铁、锰、铝氧化物固体吸附剂对胡敏酸和富里酸吸附机理研究

研究了Fe2O3、MnO2或Al2O3固体吸附剂对胡敏酸和富里酸的吸附机制和影响因素。结果表明:相同pH下,Fe2O3、MnO2或Al2O3固体吸附剂对腐殖酸的吸附量随着腐殖酸(胡敏酸HA和富里酸FA)有机碳浓度的增加而增加;不同pH下,对HA的吸附量依照pH3·0>pH5·0>pH7·0的顺序递减。相同pH下,随着HA有机碳浓度的增加,三种固体吸附剂对HA的吸附百分率减小。相同pH下,三种固体吸附剂对FA的吸附百分率呈单峰形,随着酸度的降低,峰位向添加的有机碳低浓度处迁移。吸附量用Langumuir方程拟合能得到极显著相关的方程,在相同pH下,三种固体吸附剂吸附HA的最大吸附量Smax和吸附亲和力常数K小于FA,而标准自由能变ΔGmo却略大于FA;298·2K温度下,三种固体吸附剂吸附胡敏酸和富里酸的ΔGmo<0,表明在等温等压不做非体积功情况下吸附是自发进行的反应。     

不同磺化腐殖酸磷肥提高冬小麦产量和磷素吸收利用的效应研究

【目的】腐殖酸对磷肥增效的调控效应与其结构性密切相关。本文比较了不同磺化反应方法制备的腐殖酸磷肥对冬小麦磷素利用的影响,为制备调控磷肥专用的腐殖酸增效载体提供依据。【方法】采用磷酸与氢氧化钾反应法制备普通磷肥 (P)、普通腐殖酸磷肥 (HAP),并采用加双氧水、硝酸等方法制备了四种磺化腐殖酸磷肥 (HA1P、HA2P、HA3P和HA4P)。用田间土柱栽培试验方法,在等磷量基础上,设置普通磷肥 (P)、普通腐殖酸磷肥 (HAP)、磺甲基化腐殖酸磷肥 (HA1P)、双氧水+磺甲基化腐殖酸磷肥 (HA2P)、硝酸+磺甲基化腐殖酸磷肥 (HA3P)、双氧水+硝酸+磺甲基化腐殖酸磷肥 (HA4P) 6个处理,同时设置不施磷肥对照 (CK) 处理和施用等量腐殖酸处理 (C-HA、C-HA1、C-HA2、C-HA3、C-HA4)。调查了小麦产量和产量构成及经济效益,分析了0—80 cm土壤有效磷含量。【结果】1) 与CK相比,普通腐殖酸 (C-HA) 和磺化处理腐殖酸 (C-HA1、C-HA2、C-HA3、C-HA4) 对小麦籽粒产量无显著影响。与P处理比较,HAP、HA1P、HA2P、HA3P、HA4P处理的小麦籽粒产量分别提高了6.3%、17.8%、10.1%、17.5%、11.1%,4个腐殖酸磺化磷肥 (HA1P、HA2P、HA3P、HA4P) 处理均高于普通腐殖酸磷肥 (HAP) 处理。2)与HAP比较,磺化腐殖酸磷肥处理HA1P、HA2P、HA3P、HA4P分别提高小麦地上部磷吸收量12.3%、12.3%、9.2%、10.8%,其中HA1P和HA2P处理最高。3）与HAP比较,磺化腐殖酸磷肥处理HA1P、HA3P分别提高小麦磷肥农学效率23.6%和7.1%。4）与HAP比较,磺化腐殖酸磷肥处理HA1P、HA2P、HA4P可分别提高0—20 cm土层土壤速效磷含量17.5%、16.2%、17.2%。【结论】磺化腐殖酸磷肥比普通腐殖酸磷肥可以更有效地提高土壤中磷肥的有效性,提高冬小麦对磷素的吸收利用,进而提高冬小麦籽粒产量。四种磺化工艺中,以磺甲基化处理的腐殖酸磷肥 (HA1P) 效果最优。     

