不同形式的光谱参量对春玉米氮素营养诊断的比较

选择适宜的光谱参量,对利用光谱技术进行作物营养诊断精确度的提高是至关重要的。该文对单因素氮处理下春玉米（Zea may L.）不同层位叶片光谱反射率与氮含量作了相关分析,探讨了叶片水平上单波段光谱反射率（R）、单波段光谱反射率的对数（LgR）、双波段组合光谱反射率（R1+R2）、以及对数形式的双波段组合光谱反射率（LgR1+ LgR2）4种形式光谱参量对氮素营养诊断的可靠性。结果表明,第6片完全展开叶叶片光谱反射率与氮含量在可见光波段存在较高的负相关关系,以550和720 nm两波段组合的光谱参量（LgR550+LgR720和Lg(R550+R720)）建立的线性回归方程的拟合度最好;不同生育期应选择对养分盈亏敏感的叶片作为营养诊断的光谱监测目标,不同生育期叶片氮素营养的光谱敏感波段不同,应选择二者相关性高的波段,较为适宜的光谱参量形式与营养成分建立估算模型。研究表明,经对数处理后的光谱参量,无论是单波段还是双波段,拟合方程的精度都有不同程度的提高,且方程的稳定性也增强,说明对数形式的光谱参量提高了对氮素营养诊断的精确度。     

基于高光谱的中国干旱区棉花遥感估产（英）

该文测定了棉花盛蕾期至吐絮后期各时期冠层的高光谱反射率以及产量,并对棉花产量与冠层光谱植被指数进行相关分析。结果表明：棉花各生育期可见光波段、近红外波段及短波红外波段光谱反射率与产量间分别呈显著负相关、显著正相关与显著负相关。根据棉花冠层光谱波形特征,利用植被红边波段560 nm反射峰、670 nm吸收谷、近红外波段890 nm反射峰、980和1?210 nm两个弱水汽吸收谷、短波红外1?650和2 200 nm反射峰,设计归一化差值光谱指数,并与棉花产量进行相关分析,上述波段组合定义的归一化差值光谱指数与产量在各生育期均达显著或极显著相关。VARI_700抗大气植被指数在各生育期均达极显著相关。     

不同生育期冬小麦光谱特征对叶绿素和氮素的响应研究

研究测定了不同施氮水平条件下冬小麦冠层在七个典型生育期叶片叶绿素、地上部分全氮含量以及冠层光谱,分析了单波段反射率、可见光和近红外波段组合而成的归一化植被指数(NDVI)、比值植被指数(RVI)与相应时期叶片叶绿素和地上部分全氮含量的相关性。结果表明,施氮量增加,两个农学参量、冠层近红外波段反射率都随之增加,但当施氮量增加到300kg hm-(2一次性施入)时,上述各项指标均降低;整个生长期中孕穗期在近红外区域反射率最高,与可见光波段反射率相差最大;除分蘖期外,其它时期单波段510nm～1100nm反射率、NDVI、RVI与叶绿素和全氮含量显著相关,植被指数的相关性较单波段高,且从分蘖期到乳熟期,相关性逐渐增强;整体来讲,可见光中560nm、660nm和近红外760nm、1100nm和1200nm组合的NDVI在各生育期与两个农学指标的相关性较好,选择NDVI(560,760)可以准确拟合叶片叶绿素和地上部分全氮含量。     

不同轮作和氮肥分配季节下土壤氮素供应和油菜氮素吸收差异

【目的】土壤氮素供应受到土地利用方式影响,明确土壤氮素供应特性是合理施肥的基础。研究不同轮作方式下油菜季土壤氮素供应特征和油菜氮素吸收规律,可以为油菜氮肥施用提供科学依据。【方法】本试验为同田对比田间试验,采用裂区试验设计,主处理为两种轮作方式,即水旱轮作 (水稻?油菜轮作) 和旱地轮作 (棉花稻?油菜轮作);副处理为氮肥 (N 150 kg/hm2) 施用季节。每种轮作方式下设3个氮肥施用季节处理,分别为:1) 两季均不施氮肥(N_0-0);2) 水稻/棉花季施氮,油菜当季不施氮(N_150-0);3) 水稻/棉花季不施氮,油菜当季施氮(N_0-150)。通过原位矿化培养方法测定油菜不同生育期土壤氮素净矿化量,同时测定油菜在不同生育期内氮素吸收量。【结果】与两季均不施氮相比,油菜季施氮,稻油轮作下土壤氮净矿化累积量显著增加101.2 kg/hm2,油菜氮素吸收增加76.8 kg/hm2;棉油轮作条件下,土壤氮净矿化累积量显著增加了110.0 kg/hm2,油菜氮素吸收增加96.2 kg/hm2。从分配比例上分析,在油菜苗期—薹期,稻油轮作土壤氮素净矿化量占累计矿化量的52.3%,棉油轮作为64.5%,棉油轮作高于稻油轮作;然而在油菜花期—成熟期,稻油轮作土壤氮素净矿化量高于棉油轮作。与土壤氮素净矿化相一致,在油菜苗期—薹期,棉油轮作油菜氮素吸收量比稻油轮作高37.1 kg/hm2,棉油轮作有利于油菜前期氮素吸收;而油菜生长后期稻油轮作比棉油轮作多吸收氮素18.2 kg/hm2。稻油轮作有利于油菜后期氮素吸收。【结论】棉油轮作条件下,残留棉花叶片养分释放快,有利于油菜生长前期 (苗期—薹期) 土壤氮素供应;而稻油轮作条件下,残留水稻根茬养分释放慢则有利于油菜生长后期 (花期—成熟期) 土壤氮素供应。因此棉油轮作有利于油菜前期生长,稻油轮作有利于油菜后期生长。稻油轮作条件下在油菜生长前期可适量增加氮肥供应,后期降低氮肥供应;棉油轮作下在油菜生长前期适量降低氮肥供应,后期增加氮肥供应。     

