不同供钾水平对胡麻花后干物质转运分配及钾肥利用效率的影响

以胡麻坝选3号为材料,设置不施钾、低钾(18.75 kg K2O·hm-2)、中钾(37.5 kg K2O·hm-2)和高钾(56.25 kg K2O·hm-2)4个施钾(K2O)水平,于2011年-2012年在河北省张家口市开展田间试验,研究了不同施钾量对胡麻花后干物质转运分配及钾素利用效率的影响。结果表明,胡麻不同生育阶段各器官干物质的积累、转运和分配趋势基本一致,其变化量与施钾量有密切关系。不同施钾水平下,胡麻单株干物质总积累量呈现"先升后降"的变化趋势,且中钾水平下不同生育阶段干物质总积累量最大,较不施钾、低钾和高钾处理分别高出10.41%~42.93%、8.24%~35.78%和7.34%~31.71%。叶和茎是胡麻花后干物质积累的主要器官,分别占全株干物质量的29.85%~37.24%、32.11%~56.78%。现蕾期干物质在叶部和茎部的分配率分别为23.12%~29.92%和61.17%~72.76%,到子实期分别下降到8.35%~14.09%和42.67%~49.33%,转运到籽粒中的干物质量为全株的4.11%~15.58%。各器官中,主茎干物质输出最多,转运率高达11.23%~33.37%。与不施钾相比,施钾处理下籽粒产量增加14.90%~30.11%,其中,中钾处理的钾肥农学利用率、钾肥偏生产力和钾肥吸收利用率最高,分别为14.80~17.15kg·kg-1、41.16~64.44 kg·kg-1和61.49~65.21kg·kg-1。综合籽粒产量和钾肥施用效果,施钾量为37.5kg·hm-2为胡麻实现高产和高效的最优施肥模式。     

灌溉量和施氮量对油用亚麻茎秆抗倒性能及产量的影响

为明确灌水和施氮对油用亚麻(Linum usitatissimum L.)抗倒伏能力和产量的影响,以‘陇亚杂1号’为材料,于2012—2013年以灌溉量为主处理(W1:2 700 m3·hm-2;W2:3 300 m3·hm-2),施氮量为副处理[纯氮量分别为N0:0 kg·hm-2(CK);N1:37.5 kg·hm-2(低氮);N2:112.5 kg·hm-2(中氮);N3:225 kg·hm-2(高氮)],研究灌溉量和施氮量对与油用亚麻抗倒性能相关的形态学特性、茎秆强度、抗倒伏指数及茎秆化学组分含量、产量构成因子及产量的影响。结果表明,随灌溉量的增加,茎秆强度和抗倒伏指数下降,株高增加,重心上移,茎粗、茎壁厚度降低,地上部干重增加,根干重减少,根冠比下降,同时茎秆中纤维素、木质素、可溶性糖和淀粉的含量下降;随施氮量的增加,茎秆强度和抗倒伏指数先升高后降低,株高和重心高度增加,茎粗、茎壁厚度、根干重和根冠比先增后减,地上部干重增加,茎秆中各化学组分含量及产量也先增加后降低。进一步分析发现抗倒伏指数与茎秆强度、茎粗、茎壁厚度、根干重、根冠比、纤维素含量、木质素含量、可溶性糖含量及淀粉含量均呈正相关关系,与株高、重心高度、地上部干重呈负相关关系。低灌水处理(W1)的茎秆强度、抗倒伏指数和产量分别比高灌水处理(W2)高30.55%、41.06%和0.53%,过多灌水不利于油用亚麻茎秆抗倒伏性能和产量的提高;中氮处理(N2)的茎秆强度分别比不施氮(CK)和高氮(N3)处理高36.8%和3.95%,产量分别高15.9%和0.8%,可见油用亚麻的栽培中施氮量不能过高或过低。因此,生产上采用适宜的灌溉量和施氮量是防止油用亚麻倒伏、获得高产、提高生产效益的重要措施。在本试验区,同等肥力土壤条件下,以灌溉量2 700 m3·hm-2和纯施氮量112.5 kg·hm-2为宜。     

