鲜食葡萄的硅肥施用效应及其安全评价

通过两年(2015~2016年)田间小区试验,比较研究了水淬渣硅肥与钢渣硅肥对无核紫和红地球葡萄生长、产量、果实丙二醛(MDA)含量和抗氧化物酶活性及叶片和土壤重金属含量的影响,并分析了土壤环境风险。结果表明,施硅可显著提高土壤有效硅和叶片含硅量(P0.05),收获期两种硅肥处理的土壤有效硅和叶片含硅量分别比CK处理提高9.9%~13.0%和28.4%~41.7%;施硅处理均显著提高了两种葡萄叶片干物质量、厚度和产量(P0.05),其中水淬渣和钢渣硅肥处理的葡萄产量较CK处理分别提高15.5%和11.1%;硅肥处理较CK处理可提高葡萄果实超氧化物歧化酶(SOD)、过氧化物酶(POD)等抗氧化酶活性,降低MDA含量,但各处理间差异不显著(P0.05)。两种钢渣硅肥施用均对土壤重金属含量无显著影响;对葡萄叶片中Cu、Hg含量无显著影响,而As、Cd、Pb和Cr含量均显著降低;各处理土壤重金属综合污染指数均小于1。总之,两种钢渣硅肥施用可提高葡萄产量,降低葡萄叶片重金属含量,且未对土壤环境造成安全风险。其中,水淬渣硅肥效果优于钢渣硅肥。     

长期施用不同有机肥对甘薯产量和土壤生物性状的影响

以花生—甘薯轮作的长期定位试验为研究对象,研究不同(类)有机肥对甘薯产量、土壤微生物丰度和酶活性的影响,为选取合适的有机肥在提高作物产量和改善土壤生物性状方面提供依据。共选取5个施肥处理:(1)CK,空白对照;(2)NPK,单施化肥;(3)NPK+SR,化肥+稻草;(4)NPK+M,化肥+商品有机肥;(5)NPK+P,化肥+猪粪。结果表明:与CK相比,NPK、NPK+SR、NPK+M和NPK+P处理均显著增加鲜薯产量和地上部生物量(P<0.05),其中NPK+P处理效果最好。与CK比较,NPK处理显著降低土壤细菌、真菌、固氮菌和活化有机磷微生物的丰度(P<0.05),而NPK+SR、NPK+M和NPK+P处理在不同程度上缓解了NPK处理对土壤微生物丰度的抑制作用。土壤酶的加权平均值(GMea)在一定程度上可用来评价土壤酶的总体活性。与CK相比,NPK、NPK+SR和NPK+M处理的土壤酶活性显著降低(P<0.05),而NPK+P处理的土壤酶活性有所提高;对于土壤单一酶活性,NPK+P处理与CK比较显著降低土壤脲酶活性(P<0.05),但显著提高酸性磷酸酶、碱性磷酸酶和过氧化氢酶活性。此外,主成分和相关性分析表明,土壤养分和土壤有机碳与鲜薯产量和地上部生物量显著正相关,土壤pH是驱动土壤微生物丰度和土壤酶活性变化的主要因素。因此,长期有机无机肥配施通过提高土壤养分、有机碳含量以及调节土壤pH变化在提高甘薯产量和改善土壤生物性状方面取得良好效果。总体来说,化肥配施猪粪在培肥地力和增产增收方面效果最佳。     

