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The effects of facility vegetable cultivation years (three, nine, fourteen or seventeen years) on biodiversity and abundance of soil microorganisms, such as bacteria, ammonia oxidizing bacteria (AOB) and nirK type denitrifying bacteria, in the greenhouse soils in Wuwei of Gansu Province, China were determined by the combined analyses of terminal restriction fragment length polymorphism (T-RFLP) and real-time quantitative PCR. The results showed that the dominant population structure and abundance of bacteria, AOB, nirK type denitrifying bacteria in the soils were significantly different from those in the farmland fields. The dominant population also changed with the cultivation years. With the increase of vegetable cultivation years, the abundance of 16S rRNA and nirK gene in the 0-20 cm soil layer first increased and then decreased, with the maximum values of 9.67×109 and 2.30×107 copies . g-1 soil at year 14 and year 9, being as 1.51 and 1.52 times of that of the 3-year, respectively. However, the abundance of amoA gene showed an opposite trend. The amoA gene copy number in the 14-year sample was 3.28×107 copies g-1 soil, which was only 45.7% of that of the 3-year. These results illustrated that the ecological adaptation mechanisms of the different functional microorganisms involved in nitrogen cycling had significant differences in the facility vegetable soils, and provided a base for further researches on exploring and explaining the characteristics and adaptation mechanisms of microorganisms in greenhouse soil. [ABSTRACT FROM AUTHOR]

Arsenic hazard is severe serious to environment and human health. In recent years, arsenic is paid high concern as a toxic metallic element. This paper summarized the latest research results at home and abroad, deemed that there existed an obvious tendency of arsenic accumulation in arable land in China. The paper also analyzed the natural and anthropogenic sources of arsenic. Meanwhile, this paper systematically introduced the related control measures adopted at present including the physics, chemistry, biology, and agronomy methods, from the angle of removing arsenic from arable land and reducing its effectiveness. Furthermore, this paper prospected the future research direction and hotspots. [ABSTRACT FROM AUTHOR]

The community structure and abundance of nirK-type denitrifying bacteria in different soil layers (0-20 cm and 20-40 cm) under various fertilization regimes in Wuwei, Gansu Province were investigated by the combination of terminal restriction fragment length polymorphism (T-RFLP) and real-time quantitative PCR. Results showed that the nirK-type denitrifying bacteria community structure was significantly affected by fertilization regimes, especially for 70, 156 and 190 bp T-RFs that represented the dominant populations in greenhouse soil. Fertilization regimes significantly influenced the abundance of nirK gene in the 0-20 cm soil layer with the highest abundance of nirK gene copy number (2. 16x107 copies·g-1 soil) detected in the manure treatment (M), which was 2. 04 and 2. 02 times of that in the control (CK) and chemical fertilizer (NPK) treatments, respectively. Both the dominant population and abundance of nirK-type denitrifying bacteria in the greenhouse soil were significantly different between the 0-20 cm and 20-40 cm soil layers, and the nirK-type denitrifying bacteria community structure and abundance in the greenhouse soil were obviously different from that in the field. Soil pH, soil organic matter content and nitrate-N content had the greatest influence on the bacterial community composition. Phylogenetic analysis indicated that there were not only anaerobic nirK-type denitrifying bacteria in greenhousesoil, but also aerobic denitrifying bacteria, such as Rhizobium, Ochrobactrum, Agrobacterium. [ABSTRACT FROM AUTHOR]

A pot experiment was conducted to study the effects of exogenous dimethylarsinic acid (DMA) on the growth of Brassica campestris and the bioavailability of soil arsenic (As). With the increasing concentration of applied DMA, the emergence rate and biomass of B. campestris increased at low concentration DMA, but decreased at high concentration DMA. When the DMA concentration reach ed 90 mg·kg-1, the emergence rate and biomass of B. campestris in the second cropping decreased by 9.5% and 57.0%, respectively,compared with those in the control, indicating that exogenous DMA had longer term effects on the growth of B. campestris. The soil available As and the As uptake by B. campestris all increased with increasing concentration of exogenous DMA, and there existed significant correlations among them. After applied into soil, the exogenous DMA demethylated, with As(V) as the main product and lesser amount of As (III), and the concentrations of soil As(V) and As(III) increased with increasing application rate of exogenous DMA. [ABSTRACT FROM AUTHOR]

A sampling survey was conducted in the typical areas in Shouguang County of Shandong Province to study the characteristics of arsenic (As) concentration and speciation in greenhouse vegetable soil. The total As concentration in the surface (0-20 cm) and subsurface (20-40 cm) soil was averagely 8-27 and 7-93 mg·kg-1, being 19% and 23% higher than that of the control (open field soil), and the soluble As (AE-As) concentration was 0-13 and 0-06 mg·kg-1, 63% and 200% higher than that of the control, respectively. The ratio of residual As (O-As) to total arsenic reached more than 63-0%, and the concentrations of different As speciation decreased in the order of O-As > iron-bound As (Fe-As) > calcium bound As (Ca-As) > aluminum bound As (Al- As) > AE-As. With the increasing planting years, the AE-As concentration enhanced significantly, and the Al-As concentration also increased to some degree. After 15 years planting, the AE-As concentration in surface and subsurface soil increased by 75-0% and 150-0%, and Al-As concentration increased by 51-6% and 190-4%, respectively, while the concentrations of Fe-As and Ca-As all decreased to some degree. [ABSTRACT FROM AUTHOR]

