基于Sentinel-2卫星数据的灌区农田土壤水盐协同反演

土壤含水量（soil water content, SWC）和土壤含盐量（soil salt content, SSC）是影响作物生长和农业生产力的重要因素。光学卫星图像已成为SWC和SSC估计的主要数据源。然而,在SWC或SSC变化较大地区,土壤水分和盐分会影响对方对光谱反射率的响应,使得SSC和SWC的反演精度较差。对此,该研究提出了一个半解析性的反射率模型—RVS模型,来模拟植被光谱反射率（R_v）对作物根区土壤含水量和含盐量的响应;并通过构建的RVS模型,对植被覆盖区域的土壤含水量和土壤含盐量进行同步监测。研究表明：RVS模型在反演研究区土壤含盐量和含水量时,精度较为可靠(水分：决定系数R²为0.63～0.74,均方根误差为0.017～0.028;盐分：决定系数R²为0.68～0.75,均方根误差为0.0525～0.0617)。在作物生长过程中,植被光谱反射率对深层土壤的含水量和含盐量的响应比对浅层土壤的含水量和含盐量的响应更加明显,而且随着作物的生长,影响光谱反射率的主导因素从土壤水分慢慢转向土壤盐分和水盐相互作用。该研究在一定程度上揭示了土壤水分、盐分、水盐交互作用对作物光谱反射率的干扰过程,实现土壤水分和盐分的同步监测,对实现区域尺度上土壤含盐量和含水量的精准监测具有一定的意义。     

光照与阴影对无人机热红外遥感监测土壤含水率的影响

为探究作物冠层受阳光直射或阴影遮挡对无人机热红外遥感诊断作物水分胁迫、监测土壤含水率的影响，该研究以不同灌溉处理的夏玉米为研究对象，将热红外图像划分为光照冠层、阴影冠层、光照土壤、阴影土壤4个部分，分别提取光照温度与阴影温度后计算了11:00、13:00、15:00的冠气温差（冠层温度与大气温度之差，ΔT）、作物水分胁迫指数（crop water stress index，CWSI）、蒸发比（潜热通量与有效能量的比值，evaporative fraction，EF），并对比了3种指数在不同时刻使用光照温度（ΔT_L、CWSI_L、EF_L）与阴影温度（ΔT_S、CWSI_S、EF_S）后对土壤含水率的监测效果变化情况。结果表明：1）3种指数的监测效果会随时间发生变化，11:00与15:00时EF监测效果较好，13:00时CWSI监测效果较好，ΔT的监测效果较差但随时间波动最小；2）拔节期在区分光照温度与阴影温度后监测效果在11:00时提升幅度最大，EF、EF_S、EF_L的R²分别为0.54、0.65、0.78，CWSI、CWSI_S、CWSI_L的R²分别为0.47、0.64、0.70，抽雄期与灌浆期使用光照温度对监测效果提升不大，但使用阴影温度的指数监测效果有明显降低，在13:00时CWSI_S较CWSI有最大降幅，R²降幅分别为0.11、0.06；3）在拔节期与抽雄期使用11:00的EF_L，在灌浆期使用13:00的CWSI能取得最好的土壤含水率监测效果，预测土壤含水率的R²分别为0.75、0.75、0.89。该研究可以为无人机热红外监测土壤含水率提供参考。     

HDXRF法农田土壤镉测定结果准确度评价与精准校正模型构建

以甘肃白银某污灌区重金属污染农田土壤为研究对象，对影响高精度便携式X荧光光谱（HDXRF）法总镉（Cd_T）测定精度的主要因素进行了筛选，分别研究了土壤水分、有机质类型与含量、土壤类型对HDXRF法Cd_T测定的影响，并采用相对误差（RE）、相对标准偏差（RSD）和决定系数（R²）对测定结果的准确度和精密度进行了评价。结果表明：HDXRF法Cd_T测定的RE≤10%、RSD≤10%、R²>0.99，符合农田土壤环境质量监测技术规范和美国环境保护署标准的准确度和精密度规定。HDXRF法Cd_T测定结果随着土壤水分含量的增加呈指数衰减趋势，衰减方程为y=0.803e^–1.3284x，衰减系数（μ_ω）为–1.328 4，R²为0.984 5。HDXRF法Cd_T测定结果与有机质含量呈显著的负相关关系（r=–0.955），且腐殖酸（HA）比泥炭（Peat）对测定结果的影响更大，HA与测定结果的校正方程为y=–1.555x +0.780，R²为0.934 4。土壤类型对HDXRF法Cd_T测定结果存在一定的影响，相对于红壤和水稻土，灰钙土的测定结果与传统实验室分析方法测定结果更接近。总之，虽然HDXRF法Cd_T测定结果受多种因素影响，但通过校正模型校正，其校正结果的可靠性能够满足Cd污染农田土壤精准调查需求。     

