氮添加对滇中高原森林凋落物养分残留及其持水性的影响

为揭示森林生态系统养分循环和水分循环对氮沉降的响应机制,以滇中高原华山松(Pinus armandii)和云南松(Pinus yunnanensis)为研究对象,开展野外氮添加下凋落叶、枝原位分解研究试验,设置对照、低氮、中氮和高氮共4个处理,利用尼龙网袋法和室内浸泡法,探究凋落叶、枝养分元素残留率、持水量和持水率及吸水速率对氮添加的响应。结果表明:(1)随着分解时间的持续,2种林分凋落叶、枝碳(C)、氮(N)、磷(P)分别呈释放、富集—释放、富集过程,凋落叶C、N、P残留率显著小于凋落枝(p＜0.05);(2)凋落叶最大持水量和最大吸水速率显著大于凋落枝(p＜0.05),分解24个月时,与CK相比,LN处理下2种林分凋落叶、枝C,华山松凋落叶N残留率降低1.98%~7.27%,10.79%,HN处理下2种林分凋落叶、枝C,华山松凋落叶、枝和云南松凋落枝N,华山松凋落枝P残留率则增加4.26%~9.08%,11.94%~44.51%,42.42%;(3)分解24个月时,与CK相比,LN、MN和HN处理华山松凋落叶、枝和云南松凋落叶最大持水量和最大吸水速率分别降低11.44%~25.24%,5.81%~32.23%,云南松凋落枝则增加15.48%~24.26%,17.97%~23.74%。 (4)2种林分凋落叶、枝持水量随浸泡时间延长而增加,而吸水速率则为降低,持水量与浸泡时间的关系均呈对数函数关系(m=a+bln t),吸水速率与浸泡时间的关系呈幂函数关系(v=at^-b)。(5)C与云南松凋落枝持水性呈正相关关系(p＜0.05),N与华山松凋落枝、P与华山松和云南松凋落叶持水性呈负相关关系(p＜0.05)。综上,氮添加通过改变凋落物分解过程中C、N、P养分元素残留特征进而影响其持水性。     

湖南省紫鹊界梯田区人工林凋落物持水特性

通过对湖南省紫鹊界梯田区竹林与杉树混交林、竹林、草地、杉树林及板栗林5种植被凋落物样地调查,采用浸水实验和释水实验测定了各种类型凋落物的持水率、吸水速率、释水量和释水速率。结果表明,5种植被凋落物均具有较强的持水能力,最大持水率依次为420%(竹林与杉树林混交林),310%(竹林),283%(草地),252%(杉树林)和226%(板栗林);凋落物的持水率与浸泡时间之间呈对数函数关系,吸水速率与浸泡时间之间呈幂函数关系,释水量与释水时间之间呈对数函数关系,释水速率与释水时间之间呈幂函数关系,且以上函数拟合的相关系数R²均达到0.9以上。     

马缨杜鹃不同花叶比例凋落物的分解程度和持水性能研究

为揭示马缨杜鹃花叶凋落物对百里杜鹃保护区生态水文功能的影响,采用凋落物分解袋法及室内浸泡法对马缨杜鹃花、叶凋落物分解过程中的持水性能进行研究。结果表明:(1)马缨杜鹃花叶混合凋落物的累积分解率随分解时间及花比例的增加而增加,各花叶混合凋落物累积分解率在纯花及纯叶凋落物之间变化。(2)马缨杜鹃花叶混合凋落物的持水率与浸水时间呈对数函数关系(R=aln t+b,R~20.80),浸水初期2 h内迅速增加,2～8 h时缓慢增加,8 h后趋于平缓并逐渐达到饱和;而凋落物的持水速率均随着浸泡时间的增加而下降,持水速率与浸泡时间呈幂函数关系(V=kt~n,R~20.99),持水速率在浸水初期4 h最大,后逐渐趋于一致;(3)马缨杜鹃花叶混合凋落物最大持水率随着分解时间及花比例的增加逐渐升高,但不同花叶比例凋落物持水率的差异逐渐减小;(4)马缨杜鹃花叶凋落物最大持水量受分解率和最大持水率的共同调控,在分解0～360天时随花比例增加而增加,分解450天后花叶比例不再影响马缨杜鹃林下凋落物层的最大持水量。整体来看,马缨杜鹃花凋落物对叶凋落物分解及花叶凋落物持水功能有很大的影响,对花凋落物进行回收利用不宜超过现存量的50%。     