多效唑叶喷施对胡麻抗倒伏能力和籽粒产量的影响

倒伏是影响胡麻高产优质的因素之一,有效防止倒伏是目前胡麻生产上亟待解决的问题。在大田试验条件下,喷施清水作对照(A0),研究了胡麻现蕾期和盛花期叶面喷施多效唑50 mg·L^(-1)(A1)、100 mg·L^(-1)(A2)、150 mg·L^(-1)(A3)对籽粒产量和抗倒伏相关性状的影响。结果表明:多效唑叶面喷施可以明显降低胡麻的株高和重心高度,全生育期分别降低了8. 91%和10. 6%。胡麻植株茎粗在青果期达到最大值,其中A3处理的茎秆最粗,较A0处理显著增加24. 3%。在胡麻现蕾期,各处理的茎秆壁厚最大,此后逐渐递减,A1处理在青果期和成熟期的壁厚最大,比A0处理显著增加11. 8%和14. 9%。A2处理对胡麻青果期和成熟期茎秆抗倒伏指数的影响较大,较A0处理分别显著增加30. 0%和25. 3%。相关分析表明,胡麻青果期株高、重心高度与茎秆抗倒伏指数呈显著、极显著负相关关系,而成熟期壁厚和茎粗与茎秆抗倒伏指数有极显著、显著正相关关系。胡麻茎秆中木质素和纤维素含量随着胡麻生育时期的顺延表现出逐渐递增的趋势,成熟期茎秆中木质素和纤维素含量以A2处理的最多,分别较A0处理增加12. 3%、8. 43%。不同浓度多效唑处理下胡麻的籽粒产量从高到低的顺序依次为A2> A3> A1,A1、A2、A3增产率分别为10. 0%、17. 9%和13. 9%。综合分析,在本试验条件下100 mg·L^(-1)多效唑是最佳喷施浓度,在增产的同时可以有效地增强胡麻的抗倒伏能力,是较适宜的防倒增产栽培措施。     

施钾量对川中丘陵区春玉米基部节间特性及抗倒伏能力的影响

为探明提高川中丘陵区春玉米抗倒伏能力的适宜施钾量,2013—2014年开展田间试验,采用单因素随机区组设计,设置5个施钾量：0、45、90、135和180 kg·hm-2,测定吐丝期和灌浆期玉米基部节间物质积累特征、化学组分、力学指标、倒伏率以及籽粒产量。结果表明,相比无钾肥处理,施钾处理增产1.19%～8.43%(2013年)、1.75%～9.19%(2014年),植株倒伏率降低11.11%～44.44%(2013年)、12.50%～52.10%(2014年)。玉米倒伏率与吐丝期和灌浆期基部第2节至第5节的硬皮穿刺强度、茎秆压碎强度、茎秆折断强度和纤维素含量呈显著负相关,与吐丝期基部第2节至第3节的鲜重和鲜密度、灌浆期基部第2节至第5节钾含量呈显著负相关,与灌浆期基部第2节至第5节可溶性糖含量和淀粉含量呈显著正相关。施用钾肥能提高玉米茎秆基部第2节间至第5节间的鲜重和干重。基部第2节至第5节的纤维素含量、硬皮穿刺强度、茎秆压碎强度和折断强度随着施钾量的增加呈现先增加后下降的趋势,其中钾肥用量为90 kg·hm-2时的数值最大。综上所述,施用95.0～121.0kg·hm^-2...     

