宁夏压砂地砾石元素淋溶影响因素研究

研究压砂地元素淋溶对宁夏回族自治区压砂地土壤环境维护以及健康发展至关重要。为研究宁夏中卫地区压砂地在不同补水量、盐分处理和温度下的元素淋溶规律,采用电感耦合等离子体发射光谱仪及电感耦合等离子体质谱仪,测定了宁夏回族自治区中卫市环香山地区2种压砂砾石的元素含量,并根据当地多年降雨灌溉资料以及气象温度水质等数据,通过室内试验分析不同补水量、盐分及温度对压砂砾石元素淋溶的影响,同时运用多元回归法分析各影响因子对元素淋溶量变化的贡献率。结果表明:1)水分的参与对压砂砾石元素淋溶有促进作用。随着补水量的增加,绿色板岩各元素淋溶量呈波动增加趋势,红色砂岩Na、Si、Cl元素淋溶量随补水量的增加逐渐增大,Mn、Ba元素淋溶量在补水量为397 mL时出现峰值,随后淋溶量减小,通过拟合方程发现压砂砾石元素淋溶量与补水量呈对数函数关系,且拟合度较高(R20.99)。2)随着矿化度的增加,元素淋溶量呈现先增大后减小的趋势,且在矿化度为3 g/L左右时的NaCl溶液处理下元素淋溶量达到最大值,然后逐渐减小。且通过拟合方程发现,压砂砾石元素淋溶量与盐分呈2次多项式关系。3)影响宁夏中卫地区元素淋溶量影响因子中,补水量对其元素淋溶量的影响最大,温度次之,盐分最小。研究可为压砂地土壤健康发展与可持续利用提供依据。     

冻融过程对高寒区渠道基土力学特性的影响

高寒区复杂的环境场是渠道基土劣化的重要原因,并由此诱发渠系工程的灾变。开展了湿干循环及湿干冻融耦合循环下膨胀性渠道基土的三轴固结排水剪切试验,描述了渠道基土的应力-应变关系、弹性模量、破坏强度和抗剪强度指标的变化特征,探讨了湿干冻融耦合循环中的冻融过程对渠道基土力学特性的影响。结果表明:湿干循环和湿干冻融耦合循环次数的增长使得渠道基土的应力-应变关系由一般硬化型往弱硬化型(弱软化型)发展,湿干冻融耦合循环过程中的冻融过程加剧了这一转变的发展。同时,湿干冻融耦合循环中的冻融过程易造成渠道基土的弹性模量、破坏强度、黏聚力在耦合循环初期大幅下降,而这一影响随着湿干冻融耦合循环次数的增长逐渐弱化。7次湿干循环后,试样的弹性模量、破坏强度、黏聚力和内摩擦角分别衰减了约13.1%～33.3%、21.2%～27.6%、39.1%和15.6%,低于7次湿干冻融耦合循环后22.3%～34.5%、22.2%～30.9%、44.0%、11.7%的衰减幅度,表明湿干冻融耦合循环中的冻融过程加剧了渠道基土力学性能的衰减,但对试样内摩擦角影响较小。另外,湿干冻融耦合循环中的冻融过程造成低围压下的渠道基土损伤较为明显,以传统弹性模量形式表征渠道基土的损伤度在在一定程度上低估了湿干循环及湿干冻融耦合循环过程对于渠道土体的损伤程度,在高寒区膨胀土渠系工程相关计算与分析中,还应充分考虑渠道土体的破坏强度衰减。研究成果可为北疆供水工程的建设与维护提供一定科学依据。     

煤矸石改良膨胀土特性及其最佳掺量条件下的孔隙结构表征

为减小膨胀土对土木工程设施及农业生态环境的危害,进行掺加煤矸石粉改良膨胀土的试验研究。该文以内蒙古兴和县高庙子乡的膨胀土和煤矸石为研究对象,通过无荷膨胀试验、有荷膨胀试验和收缩试验确定煤矸石粉的最佳掺量,对最佳煤矸石粉掺量的膨胀土进行干湿循环试验,利用直剪试验测定每次干湿循环后试件的抗剪强度指标;通过压汞试验测得孔隙特征值,从微观角度揭示强度变化机理。试验结果表明:煤矸石粉掺量为6%时抑制膨胀土的胀缩性效果最佳;干湿循环作用使素膨胀土黏聚力和内摩擦角均有所衰减,掺入煤矸石粉后强度衰减得到控制;随干湿循环次数的增加孔径逐渐向大孔范围聚集,团粒结构增多,使素膨胀土的抗剪强度指标降低;经过5次干湿循环,掺加煤矸石粉土样的大孔孔隙密度比素膨胀土降低约35%,煤矸石有效阻止膨胀土的强度劣化。     

