褐土中铁的氧化还原与碳素转化

采用泥浆厌氧恒温培养的方法,研究了光照对旱作褐土中氧化铁的厌氧还原过程的影响,探讨了土壤中铁氧化物的还原-氧化过程与碳素转化的关系。结果表明,旱作褐土中游离铁氧化物的55.31%可在厌氧避光条件下发生还原,厌氧光照条件下游离铁氧化物的还原率最大仅为38.90%,还原产生的Fe(Ⅱ)可能被蓝细菌中的鱼腥蓝细菌属光合过程产生的氧氧化,40 d培养后其游离铁氧化物还原率低至7.95%。厌氧避光条件下培养40 d后土壤中水溶性总碳、无机碳含量分别增加了69%和246%,厌氧光照条件下水溶性总碳和无机碳则呈现先增加后降低的趋势,40 d培养后仅为反应前的47%和70%。水溶性总碳和无机碳含量分别与Fe(T)和Fe(Ⅱ)含量呈极显著线性正相关关系。     

厌氧条件下水稻土中铁硫循环与光照的关系

采用恒温厌氧培养试验研究了黑暗、光照、黑暗转光照和光照转黑暗条件下水稻土中硫酸盐还原和铁的氧化还原.结果表明光照是调控土壤铁、硫生物化学转化的一个关键环境因素,光照对铁、硫还原的抑制作用体现在5d后.黑暗培养30 d土壤游离铁的70.07％可被还原;光照培养时35.60 μmol g-1Fe(Ⅲ)先被还原后被氧化,30 d后仍有32.70％的游离铁被还原,转黑暗后被氧化的铁可再次被还原.黑暗时土壤中99.50％的水溶性硫酸盐(WSS)在可5d内被还原,光照培养30 d有42.73％的WSS被还原.水溶性无机碳(WSIC)与体系中Fe(Ⅱ)和WSS之间存在显著相关关系.无光照转换时水溶性有机碳(WSOC)与Fe(Ⅱ)和WSS的转化速率存在显著正相关关系;黑暗条件下WSOC＞ 7.89 μmol g-1时,体系中Fe(Ⅲ)和WSS还原;光照条件下WSOC＞ 8.27 μmol g-1时体系中Fe(Ⅲ)还原,WSOC＞8.40μmol g-1时WSS还原.     

水稻土中铁氧化还原循环的光照水分效应

水稻土中铁的氧化还原循环与CO2和CH4排放关系密切。采用恒温厌氧培养试验分别在黑暗、光照条件下研究了不同水分状况对水稻土中铁氧化还原过程、水溶性碳含量及CO2和CH4排放的影响。结果表明,水分和光照是调控土壤铁氧化还原过程及其耦合的碳转化过程的关键环境因子。避光时增加含水量缩短铁还原最大速率出现的时间,促进CH4排放。光照条件下含水量小于50%时增加含水量可促进亚铁的再氧化,大于50%时则抑制了亚铁的再氧化。避光时增加含水量可增加体系的水溶性无机碳含量(WSIC),WSIC与CH4的排放存在显著正相关关系。光照可显著降低体系的WSIC,降低幅度随含水量的增加而增大。在含水量25%～200%范围内,光照可使CO2和CH4排放量分别降低95.80%和96.08%。     

旱作褐土中氧化铁的厌氧还原与光合型亚铁氧化特征

土壤中铁的氧还过程与碳氮转化及自净能力关系密切,已还原亚铁的氧化受土壤性质的影响。采用室内恒温培养试验研究了旱作褐土中铁还原氧化过程、及其与水溶性碳、NO3-、SO42-的关系。结果表明旱作褐土中铁氧化物在厌氧光照条件下可先被还原后被再次氧化,其再氧化量介于1.46~3.00 mg g-1之间,平均2.09 mg g-1;再氧化速率常数介于0.23~0.80 d-1之间,平均0.48 d-1。再氧化量与土壤无定形铁、水溶性硫酸盐含量、阳离子交换量显著负相关,与土壤总氮、总磷显著正相关;再氧化速率常数与土壤有机碳显著负相关,与黏粒含量极显著正相关。厌氧光照培养可使旱作褐土水溶性无机碳平均降低52.74%,水溶性NO3-降低92.15%,水溶性SO42-增加55.38%。研究结果为深入理解旱作土壤潜在的微生物铁循环转化方式提供理论支持。     

