher, but bound residues and mineralization rates of 14C-metsulfuron-methyl were lower in the soil with a higher pH than in the acid soils. Increasing the soil moisture contents significantly enhanced mineralization of 14C-metsulfuron-methyl in the soils. The half-lives of 14C-metsulfuron-methyl at 50, 40, and 20% WHC were 73–267, 110–385, and 165–462 days, respectively. Furthermore, the dynamics of the extractable and bound residues of 14C-metsulfuron-methyl were affected significantly by soil moisture. The level of the extractable residues increased with increasing moisture contents during the initial 14 days after metsulfuron-methyl application (DAA) in all soils, and the trend was maintained for the alkaline soil from 28DAA to 84DAA, but the opposite was observed for the five acidic soils. The formation of the bound 14C-metsulfuron-methyl residues decreased when soil moisture contents were increased in all the soils over the whole incubation period. The data obtained in the present study indicate that soil moisture would not only affect microbial activity, but also alter the distribution of metsulfuron-methyl residues between extractable and bound fractions, both of which may affect metsulfuron-methyl degradation.

Phospholipid fatty acid (PLFA) analysis has become a popular and powerful method for characterizing soil microbial communities. However, little work has been done to compare different extraction procedures. In this study, the effects of single or consecutive extractions, varying soil weights, alternative solid phase extraction (SPE) tubes and a comparison of extractions from fresh soil and that from soil previously stored freeze-dried at − 70 °C for 1 year were determined. About 90–95% of PLFAs were extracted by the method used in this paper. More individual PLFAs and changes in PLFA peak distributions (profiles) were found with increasing soil sample weights, which suggests that for each set of experiments, the soil weight should be constant. Home-made SPE tubes used in this study can give almost as good results as the commercial standard ones, which significantly decreased costs. The total PLFA concentrations decreased by more than 28% following storage of the freeze-dried soils for 1 year at − 70 °C. The PLFA profiles also changed during storage over this period, suggesting that PLFA analyses are best done as soon as possible after sampling.