Poultry broiler litter (BL) is widely used as an alternative source of N, P, and K for crops and forages and is often applied at excessive rates of both N and P. Soil samples were periodically collected from experiments with BL at two locations in Alabama, a Coastal Plain site and a Tennessee Valley site, from 1991 though 2000. The objective was to determine the accumulation and movement of plant nutrients and metals in soil profiles when BL is compared with ammonium nitrate (AN) as a source of N for cotton (Gossypium hirsutum L.) and corn (Zea mays L.). The Tennessee Valley site was fertilized and cropped for 3 yr, and the Coastal Plain site was fertilized and cropped for 12 yr. The two N sources were applied at rates from 0 to 269 kg N ha21 based on total N in the material. Incremental soil samples to a depth of 1 m were taken periodically from 1990 through 2000. Broiler litter maintained surface soil pH on the coarse-textured soil at the Coastal Plain site whereas AN resulted in a decline in pH. There were no significant differences in surface soil pH due to source on the finer textured Tennessee Valley site. Application of BL resulted in increasing accumulations of total soil organic C, total N, and Mehlich-1 extractable Ca, Mg, P, K, B, Zn, and Cu as the rates increased from 134 to 269 kg N ha21 as BL (approximately 4.48–8.96 Mg ha21 yr21) over a 10-yr period. While differences in NH4-N and NO3-N were observed to a 1-m depth due to treatment, soil concentrations were very low compared with standards used in the presidedress soil nitrate test for corn (PSNT). No significant accumulations of heavy metals were observed during the experiments.

运用土培、石英砂培、有机酸释钾实验及矿物X衍射分析研究了不同基因型籽粒苋（Amaranthus spp.）对土壤矿物钾的吸收利用及基机制。结果表明，籽粒苋能有效地利用土壤和云母（黑云母和金云母）中的钾；籽粒苋品种R104、CX-4对钾的吸收量高于一般型品种（CX-77）；籽粒苋根系能引起云母矿物向螵石转化；籽粒苋根系分泌物中的划酸比一般有机酸具有更高的释放矿物中钾素的能力。

环境问题是当前人类生存与发展过程中所面临的重大问题。生物修复技术是解决环境污染，恢复被人类活动破坏的生态系统，实现人类社会可持续发展的重要手段之一。近年来，我国生物修复技术研究与应用蓬勃发展，取得了显著成绩。其内容主要包括微生物修复技术、重金属污染的植物修复技术、矿山废弃地生态恢复技术、固体废弃物资源化技术、垃圾填埋场生态修复技术及湖沼生态恢复技术等。在高效特异微生物与重金属超富集植物筛选及其机理研究上取得了一系列的突破，已筛选出近50种针对农药、石油、多环芳烃等有机污染物的高效特异菌种和As、Cd、Mn、Zn等12种重金属的超富集植物。今后应注意吸收其他学科的理论知识，拓宽研究领域，注重生物修复的机理研究及相关分子生物学技术的开发与应用；开展全国范围的环境污染调查与风险评估工作；建立污染环境修复的法规与标准；从而促进生物修复技术的持续发展，为国民经济发展及环境与健康保护服务。

Arsenic concentrations in a much larger fraction of U.S. groundwater sources will exceed the maximum contaminant limit when the new 10 μg L−1 EPA standard for drinking water takes effect in 2006. Thus, it is important to develop remediation technologies that can meet this new standard. Phytoremediation of arsenic-contaminated groundwater is a relatively new idea. In this research, an arsenic-hyperaccumulating fern, commonly known as Chinese Brake fern (Pteris vittata L.), was grown hydroponically to examine its effectiveness in arsenic removal from what is believed to be herbicide-contaminated groundwater. One plant grown in 600 mL of groundwater effectively reduced the arsenic concentration from 46 to less than 10 μgL−1 in 3 days. Re-used plants continued to take up arsenic from the groundwater, albeit at a slower rate (from 46 to 20 μg L−1 during the same time). Young fern plants were more efficient in removing arsenic than were older fern plants of similar size. The addition of a supplement of phosphate-free Hoagland nutrition to the groundwater had little effect on arsenic removal, but the addition of phosphate nutrition significantly reduced its arsenic affinity and, thus, inhibited the arsenic removal. This study suggested that Chinese Brake has some potential to remove arsenic from groundwater.