A pot experiment with arsenic-contaminated red soil was conducted to study the effects of applying pig dung and chicken manure on the growth and arsenic absorption of pakchoi (Brassica chinensis), and on soil available arsenic. Applying pig dung and chicken manure to the arsenic- contaminated red soil increased the biomass of pakchoi to some extent. Comparing with the control, applying pig dung increased the pakchoi biomass significantly (P<0.05). The soil available arsenic content after applying pig dung increased by 394.9%-1033.6% (P<0.05), and that after applying chicken manure increased by 30.4%-94.1%. Organic fertilization promoted the arsenic absorption of pakchoi, with the arsenic uptake after applying pig dung increased by 20.7%-53.9%. The application of pig dung and chicken manure to arsenic-contaminated red soil could somewhat increase the soil available arsenic content and the arsenic uptake by crops,and thus, increase the risks of agricultural product quality and environment/. [ABSTRACT FROM AUTHOR]

Utilizing fungi to remediate arsenic-contaminated soil and water body has a great potential, which has been focused and highlighted in environmental sciences. Though the arsenic in environment can not be biodegraded as organic contaminants, its bioavailability can be affected by microorganisms via the processes oxidation/ reduction, absorption/ desorption, methylation/ demethylation, and precipitation/ dissolution, etc. , and thereby, its toxicity could be reduced, and the arse nic-contaminated environment could be remediated. This paper introduced the action mechanisms of microorganisms on arsenic, summarized the research progress in the arsenic bioaccumulation and bio-volatilization by fungi, and discussed the feasibility of utilizing fungi in the remediation of arsenic-contaminated soil, aimed to provide theoretical reference for the bioremediation strategies of arsenic-contaminated soils. [ABSTRACT FROM AUTHOR]

A total of thirteen fungal strains with higher arsenic (As)-tolerance ability were isolated from six As-contaminated soil samples collected from the mining areas of Shimen County and Chenzhou City in Hunan Province. Among the strains isolated, Penicillin janthinellum, Fusarium oxysporum, and Trichoderma asperellum had the highest As-tolerance ability, based on the morphological identification and phylogenetic analysis. Culture experiment showed that on the solid plates with 30000, 30000, and 20000 mg·L-1 of As, P. janthinellum, F. oxysporum, and T. asperellum had a better colony growth, and after cultured in the liquid medium with 0-50, 0-50, and 0-80 mg·L-1 of As for 2 days, respectively, the dry mycelia masses of the three strains all increased with increasing As concentration. When the As concentration reached 50, 50, and 80 mg·L-1, respectively, the fungal biomass of F. oxysporum, T. asperellum, and P. janthinellum increased significantly, compared with CK. High concentration As had no significant effects on the sporalation of the three fungal strains. [ABSTRACT FROM AUTHOR]

An incubation test was conducted to study the transformation of exogenous dimethylarsenic acid (DMA), monomethylarsenic acid (MMA), and arsenate [As(V)] in soil under the condition of 35% of water-holding capacity. After added into soil, the concentrations of test arsenic forms all showed a decreasing trend with time. The DMA and MMA were mainly demethylated, and after 120 days incubation at constant temperature and humidity, transformed into As(V). A small amount of MMA was detected in the treatment with added DMA on the 120th day of incubation, and a small amount of DMA was detected in the treatment with added MMA during the period of 7-60 days incubation. By the end of the incubation test, the concentrations of added DMA and MMA in soil decreased significantly (P<0.01), with the decrement being 99.5% and 94.3% and the concentration of transformed As(V) increased by 4.61 and 5.15 times, respectively. Comparing with DMA and MMA, the As(V) after added into soil had less form transformation. [ABSTRACT FROM AUTHOR]

A pot experiment was conducted to study the speciation transformation of exogenous dim- ethyl arsenic (DMA) in soil. The added DMA was mainly transformed into arsenate [As(V)], accompanied with a small amount of monomethyl arsenic (MMA). When the concentration of added DMA was 30 mg·kg-1, the transformation rate was the highest, being 6.71%, 8.11%, 11.33%, and 19.32% when the cultivation time was 10, 15, 30, and 40 days, respectively. With increasing concentration of added DMA, soil soluble arsenic (AE-As) had an increasing trend, but decreased as the cultivation time increased. Comparing with CK, the addition of DMA increased the concentrations of soil arsenic bounded to aluminum (Al-As), iron (Fe-As), calcium (Ca-As), which was possibly due to the adsorption or fixation of added DMA and its transformation products by the oxides or hydroxides of soil aluminum, iron, and calcium. [ABSTRACT FROM AUTHOR]