黄土丘陵区微地形梯度下草地群落及土壤对氮、磷添加的响应

为研究N,P添加对草地群落及土壤的影响,试验以黄土丘陵区安塞综合试验站草地群落为研究对象,通过在不同坡向、坡位定量添加N,P营养元素的方法,研究群落地上和地下生物量、叶片和根系及土壤养分的变化特征。结果表明:(1)N处理和N+P处理地上生物量分别比对照(CK)处理增加24.21%和43.92%,而地下生物量分别减小12.19%和8.53%;(2)平均叶片N含量变化趋势为N+P处理N处理CK处理,与CK处理相比分别增加26%和17%;叶片P和K含量增加不显著;CK处理组、N处理组和N+P处理组的平均叶片N/P值分布范围分别为12.58~24.28,16.67~4.82,12.56~23.07,总体趋势为NCKN+P,无显著差异(p0.05);(3)CK处理、N处理和N+P处理根系N含量的取值范围分别为5.20~12.78g/kg,5.42~14.30g/kg,10.16~17.70g/kg,N处理和N+P处理分别增加34.38%和63.45%;根系P含量的取值范围分别为0.22~0.38g/kg,0.38~0.87g/kg,0.63~0.94g/kg,方差分析表明施肥处理组根系P含量显著增加(p0.05);根系K含量没有显著变化;根系N/P比的取值范围分别为26.02~49.94,14.23~20.67,12.46~21.28,施肥处理后根系N/P呈下降趋势;(4)施肥对土壤有机C的影响不显著;土壤全N含量均显著增加(p0.05);土壤全P含量、速效K和N/P比值含量增加,但无显著差异。表明N,P添加能够改善黄土丘陵区土壤养分状况,缓解植物生长的养分限制情况,促进植物其他营养元素的吸收,并使得植物体养分更多分配于地上部分。     

生物炭基肥料对小麦生长、养分吸收及土壤肥力的影响

生物炭基肥料的研制是生物炭在农业应用中的重要方向。通过温室盆栽试验,研究了添加不同数量生物炭制作的肥料施入土壤中对小麦生长发育及土壤肥力的影响。结果表明,(1)小麦生育期内,施用生物炭占辅料75%及以上的处理(NPB3、NPB4)较对照处理均显著提高小麦地上部干重、地下部干重、总干重,其中辅料100%为生物炭(NPB4)的处理均达到显著水平,但各处理对小麦千粒重没有显著影响;(2)生物炭基肥料显著提高了小麦对N、P的吸收,提高幅度顺序为NPB4NPB3NPB2NPB1CK,其中小麦N吸收平均提高了19.07%,P吸收平均提高了15.00%;(3)土壤中有机质含量表现为NPB4NPB3NPB2NPB1CK,且与生物炭添加量呈显著正相关(p0.05);(4)土壤碱解氮和有效磷含量大多呈先降低后升高的趋势,表明生物炭基肥料可持续供给小麦在生长后期对土壤中养分的需求。     

利用牛粪和黑土构建肥沃耕层对沙性土壤有机质及养分含量的短期影响

沙性土壤养分含量偏低,保肥供肥能力差是限制作物产量的最主要因素。本研究以内蒙古赤峰市的典型沙性土壤为研究对象,以未进行肥沃耕层构建的处理(F_0)为对照,分析了不同肥沃耕层构建深度(0～20 cm(D_(20))、0～35 cm(D_(35))和0～50 cm(D_(50)))和构建物料(黑土(F_1)和发酵牛粪(F_2))对沙性土壤有机质及养分含量的短期影响。结果表明,与对照相比,黑土和发酵牛粪中的有机物经过一个生长季的分解后显著提高了沙性土壤的土壤肥力。与F_0处理相比,F_1和F_2处理土壤有机质含量增加了0.98～4.83倍,土壤有机质储量增加了0.43～2.55倍,同时土壤的全氮、速效氮、全磷、速效磷和速效钾含量也表现出不同程度的显著增加(P0.05),说明施用黑土和发酵牛粪能够达到构建沙性土壤肥沃耕层的目的。从肥沃耕层构建物料的培肥效果角度分析发酵牛粪优于黑土;从减少机械成本投入角度分析,0～35 cm为最佳构建深度。建议沙性土壤区域通过施用发酵牛粪或者其他有机物料构建深度为0～35 cm的肥沃耕层,以期提高土壤肥力和农业生产能力。     

