人工降雨条件下秸秆覆盖及留茬的水土保持效应

通过人工模拟降雨试验,研究了秸秆覆盖及留茬的水土保持效应。结果表明,秸秆覆盖和留茬均可延缓径流产生,其中5 000和3 000 kg/hm2秸秆覆盖分别能使初始产流时间延后427%和19%,而30 cm高留茬及15 cm低留茬覆盖则可分别延后初始产流时间107%和76%。5 000 kg/hm2覆盖量下累积径流量较对照减少了61.72%,土壤侵蚀量减少了86.7%;3 000 kg/hm2覆盖量下累积径流量减少了6.26%,土壤侵蚀量减少了60.1%,实施覆盖能够有效抑制水土流失,且以高覆盖量的作用效果更为显著。30 cm高留茬的土壤侵蚀量较对照减少了62.9%,15 cm低留茬覆盖减少25.6%,留茬能够有效防止土壤侵蚀,但对径流量无明显影响。     

秸秆覆盖和留茬的田间水土保持效应

通过人工模拟降雨试验,研究秸秆覆盖和留茬在玉米生育期的水土保持效应.结果表明:覆盖和留茬在玉米不同生育期均可有效减少土壤侵蚀,覆盖的效果更为明显,其产沙量最大可减少75％,留茬的产沙量最大可减少29％.相同秸秆用量下实行覆盖的水土保持效应较留茬明显.覆盖结合留茬减弱土壤侵蚀的效果明显,在玉米各生育期的产沙量均有大幅减少,低覆盖高留茬减幅最大为85％,高覆盖低留茬减幅最大为78％;在抽穗期对径流强度也有削弱,低覆盖高留茬的径流量减少23％,高覆盖低留茬减少15％,相同秸秆用量下低覆盖高留茬对水土流失的抑制较高覆盖低留茬明显.     

民勤荒漠区柠条防护林平茬复壮技术研究

为了促进腾格里沙漠荒漠区防护林持续稳定发展,对防护林内衰退的柠条样地进行了植物多样性调查及不同留茬高度的平茬试验,选取萌条数量、株高、冠幅、萌条地径、平茬后土壤含水量5项指标评价平茬效果,结果表明:①50年柠条人工林内的植物种类有8种,以柠条、梭梭、沙米和多裂骆驼蓬为优势种,植被总盖度为34.91%;②平茬两年不同留茬高度处理柠条的株高、冠幅和地径均随着时间增加呈增长趋势,萌条数量则呈减少趋势,留茬高度对萌条生长状况有显著影响(P<0.05),不同留茬高度平茬效果为15 cm>20 cm>10 cm>5 cm>0 cm;③平茬样地土壤含水量显著大于未平茬样地。     

稻茬高度影响轮作紫云英生长及还田效应

大田试验条件下,研究了水稻机械收割不同留茬高度(15cm 、30cm 、40cm,分别标注低茬、中茬、高茬)对轮作紫云英生长、养分积累以及翻压还田后土壤养分、化学性状和微生物量等的影响。结果表明：稻茬高度显著影响轮作紫云英生长、养分积累以及翻压还田效果。紫云英单位面积株数随留茬高度的降低而显著减少；除单株分枝数外,植株株高、茎粗、单株鲜、干重均表现为高茬处理＞中茬处理＞低茬处理,高、低茬处理间差异显著或极显著。产草量受稻茬高度影响明显,单位面积鲜、干草产量均随稻茬高度的降低而显著减少,高茬处理的紫云英鲜、干草产量均最高,分别达到19.22t.hm_^-2和3.27 t.hm_^-2,较低茬处理每公顷增加15.21 t和2.53 t。不同稻茬高度处理的紫云英植株碳及氮、磷、钾含量无显著差异,植株养分积累量则随稻茬高度增加而显著增加,各养分积累量变化趋势一致；不同处理紫云英翻压还田后土壤pH值变化差异不显著,但均较试验前略有上升；土壤电导率则表现为高茬处理大于中、低茬处理,处理间差异极显著; 翻压后土壤养分变化差异较大,各养分含量均表现为随水稻留茬高度降低而减少的趋势,高留茬处理土壤的有机质、全氮、碱解氮、有效磷、速效钾含量分别较低留茬处理增加41.51%、27.35%、34.96%、68.78%、82.12%。不同处理紫云英翻压还田后,土壤可培养微生物数量存在差异。三大类微生物细菌、真菌、放线菌的数量均以高茬处理最高,除放线菌外,差异均达显著水平,其中,对细菌数量的影响最为明显,高茬处理极显著大于中、低茬处理,中、低茬处理间差异显著。综上,水稻留高茬(茬高40cm)轮作紫云英可获得较高的生物量和养分积累,翻压还田后土壤培肥效果显著优于中、低茬(茬高≦30cm)收割的处理。     

