[Arsenic Methylation Efficiency Changes During Paddy Soil Drying and Its Key Influencing Factors Analysis].

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.

Influence of straw-derived humic acid-like substance on the availability of Cd/As in paddy soil and their accumulation in rice grain.

Humic acid amendments have been widely advocated for the remediation of heavy metal-contaminated soil. However, the impacts of straw-derived humic acid-like substances on the remediation of cadmium (Cd) and arsenic (As) co-contaminated paddy soil remain unclear and the potential mechanism required clarification. In this study, we employed a pot experiment and chose a straw-derived humic acid-like substance (BFA) as the amendment with four doses to investigate how BFA affects the availability of Cd and As in soil and their accumulation in rice. The results showed that grain Cd decreased by 25.65-36.03%, while there was no significant change in total As (TAs) with the addition of BFA. The contents of DCB-Fe, DCB-As and DCB-Cd on the root surface decreased by 6.07-40.54% during the whole growth stage. The addition of BFA significantly decreased the pe + pH and enhanced the transformation of crystalline iron oxides (Fed) into amorphous forms (Feo) in the soil. The CaCl2-extractable Cd decreased and the KH2PO4-extractable As increased with the decrease in pe + pH and Fed and the relative increase in Feo. The correlation analysis showed that the decrease in availability of Cd and translocation factor of Cd effectively decreased the grain Cd and the decrease in DCB-Cd may also contribute to decreasing the uptake of Cd by rice. However, the increase in As of roots and shoots might play key roles in restricting the transport of As to rice grains. Consequently, the addition of BFA could effectively reduce the Cd accumulation in rice under flooding conditions, while no risk of As accumulation in rice grain was observed. The present work provides a new perspective for the application of straw-derived humic acid-like substances as amendments on Cd-As co-contaminated soils, which should be advocated as an eco-friendly, economical and effective soil amendment in the future.

Cadmium and arsenic availability in soil under submerged incubation: The influence of humic substances on iron speciation.

Humic substances (HSs), as electron shuttles, are associated with iron oxide transformation, yet the manner by which HSs affect Cd/As availabilities during this process under anaerobic conditions remains unclear. Two HSs (humic sodium, HA-Na, and biochemical fulvic acid, BFA) were applied at 0, 1, 2, and 4 gCkg-1 in a submerged incubation experiment. The dissolved, extractable and fractions of Cd/As and different iron oxides in soils were monitored. The addition of both HA-Na and BFA decreased the CaCl2-extractable Cd by 12.66-93.13%, and increased the KH2PO4-extractable As by 18.81-71.38% on the 60th day of incubation. The soil Eh and crystalline iron oxides (Fed) decreased, while amorphous iron oxides (Feo) and dissolved As increased after addition of both HSs. However, the two HSs had opposite effects on soil pH and dissolved Cd at the end of the incubation. HA-Na immobilized 19.47-85.99% more available Cd than did BFA over the incubation, although the extent of immobilization was similar with the maximum application rate on the 60th day. BFA mobilized 5.22-26.12% more available As than did HA-Na. XPS data showed that FeOOH decreased while the FeO component increased over the incubation. Correlation analysis and SEM showed that the reduction in the soil Eh and Fed and relative increase in Feo increased the available Cd, while decreased the available As. Consequently, the addition of HA-Na and BFA, particularly combined with flooding irrigation management, could effectively reduce the available Cd in Cd-contaminated soil. However, this method should be used with caution in As-contaminated soil.

Effects of green manure planted in winter and straw returning on soil aggregates and organic matter functional groups in double cropping rice area.

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.

Effects of composited organic mobilizing agents and their application periods on cadmium absorption of Sorghum bicolor L. in a Cd-contaminated soil.

Organic mobilizing agents have been advocated for phytoremediation of heavy metals contaminated soils, while the effects of application period of such agents remain unclear. A pot experiment was conducted, with two composited organic agents (oxalic acid or citric acid + dissolved organic fertilizer (OA + DOF and CA + DOF)) and four application periods (seeding, jointing, flag leaf and heading stages) of sorghum (Sorghum bicolor L.), to investigate their impacts on Cd bioavailability in soil. Results indicated that application of the two composited agents increased soil dissolved organic carbon (DOC) and DTPA extractable Cd by 7.31-49.13%, Cd contents in roots and shoots by 21.49-72.10%, bioaccumulation factor (BCF) and translocation factor (TF) of shoots by 4.44-71.99%, while reduced soil pH by 0.25-0.53 units, respectively. Most of these indices increased with the application periods, and largely peaked with their application during the flag leaf to heading stages. Meanwhile, the maximum sorghum biomass (132.84 g pot-1) and Cd bioaccumulation quantity (BCQ, 0.71 mg pot-1) in shoots were obtained for the CA + DOF applied at the heading. The DTPA extractable Cd was closely related to soil pH and DOC. Similar close relationships were observed between the Cd contents in shoots and soil DTPA extractable Cd, pH and DOC. The BCQ of Cd was positively related to the shoots biomass rather than their Cd contents. Therefore, the sorghum combined with the CA + DOF may be advocated as an alternative phytoremediation mode in Cd-contaminated soils, and the mobilizing agent should be primarily applied at the heading stage.