再生水盐分在亚热带不同土壤中的迁移特性及其差异

为了合理评价再生水灌溉盐分对土壤环境的影响,分析盐溶液淋溶亚热带土壤流出液盐分变化规律及其对土壤化学性质的影响差异,该文采用定水头入渗法,模拟不同浓度钠盐溶液淋溶黏性潮土、沙性潮土、红壤、紫色土、水稻土等5种亚热带地区土壤,并观测土壤流出液电导率（EC）和pH值的差异。试验结果表明：1）高浓度盐溶液对黏粒含量较高的红壤、紫色土、黏性潮土的穿透能力弱于黏粒含量较低的水稻土和沙性潮土。同等浓度水平处理达到相同的穿透程度,酸性土壤（红壤、紫色土、水稻土）能承受更多的低质水量。2）盐分在土壤中的迁移速度主要由土壤理化性质决定,土壤黏粒含量、交换性铝含量会显著减缓盐分在土壤中的迁移能力,而土壤粉粒含量、EC、pH值以及交换性钙、镁含量会促进盐分在土壤中的迁移。盐分更容易穿透碱性土壤（黏性潮土和沙性潮土）而流出,碱性土壤流出液相对EC最大变化速率比酸性土壤高36%。基于Boltzmann函数拟合表明,入渗水盐浓度及土壤理化性质对模型参数有显著影响（P<0.05）。3）土壤化学性质受入渗液盐分浓度的影响程度不仅与土壤本身的化学性质有关,也与土壤质地中的粉粒、黏粒含量有极显著的关系（P<0.01）。各浓度盐溶液对碱性土壤的pH值影响不明显,对酸性土壤的pH值影响较大,其流出液pH值减少1.6～2.6个单位,其中红壤的pH值变化最大,其次为紫色土。入渗液EC高于4.77 dS/m的处理对土壤流出液的稳定pH值影响增幅不明显。因此,利用低质水灌溉时要依据土壤理化性质合理限定水中盐浓度。     

均衡施肥对滩涂盐碱农田稻麦轮作系统土壤养分与作物生长和养分吸收的影响

以耐盐小麦和水稻为材料,研究了滩涂盐碱地养分均衡对轮作稻麦生长和养分吸收的影响。试验设不施肥(CK)、常规施肥(TF)、中量元素肥料+常规施肥(TS)、螯合态微量元素肥+常规施肥(TM)和中量元素肥料+螯合态微量元素肥料+常规施肥(TSM)5个处理。结果表明:(1)大量元素方面,小麦季TSM处理显著提高了土壤碱解氮和速效钾水平,分别较TF处理增长23.22%和7.10%;水稻季TSM处理土壤有效磷和速效钾显著提高,较TF处理分别提高19.78%和7.44%;稻麦轮作体系均衡施肥(TSM)显著降低了土壤含盐量,由3.09 g/kg土降为1.88 g/kg土;(2)中微量元素方面,小麦季TSM处理显著提高了土壤S、Fe含量,分别较TF处理增长了196.3%、13.75%;水稻季TSM处理土壤Si、Ca、Fe、Mn含量较TF处理显著提高,分别增加了27.42%、11.60%、12.05%、16.20%;(3)TSM处理小麦和水稻生物量明显提高,较TF处理增长了19.47%和20.12%,且TSM处理较TF处理作物养分含量显著提高(P0.05);(4)施肥处理明显提高了稻麦植株中各营养素的积累,作物产量增加,TSM处理小麦和水稻较CK分别增产了14.37%和46.46%,与TF处理相较,小麦增产7.55%,水稻增产效果不显著。综上所述,均衡施肥有效提高了养分库容和养分利用效率,促进了盐碱地轮作稻麦生长和产量形成。因此,在常规施肥的基础上配施中微量元素肥料作为优选的均衡施肥模式可作为滩涂盐土粮食轮作区主要施肥模式加以推广应用。     

