不同有机物料与化肥配施对土壤真菌群落结构和生态功能的影响

为减少土壤土传病害,保障农田土壤健康,指导有机物料合理利用,在有机物料用量和化肥用量一致的基础上,设置单施化肥（CK）、羊粪+化肥（A）、木薯渣+化肥（P）、木本泥炭+化肥（M）、味精废浆料+化肥（I）5个处理,以玉米为供试作物进行了有机物料与化肥配施试验,观察了不同处理下土壤真菌群落结构的变化。结果表明：施用有机物料降低了土壤真菌群落多样性,但提高了真菌群落丰富度,其中味精废浆料配施化肥处理的真菌群落丰富度最高,各处理土壤中优势真菌门类均为子囊菌门、担子菌门和被孢菌门。施用有机物料后,木薯渣、木本泥炭和味精废浆料处理的子囊菌门的相对丰度均增加,担子菌门的相对丰度均降低;而羊粪处理表现出相反趋势,子囊菌门的相对丰度降低,担子菌门的相对丰度增加。冗余分析结果表明,土壤pH是影响真菌群落的主要环境因子,其次为有机质、电导率和速效钾,而碱解氮和有效磷的影响较小。另外,有机物料与化肥配施可以提高腐生营养型和共生营养型真菌的比例,减少病原菌的数量,其中以木本泥炭与化肥配施的效果更显著,这有利于维持土壤生态系统的稳定,为作物生产提供健康的土壤条件。     

硒砂瓜连作对土壤真菌群落结构的影响

硒砂瓜是宁夏地区重要的经济作物,其连作严重影响硒砂瓜产量和品质。目前硒砂瓜连作对土壤真菌群落结构的影响尚不清楚。本研究采用Illumina MiSeq高通量测序技术,探讨硒砂瓜连作对土壤真菌群落结构的影响。研究发现,硒砂瓜连作土壤中真菌群落多样性指数和丰富度指数随连作年限的增加先上升后下降。供试土壤样本中共检测到真菌8门、25纲、244属,其中子囊菌门（Ascomycota）、接合菌门（Zygomycota）是优势菌门,占90%以上。与对照相比,连作30年土壤中子囊菌门丰度下降32.51%,接合菌门丰度上升29.89%。供试土壤中真菌主要的优势属为被孢霉属（Mortierella）、绿僵菌属（Metarhiziun）、假霉样真菌属（Pseudallescheria）、镰刀菌属（Fusarium）和青霉属（Penicillium）。与对照相比,连作5年土壤中假霉样真菌属丰度增加45.81%,连作10年土壤中镰刀菌属丰度增加26.74%,连作15年土壤中绿僵菌属下降26.83%,连作20年土壤中青霉属增加29.68%,连作25年土壤中绿僵菌属减少18.30%,连作30年土壤中被孢霉属丰度上升29.89%。土壤理化性质与硒砂瓜连作年限间无显著相关性,而与土壤真菌群落结构存在显著的相关性。土壤全磷、碱解氮、有效磷含量是影响土壤真菌群落最主要的因素。研究结果表明,导致硒砂瓜连作障碍的主要原因不是土壤理化性质变化,而是土壤真菌群落结构的改变。研究结果可为硒砂瓜土传病害的生物防治提供参考依据。     

生物炭连续还田对苏打盐碱水稻土养分及真菌群落结构的影响

以苏打盐碱土为供试土壤,设置0,3.0,7.5,12.0,16.5 t/hm² 5个梯度生物炭还田量,通过盆栽试验研究不同量生物炭连续多年还田对苏打盐碱水稻土养分及真菌群落结构的影响。结果表明：（1）不同量生物炭还田后,提高了土壤pH、有机质、速效钾、有效磷和全磷含量,土壤全氮和全钾含量呈现先增加后降低的趋势,对盐碱土起到了改良的效果。（2） Illumina MiSeq测序结果表明,还田量为7.5 t/hm²时,Aphelidiomycota、担子菌门以及链格孢属的相对丰度显著高于对照;还田量为12.0 t/hm²时,子囊菌门、毛霉亚门以及被孢霉属的相对丰度显著高于对照,相关分析显示土壤理化特性与菌门和菌属的相对丰度关系密切,表明生物炭通过调节土壤的理化特性,从而影响真菌的相对丰度。（3）生物炭还田处理对土壤真菌α多样性影响不显著,对土壤真菌群落结构产生一定的影响,其中高生物炭还田量处理对其影响更为显著。进一步利用冗余分析（RDA）研究影响群落结构变化的环境因子表明,全钾含量对群落结构影响最大。     