海拔和坡向对高寒灌丛草甸凋落物水源涵养功能的影响

以康定县折多山高寒山地灌丛草甸凋落物为研究对象，采用室外调查及室内测定结合的方法分析了凋落物蓄积量、持水及失水过程，以期探讨不同海拔和坡向凋落物水源涵养功能的差异。结果表明：（1）研究区凋落物的蓄积量在4.02~4.77 t/hm²波动，均表现出随着海拔的升高而逐渐降低，且半阴坡>半阳坡，海拔对凋落物蓄积量呈极显著影响（P<0.01）；（2）研究区凋落物最大持水量与蓄积量表现出一致的规律，有效拦蓄量最大为3 800 m半阳坡（5.95 t/hm²），最小为3 800 m半阴坡（2.53 t/hm²）；（3）枯落物持水量与浸水时间关系式为：W_t=aln （t）+b；枯落物吸水速率与浸水时间关系式为：V=ktⁿ；失水量与失水时间呈显著对数关系（R²>0.95，P<0.01），失水速率与失水时间呈显著幂函数关系（R²>0.99，P<0.01）。可见，该地区灌丛草甸凋落物的水源涵养功能在不同海拔和坡向间有明显分异特征，控制放牧减轻草甸退化和增加该生态系统的物种多样性能有效提高该区凋落物水源涵养功能。     

晋西黄土区典型林分枯落物层水文生态特性研究

选择山杨栎类次生林（以下简称次生林）、刺槐林、侧柏林、油松林为研究对象，通过样地调查，结合室内浸泡方法，对比分析枯落物（未分解层、半分解层）的水文特征指标，研究典型林分枯落物层水文生态特性。结果表明：（1）枯落物厚度为3.93~4.95 cm，刺槐林最大，油松林最小；蓄积量为次生林最大（19.28 t/hm²），侧柏林（18.03 t/hm²）和刺槐林（17.57 t/hm²）次之，油松林最小（14.73 t/hm²），未分解层蓄积量小于半分解层。（2）枯落物最大持水量（率）为30.92~61.31 t/hm²（197%~320%），次生林最大，依次为刺槐林、侧柏林，最小为油松林。（3）枯落物有效拦蓄存在显著差异（P>0.05），表现为次生林（31.29 t/hm²） > 刺槐（22.20 t/hm²） > 侧柏（18.19 t/hm²） > 油松（13.94 t/hm²），有效拦蓄率为107%~173%。（4）在浸水2 h内，枯落物持水量和吸水速率变化以次生林与刺槐林最为迅速，半分解层较未分解层变化迅速；持水过程中，两者与时间分别呈对数函数（R²>0.89）和幂函数关系（R²>0.99）。在4种林地中，次生林林下枯落物水文生态潜力最优，油松纯林最差，表现为次生林 > 刺槐 > 侧柏 > 油松。刺槐是除次生林外的3种人工林中最优林种。建议研究区内合理优化恢复树种配置，以提高水文生态功能。     

滨海沙地不同人工林凋落物现存量及其持水特性

为了研究滨海沙地沿海防护林凋落物水源涵养功能,采用野外调查和室内浸泡相结合,对滨海沙地4种典型人工林(木麻黄林、湿地松林、尾巨桉林和纹荚相思林)不同分解阶段的凋落物现存量、持水率、持水量和吸水速率进行研究。结果表明:相同林龄的4种人工林凋落物现存量表现为木麻黄林(19.12 t/hm~2)湿地松林(17.51 t/hm~2)尾巨桉林(10.90 t/hm~2)纹荚相思林(10.13 t/hm~2),半分解层凋落物储量占比高于未分解层;4种人工林最大持水率在140.55%～206.47%,为尾巨桉林纹荚相思林木麻黄林湿地松林,最大持水量在20.75～30.85 t/hm~2,为木麻黄林湿地松林尾巨桉林纹荚相思林,4种人工林凋落物最大持水率和最大持水量均为半分解层大于未分解层,不同分解阶段凋落物持水率和持水量与浸水时间呈对数关系;4种人工林不同分解阶段凋落物平均吸水速率在前0.25 h内差异较大,未分解层中尾巨桉林最大为2.05 mm/h,半分解层中湿地松林最大为4.32 mm/h,不同分解阶段凋落物吸水速率与浸水时间均存在幂函数关系;凋落物有效拦蓄深为木麻黄林(2.45 mm)湿地松林(2.04 mm)尾巨桉林(1.87 mm)纹荚相思林(1.72 mm)。综合来看,木麻黄林凋落物的持水能力最强,湿地松林次之,之后是尾巨桉林和纹荚相思林,说明从凋落物水源涵养能力来看,木麻黄林和湿地松林更利于滨海沙地的水源涵养。     