An incubation test was conducted to study the dynamics of exogenously supplied dimeth-ylarsenic acid (DMA), monomethylarsonic acid (MMA), and As(V) in soil under flooding. With the increasing time of incubation, the exogenously supplied DMA and MMA were mainly trans-formed into As(V), and the As(V) concentration increased, being significantly higher after incubated for 150 days, compared with that after incubated for 1 day. The exogenously supplied DMA was demethylated into As(V) within 30 days, accompanied by a little As(III), while the transformation rate of exogenously supplied MMA was rather slow within 60 days, accompanied by a little As(III) and DMA. The exogenously supplied As(V) decreased with increasing time of incubation, and its form had less change except that a little As(III) occurred. [ABSTRACT FROM AUTHOR]

A simulating incubation test was conducted to evaluate the effects of exogenous dissolved organic matter (DOM) and incubation temperature on the copper forms in red soil. Comparing with the control, adding different amount of DOM increased the content of soil exchangeable Cu, but decreased the content of soil Fe-Mn bound Cu. With increasing time of incubation, the content of soil exchangeable Cu in all DOM-added treatments had a decreasing trend. By the end of the incubation, treatment 250 mg DOM∙L-1 had the highest contents of soil exchangeable Cu and carbonate bound Cu, while treatment 500 mg DOM∙L-1 had the highest content of soil Fe-Mn bound Cu. In the treatments with DOM addition, the content of soil organic bound Cu increased by 10.67% - 23.66%, compared with the control. At incubation temperature 25 °C and 45 °C, the contents of soil exchangeable Cu and Fe-Mn bound Cu decreased with increasing time of incubation; while at 5 °C, an opposite trend was observed. At these three temperatures, the content of soil carbonate bound Cu in treatments with DOM addition increased with incubation time. The content of soil organic bound Cu increased with increasing temperature, but that of soil residual Cu decreased at lower temperature (5 °C). [ABSTRACT FROM AUTHOR]

A systematic investigation was carried out on the arsenic content in the soils and plants surrounding Shimen arsenic sulphide mine. The arsenic content in top soils (0-20 cm) was averagely 99.51 mg∙kg-1, being 5. 34 times higher than that of the background value in Hunan Province and 8.70 times higher than that of local farmland soil. The topsoil arsenic content in paddy field and dry land was 43.51 and 115.1 mg∙kg-1, respectively, being 0.45 and 1.87 times higher than that of the grade II level (paddy field 30 mg∙kg-1; dry land 40 mg∙kg-1) commended by the National Soil Quality (GB 15618-1995), and the corresponding arsenic exceeding rate was 62.5% and 50.0%, respectively. The arsenic content in edible parts of foodstuff, vegetables, and fruits was 0.16, 0.06, and 0.01 mg∙kg-1, respectively, and the arsenic exceeding rate of crop samples compared to food security standard ranked in the order of foodstuff > vegetables > fruits. Rice and sweet potato were relatively seriously contaminated by arsenic. The highest arsenic content of rice was up to 0.84 mg∙kg-1, which was 4.6 times higher than that of the National Standard, with the exceeding rate of 62.5%. Statistical analysis demonstrated that there was a positive correlation between the arsenic contents of soil and plant. The average daily intake of arsenic by local people through the consumption of the crops was 6.416 μg∙kg-1 ∙d-1, which was much higher than the standard commended by WHO, and the related health risk index was 21.39, which was 14.39 times higher than that in the control region. [ABSTRACT FROM AUTHOR]

This paper analyzed the current situation of heavy metal contamination in cropland soils in China, and discussed the input, output, and balance of heavy metals in cropland ecosystems. It was considered that heavy metals had definite accumulation in cropland ecosystems, but overall speaking, this accumulation had relatively small environmental risk, and only some plants, especially vegetables, accumulated heavy metals over the standards. In mining areas, adjacent areas of smelting plants, and the farming areas using larger amounts of related wastes, the heavy metals content in plants and soils was at least ten times higher than that in normal croplands, existing larger environmental risk. Aiming at the current situation of heavy metal contamination of farmland soils in China, some effective regulation measures for the heavy metal cycling in the cropland ecosystems were proposed, and the further research prospects in related fields were discussed. [ABSTRACT FROM AUTHOR]

Taking the facility vegetable fields having been planted for 1-12 years and the adjacent wheat land in Shouguang City of Shandong Province as test objects, this paper studied the distribution characteristics of arsenic (As), cadmium (Cd), copper (Cu), zinc (Zn), chromium (Cr), and nickel (Ni) in their soil profiles (0-150 cm). With the increase of soil depth, the test heavy metals contents in the soil profiles all had a decreasing trend, and in the same soil layers, the contents were obviously higher in facility vegetable fields than in wheat land. Comparing with those in the same soil layers of wheat land, the average contents of As, Cd, Cu, Zn, Cr, and Ni in 0-20 and 120-150 cm soil layers of facility vegetable fields were 35.0%, 146.2%, 65.6%, 36.4%, and 21.5%, and 10.6%, 178.5%, 19.4%, 20.2%, 15.2%, and 9.3% higher, respectively, and the average contents of the heavy metals in 20-120 cm soil layer of facility vegetable fields were also higher in some degree. In the 0-20 cm soil layer of facility vegetable fields, the Cd, Cu, and Zn contents had significant positive correlations with planting years (P<0.05), with the accumulation rates of Cd, Cu, and Zn being 0.027, 1.153, and 2.830 mg∙kg-1∙a-1, respectively. In facility vegetable fields, the test six heavy metals contents were significantly positively correlated with the contents of soil organic carbon and total nitrogen, and the Cd, Cu, Zn, and Cr contents were significantly correlated with the content of soil total phosphorus (P<0.01). Applying organic fertilizer could induce the heavy metals accumulation in the soils of facility vegetable fields to some extent. [ABSTRACT FROM AUTHOR]