冻融作用对棕壤团聚体及其重金属镉赋存形态的影响

以重金属Cd为单一污染源的棕壤作为供试土壤,设定-10,-20,-30℃三个温度作为冻结温度,10℃作为融化温度进行土壤冻融循环试验。通过测定冻融作用后土壤团聚体粒径组成、土壤质量平均直径、土壤团聚体粒径中Cd的质量负载率以及赋存形态,研究冻融作用对棕壤团聚体稳定性及Cd在不同团聚体粒径中分布与赋存形态的影响。结果表明:(1)土壤经过冻融作用后,2mm的团聚体比例显著增加(P0.05),增加范围为38.4%~54.6%,土壤质量平均直径显著增加(P0.05);(2)经过冻融作用后,重金属Cd主要富集在2mm的团聚体粒径中,所占比例为51.2%~57.2%;(3)冻融作用使土壤及不同粒径团聚体中交换态Cd和有机结合态Cd含量显著降低(P0.05),铁锰氧化物结合态Cd和残渣态Cd含量显著增加(P0.05)。     

胶泥心墙砂砾石土坝在中卫山区的推广

受地形条件的限制,中卫山区的群众在实施建坝蓄水、防洪排涝、淤地造田这项治理水土流失、改善农业生产条件的有效措施时难度大、进展慢。当地群众因地制宜,结合实际,探索发展先进的建坝经验,提出在山区修建胶泥心墙砂砾石土坝这一构想。这种坝体主要是在坝体中央部分用胶泥作为防渗体,上下游采用沟道均质砂砾石料作为筑坝材料,经碾压施工而成型,可以最大限度地利用当地丰富的红黏土及砂砾石资源,因此具有投资小、取材方便、便于施工等特点,可进一步推广应用。     

干湿循环下云南非饱和红土土—水特性研究

以云南红土为研究对象,以脱湿、吸湿引起的干湿循环作为控制条件,考虑初始干密度(1.20,1.25,1.30g/cm3)、初始含水率(30.0%,33.0%,36.0%)、预固结压力(0,50,100,200kPa)、过筛粒径(0.5,1.0,2.0mm)等影响因素,通过压力板仪法,研究干湿循环下云南非饱和红土的土—水作用特性。结果表明:干湿循环过程中,不同影响因素下红土的基质吸力随含水率的增大而减小,其土—水特征曲线呈直线型或"倒J"形,其脱湿变化过程可以分为快速脱湿、缓慢脱湿、稳定脱湿3个阶段,对应的吸湿变化过程也可以分为快速吸湿、缓慢吸湿、稳定吸湿3个阶段。相同基质吸力下,随初始干密度、初始含水率、预固结压力的增大,红土的含水率增大;随粒径的增大,红土的含水率减小。初始干密度、预固结压力、粒径(0.5mm除外)影响下的红土的土—水特征曲线可采用幂函数关系进行拟合,不同初始含水率、粒径0.5mm时的土—水特征曲线可采用线性函数关系进行拟合。红土脱湿过程的含水率高于吸湿过程的含水率,脱湿—吸湿过程中的土—水特征曲线存在滞后现象,其实质在于干湿循环作用下红土具有孔隙效应、瓶颈效应、角度效应的综合结果。     

冻融对东北黑土风干团聚体与水稳性团聚体组成及稳定性的影响

为保护我国黑土资源,实现可持续利用,研究冻融作用对黑土团聚体稳定性的影响及冻-融作用机制具有重要的理论价值和实际意义。本文以黑龙江省克山、嫩江农田表层(0～20 cm)黑土为材料,通过室内冻融交替模拟试验,分别测定初始含水率和循环次数对黑土风干团聚体与水稳性团聚体组成及稳定性的影响。研究结果表明:风干团聚体与水稳性团聚体中较大粒径组( 2 mm)团聚体随着冻融循环次数的增加呈逐渐减小的趋势,而较小颗粒粒径组(0.5 mm)团聚体则呈增加趋势。冻融过程中土壤初始含水量显著影响风干团聚体和水稳性团聚体的稳定性。随着初始含水量的增加,冻融显著降低黑土风干团聚体的平均重量直径(MWD)。土壤含水率为50%田间持水量时,冻融明显增加黑土水稳性团聚体的MWD。随着冻融循环次数的增加,风干团聚体小团聚体含量(WSA 0.25)、团聚体破坏率(PAD0.25、PAD1.0)和MWD均明显降低。本研究结果显示:冻融过程中适宜的土壤含水量有助于增加黑土水稳性团聚体的稳定性。这些发现有助于深入了解冻融过程对黑土侵蚀过程的影响与作用机制。     