增密扩行对宽幅匀播胡麻抗倒伏能力及籽粒产量的影响

为进一步提高旱作农业区胡麻(Linum usitatissimum L.)抗倒伏能力和籽粒产量，本研究以胡麻品种定亚26为试验材料，于2021年通过田间裂区试验，研究了宽幅(10 cm)播种技术下增密(750、850和950粒·m^-2)扩行(15、20和25 cm行距)对胡麻抗倒伏性和产量的影响。结果表明，随着胡麻种植密度的增加，植株株高和重心高度均增大，850和950粒·m²分别较常规播种密度(750粒·m²)平均增加8.96%和9.13%，茎粗、单株鲜重、茎秆强度、抗折力和抗倒伏指数分别降低9.58%、18.08%、11.11%、34.30%和22.46%，差异达显著水平。在950粒·m^-2密度水平下，与常规条播相比，宽幅匀播有利于缓解胡麻株高的快速增长，增大茎粗，增强茎秆抗倒伏能力，其中10 cm幅宽处理下15和20 cm行距青果期茎秆强度、抗折力、抗倒伏指数分别提高1.71%和10.67%、6.58%和19.30%、13.62%和20.71%，且差异达显著水平；籽粒产量显著高出19.85%～...     

磷钾配施对基质栽培番茄品质、产量及养分积累的影响

为探明基质栽培番茄合理的磷钾用量,改善番茄品质,提高肥料利用率,采用周年栽培、二因素裂区设计的方法,研究了不同磷水平(P1:303.8,P2:258.2,P3:212.6 kg hm-2)和钾水平(K1:810.0,K2:745.2,K3:680.4,K4:615.6 kg hm-2)配比对设施番茄品质、产量及基质微生物的影响。结果表明:与常规施肥量处理(P1K1)相比,磷钾配施能够提高番茄产量,改善品质;在各施肥处理中,P3K3处理产量最高、达146.8 t hm-2,较对照P1K1处理增产10.62%。品质指标Vc含量以P3K2处理为最高,为32.98mg 100 g-1;而番茄红素含量以P3K3处理最高,为7.42 mg 100 g-1,且处理间差异显著。与常规施肥量处理(P1K1)相比,磷钾肥减量配施处理的基质细菌数明显增多、细菌/真菌比值上升。此外,磷钾配施对果实养分积累量依次表现为N> P> K,且肥料利用率显著提高,磷肥利用率和钾肥利用率增幅分别为7.78%～23.74%和0.69%～19.19%.综合品质、产量和肥料利用率等指标,可以认为P3K3处理(P2O5212.6 kg hm-2+K2O 680.4 kg hm-2)效果最佳。研究结果可以为基质栽培番茄合理施肥提供参考依据。     

氮磷钾肥用量对紫云英产量效应的研究

采用"3414"肥料效应试验设计方案对紫云英氮、磷、钾肥施用效应及养分的交互作用进行了研究,结果表明:与不施肥处理(CK)相比,13个施肥处理紫云英鲜草平均增产21.1 t·hm-2,平均产量为不施肥处理的2.35倍;分别固定磷(P2O5 60 kg·hm-2)、钾(K2O 60 kg·hm-2)肥,氮(N75 kg·hm-2)、钾(K2O 60 kg·hm-2)肥和氮(N 75 kg·hm-2)、磷(P2O5 60 kg·hm-2)肥用量,在施N 0～112.5 kg·hm-2,P2O5 0～90 kg·hm-2和K2O 0～90 kg·hm-2范围内,紫云英产量随相应肥料用量的增加而显著提高,N、P、K各养分施用的最高增产率分别为65.0%、27.8%和44.5%;从养分效率看,中量水平的氮(N 75.0 kg·hm-2)、磷(P2O5 60 kg·hm-2)和低量水平的钾(K2O 30 kg·hm-2)增产效果最好;氮、磷、钾肥之间存在一定的交互作用,互相影响肥效的发挥,中量水平的养分用量(N 75.0 kg·hm-2、P2O5 60 kg·hm-2和K2O 60 kg·hm-2)有利于各养分效果的发挥.结果说明,施肥对紫云英增产效果明显,氮、磷、钾肥用量和配比是影响紫云英产量的重要因素.     

