外源二甲基砷对油菜生长及土壤中砷生物有效性的影响

通过盆栽试验研究了土壤中添加外源二甲基砷(DMA)对油菜(Brassica campestris)生长及土壤中砷生物有效性的影响.结果表明:随着外源DMA添加量的增加,油菜的出苗率和生物量均在一定程度上表现出了低浓度促进而高浓度抑制的现象.当外源DMA添加量达到90 mg·kg-1时,第2季盆栽油菜的出苗率和生物量与对照相比分别下降了9.5%和57.0%,表明DMA对油菜生长的影响具有长期性;随着外源DMA浓度的增加,土壤中有效态砷及油菜体内的砷含量均表现出增加的趋势,相关性分析表明,该三者间具有极显著相关关系;添加入土壤中的DMA主要发生去甲基化作用,产物主要为As(V)及少量的As(Ⅲ),且随着外源DMA添加量的增加,As(V)和As(Ⅲ)的浓度均表现出增加的趋势.     

好气条件下不同形态外源砷在土壤中的转化

在35%的田间持水量下,通过模拟试验研究了外源二甲基砷酸盐（DMA）、一甲基砷酸盐（MMA）、五价无机砷［As(V)］在土壤中的形态转化.结果表明: 外源砷进入土壤后,其含量均有随时间推延而逐渐下降的趋势,两种不同形态的有机砷DMA和MMA在土壤中主要发生脱甲基化过程,经150 d的恒温恒湿培养,其在土壤中主要转化为As(V),DMA处理仅在120 d时检测到少量MMA,而MMA处理则在7～60 d内均有少量的DMA生成.培养结束时土壤中DMA和MMA含量均显著降低(P<0.01),降幅分别为99.5%、94.3%,而两者的主要转化产物As(V)的含量则分别显著增加了4.61和5.15倍.表明外源有机态砷在土壤中基本上被转化为无机形态;与有机态外源砷相比,外源As(V)进入土壤后其形态基本上没有发生转化.     

淹水条件对土壤砷形态转化的影响

通过淹水条件下的培养试验, 探讨了外源二甲基砷酸（DMA）、一甲基砷酸（MMA）、砷酸盐［As(V)］在土壤中的动态转化规律. 结果表明: 随着培养时间的推移, 加入土壤中的DMA和MMA均主要转化为As(V), 且土壤中As(V)含量均呈增加趋势, 培养到150 d时土壤中As(V)含量均显著高于1 d时的含量(P<0.01). 外源DMA通过脱甲基化作用, 在30 d内即基本转化为As(V), 且有少量的亚砷酸盐［As(Ⅲ)］生成; 而外源MMA的转化速度相对较慢, 培养60 d后才基本完成向As(V)的转化, 同时伴随少量DMA和As(Ⅲ)的生成; 在淹水条件下外源As(V)含量随培养时间的增加而逐渐降低,该过程中除有少量As(Ⅲ)生成外,其形态基本未发生改变.     

山东寿光设施菜地土壤砷含量及形态

通过典型区域采样调查,系统探讨了山东寿光市设施菜地中砷的含量及其形态特征.结果表明: 设施菜地表层(0～20 cm)和亚表层(20～40 cm)土壤中总砷含量分别为8.27、7.93 mg·kg^-1,是对照土壤的1.19和1.23倍,易溶性砷(AE-As)含量分别为0.13、0.06 mg·kg^-1,是对照土壤的1.63和3.00倍; 土壤中的砷主要以残渣态砷(O-As)存在,其含量占总砷的63.0%以上,其他形态砷含量依次为铁型砷(Fe-As)>钙型砷(Ca-As)>铝型砷(Al-As)>AE-As; 随着种植年限的延长,土壤中AE-As含量显著增加,Al-As含量也有不同程度提高,种植15 a设施菜地表层和亚表层土壤中的AE-As含量分别比对照提高了75.0%和150.0%,Al-As含量分别提高了51.6%和190.4%,而Fe-As和Ca-As含量则均有不同程度的下降.     