干湿循环对土壤斥水性的影响

处于地表的各类土壤总是处于不断的干湿循环过程,土壤性质也会因此而发生改变。本文通过试验对干湿循环过程中斥水性土壤的"斥水–亲水"特性展开研究,试验结果表明:干湿循环对斥水性土壤的接触角及斥水性有重要影响。在干湿循环过程中,增湿时的初始状态不同则其初始接触角会发生变化,土壤斥水性对初始状态的敏感性随着黏粒含量的增加而增大。干湿循环开始时,土壤越干则初始接触角越大。当黏土和黏壤土试样含水量减小时,增湿或脱湿过程中滴水穿透时间(waterdroppenetrationtime,WDPT)先增加后减小,在某一时刻达到峰值,试样含水量相同时,脱湿过程所对应的WDPT要明显小于增湿过程,两种类型的土样在干湿循环中均没有临界含水量。随着含水量的降低,壤质砂土的WDPT是不断增加的,且干湿循环过程中斥水性砂土并没有出现峰值,存在明显的临界含水量。     

滤纸法测定干湿循环下膨胀土基质吸力变化规律

为了获得干湿循环作用下膨胀土基质吸力的变化规律,首先采用人工模拟降雨和蒸发的方法开展了膨胀土室内干湿循环试验,然后利用滤纸法进行了不同含水率下试样的基质吸力测定试验,获得了干湿循环条件下膨胀土的土水特征曲线,求出了相应的进气值与残余值,结合Fredlund土水特征曲线模型对经历不同干湿循环次数下的土壤土水特征曲线进行了拟合,最终建立了考虑干湿循环效应的膨胀土土水特征曲线模型。结果表明:1)随着干湿循环次数的增加,土壤的进气值呈下降趋势,从循环1次时的134.5 k Pa降至循环4次时的58.5 k Pa,降幅达56.5%。从循环1次至2次的进气值下降较大,往后降幅明显减小,趋于基本稳定,这表明对土壤进气值的影响以初次干湿循环为主。2)残余值亦呈下降趋势,从循环1次时的1 040.5降至循环4次时的528.5 k Pa,降幅达49.2%。每经历一次干湿循环,残余值降幅均较大,尚未趋于稳定,这表明干湿循环效应对土壤残余值的影响比对土壤进气值的影响要大。3)新建土水特征曲线模型中的拟合参数与干湿循环次数成较好线性关系,表明随着干湿循环次数的增加,土壤进气值逐渐减小,水分变化速率有所降低,而残余含水率逐渐增加。该成果可为深入研究土壤基质吸力及其工程应用提供参考。     

W-OH砒砂岩固结体干湿循环特性及其细观机理

[目的]对W-OH砒砂岩固结体干湿循环特性及其细观机理进行研究,为实现W-OH固结改良砒砂岩及其耐久性研究提供科学依据。[方法]采用W-OH(亲水性聚氨酯材料)对砒砂岩进行固结处理,基于无侧限抗压试验、三轴抗压试验,研究其在干湿循环条件下的力学性能,并结合SEM,EDS和称重法对其干湿循环后样品微观结构、元素和质量损失进行分析,以获得其破坏机理。[结果]W-OH砒砂岩固结体的无侧限抗压强度、弹性模量和黏聚力在1～3次干湿循环后升高;在3～9次干湿循环后,固结体的力学强度降低;9次之后,剩下高黏结力的W-OH胶结体包裹于砒砂岩颗粒表面,力学强度趋于稳定。内摩擦角在1～9次干湿循环后上下波动,9次干湿循环后趋于稳定。采用碳元素分析和质量损失分析相结合的方法对土样中W-OH流失特性进行评价,发现土样在1～9次干湿循环中W-OH胶结体逐渐降低,并在9次干湿循环后达到稳定,这与上述宏观力学变化的规律相似,验证了破坏机理,为判断其长期特性提供理论依据。[结论]研究表明可将9次干湿循环后达到稳定的W-OH砒砂岩固结体的力学性质作为土体的长期力学特性。     

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.