淹水对石灰性土壤无机磷形态转化的影响

  【目的】  磷肥施入土壤后大部分转化为与铁氧化物关系密切的Fe-P和O-P,而淹水后土壤中铁的氧化还原过程可能影响与铁氧化物结合的磷的形态及有效性的变化。研究不同施磷处理下淹水土壤Fe (II) 、无机磷组分等的变化,以期明确淹水后土壤无机磷形态及磷有效性变化及其与铁氧化还原过程的关系。  【方法】  用不施磷土壤 (P0) 和连续6年施用P 180 kg/hm2的土壤 (P180) 进行室内模拟培养试验。将土壤装于西林瓶内,加水模拟淹水条件,西林瓶密封后,分别在避光或者光照条件下,于 (30 ± 1)℃恒温培养40天。测定供试土壤以及淹水培养土壤中的速效磷、无机磷以及不同形态无机磷组分含量,测定培养过程Fe (II) 的动态变化,以探讨磷形态转化与铁氧化还原过程的关系。  【结果】  施用磷肥显著增加土壤中的速效磷含量和无机磷总量,P0处理土壤速效磷含量为 (7.65 ± 1.65) mg/kg,P180处理土壤速效磷含量高达 (33.5 ± 2.01) mg/kg。施入土壤中的磷只有很小部分以Ca₂-P存在,主要以Ca₁₀-P、Ca₈-P、Al-P和Fe-P形态存在。避光淹水培养后,土壤速效磷含量增加,P0和P180处理土壤速效磷含量的增量分别为8.44、2.95 mg/kg。淹水培养降低了土壤Ca₈-P含量,提升了Fe-P、O-P、Al-P含量。光照和避光条件下P180处理土壤中Ca₈-P含量分别降低106.8、156.2 mg/kg,Fe-P含量分别增加23.4、47.0 mg/kg,O-P含量分别增加64.1、92.9 mg/kg,Al-P含量分别增加38.8、34.7 mg/kg,避光时Ca₈-P降幅以及Fe-P和O-P的增量均大于光照条件下。避光条件下,铁还原量和还原最大速率与Ca₈-P变化量之间存在显著负相关关系,与Fe-P、O-P增量之间存在显著正相关关系。  【结论】  淹水条件下,石灰性土壤中的Fe (Ⅲ) 还原形成Fe (Ⅱ) 和Fe (Ⅲ) 混合物,增加了铁氧化物的比表面积和磷吸附点,可促进Ca₈-P向O-P、Fe-P和Al-P转化。光照降低了Fe (Ⅲ) 的还原量,可能是Ca₈-P向O-P、Fe-P和Al-P转化率低的原因之一。     

黄河中下游湿地土壤铁还原氧化过程的温度敏感性

土壤中铁的还原氧化过程因与重金属的生物有效性、有机污染的降解及含碳温室气体排放等环境问题关系密切而备受关注。温度可能通过影响铁还原菌或者Fe(II)氧化菌的活性、底物的生物可用性等而影响铁的还原过程。以黄河中下游地区新乡市原阳大米产区的湿地土壤为样品,利用厌氧泥浆控温培养试验方法研究了黄河中下游湿地中土壤铁还原氧化过程的温度敏感性。结果表明:黄河中下游湿地土壤铁的还原容量在16~31℃范围内不受温度影响,但在16~40℃之间升高温度可显著增加铁还原过程的最大速率、速率常数,亦可缩短最大速率出现的时间。铁还原的温度敏感系数介于1.18~3.05之间,且随温度上升而升高。光照可降低铁还原的温度敏感性,平均降幅39.0%。光照时土壤中Fe(II)氧化对温度不敏感。光照条件和铁氧化物的种类和数量可能是影响土壤有机碳矿化的因素之一。研究结果对于深入理解土壤铁的生物地球化学循环及其与土壤呼吸的关系具有重要意义。     

