贵州典型喀斯特流域土壤氧化铁特征分异及其影响因素

探究亚热带喀斯特流域土壤氧化铁特征及其分异,对认识这类特殊地域综合体上土壤的发生发育及类型演化等具有重要意义。以贵州省普定县后寨河流域内53个典型剖面土壤为研究对象,测定诊断表层和诊断表下层不同形态氧化铁含量并计算其风化度指标,分析土壤氧化铁特征及其分异情况,探讨成土环境和土壤属性对氧化铁特征分异的影响。结果表明：由诊断表层至诊断表下层,全铁、游离铁呈增加趋势,平均增幅分别为25.54%和39.63%,铁氧化物具有在诊断表下层富集的特征;诊断表层铁活化度高于诊断表下层,而铁游离度和铁晶胶率与之相反。大部分诊断表下层土壤游离铁在30 g·kg?1以上,铁游离度≥50%,铁活化度< 30%,土壤处于中期脱硅富铝化阶段。母岩、土地利用、流域部位、有机质、pH、黏粒阳离子交换量和质地等对不同形态土壤氧化铁含量及其风化度指标分异均有显著影响（P<0.05）;地理探测器分析表明,母岩与有机质对各氧化铁特征（除铁游离度）分异的解释力较大,二者交互作用下的q值最大（全铁41.9%、游离铁39.8%、非晶质铁40.1%、铁活化度41%、铁晶胶率52.5%）,因此母岩和有机质为亚热带喀斯特流域土壤氧化铁特征分异的主控因子。     

消落带土壤铁的形态变化及其对有效磷的影响

Fe3+还原为Fe2+的过程中会增加磷酸铁的溶解,影响磷的化学行为及有效性。本文采用室内模拟试验研究了三峡库区消落带土壤铁的形态变化及其对有效磷的影响。消落带旱地和水田土壤经淹水和落水处理后,活性铁、水溶性铁增加,其他各形态铁变化较小。旱地土壤在不同的有机质和淹水落水处理下,其活化铁、游离铁、络合铁、水溶性亚铁、和交换性亚铁均为淹水处理高于落水处理,其中活性铁在各处理间呈现出显著性差异,其他则各处理间差异均未达到显著性水平;水田下层活性铁高于上层,且落水处理间呈显著差异。氧化铁及亚铁之间总处于不断的相互转化中,活性铁、络合铁和有机质正相关。旱地土壤中的有效磷各处理间差异显著,水田有效磷淹水处理高于落水处理。     

贵州雷公山土壤发生学性状的垂直变化特征研究

为了解我国亚热带山地土壤发生学性状随海拔的垂直变化特点,选择位于亚热带常湿润气候区的贵州省雷公山作为研究对象,调查与采样分析了不同海拔高度的17个土壤剖面的理化性状及其与海拔的关系。结果表明,雷公山土壤的众多发生学性状与海拔高度存在显著的相关,随着海拔的升高,呈现土壤矿物质风化减弱而有机质和养分积累增强的变化趋势。表土层厚度、砾石、有机质、全氮和全磷含量、腐殖质的H/F比,土壤粉砂含量、粉黏比、CEC、ba值、氧化铁活化度、黏粒Sa值、黏粒矿物中蛭石和云母相对比例均随海拔的升高而增加;而土体厚度、表土胡敏酸E4/E6比值、土壤黏粒含量、游离氧化铁含量、氧化铁游离度和黏粒矿物中高岭石相对比例则随海拔升高而下降。研究土壤酸化明显,pH和盐基饱和度普遍较低,随海拔升高的变化趋势不明显。研究认为,雷公山地区土壤发生学性状主要受现代成土环境影响,随海拔变化的温度可能是控制这一地区土壤空间变异的主要因素。区内土壤主要发生学性状随海拔升高呈波动状变化,多数发生学性状具有协同变化的特征;不同地理发生学分类土壤带间发生学性状存在一定的差异。根据中国土壤系统分类,研究区土壤类型主要为淋溶土和雏形土,二者也不存在海拔上的明显分界,而呈现复合分布。     