Cadmium (Cd) accumulation in vegetable plantation land soils under a greenhouse was investigated in Shouguang County, Shandong Province, China. A total of 128 soil samples were collected from different agricultural fields. Soil samples were digested with the mixture of hydrogen peroxide (H2O2) and nitric acid (HNO3), and Cd content in the digested solution was detected with inductively coupled plasma-mass spectrometry (ICP-MS). The results indicated that the concentration of Cd in the greenhouse vegetable field was significantly more than that in open vegetable field, cotton field, wheat/maize field, and uncultivated soils. Cadmium concentration increased with the cultivation age, and the related accumulation rate was 0.0289 mg Cd kg-1y-1 in a greenhouse vegetable field. Organic fertilizer such as livestock manure was the major source for Cd accumulation in the greenhouse vegetable field with the average input amount of 70.7 g Cd ha-1 y-1 from organic manure. Thus, a decrease of Cd input from organic fertilizer into greenhouse soils is necessary. [ABSTRACT FROM AUTHOR]

Based on the analysis of the sources and existing forms of soil arsenic, this paper approached the inter-transformation of different arsenic forms in soil. In the meanwhile, the extraction and determination methods of different soil arsenic forms were also compared. It was considered that HPLC-HG-AFS had the advantages of high sensitivity, low detection limit, better selectivity, low operation cost, and less inter-transformation of different arsenic forms, being able to be used as the prior method for the detection of different arsenic forms. Combining with previous research results, the form transformation of arsenic in soil and the promising research aspects were also discussed. [ABSTRACT FROM AUTHOR]

The straight head disease of rice is one of the main problems limiting rice production. Arsenic (As) methylation in paddy soils is considered to be highly related to the occurrence of the straight head disease. As a typical field practice, rice fields are usually drained during the late tillering stage and the mid-late grain filling stage. Nevertheless, the key influencing factors on the As methylation efficiency during paddy soil drying remain unclear. In this study, an indoor cultivation experiment was set up to simulate the drying process of paddy soil. Two As-contaminated soils collected from Xingren (XR) in Guizhou province and Nandan (ND) in Guangxi province were used as test soils. Each soil was treated with the addition of rice straw (RS) and without rice straw (CK). With the drying of paddy soil (0, 24, 36, 48, and 60 h), the changes in soil Eh, pH, total organic carbon (TOC), and As chemical species in the porewater were determined. The abundance of the As methylation functional gene ( arsM ), sulfate-reducing bacteria (harboring dsrA , As methylation-related microorganism), and methanogens (harboring mcrA , As demethylation-related microorganism), as well as the diversity of arsM -harboring microorganisms, were also observed. The results showed that during the process of drying paddy soil, soil Eh changed from -300--200 mV under complete flooding to -150--50 mV after drying; however, the change in soil pH was not obvious. The concentrations of inorganic As (iAs) and dimethylarsenic (DMAs) in porewater significantly increased ( P <0.05) with the drying process. Additionally, the concentration of DMAs in the RS treatment was prominently higher than that in CK. Compared with XR soil, the concentration of DMAs in ND soil was higher. As a function of soil drying time, the As methylation efficiency of XR soil (XR-CK and XR-RS) slightly increased but was not significant ( P >0.05), whereas the As methylation efficiency of ND soil (ND-CK and ND-RS) increased significantly ( P <0.05). After the drying time reached 60 h, the As methylation efficiency of ND-CK and ND-RS increased by 61.8% and 23.2%, respectively, compared with those at the early stage of drying (0 hours). The copy numbers of the arsM and dsrA genes greatly increased with the extension of drying time, whereas an opposite trend was observed for the copy number of the mcrA gene. Furthermore, the addition of straw obviously increased the gene abundance of whole bacteria and arsM -, dsrA -, and mcrA -harboring bacteria. Based on the multi-factor analysis of variance and the redundancy analysis, it was found that the test soil type, straw addition, drying time, and their interaction had a critical influence on the changes in As species, As methylation efficiency, and the gene abundance in soils. TOC, Eh, and the functional genes associated with As methylation were positively linked with the methylated As content in soil porewater but negatively correlated with that of iAs. According to the sequence of the arsM -harboring microbe, it was clearly demonstrated that a community shift of As-methylating microbe occurred with the soil drying. Here, the following conclusions were derived:① the drying process did not lower the As methylation efficiency in paddy soil. On the contrary, in this study, the As methylation efficiency, especially that for ND soil, remarkably improved. The addition of straw notably promoted the As methylation efficiency and the content of DMAs in porewater. ② An increasing tendency was observed for the abundance of microbes related to As methylation, whereas a reverse trend was indicated for microbes related to As demethylation. The community shift of arsM -harboring microbes might be the crucial reason for the improved As methylation efficiency during the soil drying. These observations contribute to a better understanding of the As methylation process during paddy soil drying and will shed light on the future mitigation of rice straight head disease in paddy soils.