豫西旱作褐土剖面土壤的氧化铁还原与亚铁氧化特征

土壤铁氧化物的氧化还原过程不仅与重金属的生物有效性和有机污染物降解转化关系密切,也与旱地土壤肥力关系密切,因而备受关注。然剖面土壤耕层以下是否存在铁氧化物的还原、氧化过程,其特征如何尚未可知。本文采用恒温厌氧泥浆培养的方法研究旱地褐土剖面中铁的氧化还原特征。结果表明,旱地土壤剖面0~100cm中均存在铁的厌氧还原过程,还原潜势、最大速率均随剖面深度增加而显著降低;剖面0~80cm土层中均存在光合型Fe(II)氧化现象,0~40cm土层Fe(II)氧化量和氧化速率显著高于40~80cm。剖面的铁氧化还原过程不仅受有机碳含量影响,也受N、K等养分元素的影响。结果可为拓展对铁氧化还原微生物生境的认识、深入理解土壤剖面中铁氧化还原过程提供依据。     

水稻土中铁还原与无机磷有效性的关系

采集我国吉林省吉林市(1号)、四川省邛崃市(2号)、江西省安福县(3号)及广东省雷州半岛(4号)等地区的四种典型水稻土,通过模拟厌氧培养试验,研究在厌氧还原条件下不同水稻土中Fe(II)产生量、有效性磷浓度及A l-P、Fe-P和O-P等无机磷形态变化情况。结果表明,淹水后四种水稻土中Fe(II)含量均有不同程度的增加,土壤有效磷浓度也呈现相同的变化趋势。淹水60天后在1、2、3、4号土壤中,Fe(II)的净增加量分别为5.5mg g-1,4.3mg g-1,2.1mg g-1和3.7mg g-1;有效磷的增加量分别为50 mg kg-1,18.6 mg kg-1,23 mg kg-1和12.4 mg kg-1。厌氧培养30天内土壤Fe(II)产生量与有效磷浓度的变化呈极显著的相关关系。在1、2、3、4号土壤中,Fe(II)与有效磷的相关系数依次为0.9679、0.9744、0.8949和0.7501。     

控制光照条件下添加SO_4~（2-）对水稻土中Fe（Ⅲ）还原的影响

为探讨光照和硫酸盐对微生物Fe（Ⅲ）还原的影响,在光照和光暗转换条件下,采用厌氧泥浆恒温培育方法分别在四川和天津2种石灰性水稻土中添加不同浓度硫酸盐溶液（20、50、800mmol·kg-1）,培养过程中定期测定土壤泥浆的Fe（Ⅱ）、叶绿素a含量和pH值。结果表明：光照条件下,添加20mmol·kg-1和50mmol·kg-1硫酸盐能减缓光照培养中因为蓝细菌光合作用放氧引起的Fe（Ⅱ）氧化反应,Fe（Ⅱ）氧化反应启动时间与对照处理相比延迟3～7d;蓝细菌在光照培养5d后开始迅速繁殖生长,叶绿素a增长速率表现为随硫酸盐浓度增大而增加,其最终含量在四川和天津水稻土中分别为20mg·kg-1和16mg·kg-1;800mmol·kg-1硫酸盐则完全抑制了Fe（Ⅱ）的重新氧化,且在整个培养周期中没有发现光合细菌存在。pH值变化呈现先微弱下降后升高的趋势,但始终维持在弱碱性范围内。当由光照转入避光培养后,Fe（Ⅱ）累积量又重新回升,增长速率表现为对照〉20mmol·kg-1S处理〉50mmol·kg-1S处理。表明光照并非直接影响铁还原微生物,而是通过光合微生物繁殖间接影响铁还原过程。     

生物炭对淹水土壤中溶解性有机质含量及组成特征的影响

为了探究生物炭对土壤中溶解性有机质(DOM)的影响,采用向水稻土中添加生物炭的厌氧泥浆培养试验,分析添加生物炭后对不同培养阶段的厌氧泥浆中水溶性有机碳(DOC)含量、DOM组成、荧光光谱特性及土壤中Fe(III)还原特征的影响。结果表明:添加生物炭可增加水稻土中DOC含量及影响紫外光谱特征值(SUVA₂₅₄),引起DOM组分种类和相对含量变化,不同类型土壤间的变化存在差异,酸性水稻土中的作用更为明显。水稻土中Fe(III)的还原效率在添加生物炭下得到促进,同时对土壤的初始pH也产生一定影响。相关分析结果揭示添加生物炭可通过调节SUVA₂₅₄、DOM组成和体系pH,从而影响厌氧水稻土中的硝酸盐还原、铁还原及产甲烷过程。     

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.