弧形齿滚扎式残膜回收机的设计及参数优化

针对现有残膜回收机具存在残膜捡拾机构复杂、可靠性差、边膜回收率及卸膜率低等问题,从工作部件受力、捡拾机构运动轨迹的角度对起膜铲、残膜捡拾机构、卸膜机构等关键部件进行了研究,设计了一种弧形齿滚扎式残膜回收机。为探明拾膜钉齿扎膜过程中钉齿、地膜和土壤的形变、受力情况,从而指导机具的设计,运用ANSYS软件对弧形齿滚扎式捡拾机构捡拾地膜过程进行非线性有限元动力学仿真分析,仿真结果显示:在捡拾地膜过程中,钉齿末端变形最大,根部应力最大;地膜最大变形发生在与钉齿末端接触位置;土壤受到钉齿扰动变形量小。运用Box-Benhnken的中心组合方法,以机具行进速度、边膜铲铲翼与铲柄夹角、钉齿入土深度为试验因素,起边膜率、残膜捡拾率、卸膜率为试验指标,进行三因素三水平二次回归试验,建立了响应面回归模型,分析了各因素对试验指标的显著性并对因素进行了综合优化。确定最优试验参数为:机具行进速度为4.0 km/h、边膜铲铲翼与铲柄夹角为90°和钉齿入土深度为55 mm。在该条件下进行田间试验,得到起边膜率为93.5%、残膜捡拾率为87.4%、卸膜率为87.1%,与优化理论值相对误差均小于4个百分点,研究结果为残膜回收机具结构设计及工作参数选择提供理论基础和技术参考。     

曲轴式棉田地表残膜回收机捡膜特性分析及工作参数优化

针对"11SM-1.7型曲轴式残膜回收机"核心捡膜部件作业参数不合理、残膜回收率较低、卸膜阻力较大等问题,该文分析了曲轴式残膜回收机结构与工作原理,建立弧形齿捡拾装置的运动模型,运用MATLAB编程分析了往复式偏心弧形齿尖运动特性和漏捡率。在棉杆收获后进行田间正交试验,分析捡拾齿角速度、捡拾齿半径、捡拾齿入土深度、残膜回收机前进速度不同参数组合对残膜回收率和卸膜率的影响并优化参数组合。结果表明捡拾齿入土深度35 mm、机具前进速度1.3 m/s、捡拾齿转动角速度60 r/min、捡拾齿半径245 mm时,残膜捡拾率最高为93.2%、卸膜率最高为94.6%、残膜漏捡率为1.61%,研究结果可为新型残膜回收机的研制提供理论基础和参考。     

随动式秸秆还田与残膜回收联合作业机设计与试验

针对新疆棉田秋后残膜捡拾率低、膜杂分离效果差等问题,设计了一种随动式秸秆还田与残膜回收联合作业机,整机主要由秸秆粉碎装置和残膜捡拾装置组成。根据新疆棉花种植模式与作业要求对整机的关键部件进行了设计,确定了粉碎刀轴、甩刀、链板总成和起膜齿等零部件的结构参数。选取甩刀转速、机器前进速度和起膜齿入土深度为影响因素,秸秆粉碎长度合格率、残膜捡拾率和膜杂分离率为响应指标,进行了三因素五水平正交旋转中心组合试验。通过Design-Expert V8.0.6.1软件进行方差分析,建立了影响因素与评价指标的数学回归模型,分析了显著因素对响应指标的影响,优化试验参数,确定最优参数组合为:甩刀转速1200 r/min,机器前进速度4.5 km/h,起膜齿入土深度100 mm。根据最优参数组合进行田间试验,结果表明:在优化参数组合下,秸秆粉碎长度合格率的均值为89.37%、残膜捡拾率和膜杂分离率的均值分别为90.31%和93.16%,表明该联合作业机满足秸秆粉碎还田与残膜回收的技术要求。该研究成果有利于提高残膜捡拾机作业效果,解决新疆棉田残膜污染问题。     

滚刀式青贮玉米起茬及残膜回收联合作业机的设计与试验

为提高新疆青贮玉米地残膜机械化回收水平,研究大根茬对残膜机械化回收的影响,解决残膜回收率低、膜茬缠绕易堵塞等机具工作难题,该文研究设计了一种滚刀式青贮玉米起茬及残膜回收联合作业机。该机关键工作部件为滚刀起茬、滚筒拾膜和脱膜辊等装置,作业时采取滚刀结构将玉米大根茬起出,解决了大根茬对残膜回收的影响,随后通过滚筒拾膜机构将地膜挑起,由脱膜辊装置将滚筒上的地膜拨送至膜箱。根茬起茬率、地膜捡拾率是评价起茬及残膜回收联合作业机性能的主要指标,该文利用Design Expert软件设计了三因素三水平二次回归正交试验,以滚刀入土深度、机具前进速度、滚刀刀轴转速为影响因素,建立了响应面三维模型。分析得到滚刀入土深度及机具前进速度对机具残膜捡拾率影响显著(P0.01),而滚刀入土深度及滚刀刀轴转速对机具根茬起茬率影响显著(P0.01),通过方程推导出机具最佳工作参数为滚刀入土深度18.50 mm、机具前进速度4.57 km/h、滚刀刀轴转速906.43 r/min。大田试验结果表明,在工作参数为前进速度4.5 km/h,滚刀入土深度20 mm,刀轴转速900 r/min作业条件下,根茬起茬率达到88.25%、残膜捡拾率达到84.62%,与理论推导值对比误差均小于4%。该机通过滚刀式起茬能够解决青贮玉米地根茬对残膜回收的影响,可为玉米等大根茬类作物残膜回收机的研究提供参考。     