长期有机无机肥配施对东北黑土真菌群落结构的影响

【目的】分析长期有机无机肥配施对土壤真菌丰度、多样性及其群落特征的影响,探讨东北黑土真菌群落变化与施肥的相关性,为进一步调节土壤微生物结构,改善其生态功能提供参考依据。【方法】依托黑龙江省农业科学院36年长期定位试验站,选取4个不同施肥处理:不施肥处理（CK）、有机肥处理（M）、氮磷钾无机肥处理（NPK）和有机肥配施无机肥处理（MNPK）的耕作层土壤为研究对象,以真菌ITS基因为分子标靶借助qPCR技术和Illumina Miseq高通量测序平台,研究不同施肥处理对黑土中真菌群落丰度、多样性和组成的影响,并与土壤化学性质进行偶联分析,揭示群落与施肥的相关性。【结果】长期施用无机肥显著降低土壤pH,而有机无机配施可以有效缓解土壤酸化。NPK处理的ITS基因丰度显著高于MNPK;MNPK处理的细菌/真菌比值（26.91104）显著大于NPK,各处理比值由高到低为MNPK M CK NPK。细菌/真菌比值与土壤pH正相关;MNPK处理的真菌多样性指数值略大于NPK。Ascomycota和Zygomycota为土壤中主要真菌门,不同施肥处理之间真菌组成的相对丰度存在显著差异,对照处理Ascomycota的相对丰度为45.35%,MNPK和NPK处理分别为50.93%和56.16%。有机肥有利于降低病原真菌相对丰度,具有高度侵染性的Cochliobolus在MNPK（0.41%）和M（0.39%）中的相对丰度显著小于CK（3.25%）和NPK（2.08%）。CCA分析表明,土壤理化性质共解释土壤真菌群落结构变化的73.3%,有效磷（贡献量为32.4%,P=0.002）、铵态氮（贡献量为14.8%,P=0.01）和硝态氮（贡献量为16.2%,P=0.048）是3个重要的影响因子。【结论】不同施肥条件下土壤真菌丰度、多样性,以及菌群组成特征不同。与无机肥相比,有机肥无机肥配施能够有效改善真菌群落结构,降低真菌的丰度,增加真菌多样性,并提高土壤pH,减缓土壤酸化。土壤有效磷、铵态氮和硝态氮含量是影响黑土土壤真菌群落结构变化重要因素。     

不同有机物料强还原处理对植烟土壤微生物群落的影响

【目的】本文探究了在厌氧强还原条件下,豆渣、甘蔗渣单施及其等比例混合物施用后,不同处理间土壤理化性质与微生物群落变化的相关关系。【方法】应用Tax4Fun及FUNGuild分别对细菌和真菌群落进行功能预测,采用Vegan和pheatmap等R语言软件包完成统计分析和绘图,利用生物信息学方法分析不同样本中微生物群落结构和多样性变化,确定微生物与RSD技术之间的相关性。【结果】结单一用蔗渣和豆渣的RSD处理都提高了真菌群落丰富度。在门的水平上,放线菌（Actinobacteria）、厚壁菌门（Firmicutes）、酸菌门（Acidobacteria）、子囊菌门（Ascomycota）和担子菌门（Basidiomycota）的相对丰度发生变化,揭示了处理间群落结构存在显著差异。此外,RSD还有效降低了镰刀菌属（Fusarium）、链格孢属（Alternaria）等土传病原菌的丰度。斯皮尔曼相关性分析说明全氮、全磷、碱解氮、速效钾、pH和有机质是造成群落结构差异的主要影响因子。功能注释结果显示RSD技术能提高土壤中细菌群落萜类和多酮类化合物代谢的功能活性及腐生真菌的丰度。【结论】单独施用豆渣...     

