不同时期施钾对甘薯光合产物运转动力的调控

【目的】通过甘薯不同时期施用钾肥的大田试验,探讨不同时期施用钾肥对甘薯光合产物运转动力的调控效应。【方法】选用典型的食用型甘薯品种"北京553",以硫酸钾(K2SO4)为供试肥料,于2011 2012年2个生长季在山东农业大学农学试验站进行大田试验。试验处理为:不施用钾肥(CK)、全部钾肥基施(JS)、全部钾肥封垄期追施(FS)和全部钾肥高峰期追施(GS)。分析不同时期施用钾肥对功能叶光合产物的输出能力、运输茎的农艺特性、源-库间光合产物运输的渗透动力(茎顶-基部间碳水化合物、氨基酸和K+浓度梯度)及块根中光合产物积累特性的影响。【结果】施用钾肥可显著提高块根鲜薯产量和干重,提高块根膨大速率,其中,基施和封垄期追施钾肥处理增幅较大。基施钾肥显著降低生长前期(栽秧后50 d左右)功能叶碳水化合物含量和蔗糖/淀粉比值,提高生长中后期(栽秧后110 d、170 d左右)功能叶中蔗糖和蔗糖/淀粉比值,增幅分别为10.01%和27.14%(2011),16.16%和61.57%(2012),提高该时期功能叶蔗糖的输出能力。基施还提高生长前期基部茎粗,两年增幅均在20%以上,增大光合产物运输的横截面积;基施和封垄期追施钾肥处理提高生长中后期分枝数,基施处理两年增幅的均值为36.53%和48.44%,封垄期追施的为19.60%和46.17%;同时,降低生长中后期源-库距离,提高有效距离(51—200 cm)所占比例。茎顶部到基部间氨基酸和K+浓度逐渐降低,施用钾肥能提高该浓度梯度的降幅,提高渗透动力,以基施和封垄期追施效果较好,其中,氨基酸浓度两处理的平均增幅分别为87.58%和39.56%,K+浓度的平均增幅分别为272.81%和75.58%。基施钾肥显著降低生长前中期茎基部蔗糖和淀粉含量,基施和封垄期追施钾肥可显著降低生长后期茎顶部和基部蔗糖含量,同时降低淀粉含量。【结论】施用钾肥可减少生长前期功能叶中淀粉的合成,保证块根中光合产物的充足供应,扩大运输通道的横截面积,提高茎部运输的渗透动力促进茎基部光合产物的卸载,及时形成较强的库,提高生长中后期功能叶蔗糖含量和可运输态(蔗糖)的比例,增加光合产物运输通道数量,降低运输距离,提高运输有效性,并提高茎部运输的渗透动力,促进茎基部光合产物卸载,促进块根的膨大,形成高产。在本试验条件下,基施钾肥处理最优。     

低钾胁迫下不同钾效率甘薯的钾吸收利用规律研究

以钾高效品种徐薯28和低效品种济薯22为材料,采用室内土培试验研究了不同施钾量下,甘薯钾的积累与分配及利用规律。结果显示:不施钾显著促进甘薯地上部生长,抑制块根膨大,但品种间变幅不同,钾高效型徐薯28具有更强的根系膨大能力。徐薯28苗期地上部钾浓度显著高于济薯22,叶片和叶柄钾含量分别比济薯22高33.1%、33.9%;但收获期徐薯28植株钾含量为8.7 g/kg,显著低于济薯22的9.8 g/kg。施钾或不施钾下,收获期徐薯28钾分配系数分别为4.2、3.2,济薯22分别为2.0、1.5,表明徐薯28将钾更多分配到块根部分,而济薯22更多分配到茎叶部分。各处理的块根钾利用效率(KIUE-T)为65.1~135.9,施钾及不施钾下,徐薯28块根钾利用效率都显著高于对应的济薯22处理。甘薯植株内钾含量高低是决定济薯22及徐薯28钾利用效率高低的关键因素。因此,两甘薯基因型间钾的利用效率差异主要体现在:徐薯28即使在不施钾下,苗期地上部尤其是茎叶能维持较高的钾含量,为后期块根膨大奠定基础,而收获期维持较高的钾分配系数及植株较低的钾浓度,而济薯22则相反。     