采石场松散体坡面平铺生态袋绿化的水土保持效应

为研究生态袋技术在采石场松散体坡面的水土保持效应,利用2011年北京市房山区周口店镇采石场的10次产流资料,采用径流小区观测法,研究了生态袋技术在不同平均雨强(1.02,5.07和12.05mm/h)和不同坡度(20°,25°,30°,35°)条件下对裸露松散体坡面的水土保持效应.结果表明,生态袋技术可以显著减少松散体坡面径流深和泥沙含量,其径流深和产沙量均小于对照,在不同平均雨强和坡度下可平均减少25.2％的径流深和53.1％的产沙量,在不同坡度下可平均减少23.5％的径流深和60.6％的产沙量.当平均雨强为12.05 mm/h和坡度为35°时的减流减沙效应最显著.相关分析结果表明,径流深、产沙量和雨强、坡度呈良好的相关关系.平铺生态袋绿化是解决松散体坡面水土流失的重要措施之一.     

地面覆盖条件下雨强和坡度对红黏土坡面侵蚀过程的影响

为揭示地面覆盖条件下第四纪红黏土坡面在不同雨强和坡度时的侵蚀变化规律,选取3个降雨强度(1.0,1.5,2.0 mm/min)和3个坡度(10°,15°,20°),通过人工模拟降雨试验,分析坡面产流、产沙、入渗特征,并以15°为例计算覆盖坡面的减流减沙效益。结果表明:(1)坡面产流时间随雨强和坡度增加而提前,覆盖对产流时间有明显的滞后作用,雨强的增加会削弱覆盖延缓产流的作用;坡面径流率呈现前期增长,后期趋于稳定的变化特征;(2)当坡度一定,雨强从1.0 mm/min增加至2.0 mm/min,累积侵蚀量增加1.89～2.96倍;雨强一定,坡度从10°增加至20°,累积侵蚀量增加1.91～3.45倍;(3)坡面初始入渗率和入渗总量随坡度的增加而减小,而雨强的增大会增加坡面初始入渗率,减少入渗总量;(4)15°条件下覆盖坡面的径流量和泥沙量较裸坡平均减少50.26%和95.31%,松针覆盖的水土保持效益显著,且减沙效应大于减流效应;(5)坡度对覆盖坡面累积产流量和累积产沙量的影响程度大于雨强,不同雨强、坡度下累积径流量与累积产沙量呈现幂函数关系(R~20.97)。研究结果可为南方红壤丘陵区林下水土流失治理与生态恢复提供参考。     

留茬高度对小叶锦鸡儿光合生理和生长特征的影响

[目的] 研究不同留茬高度小叶锦鸡儿生长和光合生理的变化规律,揭示不同留茬高度下小叶锦鸡儿生长和光合能力的强弱,探索其平茬时的最适留茬高度,为寻求合理抚育管理措施、指导小叶锦鸡儿生产实践提供理论依据。[方法] 选择2003年人工种植小叶锦鸡儿为研究材料,设置未平茬（CK）、留茬高度5 cm （T₁）,10 cm （T₂）,15 cm （T₃）,20 cm （T₄）,25 cm （T₅）共6个处理于2018年秋季进行平茬,分别测定次年生长季小叶锦鸡儿生长和光合生理指标。[结果] 平茬能显著提高小叶锦鸡儿株高、冠幅、新稍长的增长;不同留茬高度处理净增长量均不同,留茬高度15 cm处理株高、冠幅长和宽度、新稍长净增长量值最高,分别较未平茬处理增加了203.44%,278.10%,292.59%,385.43%;留茬高度5,10和20 cm处理的净增长量次之,留茬高度25 cm的值最低,较未平茬处理分别增加了25.15%,26.38%,25.93%,88.48%;一定留茬高度平茬能显著提高小叶锦鸡儿净光合速率（P_n）、蒸腾速率（T_r）和水分利用效率（WUE）;不同处理小叶锦鸡儿日变化均有不同程度的光合、蒸腾“午休”现象;留茬高度15 cm处理叶片P_n,T_r,WUE日均值均最高,分别比未平茬处理增加了2.52,0.37和1.52倍;留茬高度5,10和20 cm处理次之,留茬高度25 cm处理值最低,其P_n和WUE值分别比未平茬处理增加了0.45和0.32倍,而T_r值比未平茬处理降低了0.02倍。[结论] 平茬后次年生长季内,留茬高度15 cm的平茬小叶锦鸡儿具有较强的生长补偿和光合能力,留茬5,10和20 cm植株的生长补偿和光合能力次之,留茬25 cm植株的生长补偿和光合能力最弱。     