锰离子与胡敏酸络合反应特征研究

采用离子交换平衡法研究了在不同酸度、离子强度、温度条件下胡敏酸(HA)与Mn2+络合反应稳定性和热力学特征。结果表明,在相同离子强度、反应温度条件下,随着pH的升高,HA与Mn2+络合反应稳定常数增大;络合反应配位数在pH 3.0～5.0范围内随着pH的升高而增加,在5.0～7.0范围内随着pH的升高而降低;离子强度增加,HA与Mn2+络合反应表观稳定常数增加,离子强度从0.00升至0.10 mol L-1,HA与Mn2+络合反应配位数增加,但离子强度从0.10 mol L-1继续上升至0.15 mol L-1,配位数呈现下降的趋势;胡敏酸络合Mn2+标准自由能变ΔGmθ、焓变ΔHθm、熵变ΔSθm在298.2K、308.2K温度下均为负值,反应是自发进行的放热反应,较低的温度有利于反应的进行。     

煤基腐殖酸吸附Cu~(2+)特征的影响因素

为有效发挥煤基腐殖酸在缓解农田Cu2+污染和提升作物Cu2+生物有效性等方面的作用,采用新疆风化煤所提取的腐殖酸(煤基HA)作为吸附剂,应用批量平衡法研究pH、共存阳离子、温度和接触时间等因素影响下,煤基HA对Cu2+离子的吸附特征。结果表明:pH是影响煤基HA吸附Cu2+的最主要因素,pH值3~6时Cu2+吸附率急剧增加,增长曲线整体呈"S"形。共存Na+浓度增加(0~1.0mol/L),Cu2+在煤基HA上的吸附受抑制。298K和318K温度影响下的2条吸附等温曲线存在共性,均表现为先增加后趋于平衡的特点,其中,Langmuir方程对其规律的描述最为贴切。温度(298~318K)和初始Cu2+浓度(0~1 000mg/L)均与Cu2+的吸附数量呈正相关,自发、吸热及混乱度增加是该热力学吸附过程的三大特点。煤基HA对Cu2+的动力学吸附可大致分为快速提升和缓速平衡2个阶段,Elovich和双常数方程能很好描述该过程。温度有利于反应速率的提升,但其未能对吸附后表面结构的有序度产生影响。     

酸性条件下H+Ca2+在红壤表面反应的能量特征

用自行设计的动力学装置研究了酸性条件下H -Ca2 在红壤表面的反应动力学能量特征。结果表明 ,酸性条件下Ca2 吸附分为快反应和慢反应。用一级动力学方程拟合的Ca2 最大吸附量随酸度增加显著下降 ,随温度升高提前达到平衡。用双常数方程描述Ca2 在吸附点位能量分布的不均匀性 ,用扩散速率常数计算的活化能 (Eb )随酸度的增加而增加 ,Ca2 扩散需克服的能障加大 ;ΔH 值为正 ,温度升高可促进Ca2 的扩散 ;ΔS 值均为负 ,说明吸附反应使体系有序度增加。原液pH为 4 .5和 5 .6时 ,流出液的pH急剧下降 ,H 表观释放量用一级动力学和双常数方程拟合为最佳模型 ,其次是Elovich方程、扩散方程和零级方程 ;pH5 .6处理时H 、Al3 扩散进入溶液克服的能障比pH 4 .5处理的小 ,后者质子扩散需热能较大而不易进行 ;H 扩散活化焓变为正 ,其扩散是吸热过程。pH 3.5时流入液比流出液的pH高 ,是由于土壤的缓冲作用、土壤表面质子化和硫酸根专性吸附释放羟基 ;当溶液中H 超过一定数量后 ,向颗粒表面扩散的H 量比向外释放的多 ,反应初期的H 消耗是快反应过程。H 消耗的活化能及热焓比其释放的低 ,更有利于H 的吸附 ,因H 对矿物的溶蚀成为速率控制步骤 ,H 对矿物的溶解可用扩散方程和Elovich方程描述     