To explore the mechanism of exogenous organic materials enhancing soil organic carbon and soil fertility, based on a long-term experiment located in Hengyang Red Soil Experimental Station, we examined the effects of winter green manure and straw returning patterns (CK, winter fallow; MV, winter Chinese milk vetch; S, early-season rice straw total returning; DS, early-season and late-season rice straw total returning; SMV, winter Chinese milk vetch + early-season rice straw total returning; DSMV, winter Chinese milk vetch + early-season and late-season rice straw total returning) on soil aggregates and organic functional groups. The results showed that the proportion of super aggregates (>2 mm) and macroaggregates (0.25-2 mm) in double cropping rice soil was the highest with a ratio of about 72.1%-81.8%, and the organic carbon content in the two kinds of aggregates was as high as 12.1-20.7 g·kg -1 , accounting for 22.7%-59.0% of the total organic carbon. The main organic functional group in paddy soil was polysaccharides, followed by aliphatic carbon and aromatic carbon. The abundance of all those groups was affected by winter Chinese milk vetch growing and straw returning. Compared with other treatments, DSMV significantly increased the proportion of super aggregates (>2 mm) and macroaggregates (0.25-2 mm) and favored the accumulation of inert carbon such as aromatic carbon in the two kinds of aggregates. DSMV could enhance the stability of soil aggregates and organic matter, which had high potential in the real agricultural production.

To acquire a feasible method for a rapid comparison of the cadmium (Cd) accumulation capacities of different leafy vegetables, using substrate cultivation with different contents of Cd and cultivation time, we compared the observed Cd accumulation capacity with these obtained in the field. The results showed that the Cd content and bio-concentration factors (BCFs) value in the aboveground tissue of leafy vegetable varied significantly with Cd content and cultivation time. Multi-factor analysis of variance showed that vegetable variety, cultivation time, Cd content in substrate and their interaction had significant effects on BCFs of Cd in leafy vegetable. Leafy vegetable variety was the dominant factor affecting BCFs of Cd in leafy vegetable and controlled its absolute level. When Cd content in the substrate reached 1.0 mg·kg -1 with a cultivation of 10 days, the correlation coefficient of Cd BCFs between the substrate cultivation and field experiments was the highest, with a R 2 value of 0.90. The results of cluster analysis and one-way ANOVA had the highest consistence with the field results. Comparatively, the substrate cultivation with Cd content of 1.0 mg·kg -1 and a cultivation of 10 days showed a good reproducibility and stability in reflecting the difference in Cd accumulation capacities of different leafy vegetable varieties. The Cd-rich substrate cultivation could be used to screen the vegetables with low Cd accumulation and also would promote the field application of the vegetables with low Cd accumulation in the Cd-contaminated area of China.

Application of organic amendments is an effective approach for improving soil organic carbon and soil fertility. To investigate the effects of different organic amendments on soil organic carbon and its labile fraction content, a batch of incubation experiments was conducted on the fluvo-aquic soil in Dongting Lake region, Hunan Province. There were six treatments, including soil amended with rice straw, soil amended with Chinese milk vetch, soil amended with bio-organic fertilizer, soil amended with pig manure, and soil amended with rice straw-derived biochar, with unamended soil as control. Each treatment had the same amount of carbon input. After 180 days of incubation, application of organic amendments increased soil labile organic carbon content. Application of bio-organic fertilizer, pig manure and rice straw-derived biochar significantly increased soil organic carbon content by 26.1%, 9.7% and 30.7%, respectively. There was no significant change in soil organic carbon content in rice straw and Chinese milk vetch treatments which were more favourable to the accumulation of soil dissolved organic carbon and microbial biomass carbon. Pig manure was more favourable to the accumulation of soil dissolved organic carbon. Bio-organic fertili-zer could benefit the accumulation of soil microbial biomass carbon and readily oxidizable organic carbon. Rice straw-derived biochar could promote the accumulation of soil microbial biomass carbon and light fraction organic carbon. Compared with rice straw, soil carbon pool management index was increased by 31.8%, 111.6%, 62.2% and 50.7% in Chinese milk vetch, bio-organic fertilizer, pig manure and rice straw-derived biochar treatments, respectively. The performance of bio-organic fertilizer, pig manure, and rice straw biochar was better than rice straw and Chinese milk vetch from the perspective of soil carbon sequestration and soil carbon pool management index.