基于夏玉米光谱特征的叶绿素和氮素水平及氮肥吸收利用研究

本文首先分析不同施 N 水平条件下夏玉米冠层在6个典型生育期的光谱特征曲线,然后计算了可见光和近红外波段光谱反射率组成的归一化植被指数(NDvI)及相应时期叶片叶绿素含量和地上部分全N含量2个重要指标以及孕穗期冠层NDVI和几个N肥吸收利用效率的相关性.结果表明,孕穗期冠层光谱反射率在近红外区域反射率最大,且其可见光和近红外区域反射率差异最大:从苗期到孕穗期,NDVI和叶绿素、全N含量的相关性逐渐增强,到抽雄期减弱,灌浆期又有所增强;整体来讲绿色归一化植被指数 GNDNI(560,760)在各生育期与不同农学参量的相关性比其他波段组合的指数好,其次为NDVI(660,760)波段组合.随着施N量的增加,N肥利用效率、收获指数和N肥收获指数、N素农艺效率以及N肥回收效率均逐渐降低,对各N肥吸收利用指数的预测以NDVI(660,760)、NDVI(660,1100)和GNDVI(560,760)较理想.     

基于高光谱和参数优化支持向量机的水稻施氮水平分类研究

为探索水稻氮素营养的快速、无损诊断方法以及构建基于高光谱技术的水稻氮素营养状况分类识别模型。本研究以 4种不同施氮水平的“中嘉早 17”水稻分蘖期顶部第三完全展开叶叶片(简称顶三叶)为研究对象,测定各叶片的可见光到近红外波段(350～ 2500 nm)内的光谱数据,对所获取的光谱数据进行平滑处理和归一化处理,以消除噪声及量纲的影响,并采用主成分分析(PCA)的方法进行数据降维至 22维,同时分别选用基于网格搜索算法、粒子群算法和遗传算法优化参数的支持向量机进行水稻氮素营养状况分类识别模型的建立。研究结果表明:1)不同施氮水平下的水稻叶片光谱反射率曲线走势大致相同,但不同施氮水平下 780～ 1 300、1 400～ 1 850及 1 900～ 2500 nm波段光谱反射率存在一定的差别;2)优化参数后的 SVM模型与默认参数下的 SVM模型相比,其训练集与测试集分类识别效果都要优于默认参数下的 SVM模型。其中,以遗传算法优化参数的 SVM模型识别分类效果最佳,训练集和测试集识别准确率分别为 99.375%、98.750%,测试集的4种施氮水平(施氮量从低到高)识别准确率分别为 100%、95%、100%和 100%。结果表明利用高光谱技术能够很好地进行水稻氮素营养状况的定性诊断研究。为快速水稻氮素营养诊断提供了一种新途径,为精确施氮提供了技术支撑和理论依据。     

不同施肥长期定位试验地夏玉米冠层光谱特征研究

以黄淮海地区典型冬小麦-夏玉米轮作区的长期定位施肥试验为研究对象,筛选对氮、磷、钾三种营养元素及产量最敏感的波段和生育期,为监测不同时期作物营养胁迫情况和估产提供依据。系统分析了氮、磷、钾单一养分缺乏和两种或两种以上营养元素同时缺乏时典型生育期夏玉米冠层反射光谱特征、收获后秸秆和子粒氮、磷、钾及产量的变化规律。结果表明,缺素使冠层光谱反射率在可见光波段增加,在近红外波段降低。作物秸秆、子粒含氮量和含钾量及产量与可见光波段反射率呈负相关,与近红外区域7601~300 nm反射率呈正相关;秸秆含磷量与各反射率的相关性不明显,子粒含磷量与冠层光谱之间无明显规律。整体上,560和810 nm分别为收获期作物含氮量在可见光和近红外两个区域的敏感波段,开花期为夏玉米氮素诊断的敏感时期;夏玉米钾素在可见光和近红外区域的敏感波段分别为680和810 nm,拔节期为诊断钾素的敏感时期。整个生育期各单波段反射率与产量均呈极显著相关关系,拔节期关系最密切。说明在明确主导养分限制的前提下,利用作物冠层光谱来监测氮素和钾素的丰缺以及准确估产是可行的。     