秸秆不同还田方式对污染土壤砷形态的影响

为探讨秸秆还田对农田土壤砷形态的影响, 采用室内土壤培养试验, 探究旱作和水淹条件下秸秆灰分还田、秸秆粉碎还田对污染农田土壤砷赋存形态的影响。结果表明: 在旱作条件下, 秸秆灰分还田松散结合态砷含量相比对照试验提高了102%, 钙型砷含量降低了30.3%; 秸秆粉碎还田松散结合态砷、钙型砷含量分别增加了43.3%、21.7%, 铝型砷、铁型砷含量降低。水淹条件下, 秸秆灰分还田、粉碎还田松散结合态砷含量相比对照试验提高了105%、210%, 钙型砷含量降低, 铝型砷、铁型砷含量升高, 残渣态砷含量降低。秸秆还田上覆水pH升高、Eh降低、砷浓度升高, 粉碎还田、秸秆灰分还田上覆水砷浓度分别达对照试验的26倍和6倍, Eh与上覆水砷浓度存在显著负相关, r=-0.876(P=0.01)。研究表明, 两种秸秆还田方式均能增加砷的活性, 若在砷污染土壤中用秸秆灰分或粉碎秸秆还田可能会增加砷的环境风险。     

外源磷对苗期小麦和水稻根际砷形态及其生物有效性的影响

采用土(中度砷污染土)-土根袋培养的方法研究了两个浓度的外源磷(P)对苗期小麦和水稻根际砷(As)形态分布及其生物有效性的影响.结果表明:(1)两种作物生长的土壤中各砷形态的分配比例依次为:结晶铁锰或铁铝水化氧化物结合态(45%～52%)＞无定形和弱结晶铁铝或铁锰水化氧化物结合态(26%～34%)＞专性吸附态(12%～14%)＞残渣态(4%～7%)＞非专性吸附态(0.09%～0.25%).(2)添加外源磷浓度为100 mg·kg-1与不施磷处理相比显著提高了两种作物地上部的生物量(p＜0.01).(3)苗期小麦在添加100 mg·kg-1外源磷时,不仅促进了作物生长而且抑制根中砷向地上部的转运.(4)任何磷处理下,水稻对砷的吸收能力以及由根系向地上部转移能力均高于小麦.因此,在轻中度砷污染土壤上与水稻相比更适宜种植小麦(或其他旱作植物);而在水稻种植季,可以通过添加适量磷肥(100 mg·kg-1)来减弱砷在水稻体内的累积.     

外源水溶性有机物及温度对红壤铜形态的影响

利用模拟培养试验研究了外源水溶性有机物（DOM）添加量和培养温度对红壤中Cu形态的影响. 结果表明: 与不添加DOM比较, 添加不同量的DOM均可提高土壤中交换态Cu的含量、降低铁锰结合态Cu含量; 随着培养时间的延长,不同DOM添加量下土壤交换态Cu含量呈逐渐下降趋势;至试验结束时,DOM添加量为250 mg·L^-1时土壤交换态和碳酸盐结合态Cu含量最高, 添加量为500 mg·L^-1时铁锰结合态Cu含量最高;不同DOM添加量下, 土壤中有机结合态Cu含量较CK增加10.67%～23.66%. 在25 ℃和45 ℃温度条件下, 添加DOM后土壤交换态和铁锰结合态Cu含量均随培养时间的延长呈下降趋势, 但在5 ℃下变化趋势相反; 3种温度下添加DOM后土壤碳酸盐结合态Cu含量有随培养时间延长而增加的趋势. 随着培养温度的升高,土壤有机结合态Cu含量增加, 但在温度较低(5 ℃)时土壤残渣态Cu含量下降.     