酸性条件下可变电荷土壤对铜吸附动力学特征

用自行设计的动力学装置,研究了酸性条件下Cu在可变电荷土壤表面的反应动力学吸附特征。结果表明,在酸性条件下,Cu吸附过程分为快反应和慢反应。从一级动力学方程拟合的参数可知,3种土壤的最大吸附量依次为砖红壤〉赤红壤〉红壤,Cu最大吸附量随酸度增加显著下降;用Elovich方程和抛物线扩散方程常数b值,解释离子的表观扩散速率,3种土壤的b值依次为砖红壤〉赤红壤〉红壤,且随酸度的增大而降低。从相关系数的比较看,Elovich方程在描述Cu的吸附数据比一级动力学方程和抛物线扩散方程要差。在Cu吸附过程中,pH为5．5和4．3时,红壤和赤红壤流出液中有质子释放,质子的释放可能涉及铜离子的水解;而砖红壤在pH为5．5有质子的释放,pH4-3时有质子的消耗。当原液pH为3.3和3．8时,都存在质子的消耗。3种土壤H＋的消耗过程有较大的区别,砖红壤上快速消耗H＋鱼-远远大于红壤和赤红壤。反应初期,H＋质子的消耗是快速反应,主要包括土壤交换阳离子的缓冲作用、土壤表面的质子化及硫酸根专性吸附释放的羟基中和H＋质子;而以后的反应中,H＋质子对矿物的溶解是一缓慢过程。     

氟离子、磷酸根和铬酸根在可变电荷土壤表面吸附过程中羟基释放动力学

用恒pH自动电位滴定装置研究了氟离子(F-)、磷酸根(H2PO4-)和铬酸根(CrO42-)在3种可变电荷土壤表面吸附过程中羟基(-OH)释放的动力学。研究结果表明,3种阴离子在可变电荷土壤表面吸附时-OH释放量的大小顺序为:F->>H2PO4->CrO42-,这与土壤对3种阴离子吸附量的大小顺序一致。pH对不同阴离子体系中-OH释放的影响不同,在F-体系中,pH5.0时-OH释放量最高,其次为pH6.0时,pH4.0时-OH释放量最小;CrO42-体系中-OH释放量随pH的增加而减小;pH对H2PO4-体系中-OH释放的影响较小。Elovich方程(Y=a kln(t))能够很好拟合2～60min之间的动力学数据,说明-OH释放的速率随时间增加而减小。比较速率常数k的大小可以发现,虽然F-体系中3种可变电荷土壤在前2min释放的-OH量有很大差异,但在2～60min内,-OH释放速率差别不大。在H2PO4-和CrO42-体系中,-OH释放速率的大小顺序是:昆明砖红壤>徐闻砖红壤>江西红壤,与土壤铁、铝氧化物含量一致。     

腐植酸吸附土壤Cr(Ⅵ)条件优化

在单因素试验基础上,采用二次回归正交旋转组合设计对腐植酸去除土壤中Cr(Ⅵ)进行了优化,建立了土壤Cr(Ⅵ)潜在去除率与HA浓度(x1)、pH(x2)、反应接触时间(x3)和反应温度(x4)四个因素间的正交回归模型:Y=60.27012-2.22158X1+2.92002X3-4.29138X21-2.53068X22-2.00566X24-2.35375X1X2+3.68250X1X3-1.99875X1X4-1.99875X2X3+3.68250X2X4-2.35375X3X4。从模型推知,当HA浓度为1.86 g/L、pH值5.5、振荡时间为8.6h和反应温度25.2℃时,土壤中Cr(Ⅵ)潜在去除率最大,达80.0%。验证结果与模型值相符。     