应用IKONOS卫星影像监测冬小麦氮营养状况

应用从高精度卫星影像获取的光谱植被指数和单波段光谱反射值与冬小麦拔节期氮素营养状况进行了相关分析,结果发现:高精度卫星光谱归一化植被指数、绿植被指数、比值植被指数、优化土壤调节植被指数和单波段光谱反射值红外波段与拔节期小麦叶片叶绿素仪读数、茎基部硝酸盐含量、地上部生物量和地上部吸氮量等都有显著的线性正相关关系,相关系数范围在0.651~0.860之间。而红光波段、绿光波段则与拔节期小麦氮营养诊断指标呈显著线性负相关关系,相关系数范围在-0.803~-0.574之间。且上述光谱植被指数和单波段反射值均与小麦拔节期优化施氮量有很好的相关关系。因此,可以应用高精度卫星影像结合地面土壤植株测试进行冬小麦拔节期的冠层氮营养诊断和氮肥推荐。     

春玉米磷素营养的光谱响应及诊断

通过盆栽试验监测不同磷营养水平春玉米典型生育期叶片光谱变化,并对叶片光谱反射率与叶片磷含量做了相关分析。结果表明,春玉米大喇叭口期是磷素营养的光谱响应敏感期,3507～30.nm和14201～800.nm是磷素营养的光谱敏感波段。该生育期构建的单波段高光谱变量、窄波段光谱变量和宽波段光谱变量与叶片磷含量都存在显著或极显著的回归关系;窄波段光谱变量比值指数R6725/6256和R61745/15856与叶片磷含量的回归关系达到了极显著水平,R625/555达到显著水平。可见光波段光谱变量与磷含量的回归关系优于近红外波段光谱变量与磷含量的回归关系,表明可见光波段叶片光谱反射率可能更适合春玉米磷营养状况的评价。不同波段宽度的光谱变量分析表明,在敏感波段范围内,801～00.nm波段平均的叶片宽波段光谱反射率没有降低对叶片磷含量的估算精度。     

基于玉米叶片光谱特征的土壤无机氮含量估算模型的建立与验证

  【目的】  作物叶片颜色反映土壤养分的供应状况。研究作物叶片氮素相关的特征光谱信息与土壤无机氮含量的关系,以建立基于叶片光谱信息的土壤无机氮含量诊断模型,实现利用高光谱技术对作物和土壤进行实时监测。  【方法】  在两年(2017—2018) 的玉米 (郑单958) 田间试验中,设置6个施氮水平,施氮量分别为0、60、120、180、240、300 kg/hm2。在玉米的拔节期、大喇叭口期、开花吐丝期、灌浆期测定叶片高光谱反射率,对植株和土壤样品进行采集,分析土壤无机氮含量的变化,明确叶片光谱反射率与土壤无机氮含量的关系,利用光谱参数和偏最小二乘回归法 (partial least squares regression,PLSR) 建立诊断模型并进行模型精度的评价。  【结果】  施氮处理土壤无机氮含量显著高于不施氮处理,随着生育期的推移,土壤无机氮含量呈递减趋势,追肥可显著提高土壤无机氮含量。拔节期和开花吐丝期叶片光谱反射率与土壤无机氮含量在可见光波段呈负相关关系,在近红外波段呈正相关关系;大喇叭口期两者在可见光波段呈负相关关系,灌浆期两者无明显相关关系。在光谱参数模型中,4个生育期土壤无机氮含量预测的最佳光谱指数分别为RVI-2、RSI (534,726)、RSI (567,519) 和RVI-2,其回归模型验证集的R2分别为0.642、0.749、0.696、0.540。在PLSR预测模型中,利用PLSR建立的诊断模型验证集的R2分别为0.876、0.838、0.765、0.595,RPD (ratio of percent deviation) 分别为2.140、2.077、2.002、1.369。  【结论】  基于叶片光谱反射率建立的PLSR估算模型,在玉米的拔节期、大喇叭口期、开花吐丝期均能很好地预测土壤无机氮含量。因此,利用叶片光谱特征诊断土壤无机氮含量具有一定的可行性。     

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.