Mining, smelting and other activities result in arsenic accumulation in soils, with adverse impacts on the quality and safety of agricultural products and soil microorganisms. We monitored the changes of available arsenic content with incubation time after the addition of exogenous arsenic to the yellow soil (YS) and soil derived from purple sandy shale (RS). The community changes of bacteria and archaea in soils without spiked arsenic and soils after 1, 30 and 360 days of exogenous arsenic stress were measured by MiSeq high-throughput sequencing, to investigate the community adaptative mechanism of bacteria and archaea in soil under arsenic stress. Results showed that the available arsenic content in soils decreased gradually with time, which significantly affected the composition of soil bacteria and archaea community. The abundance of dominant bacterial group changed significantly, whereas only archaea with lower abundance changed obviously, and little change occurred in dominant archaea group, indicating that archaea community had high arsenic tolerance and stability. Compared with the arsenic stress time, soil arsenic availability had greater impacts on community structures of bacteria and archaea. The results could provide refe-rences for safe utilization and microbial remediation of arsenic-contaminated cropland.

Based on the typical greenhouse vegetable production system in Siping City, Jilin Province, 124 soil samples were collected from greenhouse soils growing vegetables (GSGV), fields growing maize (FGM), and forest soil (FS) under different land utilization patterns. In addition, other samples including greenhouse vegetables (81), fertilizers (50), and irrigation water (10) were also collected in the studied region. To illustrate the accumulation characteristics of heavy metals in GSGV and greenhouse vegetables, the heavy metal content of different samples was measured using inductively coupled plasma mass spectrometry (ICP-MS) technology. The results indicated that the heavy metal content in GSGV was much higher than that in FGM and FS except for lead (Pb). Heavy metals including cadmium (Cd), copper (Cu), chromium (Cr), nickel (Ni), and zinc (Zn) in GSGV presented with various degrees of accumulation. The mean value of Cd content in the soils in the investigation region was 0.45 mg·kg -1 , with about 42.8% of all the soil samples exceeding the Cd content criterion of the Environmental Quality Evaluation Standard for Farmland in Greenhouse Vegetable Production (HJ 333-2006). The content of the other heavy metals was in the normal range, and all met the regulations of the standard. In comparison with different vegetable categories, leafy vegetables showed much higher heavy metal concentrations (Cd 0.033 mg·kg -1 fresh weight) than did fruity ones. In total, about 2.5% and 1.2% of vegetable samples exceeded the regulated values of Cd and Pb recommended by the Standard of Food limits, respectively. With the cultivation time prolonged, heavy metal concentration in soils and vegetables all increased synchronously as the pH value decreased. The content of heavy metals in greenhouse vegetables was significantly influenced by soil pH and organic matter. It can be concluded that the health risk of greenhouse vegetables increased with GSGV accumulating more heavy metals due to the substantial application of chemical fertilizer and manure containing high level of heavy metals.

The nitrogen (N) and phosphorus (P) balance was studied and the eco-economic benefits of N and P were evaluated for the paddy field in a red soil area, under the fertilization treatments of no fertilization (CK), chemical fertilizer (NPK), organic fertilizer (M), and chemical fertilizers combined with organic fertilizers (NPKM, NPM, NKM), based on the long-term experiment started in 1982, to optimize fertilizer application and reduce N and P losses. The results indicated that the slight N surplus (27.10 kg·hm -2 ) and P deficit (-6.85 kg·hm -2 ) were obtained in CK, while the N and P surplus respectively with 110.94-243.98 kg·hm -2 and 19.06-67.49 kg·hm -2 in other treatments were obtained. The treatments NPK and M had no effects on the N and P balance. Under the same fertilization rates, the N surplus in treatment NPKM was lower than that in treatments NPM and NKM by 6.3% and 12.9%, while the P surplus was lower by 3.7% and 13.8%, respectively. The total-N, total-P, alkali-hydrolyzable N, and available P contents in the 0-20 cm soil layer increased under the treatments of NPKM. Comparatively, the available P contents were relatively higher in the 20-40 cm soil layer under the treatments of high P application rates. Furthermore, the NPKM treatment had the highest eco-economic benefit value of 0.762, which indicated the optimized fertilizer application for the paddy fields in the red soil area. The treatment CK had the lowest eco-economic benefit values with 0.560. Based on the observations, the N and P (in P 2 O 5 ) fertilization respectively at the rates of 157.71 kg·hm -2 and 112.18 kg·hm -2 could well maintain the N and P balance for the paddy field in the red soil area.