随动式残膜回收机清杂系统作业参数优化

残膜是一种可循环利用材料,残膜回收过程中只有将残膜和作物秸秆、土壤等杂质分离,才能实现残膜的回收利用,减少残膜污染。针对目前回收残膜含杂率高的问题,该文设计了一种随动式残膜回收机清杂系统。为明确该系统的作业性能,提高残膜回收作业质量,进行了随动式残膜回收机清杂系统作业参数优化。通过对工作原理、工作条件及膜杂分离影响因素的分析,确定以机具前进速度、地膜输送链速度、捡拾滚筒安装位置和二级杂质输送装置转速为试验因素,以残膜捡拾率、膜杂分离率和杂质输送效率为试验指标,根据二次回归正交组合试验设计原理,进行了四因素五水平回归正交组合田间试验设计。利用Design-Expert软件对试验结果进行响应面分析,得到各因素与试验指标之间的数学模型,分析得出影响残膜捡拾率和膜杂分离率的主次因素依次是捡拾滚筒安装位置、机具前进速度、地膜输送链速度和二级杂质输送装置转速;影响杂质输送效率的主次因素依次为二级杂质输送装置转速、捡拾滚筒安装位置、地膜输送链速度和机具前进速度。根据优化目标的重要程度,对回归模型进行多目标优化,得出清杂系统最佳作业参数组合为:机具前进速度1.26 m/s、地膜输送链速度1.55 m/s、捡拾滚筒安装位置-17 mm(即以支架长孔中心与捡拾滚筒中心在竖直方向重合为原点,向机具前进方向调整17 mm)、二级杂质输送装置转速为205 r/min,在最优参数组合下残膜捡拾率为90.19%,膜杂分离率为92.21%,杂质输送效率为89.6%。并通过田间试验验证了最优组合,试验结果显示:残膜捡拾率为91.54%、膜杂分离率为90.37%、杂质输送效率为88.4%,与预测值误差分别为1.50%、2.00%和1.34%,参数优化结果可靠。研究结果可为提升随动式残膜回收机清杂系统作业质量提供参考。     

压秆式棉田地膜回收机的设计与试验

针对棉秆回收需求和现有滚筒式地膜捡拾机构可靠性差、缠膜严重、回收地膜含膜率低等问题，该研究设计了一种压秆式棉田地膜回收机，可一次性完成拾膜、脱膜以及除杂作业。结合相关作业性能要求，通过运动学和动力学分析确定了束秆盒、拾膜滚筒和脱膜机构的结构参数，并完成了关键部件的工作参数分析。为验证机具捡拾除杂作业性能，以机具前进速度、钩齿入土深度、拾膜滚筒转速为试验因素，拾膜率、含膜率为试验指标，进行了三因素三水平响应面试验，得到各因素的响应面模型，分析了各因素对作业效果的影响，并对各因素进行优化。试验结果表明，当拾膜滚筒转速为65 r/min，机具前进速度为5 km/h，钩齿入土深度为50 mm时作业效果最佳，以优化后的结果进行验证试验，结果表明，平均拾膜率为86.8 %，平均含膜率为14.9 %，研究结果可为后续留秆收膜机具的设计提供参考。     

滚筒式残膜回收机的性能试验研究

针对“11SM-1.5型滚筒式残膜回收机”核心工作参数匹配不合理,机具在作业时,常常由于使用者操作方式与水平存在差异,影响残膜回收的总体拾膜性能,进而降低残膜拾净率.滚筒式残膜回收机是一种以弧线往复式挑膜装置为核心部件的典型残膜回收机具,该研究根据滚筒式残膜回收机的结构和工作原理,分析弧线往复式挑膜装置的挑膜齿尖运动轨迹特点,确定影响机具性能的主要因子为挑膜装置转速、机具前进速度和挑膜齿入土深度,采用正交试验分析法进行田间试验,分析不同参数配比对残膜拾净率的影响,得出各因素的影响显著性及主次顺序.综合考虑挑膜装置各项指标,选择最优的水平组合,获取机具的最佳工作参数匹配,即:挑膜装置转速45 r/min、机具工作速度4km/h和挑膜齿入土深度35 mm时,残膜拾净率为88.2％,达到残膜回收机设计标准,比目前成熟的秸秆还田联合式残膜回收机的官方测定捡拾率高6.2个百分点,为机具优化设计提供数据参考,进而指导实际生产.     