氧化/磺化腐殖酸对潮土中Cu、Zn、Fe、Mn有效性的影响

【目的】研究比较改性腐殖酸对潮土微量元素有效性的影响及其作用机理,以期为开发提高微量元素有效性的专用腐殖酸功能材料提供科学依据。【方法】采用土壤培养法,将腐殖酸 (HA)、氧化腐殖酸 (YHA) 和磺化腐殖酸 (SHA) 分别按30、100、300 mg/kg用量与干土混匀装入培养瓶中,调节含水量至田间持水量的60%,置于25℃人工气候箱中进行恒温培养,并保持土壤湿度恒定。分别在培养第3、7、15、30、60天取样,测定土壤有效铜、锌、铁、锰含量。【结果】三种腐殖酸对土壤Cu、Zn、Fe、Mn有效性的影响大小依次为HA>YHA>SHA。施用30～300 mg/kg 腐殖酸 (HA) 可显著提高土壤有效铜含量,特别是在15～30天内,土壤有效铜含量提升幅度可达51.3%,明显优于氧化腐殖酸和磺化腐殖酸;施用三种腐殖酸30～300 mg/kg可在15天内增加土壤有效锌含量,其中以腐殖酸 (HA) 效果最好,土壤有效锌含量增幅可达11.8%～20.3%,优于氧化腐殖酸、磺化腐殖酸;30～100 mg/kg用量下,施用腐殖酸 (HA) 可在15天内使土壤有效锰含量提升5.6%,效果优于氧化腐殖酸和磺化腐殖酸,300 mg/kg用量下,磺化腐殖酸可使土壤有效锰含量提升13.6%;施用30～300 mg/kg的腐殖酸 (HA) 一周后,土壤有效铁含量提高4.3%～7.2%,磺化腐殖酸或氧化腐殖酸用量分别在30 mg/kg和300 mg/kg时可提高土壤铁有效性。【结论】施用腐殖酸可显著提升潮土铜的有效性,但对潮土锌、锰、铁有效性的影响呈现出阶段性变化,不同结构腐殖酸对潮土微量元素有效性的影响差异较大,以HA对元素有效性的影响最大。因此,腐殖酸应用于提升微量元素有效性时,需考虑腐殖酸本身性质及施用时期等因素。     

酸性条件下红壤表面Zn^2＋-H^＋反应动力学的能量特征

用自行设计的动力学装置研究了酸性条件下Zn在红壤表面的反应动力学能量特征。结果表明,酸性条件下,Zn吸附分为快反应和慢反应。用一级动力学方程拟合的Zn最大吸附量：pH5.5处理Zn的最大吸附量在289 K时为1.79 mmol.kg^-1,在313 K时为2.62 mmol.kg^-1;pH3.3处理Zn的最大吸附量在289 K时为0.12 mmol.kg^-1,在313 K时为0.16 mmol.kg^-1。即吸附量随酸度增加显著下降,随温度升高明显增加。用扩散速率常数计算的活化能（ΔE＊）：pH5.5处理Zn的ΔE＊为9.05 kJ.mol^-1,pH3.3处理Zn的ΔE＊为12.02 kJ.mol^-1,随酸度的增加ΔE＊增加,Zn扩散需克服的能障加大,Zn吸附量降低。ΔH值为正,温度升高可促进Zn的扩散;ΔS值均为负,说明吸附反应使体系有序度增加。原液pH为5.5时,流出液的pH急剧下降;pH4.3、pH3.8和pH3.3时流出液比流入液的pH高,是由于土壤的缓冲作用和土壤表面质子化;当溶液中H＋超过一定数量后,反应初期的H＋消耗是快反应过程,H＋对矿物的溶蚀成为速率控制步骤。     

低氮和干旱胁迫对富士和秦冠生长及氮素利用的影响

【目的】以富士（Fuji）、 秦冠（Qinguan）嫁接在平邑甜茶（Malus hupehensis Rehd.）上的当年生盆栽苗为试验材料,采用砂培方法,研究了缺氮胁迫和干旱对富士和秦冠生长情况、 光合参数、 植株各部位氮磷钾含量及氮素利用效率的影响,分析比较了低氮干旱条件下富士和秦冠生长及氮素利用的差异,以期为果树生产高效肥水利用提供理论指导。【方法】试验共设四个处理: 正常氮正常水（ZZ）、 低氮正常水（DZ）、 正常氮干旱（ZG）、 低氮干旱（DG）。氮素和水分均设置两个水平,分别为正常氮（6 mmol/L NO-3-N）、 低氮（0.3 mmol/LNO-3-N）、 正常供水（保持盆中砂子相对含水量为饱和含水量的80%~85%）、 干旱处理（保持盆中砂子相对含水量为饱和含水量的60%~65%）。【结果】富士和秦冠的生物量（茎和叶）、 株高茎粗等生长指标以及光合速率、 气孔导度、 蒸腾速率均为正常氮正常水（ZZ）＞低氮正常水（DZ）＞正常氮干旱（ZG）＞低氮干旱（DG）,并且相对应处理下秦冠的以上指标均高于富士;正常供水下,缺氮处理使富士、 秦冠的根冠比比正常氮处理均有所增加,富士提高了2.05%,秦冠提高了22.40%。富士和秦冠的氮、 磷、 钾含量均表现出正常氮正常水（ZZ）＞低氮正常水（DZ）＞正常氮干旱（ZG）＞低氮干旱（DG）; 氮、 钾元素含量在植株各部位的分布顺序依次是叶＞根＞茎,磷元素则是根＞叶＞茎;光合氮素利用效率（PNUE）和氮素利用效率表现为秦冠处理之间差异极显著,富士处理之间差异不显著;秦冠的PNUE和NUE明显高于富士,在低氮正常水（DZ）处理下,秦冠氮肥利用率比富士高42.07%,在低氮干旱（DG）处理下高64.14%;低氮胁迫下富士和秦冠的NUE显著提高,并且秦冠提高的幅度高于富士。【结论】施用氮肥能够显著提高富士与秦冠的干物质量,同等水肥条件下,秦冠生长优于富士;水分亏缺会减少叶片对氮的吸收,干旱条件下适度增施氮肥,可提高果树的抗旱能力;低氮干旱胁迫下秦冠的生长指标、 光合指标及氮素利用效率指标均优于富士,表现出较强的抗低氮干旱胁迫的能力。     