三峡水库消落区土壤磷素释放与富营养化

三峡工程建成后,其独特的水库调度方式将在库周形成垂直距离为30m的消落区,淹没陆地面积632km2。消落区土壤受库水周期性的淹没、出露、冲刷、淤积,加上耕作和施肥影响,将形成一个脆弱生态系统。湖库消落区土壤是污染物的源或汇。消落区土壤磷素释放对水体富营养化有重要影响。研究消落区土壤磷负荷及其释放机制,可以为水库磷负荷提供基础数据,给消落区土地利用方式提供决策依据。淹水土壤磷素释放是与多个因子相关的复杂过程。本文分析了消落区土壤磷释放对富营养化的潜在影响,综述了土壤磷素释放的影响因素:磷形态、有机质、铁、铝、pH、温度和微生物。重点讨论了土壤在淹水—干燥—淹水条件下土壤性质变化和土壤磷素释放机制。一般认为,土壤淹水后,土壤氧化还原电位降低,提高了磷的有效性,促进了磷释放。干—湿交替比连续淹水释放磷是增加或减少,目前还存在争论。     

三峡水库消落区土壤磷素释放与富营养化

三峡工程建成后，其独特的水库调度方式将在库周形成垂直距离为30m的消落区，淹没陆地面积632km^2。消落区土壤受库水周期性的淹没、出露、冲刷、淤积，加上耕作和施肥影响，将形成一个脆弱生态系统。湖库消落区土壤是污染物的源或汇。消落区土壤磷素释放对水体富营养化有重要影响。研究消落区土壤磷负荷及其释放机制，可以为水库磷负荷提供基础数据．给消落区土地利用方式提供决策依据：淹水土壤磷素释放是与多个因子相关的复杂过程。本文分析了消落区土壤磷释放对富营养化的潜在影响，综述了土壤磷素释放的影响因素：磷形态、有机质、铁、铝、pH、温度和微生物。重点讨论了土壤在淹水-干燥-淹水条件下土壤性质变化和土壤磷素释放机制，一般认为，土壤淹水后，土壤氧化还原电位降低，提高了磷的有效性，促进了磷释放。干-湿交替比连续淹水释放磷是增加或减少，目前还存在争论。     

三峡库区消落带土壤对磷的吸附和淹水下磷的形态变化

三峡水库建成后在库区周边形成落差30m的消落带,消落带土壤对磷的吸附固定和磷的去向直接影响到周围的水环境。通过批处理和模拟培养法研究了三峡库区小江流域沿岸消落带的黄壤、紫色土在淹水期间铁的形态变化,磷的吸附及形态转变,结果表明：（1）供试黄壤和紫色土在淹水后,晶形铁氧化物含量明显下降,非晶形铁含量有增加趋势,土壤对磷的吸附量增加;(2)淹水期间土壤Olsen-P含量呈下降趋势,而Fe-P和Al-P含量增加,模拟显示黄壤和紫色土在淹水15d后的磷吸附容量增加70.8%和9.5%;（3）用pH 5和pH 9的0.1mol L-1CaCl2、KCl、NH4Cl溶液培养的黄壤,其Olsen-P、Fe-P、Al-P含量均明显增加,意味着消落带土壤中若施加K、Ca或尿素时,土壤有效磷可能增加,这可导致CaCl2提取磷的增多并影响库区水的含磷量,从而影响库区水质。     

黄土高原淋溶土黏粒、氧化铁与颜色的关系及发生学解释——以山西土系调查的31个黏化层为例

以黄土高原山西省14个淋溶土剖面的31个偏红的黏化层(Bt)为研究对象,分析了其全铁、游离氧化铁、无定形态氧化铁的含量与土壤颜色参数、黏粒含量之间的相关性,并建立了定量关系模型。结果表明:Bt的黏粒含量与氧化铁含量之间呈极显著正相关(P<0.01);颜色的红度与全铁、游离氧化铁和无定形氧化铁含量之间均呈极显著正相关(P<0.01),其中游离氧化铁是最直接的土壤红色"染色剂";其他色调、明度与彩度等颜色参数与土壤全铁、游离氧化铁含量之间亦呈现出显著的相关性,这也间接说明了黏粒含量与土壤颜色具有一定相关性。野外观测发现,某些黏化层结构体表面颜色较结构体内基质颜色更红,证实了在土壤结构体表面氧化铁随着黏粒在土壤空隙中的迁移淀积。黄土高原淋溶土偏红的黏化层多是来自由于土壤侵蚀而出露地表或接近地表的第三纪保德红土和第四纪红黏土,其黏粒含量、土壤颜色等指标均表明第三纪的古气候条件较第四纪更为湿热。     