The changing trend of soil available phosphorus (Olsen-P) content in soil and its relationship with soil phosphorus surplus and crop yield are fundamental when making appropriate phosphate fertilizer recommendations. In this paper, the influences of long-term fertilization on crops phosphorus uptake, soil phosphorus surplus, changing trend of soil available phosphorus content and relationships of soil available phosphorus content with soil phosphorus surplus and crop yield were investigated through 34 years (1981-2015) long-term trial in loessial soil region on the Loess Plateau. The experiment had a completely-randomized-block split-plot design in triplicate. Two main-plot treatments were no farmyard manure and farmyard manure (M), and four subplot treatments were CK (no fertilizer), N (application of chemical fertilizer N), NP (application of chemical fertilizer NP) and NPK (balanced application of chemical fertilizer NPK), respectively. The results showed that fertilization treatments and crop types significantly influenced uptake amount of phosphorus and soil phosphorus surplus. Averaged over time from 1981 to 2015, wheat mean phosphorus uptake amounts of CK, N, NP, NPK, M, MN, MNP and MNPK were 8.63, 10.64, 16.22, 16.21, 16.25, 17.83, 20.39 and 20.27 kg·hm -2 , while rape phosphorus uptakeamounts of eight treatments were 4.40, 8.38, 15.08, 15.71, 10.52, 11.23, 17.96 and 17.66 kg·hm -2 , respectively. The surplus amount of soil phosphorus significantly correlated with the amount of phosphorus applied to soil. When soil phosphorus surplus amount equal zero, wheat and rape phosphorus input amounts were 10.47 kg·hm -2 and 6.97 kg·hm -2 , respectively. Soil phosphorus surplus amount significantly influenced the changing trend of available phosphorus content in soil. CK and N treatments had no phosphorus input, and soil available phosphorus content exhibited a declining trend, annually decreased by 0.16 mg·kg -1 and 0.15 mg·kg -1 , respectively. In contrast, NP, NPK, M, MN, MNP and MNPK six treatments were applied with phosphate fertilizer every years, and available phosphorus content gradually increased along with the duration of trial, with annual increase by 0.02-0.33 mg·kg -1 . Soil available phosphorus content significantly correlated with phosphorus accumulative surplus amount, and the linear models were y=0.012x+9.33 and y=0.009x+11.72 in manure and no manure treatments, respectively. In no manure treatments, wheat yields significantly positively correlated with soil available phosphorus content, however, in manure treatments, their relationships did not reach a significant level. The relationship of wheat grain yield with available phosphorus content could be significantly fitted by piecewise linear model, and available phosphorus agronomy threshold of wheat was 14.99 mg·kg -1 . Rape grain yield also increased with increasing soil available phosphorus content, but the relationship was not significant. This indicated when soil available P content is higher than 14.99 mg·kg -1 , application of phosphate fertili-zer should be reduced or even avoided for planting wheat in loessial soil region on the Loess Plateau.

Nitrogen fertilizer use efficiency is a key parameter to determine recommended nitrogen fertilizer amount and evaluate the effects of nitrogen fertilizer application. The effects of long-term fertilization on annual and accumulated nitrogen fertilizer use efficiency and the relationship between them were studied using a 34-year fertilization experiment (1981-2015) in loessial soil region. The results showed that fertilization had significant influence on annual and accumulated nitrogen ferti-lizer use efficiency of wheat, rape and flax in the period of 1983-2015. The highest mean annual nitrogen fertilizer use efficiency of wheat was achieved in N, P and K combination (NPK), thesecond was N combined with P (NP), 77.7% and 62.0% higher than N application alone respectively. The highest mean annual nitrogen fertilizer use efficiency of rape was achieved in NPK, the second was manure (M), N, P and K combination (MNPK), 93.7% and 65.6% higher than N application alone respectively. The annual nitrogenfertilizer use efficiency of M combined with N (MN) increased significantly compared with N application alone. The annual nitrogen fertilizer use efficiency of M, N and P combination (MNP) decreased significantly compared with NP. The annual nitrogen fertilizer use efficiency of MNPK decreased significantly compared with NPK.There was significant positive linear relationship between annual nitrogen fertilizer use efficiency and crop yield. The correlation between accumulated nitrogen fertilizer use efficiency and crop yield was not significant. It indicated that the annual nitrogen fertilizer use efficiency could be more effective in representing fertilizer use efficiency characteristics under given soil fertility levels, crop varieties and environmental conditions compared with accumulated nitrogen fertilizer use efficiency.

An incubation test was conducted to study the bioavailability and fractionations of exogenous arsenite [As(3)] during the aging period in three soils originated from different parent materials, including quaternary red clay, purple sandy shale and granite. The results indicated that the exogenous arsenite As(3) were totally transformed into As(V) after 120 d aging. The available As content in soils derived from the three soils generally decreased sequentially throughout the aging period in the order of purple sandy shale, granite and quaternary red clay. The pseudo-second-order model well fitted the change of available As content with aging time (P＜0.05). Soil pH, organic matter (SOM) content and the concentrations of Fe, Al and Mn oxides were the main factors influencing the red soil arsenic in aging, especially, Mn oxides played a more crucial role than Fe and Al oxides in As aging (P＜0.05). Correlation analysis revealed that the non-specially and specially absorbed As constituted the primary forms of available As.

Utilizing fungi to remediate arsenic-contaminated soil and water body has a great potential, which has been focused and highlighted in environmental sciences. Though the arsenic in environment can not be biodegraded as organic contaminants, its bioavailability can be affected by microorganisms via the processes oxidation/reduction, absorption/desorption, methylation/demethylation, and precipitation/dissolution, etc., and thereby, its toxicity could be reduced, and the arsenic-contaminated environment could be remediated. This paper introduced the action mechanisms of microorganisms on arsenic, summarized the research progress in the arsenic bioaccumulation and bio-volatilization by fungi, and discussed the feasibility of utilizing fungi in the remediation of arsenic-contaminated soil, aimed to provide theoretical reference for the bioremediation strategies of arsenic-contaminated soils.