不同种类夏绿肥对设施土壤的改良效应

通过盆栽试验研究了3种夏绿肥(羊角豆、柽麻、决明)种植和翻压对设施土壤养分和盐基离子含量的影响,旨在为温室大棚夏季休闲期种植绿肥改良土壤提供科学依据。结果表明:1)种植羊角豆、决明、柽麻60 d后,与对照处理相比,羊角豆、决明、柽麻处理均显著增加了土壤的有效磷含量,增加比例分别为8.6%、13.2%、25.7%;羊角豆和决明处理显著降低了土壤电导率,降低比例分别为25.0%和33.3%,对设施土壤次生盐渍化具有显著的改良趋势。决明、柽麻处理显著降低了(K~++Na~+)/(Ca~(2+)+Mg~(2+)),降低比例分别为17.0%、35.6%,有助于土壤胶体的凝聚和土壤团粒结构的形成。2)绿肥翻压110 d后,与对照处理相比,羊角豆和决明处理电导率变化不显著,柽麻处理显著增加了电导率,增加比例为50.0%。羊角豆、决明、柽麻均显著增加了土壤的速效钾含量,增加比例分别为23.7%、5.7%、9.4%;羊角豆和决明处理显著增加了土壤全氮含量,增加比例分别为17.8%和26.0%;决明、柽麻均显著降低了(K~++Na~+)/(Ca~(2+)+Mg~(2+)),降低比例分别为24.1%、18.5%,表明3种绿肥翻压后,培肥效果显著。3)综合来看,种植绿肥有显著改良土壤次生盐渍化的趋势,而绿肥翻压后培肥效果更为显著。因此,温室大棚夏季休闲期,可通过种植生长周期短、吸附能力强的夏绿肥降低土壤的盐基离子总量,改良土壤,但不宜翻压。3种夏绿肥中,推荐决明作为设施大棚夏季休闲期改良土壤的填闲作物。     

钙、 硼对常山胡柚叶片养分、 果实产量及品质的影响

【目的】研究叶片矿质营养元素含量的季节性变化,对探明植物体中营养元素的丰缺状况、 调控养分代谢、 提高果实产量和改善品质具有重要意义。本研究结合常山胡柚园土壤养分状况,通过连续4年施用钙肥和硼肥,研究钙、 硼对常山胡柚叶片矿质营养元素含量的季节变化、 果实产量及品质的影响。【方法】采用田间定位试验,以13年生枳砧常山胡柚为试验材料,设4个处理,1)CK(对照); 2)Ca(每株0.5 kg生石灰粉); 3)B(每株25 g 硼砂); 4)Ca+B(每株0.5 kg生石灰粉+ 25 g 硼砂)。于试验的第4年采集常山胡柚不同生长期当年生春梢叶片及成熟期果实样品,并对常山胡柚叶片矿质营养元素含量的季节变化、 果实品质进行分析。【结果】常山胡柚叶片各矿质养分在果实逐渐成熟过程中总体呈现先增后降的变化规律,其中叶片氮(N)、 钾(K)、 镁(Mg)和锌(Zn)在果实坐果期达到最大值,磷(P)在果实膨大前中期(8月份)到达最大值,钙(Ca)、 硼(B)、 铁(Fe)、 锰(Mn)和铜(Cu)在果实膨大后期(9月份)出现最高值。钙、 硼肥施用均可提高常山胡柚果实各发育时期叶片Ca、 B、 N、 K、 Fe、 Mn和Cu含量,但明显抑制叶片Zn的吸收,其中钙、 硼配施对成熟叶片(8~9月份)Ca含量存在显著正交互效应,但对提高叶片B含量无显著交互作用。施钙、 硼肥可不同程度提高常山胡柚2年平均产量,增产率达到1.8%~21.4%,其中各处理增产率顺序为Ca+B＞B≥Ca,且单施硼可显著提高2年累积产量,钙硼配施对单年产量、 2年平均产量均存在显著正交互效应。钙、 硼肥单施对果实品质无显著性影响,但钙硼配施可显著降低可滴定酸含量,显著提高固酸比。【结论】常山胡柚坐果期(4月份)为叶片N、 P、 K、 Mg和Zn吸收的关键时期,果实膨大期(8~9月份)为叶片Ca、 B、 Fe、 Mn和Cu吸收的重要时期。钙、 硼配施既可明显提高常山胡柚叶片中矿质营养元素含量(P和Zn除外),又能显著提高果实产量和品质。     