Pasture Vegetation Elemental Analysis by Laser-Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy (LIBS) is a new technique for the analysis of plant material. This study investigates the application of LIBS to pasture-based plant samples. The LIBS measurements were obtained from pelletized pasture samples (100 samples) that had been also analyzed by inductively coupled plasma–optical emission spectroscopy (ICP-OES) following microwave digestion for calibration and comparison purposes. Comparisons for elements sodium (Na), potassium (K), magnesium (Mg), calcium (Ca), manganese (Mn), iron (Fe), copper (Cu), zinc (Zn), boron (B), phosphorus (P), and sulfur (S) showed that LIBS could be used for almost all the standard profile total elements with concentrations down to low mg/kg levels (observed error of Na: 0.024 percent, K: 0.18 percent, Mg: 0.016 percent, Ca: 0.073 percent, P: 0.017 percent, Mn: 31 mg/kg, Fe: 150 mg/kg, Zn: 6.6 mg/kg, and B: 1.1 mg/kg). Elemental analysis at less than mg/kg levels was not possible using LIBS. The elements S and Cu were particularly difficult to analyze with reliability using LIBS at the concentration levels found in the plant samples. Replacing microwave digestion and subsequent ICP analysis with a direct analysis of dried plant samples using LIBS has the potential to improve the productivity and reduce the cost of testing.     

Faculty positions:Center for Agricultural Resources Research,Chinese Academy of Sciences

正The Center for Agricultural Resources Research(CARR),the Institute of Genetics and Developmental Biology(IGDB),Chinese Academy of Sciences,invites applicants for several research group leader positions.CARR is one of the research organizations in Chinese Academy of Sciences(CAS).We seek nominations and applications from individuals who have expertise and a record of accomplishment in research areas related to ecology,agro-hydrology,     

Macroinvertebrates in North American tallgrass prairie soils: effects of fire, mowing, and fertilization on density and biomass

The responses of tallgrass prairie plant communities and ecosystem processes to fire and grazing are well characterized. However, responses of invertebrate consumer groups, and particularly soil-dwelling organisms, to these disturbances are not well known. At Konza Prairie Biological Station, we sampled soil macroinvertebrates in 1994 and 1999 as part of a long-term experiment designed to examine the effects and interactions of annual fire, mowing, and fertilization (N and P) on prairie soil communities and processes. For nearly all taxa, in both years, responses were characterized by significant treatment interactions, but some general patterns were evident. Introduced European earthworms (Aporrectodea spp. and Octolasion spp.) were most abundant in plots where fire was excluded, and the proportion of the total earthworm community consisting of introduced earthworms was greater in unburned, unmowed, and fertilized plots. Nymphs of two Cicada genera were collected (Cicadetta spp. and Tibicen spp.). Cicadetta nymphs were more abundant in burned plots, but mowing reduced their abundance. Tibicen nymphs were collected almost exclusively from unburned plots. Treatment effects on herbivorous beetle larvae (Scarabaeidae, Elateridae, and Curculionidae) were variable, but nutrient additions (N or P) usually resulted in greater densities, whereas mowing usually resulted in lower densities. Our results suggest that departures from historical disturbance regimes (i.e. frequent fire and grazing) may render soils more susceptible to increased numbers of European earthworms, and that interactions between fire, aboveground biomass removal, and vegetation responses affect the structure and composition of invertebrate communities in tallgrass prairie soils.     