稻田土壤真菌群落结构与功能对化肥 减量配施紫云英还田的响应

为探明长期化肥减量与紫云英还田配施对稻田土壤真菌群落组成结构及功能特性的影响,以豫南稻区紫云英- 水稻田间定位试验为研究对象,选取了空白对照(CK)、单施化肥(F100)、80% 化肥和22.5 t/hm² 紫云英还田量配施(MV1F80)、80% 化肥和45 t/hm² 紫云英还田量配施(MV2F80)、60% 化肥和22.5 t/hm² 紫云英还田量配施(MV1F60)、60% 化肥和45 t/hm² 紫云英还田量配施(MV2F60)6 个处理。通过采用高通量测序方法比较不同施肥处理对土壤真菌群落多样性、组成和结构特性的影响;采用FUNGuild 功能预测的方法分析不同施肥处理间功能类群的丰度差异。结果表明,化肥减量与紫云英还田配施较CK 处理显著提高了Shannon 指数和Shannoneven指数,且Shannon 指数和Shannoneven 指数均与全氮呈显著正相关。门分类水平上,化肥减量与紫云英还田配施较CK 显著降低了子囊菌门(Ascomycota)相对丰度,增加了担子菌门(Basidiomycota)相对丰度;属分类水平上,化肥减量与紫云英还田配施处理的翅孢壳属(Emericellopsis)和无色穗孢属(Achroiostachys)相对丰度显著低于CK,镰刀菌属(Fusarium)相对丰度显著低于F100 处理。此外,冗余分析(RDA)发现,影响土壤真菌群落结构和组成的主要环境因子为土壤容重、有机碳、全氮、全磷和全钾。从真菌功能预测分析来看,化肥减量与紫云英还田配施较F100 处理显著降低了动物病原菌- 内生菌- 地衣寄生菌- 植物病原菌- 土壤腐生菌- 木质腐生真菌功能类群丰度。由此可见,化肥减量与紫云英还田配施通过改善土壤肥力属性,改变了稻田土壤真菌群落组成、结构、多样性及功能特性,在一定程度上降低了土壤潜在致病菌丰度,有助于豫南稻区土壤健康和可持续发展。     

不同土壤改良剂对酸化土壤微生物群落结构的影响

酸化土壤中微生物多样性降低是土壤养分减少、土传病害高发、作物产量和品质降低的重要原因。施用碱性土壤改良剂是改善酸化土壤理化特性、减少土传病害发生、提高作物产量的有效手段。为了明确不同碱性土壤改良剂对土壤微生物群落结构及多样性的影响,通过盆栽试验比较施用生石灰（S1）及氨基酸生态肥（S2）和黄腐酸水溶肥（S3）对酸化土壤微生物群落结构的改良效果。结果表明,施用3种土壤改良剂后土壤细菌丰富度和多样性均降低,而真菌群落物种丰富度没有显著变化。改良后土壤的主导菌门与改良前相同,而主导菌属存在较大差异。Iamia、Peroneutypa为S1处理特有主导菌属,节核细菌属（Arthrobacter）、德巴利酵母属（Debaryomyces）、Paraphaeosphaeria为S2处理特有主导菌属。根霉菌属（Rhizopus）、裂褶菌属（Schizophyllum）为S3处理特有主导菌属。各改良土壤中,S1处理对细菌的筛选作用最强,S2处理对真菌群落的影响最大,而S3处理相对丰度增加的菌属最多。3种土壤改良剂均能够抑制有害土壤微生物的生长和定殖,但抑制机制可能存在差异。综上所述,3种土壤改良剂均能...     