不同林型农田防护林植物与土壤理化指标及功能基因差异

为探讨土壤生态(土壤理化指标及化学计量比)与叶片元素间的相互关系,为林地土壤养分管理及合理施肥提供理论依据,在黑龙江省拜泉县选取落叶松纯林、樟子松纯林、樟子松落叶松混交林3种典型农田防护林类型为研究对象,分析比较了3种农田防护林叶片和土壤的碳、氮、磷含量及其化学计量比。结果表明：混交林的根际土壤电导率、硝态氮含量、全磷含量均显著高于纯林土壤,氮磷比显著低于纯林土壤(P<0.05),混交林落叶松根际土壤电导率和有机碳、全磷、碱解氮、硝态氮含量均为最高,全氮、铵态氮、速效磷含量也较高;混交林落叶松叶片氮含量及磷含量均显著高于混交林樟子松(P<0.05),落叶松纯林和混交林落叶松的叶片氮磷比显著低于樟子松纯林(P<0.05);3种林型的树种叶片氮磷比均小于14,土壤全磷含量均低于全国森林平均磷含量,植物生长一定程度上受到了叶片氮元素及土壤磷元素的限制;土壤硝态氮含量是土壤中最大的影响因子,真菌基因(ITS)、嗜酸基因(Acidobacteria)、碱性磷酸酶基因(phoD)这3种基因的拷贝数与其呈显著正相关(P<0.05),也与土壤有机碳含量、全磷含量、速效磷含量、碳...     

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.     

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.     

Genetic similarities among Spanisch populations of Agropyron, Elymus and Thinopyrum, using PCR-based markers

Arbitrary oligonucleotides were used as primers to amplifygenomic DNA of 48 wild Spanish populations of Agropyroncristatum, Elymus hispanicus,E. caninus,E. repens,Thinopyrum curvifolium, Th.junceum and Th.intermedium. Genetic diversity was analysedusing nineteen primers. The number of amplified products ranged from8 to 18 per primer and a total of 240 markers were scored. Differentlevels of intraspecific genetic diversity were found, the allogamousspecies E. repens andTh. intermedium being themost variable. Jaccard's similarity coefficients for internalmeasure within and between populations were used to produce a clusterdiagram. The results demonstrate differences in the degree ofsimilarity between taxonomic units. Interpopulational variability andinterspecific genomic relationships of these species arediscussed.     

Mycorrhizae,biocides, and biocontrol. 4. Response of a mixed culture of arbuscular mycorrhizal fungi and host plant to three fungicides

The effects of three commonly used fungicides on the colonization and sporulation by a mixture of three arbuscular mycorrhizal (AM) fungi consisting of Glomus etunicatum (Becker & Gerd.), Glomus mosseae (Nicol. & Gerd.) Gerd. & Trappe, and Gigaspora rosea (Nicol. & Schenck) in symbiosis with pea plants and the resulting response of the host-plant were examined. Benomyl, PCNB, and captan were applied as soil drenches at a rate of 20 mg active ingredient kg^-1 soil 2 weeks after transplanting pea seedlings in a silty clay-loam soil containing the mixed inocula of AM fungi (AM plants). Effects of fungicides were compared to untreated plants that were inoculated with fungi (AM control). The effect of mycorrhizal inoculation on plant growth was also examined by including nonmycorrhizal, non-fungicide-treated plants (non-AM control). Fungicides or inoculation with AM fungi had only a small effect on the final shoot weights of pea plants, but had greater effects on root length and seed yield. AM control plants had higher seed yields and lower root lengths than the corresponding non-AM plants, and the fungicide-treated AM plants had intermediate yields and root lengths. Seed N and P contents were likewise highest in AM control plants, lowest in non-AM plants, and intermediate in fungicide-treated AM plants. All three fungicides depressed the proportion (%) of root length colonized by AM fungi, but these differences did not translate to reductions in the total root length that was colonized, since roots were longer in the fungicide-treated AM plants. Pea plants apparently compensated for the reduction in AM-fungal metabolism due to fungicides by increasing root growth. Fungicides affected the population of the three fungi as determined by sporulation at the final harvest. Captan significantly reduced the number, relative abundance, and relative volume of G. rosea spores in the final population relative to the controls. The relative volume of G. etunicatum spores was greater in all the fungicide-treated soils, while G. mosseae relative volumes were only greater in the captan-treated soil. These findings show that fungicides can alter the species composition of an AM-fungal community. The results also show that AM fungi can increase seed yield without enhancing the vegetative shoot growth of host plants.