残膜捡拾压缩车及其作业工艺设计与试验

为解决残膜回收时捡拾率低、机具集膜箱存储量小、机械化作业过程不连续等问题,研制了一种棉田残膜捡拾压缩车,该机主要由清杂机构、捡膜机构、脱膜输送机构、压缩机构等组成,可同时完成残膜杂质分离、残膜捡拾、脱膜输送和压缩作业.通过对样机关键作业部件的设计,确定了清杂辊、捡膜机构和脱膜输送装置的结构及工作参数,并分析了机具作业过程.样机分别在3种残膜分段回收工艺:搂集—捡压、秸秆还田—搂集—捡压、秸秆还田—捡压中进行试验,田间试验表明,机具作业速度在5~7 km/h,清杂辊转速为240 r/min,捡膜机构转速为90 r/min,脱膜辊转速为1000 r/min时,在回收工艺一搂膜距离≤40 m,回收工艺二搂膜距离≤60 m时,膜堆残膜捡拾率大于80%,清杂率大于78%;在回收工艺三中,棉杆残留根茬高度≤80 mm时,未集堆地表残膜捡拾率达到88.21%,机具缠膜率小于2%,机具可一次性捡拾压缩回收8 hm2田间残膜.     

齿链复合式残膜回收机设计与试验

针对摆杆驱动式残膜回收机拾膜机构漏捡、卸膜机构回带地膜等问题,该文设计了一种齿链复合式残膜回收机。为了提高残膜回收率,该机具采用齿链式拾膜机构和杆齿式拾膜机构配合拾膜,并采用固定刮板式卸膜机构卸膜。为确保机具的可靠性,通过对拾膜、卸膜机构工作机理和动力学分析,获得拾膜机构运动轨迹和方程,确定了实现残膜捡拾、输送和脱卸的条件。以机具行进速度、拾膜齿入土深度、齿链式拾膜机构与杆齿式拾膜机构转速比(速比)为试验因素,拾膜率和缠膜率为响应值,进行了三因素三水平响应面试验,得到各因素的响应面模型,分析了各因素对作业效果的影响,并对各因素进行优化。结果表明,试验因素对拾膜率的影响大小顺序为:速比>机具行进速度>拾膜齿入土深度;对缠膜率的影响大小顺序为:机具行进速度>拾膜齿入土深度>速比。以优化后的结果进行验证试验,结果表明,当机具行进速度0.9 m/s,拾膜齿入土深度42 mm,速比0.6时作业效果最佳,拾膜率87.2%,缠膜率1.6%,拾膜率与理论优化值相差1.3%,缠膜率与理论优化值相差6.3%,误差较小,优化模型可靠,研究结果可为齿链复合式残膜回收机最佳工作参数的选择提供参考。     

链条导轨式地膜回收机的设计与试验

针对马铃薯等作物收获后的残膜所造成的"白色污染"难题,改进现有残膜回收机存在的捡膜能力低、漏膜、膜土分离难、缠膜、卸膜不净等问题,提出了一种链条导轨式地膜回收方案。链条上相邻两排错位排列的捡膜齿与起膜铲合理配置,提高残膜捡拾率;分列结构的地膜托板具有漏土功能,较好实现膜土分离;托板弹簧可实现捡膜齿与托板之间的间隙大小随捡膜输送量的多少而自动调整,有效防止输送过程中的丢膜和堵塞现象,保证残膜输送到集膜箱上方;捡膜齿在环形导轨之间向后上方滑动到卸膜端时逐渐后缩至退出环形导轨而实现膜齿分离,卸膜叶轮与卸膜导轨协调配合完成卸膜作业,有效解决卸膜过程中不易脱膜和缠膜的难题;起膜机构、捡膜机构和卸膜机构固联在固定架上,通过角度调节杆来对固定架的角度进行调节实现松土起膜铲入土角度的要求。设计制作了捡膜、卸膜、集膜于一体的链条导轨式地膜回收机。试验结果表明:机器能够一次完成松土起膜、残膜捡拾输送、卸膜和残膜收集作业,马铃薯收获后的残膜捡拾回收率在92%以上。该设计较好解决了马铃薯地膜机械化回收难题,并为其他作物地膜回收机械设计提供参考。     

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.     

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.     

In-situ enrichment and analysis of atrazine-degrading microbial communities using atrazine-containing porous beads

We examined the community composition of microbes that colonized atrazine-containing beads buried in agricultural soils that differed in atrazine treatment history. Bacterial abundance was 5-40-fold greater in atrazine-fortified beads. In beads containing 20 mg atrazine kg⁻¹ buried in soil with a history of atrazine application (conditioned soil), the abundance of Actinobacteria increased approximately 80-fold whereas in control soil, Actinobacteria were enriched only 10-fold and the gamma-Proteobacteria and Planctomycetes increased by 60- and 25-fold, respectively. The gamma-Proteobacteria were enriched by 120- and 230-fold in beads containing 200 mg atrazine kg⁻¹ in conditioned and control soil, respectively. The results demonstrate that BioSep^® beads are a suitable matrix for recruiting a diverse subset of the bacterial community involved in atrazine degradation.