[Effects of different organic amendments on soil organic carbon and its labile fractions in the paddy soil of a double rice cropping system]. / æœ‰æœºç‰©æ–™è¿˜ç”°å¯¹åŒå­£ç¨»ç”°åœŸå£¤æœ‰æœºç¢³åŠå ¶æ´»æ€§ç»„åˆ†çš„å½±å“.

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.

[Effects of exogenous arsenic stress on bacterial and archaeal communities in two types of soils]. / å¤–æºç ·èƒè¿«å¯¹ä¸¤ç§åœŸå£¤ä¸­ç»†èŒå’Œå¤èŒç¾¤è½çš„å½±å“.

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.

[Comparison in cadmium accumulation capacities of different leafy vegetables through cadmium-rich substrate cultivation]. / åˆ©ç”¨å¯Œé•‰åŸºè´¨æ ½åŸ¹å¿«é€Ÿæ¯”è¾ƒä¸åŒå¶èœé•‰ç´¯ç§¯èƒ½åŠ›çš„å·®å¼‚.

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 R2 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.

[Accumulation Characteristics of Heavy Metals in Greenhouse Soil and Vegetables in Siping City, Jilin Province].

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.

[Effects of different fertilization regimes on nitrogen and phosphorus balance and eco-economic benefits in red paddy field.] / 不同施肥措施对红壤稻田氮磷平衡及生态经济效益的影响.

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 P2O5) 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.

[Effects of long-term fertilization on nitrogen fertilizer use efficiency in loessial soil region on the Loess Plateau, Northwest China]. / 长期施肥对黄土高原黄绵土氮肥利用率的影响.

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.

[Soil Olsen-P content changing trend and its relationship with phosphorus surplus and crop yield under long-term fertilization in loessial soil region on the Loess Plateau, China]. / é•¿æœŸæ–½è‚¥é»„ç»µåœŸæœ‰æ•ˆç£·å«é‡æ¼”å˜åŠå ¶ä¸Žç£·ç´ å¹³è¡¡å’Œä½œç‰©äº§é‡çš„å ³ç³».

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.

[Aging process of arsenite [As(3)]in soils originated from different parent materials.] / 外源As(⠢)在不同母质发育土壤中的老化过程.

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.

[Effects of vegetable cultivation years on microbial biodiversity and abundance of nitrogen cycling in greenhouse soils].

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 x 10(9) and 2.30 x 10(7) copies x 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 x 10(7) copies x 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.

[Effects of different fertilization regimes on abundance and community structure of the nirK-type denitrifying bacteria in greenhouse vegetable soils].

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 (2.16 x 10(7) copies x 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 greenhouse soil, but also aerobic denitrifying bacteria, such as Rhizobium, Ochrobactrum, Agrobacterium.

[Effects of exogenous dimethylarsinic acid on Brassica campestris growth and soil arsenic bioavailability].

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 reached 90 mg x 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.

[Concentration and speciation of arsenic in greenhouse vegetable soil in Shouguang County of Shandong Province].

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 x 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 x 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 (AlAs) > 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.

[Effects of organic fertilization on arsenic absorption of pakchoi (Brassica chinensis) on arsenic-contaminated red soil].

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.

[Soil arsenic content and its health risk assessment for agricultural products in the region surrounding Shimen arsenic sulphide mine].

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 x 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 x kg(-1), respectively, being 0.45 and 1.87 times higher than that of the grade II level (paddy field 30 mg x kg(-1); dry land 40 mg x 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 x 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 x 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 microg x kg(-1) x 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.

[Effects of exogenous dissolved organic matter and temperature on copper forms in red soil].

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 x L(-1) had the highest contents of soil exchangeable Cu and carbonate bound Cu, while treatment 500 mg DOM x 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 degrees C and 45 degrees C, the contents of soil exchangeable Cu and Fe-Mn bound Cu decreased with increasing time of incubation; while at 5 degrees 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 degrees C).