晋西黄土丘陵区不同人工林枯落物持水特性研究

为了定量评价森林枯落物的水文功能,通过野外观测和浸水法实验,调查了晋西黄土丘陵区不同人工林枯落物的蓄积量,分析了枯落物的持水能力与过程,并对枯落物持水量、吸水速率与浸泡时间的相互关系进行了研究。结果表明,枯落物蓄积量为6.81~56.64t/hm²,由大到小表现为:落叶松×白桦>落叶松>侧柏>油松×刺槐>油松>白桦>柠条>刺槐不同森林类型的枯落物最大持水量为10.08~100.78t/hm²,最大持水率变化范围为146.54%~203.74%,最大拦蓄量为9.41~88.65t/hm²,有效拦蓄量为7.90~73.53t/hm²枯落物浸水实验结果表明,枯落物持水量与浸水时间存在对数曲线关系,而枯落物吸水速率与浸泡时间呈反函数关系,在浸泡最初的0.5h持水量迅速增加,随后增幅减小,在12h以后枯落物吸水基本达到了最大值,持水量趋于动态平衡。表明落叶松×白桦混交林林下枯落物是8种林地中持水性最优的,刺槐纯林枯落物持水特性最差。     

草海流域3种优势树种凋落物叶分解历程中的水文特征

采用凋落物分解网袋法对草海湿地流域森林优势植物青冈（Cyclobalanopsisglauca）、桤木（Alnus cremastogyne）和云南松（Pinus yunnanensis）凋落物叶分解特性展开研究,揭示凋落物叶分解过程中自然持水率、最大持水率、最大拦蓄率、有效拦蓄率及凋落物持水率规律等。结果表明:（1）凋落物叶自然持水率随分解时间的增加呈先增后降趋势。凋落物叶自然持水率在分解历程中存在极显著性差异（青冈:F=213.79,P < 0.01;桤木:F=77.53,P < 0.01;云南松:F=179.12,P < 0.01）。（2）凋落物叶持水率（R_t）与浸水时间（t）呈显著正相关关系（P < 0.05）,回归分析得到凋落物叶持水率（R_t）与浸水时间（t）符合对数函数方程R_t=a+blnt;凋落物叶持水速率（v）与浸水时间（t）呈显著负相关关系（P < 0.05）,持水速率（v）与浸水时间（t）符合幂函数方程v=at^-b。（3）凋落物叶最大拦蓄率、有效拦蓄率随分解时间的推移,呈逐渐增加趋势。     

南亚热带5种典型人工林凋落物水文效应

以广西国有高峰林场的5种不同人工林(马尾松林、杉木林、桉树林、米老排林、红锥林)为研究对象,结合野外调查和室内浸水法,对各人工林凋落物层的水文效应进行定量分析。结果表明:(1)5种林分凋落物蓄积量范围在1.96～9.05 t/hm~2,大小顺序为红锥林杉木林马尾松林桉树林米老排林。(2)5种林分凋落物中,杉木林最大持水量最大,为14.23 t/hm~2,马尾松林最小,为6.26 t/hm~2;米老排林凋落物最大持水率最大,为577.98%,红锥林最小,为135.46%。(3)杉木林凋落物的有效拦蓄量最大,为10.18 t/hm~2,马尾松林最小,为4.07 t/hm~2;米老排林凋落物有效拦蓄率最大,为463.35%,红锥林最小,为92.38%。(4)回归分析表明,凋落物持水量与浸水时间的关系符合对数函数关系(Q=aln t+b(R~20.773)),凋落物吸水速率和浸水时间的关系符合幂函数关系(V=kt~n(R~20.997))。持水过程中,各林分凋落物均表现为在1 h内持水量迅速增加,1 h后增加速度变慢,在10～12 h之后,吸水基本停止。综上,杉木林、米老排林凋落物层水源涵养功能较强。     

大辽河流域水源涵养林枯落物持水特性研究

为探求大辽河流域水源涵养林枯落物的持水特性,以大辽河流域红松、落叶松、蒙古栎、杨桦、山杨、杂木林、胡桃楸灌木林和荒草地为研究对象,通过野外观测和浸水法,建立了枯落物持水量、吸水速率和浸泡时间的相互关系。结果表明:(1)不同林分枯落物总厚度和现存量为蒙古栎最大,分别为4.83cm和30.70t/hm²;灌木林最小,分别为0.65cm和3.32t/hm²。(2)最大持水量为3.97~36.02t/hm²,最大拦蓄量为3.34~34.06t/hm²,有效拦蓄量为0.85~20.39t/hm²,均表现为蒙古栎林最大,而灌木林和草地最小。(3)浸水实验结果表明,枯落物持水量与浸泡时间之间存在对数关系,枯落物吸水速率与浸泡时间之间存在幂函数关系,不同森林类型枯落物持水量和吸水速率随时间的动态变化规律基本相似。     

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.