基于RCSODS的东南沿海水稻施肥量决策

应用RCSODS模型,根据东南沿海福建稻区8个代表县(市)的土壤理化性状和水稻生长期气温资料,模拟计算了各地稻田的土壤供肥量;结合主栽品种的目标产量和肥料利用率,模拟计算了早晚稻的合理施肥量。结果表明:在研究区域土壤有机质含量与全氮含量适中,磷、钾含量普遍偏低以及土壤偏酸性的情况下,要实现水稻现有水平的目标产量,早稻需施纯氮56.98~231.85kg.hm-2,其中大部分稻田需施133.9~231.85kg.hm-2;需施磷肥(P2O5)73.28~173.57kg.hm-2,其中缺磷稻田需施132.69~173.57kg.hm-2;需施钾肥(K2O)15.41~257.63kg.hm-2。晚稻需施纯氮64.63~237.93kg.hm-2,大部分稻田需施纯氮167.77~237.93kg.hm-2;需施磷肥(P2O5)88.76~176.72kg.hm-2,其中缺磷的稻田应施磷肥(P2O5)155.38~176.72kg.hm-2;需施钾肥(K2O)50.41~315.96kg.hm-2。比较福建稻区的实际施肥量与模拟施肥量,可以看出:目前氮肥施用量总体上比较适宜,而磷肥和钾肥施用量则明显不足。     

不同类型生态区稻-稻种植制度中钾肥效应及钾素平衡研究

研究了在丘陵生态区和洞庭湖生态区稻-稻种植制度中钾肥对水稻产量和钾肥效应及钾素平衡的影响。结果表明,在施钾量为0、112.5、150和187.5K2O kg hm-2的条件下,在丘陵生态区红黄泥田上,150K2O kg hm-2的施钾水平已达到较高的产量;洞庭湖生态区的紫潮泥田中缓效钾与速效钾含量均较高,目前施钾效应不明显。两种类型生态区土壤上施用氮肥的增产效果明显地大于施用钾肥。丘陵生态区红黄泥田上的3个施钾处理两季水稻吸收来自肥料钾的百分数比例均高于洞庭湖生态区的紫潮泥田。丘陵生态区红黄泥田上的3个施钾处理早稻钾素利用率平均为35.0%,晚稻为51.8%;洞庭湖生态区紫潮泥的3个施钾处理早稻钾素利用率平均为27.1%,晚稻为42.6%。肥料氮的利用率随钾肥施用量的增加而提高,这一趋势在晚稻上更为明显。在每季水稻施钾量为112.5、150、187.5 K2Okg hm-2的条件下,钾素平衡出现亏缺。在早稻施氮量165N kg hm-2(丘陵生态区),150N kg hm-2(洞庭湖生态区)和晚稻施氮量180N kg hm-2的条件下,两种类型生态区土壤上的氮素平衡中氮均出现盈余,且氮素盈余量随钾肥用量的增加而下降。     

不同施钾处理对棉田土壤钾素形态与土壤肥力的影响

选取长江流域棉区2个土壤肥力不同的试验地点,研究施钾量与施钾时期对棉田土壤钾素形态与土壤肥力的影响。结果表明:随一次性基施钾量的增加,2个试验点土壤水溶性钾、非特殊吸附钾、特殊吸附钾和缓效钾含量均显著增加,矿物钾含量变化不显著;土壤速效氮和速效磷含量降低,土壤有机质、全氮与全磷含量没有明显变化。增施钾肥促进土壤脲酶、转化酶和磷酸酶活性提高,但高钾处理(300kg K2O/hm2)显著抑制其活性,施钾对过氧化氢酶活性没有影响。施钾显著提高植株钾素累积量、生物量及皮棉产量。在150kg K2O/hm2施钾量下,分期施钾处理(50%基施+50%初花期追施)的土壤养分、酶活性以及皮棉产量均与一次性基施处理没有显著差异;而在300kg K2O/hm2施钾量下,分期施钾处理各项指标均显著高于一次性基施。2个试验点均以基施150kg K2O/hm2+追施150kg K2O/hm2处理土壤肥力与棉花产量最高。     

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.     

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.     

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.