光谱技术结合水分校正与样本增广的棉田土壤盐分精准反演

棉田土壤盐分的精准反演对于棉花的种植管理具有重要意义。水分和盐分作为主要环境因素,共同影响棉田土壤的波谱特征,两者之间的耦合关系直接影响土壤盐分的检测分析。为了提高基于光谱技术构建的模型对棉田土壤盐分信息解析的准确性与可靠性,该研究联用可见/短波近红外（400～1 000 nm）和长波近红外（960～1 693 nm）技术,采集不同含水率与含盐量的新疆地区土壤样本的光谱;结合外部参数正交法（external parameter orthogonalization,EPO）,校正不同标样集与不同波段光谱中的土壤含水率干扰信息;引入基于不同卷积步幅的深度卷积对抗网络（deep convolutional generative adversarial networks,DCGAN）,进行样本增广与质量评估;参考三层残差神经网络设计一维卷积神经网络RNet,最终构建基于EPO-DCGAN-RNet的优化模型,用于棉田土壤盐分的反演。结果表明,与传统机器学习方法和基于VGG或EfficientNet结构一维卷积神经网络相比,该研究提出的EPO-DCGAN-RNet方法能够有效地滤除水分对盐分反演的影响、提高模型对特征波段的挖掘能力、降低深度学习算法对样本量的依赖性,并能得到更优的模型预测性能。EPO-DCGAN-RNet的建模集R²和均方根误差分别为0.942、115.420 μS/cm,验证集R²和均方根误差分别为0.910和136.472 μS/cm。研究结果可为新疆棉田土壤盐分快速精准检测提供理论指导和技术支持,有助于促进盐碱地区棉花种植的水肥科学管理。     

基于光谱指数与机器学习算法的土壤电导率估算研究

土壤盐分是干旱区土壤盐渍化评价的重要指标。以新疆维吾尔自治区渭干河-库车河三角洲绿洲为例,基于土壤电导率 (Electrical conductivity,EC) 及可见光-近红外 (Visible and near infrared, VIS-NIR) 光谱数据,通过蒙特卡洛交叉验证 (Monte Carlo cross validation, MCCV) 确定364个有效样本。采用原始光谱 (Raw reflectance, R) 及其经过微分、吸光度 (Absorbance, Abs)、连续统去除 (Continuum removal, CR) 等6种预处理后的数据构建光谱指数。基于遴选出的21个最优指数,采用BP神经网络 (Back propagation neural network, BPNN)、支持向量机 (Support vector machine, SVM)、极限学习机 (Extreme learning machine, ELM) 三种算法对EC进行估算,并引入偏最小二乘回归 (Partial least squares regression, PLSR) 进行比较。结果表明：在基于R与6种光谱预处理数据构建的21个最优光谱指数之中,R_FD_RSI (R₁₉₁₃,R₂₁₄₂) 表现最佳 (r = 0.649) ;与PLSR相比,机器学习算法能够显著提高模型的估算精度,R²提高了34.55%。三种机器学习算法模型中,ELM表现最优 (R² = 0.884, RMSE = 3.071 mS?cm^-1, RPIQ = 2.535) 。本研究中所构建的光谱指数在兼顾遥感机理的同时能深度挖掘更多的隐含信息,并且基于机器学习算法的土壤EC估算模型精度显著提高,为干旱区土壤盐分定量估算提供了科学参考。     

烤烟成熟鲜烟叶生化组分高光谱估算方法筛选

为实现实时无损快速预测鲜烟叶的品质生化组分、筛选估算生化组分最佳的方法,使用ASD Fieldspec FR2500对烤烟成熟鲜烟叶进行了反射率、透射率光谱测定和常规生化组分分析。对可见近红外波段(350～1650 nm)单波段光谱和选用已有100种光谱指数共两类光谱参量进行了与生化组分之间线性函数、幂函数、指数函数共3种形式相关分析和基于决定系数的筛选。结果表明,对于叶绿素a、叶绿素b、类胡萝卜素、钾估算方法分别是Gitelson and Merzlyak2(GM₂) (R²=0.81)、光化学指数2(PRI₂) (R²=0.80)、Gitelson and Merzlyak2(GM₂) (R²=0.83)、1420 nm吸收峰开始位置(λs₁₄₂₀) (R²=0.67)的线性拟合最优。对于总糖、比叶重、氮、烟碱最优方法分别是在532 nm反射率一阶微分线性拟合(R²=0.54)、在1423 nm透射率线性拟合(R²=0.45)、在666 nm反射率倒数对数一阶微分的幂函数拟合(R²=0.44),在1135 nm反射率倒数对数二阶微分的线性拟合(R²=0.20)。通过筛选的光谱方法可以评估烟叶的品质状况。     