Variation in quality parameters between and within 14 Nordic tree fruit and berry species

Abstract

A 3-year study was carried out to investigate quality parameters in 14 tree fruit and berry species grown in southern Norway. The species were blueberry, apple, aronia, sour cherry, sweet cherry, red raspberry, strawberry, blackcurrant, gooseberry, red currant and elderberry, harvested along with wild bilberry, cloudberry and lingonberry. Significant differences between species were identified for all quality parameters. The coefficient of variation between species was lowest for pH (12.5%), dry matter (18.9%) and soluble solids (25.3%), followed by titratable acids (59.3%), total phenolics (83.8%), antioxidant capacity FRAP (85.7%) and antiradical power by the DPPH-assay (97.8%), total monomeric anthocyanins (132%) and ascorbic acid (137%). Average coefficient of variation within species were lower and ranged from 4 (pH) to 62% (ascorbic acid). Only the FRAP values were significantly affected by harvesting year with lower levels in 2004 than in 2005 and 2006. There were significant interactions between species and harvesting year for dry matter, soluble solids, pH, ascorbic acid and FRAP. The results indicate generic ranges in composition within species independent upon growing location and climate, and the composition of the tree fruits and berries is not likely to deviate from these ranges. It is concluded that desirable composition of tree fruits and berries and their products should primarily be achieved by selection among species rather than searching fors broadened variation within individual species.     

Potassium Fixation and Release Characteristics in Rhizosphere and Nonrhizosphere Soils for a Rapeseed–Rice Cropping Sequence

Potassium (K) fixation and release in soil are important factors in the long-term sustainability of a cropping system. Changes in K concentration and characteristics of K fixation and release in rhizosphere and nonrhizosphere soils in the rapeseed (Brassica napus L.)–rice (Oryza sativa L.) rotation were investigated using a rhizobox system. The concentrations of different forms of K in both rhizosphere and nonrhizosphere soils decreased with plants compared to without plants, regardless of K fertilizer application. Potassium uptake by crops mainly came from the rhizosphere soil. In the treatment without K fertilizer (–K), the main form of K supplied by the soil to the crops was 1.0 mol L^?1 nitric acid (HNO₃) nonextractable K, followed by nonexchangeable K, and then exchangeable K. In the treatment with K fertilizer (+K), the main K forms supplied by the soil to the crops were exchangeable K and nonexchangeable K. The amount and rate of K fixation after one cycle of the rapeseed–rice rotation was greater in rhizosphere soil than in nonrhizosphere soil. The amount and rate of K fixation of soil in the +K treatment were significantly less than in the –K treatment. The cumulative amounts of K released with 1.0 mol L^?1 ammonium acetate (NH₄OAc) and 1.0 mol L^?1 HNO₃ extraction increased with the increasing numbers of extractions, but the K-releasing power of soil by successive extraction decreased gradually and finally became almost constant. The release of K was less in rhizosphere soil than in nonrhizosphere soil. The release of K in the +K treatment was similar to that in the –K treatment in rhizosphere soil, but the K release in nonrhizosphere soil was greater with the +K than the –K treatment. Overall, the information obtained in this study will be helpful in formulating more precise K fertilizer recommendations for certain soils.     

Electron donor and pH relationships for biologically enhanced dissolution of chlorinated solvent DNAPL in groundwater

Biologically enhanced dissolution offers a method to speed removal of chlorinated solvent dense non-aqueous-phase liquid (DNAPL) sources such as tetrachloroethene (PCE) and trichoroethene (TCE) from aquifers. Bioremediation is accomplished by adding an electron donor to the source zone where fermentation to intermediates leading to acetic acid and hydrogen results. The hydrogen and possibly acetic acid are used by dehalogenating bacteria to convert PCE and TCE to ethene and hydrochloric acid. Reductive dehalogenation is thus an acid forming process, and sufficient alkalinity must be present to maintain a near neutral pH. The bicarbonate alkalinity required to maintain pH above 6.5 is a function of the electron donor: 800 mg/L of bicarbonate alkalinity is sufficient to achieve about 1.2 mM TCE dechlorination with glucose, 1.7 mM with lactate, and a much higher 3.3 mM with formate. Laboratory studies indicate that in mixed culture, formate can be used as an electron donor for complete conversion to ethene, contrary to pure cultures studies indicating it cannot. Various strategies can be used to add electron donor to an aquifer for DNAPL dehalogenation while minimizing pH problems and excessive electron donor usage, including use of injection-extraction wells, dual recirculation wells, and nested injection-extraction wells.     