黄河下游河岸坡面产流产沙特征及其与汇流路径长度关系

植被和地形是影响坡面侵蚀过程的重要因子,探讨两者交互作用下坡面产流产沙和汇流特征对深入理解坡面侵蚀过程和水土保持具有重要意义。采用模拟降雨试验,探讨不同降雨强度(54和90 mm·h~(-1))、坡度(5°、10°、15°、20°)和植被盖度(0%、15%、30%)下黄河下游河岸坡面的侵蚀产流、产沙特征,并基于水文连通性模型——汇流路径长度指数(Flowlength)探究植被和地形在土壤侵蚀过程中的作用以及汇流长度与产流产沙特征的关系。结果表明:54和90 mm·h~(-1)雨强下,不同植被盖度对径流流速均有减缓作用,而90 mm·h~(-1)雨强下30%盖度的减缓作用较为明显;径流总量和径流深随坡度和植被盖度增加而逐渐减少的变化基本一致,随雨强增加,受坡度影响逐渐增大。54 mm·h~(-1)雨强下,当坡度15°时,侵蚀产沙量随坡度增加增幅较小;当坡度15°后,侵蚀产沙量增幅较大。90mm·h~(-1)雨强下,当坡度15°时,侵蚀产沙量随坡度增加而增加;当坡度15°后,其随坡度增加而减少。相关分析表明,坡度对产沙量、产流量和径流深均具有显著影响,显著水平分别为P 0.001、P 0.01和P 0.05;植被盖度仅对平均流速影响显著(P 0.05)。但植被盖度对汇流路径长度影响极为显著(P 0.001),裸坡的汇流路径长度明显大于植被覆盖坡面;坡面产流产沙量随汇流路径长度的增加基本呈增加趋势。在坡度和植被盖度交互作用下,坡面产流所引发的土壤侵蚀效应受坡度影响较为明显,而在汇流过程所引发的土壤侵蚀效应中,植被的影响明显大于坡度。     

人工模拟降雨条件下花岗岩红壤坡面侵蚀过程与特征分析简

通过室内人工模拟降雨试验,研究降雨强度、坡度及地表覆盖3因素对花岗岩红壤坡面侵蚀过程的影响.结果表明：1）起始产流时间随降雨强度和坡度的增加而有所提前,而地表覆盖能延缓起始产流时间;2）在不同降雨强度和坡度条件下,径流率从产流初期开始都快速增加,7 ～ 10 min后达到稳定,且随着降雨强度和坡度增加,径流率也显著增加;3）随着降雨强度的增大,产沙率明显增大,且降雨强度越大,坡度对产沙率的影响越明显;4）降雨强度和径流总量、产沙总量之间相关性极显著,其相关系数分别为0.892和0.799;5）地表覆盖具有良好的减沙作用,其减沙效益超过90％.     

河岸植被对坡面径流侵蚀产沙的阻控效果

河岸植被在流域水土保持与非点源污染控制方面具有重要作用。为探究河岸植被阻控坡面径流侵蚀产沙效果及其影响因素,该文通过野外模拟径流冲刷试验,定量分析了北江干流河岸植被阻控坡面径流和侵蚀产沙的特征,探讨了河岸植被对径流与泥沙相互关系的影响以及河岸植被阻控效果与坡度和放水强度的关系。结果表明,(1)植被的存在延迟了坡面初始产流时间、降低了坡面径流系数、减弱了径流侵蚀力,放水强度和坡度越大,坡面产流时间越早、径流系数越大、植被对径流的拦截效果越低,其中,植被对不同坡度上径流系数的平均阻控效果分别为3.35%、3.36%、4.28%和3.17%,对不同放水强度下径流系数的平均阻控效果分别21.69%、17.40%和10.01%,对坡面径流侵蚀力的阻控效果分别为60.00%、32.23%、27.29%和22.76%;(2)植被坡对坡面累积泥沙量的阻控效果分别为60.14%、32.83%、24.19%和20.86%,植被的存在可以有效提高土壤的抗侵蚀能力并减少侵蚀产沙量和降低侵蚀泥沙中值粒径,植被阻控泥沙的效果大于其阻控径流的效果;(3)相关性分析表明,产流时间与累积泥沙量、粒径均呈显著负相关,植被的存在一定程度上改变了退流时间与两者之间的关系;径流系数、径流侵蚀力与累积泥沙量、粒径均呈显著正相关;植被对累积泥沙量和径流侵蚀力的阻控效果与随坡度和放水强度的增加而降低。综上,河岸植被对坡面径流和泥沙具有不同的阻控效果,且受坡度和放水强度影响显著,研究结果可为流域水土保持与河岸植被建设提供支持。     

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.