水库消落带土壤颗粒组成分形及其空间分异特征

颗粒组成作为土壤的基本物理特性,对土壤结构、力学性质、肥力特征等均有明显影响。降雨径流、波浪和重力等多重营力作用下的消落带土壤侵蚀过程导致表层土壤颗粒发生了重新分布。为了研究水库消落带土壤颗粒组成的空间分异特征,以三峡水库典型消落带为研究对象,在不同海拔位置分别采集了0—10 cm和10—20 cm层的土壤用于测定颗粒组成,并利用分形理论计算出体积分形维数。结果表明:(1)三峡水库消落带土壤颗粒组成以粉粒为主,占总体积的72.6%～86.5%,且随着海拔的增加而升高; 从不同土层深度来看,0—10 cm层黏粒含量明显低于10—20 cm层。(2)消落带不同海拔位置的土壤体积分形维数具有明显异质性,且与海拔呈正相关(R²=0.74),而在不同土层之间具有弱变异性(C_v<2)。(3)体积分形维数与黏粒、粉粒含量均呈显著正相关(p<0.01),与砂粒含量呈显著负相关(p<0.01),且与黏粒的线性相关性最强。综上,消落带土壤颗粒组成在不同海拔存在较大差异(p<0.01),但在土层深度上无显著差异(p>0.01); 150～160 m海拔区间和0—10 cm层土壤具有明显的粗粒化现象。     

三峡库区消落带土壤化学性质变化

为研究三峡库区消落带水淹和未水淹区域土壤化学性质的差异,以及探讨水位涨落对消落带土壤化学性质影响,试验分别于2008年、2009年、2013年的9月,对消落带水淹和未水淹区域土壤(0-5,5-10,10-15cm)的养分含量和pH值进行测定。结果表明:(1)2008年、2009年、2013年消落带未水淹区域各层土壤的速效氮、速效磷、速效钾和有机质含量均大于水淹区域,2013年其含量差异的幅度较大,依次为6.06%~17.01%,40.55%~50.23%,26.90%~46.89%和14.64%~45.51%;较未水淹区域,水淹区域各层土壤的pH值呈缓慢上升趋势。(2)受不同水位涨落周年的影响,各层土壤速效氮、速效磷、速效钾、全氮、全磷、有机质含量均表现为:经历0次水位涨落区域1次水位涨落区域5次水位涨落区域,而土壤pH值变化趋势与其相反;受水位涨落影响后,土壤的全钾含量表现出一定程度的积累。研究表明,水位涨落可导致消落带土壤速效氮、速效磷、速效钾、全氮、全磷、有机质含量的大量流失和pH的显著增高。     

长期紫云英还田与化肥配施下水稻土团聚体中铁氧化物的演变规律

铁氧化物是土壤团聚体重要的胶结物质,其主要存在于土壤黏粒中。为探索紫云英还田并配施化肥下土壤团聚体中铁氧化物的变化规律及其在不同粒级黏粒组分中的富集特点,以湖南省南县长期紫云英还田的水稻土为研究对象,选择单施紫云英（MV）、单施化肥（F100）、紫云英配施全量化肥（MV+F100）和紫云英配施80%化肥（MV+F80）4个处理,通过湿筛和离心分离土壤团聚体（>250、53~250 和2~53 μm）和黏粒（<2 μm）,测定不同处理土壤团聚体及其黏粒中铁氧化物的含量,并分析它们与团聚体稳定性的关系。结果表明：（1）与MV和F100相比,紫云英与全量化肥配施增加了>250 μm粒级团聚体的含量,降低了53~250 μm粒级团聚体含量,团聚体平均重量直径（MWD）和几何平均直径（GMD）分别提高了8.2%~20.5%和4.1%~8.5%。（2）与MV相比,紫云英与化肥配施显著提高了各粒级团聚体、2~53 μm团聚体黏粒和自由态黏粒非晶质铁的含量（12.7%~55.6%,52.4%~54.9%和45.9%~48.6%）,降低了>250和53~250 μm团聚体非晶质铁的富集率（32.8%~36.8%和17.2%~28.4%）。而与F100相比,2~53 μm团聚体和团聚体黏粒非晶质铁的含量以及富集率均显著降低（3.5%~21.3%、29.2%~30.4%和10.9%~26.9%）。（3）>250 μm团聚体含量与团聚体黏粒的非晶质铁含量、铁的活化度呈极显著正相关,与团聚体黏粒的游离铁含量、非晶质铁的富集率呈显著正相关。团聚体的MWD和GMD与>250μm团聚体含量呈极显著正相关,而与<2 μm团聚体含量呈极显著负相关。>250、2~53 μm团聚体黏粒和自由态黏粒的游离铁是团聚体MWD和GMD最重要的影响因子。紫云英与化肥配施,能够提高团聚体黏粒铁氧化物的含量,促进>250 μm团聚体的形成,从而增强团聚体的稳定性。     

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.