砂培条件下施加钙、砷对蜈蚣草吸收砷、磷和钙的影响

在砂培条件下 ,研究施加钙、砷对蜈蚣草生长和砷、磷和钙的吸收及转运的影响。添加砷对蜈蚣草的生物量 (根、叶柄和羽叶的干物重 )虽未达到显著影响 (p<0 .0 5) ,但添加 0 .1 mmol/L砷时 ,表现出刺激生长效应。提高介质中钙浓度明显抑制蜈蚣草根系生长 ,钙浓度过高还会显著限制地上部生长。供应 0 .0 3mmol/L钙时 ,蜈蚣草羽片砷浓度为 42 1 8mg/kg,明显高于 2 .5和 5 mmol/L钙处理下相应的砷浓度。砷的转运系数 (羽片 /根 )随着介质中砷浓度的升高而增大 ,随着介质中钙浓度的升高而减少。这说明一定范围内提高介质中砷浓度促进砷向地上部运输 ,而钙却明显抑制砷向地上部转运。钙和砷浓度过高时 ,植株均会出现中毒症状。钙中毒表现为叶脉变褐和叶肉坏死 ;而砷中毒现象表现在叶尖和叶缘变褐。介质中砷限制蜈蚣草根部对磷的吸收 ,但对地上部磷浓度无显著影响。介质中添加砷 ,植物体内钙浓度升高 ,可能起缓解砷毒的作用。钙、砷对蜈蚣草羽片砷累积量和总累积量均有极显著的交互作用 ,钙是负交互效应 ,砷是正交互效应。添加 2 .5和 5.0 mmol/L钙时 ,相对于 0 .0 3 mmol/L钙处理分别减少地上部砷累积量 2 0 .8%和73.1 %。这表明在应用蜈蚣草进行植物修复时 ,介质中出现过高浓度的钙是不利于提高土壤修复效率     

影响根癌农杆菌介导的木薯遗传转化因素分析

采用根癌农杆菌介导的叶盘转化法,以我国南方地区主栽木薯品种—华南8号的胚状体子叶为受体,对影响木薯遗传转化效率的主要因素进行了分析。研究结果表明,在木薯的遗传转化中,选用GV3101作为浸染外植体的农杆菌菌株,将感染时间和共培养时间分别控制在30~45 min和3~4 d、菌液浓度（OD₆₀₀）采用0.45、并添加200 μmol·L^-1的乙酰丁香酮（AS）均可明显提高其转化效率,但若对外植体进行预培养反而会降低其转化效率。利用该体系从453块外植体中共转化获得10株抗性再生植株,经PCR和Southern杂交检测,有8株木薯的基因组中已整合进了外源基因glgC336,转化率为1.77%。     

温度对土壤中外源氨基酸、多肽的矿化及其吸收动力学的影响

研究了不同温度（1 ℃、15 ℃和25 ℃）对3种园艺生产系统（有机生产系统OS、转换期生产系统TS、常规生产系统CS）土壤中外源添加氨基酸、多肽的矿化及其吸收动力学特性的影响.结果表明：随着温度的升高,外源添加的氨基酸和多肽在土壤中的矿化速度加快.在1 ℃、15 ℃和25 ℃下,3种供试土壤中谷氨酸（Glu）的平均半衰期分别为13.3、6.8和5.5 h;而谷氨酰 苯丙氨酸（Glu-Phe）的平均半衰期则分别为29.7、7.5和4.4 h.土壤的氨基酸、多肽的吸收动力学试验表明,土壤对氨基酸、多肽的吸收速率随着外源添加氨基酸和多肽浓度及温度的增加而提高.土壤对氨基酸的最大吸收速率(V_max)和亲和力（K_m）及对多肽的吸收速率（V_h）均随温度的升高而增大.在0～2.5 mmol·L^-1浓度范围内,土壤对氨基酸的吸收动力学曲线遵循经典的米氏动力学曲线,而多肽则表现为线性模式.3种园艺生产系统土壤的氨基酸和多肽的周转速率、吸收动力学参数（V_max、K_m和V_h）均表现为OS>TS>CS.总之,温度显著影响了氨基酸、多肽在土壤中的矿化及其吸收动力学特性.     

The response of tomato (Lycopersicon esculentum) to different concentrations of inorganic and organic compounds of arsenic

Tomato plants were cultivated in greenhouse and water solutions of arsenite (As(III)), arsenate (As(V)), methylarsonic acid (MA) and dimethylarsinic acid (DMA) were applied individually into cultivation substrate at two As levels, 5 and 15 mg kg⁻¹ of the substrate. Comparing the availability of arsenic compounds increased in order arsenite = arsenate < MA < DMA where the arsenic contents in plants decreased during vegetation period. Within a single plant, the highest arsenic concentration was found in roots followed in decreasing order by leaves, stems, and fruits regardless of arsenic compound applied. Arsenic toxicity symptoms reflected in suppressed growth of plants and a lower number and size of fruits were most significant with DMA treatment. However, the highest accumulation of arsenic by plants growing in the soil containing DMA was caused by higher mobility of this compound in the soil due to its lower sorption affinity. Our results confirmed substantial role of transformation processes of arsenic compounds in soil in uptake and accumulation of arsenic by plants.     