盐分胁迫对不同品种甘薯苗期离子吸收和分配的影响

选取3种类型共6个甘薯品种(阜薯062-20,浙紫1号,徐薯18,白尾稍,烟薯25,徐菜1号),比较NaCl(0、85 mmol/L)处理20 d后,盐分对甘薯幼苗离子吸收和分配的影响。结果表明:盐分胁迫抑制甘薯幼苗的生长,以阜薯062-20、浙紫1号、徐薯18受影响相对较轻。盐分胁迫下植株大量积累Na+和Cl-,并抑制Ca2+和K+的积累;地上部Na+、Cl-的积累量明显高于根系。白尾稍、烟薯25、徐菜1号Na+和Cl-含量显著高于其他品种。NaCl处理下,阜薯062-20、浙紫1号、徐薯18甘薯幼苗的K+/Na+略高于白尾稍、烟薯25、徐菜1号;品种间Ca2+/Na+差异不大,但阜薯062-20、浙紫1号、徐薯18的SCa,Na较高。因此,6个甘薯品种中,阜薯062-20、浙紫1号、徐薯18苗期耐盐性表现更好。     

氮肥施用量对甘薯产量和品质性状的影响

【目的】氮是影响作物产量和品质性状的重要因素,合理施氮是提高作物产量和改善品质的主要途径。研究施氮量对甘薯块根产量形成、营养品质和淀粉糊化特性的影响,对于明确江苏徐淮地区甘薯种植的适宜施氮量具有重要意义。【方法】本文选用淀粉型甘薯品种徐薯22和兼用型甘薯品种徐薯28为试验材料,设置5个施氮水平0、60、120、180、240 kg/hm2。调查了甘薯不同生育期的叶面积指数、光合势、干物质积累和产量构成要素,采用分光光度法测定了块根主要营养品质指标,利用Tech-master型RVA快速测定淀粉谱粘滞特性,分析明确施氮量对块根主要品质指标和淀粉糊化特征值的影响。【结果】施氮N 60 kg/hm2增加了各生育期甘薯的叶面积,提高了甘薯的光合势,显著增加了块根产量(徐薯28增产16.38%,徐薯22增产9.31%),过量施氮(N 240 kg/hm2)则产量降低。施氮并未显著降低块根中的淀粉和直链淀粉含量,但明显增加了可溶性糖和蔗糖含量。施氮显著提高最高粘度、最低粘度、最终粘度和消减值。相关分析显示,直链淀粉含量与最高粘度值和崩解值呈极显著或显著负相关(相关系数分别为-0.90**和-0.71*);直链淀粉含量与消减值呈显著正相关(相关系数为0.73*)。【结论】综合考虑甘薯的产量和品质,在本实验条件下甘薯较为适宜的氮肥用量约为60 kg/hm2。     

有机多肽酶活性促进剂施用方式对鲜食型甘薯干物质积累分配、产量及品质的影响

为探究有机多肽酶活性促进剂对鲜食型甘薯产量和品质的调控效应,在大田条件下,以鲜食型甘薯品种龙薯9号和苏薯8号为供试材料,每个品种设置全生育期不喷施有机多肽酶活性促进剂(CK)、有机多肽酶活性促进剂栽插前蘸根+栽后40 d叶面喷施(P1)和有机多肽酶活性促进剂栽插时灌根+栽后40 d叶面喷施(P2)3个处理,研究其对鲜食型品种干物质积累分配、产量及品质的影响。结果表明,2个品种的P1和P2处理生长中后期叶片的磷酸蔗糖合成酶(SPS)活性、蔗糖含量、收获期植株总干重和块根干重均显著高于CK。龙薯9号各处理收获期的侧枝茎和块根干物质分配比例均无显著差异,P1和P2处理的主茎下部叶、主茎下部茎干物质分配比例均显著低于CK;苏薯8号P2处理的主茎下部叶、主茎下部茎、侧枝茎和侧枝生长点干物质分配比例均显著低于CK和P1处理,块根干物质分配比例显著高于CK和P1,分别提高8.98%和6.23%。龙薯9号P2处理收获期块根可溶性糖含量与P1无显著差异,但显著低于CK,降低5.22%,P2处理的块根淀粉含量显著高于CK和P1,分别提高18.76%和9.23%,干率与P1处理无显著差异,但均显著高于CK,分别提高4.56%和5.71%;苏薯8号块根的可溶性糖含量各处理无显著差异,且P2处理的块根淀粉含量和干率与P1均无显著差异,但显著高于CK,其中淀粉含量提高6.13%,干率提高4.51%。2个品种P2处理的块根产量均显著高于CK和P1,其中龙薯9号分别提高30.46%和14.42%,苏薯8号分别提高27.72%和11.69%。综上,施用有机多肽酶活性促进剂有利于提高鲜食型品种块根产量和淀粉含量,其中P2处理增产幅度最高,其对可溶性糖含量的调控存在品种间差异。本研究为鲜食型甘薯提质增效和生态种植技术提供了理论依据。     