基于改进CNN的猕猴桃根区土壤含水率反演方法

为解决无人机遥感领域根据冠层光谱信息对猕猴桃果树根系土壤含水率（root soil water content, RSWC）进行反演时,现有算法对冠层图像信息分析不足的问题,该研究对传统卷积神经网络模型进行改进,提出一种复合视觉卷积回归神经网络（compound visual convolutional regression network, CVCRNet）,该网络复合两种不同尺寸卷积层对图像数据进行卷积特征提取,并使用全连接层对卷积特征值进行降维,从而直接以多光谱图像为分析对象对RSWC进行反演,充分利用多光谱图像内所有数据,提升反演精度。研究采集徐香猕猴桃果树果实膨大期（5—9月）冠层多光谱信息和深度40 cm处的RSWC,把基于图像的CVCRNet网络反演方法与基于植被指数的传统反演方法进行对比,CVCRNet训练结果在验证集R²为0.827,RMSE为0.787%,相较于传统方法在验证集R²为0.759,RMSE为0.983%,反演结果相关性有了明显提升,准确率也有得到一定提高。结果表明,改进后的CNN网络能够作为冠层信息反演的重要工具,在冠层复杂的场景下达成良好的土壤数据反演效果。     

双针热脉冲测定冻土热特性的数值模拟方法

使用双针热脉冲(dual probe heat pulse, DPHP)测定冻土热特性时施加热脉冲后会导致加热探针周围的冰融化,使用目前常用的仅考虑热传导（忽略融化相变、冰水两相分界面）的解析解处理DPHP温度数据,会导致在-5 ℃至0 ℃温度范围内无法准确测量热导率 (λ) 和比热 (C_v)。为了能够准确测定冻土的 λ 和 C_v,有必要考虑DPHP加热过程中引起的冰融化的相变潜热。该研究基于COMSOL仿真软件模拟了考虑相变潜热、相变区间以及移动冰水界面的DPHP测量过程,采用随温度非线性变化的真实冻土热特性进行模拟,并与真实冻土的DPHP测量数据对比。结果表明：1）COMSOL仿真在不考虑相变条件下与无限线性热源模型结果完全吻合（R² = 0.9989）;2）当土壤初始温度低于-5 ℃时,考虑相变发生的COMSOL仿真能够准确模拟试验结果,表现出较高的相关性（R² > 0.93）,在-2 ～ 0 ℃的土壤初始温度范围内,无限线性热源模型的结果与试验测量显著偏离（R² < 0.0013）;3）在不同土壤初始温度下,相变温度为-1.5 ～ -0.5 ℃的仿真结果与试验数据具有较高的相关性（R² > 0.7）。本研究结果检验了有限元仿真用于真实冻土DPHP研究的可行性,可为准确预测冻土热特性的研究提供方法。     

基于土壤光谱特征的宁夏银北地区盐碱地盐分预测研究

对宁夏回族自治区银北地区盐碱地野外土壤表层光谱反射率和土壤全盐及盐分进行定量分析,筛选出各土壤盐分指标的敏感波段,然后采用全回归和逐步回归的方法建立各盐分的预测模型。结果表明：表层土壤高光谱反射率r,及其平滑去嗓处理后的值R,lg(R)与全盐含量呈极显著正相关关系,1/R,lg(1/R)与全盐呈极显著负相关关系,(R)'和〔lg(1/R)〕'在特定单波段处表现较佳;土壤表层光谱反射率与CO₃^2-的相关性最强,其次是SO₄^2-;土壤光谱反射率与Na⁺的相关性在各种变换方法下均较强,其次为Mg²⁺,与Ca²⁺的相关性最弱。基于R的逐步回归方程为全盐含量预测的最佳模型;基于土壤光谱反射率拟合土壤CO₃^2-的准确度略高于对土壤HCO₃^-;敏感波段估测土壤SO₄^2-含量的决定系数明显高于其他阴离子;采用〔lg(1/R)〕'逐步回归得到的方程拟合土壤Na⁺,K⁺和Mg²⁺含量相对于其他变换方式效果更理想。预测模型中对土壤全盐和Na+的模型精度较高,预测能力强;光谱对土壤SO₄^2-和Mg²⁺的预测能力也较强;对土壤Cl^-和Ca²⁺的预测稳定性、预测能力和精度都较差。     

被动荧光探测水分胁迫对玉米叶片影响的初步研究

利用叶绿素荧光被动探测方法初步探讨了水分胁迫对玉米叶片生理机能的影响。水分胁迫梯度通过将离体叶片放在干燥器时间不同而获得。室内采用积分球耦合ASD光谱仪，结合加/不加滤光片照明的方法得到反射率差值光谱，即代表叶绿素荧光光谱。结果表明随着叶片含水率的降低，叶绿素荧光发射峰的位置几乎没有变化，峰高在686 nm处有先上升后逐渐降低的趋势，在740 nm处则缓慢下降。双峰比值Dif₆₈₆/Dif₇₄₀与叶片含水率呈负相关关系(R²=0.3850，n=21)，不同水分胁迫程度下利用调制式荧光仪测定的荧光参数Fv/Fm与740 nm荧光光谱峰值线性正相关，与双峰比值有负相关趋势。表明该被动方法可以探测水分胁迫引起的叶片光系统受胁状况，为田间被动遥感探测植物叶绿素荧光和生理状态提供参考。     

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.