Arsenic species that cause release of iron from ferritin and generation of activated oxygen

The in vitro effects of four different species of arsenic (arsenate, arsenite, monomethylarsonic acid, and dimethylarsinic acid) in mobilizing iron from horse spleen ferritin under aerobic and anaerobic conditions were investigated. Dimethylarsinic acid (DMA(V)) and dimethylarsinous acid (DMA(III)) significantly released iron from horse spleen ferritin either with or without the presence of ascorbic acid, a strong synergistic agent. Ascorbic acid-mediated iron release was time-dependent as well as both DMA(III) and ferritin concentration-dependent. Iron release from ferritin by DMA(III)) alone or with ascorbic acid was not significantly inhibited by superoxide dismutase (150 or 300 units/ml). However, the iron release was greater under anaerobic conditions (nitrogen gas), which indicates direct chemical reduction of iron from ferritin by DMA(III), with or without ascorbic acid. Both DMA(V) and DMA(III)) released iron from both horse spleen and human liver ferritin. Further, the release of ferritin iron by DMA(III)) with ascorbic acid catalyzed bleomycin-dependent degradation of calf thymus DNA. These results indicate that exogenous methylated arsenic species and endogenous ascorbic acid can cause (a) the release of iron from ferritin, (b) the iron-dependent formation of reactive oxygen species, and (c) DNA damage. This reactive oxygen species pathway could be a mechanism of action of arsenic carcinogenesis in man.     

控制性分根区交替滴灌对苹果幼树形态特征与根系水分传导的影响

采用固定滴灌(根区一侧固定供水)、控制性分根区交替滴灌(根区两侧交替供水)和常规滴灌(紧贴幼树基部供水)3种灌水方式和3种灌水定额(固定滴灌和交替滴灌均为10、20和30 mm,常规滴灌为20、30和40 mm),对比研究了控制性分根区交替滴灌对苹果幼树形态特征与根系水分传导的影响.结果表明： 交替滴灌的根区两侧土壤出现反复干湿交替过程,常规滴灌的根区两侧土壤含水率差异不显著.在灌水定额相同时,灌水侧的土壤含水率在3种灌水方式间差异不显著.与常规滴灌和固定滴灌相比,交替滴灌显著增加了苹果幼树的根冠比、壮苗指数和根系水分传导,在30 mm灌水定额处理下,交替滴灌的根冠比分别增加31.6%和47.1%,壮苗指数增加34.2%和53.6%,根系水分传导增加9.0%和11.0%.3种灌水方式下,根干质量和叶面积均与根系水分传导呈显著线性正相关.控制性分根区交替滴灌增强了苹果幼树根系水分传导的补偿效应,促进了根系对水分的吸收利用,有利于干物质向各个器官均衡分配,显著提高了根冠比和壮苗指数.     

Effects of Chemical Speciation on the Mineralization of Organic Compounds by Microorganisms

The mineralization of 1.0 to 100 ng each of four complexing compounds—oxalate, citrate, nitrilotriacetate (NTA), and EDTA—per ml was tested in media prepared in accordance with equilibrium calculations by a computer program so that the H, Ca, Mg, Fe, or Al complex (chemical species) was predominant. Sewage microorganisms mineralized calcium citrate more rapidly than iron, aluminum, or hydrogen citrate, and magnesium citrate was degraded slowest. Aluminum, hydrogen, and iron oxalates were mineralized more rapidly than calcium oxalate, and magnesium oxalate was decomposed slowest. Sewage microorganisms mineralized calcium NTA but not aluminum, magnesium, hydrogen, or iron NTA or any of the EDTA complexes. Pseudomonas sp. mineralized calcium and iron citrates but had no activity on hydrogen, aluminum, or magnesium citrate. Pseudomonas pseudoalcaligenes mineralized calcium, iron, hydrogen, and aluminum citrates but had little activity on magnesium citrate. Pseudomonas alcaligenes used calcium, iron, hydrogen, and aluminum oxalates readily, but it used magnesium oxalate at a slower rate. Listeria sp. destroyed calcium NTA but had no effect on hydrogen, iron, or magnesium NTA. Increasing the Ca concentration in the medium enhanced the breakdown of NTA by Listeria sp. The different activities of the bacterial isolates were not a result of the toxicity of the complexes or the lack of availability of a nutrient element. NTA mineralization was not enhanced by the addition of Ca to Beebe Lake water, but it was enhanced when Ca and an NTA-degrading inoculum were added to water from an oligotrophic lake. The data show that chemical speciation influences the mineralization of organic compounds by naturally occurring microbial communities and by individual bacterial populations.     