The fact that heavy metals can enter various domains of the plant system through foliar pathways spurred us to explore if the fronds of the Chinese brake fern (Pteris vittata L.), a hyperaccumulator of arsenic, a carcinogenic metalloid, was proficient in absorbing arsenic in the form of sprays. The specific objective of this study was to investigate the impact of frond age, form of arsenic, and time of application on the absorption of foliar-applied arsenic by the brake fern; also examined were the effects of foliar sprays on surface ultrastructure and arsenic speciation in the frond following absorption. Foliar sprays of different arsenic concentrations (0, 50, 100, 200, and 400 ppm) were applied to young and fertile fronds. A positive linear relationship existed between arsenic concentration and absorption; the arsenic concentration of fronds increased from 50 to 200 ppm. Time-course analysis with excised pinnae indicated an initial linear increase followed by a plateau at 48 h. The young fronds with immature sori absorbed more arsenic (3100 ppm) than the fertile mature fronds (890 ppm). In the frond, the arsenic absorption was greatest in the lamina of the pinnae followed by the sori and the rachis. Applying arsenic during night (20: 00-22: 00h) or afternoon (12: 00-14: 00h) resulted in greater absorption of arsenic than the application in the morning (08: 00-10: 00h). The arsenic absorption was greater through abaxial surfaces than through adaxial surfaces. The brake fern absorbed more arsenic when it was applied in the form of arsenite. Regardless of the form of arsenic and the surface it was applied to, arsenic occurred as arsenite, the reduced and the most toxic form of arsenic, after having been absorbed by the fronds. Scanning electron microscopy revealed no surface morphological alterations following all arsenic sprays. The study unequivocally illustrated that the Chinese brake fern absorbed foliar-applied arsenic with great efficiency. Consequently, the arsenic concentrations in the fronds transcended the levels of hyperaccumulation; such a characteristic could be exploited in the phytoremediation of groundwater contaminated with arsenic.

Understanding the arsenic (As) detoxification mechanisms employed by the newly discovered As hyperaccumulator Chinese Brake fern (Pteris vittata L.) is important to optimize As accumulation capability. The present experiment was carried out to determine the location of As reduction and thiol formation in Chinese Brake fern and the ability of excised plants to absorb As under P influence. Live Chinese Brake ferns were separated into three parts: pinnae (leaflets), fronds (aboveground biomass, de-rooted), and roots (belowground biomass, de-topped). The excised plants were then exposed to 0.5-strength Hoagland nutrient solutions containing 667 M As (III), As (V), or monomethylarsonic acid (MMA) and 0 M P or 500 M P for 1 day. Arsenate and arsenite were separated using an As speciation cartridge and As was determined by graphite furnace atomic absorption spectrophotometry (GFAAS). The pinnae absorbed the greatest amounts of As followed by fronds and roots. In the presence of P, the phytoavailability of As species was As (III)>MMA>As (V) for pinnae and roots and As (V)>As (III) ≌MMA for fronds. The fact that As (III) was the predominant form in excised aerial tissues whereas As (V) was the main form in excised roots clearly demonstrated that As reduction occurred mostly in the fronds, mainly in the pinnae. Absorption of As species resulted in formation of thiol, with MMA causing the greatest level of formation. Although addition of P to the solution suppressed As (V) accumulation in excised pinnae and roots, it enhanced As (V) reduction, and reduced thiol production. The results suggested that the ability to efficiently reduce As (V), facilitated by P, and to quickly produce thiols might have both contributed to the capability of Chinese Brake fern to hyperaccumulate As.