钾素对食用型甘薯糖代谢相关酶活性的影响

为了探讨钾素提高甘薯块根可溶性糖含量的生理基础。选用典型的食用型甘薯品种北京553,设置不同施钾处理,于2009～2010年2个生长季在山东农业大学农学试验站进行试验。采用甘薯块根膨大过程中定期取样的方法,测定块根可溶性糖和淀粉含量及相关酶活性、功能叶蔗糖含量及相关酶活性。结果表明,与对照比较,施用钾肥能显著提高块根产量、可溶性糖及各糖组分含量,其中K2O用量为24 g/m2处理增幅最大,为最适用量。进一步研究发现,适宜供钾处理显著提高了功能叶磷酸蔗糖合成酶活性和蔗糖含量,生育期内平均增幅分别为10.31%和34.13%,同时提高了块根中蔗糖合成酶、不溶性酸性转化酶的活性,生育期内平均增幅为16.47%和3.66%,在提高源端光合产物供应的同时促进蔗糖在库端的卸载,促进块根中淀粉和可溶性糖的积累;适宜供钾处理还提高了块根中-和-淀粉酶的活性,生育期内平均增幅分别为26.06%和14.64%,促进淀粉向可溶性糖转化。此外,适宜供钾处理还显著提高了生长前期和后期块根中可溶性酸性转化酶活性、以及生长后期块根中蔗糖-蔗糖果糖基转移酶活性,促进了葡萄糖、果糖和果聚糖在块根中的积累。在甘薯收获期,块根可溶性糖和淀粉含量分别提高了13.52%和3.02%。即钾肥能够增加块根中蔗糖的供应量、促进块根对蔗糖的吸收、促进淀粉水解,是其提高块根可溶性糖含量的生理原因。     

钾肥基施利于甘薯块根产量的形成

【目的】 研究不同施钾方法对甘薯块根产量形成的影响,可为甘薯高产稳产寻找合理的钾肥施用方法,并阐明其增产机理。【方法】 选取典型的食用型甘薯品种红香蕉和北京553为试材,于2013~2014年两个生长季在山东农业大学农学试验站进行田间试验。设4个施钾处理:不施钾肥（CK）、全部钾肥基施（JS）、全部钾肥封垄期追施（FS）、基施钾肥和封垄期追施钾肥各占50%（1/₂ JS+1/₂ FS）。在主茎第4、5片展开叶上标记13CO₂,24、48和96 h后取样,用质谱仪（Isoprime 100）测定不同部位的13C含量。从甘薯栽秧后50 d开始,每隔20 d取样直到收获。按根、茎、叶、柄四部分分别称重,将主茎自功能叶所在位置至基部等分为三段,取上、下两端用于测定蔗糖含量。收获期测定生物产量和块根产量,计算经济系数。【结果】 甘薯施用钾肥能显著提高生物产量、经济系数和块根产量,增产21.33%~34.38%。各施钾处理之间比较,生物产量差异不显著,经济系数和块根产量差异显著,其中基施钾肥处理的经济系数和块根产量最高。栽秧后50 d,基施钾肥处理植株干物质积累量和功能叶光合产物在块根中的分配率都显著高于其他施钾处理。栽秧后50 d和110 d,基施钾肥处理光合产物源端装载和库端卸载的效率显著高于其他处理,栽秧后150 d,所有施钾肥处理趋于一致。栽秧后50 d,基施钾肥处理光合产物转运效率显著高于其他施钾处理,栽秧后100 d和150 d,施钾肥处理间效果趋于一致。在栽秧后50~130 d,基施钾肥处理的块根膨大速率一直高于其他施钾处理。【结论】 在相同供试土壤和气候条件下,钾肥施用时间越早,越有利于甘薯早发、快长,促进块根早形成、快膨大;光合产物由叶片向块根运转效率的高值持续期越长,越有利于提高光合产物在块根中的分配。因此,全部钾肥基施甘薯经济系数和块根产量最高,是最经济有效的施肥方法。     