Kinetics of arsenic methylation by freshly isolated B6C3F1 mouse hepatocytes

The toxic and carcinogenic effects of arsenic may be mediated by both inorganic and methylated arsenic species. The methylation of arsenic(III) is thought to take place via sequential oxidative methylation and reduction steps to form monomethylarsenic (MMA) and dimethylarsenic (DMA) species, but recent evidence indicates that glutathione complexes of arsenic(III) can be methylated without oxidation. The kinetics of arsenic methylation were determined in freshly isolated hepatocytes from male B6C3F1 mice. Hepatocytes (>90% viability) were isolated by collagenase perfusion and suspended in Williams' Medium E with various concentrations of arsenic(III) (sodium m-arsenite). Aliquots of the lysed cell suspension were analyzed for arsenic species by hydride generation-atomic absorption spectrometry. The formation of MMA(III) from sodium arsenite (1 microM) was linear with respect to time for >90 min. DMA(III) formation did not become significant until 60 min. MMA(V) and DMA(V) were not consistently observed in the incubations. These results suggest that the glutathione complex mechanism of methylation plays an important role in arsenic biotransformation in mouse hepatocytes. Metabolism of arsenic(V) was not observed in mouse hepatocytes, consistent with inhibition of arsenic(V) active cellular uptake by phosphate in the medium. The formation of MMA(III) increased with increasing arsenic(III) concentrations up to approximately 2 microM and declined thereafter. The concentration dependence is consistent with a saturable methylation reaction accompanied by uncompetitive substrate inhibition of the reaction by arsenic(III). Kinetic analysis of the data suggested an apparent K(M) of approximately 3.6 microM arsenic(III), an apparent V(max) of approximately 38.9 microg MMA(III) formed/L/h/million cells, and an apparent K(I) of approximately 1.3 microM arsenic(III). The results of this study can be used in the physiologically based pharmacokinetic model for arsenic disposition in mice to predict the concentration of MMA(III) in liver and other tissues.     

增温对南亚热带森林土壤磷形态的影响及其对有效磷的贡献

磷(P)是森林生态系统生产力的重要限制性元素。土壤磷的有效性取决于磷的存在形态及其转化过程。目前有关增温如何调控磷形态转化过程, 从而促进土壤有效磷含量增加的机制尚未明确。该研究以南亚热带森林为研究对象, 采用沿海拔高度从300 m下降至30 m以模拟温度自然上升的方法, 采集该林型0-10、10-20、20-40 cm的土壤, 并用适用于酸性土壤的连续浸提方法分离不同形态磷, 研究增温对土壤不同形态磷含量的影响, 探讨土壤不同形态磷与有效磷的关系, 识别对土壤有效磷在增温背景下增加有重要贡献的磷组分。结果表明增温使0-10 cm的无机钙磷(Ca-Pi)及20-40 cm的无机铁磷(Fe-Pi)和总无机磷含量分别显著增加了65.5%、17.9%和18.5%, 但对总有机磷及各有机磷组分含量均无显著影响。土壤不同形态磷与有效磷含量的相关分析表明, 有效磷与无机态的不同形态磷及有机铝磷、有机铁磷含量均显著正相关, 其中与Fe-Pi含量的相关性最强。通过土壤不同形态磷与有效磷含量的通径分析进一步发现, 无机铝磷、Fe-Pi是土壤磷转化过程中的重要中间过渡性磷组分, 且Fe-Pi是促进有效磷含量增加最重要的直接贡献磷组分。结合前期研究结果, 增温可能增大了凋落物磷对土壤磷的输入, 还可能强化了土壤的吸附和沉淀过程, 使得更多进入到土壤的溶解态磷转化为Ca-Pi、Fe-Pi等缓效磷源, 其中Fe-Pi可能成为南亚热带森林在气候变暖背景下最重要的有效磷来源。