Biodiversity and ecogeography of wild Lactuca spp. in some European countries

Staff members of the Department of Botany of Palacký University in Olomouc and Gene Bank Department – Workplace Olomouc, Research Institute of Crop Production in Prague, Czech Republic, conducted an expedition in seven European countries (Austria, Czech Republic, France, Germany, Italy, the Netherlands, Switzerland) in August/September 1999 to collect wild Lactuca spp. germplasm and study its geographic distribution, ecology and biodiversity. During the mission, more than 600 locations were visited resulting in the collection of 602 seed samples (accessions) of wild Lactuca species and 13 seed samples of related genera (Chondrilla and Mycelis). Lactuca serriola f. serriola, L. serriola f. integrifolia, L. saligna and L. viminea subsp. chondrilliflora were prevalent in southern Europe (Italy, France), however, only L. serriola was common in central and western Europe (Austria, Czech Republic, Germany, Netherlands, Switzerland). The greatest diversity of Lactuca species was found in France, where also the most seed samples (165) were collected. The most characteristic habitats with a high density of Lactuca spp. populations were observed along roads and highways, grassy ditches, ruderal communities, and dust-heaps. Natural infections by powdery mildew (Erysiphe cichoracearum) and downy mildew (Bremia lactucae) on some wild Lactuca spp. were observed. Recent observations concerning the geographic distribution, population structure, habitats, and natural occurrence of diseases of Lactuca spp. are discussed. This assemblage of genetic resources of Lactuca spp. can serve as the basis of future studies of species diversification, spatial population structure, plant microevolution, domestication processes, and genetic variability of host-parasite interactions.     

Responses of native legume desert trees used for reforestation in the Sonoran Desert to plant growth-promoting microorganisms in screen house

Three slow-growing legume trees used for desert reforestation and urban gardening in the Sonoran Desert of Northwestern Mexico and the Southwestern USA were evaluated whether their growth can be promoted by inoculation with plant growth-promoting bacteria (Azospirillum brasilense and Bacillus pumilus), unidentified arbuscular mycorrhizal (AM) fungi (mainly Glomus sp.), and supplementation with common compost under regular screenhouse cultivation common to these trees in nurseries. Mesquite amargo (Prosopis articulata) and yellow palo verde (Parkinsonia microphylla) had different positive responses to several of the parameters tested while blue palo verde (Parkinsonia florida) did not respond. Survival of all tree species was over 80% and survival of mesquite was almost 100% after 10 months of cultivation. Inoculation with growth-promoting microorganisms induced significant effects on the leaf gas exchange of these trees, measured as transpiration and diffusive resistance, when these trees were cultivated without water restrictions.     

Increase in auxiliary photoprotective photosynthetic pigments in wheat seedlings induced by Azospirillum brasilense

Inoculation of wheat seedlings with the plant growth-promoting bacterium Azospirillum brasilense Cd was immobilized in alginate microbeads and, without applying any stress, significantly increased the quantity of several photosynthetic pigments, such as chlorophyll a, chlorophyll b, and the auxiliary photoprotective pigments violaxanthin, zeaxanthin, antheroxanthin, lutein, neoxanthin, and β-carotene. This resulted in greener plants with no apparent visible stress. After monitoring the quantity of photosynthetic pigments for 4 weeks, we observed that inoculated plants had higher quantities of pigments in shoot and stem. The greatest difference in the quantity of all pigments between inoculated and noninoculated plants occurred in the first week of growth. Regardless of treatment, the quantity of pigments in stems was three to four times less than the quantity of these pigments in shoots. Application of Azospirillum, either as liquid inoculant or as alginate microbeads, did not alter the positive effect of the bacteria on pigment production or the positive response of the plants towards A. brasilense Cd inoculation.