Uptake of arsenic (As) and its distribution in Chinese Brake fern (Pteris vittata L.), an As hyperaccumulator, and Boston fern (Nephrolepis exaltata L.), a nonhyperaccumulator, in the presence of phosphorus (P), were characterized by employing a hydroponic experiment with a complete three-factorial design. Two levels of As (100 and 1000 mM) and four levels of P (0, 100, 500, and 1000 mM) were used in this study. Arsenic uptake rates on the basis of root fresh weight for the two ferns were similar at low As concentration (100 mM). At high As concentration (1000 mM), however, As uptake rates (373–987 nmol g 1fwt h 1) of P. vittata were significantly

This study compared the roles of root exudates collected from two fern species, the As hyperaccumulating Chinese Brake fern (Pteris vittata L.) and the As-sensitive Boston fern (Nephrolepis exaltata L.), on As-mobilization of two As minerals (aluminum arsenate and iron arsenate) and a CCA (chromated copper arsenate)-contaminated soil as well as plant As accumulation. Chinese Brake fern exuded 2 times more dissolved organic carbon (DOC) than Boston fern and the difference was more pronounced under As stress. The composition of organic acids in the root exudates for both ferns consisted mainly of phytic acid and oxalic acid. However, Chinese Brake fern produced 0.46 to 1.06 times more phytic acid than Boston fern under As stress, and exuded 3-5 times more oxalic acid than Boston fern in all treatments. Consequently, root exudates from Chinese Brake fern mobilized more As from aluminum arsenate (3-4 times), iron arsenate (4-6 times) and CCA-contaminated soil (6-18 times) than Boston fern. Chinese Brake fern took up more As and translocated more As to the fronds than Boston fern. The molar ratio of P/As in the roots of Chinese Brake fern was greater than in the fronds whereas the reverse was observed in Boston fern. These results suggested that As-mobilization from the soil by the root exudates (enhancing plant uptake), coupled with efficient As translocation to the fronds (keeping a high molar ratio of P/As in the roots), are both important for As hyperaccumulation by Chinese Brake fern.

Ion-pair reverse-phase HPLC–inductively coupled plasma (ICP) MS was employed to determine arsenite [As (III)], dimethyl arsenic acid (DMA), monomethyl arsenic (MMA) and arsenate [As (V)] in Chinese brake fern (Pteris vittata L.). The separation was performed on a reverse-phase C18 column (Haisil 100) by using a mobile phase containing 10mM hexadecyltrimethyl ammonium bromide (CTAB) as ion-pairing reagent, 20mM ammonium phosphate buffer and 2% methanol at pH 6.0. The detection limits of arsenic species with HPLC-ICP-MS were 0.5, 0.4, 0.3 and 1.8 ppb of arsenic for As (III), DMA, MMA, and As (V), respectively. MMA has been shown for the first time to experimentally convert to DMA in the Chinese brake fern, indicating that Chinese brake fern can convert MMA to DMA by methylation.

Arsenic (As)-contaminated soil and water vary with pH and concentrations of As and P. This study examined the effects and interactions of three factors, pH, As and P, on As hyperaccumulator Pteris vittata L. to optimize plant growth and maximize As removal from contaminated sites, especially water. Two sets of hydroponic experiments were conducted using three-factor, five-level central composite design. Five levels of pH (4.5/8.0), As (0/668 mM), and P (0/1000 mM) were used to understand their individual as well as interactive effects. Plant biomass and uptake of P and As were impacted by all the three factors. Phosphorus inhibited As uptake at all concentrations, whereas As below 334 mM benefited plant growth and P uptake. Enhanced plant biomass was most likely a result of increased P uptake. Low pH enhanced plant uptake of As (pH5/5.21) and P (pH5/6.25). The fern had a relatively high biomass and P uptake at low pH/low As or high pH/high As. The referencing saddle points (turning points) were pH 6.33 and As 359 mM for plant biomass and pH 5.87 and As 331 mM for P uptake based on the response surface plot. The results suggested that optimum plant growth could be achieved by adjusting pH corresponding to As levels in the growth media, and maximum plant As hyperaccumulation by maintaining minimum P concentrations with medium pH5/5.21. Our results should be useful for developing strategies to remediate As-contaminated water using Chinese Brake fern. Published by Elsevier B.V.