不同有机肥对植烟红壤真菌群落结构及功能的影响

  【目的】  研究植烟土壤中与养分循环相关的真菌群落结构和功能类群对不同有机肥施用的响应,为指导烤烟合理施肥、减缓连作障碍和土传病害提供科学依据。  【方法】  选择烤烟品种‘云烟87’为供试作物,以当地农业废弃物为原料堆制有机肥,设置6个处理:单施化肥 (CK)、鸡粪有机肥 (T1)、芝麻饼肥 (T2)、菜籽饼肥 (T3)、牛粪 (T4)、稻草 (T5),所有处理氮磷钾总量和比例用化肥调整为一致。随机区组田间试验,每个处理3次重复。采用高通量测序结合FUNGuild分析方法,测定分析烟草不同生长阶段各处理的土壤真菌群落结构、多样性、组成及群落功能。  【结果】  结合UPGMA聚类分析和主坐标分析 (PCoA) 发现,相比T2和T3处理,T5、T4和T1处理在烟草旺长期对土壤真菌群落结构的影响较大;成熟期T2与T3处理对土壤真菌群落结构的影响逐渐增大,且超过T4和T5处理。相比CK,T2、T3及T5处理中腐生营养型真菌比例分别显著提高了262.0%、64.0%和198.0%。其中T5处理土壤中腐生营养型真菌所占比例超过病理营养型真菌,成为其主要优势菌群;T1、T2及T4处理的土壤共生营养型真菌分别显著增加了80.0%、320.0%和85.71%。T1、T2和T4处理分别提高了土壤中植物病原菌Monographella (408.98%)、Microidium (93.63%)、Gibberella (559.22%) 的相对丰度。  【结论】  相比单施化肥处理,有机肥会导致土壤真菌群落结构发生变化,且不同有机肥的影响程度和时期均不同,其主要是增加了土壤腐生营养型真菌的比例,更有利于土壤生态系统的稳定和健康。5种供试有机肥处理中,稻草配施化肥最有利于降低长期烟稻轮作的土传病害风险,提高土壤肥力,鸡粪和菜籽饼次之;芝麻饼和牛粪在提高腐生营养型和共生营养型真菌比例的同时,也会增加烟稻轮作体系中水稻赤霉病及烟草根腐病风险。     

不同程度重金属污染对稻田土壤真菌群落结构的影响

为了研究土壤真菌群落结构在不同程度重金属污染中的变化,本文用Illumina Hi Seq高通量测序技术分析了苏南地区某金属冶炼厂和加工产业区的重金属污染水稻土的真菌群落结构,发现不同程度重金属污染对水稻季土壤真菌丰度和群落结构均有显著影响。经过真菌主成分分析发现,PC1影响因素对样品处理差异的贡献率是35.96%,PC2影响因素对样品处理差异的贡献率是21.48%;通过真菌冗余度分析发现,重金属Pb和Cu污染对土壤真菌群落结构的影响显著;通过对真菌属水平的相对丰度分析表明,重金属污染会显著降低敏感真菌的丰度,如被孢霉属相对丰度最高降低了87.50%、木霉属最高降低了99.46%、离壳菌属和菇属最高降低了100.00%,同时耐性真菌的相对丰度会提高,如类球囊霉属的相对丰度最高增加了98倍、四枝孢霉属最高增加了56倍、根囊壶菌属最高增加了2.62倍。综上所述,不同程度重金属污染对稻田土壤真菌群落结构有显著影响,且随着污染程度的增加,抗逆真菌相对数量和种类显著增加,敏感真菌的相对数量急剧减少,真菌群落结构随着重金属污染程度增加进一步分化。     

长期连作及强还原土壤灭菌处理对烤烟根际土壤真菌群落的影响

烤烟是重要的经济作物,连作障碍已成为限制其产业发展的主要原因之一,研究长期连作及强还原土壤灭菌处理(RSD)对烤烟根际土壤真菌群落的影响,为缓解烤烟连作障碍提供理论基础。选取烤烟连作 3、5和 7年根际土壤分析理化性质和真菌群落演替规律。选取烤烟连作 3年样地实施强还原土壤灭菌处理(RSD),与未处理(3年)对比,以此评价 RSD修复效果。结果表明:(1)连作处理显著降低烤烟根际土壤 pH及总碳和总氮的含量,RSD处理较未处理(3年)显著提升土壤总碳和总氮的含量。(2)测序结果表明,连作处理显著促进真菌群落 Alpha多样性,主坐标轴分析和聚类分析表明连作处理显著改变真菌群落结构,真菌群落相对丰度的变化及 FUNGuild数据库比对结果表明,连作处理促使病原菌丰度增加。(3)与未处理(3年)相比,RSD处理显著降低真菌群落多样性和病原菌丰度。(4)相关性热图分析表明病原菌相对丰度与 pH、总碳和总氮含量呈显著负相关。因此,长期连作烤烟导致根际土壤质量退化,造成病原菌增多;RSD处理对连作土壤的质量和真菌群落具有良好的修复效果。     

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.     

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.