Field experiments were conducted on the double rice cropping paddy field in red soil area to evaluate the influence of cropping system innovation on soil profile form and related soil characteristics. Four cropping systems of rice-rice-Chinese Milkvetch (Astragalus sinicus Linn.), forage, paddy-upland rotation, and upland were substituted for the double rice cropping system. The results indicated that compared with those under double rice cropping system, the thickness of cultivated horizon under upland cropping system increased by 4 cm, that of plow pan declined by 2 cm, > 2 mm aggregates in wet-sieved particle-size fractions increased by 6.94%, wet-sieved mean-mass diameter increased by 0.37 mm, contents of humic acid carbon and fulvic acid carbon increased by 0.15 and 0.49 g kg(-1), respectively, and quotient of aggregates water stability was 0.78 times higher. Under paddy-upland rotation, the quotient of aggregates water stability was higher (95.86), while soil nutrient contents changed a little. Under rice-rice-Chinese Milkvetch system, soil organic matter content increased by 1.3 g kg(-1), quotient of aggregates water stability declined by 8.82, but other parameters had less changes. Under forage system, the thickness of cultivated and transitional horizons increased by 2 cm and 9 cm, respectively, quotient of aggregates water stability increased by 1.39, while the contents of soil organic matter and total potassium decreased by 5.6 and 2.8 g kg(-1), respectively. Among all test cropping systems, forage system had the greatest changes in soil characteristics. It was completely feasible to substitute the local double rice cropping system for paddy-upland rotation or upland cropping, particularly in the areas where full irrigation was not available. However, attention should be paid to the decrease of soil potassium content when the cropping system innovation was practiced.

Amendments are widely applied in agricultural soils to improve soil quality and crop yield. Effects of three amendments, lime, manure, and sepiolite on cadmium (Cd) and zinc (Zn) bioavailability in contaminated paddy soils were studied by pot experiment with cultivating rape. There were eight treatments, including lime, manure, and sepiolite separately applied and combined with others in contaminated soil. The biomass yield of rape was investigated after harvest. The amounts of absorbed Cd and Zn in harvested rape with application amendments were determined. Besides soil pH, different forms of Cd and Zn in the conducted soils were also measured. Results showed that the yield of rape increased after amendments application. The treatment of lime and manure co-application showed the highest increasing yield by more than 170% comparing with no amendments application in the eight treatments. The amount of absorbed Cd and Zn in rape decreased after the three amendments application. Lime application showed the best effect to decrease the heavy metal content in rape when amendments were separately applied. However, sepiolite could hardly decrease the content in rape after separately applied in contaminated soil. It was mainly due to the decrease of exchangeable Cd and Zn, which was available for rape, after lime application. Soil pH in these treatments increased in response. Accordingly, the carbonate combined and the Fe-Mn oxide fractions, which were unavailable in soil for rape, increased greatly. The uptake coefficient of Cd was higher than that of Zn. It indicated that Cd was more movable in soil and lime application could obviously decrease the uptake coefficient. The remediation efficiency was significantly improved in the treatment of co-application with lime and manure in Cd-Zn contaminated paddy soil. Compared with control (CK), it increased 13.5 times for Cd and 2.4 times for Zn, respectively.

Based on the monitoring of soil fertility, this paper studied the characteristics of microbial biomass C (MBC) and N (MBN) in paddy soils derived from different parent materials in Hunan Province. The results showed different fertilization systems had different effects on soil MBC and MBN. After 18 years fertilization, the MBC and MBN in different paddy soils had similar variation trend, with the sequence of paddy soil derived from lake sediment > from river alluvium and quaternary red earth > from limestone > from shale. Soil MBC content ranged from 259.5 to 864.4 mg x kg(-1), while MBN ranged from 8.7 to 70.7 mg x kg(-1). Fertilization could increase soil MBC and MBN markedly. Organic fertilizer was the main element for the promotion of soil MBC and MBN, and combined application of organic and inorganic fertilizers could obtain the greatest effect. The increment of soil MBC and MBN after applying inorganic fertilizer and its combination with organic fertilizer was 407.6 and 59.2 mg x kg(-1), in maximum, and the maximum increasing rate was 102.8% and 514.8%, respectively, compared with no fertilization.

The study on the soil arsenic (As) accumulation under different types of agricultural use in Shouguang of Shandong Province showed that farmland soils had an average As content of 9. 63 mg x kg(-1) , with the highest being 15. 15 mg x kg(-1) . Compared with the local background value (9. 3 mg As x kg(-1)) , 53. 1% of soil samples was detected as As enrichment. The soil As content was high in the west, east and north parts of Shouguang, relatively lower in the middle part, and the lowest in the south part. Different agricultural use had an obvious effect on the soil As content, which was decreased in the order of wheat/maize land > cotton field > protected vegetable land > uncovered vegetable land. Such a difference in soil As content was mainly affected by agricultural activities. With the increasing year of vegetable planting, soil As content had an increasing trend, because the As input from pig dung and chicken feces was the main source of soil As in protected vegetable land. Soil As enrichment could be reduced to some degree by applying soybean cake fertiliz-