低温对缺钼冬小麦幼苗生长的影响Ⅰ.对糖代谢的影响

对三叶一心的缺钼冬小麦进行 24h低温处理 (- 5℃～ 0℃ )后 ,冬小麦幼苗出现缺钼症状 ,并迅速波及整个植株 ,下部叶片尤为严重。缺钼及低温对幼苗地上部、根干重无明显影响 ;但经低温处理的冬小麦幼苗叶片色素含量下降 ,以叶绿素a +b减少最为明显 ;缺钼植株上部叶片在低温处理到 24h时 ,K+渗漏速率出现最大值 ,下部叶片在 9h时即达到高峰。常温下 ,供钼能提高冬小麦功能叶 (倒二叶 )可溶性总糖、蔗糖含量 ,同时使倒三叶中可溶性总糖、蔗糖含量也保持在较高水平 ;低温条件下 ,供钼植株倒三叶、功能叶可溶性总糖、蔗糖含量明显降低 ,缺钼植株功能叶糖含量下降 ,但倒三叶含量上升     

氮钾配施对甘薯茎叶生长、产量形成及干物质分配的影响

研究氮钾配施对甘薯生长发育、产量形成及干物质分配的影响,为甘薯安全高效施肥提供理论依据。以鲜食型甘薯品种"泰薯14"为材料,设置不同氮钾肥配比,探讨不同氮钾肥配比对甘薯茎叶生长、产量及其形成、干物质积累与分配等指标的影响。结果表明:氮、钾用量分别为9、18 g/m~2(N1K1)处理能够显著增加甘薯单株结薯数和单薯重,提高甘薯块根膨大速率,从而提高甘薯块根产量。施钾处理K1甘薯块根产量、块根膨大速率、商品薯率、单株结薯数和单薯重均高于单施氮肥处理,N1K1处理甘薯产量、单株结薯数和单薯重最高,氮钾肥配施可以缓解甘薯茎叶旺长的趋势,降低甘薯茎叶与块根重量比值,提高干物质向块根的分配,N1K1处理效果最显著。本试验N1K1处理为最佳氮钾肥配比,能够促进甘薯地上部与地下部协调生长,促进甘薯快速膨大,提高甘薯块根产量。     

长期施用磷肥对甘薯主要品质性状与淀粉RVA特性的影响

选择4个不同淀粉类型甘薯品种为材料,以1980年建立的砂壤质潮土土壤肥力与肥料效益长期监测基地（徐州点）的长期肥料定位试验为研究平台,研究了对照（CK）、氮钾处理（NK）与氮磷钾处理（NPK）3种处理下对甘薯主要品质性状和RVA特性的影响。结果表明,施磷处理增产效果显著（F=7.45, P 0.01）,徐薯18增幅最大,达45.49%;而且有利于甘薯块根内干物质积累,4个品种干率表现为NKP＞NK;淀粉量差异都呈显著或极显著水平（F=4.28,P0.01）,其中,徐薯18和徐薯22增幅分别达57.89%和60.1%。施磷对有利于甘薯蛋白质的积累,以豫薯10增幅最大,达37.89%;但甘薯块根含糖量(可溶性糖与还原糖)出现不同程度下降趋势。4个品种甘薯淀粉RVA谱表现为典型的Ａ型或C型特征,长期施磷（NPK）处理与NK处理间对比）甘薯淀粉RVA特征谱参数差异存在明显差异,4个品种最高粘度值（PKV）差异明显（F=10.26,P0.01）;徐薯18最低粘度值（HPV）差异极显著水平,其它处理差异程度不一;徐薯18、徐薯25最终粘度（CPV）差异呈极显著水平,豫薯10呈显著差异;徐薯18、徐薯22崩解值（BDV）差异显著,豫薯10回复值（CSV）呈极显著差异。4个品种在各处理下出峰时间与糊化温度差异都不明显。     

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.